const std = @import("std");
const parser = @import("parser.zig");
const shell = @import("shell.zig");
const builtins = @import("builtins.zig");

const BUILTINS = [_][]const u8{ "echo", "exit" };

fn longestCommonPrefix(strings: []const []const u8) []const u8 {
    if (strings.len == 0) return "";
    var min_len: usize = strings[0].len;
    for (strings[1..]) |s| {
        if (s.len < min_len) min_len = s.len;
    }

    var i: usize = 0;
    while (i < min_len) : (i += 1) {
        const c = strings[0][i];
        for (strings[1..]) |s| {
            if (s[i] != c) return strings[0][0..i];
        }
    }
    return strings[0][0..min_len];
}

fn findAllMatches(allocator: std.mem.Allocator, partial: []const u8) !std.ArrayList([]const u8) {
    var matches = std.ArrayList([]const u8){};

    for (BUILTINS) |builtin| {
        if (std.mem.startsWith(u8, builtin, partial)) {
            const duped = try allocator.dupe(u8, builtin);
            try matches.append(allocator, duped);
        }
    }

    const path_env = std.posix.getenv("PATH") orelse return matches;

    var path_iter = std.mem.splitScalar(u8, path_env, ':');
    while (path_iter.next()) |dir_path| {
        if (dir_path.len == 0) continue;

        var dir = std.fs.openDirAbsolute(dir_path, .{ .iterate = true }) catch continue;
        defer dir.close();

        var iter = dir.iterate();
        while (iter.next() catch continue) |entry| {
            if (entry.kind == .file or entry.kind == .sym_link) {
                if (std.mem.startsWith(u8, entry.name, partial)) {
                    const stat = dir.statFile(entry.name) catch continue;
                    if (stat.mode & 0o111 != 0) {
                        var already_exists = false;
                        for (matches.items) |existing| {
                            if (std.mem.eql(u8, existing, entry.name)) {
                                already_exists = true;
                                break;
                            }
                        }
                        if (!already_exists) {
                            const duped = allocator.dupe(u8, entry.name) catch continue;
                            matches.append(allocator, duped) catch {
                                allocator.free(duped);
                                continue;
                            };
                        }
                    }
                }
            }
        }
    }

    return matches;
}

fn tryComplete(allocator: std.mem.Allocator, partial: []const u8) ?[]const u8 {
    var matches: usize = 0;
    var match: ?[]const u8 = null;
    var match_is_builtin = false;

    for (BUILTINS) |builtin| {
        if (std.mem.startsWith(u8, builtin, partial)) {
            matches += 1;
            if (matches == 1) {
                match = builtin;
                match_is_builtin = true;
            }
            if (matches > 1) {
                if (match != null and !match_is_builtin) {
                    allocator.free(match.?);
                }
                return null;
            }
        }
    }

    const path_env = std.posix.getenv("PATH") orelse {
        if (matches == 1 and match != null) {
            return allocator.dupe(u8, match.?) catch null;
        }
        return null;
    };

    var path_iter = std.mem.splitScalar(u8, path_env, ':');
    while (path_iter.next()) |dir_path| {
        if (dir_path.len == 0) continue;

        var dir = std.fs.openDirAbsolute(dir_path, .{ .iterate = true }) catch continue;
        defer dir.close();

        var iter = dir.iterate();
        while (iter.next() catch continue) |entry| {
            if (entry.kind == .file or entry.kind == .sym_link) {
                if (std.mem.startsWith(u8, entry.name, partial)) {
                    const stat = dir.statFile(entry.name) catch continue;
                    if (stat.mode & 0o111 != 0) {
                        if (match != null and match_is_builtin and std.mem.eql(u8, match.?, entry.name)) {
                            continue;
                        }

                        matches += 1;
                        if (matches == 1) {
                            match = allocator.dupe(u8, entry.name) catch continue;
                            match_is_builtin = false;
                        } else {
                            if (match != null and !match_is_builtin) {
                                allocator.free(match.?);
                            }
                            return null;
                        }
                    }
                }
            }
        }
    }

    if (matches == 1 and match != null) {
        if (match_is_builtin) {
            return allocator.dupe(u8, match.?) catch null;
        } else {
            return match.?;
        }
    }
    return null;
}

fn enableRawMode(fd: std.posix.fd_t) !std.posix.termios {
    const original = try std.posix.tcgetattr(fd);
    var raw = original;

    raw.lflag.ICANON = false;
    raw.lflag.ECHO = false;

    raw.cc[@intFromEnum(std.posix.V.MIN)] = 1;
    raw.cc[@intFromEnum(std.posix.V.TIME)] = 0;

    try std.posix.tcsetattr(fd, .FLUSH, raw);
    return original;
}

fn disableRawMode(fd: std.posix.fd_t, original: std.posix.termios) !void {
    try std.posix.tcsetattr(fd, .FLUSH, original);
}

fn readCommand(allocator: std.mem.Allocator, history: std.ArrayList([]const u8)) !?[]const u8 {
    const stdin = std.fs.File.stdin();
    const stdout = std.fs.File.stdout();

    const stdin_fd = stdin.handle;

    const is_tty = std.posix.isatty(stdin_fd);
    const original_termios = if (is_tty) try enableRawMode(stdin_fd) else null;
    defer if (original_termios) |orig| disableRawMode(stdin_fd, orig) catch {};

    var buffer = std.ArrayList(u8){};
    defer buffer.deinit(allocator);

    var byte: [1]u8 = undefined;
    var last_tab_partial: ?[]const u8 = null;
    var last_was_tab = false;
    var history_index: ?usize = null; // Track which history entry is displayed

    while (true) {
        const bytes_read = try stdin.read(&byte);
        if (bytes_read == 0) return null;

        const c = byte[0];

        if (c == '\n' or c == '\r') {
            if (last_tab_partial) |p| allocator.free(p);
            return try buffer.toOwnedSlice(allocator);
        } else if (c == 27 and is_tty) {
            var seq: [2]u8 = undefined;
            var seq_len: usize = 0;

            if (try stdin.read(seq[0..1]) > 0) {
                seq_len = 1;
                if (seq[0] == '[') {
                    if (try stdin.read(seq[1..2]) > 0) {
                        seq_len = 2;
                        if (seq[1] == 'A') {
                            const new_index = if (history_index) |idx|
                                if (idx > 0) idx - 1 else idx
                            else if (history.items.len > 0)
                                history.items.len - 1
                            else
                                null;

                            if (new_index) |idx| {
                                history_index = idx;

                                while (buffer.items.len > 0) {
                                    _ = buffer.pop();
                                    try stdout.writeAll("\x08 \x08");
                                }

                                const cmd = history.items[idx];
                                try buffer.appendSlice(allocator, cmd);
                                try stdout.writeAll(cmd);

                                last_tab_partial = null;
                                last_was_tab = false;
                            }
                        } else if (seq[1] == 'B') {
                            if (history_index) |idx| {
                                if (idx + 1 < history.items.len) {
                                    history_index = idx + 1;

                                    while (buffer.items.len > 0) {
                                        _ = buffer.pop();
                                        try stdout.writeAll("\x08 \x08");
                                    }

                                    const cmd = history.items[idx + 1];
                                    try buffer.appendSlice(allocator, cmd);
                                    try stdout.writeAll(cmd);
                                } else {
                                    while (buffer.items.len > 0) {
                                        _ = buffer.pop();
                                        try stdout.writeAll("\x08 \x08");
                                    }
                                    history_index = null;
                                }

                                last_tab_partial = null;
                                last_was_tab = false;
                            }
                        }
                    }
                }
            }
        } else if (c == '\t' and is_tty) {
            const partial = buffer.items;
            if (partial.len > 0 and std.mem.indexOf(u8, partial, " ") == null) {
                var matches = try findAllMatches(allocator, partial);
                defer {
                    for (matches.items) |m| allocator.free(m);
                    matches.deinit(allocator);
                }

                const is_double_tab = last_was_tab and last_tab_partial != null and std.mem.eql(u8, last_tab_partial.?, partial);

                if (matches.items.len == 0) {
                    try stdout.writeAll("\x07");
                    last_was_tab = true;
                    if (last_tab_partial) |p| allocator.free(p);
                    last_tab_partial = try allocator.dupe(u8, partial);
                } else if (matches.items.len == 1) {
                    const completion = matches.items[0];
                    if (completion.len > partial.len) {
                        const remaining = completion[partial.len..];
                        try stdout.writeAll(remaining);
                        try buffer.appendSlice(allocator, remaining);
                    }
                    try stdout.writeAll(" ");
                    try buffer.append(allocator, ' ');

                    last_was_tab = false;
                    if (last_tab_partial) |p| allocator.free(p);
                    last_tab_partial = null;
                } else {
                    const lcp = longestCommonPrefix(matches.items);
                    if (lcp.len > partial.len) {
                        const remaining = lcp[partial.len..];
                        try stdout.writeAll(remaining);
                        try buffer.appendSlice(allocator, remaining);

                        last_was_tab = false;
                        if (last_tab_partial) |p| allocator.free(p);
                        last_tab_partial = null;
                    } else if (is_double_tab) {
                        std.mem.sort([]const u8, matches.items, {}, struct {
                            fn lessThan(_: void, a: []const u8, b: []const u8) bool {
                                return std.mem.order(u8, a, b) == .lt;
                            }
                        }.lessThan);

                        try stdout.writeAll("\n");
                        for (matches.items, 0..) |match, i| {
                            try stdout.writeAll(match);
                            if (i < matches.items.len - 1) {
                                try stdout.writeAll("  ");
                            }
                        }
                        try stdout.writeAll("\n$ ");
                        try stdout.writeAll(partial);

                        last_was_tab = false;
                        if (last_tab_partial) |p| {
                            allocator.free(p);
                            last_tab_partial = null;
                        }
                    } else {
                        try stdout.writeAll("\x07");
                        last_was_tab = true;
                        if (last_tab_partial) |p| allocator.free(p);
                        last_tab_partial = try allocator.dupe(u8, partial);
                    }
                }
            } else if (partial.len > 0) {
                const space_idx = std.mem.lastIndexOf(u8, partial, " ").?;
                const prefix = partial[space_idx + 1..];

                var matches = std.ArrayList([]const u8){};
                defer {
                    for (matches.items) |m| allocator.free(m);
                    matches.deinit(allocator);
                }

                if (std.fs.cwd().openDir(".", .{ .iterate = true })) |opened_dir| {
                    var dir = opened_dir;
                    defer dir.close();
                    var iter = dir.iterate();
                    while (iter.next() catch null) |entry| {
                        if (std.mem.startsWith(u8, entry.name, prefix)) {
                            if (allocator.dupe(u8, entry.name)) |duped| {
                                matches.append(allocator, duped) catch {
                                    allocator.free(duped);
                                };
                            } else |_| {}
                        }
                    }
                } else |_| {}

                if (matches.items.len == 0) {
                    try stdout.writeAll("\x07");
                } else if (matches.items.len == 1) {
                    const completion = matches.items[0];
                    if (completion.len > prefix.len) {
                        const remaining = completion[prefix.len..];
                        try stdout.writeAll(remaining);
                        try buffer.appendSlice(allocator, remaining);
                    }
                    try stdout.writeAll(" ");
                    try buffer.append(allocator, ' ');

                    last_was_tab = false;
                    if (last_tab_partial) |p| allocator.free(p);
                    last_tab_partial = null;
                } else {
                    try stdout.writeAll("\x07");
                }
            }
        } else if ((c == 127 or c == 8) and is_tty) {
            if (buffer.items.len > 0) {
                _ = buffer.pop();
                try stdout.writeAll("\x08 \x08");
            }
            last_was_tab = false;
            if (last_tab_partial) |p| {
                allocator.free(p);
                last_tab_partial = null;
            }
        } else if (c >= 32 and c < 127) {
            try buffer.append(allocator, c);
            if (is_tty) {
                try stdout.writeAll(&[_]u8{c});
            }
            last_was_tab = false;
            if (last_tab_partial) |p| {
                allocator.free(p);
                last_tab_partial = null;
            }
        } else if (c == '\t' and !is_tty) {
            try buffer.append(allocator, c);
        }
    }
}
pub fn main() !void {
    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    defer _ = gpa.deinit();
    const allocator = gpa.allocator();

    var history = std.ArrayList([]const u8){};
    defer {
        for (history.items) |cmd| allocator.free(cmd);
        history.deinit(allocator);
    }

    var last_written_index: usize = 0;

    if (std.posix.getenv("HISTFILE")) |histfile_path| {
        const file = std.fs.cwd().openFile(histfile_path, .{}) catch null;
        if (file) |f| {
            defer f.close();

            const file_size = f.getEndPos() catch 0;
            if (file_size > 0) {
                const buffer = allocator.alloc(u8, file_size) catch null;
                if (buffer) |buf| {
                    defer allocator.free(buf);

                    const bytes_read = f.readAll(buf) catch 0;
                    if (bytes_read > 0) {
                        var line_iter = std.mem.splitScalar(u8, buf[0..bytes_read], '\n');
                        while (line_iter.next()) |line| {
                            const trimmed = std.mem.trim(u8, line, " \r");
                            if (trimmed.len > 0) {
                                const line_copy = allocator.dupe(u8, trimmed) catch continue;
                                history.append(allocator, line_copy) catch {
                                    allocator.free(line_copy);
                                    continue;
                                };
                            }
                        }
                    }
                }
            }
        }
    }

    const stdout = std.fs.File.stdout();

    while (true) {
        try stdout.writeAll("$ ");

        const command = try readCommand(allocator, history);
        if (command) |cmd| {
            defer allocator.free(cmd);
            try stdout.writeAll("\n");
            var stdout_writer = std.fs.File.stdout().writerStreaming(&.{});
            const stdout_iface = &stdout_writer.interface;

            const cmd_copy = try allocator.dupe(u8, cmd);
            try history.append(allocator, cmd_copy);

            if (std.mem.indexOfScalar(u8, cmd, '|')) |_| {
                var segments = std.ArrayList([]const u8){};
                defer segments.deinit(allocator);

                var invalid = false;
                var start: usize = 0;
                for (cmd, 0..) |ch, i| {
                    if (ch == '|') {
                        const seg = std.mem.trim(u8, cmd[start..i], " ");
                        if (seg.len == 0) {
                            try stdout.writeAll("pipe: command not found\n");
                            invalid = true;
                            break;
                        }
                        try segments.append(allocator, seg);
                        start = i + 1;
                    }
                }
                if (invalid) continue;

                const last_seg = std.mem.trim(u8, cmd[start..], " ");
                if (last_seg.len == 0) {
                    try stdout.writeAll("pipe: command not found\n");
                    continue;
                }
                try segments.append(allocator, last_seg);

                if (segments.items.len == 1) {
                    const parsed = parser.parseCommand(cmd);
                    const result = try shell.executeCommand(allocator, stdout_iface, parsed.name, parsed.args, parsed.output_redirect, parsed.error_redirect, parsed.append_output, parsed.append_error, &history, &last_written_index);
                    if (result == .exit_shell) break;
                } else {
                    const result = try shell.executePipeline(allocator, stdout_iface, segments.items);
                    if (result == .exit_shell) break;
                }
            } else {
                const parsed = parser.parseCommand(cmd);

                const result = try shell.executeCommand(allocator, stdout_iface, parsed.name, parsed.args, parsed.output_redirect, parsed.error_redirect, parsed.append_output, parsed.append_error, &history, &last_written_index);

                if (result == .exit_shell) break;
            }
        } else {
            break;
        }
    }

    if (std.posix.getenv("HISTFILE")) |histfile_path| {
        const file = std.fs.cwd().createFile(histfile_path, .{}) catch null;
        if (file) |f| {
            defer f.close();

            for (history.items) |cmd| {
                _ = f.writeAll(cmd) catch {};
                _ = f.writeAll("\n") catch {};
            }
        }
    }
}