const std = @import("std");

pub const MessageType = enum {
    info,
    connect,
    @"pub",
    hpub,
    sub,
    unsub,
    msg,
    hmsg,
    ping,
    pong,
    @"+ok",
    @"-err",
    eos,

    fn parseMemEql(input: []const u8) ?MessageType {
        // if (std.mem.eql(u8, "INFO", input)) return .info;
        if (std.mem.eql(u8, "CONNECT", input)) return .connect;
        if (std.mem.eql(u8, "PUB", input)) return .@"pub";
        if (std.mem.eql(u8, "HPUB", input)) return .hpub;
        if (std.mem.eql(u8, "SUB", input)) return .sub;
        if (std.mem.eql(u8, "UNSUB", input)) return .unsub;
        // if (std.mem.eql(u8, "MSG", input)) return .msg;
        // if (std.mem.eql(u8, "HMSG", input)) return .hmsg;
        if (std.mem.eql(u8, "PING", input)) return .ping;
        if (std.mem.eql(u8, "PONG", input)) return .pong;
        // if (std.mem.eql(u8, "@"+OK"", input)) return .@"+ok";
        // if (std.mem.eql(u8, "@"-ERR"", input)) return .@"-err";
        return error.InvalidMessageType;
    }
};

pub const Message = union(MessageType) {
    info: ServerInfo,
    connect: AllocatedConnect,
    @"pub": Pub,
    hpub: void,
    sub: Sub,
    unsub: Unsub,
    msg: Msg,
    hmsg: void,
    ping,
    pong,
    @"+ok": void,
    @"-err": void,
    // Not an actual NATS message, but used to signal end of stream was reached in the input,
    // and we should close the reader.
    eos: void,
    pub const ServerInfo = struct {
        /// The unique identifier of the NATS server.
        server_id: []const u8,
        /// The name of the NATS server.
        server_name: []const u8,
        /// The version of NATS.
        version: []const u8,
        /// The version of golang the NATS server was built with.
        go: []const u8 = "0.0.0",
        /// The IP address used to start the NATS server,
        /// by default this will be 0.0.0.0 and can be
        /// configured with -client_advertise host:port.
        host: []const u8 = "0.0.0.0",
        /// The port number the NATS server is configured
        /// to listen on.
        port: u16 = 4222,
        /// Whether the server supports headers.
        headers: bool = false,
        /// Maximum payload size, in bytes, that the server
        /// will accept from the client.
        max_payload: u64,
        /// An integer indicating the protocol version of
        /// the server. The server version 1.2.0 sets this
        /// to 1 to indicate that it supports the "Echo"
        /// feature.
        proto: u32 = 1,
    };
    pub const AllocatedConnect = struct {
        allocator: std.heap.ArenaAllocator,
        connect: Connect,

        pub fn deinit(self: AllocatedConnect) void {
            self.allocator.deinit();
        }
    };
    pub const Connect = struct {
        verbose: bool = false,
        pedantic: bool = false,
        tls_required: bool = false,
        auth_token: ?[]const u8 = null,
        user: ?[]const u8 = null,
        pass: ?[]const u8 = null,
        name: ?[]const u8 = null,
        lang: []const u8,
        version: []const u8,
        protocol: u32,
        echo: ?bool = null,
        sig: ?[]const u8 = null,
        jwt: ?[]const u8 = null,
        no_responders: ?bool = null,
        headers: ?bool = null,
        nkey: ?[]const u8 = null,
    };
    pub const Pub = struct {
        /// The destination subject to publish to.
        subject: []const u8,
        /// The reply subject that subscribers can use to send a response back to the publisher/requestor.
        reply_to: ?[]const u8 = null,
        /// The message payload data.
        payload: []const u8,
    };
    pub const Sub = struct {
        /// The subject name to subscribe to.
        subject: []const u8,
        /// If specified, the subscriber will join this queue group.
        queue_group: ?[]const u8,
        /// A unique alphanumeric subscription ID, generated by the client.
        sid: []const u8,
    };
    pub const Unsub = struct {
        /// The unique alphanumeric subscription ID of the subject to unsubscribe from.
        sid: []const u8,
        /// A number of messages to wait for before automatically unsubscribing.
        max_msgs: ?usize = null,
    };
    pub const Msg = struct {
        subject: []const u8,
        sid: []const u8,
        reply_to: ?[]const u8,
        payload: []const u8,
    };

    const client_types = std.StaticStringMap(MessageType).initComptime(
        .{
            // {"INFO", .info},
            .{ "CONNECT", .connect },
            .{ "PUB", .@"pub" },
            .{ "HPUB", .hpub },
            .{ "SUB", .sub },
            .{ "UNSUB", .unsub },
            // {"MSG", .msg},
            // {"HMSG", .hmsg},
            .{ "PING", .ping },
            .{ "PONG", .pong },
            // {"+OK", .@"+ok"},
            // {"-ERR", .@"-err"},
        },
    );
    fn parseStaticStringMap(input: []const u8) ?MessageType {
        return client_types.get(input);
    }

    pub const parse = parseStaticStringMap;

    /// An error should be handled by cleaning up this connection.
    pub fn next(alloc: std.mem.Allocator, in: *std.Io.Reader) !Message {
        // errdefer |err| {
        //     std.debug.print("Error occurred: {}\n", .{err});

        //     // Get the error return trace
        //     if (@errorReturnTrace()) |trace| {
        //         std.debug.print("Error return trace:\n", .{});
        //         std.debug.dumpStackTrace(trace);
        //     } else {
        //         std.debug.print("No error return trace available\n", .{});
        //     }
        // }

        var operation_string: std.ArrayList(u8) = blk: {
            var buf: ["CONTINUE".len + 1]u8 = undefined;
            break :blk .initBuffer(&buf);
        };

        while (in.peekByte()) |byte| {
            if (std.ascii.isUpper(byte)) {
                try operation_string.appendBounded(byte);
                try in.discardAll(1);
            } else break;
        } else |err| switch (err) {
            error.EndOfStream => {
                return .{ .eos = {} };
            },
            else => {
                return err;
            },
        }

        const operation = parse(operation_string.items) orelse {
            return error.InvalidOperation;
        };

        switch (operation) {
            .connect => {
                // TODO: should be ARENA allocator
                var connect_arena_allocator: std.heap.ArenaAllocator = .init(alloc);
                const connect_allocator = connect_arena_allocator.allocator();
                const connect_string_writer_allocating: std.Io.Writer.Allocating = try .initCapacity(connect_allocator, 1024);
                var connect_string_writer = connect_string_writer_allocating.writer;
                try in.discardAll(1); // throw away space

                // Should read the next JSON object to the fixed buffer writer.
                _ = try in.streamDelimiter(&connect_string_writer, '}');
                try connect_string_writer.writeByte('}');
                std.debug.assert(std.mem.eql(u8, try in.take(3), "}\r\n")); // discard '}\r\n'

                // TODO: should be CONNECTION allocator
                const res = try std.json.parseFromSliceLeaky(Connect, connect_allocator, connect_string_writer.buffered(), .{ .allocate = .alloc_always });

                return .{ .connect = .{ .allocator = connect_arena_allocator, .connect = res } };
            },
            .@"pub" => {
                try in.discardAll(1); // throw away space

                // Parse subject
                const subject: []const u8 = try readSubject(alloc, in);

                // Parse byte count
                const byte_count = blk: {
                    var byte_count_list: std.ArrayList(u8) = try .initCapacity(alloc, 64);
                    while (in.takeByte() catch null) |byte| {
                        if (std.ascii.isWhitespace(byte)) {
                            std.debug.assert(byte == '\r');
                            std.debug.assert(try in.takeByte() == '\n');
                            break;
                        }

                        if (std.ascii.isDigit(byte)) {
                            try byte_count_list.append(alloc, byte);
                        } else {
                            return error.InvalidStream;
                        }
                    } else return error.InvalidStream;

                    break :blk try std.fmt.parseUnsigned(usize, byte_count_list.items, 10);
                };

                const payload = blk: {
                    const bytes = try alloc.alloc(u8, byte_count);
                    try in.readSliceAll(bytes);
                    std.debug.assert(std.mem.eql(u8, try in.take(2), "\r\n"));
                    break :blk bytes;
                };

                return .{
                    .@"pub" = .{
                        .subject = subject,
                        .payload = payload,
                    },
                };
            },
            .ping => {
                std.debug.assert(std.mem.eql(u8, try in.take(2), "\r\n"));
                return .ping;
            },
            .pong => {
                std.debug.assert(std.mem.eql(u8, try in.take(2), "\r\n"));
                return .pong;
            },
            .sub => {
                std.debug.assert(std.ascii.isWhitespace(try in.takeByte()));
                const subject = try readSubject(alloc, in);
                const second = blk: {
                    // Drop whitespace
                    while (in.peekByte() catch null) |byte| {
                        if (std.ascii.isWhitespace(byte)) {
                            in.toss(1);
                        } else break;
                    } else return error.InvalidStream;

                    var acc: std.ArrayList(u8) = try .initCapacity(alloc, 32);
                    while (in.takeByte() catch null) |byte| {
                        if (std.ascii.isWhitespace(byte)) break;
                        try acc.append(alloc, byte);
                    } else return error.InvalidStream;

                    break :blk try acc.toOwnedSlice(alloc);
                };
                const queue_group = if ((try in.peekByte()) != '\r') second else null;
                const sid = if (queue_group) |_| try in.takeDelimiterExclusive('\r') else second;
                std.debug.assert(std.mem.eql(u8, try in.take(2), "\r\n"));
                return .{
                    .sub = .{
                        .subject = subject,
                        .queue_group = queue_group,
                        .sid = sid,
                    },
                };
            },
            .unsub => {
                std.debug.assert(std.ascii.isWhitespace(try in.takeByte()));
                // Parse byte count
                const sid = blk: {
                    var acc: std.ArrayList(u8) = try .initCapacity(alloc, 8);
                    while (in.peekByte() catch null) |byte| {
                        if (std.ascii.isWhitespace(byte)) break;
                        try acc.append(alloc, byte);
                        in.toss(1);
                    } else return error.InvalidStream;
                    break :blk try acc.toOwnedSlice(alloc);
                };

                if ((try in.peekByte()) == '\r') {
                    std.debug.assert(std.mem.eql(u8, try in.take(2), "\r\n"));
                    return .{
                        .unsub = .{
                            .sid = sid,
                        },
                    };
                } else if (std.ascii.isWhitespace(try in.peekByte())) {
                    in.toss(1);
                    const max_msgs = blk: {
                        var max_msgs_list: std.ArrayList(u8) = try .initCapacity(alloc, 64);
                        while (in.takeByte() catch null) |byte| {
                            if (std.ascii.isWhitespace(byte)) {
                                std.debug.assert(byte == '\r');
                                std.debug.assert(try in.takeByte() == '\n');
                                break;
                            }

                            if (std.ascii.isDigit(byte)) {
                                try max_msgs_list.append(alloc, byte);
                            } else {
                                return error.InvalidStream;
                            }
                        } else return error.InvalidStream;

                        break :blk try std.fmt.parseUnsigned(usize, max_msgs_list.items, 10);
                    };

                    return .{
                        .unsub = .{
                            .sid = sid,
                            .max_msgs = max_msgs,
                        },
                    };
                } else return error.InvalidStream;
            },
            else => |msg| std.debug.panic("Not implemented: {}\n", .{msg}),
        }
    }
};

fn readSubject(alloc: std.mem.Allocator, in: *std.Io.Reader) ![]const u8 {
    // TODO: should be ARENA allocator
    var subject_list: std.ArrayList(u8) = try .initCapacity(alloc, 1024);

    // Handle the first character
    {
        const byte = try in.takeByte();
        std.debug.assert(!std.ascii.isWhitespace(byte));
        if (byte == '.')
            return error.InvalidSubject;

        try subject_list.append(alloc, byte);
    }

    while (in.takeByte() catch null) |byte| {
        if (std.ascii.isWhitespace(byte)) break;
        if (std.ascii.isAscii(byte)) {
            if (byte == '.') {
                const next_byte = try in.peekByte();
                if (next_byte == '.' or std.ascii.isWhitespace(next_byte))
                    return error.InvalidSubject;
            }
            try subject_list.append(alloc, byte);
        }
    } else return error.InvalidStream;
    return subject_list.toOwnedSlice(alloc);
}

fn parseJsonMessage(T: type, alloc: std.mem.Allocator, in: *std.Io.Reader) !T {
    var reader: std.json.Reader = .init(alloc, in);
    return std.json.innerParse(T, alloc, &reader, .{
        .max_value_len = std.json.default_max_value_len,
        .allocate = .alloc_always,
    });
}

fn parsePub(in: *std.Io.Reader) !Message.Pub {
    const subject = (try in.takeDelimiter(' ')) orelse return error.EndOfStream;
    const next = (try in.takeDelimiter('\r')) orelse return error.EndOfStream;
    var reply_to: ?[]const u8 = null;
    const bytes = std.fmt.parseUnsigned(usize, next, 10) catch blk: {
        reply_to = next;
        break :blk try std.fmt.parseUnsigned(usize, (try in.takeDelimiter(' ')) orelse return error.EndOfStream, 10);
    };

    in.toss(1); // LF
    const payload = try in.take(bytes);

    return .{
        .subject = subject,
        .reply_to = reply_to,
        .bytes = bytes,
        .payload = payload,
    };
}

// try returning error in debug mode, only null in release?
// pub fn parseNextMessage(alloc: std.mem.Allocator, in: *std.Io.Reader) ?Message {
//     const message_type: MessageType = blk: {
//         var word: ["CONNECT".len]u8 = undefined;
//         var len: usize = 0;
//         for (&word, 0..) |*b, i| {
//             const byte = in.takeByte() catch return null;
//             if (std.ascii.isUpper(byte)) {
//                 b.* = byte;
//                 len = i + 1;
//             } else break;
//         }

//         break :blk Message.parse(word[0..len]) orelse return null;
//     };

//     // defer in.toss(2); // CRLF
//     return switch (message_type) {
//         .connect => blk: {
//             const value: ?Message = .{ .connect = parseJsonMessage(Message.Connect, alloc, in) catch return null };

//             break :blk value;
//         },
//         .@"pub" => .{ .@"pub" = parsePub(in) catch |err| std.debug.panic("{}", .{err}) },
//         .ping => .ping,
//         else => null,
//     };
// }

// test parseNextMessage {
//     const input = "CONNECT {\"verbose\":false,\"pedantic\":false,\"tls_required\":false,\"name\":\"NATS CLI Version v0.2.4\",\"lang\":\"go\",\"version\":\"1.43.0\",\"protocol\":1,\"echo\":true,\"headers\":true,\"no_responders\":true}\r\nPUB hi 3\r\nfoo\r\n";
//     var reader: std.Io.Reader = .fixed(input);
//     var arena: std.heap.ArenaAllocator = .init(std.testing.allocator);
//     defer arena.deinit();
//     const gpa = arena.allocator();

//     {
//         const msg: Message = try Message.next(gpa, &reader);
//         const expected: Message = .{ .connect = .{
//             .connect = .{
//                 .verbose = false,
//                 .pedantic = false,
//                 .tls_required = false,
//                 .name = try gpa.dupe(u8, "NATS CLI Version v0.2.4"),
//                 .lang = try gpa.dupe(u8, "go"),
//                 .version = try gpa.dupe(u8, "1.43.0"),
//                 .protocol = 1,
//                 .echo = true,
//                 .headers = true,
//                 .no_responders = true,
//             },
//             .allocator = arena,
//         } };

//         try std.testing.expectEqualDeep(expected, msg);
//     }
//     {
//         const msg: Message = try Message.next(gpa, &reader);
//         const expected: Message = .{ .@"pub" = .{
//             .subject = "hi",
//             .payload = "foo",
//         } };
//         try std.testing.expectEqualDeep(expected, msg);
//     }
// }

// test "MessageType.parse performance" {
//     // Measure perf for parseMemEql
//     // Measure perf for parseStaticStringMap
//     // assert parse = fastest perf
// }