// a bidirectional reliable udp transport
//
// I'm going to call this the CRU protocol
//
// stands for crasa-reliable-udp
//
// packet layout of the payload

// this results in a non blocking transport engine where you can poll for when new messages are
// available. And the messages are sent through as fast as they can be, mangled/unacked messages
// are replayed by the server over time.
//
// messages will arrive from the server to the client /eventually/
//
// they will arrive out of order as well.
pub const UdpEngine = struct {
    allocator: std.mem.Allocator,
    port: u16 = 6700,
    signalExit: std.atomic.Value(bool) = std.atomic.Value(bool).init(false),
    address: std.net.Address,

    pub fn create(allocator: std.mem.Allocator) !*@This() {
        const self = try allocator.create(@This());

        self.* = .{
            .allocator = allocator,
            .address = try std.net.Address.parseIp4("0.0.0.0", 5000),
        };

        return self;
    }

    // requires a memory safe allocator, as this is the Allocator
    // that will be used to create the backing allocator on the working thread.
    pub fn serve(self: *@This(), port: u16) !void {
        self.port = port;
        self.address = try std.net.Address.parseIp4("0.0.0.0", port);
        const thread = try std.Thread.spawn(.{}, startServer, .{self});
        thread.detach();
    }

    pub fn connect(self: *@This(), host: []const u8, port: u16) !void {
        log.info("parsing host '{s}'", .{host});
        const resolved_host = if (std.mem.eql(u8, host, "localhost"))
            "127.0.0.1"
        else
            host;
        self.address = try std.net.Address.resolveIp(resolved_host, port);
        self.port = port;
        const thread = try std.Thread.spawn(.{}, startClient, .{self});
        thread.detach();
    }

    pub fn startServer(self: *@This()) void {
        const sockfd = posix.socket(
            self.address.any.family,
            posix.SOCK.DGRAM | posix.SOCK.CLOEXEC | posix.SOCK.NONBLOCK,
            posix.IPPROTO.UDP,
        ) catch |err| {
            log.err("server socket error: {any}", .{err});
            return;
        };
        defer posix.close(sockfd);

        posix.bind(sockfd, &self.address.any, self.address.getOsSockLen()) catch |err| {
            log.err("server bind error: {any}", .{err});
            return;
        };

        log.info("udp server listening on port {d}", .{self.address.getPort()});

        var buffer: [1024]u8 = undefined;
        while (!self.signalExit.load(.monotonic)) {
            var src_addr: posix.sockaddr = undefined;

            var src_len: posix.socklen_t = @sizeOf(posix.sockaddr);
            const n = posix.recvfrom(sockfd, buffer[0..], 0, &src_addr, &src_len) catch |err| switch (err) {
                error.WouldBlock => {
                    std.Thread.sleep(20 * std.time.ns_per_ms);
                    continue;
                },
                else => {
                    log.err("server recv error: {any}", .{err});
                    break;
                },
            };

            const addr = std.net.Address.initPosix(@alignCast(&src_addr));
            log.info("server recv {d} bytes from {f}", .{ n, addr });

            const msg = buffer[0..n];
            if (std.mem.eql(u8, msg, "HELLO")) {
                _ = posix.sendto(sockfd, "HELLO", 0, &src_addr, src_len) catch |err| {
                    log.err("server send error: {any}", .{err});
                    continue;
                };
                log.info("server replied HELLO", .{});
            }
        }
    }

    pub fn startClient(self: *@This()) void {
        const sockfd = posix.socket(
            self.address.any.family,
            posix.SOCK.DGRAM | posix.SOCK.CLOEXEC | posix.SOCK.NONBLOCK,
            posix.IPPROTO.UDP,
        ) catch |err| {
            log.err("client socket error: {any}", .{err});
            return;
        };
        defer posix.close(sockfd);

        const local_addr = std.net.Address.parseIp4("0.0.0.0", 0) catch |err| {
            log.err("client local addr parse error: {any}", .{err});
            return;
        };
        posix.bind(sockfd, &local_addr.any, local_addr.getOsSockLen()) catch |err| {
            log.err("client bind error: {any}", .{err});
            return;
        };

        _ = posix.sendto(sockfd, "HELLO", 0, &self.address.any, self.address.getOsSockLen()) catch |err| {
            log.err("client send error: {any}", .{err});
            return;
        };
        log.info("client sent HELLO to {f}", .{self.address});

        var buffer: [1024]u8 = undefined;
        while (!self.signalExit.load(.monotonic)) {
            var src_addr: posix.sockaddr = undefined;
            var src_len: posix.socklen_t = @sizeOf(posix.sockaddr);
            const n = posix.recvfrom(sockfd, buffer[0..], 0, &src_addr, &src_len) catch |err| switch (err) {
                error.WouldBlock => {
                    std.Thread.sleep(20 * std.time.ns_per_ms);
                    continue;
                },
                else => {
                    log.err("client recv error: {any}", .{err});
                    break;
                },
            };

            const msg = buffer[0..n];
            log.info("client recv {d} bytes", .{n});
            if (std.mem.eql(u8, msg, "HELLO")) {
                log.info("client received HELLO reply", .{});
            }
        }
    }

    pub fn shouldExit(self: *@This()) bool {
        return self.signalExit.load(.monotonic);
    }

    pub fn destroy(self: *@This()) void {
        self.allocator.destroy(self);
    }
};

const std = @import("std");
const posix = std.posix;
const log = @import("logging.zig").log;