const std = @import("std");
const network = @import("network");

const Allocator = std.mem.Allocator;
const Socket = network.Socket;

const port: u16 = 2424;

const target: []const u8 =
    \\<target version="1.0">
    \\    <architecture>armv4t</architecture>
    \\    <feature name="org.gnu.gdb.arm.core">
    \\        <reg name="r0" bitsize="32" type="uint32"/>
    \\        <reg name="r1" bitsize="32" type="uint32"/>
    \\        <reg name="r2" bitsize="32" type="uint32"/>
    \\        <reg name="r3" bitsize="32" type="uint32"/>
    \\        <reg name="r4" bitsize="32" type="uint32"/>
    \\        <reg name="r5" bitsize="32" type="uint32"/>
    \\        <reg name="r6" bitsize="32" type="uint32"/>
    \\        <reg name="r7" bitsize="32" type="uint32"/>
    \\        <reg name="r8" bitsize="32" type="uint32"/>
    \\        <reg name="r9" bitsize="32" type="uint32"/>
    \\        <reg name="r10" bitsize="32" type="uint32"/>
    \\        <reg name="r11" bitsize="32" type="uint32"/>
    \\        <reg name="r12" bitsize="32" type="uint32"/>
    \\        <reg name="sp" bitsize="32" type="data_ptr"/>
    \\        <reg name="lr" bitsize="32"/>
    \\        <reg name="pc" bitsize="32" type="code_ptr"/>
    \\
    \\        <reg name="cpsr" bitsize="32" regnum="25"/>
    \\    </feature>
    \\</target>
;

pub fn main() !void {
    const log = std.log.scoped(.Server);

    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    defer std.debug.assert(!gpa.deinit());

    const allocator = gpa.allocator();

    try network.init();
    defer network.deinit();

    var socket = try Socket.create(.ipv4, .tcp);
    defer socket.close();

    try socket.bindToPort(port);
    try socket.listen();

    var client = try socket.accept();
    defer client.close();

    const endpoint = try client.getLocalEndPoint();
    log.info("client connected from {}", .{endpoint});

    try gdbStubServer(allocator, client);

    log.info("Client disconnected", .{});
}

fn gdbStubServer(allocator: Allocator, client: Socket) !void {
    var buf: [Packet.size]u8 = undefined;
    var previous: ?[]const u8 = null;
    defer if (previous) |packet| allocator.free(packet);

    while (true) {
        const len = try client.receive(&buf);
        if (len == 0) break;

        switch (try parse(allocator, client, previous, buf[0..len])) {
            .send => |response| {
                if (previous) |packet| allocator.free(packet);
                previous = response;
            },
            .recv_ack => {
                if (previous) |packet| allocator.free(packet);
                previous = null;
            },
            .recv_nack => {},
        }
    }
}

const Action = union(enum) {
    send: []const u8,
    recv_nack,
    recv_ack,
};

fn parse(allocator: Allocator, client: Socket, previous: ?[]const u8, input: []const u8) !Action {
    const log = std.log.scoped(.GdbStubParser);

    return switch (input[0]) {
        '+' => .recv_ack,
        '-' => blk: {
            if (previous) |packet| {
                log.warn("received nack, resending: \"{s}\"", .{packet});
                _ = try client.send(packet);
            } else {
                log.err("received nack, but we don't recall sending anything", .{});
            }

            break :blk .recv_nack;
        },
        '$' => blk: {
            // Packet
            var packet = try Packet.from(allocator, input);
            defer packet.deinit(allocator);

            var string = try packet.parse(allocator);
            defer string.deinit(allocator);

            const reply = string.inner();

            _ = try client.send("+"); // Acknowledge

            // deallocated by the caller
            const response = try std.fmt.allocPrint(allocator, "${s}#{x:0>2}", .{ reply, Packet.checksum(reply) });
            _ = try client.send(response);

            break :blk .{ .send = response };
        },
        else => std.debug.panic("Unknown: {s}", .{input}),
    };
}

const Packet = struct {
    const Self = @This();
    const log = std.log.scoped(.Packet);
    const size: usize = 0x1000;

    contents: []const u8,

    pub fn from(allocator: Allocator, str: []const u8) !Self {
        var tokens = std.mem.tokenize(u8, str, "$#");
        const contents = tokens.next() orelse return error.InvalidPacket;

        const chksum_str = tokens.next() orelse return error.MissingCheckSum;
        const chksum = std.fmt.parseInt(u8, chksum_str, 16) catch return error.InvalidChecksum;

        // log.info("Contents: {s}", .{contents});

        if (!Self.verify(contents, chksum)) return error.ChecksumMismatch;

        return .{ .contents = try allocator.dupe(u8, contents) };
    }

    const String = union(enum) {
        alloc: []const u8,
        static: []const u8,

        pub fn inner(self: *const @This()) []const u8 {
            return switch (self.*) {
                .static => |str| str,
                .alloc => |str| str,
            };
        }

        pub fn deinit(self: *@This(), allocator: Allocator) void {
            switch (self.*) {
                .alloc => |string| allocator.free(string),
                .static => {},
            }

            self.* = undefined;
        }
    };

    pub fn parse(self: *Self, allocator: Allocator) !String {
        switch (self.contents[0]) {
            // Required
            '?' => {
                const ret: Signal = .Trap;

                // Deallocated by the caller
                return .{ .alloc = try std.fmt.allocPrint(allocator, "T{x:0>2}thread:1;", .{@enumToInt(ret)}) };
            },
            'g', 'G' => @panic("TODO: Register Access"),
            'm', 'M' => @panic("TODO: Memory Access"),
            'c' => @panic("TODO: Continue"),
            's' => @panic("TODO: Step"),

            // Optional
            'H' => {
                log.warn("{s}", .{self.contents});

                switch (self.contents[1]) {
                    'g', 'c' => return .{ .static = "OK" },
                    else => {
                        log.warn("Unimplemented: {s}", .{self.contents});
                        return .{ .static = "" };
                    },
                }
            },
            'v' => {
                if (substr(self.contents[1..], "MustReplyEmpty")) {
                    return .{ .static = "" };
                }

                log.warn("Unimplemented: {s}", .{self.contents});
                return .{ .static = "" };
            },
            'q' => {
                if (self.contents[1] == 'C' and self.contents.len == 2) return .{ .static = "QC1" };
                if (substr(self.contents[1..], "fThreadInfo")) return .{ .static = "m1" };
                if (substr(self.contents[1..], "sThreadInfo")) return .{ .static = "l" };
                if (substr(self.contents[1..], "Attached")) return .{ .static = "1" }; // Tell GDB we're attached to a process

                if (substr(self.contents[1..], "Supported")) {
                    const format = "PacketSize={x:};qXfer:features:read+;qXfer:memory-map:read+";
                    // TODO: Anything else?

                    const ret = try std.fmt.allocPrint(allocator, format, .{Packet.size});
                    return .{ .alloc = ret };
                }

                if (substr(self.contents[1..], "Xfer:features:read")) {
                    var tokens = std.mem.tokenize(u8, self.contents[1..], ":,");
                    _ = tokens.next(); // qXfer
                    _ = tokens.next(); // features
                    _ = tokens.next(); // read
                    const annex = tokens.next() orelse return .{ .static = "E00" };
                    const offset_str = tokens.next() orelse return .{ .static = "E00" };
                    const length_str = tokens.next() orelse return .{ .static = "E00" };

                    if (std.mem.eql(u8, annex, "target.xml")) {
                        log.info("Providing ARMv4T target description", .{});

                        const offset = try std.fmt.parseInt(usize, offset_str, 16);
                        const length = try std.fmt.parseInt(usize, length_str, 16);

                        // + 2 to account for the "m " in the response
                        // subtract offset so that the allocated buffer isn't
                        // larger than it needs to be TODO: Test this?
                        const len = @min(length, (target.len + 1) - offset);
                        const ret = try allocator.alloc(u8, len);

                        ret[0] = if (ret.len < length) 'l' else 'm';
                        std.mem.copy(u8, ret[1..], target[offset..]);

                        return .{ .alloc = ret };
                    } else {
                        log.err("Unexpected Annex: {s}", .{annex});
                        return .{ .static = "E00" };
                    }

                    return .{ .static = "" };
                }

                log.warn("Unimplemented: {s}", .{self.contents});
                return .{ .static = "" };
            },
            else => {
                log.warn("Unknown:  {s}", .{self.contents});

                return .{ .static = "" };
            },
        }
    }

    fn substr(haystack: []const u8, needle: []const u8) bool {
        return std.mem.indexOf(u8, haystack, needle) != null;
    }

    fn deinit(self: *Self, allocator: Allocator) void {
        allocator.free(self.contents);
        self.* = undefined;
    }

    pub fn checksum(input: []const u8) u8 {
        var sum: usize = 0;
        for (input) |char| sum += char;

        return @truncate(u8, sum);
    }

    fn verify(input: []const u8, chksum: u8) bool {
        return Self.checksum(input) == chksum;
    }
};

const Signal = enum(u32) {
    Hup, // Hangup
    Int, // Interrupt
    Quit, // Quit
    Ill, // Illegal Instruction
    Trap, // Trace/Breakponit trap
    Abrt, // Aborted
};