const base64Enc = std.base64.Base64Encoder.init(std.base64.standard_alphabet_chars, '=');
const base64Dec = std.base64.Base64Decoder.init(std.base64.standard_alphabet_chars, '=');

const native_endian = @import("builtin").cpu.arch.endian();

rand: Random,
writer: *std.Io.Writer,

const Self = @This();

const max_message_size = 2048;

pub fn init(writer: *std.Io.Writer) !Self {
    var prng = Random.DefaultPrng.init(blk: {
        var seed: u64 = undefined;
        try posix.getrandom(mem.asBytes(&seed));
        break :blk seed;
    });
    const rand = prng.random();

    return .{
        .rand = rand,
        .writer = writer,
    };
}

pub fn deinit(self: *Self) void {
    self.writer.flush() catch {};
}

/// Used for relay messages and connection handshake.
/// Assumes Client .init has been called.
fn broadcastInitialInterestMessage(self: *Self, msg_bytes: []u8) !void {
    const writer = self.writer;

    const total_len = ((@bitSizeOf(EthernetHeaders) + @bitSizeOf(IpHeaders) + @bitSizeOf(UdpHeaders)) / 8) + msg_bytes.len;
    std.debug.assert(writer.buffer.len >= total_len);
    _ = writer.consumeAll();

    const ether_headers: EthernetHeaders = .{
        .dest_mac = .{ 0xff, 0xff, 0xff, 0xff, 0xfe, 0xff },
        .src_mac = .{ 0xee, 0xee, 0xee, 0xee, 0xee, 0xee },
        // .src_mac = blk: {
        //     var output_bytes: [6]u8 = undefined;
        //     // const r_bytes = try writer.writableArray(6);
        //     self.rand.bytes(&output_bytes);
        //     break :blk output_bytes;
        // },
        .ether_type = 0x0800,
    };

    // @compileLog((@bitSizeOf(EthernetHeaders) / 8));
    const ip_headers: IpHeaders = .{
        // .ip_version = 0x4,
        // .header_length = 0x5,
        .total_length = @intCast(total_len - 92),
        .ttl = 0x64,
        .protocol = 0x11,
        .src_ip = .{ 0xff, 0x02, 0x03, 0x04 },
        .dest_ip = .{ 0xff, 0xff, 0xff, 0xff },
    };

    const udp_headers: UdpHeaders = .{
        .src_port = 0xbbbb,
        .dest_port = 8888,
        .length = @intCast(msg_bytes.len),
    };

    try ether_headers.write(writer);
    try ip_headers.write(writer);
    try udp_headers.write(writer);

    // Saprus
    const msg_target_bytes = try writer.writableSlice(msg_bytes.len);
    @memcpy(msg_target_bytes, msg_bytes);
    var msg_target: *align(1) SaprusMessage = try .bytesAsValue(msg_target_bytes);
    try msg_target.networkFromNativeEndian();

    std.debug.print("bytes: {x}\n", .{writer.buffer[0..writer.end]});
    try writer.flush();
}

// fn broadcastSaprusMessage(msg_bytes: []align(@alignOf(SaprusMessage)) u8) !void {}

fn broadcastSaprusMessage(msg_bytes: []u8, udp_port: u16) !void {
    const msg: *align(1) SaprusMessage = try .bytesAsValue(msg_bytes);
    try msg.networkFromNativeEndian();
    defer msg.nativeFromNetworkEndian() catch unreachable;

    var sock = try network.Socket.create(.ipv4, .udp);
    defer sock.close();

    try sock.setBroadcast(true);

    // Bind to 0.0.0.0:0
    const bind_addr = network.EndPoint{
        .address = network.Address{ .ipv4 = network.Address.IPv4.any },
        .port = 0,
    };

    const dest_addr = network.EndPoint{
        .address = network.Address{ .ipv4 = network.Address.IPv4.broadcast },
        .port = udp_port,
    };

    try sock.bind(bind_addr);

    std.debug.print("{x}\n", .{msg_bytes});

    _ = try sock.sendTo(dest_addr, msg_bytes);
}

pub fn sendRelay(self: *Self, payload: []const u8, dest: [4]u8) !void {
    var buf: [max_message_size]u8 align(@alignOf(SaprusMessage)) = undefined;
    const msg_bytes = buf[0..try SaprusMessage.calcSize(
        .relay,
        base64Enc.calcSize(payload.len),
    )];
    const msg: *align(1) SaprusMessage = .init(.relay, msg_bytes);

    const relay = (try msg.getSaprusTypePayload()).relay;
    relay.dest = dest;
    _ = base64Enc.encode(relay.getPayload(), payload);

    try self.broadcastInitialInterestMessage(msg_bytes);
}

fn randomPort(self: Self) u16 {
    return self.rand.intRangeAtMost(u16, 1024, 65000);
}

pub fn sendInitialConnection(
    self: Self,
    payload: []const u8,
    output_bytes: []u8,
    initial_port: u16,
) !*align(1) SaprusMessage {
    const dest_port = self.randomPort();
    const msg_bytes = output_bytes[0..try SaprusMessage.calcSize(
        .connection,
        base64Enc.calcSize(payload.len),
    )];
    const msg: *align(1) SaprusMessage = .init(.connection, msg_bytes);

    const connection = (try msg.getSaprusTypePayload()).connection;
    connection.src_port = initial_port;
    connection.dest_port = dest_port;
    _ = base64Enc.encode(connection.getPayload(), payload);

    try broadcastSaprusMessage(msg_bytes, 8888);

    return msg;
}

pub fn connect(self: Self, payload: []const u8) !?SaprusConnection {
    const initial_port = self.randomPort();

    var initial_conn_res: ?*align(1) SaprusMessage = null;

    var sock = try network.Socket.create(.ipv4, .udp);
    defer sock.close();

    // Bind to 255.255.255.255:8888
    const bind_addr = network.EndPoint{
        .address = network.Address{ .ipv4 = network.Address.IPv4.broadcast },
        .port = 8888,
    };

    // timeout 1s
    try sock.setReadTimeout(1 * std.time.us_per_s);
    try sock.bind(bind_addr);

    var sent_msg_bytes: [max_message_size]u8 align(@alignOf(SaprusMessage)) = undefined;
    const msg = try self.sendInitialConnection(payload, &sent_msg_bytes, initial_port);

    var response_buf: [max_message_size]u8 align(@alignOf(SaprusMessage)) = undefined;
    _ = try sock.receive(&response_buf); // Ignore message that I sent.
    const len = try sock.receive(&response_buf);

    initial_conn_res = try .networkBytesAsValue(response_buf[0..len]);

    // Complete handshake after awaiting response
    try broadcastSaprusMessage(msg.asBytes(), self.randomPort());

    if (false) {
        return initial_conn_res.?;
    }
    return null;
}

const EthernetHeaders = struct {
    dest_mac: @Vector(6, u8),

    src_mac: @Vector(6, u8),

    ether_type: u16,

    fn write(hdr: @This(), writer: *std.Io.Writer) !void {
        try writer.writeInt(u48, @bitCast(hdr.dest_mac), .big);
        try writer.writeInt(u48, @bitCast(hdr.src_mac), .big);
        try writer.writeInt(u16, hdr.ether_type, .big);
    }
};

const IpHeaders = struct {
    _: u8 = 0x45,
    // ip_version: u4,
    // header_length: u4 = 0,
    type_of_service: u8 = 0,
    total_length: u16 = 0x04,

    identification: u16 = 0,
    __: u16 = 0x0,
    // ethernet_flags: u3 = 0,
    // fragment_offset: u13 = 0,
    ttl: u8 = 0,
    protocol: u8 = 0,

    header_checksum: @Vector(2, u8) = .{ 0, 0 },
    src_ip: @Vector(4, u8),

    dest_ip: @Vector(4, u8),

    fn write(hdr: @This(), writer: *std.Io.Writer) !void {
        try writer.writeInt(u8, 0x45, .big); // ip version and header length
        try writer.writeByte(hdr.type_of_service);
        try writer.writeInt(u16, hdr.total_length, .big);
        try writer.writeInt(u16, hdr.identification, .big);
        try writer.writeInt(u16, 0x00, .big); // ethernet flags and fragment offset
        try writer.writeByte(hdr.ttl);
        try writer.writeByte(hdr.protocol);
        try writer.writeInt(u16, @bitCast(hdr.header_checksum), .big);
        try writer.writeInt(u32, @bitCast(hdr.src_ip), .big);
        try writer.writeInt(u32, @bitCast(hdr.dest_ip), .big);
    }
};

const UdpHeaders = packed struct {
    src_port: u16,

    dest_port: u16,
    length: u16,
    checksum: @Vector(2, u8) = .{ 0, 0 },

    fn write(hdr: @This(), writer: *std.Io.Writer) !void {
        try writer.writeInt(u16, hdr.src_port, .big);
        try writer.writeInt(u16, hdr.dest_port, .big);
        try writer.writeInt(u16, hdr.length, .big);
        try writer.writeInt(u16, @bitCast(hdr.checksum), .big);
    }
};

const SaprusMessage = @import("message.zig").Message;
const SaprusConnection = @import("Connection.zig");

const std = @import("std");
const Random = std.Random;
const posix = std.posix;
const mem = std.mem;

const network = @import("network");