const std = #import("std");
const Arena = std.Arena;
const c_slice = std.c_slice;
const byte_equal = std.byte_equal;
const print = std.print;
const print_usize = std.print_usize;
const exit = std.os.exit;

const ArgumentProcessingError = error{
    no_arguments,
};

const Token = struct {
    const Id = enum(u8) {
        invalid,
        keyword_unsigned_integer,
        keyword_signed_integer,
        identifier,
    };
};

const lex = fn (arena: &Arena, bytes: []const u8) *!void {
    if (bytes.length >= 0xffffffff) {
        unreachable;
    }

    const length: u32 = #cast(bytes.length);
    var i: u32 = 0;

    const line_offset_arena = try Arena.init(bytes.length + #size(Arena));
    var line_offsets = try line_offset_arena.new_array($u32, bytes.length);
    line_offsets[0] = 0;
    var line_count: u32 = 1;

    var index: u32 = 0;
    while (index < length) {
        const byte = bytes[index];
        line_count += #cast(byte == '\n');
        line_offsets[line_count] = index;

        index += 1;
    }

    index = 0;

    while (index < length) {
        const start_index = index;
        const start_character = bytes[index];
        var token_id = Token.Id.invalid;

        switch (start_character) {
            'a'...'z', 'A'...'Z', '_' => {
                while (true) {
                    const ch = bytes[index];
                    if ((ch >= 'a' and ch <= 'z') or (ch >= 'A' and ch <= 'Z') or ch == '_' or (ch >= '0' and ch <= '9')) {
                        index += 1;
                        continue;
                    }

                    break;
                }

                if (start_character == 'u' or start_character == 's' and bytes[start_index + 1] >= '0' and bytes[start_index + 1] <= '9') {
                    var index_integer = start_index + 1;
                    while (bytes[index_integer] >= '0' and bytes[index_integer] <= '9') {
                        index_integer += 1;
                    }

                    if (index_integer == index) {
                        token_id = switch (start_character) {
                            'u' => .keyword_unsigned_integer,
                            's' => .keyword_signed_integer,
                            else => unreachable,
                        };
                    } else {
                        //unreachable;
                    }
                }
            },
            else => index += 1,
        }
    }
}

const get_argument = fn (real_argument: []const u8, wanted_argument: []const u8, command_arguments: []const [&:0]const u8, i_ptr: &usize) ?[]const u8 {
    const i = i_ptr.@;

    const are_equal = byte_equal(real_argument, wanted_argument);
    if (are_equal) {
        if (i < command_arguments.length) {
            const new_i = i + 1;
            const argument = c_slice(command_arguments[new_i]);
            i_ptr.@ = new_i;
            return argument;
        } else {
            print("error: unterminated argument: '");
            print(real_argument);
            print("'\n");
            exit(1);
        }
    } else {
        return null;
    }
}

const command_exe = fn (arena: &Arena, command_arguments: []const [&:0]const u8) *!void { 
    var i: usize = 0;

    var maybe_output_argument: ?[]const u8 = null;
    var maybe_main_source_file: ?[]const u8 = null;
    var maybe_main_executable_name: ?[]const u8 = null;

    while (i < command_arguments.length) {
        const command_argument = c_slice(command_arguments[i]);

        if (get_argument(command_argument, "-o", command_arguments, i.&)) |out_arg| {
            maybe_output_argument = out_arg;
        } else if (get_argument(command_argument, "-main_source_file", command_arguments, i.&)) |src_arg| {
            maybe_main_source_file = src_arg;
        } else {
            print("error: unhandled argument: '");
            print(command_argument);
            print("'\n");
            exit(1);
        }

        i += 1;
    }

    const main_source_file = maybe_main_source_file orelse {
        print("error: no main source file specified\n");
        exit(1);
    };

    const main_executable_name = maybe_main_executable_name orelse (std.os.basename(main_source_file[0..main_source_file.length - 9]) orelse unreachable); // 9 => "/main.nat".length

    const file_descriptor = try std.os.open(#cast(main_source_file.pointer), .{});
    const file_size = try file_descriptor.get_size();
    const file_buffer = try arena.new_array($u8, file_size);
    file_descriptor.read_all(file_buffer);

    lex(arena, file_buffer);
}

const main = fn() *!void {
    const arena = try Arena.init(std.megabytes(64));
    const argument_count = std.start.argument_count;

    if (argument_count <= 1) {
        return ArgumentProcessingError.no_arguments;
    }

    const argument_values = std.start.argument_values;
    const arguments = argument_values[0..argument_count];

    const command = c_slice(arguments[1]);
    const command_arguments = arguments[2..];

    if (byte_equal(command, "build")) {
        print("TODO: build");
    } else if (byte_equal(command, "clang") or byte_equal(command, "-cc1") or byte_equal(command, "-cc1as")) {
        unreachable;
    } else if (byte_equal(command, "cc")) {
        unreachable;
    } else if (byte_equal(command, "c++")) {
        unreachable;
    } else if (byte_equal(command, "exe")) {
        command_exe(arena, command_arguments);
    } else if (byte_equal(command, "lib")) {
        unreachable;
    } else if (byte_equal(command, "obj")) {
        unreachable;
    } else if (byte_equal(command, "test")) {
        print("TODO: test");
    } else {
        unreachable;
    }
}