pub const FunctionAttributes = enum(u32) {
    none,
    _,

    const function_index = 0;
    const return_index = 1;
    const params_index = 2;

    pub const Wip = struct {
        maps: Maps = .{},

        const Map = std.AutoArrayHashMapUnmanaged(Attribute.Kind, Attribute.Index);
        const Maps = std.ArrayListUnmanaged(Map);

        pub fn deinit(self: *Wip, builder: *const Builder) void {
            for (self.maps.items) |*map| map.deinit(builder.gpa);
            self.maps.deinit(builder.gpa);
            self.* = undefined;
        }

        pub fn addFnAttr(self: *Wip, attribute: Attribute, builder: *Builder) Allocator.Error!void {
            try self.addAttr(function_index, attribute, builder);
        }

        pub fn addFnAttrIndex(
            self: *Wip,
            attribute_index: Attribute.Index,
            builder: *const Builder,
        ) Allocator.Error!void {
            try self.addAttrIndex(function_index, attribute_index, builder);
        }

        pub fn removeFnAttr(self: *Wip, attribute_kind: Attribute.Kind) Allocator.Error!bool {
            return self.removeAttr(function_index, attribute_kind);
        }

        pub fn addRetAttr(self: *Wip, attribute: Attribute, builder: *Builder) Allocator.Error!void {
            try self.addAttr(return_index, attribute, builder);
        }

        pub fn addRetAttrIndex(
            self: *Wip,
            attribute_index: Attribute.Index,
            builder: *const Builder,
        ) Allocator.Error!void {
            try self.addAttrIndex(return_index, attribute_index, builder);
        }

        pub fn removeRetAttr(self: *Wip, attribute_kind: Attribute.Kind) Allocator.Error!bool {
            return self.removeAttr(return_index, attribute_kind);
        }

        pub fn addParamAttr(
            self: *Wip,
            param_index: usize,
            attribute: Attribute,
            builder: *Builder,
        ) Allocator.Error!void {
            try self.addAttr(params_index + param_index, attribute, builder);
        }

        pub fn addParamAttrIndex(
            self: *Wip,
            param_index: usize,
            attribute_index: Attribute.Index,
            builder: *const Builder,
        ) Allocator.Error!void {
            try self.addAttrIndex(params_index + param_index, attribute_index, builder);
        }

        pub fn removeParamAttr(
            self: *Wip,
            param_index: usize,
            attribute_kind: Attribute.Kind,
        ) Allocator.Error!bool {
            return self.removeAttr(params_index + param_index, attribute_kind);
        }

        pub fn finish(self: *const Wip, builder: *Builder) Allocator.Error!FunctionAttributes {
            const attributes = try builder.gpa.alloc(Attributes, self.maps.items.len);
            defer builder.gpa.free(attributes);
            for (attributes, self.maps.items) |*attribute, map|
                attribute.* = try builder.attrs(map.values());
            return builder.fnAttrs(attributes);
        }

        fn addAttr(
            self: *Wip,
            index: usize,
            attribute: Attribute,
            builder: *Builder,
        ) Allocator.Error!void {
            const map = try self.getOrPutMap(builder.gpa, index);
            try map.put(builder.gpa, attribute.getKind(), try builder.attr(attribute));
        }

        fn addAttrIndex(
            self: *Wip,
            index: usize,
            attribute_index: Attribute.Index,
            builder: *const Builder,
        ) Allocator.Error!void {
            const map = try self.getOrPutMap(builder.gpa, index);
            try map.put(builder.gpa, attribute_index.getKind(builder), attribute_index);
        }

        fn removeAttr(self: *Wip, index: usize, attribute_kind: Attribute.Kind) Allocator.Error!bool {
            const map = self.getMap(index) orelse return false;
            return map.swapRemove(attribute_kind);
        }

        fn getOrPutMap(self: *Wip, allocator: Allocator, index: usize) Allocator.Error!*Map {
            if (index >= self.maps.items.len)
                try self.maps.appendNTimes(allocator, .{}, index + 1 - self.maps.items.len);
            return &self.maps.items[index];
        }

        fn getMap(self: *Wip, index: usize) ?*Map {
            return if (index >= self.maps.items.len) null else &self.maps.items[index];
        }

        fn ensureTotalLength(self: *Wip, new_len: usize) Allocator.Error!void {
            try self.maps.appendNTimes(
                .{},
                std.math.sub(usize, new_len, self.maps.items.len) catch return,
            );
        }
    };

    pub fn func(self: FunctionAttributes, builder: *const Builder) Attributes {
        return self.get(function_index, builder);
    }

    pub fn ret(self: FunctionAttributes, builder: *const Builder) Attributes {
        return self.get(return_index, builder);
    }

    pub fn param(self: FunctionAttributes, param_index: usize, builder: *const Builder) Attributes {
        return self.get(params_index + param_index, builder);
    }

    pub fn toWip(self: FunctionAttributes, builder: *const Builder) Allocator.Error!Wip {
        var wip: Wip = .{};
        errdefer wip.deinit(builder);
        const attributes_slice = self.slice(builder);
        try wip.maps.ensureTotalCapacityPrecise(builder.gpa, attributes_slice.len);
        for (attributes_slice) |attributes| {
            const map = wip.maps.addOneAssumeCapacity();
            map.* = .{};
            const attribute_slice = attributes.slice(builder);
            try map.ensureTotalCapacity(builder.gpa, attribute_slice.len);
            for (attributes.slice(builder)) |attribute|
                map.putAssumeCapacityNoClobber(attribute.getKind(builder), attribute);
        }
        return wip;
    }

    fn get(self: FunctionAttributes, index: usize, builder: *const Builder) Attributes {
        const attribute_slice = self.slice(builder);
        return if (index < attribute_slice.len) attribute_slice[index] else .none;
    }

    fn slice(self: FunctionAttributes, builder: *const Builder) []const Attributes {
        const start = builder.attributes_indices.items[@intFromEnum(self)];
        const end = builder.attributes_indices.items[@intFromEnum(self) + 1];
        return @ptrCast(builder.attributes_extra.items[start..end]);
    }
}