pub const Address = extern union {
    any: posix.sockaddr,
    in: Ip4Address,
    in6: Ip6Address,
    un: if (has_unix_sockets) posix.sockaddr.un else void,

    /// Parse the given IP address string into an Address value.
    /// It is recommended to use `resolveIp` instead, to handle
    /// IPv6 link-local unix addresses.
    pub fn parseIp(name: []const u8, port: u16) !Address {
        if (parseIp4(name, port)) |ip4| return ip4 else |err| switch (err) {
            error.Overflow,
            error.InvalidEnd,
            error.InvalidCharacter,
            error.Incomplete,
            error.NonCanonical,
            => {},
        }

        if (parseIp6(name, port)) |ip6| return ip6 else |err| switch (err) {
            error.Overflow,
            error.InvalidEnd,
            error.InvalidCharacter,
            error.Incomplete,
            error.InvalidIpv4Mapping,
            => {},
        }

        return error.InvalidIPAddressFormat;
    }

    pub fn resolveIp(name: []const u8, port: u16) !Address {
        if (parseIp4(name, port)) |ip4| return ip4 else |err| switch (err) {
            error.Overflow,
            error.InvalidEnd,
            error.InvalidCharacter,
            error.Incomplete,
            error.NonCanonical,
            => {},
        }

        if (resolveIp6(name, port)) |ip6| return ip6 else |err| switch (err) {
            error.Overflow,
            error.InvalidEnd,
            error.InvalidCharacter,
            error.Incomplete,
            error.InvalidIpv4Mapping,
            => {},
            else => return err,
        }

        return error.InvalidIPAddressFormat;
    }

    pub fn parseExpectingFamily(name: []const u8, family: posix.sa_family_t, port: u16) !Address {
        switch (family) {
            posix.AF.INET => return parseIp4(name, port),
            posix.AF.INET6 => return parseIp6(name, port),
            posix.AF.UNSPEC => return parseIp(name, port),
            else => unreachable,
        }
    }

    pub fn parseIp6(buf: []const u8, port: u16) IPv6ParseError!Address {
        return .{ .in6 = try Ip6Address.parse(buf, port) };
    }

    pub fn resolveIp6(buf: []const u8, port: u16) IPv6ResolveError!Address {
        return .{ .in6 = try Ip6Address.resolve(buf, port) };
    }

    pub fn parseIp4(buf: []const u8, port: u16) IPv4ParseError!Address {
        return .{ .in = try Ip4Address.parse(buf, port) };
    }

    pub fn initIp4(addr: [4]u8, port: u16) Address {
        return .{ .in = Ip4Address.init(addr, port) };
    }

    pub fn initIp6(addr: [16]u8, port: u16, flowinfo: u32, scope_id: u32) Address {
        return .{ .in6 = Ip6Address.init(addr, port, flowinfo, scope_id) };
    }

    pub fn initUnix(path: []const u8) !Address {
        var sock_addr = posix.sockaddr.un{
            .family = posix.AF.UNIX,
            .path = undefined,
        };

        // Add 1 to ensure a terminating 0 is present in the path array for maximum portability.
        if (path.len + 1 > sock_addr.path.len) return error.NameTooLong;

        @memset(&sock_addr.path, 0);
        @memcpy(sock_addr.path[0..path.len], path);

        return .{ .un = sock_addr };
    }

    /// Returns the port in native endian.
    /// Asserts that the address is ip4 or ip6.
    pub fn getPort(self: Address) u16 {
        return switch (self.any.family) {
            posix.AF.INET => self.in.getPort(),
            posix.AF.INET6 => self.in6.getPort(),
            else => unreachable,
        };
    }

    /// `port` is native-endian.
    /// Asserts that the address is ip4 or ip6.
    pub fn setPort(self: *Address, port: u16) void {
        switch (self.any.family) {
            posix.AF.INET => self.in.setPort(port),
            posix.AF.INET6 => self.in6.setPort(port),
            else => unreachable,
        }
    }

    /// Asserts that `addr` is an IP address.
    /// This function will read past the end of the pointer, with a size depending
    /// on the address family.
    pub fn initPosix(addr: *align(4) const posix.sockaddr) Address {
        switch (addr.family) {
            posix.AF.INET => return Address{ .in = Ip4Address{ .sa = @as(*const posix.sockaddr.in, @ptrCast(addr)).* } },
            posix.AF.INET6 => return Address{ .in6 = Ip6Address{ .sa = @as(*const posix.sockaddr.in6, @ptrCast(addr)).* } },
            else => unreachable,
        }
    }

    pub fn format(
        self: Address,
        comptime fmt: []const u8,
        options: std.fmt.FormatOptions,
        out_stream: anytype,
    ) !void {
        if (fmt.len != 0) std.fmt.invalidFmtError(fmt, self);
        switch (self.any.family) {
            posix.AF.INET => try self.in.format(fmt, options, out_stream),
            posix.AF.INET6 => try self.in6.format(fmt, options, out_stream),
            posix.AF.UNIX => {
                if (!has_unix_sockets) {
                    unreachable;
                }

                try std.fmt.format(out_stream, "{s}", .{std.mem.sliceTo(&self.un.path, 0)});
            },
            else => unreachable,
        }
    }

    pub fn eql(a: Address, b: Address) bool {
        const a_bytes = @as([*]const u8, @ptrCast(&a.any))[0..a.getOsSockLen()];
        const b_bytes = @as([*]const u8, @ptrCast(&b.any))[0..b.getOsSockLen()];
        return mem.eql(u8, a_bytes, b_bytes);
    }

    pub fn getOsSockLen(self: Address) posix.socklen_t {
        switch (self.any.family) {
            posix.AF.INET => return self.in.getOsSockLen(),
            posix.AF.INET6 => return self.in6.getOsSockLen(),
            posix.AF.UNIX => {
                if (!has_unix_sockets) {
                    unreachable;
                }

                // Using the full length of the structure here is more portable than returning
                // the number of bytes actually used by the currently stored path.
                // This also is correct regardless if we are passing a socket address to the kernel
                // (e.g. in bind, connect, sendto) since we ensure the path is 0 terminated in
                // initUnix() or if we are receiving a socket address from the kernel and must
                // provide the full buffer size (e.g. getsockname, getpeername, recvfrom, accept).
                //
                // To access the path, std.mem.sliceTo(&address.un.path, 0) should be used.
                return @as(posix.socklen_t, @intCast(@sizeOf(posix.sockaddr.un)));
            },

            else => unreachable,
        }
    }

    pub const ListenError = posix.SocketError || posix.BindError || posix.ListenError ||
        posix.SetSockOptError || posix.GetSockNameError;

    pub const ListenOptions = struct {
        /// How many connections the kernel will accept on the application's behalf.
        /// If more than this many connections pool in the kernel, clients will start
        /// seeing "Connection refused".
        kernel_backlog: u31 = 128,
        /// Sets SO_REUSEADDR and SO_REUSEPORT on POSIX.
        /// Sets SO_REUSEADDR on Windows, which is roughly equivalent.
        reuse_address: bool = false,
        /// Deprecated. Does the same thing as reuse_address.
        reuse_port: bool = false,
        force_nonblocking: bool = false,
    };

    /// The returned `Server` has an open `stream`.
    pub fn listen(address: Address, options: ListenOptions) ListenError!Server {
        const nonblock: u32 = if (options.force_nonblocking) posix.SOCK.NONBLOCK else 0;
        const sock_flags = posix.SOCK.STREAM | posix.SOCK.CLOEXEC | nonblock;
        const proto: u32 = if (address.any.family == posix.AF.UNIX) 0 else posix.IPPROTO.TCP;

        const sockfd = try posix.socket(address.any.family, sock_flags, proto);
        var s: Server = .{
            .listen_address = undefined,
            .stream = .{ .handle = sockfd },
        };
        errdefer s.stream.close();

        if (options.reuse_address or options.reuse_port) {
            try posix.setsockopt(
                sockfd,
                posix.SOL.SOCKET,
                posix.SO.REUSEADDR,
                &mem.toBytes(@as(c_int, 1)),
            );
            if (@hasDecl(posix.SO, "REUSEPORT") and address.any.family != posix.AF.UNIX) {
                try posix.setsockopt(
                    sockfd,
                    posix.SOL.SOCKET,
                    posix.SO.REUSEPORT,
                    &mem.toBytes(@as(c_int, 1)),
                );
            }
        }

        var socklen = address.getOsSockLen();
        try posix.bind(sockfd, &address.any, socklen);
        try posix.listen(sockfd, options.kernel_backlog);
        try posix.getsockname(sockfd, &s.listen_address.any, &socklen);
        return s;
    }
}