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// Copyright 2025 Shota FUJI
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// SPDX-License-Identifier: Apache-2.0

const std = @import("std");

pub const SerializableOptions = struct {
    field: []const u8 = "data",
    json_options: std.json.StringifyOptions = .{
        .emit_null_optional_fields = false,
    },
};

pub fn Serializable(comptime T: type, opts: SerializableOptions) type {
    const to_json = struct {
        fn to_json(ptr: *const T) callconv(.C) ?[*:0]const u8 {
            var buf = std.ArrayList(u8).init(std.heap.c_allocator);
            defer buf.deinit();

            const writer = buf.writer();

            std.json.stringify(
                @field(ptr, opts.field),
                opts.json_options,
                writer,
            ) catch return null;

            const slice = buf.toOwnedSliceSentinel(0) catch return null;
            return slice.ptr;
        }
    };

    comptime {
        if (@typeInfo(T).@"struct".layout == .@"extern") {
            @extern(&T, .{});
        }

        @export(&to_json.to_json, .{
            .name = std.fmt.comptimePrint("{s}_to_json", .{T.cname}),
        });

        const Container = t: {
            for (@typeInfo(T).@"struct".fields) |field| {
                if (std.mem.eql(u8, field.name, opts.field)) {
                    break :t field.type;
                }
            }

            @compileError(std.fmt.comptimePrint("Type \"{s}\" does not have \"{s}\" field", .{
                @typeName(T), opts.field,
            }));
        };

        for (@typeInfo(Container).@"struct".fields) |field| {
            const UnwrappedValue, const optional = switch (@typeInfo(field.type)) {
                .optional => |optional| .{ optional.child, true },
                else => .{ field.type, false },
            };

            const CValue = switch (@typeInfo(UnwrappedValue)) {
                .pointer => |pointer| switch (pointer.size) {
                    .slice => [*:0]pointer.child,
                    else => @compileError("Non-slice pointer is not supported."),
                },
                else => UnwrappedValue,
            };

            const setter = struct {
                fn set(ptr: *T, value: CValue) callconv(.C) void {
                    switch (@typeInfo(UnwrappedValue)) {
                        .pointer => |pointer| {
                            switch (pointer.size) {
                                .slice => {
                                    const copy = std.heap.c_allocator.dupe(
                                        pointer.child,
                                        std.mem.span(value),
                                    ) catch {
                                        std.log.debug("Failed to copy for {s} in {s}: out of memory", .{
                                            field.name,
                                            T.cname,
                                        });
                                        return;
                                    };

                                    if (optional) {
                                        if (@field(@field(ptr, opts.field), field.name)) |current| {
                                            std.heap.c_allocator.free(current);
                                        }
                                    }

                                    @field(@field(ptr, opts.field), field.name) = copy;
                                },
                                else => {
                                    @compileError("Non-slice pointer is not supported.");
                                },
                            }
                        },
                        else => {
                            @field(@field(ptr, opts.field), field.name) = value;
                        },
                    }
                }
            };

            @export(&setter.set, .{
                .name = std.fmt.comptimePrint("{s}_set_{s}", .{ T.cname, field.name }),
            });
        }
    }

    return T;
}

pub const DeserializableOptions = struct {
    type_field: []const u8 = "Data",
    json_options: std.json.ParseOptions = .{
        .ignore_unknown_fields = true,
    },
};

pub fn Deserializable(comptime T: type, opts: DeserializableOptions) type {
    const from_json = struct {
        fn from_json(ptr: [*:0]const u8) callconv(.C) ?*T {
            const result = std.json.parseFromSlice(
                @field(T, opts.type_field).Raw,
                std.heap.c_allocator,
                std.mem.span(ptr),
                opts.json_options,
            ) catch return null;

            defer result.deinit();

            return T.new(@field(T, opts.type_field).init(result.value) catch return null) catch return null;
        }
    };

    comptime {
        @export(&from_json.from_json, .{
            .name = std.fmt.comptimePrint("{s}_from_json", .{T.cname}),
        });
    }

    return T;
}