const builtin = @import("builtin");
const std = @import("std");

const runfiles = @import("runfiles");

const xla_pb = @import("//xla:xla_proto");
const meta = @import("meta.zig");
const mlir = @import("mlir.zig");
const ops = @import("ops.zig");
const pjrt = @import("pjrtx.zig");
const protobuf = @import("io/protobuf");
const asynk = @import("async");
const aio = @import("aio.zig");

const dialect = @import("mlir/dialects");

const assert = std.debug.assert;
const Context = @import("context.zig").Context;
const Location = mlir.Location;
const Platform = @import("platform.zig").Platform;
const Target = @import("platform.zig").Target;
const Tensor = @import("tensor.zig").Tensor;
const ShapeOf = @import("tensor.zig").ShapeOf;
const Shape = @import("shape.zig").Shape;
const Buffer = @import("buffer.zig").Buffer;
const Bufferized = @import("tensor.zig").Bufferized;
const Tracer = @import("tools/tracer.zig").Tracer;

const log = std.log.scoped(.zml_module);

test {
    std.testing.refAllDecls(@This());
}

pub const CompilationContext = struct {
    _platform: Platform,

    _mlir_ctx: mlir.Context,
    _mlir_registry: mlir.Registry,
    _mlir_canonicalizer: mlir.PassManager,

    _module: mlir.Module,

    _blocks: std.BoundedArray(mlir.Block, 64),
    _fn_cache: FnCache,
    _allocator: std.mem.Allocator,

    _buffer_to_arg: TensorToBlockArg = .{},
    _unique_id: u64 = 10000,
    _tracer: Tracer,

    const TensorToBlockArg = std.AutoHashMapUnmanaged(Tensor._Id, struct { mlir.Value, Tensor._Donation });
    threadlocal var _current: ?*CompilationContext = null;

    pub fn init(allocator: std.mem.Allocator, name: []const u8, platform: Platform) !CompilationContext {
        const mlir_registry = mlir.Registry.init() catch unreachable;
        inline for (.{ "func", "stablehlo" }) |d| {
            mlir.DialectHandle.fromString(d).insertDialect(mlir_registry);
        }
        var mlir_ctx = mlir.Context.initWithRegistry(mlir_registry, false) catch unreachable;
        mlir_ctx.loadAllAvailableDialects();

        const loc = mlir_ctx.location(@src()).named(mlir_ctx, "main");
        const module = mlir.Module.init(loc);
        module.op().setAttributeByName("sym_name", mlir.StringAttribute.init(mlir_ctx, name).as(mlir.Attribute).?);

        var canonicalizer = try mlir.PassManager.init(mlir_ctx);
        {
            var opm = canonicalizer.asOpPassManager();
            try opm.addPipeline("canonicalize");
            try opm.addPipeline("cse");
            try opm.addPipeline("canonicalize");
        }

        return .{
            ._platform = platform,
            ._mlir_ctx = mlir_ctx,
            ._mlir_registry = mlir_registry,
            ._mlir_canonicalizer = canonicalizer,
            ._module = module,
            ._blocks = .{},
            ._fn_cache = FnCache.init(allocator),
            ._allocator = allocator,
            ._tracer = Tracer.init("ai.zml.compilation"),
        };
    }

    pub fn deinit(self: *CompilationContext) void {
        self._fn_cache.deinit();
        self._mlir_ctx.deinit();
        self._mlir_registry.deinit();
        self._buffer_to_arg.deinit(self._allocator);
    }

    pub fn activate(self: *CompilationContext) void {
        _current = self;
    }

    pub fn deactivate(self: *CompilationContext) void {
        std.debug.assert(_current != null and _current.? == self);
        _current = null;
    }

    pub fn current() *CompilationContext {
        return _current.?;
    }

    pub fn target(self: *const CompilationContext) Target {
        return self._platform.target;
    }

    pub fn targetIs(self: *const CompilationContext, value: Target) bool {
        return self.target() == value;
    }

    pub fn mlirCtx(self: *const CompilationContext) mlir.Context {
        return self._mlir_ctx;
    }

    pub fn currentBlock(self: *const CompilationContext) ?mlir.Block {
        return if (self._blocks.len > 0) self._blocks.get(self._blocks.len - 1) else null;
    }

    pub fn openBlock(self: *CompilationContext, args: []const mlir.Type, locs: []const mlir.Location) !mlir.Block {
        const block = try mlir.Block.init(args, locs);
        self.pushBlock(block);
        return block;
    }

    pub fn closeBlock(self: *CompilationContext, block: *mlir.Block) void {
        const popped = self._blocks.pop();
        std.debug.assert(block.equals(popped));
    }

    fn pushBlock(self: *CompilationContext, block: mlir.Block) void {
        self._blocks.appendAssumeCapacity(block);
    }

    /// Transform a Tensor -> Tensor function into an Mlir block.
    /// `blkctx` represents values from outside the block that can be accessed inside the block.
    pub fn makeBlock(
        self: *CompilationContext,
        comptime func: anytype,
        comptime S: ops.BlockSignature,
        blkctx: S.BlkCtx,
        args: S.Args,
    ) mlir.Block {
        const N = S.nIn;
        const locations = .{mlir.Location.unknown(self.mlirCtx())} ** N;
        var input_types: [N]mlir.Type = undefined;
        fillMlirTypes(&args, self.mlirCtx(), &input_types);

        var block = self.openBlock(&input_types, &locations) catch unreachable;
        defer self.closeBlock(&block);

        // Here we want to create the block with the correct mlir types.
        // but we don't want to use the values themselves.
        // So we create a copy of the arguments, and replace values
        // by the block arguments.
        var blk_args = args;
        assert(assignBlockArguments(&blk_args, block, 0) == N);

        const loc = self.mlirCtx().location(@src());
        const block_res = @call(.auto, func, S.blkArgs(blkctx, blk_args));

        var block_res_values: [S.nOut]mlir.Value = undefined;
        self.extractValues(&block_res, &block_res_values);
        const block_ret = dialect.stablehlo.returns_(self.mlirCtx(), &block_res_values, loc);
        block.addOperationsRecursive(block_ret);

        return block;
    }

    /// Generate an MLIR function from a ZML function.
    /// The caller is responsible to have properly created the input
    /// tensors with unique tensor ids.
    pub fn generateBytecode(
        self: *CompilationContext,
        allocator: std.mem.Allocator,
        fn_name: [:0]const u8,
        comptime func: anytype,
        model: *const ModuleSignature(func).ModelT,
        args: *const ModuleSignature(func).ArgsT,
        opts: struct { add_donations_attributes: bool = false },
    ) error{OutOfMemory}!MlirFn {
        const frame = self._tracer.frameStart("generateBytecode.emit");
        errdefer self._tracer.frameEnd(frame, "generateBytecode.emit");

        // Note: only temp allocations are done in the arena,
        // the other allocations are managed by the caller.
        var arena_state = std.heap.ArenaAllocator.init(allocator);
        defer arena_state.deinit();
        const arena = arena_state.allocator();

        const model_tensor_count = countTensors(model);
        const args_tensor_count = countTensors(args);

        const tensor_count = model_tensor_count + args_tensor_count;

        const loc = self.mlirCtx().location(@src());

        const locations = try arena.alloc(mlir.Location, tensor_count);
        for (locations) |*l| l.* = mlir.Location.unknown(self.mlirCtx());
        var input_types = try arena.alloc(mlir.Type, tensor_count);
        fillMlirTypes(model, self.mlirCtx(), input_types[0..model_tensor_count]);
        fillMlirTypes(args, self.mlirCtx(), input_types[model_tensor_count..]);

        // Note: this isn't stricly necessary. We call `countTensor` on `fn_res`.
        // But it forces user to have simpler function.
        const out_tensor_count = comptime ops.staticCountTensors(ModuleSignature(func).ReturnT) orelse @compileError("Can't use " ++ @typeName(ModuleSignature(func).ReturnT) ++ " in an MLIR function, because it has a variable number of tensors");
        const fn_res_types = try allocator.alloc(mlir.Type, out_tensor_count);
        const fn_res_shapes = try allocator.alloc(Shape, out_tensor_count);
        const fn_res_donations = try allocator.alloc(Tensor._Donation, out_tensor_count);
        var fn_body = self.openBlock(input_types, locations) catch unreachable;
        {
            defer self.closeBlock(&fn_body);
            // Note: we could shrink self._buffer_to_arg once we called `func`.
            // But for now we are only compiling one function per CompilationContext.
            // So we don't need to do this since we won't reuse self._buffer_to_arg anyway.
            // const n = self._buffer_to_arg.count();
            // defer self._buffer_to_arg.shrinkRetainingCapacity(n);

            try self._buffer_to_arg.ensureUnusedCapacity(self._allocator, @intCast(tensor_count));
            const assigned_model_count = self.mapBlockArguments(model, fn_body, 0);
            const assigned_args_count = self.mapBlockArguments(args, fn_body, assigned_model_count);
            assert(assigned_model_count == model_tensor_count);
            assert(assigned_args_count == tensor_count);

            const fn_res = forward: {
                self.activate();
                defer self.deactivate();
                break :forward @call(.auto, func, .{model.*} ++ args.*);
            };

            var fn_res_values: [out_tensor_count]mlir.Value = undefined;
            self.extractValuesAndTypes(&fn_res, &fn_res_values, fn_res_types, fn_res_shapes, fn_res_donations);
            const fn_ret = dialect.func.return_(self.mlirCtx(), &fn_res_values, loc);
            fn_body.addOperationsRecursive(fn_ret);
        }

        // Donations attributes only make sense on the main function.
        const attrs: []const mlir.Attribute = if (opts.add_donations_attributes)
            try self.addDonationsAttribute(arena, fn_res_donations, tensor_count)
        else
            &.{};

        const mlir_fn = dialect.func.func(self.mlirCtx(), .{
            .sym_name = fn_name,
            .args = input_types[0..],
            .arg_attrs = attrs,
            .results = fn_res_types,
            .block = fn_body,
            .location = loc,
        });

        self._tracer.frameEnd(frame, "generateBytecode.emit");
        const canonicalize_frame = self._tracer.frameStart("generateBytecode.canonicalize");
        defer self._tracer.frameEnd(canonicalize_frame, "generateBytecode.canonicalize");
        self._mlir_canonicalizer.runOnOp(mlir_fn) catch |err| switch (err) {
            error.InvalidMlir => {
                log.err("Failed to canonicalize invalid mlir: {}", .{mlir_fn.mlirFormatter(.{})});
                // user errors should have triggered a panic before we reach this.
                @panic("ZML generated invalid mlir. Please open a bug report");
            },
        };

        return .{
            .mlir_fn = mlir_fn,
            .name = fn_name,
            .n_model = @intCast(model_tensor_count),
            .n_args = @intCast(args_tensor_count),
            .res_types = fn_res_types,
            .res_shapes = fn_res_shapes,
            .res_donations = fn_res_donations,
        };
    }

    /// Given a list of donations mapping output buffers to input buffers,
    /// generate donation attribute for each `n_args` input argument.
    fn addDonationsAttribute(self: *const CompilationContext, allocator: std.mem.Allocator, donations: []const Tensor._Donation, n_args: usize) ![]mlir.Attribute {
        const empty = mlir.DictionaryAttribute.init(self.mlirCtx(), &.{}).as(mlir.Attribute).?;

        const arg_attrs = try allocator.alloc(mlir.Attribute, n_args);
        @memset(arg_attrs, empty);

        var n_donations: usize = 0;
        for (donations, 0..) |donation, index| {
            switch (donation) {
                .no_buffer => {},
                // This is an input buffer that has been returned,
                // but without explicitly calling `reuseBuffer`.
                // So we assume the intent was to return a new buffer.
                .input_buffer => {},
                .arg => |a| {
                    n_donations += 1;
                    meta.assert(arg_attrs[a].eql(empty), "Donation error ! Argument {} has been donated twice ! To {} and to {}", .{ a, index, arg_attrs[a] });
                    arg_attrs[a] = mlir.DictionaryAttribute.init(self.mlirCtx(), &.{
                        mlir.NamedAttribute.init(
                            mlir.Identifier.get(self.mlirCtx(), "tf.aliasing_output"),
                            mlir.IntegerAttribute(.i32).init(self.mlirCtx(), @intCast(index)).as(mlir.Attribute).?,
                        ),
                    }).as(mlir.Attribute).?;
                    // log.debug("attribute: {}", .{arg_attrs[a]});
                },
            }
        }

        if (n_donations == 0) return &.{};
        return arg_attrs;
    }

    test addDonationsAttribute {
        const zml = @import("zml.zig");
        const platform = zml.testing.env();
        var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
        defer arena.deinit();
        const allocator = arena.allocator();

        const s = Shape.init(.{8}, .f16);

        const Local = struct {
            bias: Tensor,

            pub fn forward(self: @This(), x: Tensor) Tensor {
                const y = x.add(self.bias);
                return y.reuseBuffer(x);
            }
        };

        const model: Local = .{
            .bias = zml.Tensor{ ._shape = s, ._id = .{ .buffer_id = 0 } },
        };

        var comp = try zml.module.CompilationContext.init(allocator, "test", platform);
        defer comp.deinit();
        var tensor_args = .{Tensor{ ._shape = s, ._id = .{ .arg_id = 1234 } }};
        const f = try comp.generateBytecode(allocator, "test.generateBytecode.Local.forward", Local.forward, &model, &tensor_args, .{ .add_donations_attributes = true });

        var mlir_bytecode: std.ArrayListUnmanaged(u8) = .{};
        try mlir_bytecode.writer(allocator).print("{}", .{f.mlir_fn.mlirFormatter(.{})});

        // Check that the `x` input argument gives its buffer to the result tensor.
        // `%arg0` is the bias of the model, `%arg1` is `x`.
        try std.testing.expectEqual(1, f.n_model);
        try std.testing.expectEqual(1, f.n_args);
        std.testing.expect(std.mem.indexOf(u8, mlir_bytecode.items, "%arg1: tensor<8xf16> {tf.aliasing_output = 0 : i32}") != null) catch |err| {
            log.warn("Didn't produced the expected IR:\n{s}", .{mlir_bytecode.items});
            return err;
        };
    }

    /// Generates an MLIR `func.call` of the given function.
    /// If the function has not been seen yet, we generate MLIR for it,
    /// in a independent function.
    /// The main benefit of this is to generate MLIR that maps more closely
    /// to the Zig code, but compilation speed stays similar.
    pub fn callFunc(
        self: *CompilationContext,
        func_name: [:0]const u8,
        comptime func: anytype,
        model: *const ModuleSignature(func).ModelT,
        args: *ModuleSignature(func).ArgsT,
    ) ModuleSignature(func).ReturnT {
        var arena_state = std.heap.ArenaAllocator.init(self._allocator);
        defer arena_state.deinit();
        const arena = arena_state.allocator();

        // first, do the "compile" and check the bytecode
        // the result of this will also have the correct tags of the result shapes
        const dummy_result = self.generateMlirBytecodeForFunction(
            arena,
            func_name,
            func,
            model,
            args,
        ) catch unreachable; // TODO: do we like unreachable?
        const bytecode_hash = hashArgs(dummy_result.bytecode_tmp);

        const key: FnCache.Key = .{ .fn_ptr = &func, .input_hash = bytecode_hash };
        const function = self._fn_cache.getEntry(key) orelse b: {
            const full_name: [:0]const u8 = if (std.mem.eql(u8, "main", func_name))
                arena.dupeZ(u8, func_name) catch unreachable
            else
                std.fmt.allocPrintZ(arena, "{s}.{s}_{x}", .{ @typeName(ModuleSignature(func).ModelT), func_name, key.input_hash }) catch unreachable;

            log.info("addFuncToModule {any} {s}", .{ key, full_name });

            const value = self.addFuncToModule(
                arena,
                full_name,
                func,
                model,
                args,
            ) catch unreachable;

            break :b self._fn_cache.addEntry(key, value) catch unreachable;
        };

        // Note: we won't increase the size of the cache until next `call` so
        // we can use the memory there without worrying about fragmentation.

        const loc = self.mlirCtx().location(@src());

        const values = arena.alloc(mlir.Value, function.n_model + function.n_args) catch unreachable;
        extractValues(model, values[0..function.n_model]);
        extractValues(args, values[function.n_model..]);

        const op = dialect.func.call(self.mlirCtx(), function.name, values, function.res_types, loc);
        var res: meta.FnResult(func) = undefined;
        assignResults(&res, function.res_shapes, op);
        return res;
    }

    /// Visit the given struct and recursively associate the `block` arguments with the `value` field of each encountered Tensor.
    ///
    /// This is done so that we have a mapping between the arguments of the kernel associated with a module and the actual Tensors
    /// stored in the Module.
    /// Caller need to allocate required memory in self._buffer_to_arg.
    pub fn mapBlockArguments(self: *CompilationContext, v: anytype, block: mlir.Block, start: usize) usize {
        const LocalContext = struct {
            index: usize,
            block: mlir.Block,
            self: *CompilationContext,
        };
        var context = LocalContext{ .self = self, .block = block, .index = start };
        meta.visit((struct {
            fn cb(ctx: *LocalContext, tensor: *const Tensor) void {
                const arg_value = ctx.block.argument(ctx.index);
                // log.debug("mapping {} to arg {}", .{ tensor._id, ctx.index });

                const res = ctx.self._buffer_to_arg.getOrPutAssumeCapacity(tensor._id);
                if (res.found_existing) {
                    std.debug.panic("Failed compilation because received two tensors arguments with the same ID: {} and {}({}).", .{ res.key_ptr.*, tensor, tensor._id });
                } else {
                    res.value_ptr.* = .{ arg_value, .{ .arg = @intCast(ctx.index) } };
                }
                ctx.index += 1;
            }
        }).cb, &context, v);
        return context.index;
    }

    /// Create tensor from the given shapes.
    /// Each created tensor will receive a unique id, local to this CompilationContext.
    pub fn tensorFromShapes(self: *CompilationContext, ArgsT: type, allocator: std.mem.Allocator, args_shapes: anytype) ArgsT {
        const Local = struct {
            fn tensorFromShape(arg_id: *u64, shape: Shape) Tensor {
                defer arg_id.* += 1;
                return Tensor{
                    ._shape = shape,
                    ._id = .{ .arg_id = arg_id.* },
                    ._donation = .input_buffer,
                };
            }
        };
        var tensor_args: ArgsT = undefined;
        try meta.mapAlloc(Local.tensorFromShape, allocator, &self._unique_id, args_shapes, &tensor_args);
        return tensor_args;
    }

    /// Visit the given struct and extract the mlir.Value and mlir.Type associated with each tensor found.
    pub fn extractValuesAndTypes(self: *const CompilationContext, v: anytype, values: []mlir.Value, types: []mlir.Type, shapes: []Shape, donations: []Tensor._Donation) void {
        assert(values.len == types.len);
        const LocalContext = struct {
            self: *const CompilationContext,
            index: usize = 0,
            values: []mlir.Value,
            types: []mlir.Type,
            shapes: []Shape,
            donations: []Tensor._Donation,
        };
        var context = LocalContext{ .self = self, .values = values, .types = types, .shapes = shapes, .donations = donations };
        meta.visit((struct {
            fn cb(ctx: *LocalContext, tensor: *const Tensor) void {
                const value, const donation = ctx.self.getValueAndDonation(tensor.*);
                ctx.values[ctx.index] = value;
                ctx.types[ctx.index] = value.getType();
                ctx.shapes[ctx.index] = tensor._shape;
                ctx.donations[ctx.index] = donation;
                ctx.index += 1;
            }
        }).cb, &context, v);
        assert(context.index == values.len);
    }

    pub fn getValueAndDonation(self: *const CompilationContext, tensor: Tensor) struct { mlir.Value, Tensor._Donation } {
        return switch (tensor._id) {
            .buffer_id, .arg_id => if (self._buffer_to_arg.get(tensor._id)) |res|
                .{ res[0], res[1] }
            else {
                log.err("Found unknown tensor id {}({})", .{ tensor, tensor._id });
                @panic("Found unknown tensor id");
            },
            .mlir => |v| .{ v, tensor._donation },
        };
    }

    /// Visit the given struct and copies the mlir.Value associated with each tensor found.
    pub fn extractValues(self: *const CompilationContext, v: anytype, values: []mlir.Value) void {
        const LocalContext = struct {
            self: *const CompilationContext,
            index: usize = 0,
            values: []mlir.Value,
        };
        var context = LocalContext{ .self = self, .values = values };
        meta.visit((struct {
            fn cb(ctx: *LocalContext, tensor: *const Tensor) void {
                const value, const donation = ctx.self.getValueAndDonation(tensor.*);
                _ = donation;

                ctx.values[ctx.index] = value;
                ctx.index += 1;
            }
        }).cb, &context, v);
        assert(context.index == values.len);
    }
};

/// Visit the given struct and recursively counts the number of tensors found.
pub fn countTensors(v: anytype) usize {
    const LocalContext = struct {
        count: usize = 0,
    };
    var context = LocalContext{};
    meta.visit((struct {
        fn cb(inner_context: *LocalContext, _: *const Tensor) void {
            inner_context.count += 1;
        }
    }).cb, &context, v);
    return context.count;
}

/// Visit the given struct and recursively fill the `types` slice with the mlir.Type associated with encountered Tensor.
pub fn fillMlirTypes(v: anytype, mlir_ctx: mlir.Context, types: []mlir.Type) void {
    const LocalContext = struct {
        index: usize = 0,
        mlir_ctx: mlir.Context,
        types: []mlir.Type,
    };
    var context = LocalContext{ .mlir_ctx = mlir_ctx, .types = types };
    meta.visit((struct {
        fn cb(inner_context: *LocalContext, tensor: *const Tensor) void {
            inner_context.types[inner_context.index] = mlir.ext.mlirType(inner_context.mlir_ctx, tensor.shape());
            inner_context.index += 1;
        }
    }).cb, &context, v);
    assert(context.index == types.len);
}

/// Visit the given struct and recursively associate the `block` arguments with the `value` field of each encountered Tensor.
///
/// This is done so that we have a mapping between the arguments of the kernel associated with a module and the actual Tensors
/// stored in the Module.
fn assignBlockArguments(v: anytype, block: mlir.Block, start: usize) usize {
    const LocalContext = struct { index: usize, block: mlir.Block };
    var context = LocalContext{ .block = block, .index = start };
    meta.visit((struct {
        fn cb(ctx: *LocalContext, tensor: *Tensor) void {
            tensor._id = .{ .mlir = ctx.block.argument(ctx.index) };
            tensor._donation = .{ .arg = @intCast(ctx.index) };
            ctx.index += 1;
        }
    }).cb, &context, v);
    return context.index;
}

/// Visit the given struct and fill the `buffers` slice with the buffer associated with encountered Tensor.
fn fillBuffers(v: anytype, buffers: []*pjrt.Buffer) void {
    const LocalContext = struct {
        index: usize,
        buffers: []*pjrt.Buffer,
    };
    var ctx: LocalContext = .{
        .index = 0,
        .buffers = buffers,
    };
    meta.visit((struct {
        fn cb(inner_context: *LocalContext, buffer: *const Buffer) void {
            // meta.assert(!buffer._data.isDeleted(), "Can't use {} (argument buffer {}) because its pjrt buffer has been donated", .{ buffer, inner_context.index });
            inner_context.buffers[inner_context.index] = buffer._data;
            inner_context.index += 1;
        }
    }).cb, &ctx, v);
    assert(ctx.index == buffers.len);
}

/// Visit the given struct and override tensors by creating a new one using the provided PJRT buffers.
pub fn assignRawBuffers(v: anytype, platform: Platform, buffers: []*pjrt.Buffer) void {
    const LocalContext = struct {
        index: usize,
        platform: Platform,
        buffers: []*pjrt.Buffer,
    };
    var ctx: LocalContext = .{
        .index = 0,
        .platform = platform,
        .buffers = buffers,
    };
    meta.visit((struct {
        fn cb(inner_context: *LocalContext, buffer: *Buffer) void {
            const i = inner_context.index;
            if (i < inner_context.buffers.len) {
                buffer.* = Buffer.fromPjrtBuffer(inner_context.platform, inner_context.buffers[i]);
            }
            inner_context.index += 1;
        }
    }).cb, &ctx, v);
    meta.assert(ctx.index == buffers.len, "Pjrt call returned {} tensors, but the return type {s}, contains {} Buffers. Note that modules need to have a comptime know number of returned tensors.", .{ buffers.len, @typeName(@TypeOf(v)), ctx.index });
}

/// Visit the given struct and assign op results to each tensor found.
pub fn assignResults(v: anytype, shapes: ?[]Shape, op: mlir.Operation) void {
    const LocalContext = struct {
        index: usize,
        op: mlir.Operation,
        shapes: ?[]Shape,
    };
    var context = LocalContext{ .index = 0, .op = op, .shapes = shapes };
    meta.visit((struct {
        fn cb(inner_ctx: *LocalContext, tensor: *Tensor) void {
            tensor.* = Tensor.fromMlirValue(inner_ctx.op.result(inner_ctx.index));
            if (inner_ctx.shapes) |sh| {
                tensor._shape = sh[inner_ctx.index];
            }
            inner_ctx.index += 1;
        }
    }).cb, &context, v);
    assert(context.index == op.numResults());
}

/// Represents an MLIR module compiled into a PJRT executable.
/// The BaseExe is a plain old struct and doesn't have information
/// about Zig types.
const BaseExe = struct {
    /// The platform for which this module was compiled.
    platform: Platform,
    /// The PJRT executable representing the compiled module.
    exe: *pjrt.LoadedExecutable,
    /// Number of buffers in the model.
    model_buffer_count: usize,
    /// Number of buffers in the arguments.
    args_buffer_count: usize,
    /// Number of buffers in result.
    result_buffer_count: usize,
};

/// Represents a ZML model, compiled into a PJRT executable.
///
/// It's not directly callable, as it doesn't have associated model weights.
/// use `prepare` to assign weights and pre allocate memory needed to call.
pub fn Exe(comptime func: anytype) type {
    const Signature = ModuleSignature(func);
    return struct {
        const Self = @This();

        /// The raw untyped compiled module.
        inner: BaseExe,

        /// Packages the given model weight with an `Exe` to produce an `ExeWithWeights` that can be called.
        pub fn prepare(self: Self, allocator: std.mem.Allocator, model: Bufferized(Signature.ModelT)) !ExeWithWeights(func) {
            return ExeWithWeights(func).initFromModel(allocator, self.inner, model);
        }
    };
}

/// Represents a ZML model, compiled into a PJRT executable, and ready to call.
/// The buffers for the model weights are saved inside the struct and will be used in `call`.
/// You only need to pass the remaining arguments.
pub fn ExeWithWeights(comptime func: anytype) type {
    const Signature = ModuleSignature(func);
    return struct {
        const Self = @This();

        /// The raw untyped compiled module.
        inner: BaseExe,

        /// The allocator used for bookkeeping.
        allocator: std.mem.Allocator,

        /// Pre-allocated slice of buffers to use as inputs when the module is called.
        input_buffers: []*pjrt.Buffer,

        /// Pre-allocated slice of buffers to use as outputs when the module is called.
        output_buffers: []*pjrt.Buffer,

        pub fn initFromModel(allocator: std.mem.Allocator, inner: BaseExe, model: Bufferized(Signature.ModelT)) !Self {
            const input_buffers = try allocator.alloc(*pjrt.Buffer, inner.model_buffer_count + inner.args_buffer_count);
            errdefer allocator.free(input_buffers);
            fillBuffers(&model, input_buffers[0..inner.model_buffer_count]);

            const output_buffers = try allocator.alloc(*pjrt.Buffer, inner.result_buffer_count);
            errdefer allocator.free(output_buffers);

            return .{
                .inner = inner,
                .allocator = allocator,
                .input_buffers = input_buffers,
                .output_buffers = output_buffers,
            };
        }

        pub fn deinit(self: Self) void {
            self.allocator.free(self.input_buffers);
            self.allocator.free(self.output_buffers);
        }

        pub fn platform(self: Self) Platform {
            return self.inner.platform;
        }

        pub fn call(self: Self, args: Bufferized(Signature.ArgsT)) Bufferized(Signature.ReturnT) {
            fillBuffers(&args, self.input_buffers[self.inner.model_buffer_count..][0..self.inner.args_buffer_count]);
            var event: [1]*pjrt.Event = undefined;

            self.inner.exe.execute(self.inner.platform.pjrt_api, .{
                .arguments = &.{self.input_buffers.ptr},
                .num_args = self.input_buffers.len,
                .results = &.{self.output_buffers.ptr},
                .events = &event,
                // TODO: this allows to tell a specific buffer shouldn't be donated,
                // even if it has been marked as "can be donated" during compilation.
                .non_donatable_input_indices = &.{},
            }) catch unreachable;

            var result: Bufferized(Signature.ReturnT) = undefined;
            assignRawBuffers(&result, self.inner.platform, self.output_buffers);
            return result;
        }
    };
}

/// Compiles the given module with the given arguments.
/// The `model` (first fn argument), is treated differently from the other args.
/// This helps to have two separate lifetimes for the model buffers,
/// and for the arguments buffer.
fn compileInternal(
    allocator: std.mem.Allocator,
    context: *CompilationContext,
    comptime func: anytype,
    model: ModuleSignature(func).ModelT,
    args: ShapeOf(ModuleSignature(func).ArgsT),
) !BaseExe {
    var arena_state = std.heap.ArenaAllocator.init(allocator);
    defer arena_state.deinit();
    const arena = arena_state.allocator();

    var timer = std.time.Timer.start() catch null;
    const tensor_args = context.tensorFromShapes(ModuleSignature(func).ArgsT, arena, args);
    // Run in a dedicated thread because compilation relies on `threadlocal`.
    const f = try asynk.callGeneric(CompilationContext.generateBytecode, .{ context, arena, "main", func, &model, &tensor_args, .{ .add_donations_attributes = true } });
    context._module.getBody().appendOperation(f.mlir_fn);

    const loaded_executable = loadOrCompilePjrtExecutable(arena, context._platform, context._module) catch |err| {
        log.err(
            "pjrt-{s} failed to compile following valid MLIR:\n{}\n{}",
            .{ @tagName(context._platform.target), context._module.op().mlirFormatter(.{}), err },
        );
        return err;
    };

    log.debug("******** ZML generated MLIR ********", .{});
    log.debug("{}", .{context._module.op().mlirFormatter(.{})});

    if (timer) |*t| {
        const time_ms = @divFloor(t.lap(), std.time.ns_per_ms);
        if (time_ms > 1000) log.info("Compilation took {d:.3}s", .{meta.divFloat(f32, time_ms, 1000)});
    }

    return .{
        .platform = context._platform,
        .exe = loaded_executable,
        .model_buffer_count = f.n_model,
        .args_buffer_count = f.n_args,
        .result_buffer_count = f.res_types.len,
    };
}

/// Compiles a Model struct with the given configuration and shapes, for the given platform.
/// The steps are:
/// * lookup at tensors available in the store and create a `model: Model` struct with them
/// * call `model.init(init_args)` to fields of the model that aren't Tensor, ie hyperparemeters/config
/// * generate MLIR by calling `model.forward` with tensor of the given shapes and other arguments
pub fn compile(
    allocator: std.mem.Allocator,
    comptime Model: type,
    init_args: anytype,
    comptime func: @TypeOf(.literal),
    args_shapes: ShapeOf(ModuleSignature(@field(Model, @tagName(func))).ArgsT),
    buffer_store: aio.BufferStore,
    platform: Platform,
) !Exe(@field(Model, @tagName(func))) {
    var arena_state = std.heap.ArenaAllocator.init(allocator);
    defer arena_state.deinit();
    const arena = arena_state.allocator();
    var model = try aio.populateModel(Model, arena, buffer_store);

    // If the Model has a "init" function, call it with the given parameters.
    if (@hasDecl(Model, "init")) {
        // TODO(Corentin,@Improvement): Add a warning/error if there is no init function but init_args is non-void.
        @call(.auto, Model.init, .{@as(*Model, &model)} ++ init_args);
    }

    return compileModel(allocator, model, func, args_shapes, platform);
}

/// Compiles a Model struct with the given configuration and shapes, for the given platform.
/// Generate MLIR by calling `model.forward` with tensor of the given shapes and other arguments
pub fn compileModel(
    allocator: std.mem.Allocator,
    model: anytype,
    comptime func: @TypeOf(.literal),
    args_shapes: ShapeOf(ModuleSignature(@field(@TypeOf(model), @tagName(func))).ArgsT),
    platform: Platform,
) !Exe(@field(@TypeOf(model), @tagName(func))) {
    const Model = @TypeOf(model);
    const name = @typeName(Model) ++ "." ++ @tagName(func);
    log.info("Compiling {s} with {}", .{ name, args_shapes });

    var context = try CompilationContext.init(allocator, name, platform);
    defer context.deinit();

    const raw_module = try compileInternal(allocator, &context, @field(Model, @tagName(func)), model, args_shapes);

    return Exe(@field(Model, @tagName(func))){ .inner = raw_module };
}

/// Compiles a function with the given configuration and shapes, for the given platform.
/// Generate MLIR by calling the given function with tensor of the given shapes.
pub fn compileFn(
    allocator: std.mem.Allocator,
    func: anytype,
    args: ShapeOf(meta.FnParams(func)),
    platform: Platform,
) !ExeWithWeights(FnWithVoidArg(func)) {
    const name = @typeName(@TypeOf(func));
    var context = try CompilationContext.init(allocator, name, platform);
    defer context.deinit();

    const Local = struct {
        // This is the function we will actually compile.
        pub fn forward(_: void, inner_args: meta.FnParams(func)) meta.FnResult(func) {
            return @call(.auto, func, inner_args);
        }
    };

    const void_model: void = {};
    const raw_module = try compileInternal(allocator, &context, Local.forward, void_model, .{args});
    // But we set the signature so that you can call the module as you would call the function.
    return try ExeWithWeights(FnWithVoidArg(func)).initFromModel(allocator, raw_module, void_model);
}

fn FnWithVoidArg(func: anytype) type {
    const fn_info = @typeInfo(@TypeOf(func)).Fn;
    const void_param = std.builtin.Type.Fn.Param{ .is_generic = false, .is_noalias = false, .type = void };
    meta.assertComptime(!fn_info.is_generic, "Can't do reflection on generic function: {}", .{@TypeOf(func)});
    return @Type(.{ .Fn = .{
        .calling_convention = fn_info.calling_convention,
        .is_generic = false,
        .is_var_args = fn_info.is_var_args,
        .return_type = fn_info.return_type,
        .params = [1]std.builtin.Type.Fn.Param{void_param} ++ fn_info.params,
    } });
}

fn computeModuleHash(platform: Platform, module: mlir.Module) u64 {
    var hasher = std.hash.XxHash64.init(0);
    var hasher_writer = xxHash64Writer(&hasher);
    const writer = hasher_writer.writer();

    // Hash the canonicalized IR, without debug information that can change across builds.
    module.op().writeBytecode(writer);
    //module.op().print(writer, .{ .debug_info = false });
    // Writes can't fail because we are writing to a hasher.
    writer.writeAll(platform.pjrt_client.getPlatformName(platform.pjrt_api)) catch unreachable;
    const api_version = platform.pjrt_api.version();
    writer.writeInt(i64, api_version.major, .little) catch unreachable;
    writer.writeInt(i64, api_version.minor, .little) catch unreachable;

    return hasher.final();
}

const max_pjrt_executable_size = 20 * 1024 * 1024;

fn loadPjrtExecutable(arena: std.mem.Allocator, platform: Platform, module_hash: u64, compilation_cache_location: []const u8) !*pjrt.LoadedExecutable {
    const resolved_path = try std.fs.cwd().realpathAlloc(arena, compilation_cache_location);
    const compilation_cache_dir = try std.fs.openDirAbsolute(resolved_path, .{});
    var buf: [16]u8 = undefined;
    const filename = try std.fmt.bufPrint(&buf, "{x}", .{module_hash});
    const loaded_executable_file = try compilation_cache_dir.openFile(filename, .{});
    defer loaded_executable_file.close();

    const bytes = try loaded_executable_file.readToEndAlloc(arena, max_pjrt_executable_size);

    return platform.pjrt_client.deserializeAndLoad(platform.pjrt_api, bytes);
}

fn storePjrtExecutable(arena: std.mem.Allocator, platform: Platform, loaded_executable: *pjrt.LoadedExecutable, module_hash: u64, compilation_cache_location: []const u8) !void {
    const resolved_path = try std.fs.cwd().realpathAlloc(arena, compilation_cache_location);
    const compilation_cache_dir = try std.fs.openDirAbsolute(resolved_path, .{});

    const loaded_executable_file = try compilation_cache_dir.createFile(try std.fmt.allocPrint(arena, "{x}", .{module_hash}), .{});
    defer loaded_executable_file.close();

    var executable = try loaded_executable.getExecutable(platform.pjrt_api);
    defer executable.deinit(platform.pjrt_api);

    var serialize_result = try executable.serialize(platform.pjrt_api);
    defer serialize_result.deinit();

    try loaded_executable_file.writeAll(serialize_result.bytes);
}

fn loadOrCompilePjrtExecutable(
    arena: std.mem.Allocator,
    platform: Platform,
    module: mlir.Module,
) !*pjrt.LoadedExecutable {
    const tracer = Tracer.init("ai.zml.compilation");
    const compile_frame = tracer.frameStart("pjrt cached compilation");
    defer tracer.frameEnd(compile_frame, "pjrt cached compilation");
    const module_hash = computeModuleHash(platform, module);

    if (platform.compilation_options.cache_location) |compilation_cache_location| {
        log.debug("Loading module from {s}", .{compilation_cache_location});
        return loadPjrtExecutable(arena, platform, module_hash, compilation_cache_location) catch |err| {
            log.debug("Failed to load module: {}", .{err});
            return compileModuleToPjrtExecutable(arena, platform, module, module_hash);
        };
    } else {
        return compileModuleToPjrtExecutable(arena, platform, module, module_hash);
    }
}

fn compileModuleToPjrtExecutable(arena: std.mem.Allocator, platform: Platform, module: mlir.Module, module_hash: u64) !*pjrt.LoadedExecutable {
    var options: xla_pb.CompileOptionsProto = .{
        .executable_build_options = .{
            .num_replicas = 1,
            .num_partitions = 1,
        },
    };
    // Let the arena deinit, zig-protobuf deinit is very slow.
    if (platform.compilation_options.xla_dump_to) |xla_dump_to| {
        try options.env_option_overrides.append(arena, .{
            .key = .{ .Const = "xla_dump_to" },
            .value = .{ .value = .{ .string_field = .{ .Const = xla_dump_to } } },
        });
        if (platform.compilation_options.xla_dump_fusion_visualization) {
            try options.env_option_overrides.append(arena, .{
                .key = .{ .Const = "xla_dump_hlo_as_html" },
                .value = .{ .value = .{ .bool_field = true } },
            });
            try options.env_option_overrides.append(arena, .{
                .key = .{ .Const = "xla_dump_hlo_as_dot" },
                .value = .{ .value = .{ .bool_field = true } },
            });
            try options.env_option_overrides.append(arena, .{
                .key = .{ .Const = "xla_dump_fusion_visualization" },
                .value = .{ .value = .{ .bool_field = true } },
            });
        }
    }
    switch (platform.target) {
        .cuda => cuda_dir: {
            // NVIDIA recommends to disable Triton GEMM on JAX:
            // https://github.com/NVIDIA/JAX-Toolbox?tab=readme-ov-file#environment-variables
            try options.env_option_overrides.append(arena, .{
                .key = .{ .Const = "xla_gpu_enable_triton_gemm" },
                .value = .{ .value = .{ .bool_field = false } },
            });
            var r_ = try runfiles.Runfiles.create(.{ .allocator = arena }) orelse {
                log.warn("Bazel runfile not found !", .{});
                break :cuda_dir;
            };
            defer r_.deinit(arena);
            const source_repo = @import("bazel_builtin").current_repository;
            const r = r_.withSourceRepo(source_repo);
            const cuda_data_dir = (try r.rlocationAlloc(arena, "libpjrt_cuda/sandbox")).?;
            log.info("xla_gpu_cuda_data_dir: {s}", .{cuda_data_dir});
            try options.env_option_overrides.append(arena, .{
                .key = .{ .Const = "xla_gpu_cuda_data_dir" },
                .value = .{
                    .value = .{
                        .string_field = .{ .Const = cuda_data_dir },
                    },
                },
            });
        },
        .rocm => {
            // Disable Triton GEMM on ROCM. For some reason it's much, much slower when
            // enabled on CDNA and it's used on RDNA. Disable it altogether.
            try options.env_option_overrides.append(arena, .{
                .key = .{ .Const = "xla_gpu_enable_triton_gemm" },
                .value = .{ .value = .{ .bool_field = false } },
            });
        },
        else => {},
    }

    const loaded_executable = try platform.pjrt_client.compile(platform.pjrt_api, arena, module, try options.encode(arena));
    errdefer unreachable; // errdefer loaded_executable.deinit();

    if (platform.compilation_options.cache_location) |compilation_cache_location| {
        log.debug("Storing module to {s}", .{compilation_cache_location});
        storePjrtExecutable(arena, platform, loaded_executable, module_hash, compilation_cache_location) catch |err| {
            log.debug("Failed to store module: {}", .{err});
        };
    }

    return loaded_executable;
}

pub const XxHash64Writer = struct {
    hasher: *std.hash.XxHash64,

    pub const Error = error{};
    pub const Writer = std.io.Writer(*XxHash64Writer, Error, write);

    pub fn writer(self: *XxHash64Writer) Writer {
        return .{ .context = self };
    }

    pub fn write(self: *XxHash64Writer, bytes: []const u8) Error!usize {
        self.hasher.update(bytes);
        return bytes.len;
    }
};

pub fn xxHash64Writer(hasher: *std.hash.XxHash64) XxHash64Writer {
    return .{ .hasher = hasher };
}

pub fn hasTensors(comptime T: type) bool {
    if (T == Tensor) return true;

    return switch (@typeInfo(T)) {
        inline .Array, .Pointer, .Optional => |info| hasTensors(info.child),
        inline .Struct, .Union => |info| {
            inline for (info.fields) |field| {
                if (hasTensors(field.type)) return true;
            }
            return false;
        },
        else => false,
    };
}

test "hasTensors" {
    comptime {
        try std.testing.expect(hasTensors(?Tensor));
        try std.testing.expect(hasTensors(struct { u8, ?Tensor }));
        try std.testing.expect(!hasTensors(struct { u8, usize }));
    }
}

pub fn hasConstTensors(comptime T: type, comptime self_const: bool) bool {
    if (T == Tensor) return self_const;

    return switch (@typeInfo(T)) {
        inline .Array, .Optional => |info| hasTensors(info.child) and self_const,
        .Pointer => |ptr_info| hasConstTensors(ptr_info.child, ptr_info.is_const),
        inline .Struct, .Union => |info| {
            inline for (info.fields) |field| {
                if (hasConstTensors(field.type, self_const)) return true;
            }
            return false;
        },
        else => false,
    };
}

test "hasConstTensors" {
    try std.testing.expect(!hasConstTensors(?Tensor, false));
    try std.testing.expect(hasConstTensors(struct { u8, ?Tensor }, true));
    try std.testing.expect(!hasConstTensors(struct { u8, *Tensor }, true));
    try std.testing.expect(hasConstTensors(struct { u8, *const Tensor }, false));
    try std.testing.expect(!hasConstTensors(struct { *Tensor }, false));
    try std.testing.expect(!hasConstTensors(std.meta.Tuple(&[_]type{*Tensor}), false));
    try std.testing.expect(!hasConstTensors(struct { u8, usize }, false));
    try std.testing.expect(hasConstTensors(struct { [5]Tensor, usize }, true));
    try std.testing.expect(!hasConstTensors(struct { [5]Tensor, usize }, false));
}

// making this a struct force all fields to be evaluted on creation,
// which gives a better error stacktrace
// than delaying the error to when the object fields are read.
const Sign = struct {
    FuncT: type,
    ModelT: type,
    ArgsT: type,
    ReturnT: type,
};

pub fn ModuleSignature(comptime func: anytype) Sign {
    const FuncT = if (@TypeOf(func) == type) func else @TypeOf(func);
    return .{
        .FuncT = FuncT,
        .ModelT = @typeInfo(FuncT).Fn.params[0].type orelse @compileError("cannot create,ModuleSignature for function with an 'anytype' parameter"),
        .ArgsT = blk: {
            const function_info = @typeInfo(FuncT);
            if (function_info.Fn.params[1..].len == 0) {
                break :blk @TypeOf(.{});
            }

            var argument_field_list: [function_info.Fn.params.len - 1]type = undefined;
            for (function_info.Fn.params[1..], 0..) |arg, i| {
                const T = arg.type orelse @compileError("cannot create ModuleSignature for function with an 'anytype' parameter");
                argument_field_list[i] = T;
            }

            break :blk std.meta.Tuple(&argument_field_list);
        },
        .ReturnT = @typeInfo(FuncT).Fn.return_type.?,
    };
}

pub const MlirFn = struct {
    name: [:0]const u8,
    n_model: u32,
    n_args: u32,
    res_types: []mlir.Type,
    res_shapes: []Shape,
    res_donations: []Tensor._Donation,
    mlir_fn: mlir.Operation,
};

// TODO(Corentin): Remove that
pub const FnCache = struct {
    pub const Key = struct { fn_ptr: *const anyopaque, input_hash: u64 };

    // TODO: merge arenas
    cache: std.AutoHashMapUnmanaged(Key, MlirFn),
    // Arena for the cache entries
    cache_arena: std.heap.ArenaAllocator,
    // Arena for the cache data (name, res_type)
    cache_data_arena: std.heap.ArenaAllocator,

    pub fn init(allocator: std.mem.Allocator) FnCache {
        return .{
            .cache = .{},
            .cache_arena = std.heap.ArenaAllocator.init(allocator),
            .cache_data_arena = std.heap.ArenaAllocator.init(allocator),
        };
    }

    pub fn deinit(self: FnCache) void {
        self.cache_arena.deinit();
        self.cache_data_arena.deinit();
    }

    pub fn getEntry(self: *const FnCache, key: Key) ?MlirFn {
        return self.cache.get(key);
    }

    pub fn addEntry(self: *FnCache, key: Key, value: MlirFn) !MlirFn {
        var cache_data_allocator = self.cache_data_arena.allocator();

        const res_types_copy = try cache_data_allocator.dupe(mlir.Type, value.res_types);
        errdefer cache_data_allocator.free(res_types_copy);

        const res_shapes_copy = try cache_data_allocator.dupe(Shape, value.res_shapes);
        errdefer cache_data_allocator.free(res_shapes_copy);

        const res_donations_copy = try cache_data_allocator.dupe(Tensor._Donation, value.res_donations);
        errdefer cache_data_allocator.free(res_donations_copy);

        const name_copy = try cache_data_allocator.dupeZ(u8, value.name);
        errdefer cache_data_allocator.free(name_copy);

        const owned_value: MlirFn = .{
            .name = name_copy,
            .mlir_fn = value.mlir_fn,
            .n_model = value.n_model,
            .n_args = value.n_args,
            .res_types = res_types_copy,
            .res_shapes = res_shapes_copy,
            .res_donations = res_donations_copy,
        };

        try self.cache.putNoClobber(self.cache_arena.allocator(), key, owned_value);
        return owned_value;
    }
};

test FnCache {
    const zml = @import("zml.zig");
    const platform = zml.testing.env();

    const NN = struct {
        const NN_ = @This();
        layer_weights: [3]Tensor,
        layer_biases: [3]Tensor,

        pub fn forward(self: NN_, x0: Tensor) Tensor {
            var x = x0;
            for (self.layer_weights, self.layer_biases) |w, b| {
                // TODO use the `call` magic helper
                // x = ops.callFunc(ctx, NN_, "reluLayer", .{ w, b, x });
                x = NN_.reluLayer(w, b, x);
            }
            return x;
        }

        pub fn forwardRefImpl(self: NN_, x0: Tensor) Tensor {
            var x = x0;
            for (self.layer_weights, self.layer_biases) |w, b| {
                x = NN_.reluLayer(w, b, x);
            }
            return x;
        }

        pub fn reluLayer(w: Tensor, b: Tensor, x: Tensor) Tensor {
            const wx = w.dotGeneral(x, &.{.{ -1, 0 }}, &.{});
            return wx.add(b.broadcastLeft(wx.shape())).relu();
        }
    };

    const x = try zml.Buffer.fromSlice(platform, .{2}, &[_]f16{ -1, 1 });
    const nn: zml.Bufferized(NN) = .{
        .layer_weights = .{
            try zml.Buffer.fromSlice(platform, .{ 2, 2 }, &[_]f16{ 1, -1, 0, 1 }),
            try zml.Buffer.fromSlice(platform, .{ 2, 2 }, &[_]f16{ 1, 2, 1, -1 }),
            // third layer is different
            try zml.Buffer.fromSlice(platform, .{ 3, 2 }, &[_]f16{ 1, 2, 0, 1, -1, 0 }),
        },
        .layer_biases = .{
            try zml.Buffer.fromSlice(platform, .{2}, &[_]f16{ 0, 0 }),
            try zml.Buffer.fromSlice(platform, .{2}, &[_]f16{ 10, 10 }),
            try zml.Buffer.fromSlice(platform, .{3}, &[_]f16{ -10, -10, -10 }),
        },
    };
    const res = try zml.testing.compileAndCall(platform, NN.forward, .{ nn, x });
    const expected = try zml.testing.compileAndCall(platform, NN.forwardRefImpl, .{ nn, x });
    try zml.testing.expectClose(expected, res, 1e-4);
}

pub fn hashArgs(mod: anytype) u64 {
    var hasher = std.hash.Wyhash.init(0);
    hash(&hasher, mod, .DeepRecursive);
    return hasher.final();
}

pub fn hashTensor(hasher: *std.hash.Wyhash, tensor: Tensor) void {
    // Note: if we enforced 0-init dims then we could hash dims instead.
    hashArray(hasher, tensor.dims(), .Shallow);
    hash(hasher, tensor.dtype(), .Shallow);
}

const HashStrategy = std.hash.Strategy;
const tensorAwareHash = hash; // alias for when "hash" is ambiguous

/// Provides generic hashing for any eligible type.
/// Strategy is provided to determine if pointers should be followed or not.
pub fn hash(hasher: *std.hash.Wyhash, key: anytype, comptime strat: HashStrategy) void {
    const Key = @TypeOf(key);
    if (Key == Tensor) return hashTensor(hasher, key);

    if (strat == .Shallow and std.meta.hasUniqueRepresentation(Key)) {
        hasher.update(std.mem.asBytes(&key));
        return;
    }

    switch (@typeInfo(Key)) {
        .NoReturn, .Opaque, .Undefined, .Null, .ComptimeFloat, .ComptimeInt, .Type, .EnumLiteral, .Frame, .Void => return,

        // Help the optimizer see that hashing an int is easy by inlining!
        // TODO Check if the situation is better after #561 is resolved.
        .Int => |int| switch (int.signedness) {
            .signed => hash(hasher, @as(@Type(.{ .Int = .{
                .bits = int.bits,
                .signedness = .unsigned,
            } }), @bitCast(key)), strat),
            .unsigned => {
                if (std.meta.hasUniqueRepresentation(Key)) {
                    hasher.update(std.mem.asBytes(&key));
                } else {
                    // Take only the part containing the key value, the remaining
                    // bytes are undefined and must not be hashed!
                    const byte_size = comptime std.math.divCeil(comptime_int, @bitSizeOf(Key), 8) catch unreachable;
                    hasher.update(std.mem.asBytes(&key)[0..byte_size]);
                }
            },
        },
        // Note: contrary to Zig we accept hashing floats.
        // Typically the float we are going to hash here are hyperparameters,
        // and not the result of an operation, so bytes should be the same everytime.
        .Float => hasher.update(std.mem.asBytes(&key)),
        .Bool => hash(hasher, @intFromBool(key), strat),
        .Enum => hash(hasher, @intFromEnum(key), strat),
        .ErrorSet => hash(hasher, @intFromError(key), strat),
        .AnyFrame, .Fn => hash(hasher, @intFromPtr(key), strat),
        .Pointer => |info| switch (info.size) {
            .One => switch (strat) {
                .Shallow => hash(hasher, @intFromPtr(key), .Shallow),
                .Deep => hash(hasher, key.*, .Shallow),
                .DeepRecursive => switch (@typeInfo(info.child)) {
                    .Opaque, .Fn => hash(hasher, @intFromPtr(key), .Shallow),
                    else => hash(hasher, key.*, .DeepRecursive),
                },
            },
            .Slice => {
                switch (strat) {
                    .Shallow => hash(hasher, @intFromPtr(key.ptr), .Shallow),
                    .Deep => hashArray(hasher, key, .Shallow),
                    .DeepRecursive => hashArray(hasher, key, .DeepRecursive),
                }
                hash(hasher, key.len, .Shallow);
            },
            .Many,
            .C,
            => switch (strat) {
                .Shallow => hash(hasher, @intFromPtr(key), .Shallow),
                else => @compileError(
                    \\ unknown-length pointers and C pointers cannot be hashed deeply.
                    \\ Consider providing your own hash function.
                ),
            },
        },
        .Optional => if (key) |k| hash(hasher, k, strat),

        .Array => hashArray(hasher, key, strat),

        .Vector => |info| {
            if (std.meta.hasUniqueRepresentation(Key)) {
                hasher.update(std.mem.asBytes(&key));
            } else {
                comptime var i = 0;
                inline while (i < info.len) : (i += 1) {
                    hash(hasher, key[i], strat);
                }
            }
        },

        .Struct => |info| {
            inline for (info.fields) |field| {
                // We reuse the hash of the previous field as the seed for the
                // next one so that they're dependant.
                hash(hasher, @field(key, field.name), strat);
            }
        },

        .Union => |info| {
            if (info.tag_type) |tag_type| {
                const tag = std.meta.activeTag(key);
                hash(hasher, tag, strat);
                inline for (info.fields) |field| {
                    if (@field(tag_type, field.name) == tag) {
                        if (field.type != void) {
                            hash(hasher, @field(key, field.name), strat);
                        }
                        // TODO use a labelled break when it does not crash the compiler. cf #2908
                        // break :blk;
                        return;
                    }
                }
                unreachable;
            } else @compileError("cannot hash untagged union type: " ++ @typeName(Key) ++ ", provide your own hash function");
        },

        .ErrorUnion => blk: {
            const payload = key catch |err| {
                hash(hasher, err, strat);
                break :blk;
            };
            hash(hasher, payload, strat);
        },
    }
}

fn hashArray(hasher: anytype, key: anytype, comptime strat: HashStrategy) void {
    for (key) |element| {
        hash(hasher, element, strat);
    }
}