const std = @import("std");
const print = std.debug.print;
const ArrayList = std.ArrayList;
const Allocator = std.mem.Allocator;
const Thread = std.Thread;
const Mutex = std.Thread.Mutex;

const c = @cImport({
    @cInclude("errno.h");
    @cInclude("stdio.h");
    if (@import("builtin").os.tag != .windows) {
        @cInclude("sys/statvfs.h");
    }
});

const cmd = @import("cmd.zig");
const Command = cmd.Command;
const BuiltinCommand = cmd.BuiltinCommand;

const syntax = @import("syntax.zig");
const FileSpec = syntax.FileSpec;
const RedirectType = syntax.RedirectType;
const Redirect = syntax.Redirect;

const paths = @import("paths.zig");
const formatDosPath = paths.formatDosPath;
const convertTo83 = paths.convertTo83;

const cmdTypes = @import("cmd/types.zig");
pub const CommandStatus = cmdTypes.CommandStatus;
const OutputCapture = cmdTypes.OutputCapture;
const InputSource = cmdTypes.InputSource;

const STDOUT_BUFFER_SIZE: usize = 1024;
const STDERR_BUFFER_SIZE: usize = 1024;

fn isLeapYear(year: u32) bool {
    return (year % 4 == 0 and year % 100 != 0) or (year % 400 == 0);
}

pub fn executeCommand(command: Command, allocator: Allocator) !CommandStatus {
    return executeCommandWithOutput(command, allocator, null, null);
}

fn executeCommandWithOutput(command: Command, allocator: Allocator, output_capture: ?*OutputCapture, input_source: ?*InputSource) !CommandStatus {
    switch (command) {
        .Empty => return CommandStatus{ .Code = 0 },

        .Builtin => |builtin_cmd| {
            switch (builtin_cmd) {
                .EchoText => |echo| {
                    const output = try std.fmt.allocPrint(allocator, "{s}\n", .{echo.message});
                    defer allocator.free(output);
                    if (output_capture) |capture| {
                        try capture.write(output);
                    } else {
                        print("{s}", .{output});
                    }
                    return CommandStatus{ .Code = 0 };
                },
                .Cls => {
                    if (output_capture == null) {
                        // Clear screen - only works when not redirected
                        print("\x1B[2J\x1B[H", .{});
                    }
                    return CommandStatus{ .Code = 0 };
                },
                .Exit => {
                    return CommandStatus.ExitShell;
                },
                .EchoPlain => {
                    const output = "ECHO is on\n";
                    if (output_capture) |capture| {
                        try capture.write(output);
                    } else {
                        print("{s}", .{output});
                    }
                    return CommandStatus{ .Code = 0 };
                },
                .EchoOn => {
                    const output = "ECHO is on\n";
                    if (output_capture) |capture| {
                        try capture.write(output);
                    } else {
                        print("{s}", .{output});
                    }
                    return CommandStatus{ .Code = 0 };
                },
                .EchoOff => {
                    return CommandStatus{ .Code = 0 };
                },
                .Ver => {
                    const output = "MB-DOSE Version 6.22\n";
                    if (output_capture) |capture| {
                        try capture.write(output);
                    } else {
                        print("{s}", .{output});
                    }
                    return CommandStatus{ .Code = 0 };
                },
                .Date => {
                    const timestamp = std.time.timestamp();
                    const epoch_seconds = @as(u64, @intCast(timestamp));
                    const epoch_day = @divFloor(epoch_seconds, std.time.s_per_day);

                    // Calculate days since Unix epoch (1970-01-01)
                    // Unix epoch is 719163 days since year 1 AD
                    const days_since_year_1 = epoch_day + 719163;

                    // Simple algorithm to convert days to year/month/day
                    var year: u32 = 1;
                    var remaining_days = days_since_year_1;

                    // Find the year
                    while (true) {
                        const days_in_year: u64 = if (isLeapYear(year)) 366 else 365;
                        if (remaining_days < days_in_year) break;
                        remaining_days -= days_in_year;
                        year += 1;
                    }

                    // Days in each month (non-leap year)
                    const days_in_month = [_]u32{ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

                    var month: u32 = 1;
                    for (days_in_month, 1..) |days, m| {
                        var month_days = days;
                        // Adjust February for leap years
                        if (m == 2 and isLeapYear(year)) {
                            month_days = 29;
                        }

                        if (remaining_days < month_days) {
                            month = @intCast(m);
                            break;
                        }
                        remaining_days -= month_days;
                    }

                    const day = remaining_days + 1; // Days are 1-indexed

                    const output = try std.fmt.allocPrint(allocator, "Current date is {d:0>2}/{d:0>2}/{d}\n", .{ month, day, year });
                    defer allocator.free(output);
                    if (output_capture) |capture| {
                        try capture.write(output);
                    } else {
                        print("{s}", .{output});
                    }
                    return CommandStatus{ .Code = 0 };
                },
                .Time => {
                    const timestamp = std.time.timestamp();
                    const epoch_seconds = @as(u64, @intCast(timestamp));
                    const day_seconds = epoch_seconds % std.time.s_per_day;
                    const hours = day_seconds / std.time.s_per_hour;
                    const minutes = (day_seconds % std.time.s_per_hour) / std.time.s_per_min;
                    const seconds = day_seconds % std.time.s_per_min;

                    const output = try std.fmt.allocPrint(allocator, "Current time is {d:0>2}:{d:0>2}:{d:0>2}\n", .{ hours, minutes, seconds });
                    defer allocator.free(output);
                    if (output_capture) |capture| {
                        try capture.write(output);
                    } else {
                        print("{s}", .{output});
                    }
                    return CommandStatus{ .Code = 0 };
                },
                .Dir => |dir| {
                    return dir.eval(allocator, output_capture, input_source);
                },
                .Type => |type_cmd| {
                    return type_cmd.eval(allocator, output_capture, input_source);
                },
                .Sort => {
                    var lines = ArrayList([]const u8).init(allocator);
                    defer {
                        for (lines.items) |line| {
                            allocator.free(line);
                        }
                        lines.deinit();
                    }

                    // Read input lines
                    if (input_source) |source| {
                        // Read from input redirection
                        while (try source.readLine(allocator)) |line| {
                            try lines.append(line);
                        }
                    } else {
                        // Read from stdin (simplified - just show message)
                        const msg = "SORT: Use input redirection (< file.txt) to sort file contents\n";
                        if (output_capture) |capture| {
                            try capture.write(msg);
                        } else {
                            print("{s}", .{msg});
                        }
                        return CommandStatus{ .Code = 0 };
                    }

                    // Sort the lines
                    std.mem.sort([]const u8, lines.items, {}, struct {
                        fn lessThan(_: void, lhs: []const u8, rhs: []const u8) bool {
                            return std.mem.order(u8, lhs, rhs) == .lt;
                        }
                    }.lessThan);

                    // Output sorted lines
                    var output_buffer = ArrayList(u8).init(allocator);
                    defer output_buffer.deinit();

                    for (lines.items) |line| {
                        try output_buffer.writer().print("{s}\n", .{line});
                    }

                    if (output_capture) |capture| {
                        try capture.write(output_buffer.items);
                    } else {
                        print("{s}", .{output_buffer.items});
                    }

                    return CommandStatus{ .Code = 0 };
                },
                .Chdir => |chdir| {
                    return chdir.eval(allocator, output_capture, input_source);
                },
                .Copy => |copy| {
                    return copy.eval(allocator, output_capture, input_source);
                },
                .Remove => |remove| {
                    return remove.eval(allocator, output_capture, input_source);
                },
                .Mkdir => |mkdir| {
                    return mkdir.eval(allocator, output_capture, input_source);
                },
                .Rmdir => |rmdir| {
                    return rmdir.eval(allocator, output_capture, input_source);
                },
                .Rename => |rename| {
                    return rename.eval(allocator, output_capture, input_source);
                },
                .Move => {
                    const error_msg = "MOVE command not yet implemented\n";
                    if (output_capture) |capture| {
                        try capture.write(error_msg);
                    } else {
                        print("{s}", .{error_msg});
                    }
                    return CommandStatus{ .Code = 1 };
                },
                .PathGet => |path_get| {
                    return path_get.eval(allocator, output_capture, input_source);
                },
                .PathSet => |path_set| {
                    return path_set.eval(allocator, output_capture, input_source);
                },
                else => {
                    const error_msg = try std.fmt.allocPrint(allocator, "Command not implemented: {any}\n", .{builtin_cmd});
                    defer allocator.free(error_msg);
                    if (output_capture) |capture| {
                        try capture.write(error_msg);
                    } else {
                        print("{s}", .{error_msg});
                    }
                    return CommandStatus{ .Code = 1 };
                },
            }
        },

        .External => |external| {
            // Try to execute external command
            var child_args = ArrayList([]const u8).init(allocator);
            defer child_args.deinit();

            try child_args.append(external.program);
            for (external.args.items) |arg| {
                try child_args.append(arg);
            }

            var child = std.process.Child.init(child_args.items, allocator);

            // Set up pipes for capturing output
            child.stdin_behavior = if (input_source != null) .Pipe else .Inherit;
            child.stdout_behavior = if (output_capture != null) .Pipe else .Inherit;
            child.stderr_behavior = if (output_capture != null) .Pipe else .Inherit;

            const spawn_result = child.spawn();
            if (spawn_result) |_| {
                // Spawn succeeded, continue with execution
            } else |err| switch (err) {
                error.FileNotFound => {
                    const error_msg = try std.fmt.allocPrint(allocator, "'{s}' is not recognized as an internal or external command,\noperable program or batch file.\n", .{external.program});
                    defer allocator.free(error_msg);

                    if (output_capture) |capture| {
                        try capture.write(error_msg);
                    } else {
                        print("{s}", .{error_msg});
                    }
                    return CommandStatus{ .Code = 1 };
                },
                error.AccessDenied => {
                    const error_msg = "Access is denied.\n";
                    if (output_capture) |capture| {
                        try capture.write(error_msg);
                    } else {
                        print("{s}", .{error_msg});
                    }
                    return CommandStatus{ .Code = 1 };
                },
                else => {
                    const error_msg = try std.fmt.allocPrint(allocator, "Cannot execute '{s}': {}\n", .{ external.program, err });
                    defer allocator.free(error_msg);

                    if (output_capture) |capture| {
                        try capture.write(error_msg);
                    } else {
                        print("{s}", .{error_msg});
                    }
                    return CommandStatus{ .Code = 1 };
                },
            }

            // Handle input redirection
            if (input_source) |source| {
                if (child.stdin) |stdin| {
                    const writer = stdin.writer();

                    // Reset source position for reading
                    var temp_source = source.*;
                    temp_source.position = 0;

                    while (try temp_source.readLine(allocator)) |line| {
                        defer allocator.free(line);
                        try writer.print("{s}\n", .{line});
                    }
                    child.stdin.?.close();
                    child.stdin = null;
                }
            }

            // Handle output capture
            if (output_capture) |capture| {
                // Read stdout
                if (child.stdout) |stdout| {
                    var buffer: [4096]u8 = undefined;
                    while (true) {
                        const bytes_read = stdout.read(&buffer) catch break;
                        if (bytes_read == 0) break;
                        try capture.write(buffer[0..bytes_read]);
                    }
                }

                // Read stderr
                if (child.stderr) |stderr| {
                    var buffer: [4096]u8 = undefined;
                    while (true) {
                        const bytes_read = stderr.read(&buffer) catch break;
                        if (bytes_read == 0) break;
                        try capture.write(buffer[0..bytes_read]);
                    }
                }
            }

            // Wait for process to complete
            const term = child.wait() catch |err| {
                const error_msg = switch (err) {
                    error.FileNotFound => try std.fmt.allocPrint(allocator, "'{s}' is not recognized as an internal or external command,\noperable program or batch file.\n", .{external.program}),
                    else => try std.fmt.allocPrint(allocator, "Error waiting for command: {}\n", .{err}),
                };
                defer allocator.free(error_msg);

                if (output_capture) |capture| {
                    try capture.write(error_msg);
                } else {
                    print("{s}", .{error_msg});
                }
                return CommandStatus{ .Code = 1 };
            };

            // Return exit code
            switch (term) {
                .Exited => |code| return CommandStatus{ .Code = @intCast(code) },
                .Signal => |_| return CommandStatus{ .Code = 1 },
                .Stopped => |_| return CommandStatus{ .Code = 1 },
                .Unknown => |_| return CommandStatus{ .Code = 1 },
            }
        },

        .Redirect => |redirect| {
            // Check if we have any output redirections
            var has_output_redirect = false;
            for (redirect.redirects.items) |redir| {
                if (redir.redirect_type == .OutputOverwrite or redir.redirect_type == .OutputAppend) {
                    has_output_redirect = true;
                    break;
                }
            }

            var captured_output = OutputCapture.init(allocator);
            defer captured_output.deinit();

            // Prepare input redirection if needed
            var input_data: ?[]const u8 = null;
            var redirect_input_source: ?InputSource = null;
            defer if (input_data) |data| allocator.free(data);

            // Process input redirections first
            for (redirect.redirects.items) |redir| {
                if (redir.redirect_type == .InputFrom) {
                    const file_path = switch (redir.target) {
                        .Con => {
                            print("Input redirection from CON not supported\n", .{});
                            return CommandStatus{ .Code = 1 };
                        },
                        .Lpt1, .Lpt2, .Lpt3, .Prn => {
                            print("Cannot redirect input from device\n", .{});
                            return CommandStatus{ .Code = 1 };
                        },
                        .Path => |path| path,
                    };

                    // Read input file
                    const file = std.fs.cwd().openFile(file_path, .{}) catch |err| {
                        switch (err) {
                            error.FileNotFound => print("The system cannot find the file specified.\n", .{}),
                            error.AccessDenied => print("Access is denied.\n", .{}),
                            else => print("Cannot open input file.\n", .{}),
                        }
                        return CommandStatus{ .Code = 1 };
                    };
                    defer file.close();

                    input_data = file.readToEndAlloc(allocator, std.math.maxInt(usize)) catch |err| {
                        switch (err) {
                            error.AccessDenied => print("Access is denied.\n", .{}),
                            else => print("Cannot read input file.\n", .{}),
                        }
                        return CommandStatus{ .Code = 1 };
                    };

                    redirect_input_source = InputSource.init(input_data.?);
                    break; // Only handle first input redirection
                }
            }

            // Execute the command with input and output capture (only capture output if needed)
            const status = try executeCommandWithOutput(redirect.command.*, allocator, if (has_output_redirect) &captured_output else null, if (redirect_input_source) |*source| source else null);

            // Handle output redirections
            for (redirect.redirects.items) |redir| {
                if (redir.redirect_type == .InputFrom) continue; // Already handled
                const file_path = switch (redir.target) {
                    .Con => {
                        // Redirect to console - just print normally
                        print("{s}", .{captured_output.getContents()});
                        continue;
                    },
                    .Lpt1, .Lpt2, .Lpt3, .Prn => {
                        print("Cannot redirect to device\n", .{});
                        return CommandStatus{ .Code = 1 };
                    },
                    .Path => |path| path,
                };

                // Handle different redirect types
                switch (redir.redirect_type) {
                    .OutputOverwrite => {
                        // Write to file, overwriting existing content
                        const file = std.fs.cwd().createFile(file_path, .{}) catch |err| {
                            switch (err) {
                                error.AccessDenied => print("Access is denied.\n", .{}),
                                else => print("Cannot create file.\n", .{}),
                            }
                            return CommandStatus{ .Code = 1 };
                        };
                        defer file.close();

                        file.writeAll(captured_output.getContents()) catch |err| {
                            switch (err) {
                                error.AccessDenied => print("Access is denied.\n", .{}),
                                else => print("Cannot write to file.\n", .{}),
                            }
                            return CommandStatus{ .Code = 1 };
                        };
                    },
                    .OutputAppend => {
                        // Append to file
                        const file = std.fs.cwd().openFile(file_path, .{ .mode = .write_only }) catch |err| {
                            switch (err) {
                                error.FileNotFound => {
                                    // Create new file if it doesn't exist
                                    const new_file = std.fs.cwd().createFile(file_path, .{}) catch |create_err| {
                                        switch (create_err) {
                                            error.AccessDenied => print("Access is denied.\n", .{}),
                                            else => print("Cannot create file.\n", .{}),
                                        }
                                        return CommandStatus{ .Code = 1 };
                                    };
                                    defer new_file.close();

                                    new_file.writeAll(captured_output.getContents()) catch {
                                        print("Cannot write to file.\n", .{});
                                        return CommandStatus{ .Code = 1 };
                                    };
                                    continue;
                                },
                                error.AccessDenied => {
                                    print("Access is denied.\n", .{});
                                    return CommandStatus{ .Code = 1 };
                                },
                                else => {
                                    print("Cannot open file.\n", .{});
                                    return CommandStatus{ .Code = 1 };
                                },
                            }
                        };
                        defer file.close();

                        // Seek to end for append
                        file.seekFromEnd(0) catch {
                            print("Cannot seek to end of file.\n", .{});
                            return CommandStatus{ .Code = 1 };
                        };

                        file.writeAll(captured_output.getContents()) catch |err| {
                            switch (err) {
                                error.AccessDenied => print("Access is denied.\n", .{}),
                                else => print("Cannot write to file.\n", .{}),
                            }
                            return CommandStatus{ .Code = 1 };
                        };
                    },
                    .InputFrom => {
                        // Input redirection already handled above
                        continue;
                    },
                }
            }

            return status;
        },

        else => {
            const error_msg = "Command type not implemented\n";
            if (output_capture) |capture| {
                try capture.write(error_msg);
            } else {
                print("{s}", .{error_msg});
            }
            return CommandStatus{ .Code = 1 };
        },
    }
}