const builtin = @import("builtin");
const native_os = builtin.os.tag;
const std = @import("../std.zig");
const Io = std.Io;
const assert = std.debug.assert;

pub const ListenError = std.net.Address.ListenError || Io.Cancelable;

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,
    force_nonblocking: bool = false,
};

/// An already-validated host name.
pub const HostName = struct {
    /// Externally managed memory. Already checked to be within `max_len`.
    bytes: []const u8,

    pub const max_len = 255;

    pub const InitError = error{
        NameTooLong,
        InvalidHostName,
    };

    pub fn init(bytes: []const u8) InitError!HostName {
        if (bytes.len > max_len) return error.NameTooLong;
        if (!std.unicode.utf8ValidateSlice(bytes)) return error.InvalidHostName;
        for (bytes) |byte| {
            if (!std.ascii.isAscii(byte) or byte == '.' or byte == '-' or std.ascii.isAlphanumeric(byte)) {
                continue;
            }
            return error.InvalidHostName;
        }
        return .{ .bytes = bytes };
    }

    pub const LookupOptions = struct {
        port: u16,
        /// Must have at least length 2.
        addresses_buffer: []IpAddress,
        /// If a buffer of at least `max_len` is not provided, `lookup` may
        /// return successfully with zero-length `LookupResult.canonical_name_len`.
        ///
        /// Suggestion: if not interested in canonical name, pass an empty buffer;
        /// otherwise pass a buffer of size `max_len`.
        canonical_name_buffer: []u8,
        /// `null` means either.
        family: ?IpAddress.Tag = null,
    };

    pub const LookupError = Io.Cancelable || error{};

    pub const LookupResult = struct {
        /// How many `LookupOptions.addresses_buffer` elements are populated.
        addresses_len: usize,
        /// Length zero means no canonical name returned.
        canonical_name_len: usize,
    };

    pub fn lookup(host_name: HostName, io: Io, options: LookupOptions) LookupError!LookupResult {
        const name = host_name.bytes;
        assert(name.len <= max_len);
        assert(options.addresses_buffer.len >= 2);

        if (native_os == .windows) @compileError("TODO");
        if (builtin.link_libc) @compileError("TODO");
        if (native_os == .linux) {
            if (options.family != .ip6) {
                if (IpAddress.parseIp4(name, options.port)) |addr| {
                    options.addresses_buffer[0] = addr;
                    return .{ .addresses_len = 1, .canonical_name_len = 0 };
                } else |_| {}
            }
            if (options.family != .ip4) {
                if (IpAddress.parseIp6(name, options.port)) |addr| {
                    options.addresses_buffer[0] = addr;
                    return .{ .addresses_len = 1, .canonical_name_len = 0 };
                } else |_| {}
            }
            {
                const result = try lookupHosts(io, options);
                if (result.addresses_len > 0) return sortLookupResults(options, result);
            }
            {
                // RFC 6761 Section 6.3.3
                // Name resolution APIs and libraries SHOULD recognize
                // localhost names as special and SHOULD always return the IP
                // loopback address for address queries and negative responses
                // for all other query types.

                // Check for equal to "localhost(.)" or ends in ".localhost(.)"
                const localhost = if (name[name.len - 1] == '.') "localhost." else "localhost";
                if (std.mem.endsWith(u8, name, localhost) and
                    (name.len == localhost.len or name[name.len - localhost.len] == '.'))
                {
                    var i: usize = 0;
                    if (options.family != .ip6) {
                        options.addresses_buffer[i] = .{ .ip4 = .localhost(options.port) };
                        i += 1;
                    }
                    if (options.family != .ip4) {
                        options.addresses_buffer[i] = .{ .ip6 = .localhost(options.port) };
                        i += 1;
                    }
                    const canon_name = "localhost";
                    options.canonical_name_buffer[0..canon_name.len].* = canon_name.*;
                    return sortLookupResults(options, .{ .addresses_len = i, .canonical_name_len = canon_name.len });
                }
            }
            {
                const result = try lookupDns(io, options);
                if (result.addresses_len > 0) return sortLookupResults(options, result);
            }
            return error.UnknownHostName;
        }
        @compileError("unimplemented");
    }

    fn sortLookupResults(options: LookupOptions, result: LookupResult) !LookupResult {
        _ = options;
        _ = result;
        @panic("TODO");
    }

    fn lookupDns(io: Io, options: LookupOptions) !LookupResult {
        _ = io;
        _ = options;
        @panic("TODO");
    }

    fn lookupHosts(io: Io, options: LookupOptions) !LookupResult {
        const file = Io.File.openFileAbsoluteZ(io, "/etc/hosts", .{}) catch |err| switch (err) {
            error.FileNotFound,
            error.NotDir,
            error.AccessDenied,
            => return,
            else => |e| return e,
        };
        defer file.close();

        var line_buf: [512]u8 = undefined;
        var file_reader = file.reader(io, &line_buf);
        return lookupHostsReader(options, &file_reader.interface) catch |err| switch (err) {
            error.OutOfMemory => return error.OutOfMemory,
            error.ReadFailed => return file_reader.err.?,
        };
    }

    fn lookupHostsReader(options: LookupOptions, reader: *Io.Reader) error{ReadFailed}!LookupResult {
        var addresses_len: usize = 0;
        var canonical_name_len: usize = 0;
        while (true) {
            const line = reader.takeDelimiterExclusive('\n') catch |err| switch (err) {
                error.StreamTooLong => {
                    // Skip lines that are too long.
                    _ = reader.discardDelimiterInclusive('\n') catch |e| switch (e) {
                        error.EndOfStream => break,
                        error.ReadFailed => return error.ReadFailed,
                    };
                    continue;
                },
                error.ReadFailed => return error.ReadFailed,
                error.EndOfStream => break,
            };
            var split_it = std.mem.splitScalar(u8, line, '#');
            const no_comment_line = split_it.first();

            var line_it = std.mem.tokenizeAny(u8, no_comment_line, " \t");
            const ip_text = line_it.next() orelse continue;
            var first_name_text: ?[]const u8 = null;
            while (line_it.next()) |name_text| {
                if (std.mem.eql(u8, name_text, options.name)) {
                    if (first_name_text == null) first_name_text = name_text;
                    break;
                }
            } else continue;

            if (canonical_name_len == 0) {
                if (HostName.init(first_name_text)) |name_text| {
                    if (name_text.len <= options.canonical_name_buffer.len) {
                        @memcpy(options.canonical_name_buffer[0..name_text.len], name_text);
                        canonical_name_len = name_text.len;
                    }
                }
            }

            if (options.family != .ip6) {
                if (IpAddress.parseIp4(ip_text, options.port)) |addr| {
                    options.addresses_buffer[addresses_len] = addr;
                    addresses_len += 1;
                    if (options.addresses_buffer.len - addresses_len == 0) return .{
                        .addresses_len = addresses_len,
                        .canonical_name_len = canonical_name_len,
                    };
                } else |_| {}
            }
            if (options.family != .ip4) {
                if (IpAddress.parseIp6(ip_text, options.port)) |addr| {
                    options.addresses_buffer[addresses_len] = addr;
                    addresses_len += 1;
                    if (options.addresses_buffer.len - addresses_len == 0) return .{
                        .addresses_len = addresses_len,
                        .canonical_name_len = canonical_name_len,
                    };
                } else |_| {}
            }
        }
    }

    pub const ConnectTcpError = LookupError || IpAddress.ConnectTcpError;

    pub fn connectTcp(host_name: HostName, io: Io, port: u16) ConnectTcpError!Stream {
        var addresses_buffer: [32]IpAddress = undefined;

        const results = try lookup(host_name, .{
            .port = port,
            .addresses_buffer = &addresses_buffer,
            .canonical_name_buffer = &.{},
        });
        const addresses = addresses_buffer[0..results.addresses_len];

        if (addresses.len == 0) return error.UnknownHostName;

        for (addresses) |addr| {
            return addr.connectTcp(io) catch |err| switch (err) {
                error.ConnectionRefused => continue,
                else => |e| return e,
            };
        }
        return error.ConnectionRefused;
    }
};

pub const IpAddress = union(enum) {
    ip4: Ip4Address,
    ip6: Ip6Address,

    pub const Tag = @typeInfo(IpAddress).@"union".tag_type.?;

    /// Parse the given IP address string into an `IpAddress` value.
    pub fn parse(name: []const u8, port: u16) !IpAddress {
        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 parseIp6(buffer: []const u8, port: u16) Ip6Address.ParseError!IpAddress {
        return .{ .ip6 = try Ip6Address.parse(buffer, port) };
    }

    pub fn parseIp4(buffer: []const u8, port: u16) Ip4Address.ParseError!IpAddress {
        return .{ .ip4 = try Ip4Address.parse(buffer, port) };
    }

    /// Returns the port in native endian.
    pub fn getPort(a: IpAddress) u16 {
        return switch (a) {
            inline .ip4, .ip6 => |x| x.port,
        };
    }

    /// `port` is native-endian.
    pub fn setPort(a: *IpAddress, port: u16) void {
        switch (a) {
            inline .ip4, .ip6 => |*x| x.port = port,
        }
    }

    pub fn format(a: IpAddress, w: *std.io.Writer) std.io.Writer.Error!void {
        switch (a) {
            .ip4, .ip6 => |x| return x.format(w),
        }
    }

    pub fn eql(a: IpAddress, b: IpAddress) bool {
        return switch (a) {
            .ip4 => |a_ip4| switch (b) {
                .ip4 => |b_ip4| a_ip4.eql(b_ip4),
                else => false,
            },
            .ip6 => |a_ip6| switch (b) {
                .ip6 => |b_ip6| a_ip6.eql(b_ip6),
                else => false,
            },
        };
    }

    /// The returned `Server` has an open `stream`.
    pub fn listen(address: IpAddress, io: Io, options: ListenOptions) ListenError!Server {
        return io.vtable.listen(io.userdata, address, options);
    }
};

pub const Ip4Address = struct {
    bytes: [4]u8,
    port: u16,

    pub fn localhost(port: u16) Ip4Address {
        return .{
            .bytes = .{ 127, 0, 0, 1 },
            .port = port,
        };
    }

    pub const ParseError = error{
        Overflow,
        InvalidEnd,
        InvalidCharacter,
        Incomplete,
        NonCanonical,
    };

    pub fn parse(buffer: []const u8, port: u16) ParseError!Ip4Address {
        var bytes: [4]u8 = @splat(0);
        var index: u8 = 0;
        var saw_any_digits = false;
        var has_zero_prefix = false;
        for (buffer) |c| switch (c) {
            '.' => {
                if (!saw_any_digits) return error.InvalidCharacter;
                if (index == 3) return error.InvalidEnd;
                index += 1;
                saw_any_digits = false;
                has_zero_prefix = false;
            },
            '0'...'9' => {
                if (c == '0' and !saw_any_digits) {
                    has_zero_prefix = true;
                } else if (has_zero_prefix) {
                    return error.NonCanonical;
                }
                saw_any_digits = true;
                bytes[index] = try std.math.mul(u8, bytes[index], 10);
                bytes[index] = try std.math.add(u8, bytes[index], c - '0');
            },
            else => return error.InvalidCharacter,
        };
        if (index == 3 and saw_any_digits) return .{
            .bytes = bytes,
            .port = port,
        };
        return error.Incomplete;
    }

    pub fn format(a: Ip4Address, w: *std.io.Writer) std.io.Writer.Error!void {
        const bytes = &a.bytes;
        try w.print("{d}.{d}.{d}.{d}:{d}", .{ bytes[0], bytes[1], bytes[2], bytes[3], a.port });
    }

    pub fn eql(a: Ip4Address, b: Ip4Address) bool {
        const a_int: u32 = @bitCast(a.bytes);
        const b_int: u32 = @bitCast(b.bytes);
        return a.port == b.port and a_int == b_int;
    }
};

pub const Ip6Address = struct {
    /// Native endian
    port: u16,
    /// Big endian
    bytes: [16]u8,
    flowinfo: u32 = 0,
    scope_id: u32 = 0,

    pub const ParseError = error{
        Overflow,
        InvalidCharacter,
        InvalidEnd,
        InvalidIpv4Mapping,
        Incomplete,
    };

    pub fn parse(buffer: []const u8, port: u16) ParseError!Ip6Address {
        var result: Ip6Address = .{
            .port = port,
            .bytes = undefined,
        };
        var ip_slice: *[16]u8 = &result.bytes;

        var tail: [16]u8 = undefined;

        var x: u16 = 0;
        var saw_any_digits = false;
        var index: u8 = 0;
        var scope_id = false;
        var abbrv = false;
        for (buffer, 0..) |c, i| {
            if (scope_id) {
                if (c >= '0' and c <= '9') {
                    const digit = c - '0';
                    {
                        const ov = @mulWithOverflow(result.scope_id, 10);
                        if (ov[1] != 0) return error.Overflow;
                        result.scope_id = ov[0];
                    }
                    {
                        const ov = @addWithOverflow(result.scope_id, digit);
                        if (ov[1] != 0) return error.Overflow;
                        result.scope_id = ov[0];
                    }
                } else {
                    return error.InvalidCharacter;
                }
            } else if (c == ':') {
                if (!saw_any_digits) {
                    if (abbrv) return error.InvalidCharacter; // ':::'
                    if (i != 0) abbrv = true;
                    @memset(ip_slice[index..], 0);
                    ip_slice = tail[0..];
                    index = 0;
                    continue;
                }
                if (index == 14) {
                    return error.InvalidEnd;
                }
                ip_slice[index] = @as(u8, @truncate(x >> 8));
                index += 1;
                ip_slice[index] = @as(u8, @truncate(x));
                index += 1;

                x = 0;
                saw_any_digits = false;
            } else if (c == '%') {
                if (!saw_any_digits) {
                    return error.InvalidCharacter;
                }
                scope_id = true;
                saw_any_digits = false;
            } else if (c == '.') {
                if (!abbrv or ip_slice[0] != 0xff or ip_slice[1] != 0xff) {
                    // must start with '::ffff:'
                    return error.InvalidIpv4Mapping;
                }
                const start_index = std.mem.lastIndexOfScalar(u8, buffer[0..i], ':').? + 1;
                const addr = (Ip4Address.parse(buffer[start_index..], 0) catch {
                    return error.InvalidIpv4Mapping;
                }).bytes;
                ip_slice = result.bytes[0..];
                ip_slice[10] = 0xff;
                ip_slice[11] = 0xff;

                ip_slice[12] = addr[0];
                ip_slice[13] = addr[1];
                ip_slice[14] = addr[2];
                ip_slice[15] = addr[3];
                return result;
            } else {
                const digit = try std.fmt.charToDigit(c, 16);
                {
                    const ov = @mulWithOverflow(x, 16);
                    if (ov[1] != 0) return error.Overflow;
                    x = ov[0];
                }
                {
                    const ov = @addWithOverflow(x, digit);
                    if (ov[1] != 0) return error.Overflow;
                    x = ov[0];
                }
                saw_any_digits = true;
            }
        }

        if (!saw_any_digits and !abbrv) {
            return error.Incomplete;
        }
        if (!abbrv and index < 14) {
            return error.Incomplete;
        }

        if (index == 14) {
            ip_slice[14] = @as(u8, @truncate(x >> 8));
            ip_slice[15] = @as(u8, @truncate(x));
            return result;
        } else {
            ip_slice[index] = @as(u8, @truncate(x >> 8));
            index += 1;
            ip_slice[index] = @as(u8, @truncate(x));
            index += 1;
            @memcpy(result.bytes[16 - index ..][0..index], ip_slice[0..index]);
            return result;
        }
    }

    pub fn format(a: Ip6Address, w: *std.io.Writer) std.io.Writer.Error!void {
        const bytes = &a.bytes;
        if (std.mem.eql(u8, bytes[0..12], &[_]u8{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff })) {
            try w.print("[::ffff:{d}.{d}.{d}.{d}]:{d}", .{
                bytes[12], bytes[13], bytes[14], bytes[15], a.port,
            });
            return;
        }
        const parts: [8]u16 = .{
            std.mem.readInt(u16, bytes[0..2], .big),
            std.mem.readInt(u16, bytes[2..4], .big),
            std.mem.readInt(u16, bytes[4..6], .big),
            std.mem.readInt(u16, bytes[6..8], .big),
            std.mem.readInt(u16, bytes[8..10], .big),
            std.mem.readInt(u16, bytes[10..12], .big),
            std.mem.readInt(u16, bytes[12..14], .big),
            std.mem.readInt(u16, bytes[14..16], .big),
        };

        // Find the longest zero run
        var longest_start: usize = 8;
        var longest_len: usize = 0;
        var current_start: usize = 0;
        var current_len: usize = 0;

        for (parts, 0..) |part, i| {
            if (part == 0) {
                if (current_len == 0) {
                    current_start = i;
                }
                current_len += 1;
                if (current_len > longest_len) {
                    longest_start = current_start;
                    longest_len = current_len;
                }
            } else {
                current_len = 0;
            }
        }

        // Only compress if the longest zero run is 2 or more
        if (longest_len < 2) {
            longest_start = 8;
            longest_len = 0;
        }

        try w.writeAll("[");
        var i: usize = 0;
        var abbrv = false;
        while (i < parts.len) : (i += 1) {
            if (i == longest_start) {
                // Emit "::" for the longest zero run
                if (!abbrv) {
                    try w.writeAll(if (i == 0) "::" else ":");
                    abbrv = true;
                }
                i += longest_len - 1; // Skip the compressed range
                continue;
            }
            if (abbrv) {
                abbrv = false;
            }
            try w.print("{x}", .{parts[i]});
            if (i != parts.len - 1) {
                try w.writeAll(":");
            }
        }
        try w.print("]:{d}", .{a.port});
    }

    pub fn eql(a: Ip6Address, b: Ip6Address) bool {
        return a.port == b.port and std.mem.eql(u8, &a.bytes, &b.bytes);
    }
};

pub const Stream = struct {
    /// Underlying platform-defined type which may or may not be
    /// interchangeable with a file system file descriptor.
    handle: Handle,

    pub const Handle = switch (native_os) {
        .windows => std.windows.ws2_32.SOCKET,
        else => std.posix.fd_t,
    };

    pub fn close(s: Stream, io: Io) void {
        return io.vtable.close(io.userdata, s);
    }

    pub const Reader = struct {
        io: Io,
        interface: Io.Reader,
        stream: Stream,
        err: ?Error,

        pub const Error = std.net.Stream.ReadError || Io.Cancelable || Io.Writer.Error || error{EndOfStream};

        pub fn init(stream: Stream, buffer: []u8) Reader {
            return .{
                .interface = .{
                    .vtable = &.{
                        .stream = streamImpl,
                        .readVec = readVec,
                    },
                    .buffer = buffer,
                    .seek = 0,
                    .end = 0,
                },
                .stream = stream,
                .err = null,
            };
        }

        fn streamImpl(io_r: *Io.Reader, io_w: *Io.Writer, limit: Io.Limit) Io.Reader.StreamError!usize {
            const dest = limit.slice(try io_w.writableSliceGreedy(1));
            var data: [1][]u8 = .{dest};
            const n = try readVec(io_r, &data);
            io_w.advance(n);
            return n;
        }

        fn readVec(io_r: *Reader, data: [][]u8) Io.Reader.Error!usize {
            const r: *Reader = @alignCast(@fieldParentPtr("interface", io_r));
            const io = r.io;
            return io.vtable.netReadVec(io.vtable.userdata, r.stream, io_r, data);
        }
    };

    pub const Writer = struct {
        io: Io,
        interface: Io.Writer,
        stream: Stream,
        err: ?Error = null,

        pub const Error = std.net.Stream.WriteError || Io.Cancelable;

        pub fn init(stream: Stream, buffer: []u8) Writer {
            return .{
                .stream = stream,
                .interface = .{
                    .vtable = &.{ .drain = drain },
                    .buffer = buffer,
                },
            };
        }

        fn drain(io_w: *Io.Writer, data: []const []const u8, splat: usize) Io.Writer.Error!usize {
            const w: *Writer = @alignCast(@fieldParentPtr("interface", io_w));
            const io = w.io;
            const buffered = io_w.buffered();
            const n = try io.vtable.netWrite(io.vtable.userdata, w.stream, buffered, data, splat);
            return io_w.consume(n);
        }
    };

    pub fn reader(stream: Stream, buffer: []u8) Reader {
        return .init(stream, buffer);
    }

    pub fn writer(stream: Stream, buffer: []u8) Writer {
        return .init(stream, buffer);
    }
};

pub const Server = struct {
    listen_address: IpAddress,
    stream: Stream,

    pub const Connection = struct {
        stream: Stream,
        address: IpAddress,
    };

    pub fn deinit(s: *Server, io: Io) void {
        s.stream.close(io);
        s.* = undefined;
    }

    pub const AcceptError = std.posix.AcceptError || Io.Cancelable;

    /// Blocks until a client connects to the server. The returned `Connection` has
    /// an open stream.
    pub fn accept(s: *Server, io: Io) AcceptError!Connection {
        return io.vtable.accept(io, s);
    }
};