// A small utility to print information related to pressing keys. This is similar to using tools
// like `xxd` and `od -tx1z` but provides more information such as the time delay between each
// character. It also allows pressing and interpreting keys that are normally special such as
// [ctrl-C] (interrupt the program) or [ctrl-D] (EOF to signal the program should exit).
// And unlike those other tools this one disables ICRNL mode so it can distinguish between
// carriage-return (\cM) and newline (\cJ).
//
// Type "exit" or "quit" to terminate the program.
#include "config.h"  // IWYU pragma: keep

#include <errno.h>
#include <getopt.h>
#include <signal.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <termios.h>
#include <unistd.h>

#include <cstring>
#include <cwchar>
#include <memory>
#include <string>
#include <vector>

#include "common.h"
#include "env.h"
#include "fallback.h"  // IWYU pragma: keep
#include "fish_version.h"
#include "input.h"
#include "input_common.h"
#include "parser.h"
#include "print_help.h"
#include "proc.h"
#include "reader.h"
#include "signal.h"
#include "wutil.h"  // IWYU pragma: keep

struct config_paths_t determine_config_directory_paths(const char *argv0);

static const wchar_t *ctrl_symbolic_names[] = {
    nullptr, nullptr, nullptr, nullptr, nullptr, nullptr, nullptr, L"\\a",
    L"\\b",  L"\\t",  L"\\n",  L"\\v",  L"\\f",  L"\\r",  nullptr, nullptr,
    nullptr, nullptr, nullptr, nullptr, nullptr, nullptr, nullptr, nullptr,
    nullptr, nullptr, nullptr, L"\\e",  nullptr, nullptr, nullptr, nullptr};

/// Return true if the recent sequence of characters indicates the user wants to exit the program.
static bool should_exit(wchar_t wc) {
    unsigned char c = wc < 0x80 ? wc : 0;
    static unsigned char recent_chars[4] = {0};

    recent_chars[0] = recent_chars[1];
    recent_chars[1] = recent_chars[2];
    recent_chars[2] = recent_chars[3];
    recent_chars[3] = c;
    if (c == shell_modes.c_cc[VINTR]) {
        if (recent_chars[2] == shell_modes.c_cc[VINTR]) return true;
        std::fwprintf(stderr, L"Press [ctrl-%c] again to exit\n", shell_modes.c_cc[VINTR] + 0x40);
        return false;
    }
    if (c == shell_modes.c_cc[VEOF]) {
        if (recent_chars[2] == shell_modes.c_cc[VEOF]) return true;
        std::fwprintf(stderr, L"Press [ctrl-%c] again to exit\n", shell_modes.c_cc[VEOF] + 0x40);
        return false;
    }
    return std::memcmp(recent_chars, "exit", const_strlen("exit")) == 0 ||
           std::memcmp(recent_chars, "quit", const_strlen("quit")) == 0;
}

/// Return the name if the recent sequence of characters matches a known terminfo sequence.
static maybe_t<wcstring> sequence_name(wchar_t wc) {
    static std::string recent_chars;
    if (wc >= 0x80) {
        // Terminfo sequences are always ASCII.
        recent_chars.clear();
        return none();
    }

    unsigned char c = wc;
    recent_chars.push_back(c);
    while (recent_chars.size() > 8) {
        recent_chars.erase(recent_chars.begin());
    }

    // Check all nonempty substrings extending to the end.
    for (size_t i = 0; i < recent_chars.size(); i++) {
        wcstring out_name;
        wcstring seq = str2wcstring(recent_chars.substr(i));
        if (input_terminfo_get_name(seq, &out_name)) {
            return out_name;
        }
    }
    return none();
}

/// Return true if the character must be escaped when used in the sequence of chars to be bound in
/// a `bind` command.
static bool must_escape(wchar_t wc) { return std::wcschr(L"[]()<>{}*\\?$#;&|'\"", wc) != nullptr; }

static void ctrl_to_symbol(wchar_t *buf, int buf_len, wchar_t wc, bool bind_friendly) {
    if (ctrl_symbolic_names[wc]) {
        if (bind_friendly) {
            std::swprintf(buf, buf_len, L"%ls", ctrl_symbolic_names[wc]);
        } else {
            std::swprintf(buf, buf_len, L"\\c%c  (or %ls)", wc + 0x40, ctrl_symbolic_names[wc]);
        }
    } else {
        std::swprintf(buf, buf_len, L"\\c%c", wc + 0x40);
    }
}

static void space_to_symbol(wchar_t *buf, int buf_len, wchar_t wc, bool bind_friendly) {
    if (bind_friendly) {
        std::swprintf(buf, buf_len, L"\\x%X", wc);
    } else {
        std::swprintf(buf, buf_len, L"\\x%X  (aka \"space\")", wc);
    }
}

static void del_to_symbol(wchar_t *buf, int buf_len, wchar_t wc, bool bind_friendly) {
    if (bind_friendly) {
        std::swprintf(buf, buf_len, L"\\x%X", wc);
    } else {
        std::swprintf(buf, buf_len, L"\\x%X  (aka \"del\")", wc);
    }
}

static void ascii_printable_to_symbol(wchar_t *buf, int buf_len, wchar_t wc, bool bind_friendly) {
    if (bind_friendly && must_escape(wc)) {
        std::swprintf(buf, buf_len, L"\\%c", wc);
    } else {
        std::swprintf(buf, buf_len, L"%c", wc);
    }
}

/// Convert a wide-char to a symbol that can be used in our output. The use of a static buffer
/// requires that the returned string be used before we are called again.
static wchar_t *char_to_symbol(wchar_t wc, bool bind_friendly) {
    static wchar_t buf[64];

    if (wc < L' ') {  // ASCII control character
        ctrl_to_symbol(buf, sizeof(buf) / sizeof(*buf), wc, bind_friendly);
    } else if (wc == L' ') {  // the "space" character
        space_to_symbol(buf, sizeof(buf) / sizeof(*buf), wc, bind_friendly);
    } else if (wc == 0x7F) {  // the "del" character
        del_to_symbol(buf, sizeof(buf) / sizeof(*buf), wc, bind_friendly);
    } else if (wc < 0x80) {  // ASCII characters that are not control characters
        ascii_printable_to_symbol(buf, sizeof(buf) / sizeof(*buf), wc, bind_friendly);
    }
// Conditional handling of BMP Unicode characters depends on the encoding. Assume width of wchar_t
// corresponds to the encoding, i.e. WCHAR_T_BITS == 16 implies UTF-16 and WCHAR_T_BITS == 32
// because there's no other sane way of handling the input.
#if WCHAR_T_BITS == 16
    else if (wc <= 0xD7FF || (wc >= 0xE000 && wc <= 0xFFFD)) {
        // UTF-16 encoding of Unicode character in BMP range
        std::swprintf(buf, sizeof(buf) / sizeof(*buf), L"\\u%04X", wc);
    } else {
        // Our support for UTF-16 surrogate pairs is non-existent.
        // See https://github.com/fish-shell/fish-shell/issues/6585#issuecomment-783669903 for what
        // correct handling of surrogate pairs would look like - except it would need to be done
        // everywhere.

        // 0xFFFD is the unicode codepoint for "symbol doesn't exist in codepage" and is the most
        // correct thing we can do given the byte-by-byte parsing without any support for surrogate
        // pairs.
        std::swprintf(buf, sizeof(buf) / sizeof(*buf), L"\\uFFFD");
    }
#elif WCHAR_T_BITS == 32
    else if (wc <= 0xFFFF) {  // BMP Unicode chararacter
        std::swprintf(buf, sizeof(buf) / sizeof(*buf), L"\\u%04X", wc);
    } else {  // Non-BMP Unicode chararacter
        std::swprintf(buf, sizeof(buf) / sizeof(*buf), L"\\U%06X", wc);
    }
#else
    static_assert(false, "Unsupported WCHAR_T size; unknown encoding!");
#endif

    return buf;
}

static void add_char_to_bind_command(wchar_t wc, std::vector<wchar_t> &bind_chars) {
    bind_chars.push_back(wc);
}

static void output_bind_command(std::vector<wchar_t> &bind_chars) {
    if (!bind_chars.empty()) {
        std::fputws(L"bind ", stdout);
        for (auto bind_char : bind_chars) {
            std::fputws(char_to_symbol(bind_char, true), stdout);
        }
        std::fputws(L" 'do something'\n", stdout);
        bind_chars.clear();
    }
}

static void output_info_about_char(wchar_t wc) {
    std::fwprintf(stderr, L"hex: %4X  char: %ls\n", wc, char_to_symbol(wc, false));
}

static bool output_matching_key_name(wchar_t wc) {
    if (maybe_t<wcstring> name = sequence_name(wc)) {
        std::fwprintf(stdout, L"bind -k %ls 'do something'\n", name->c_str());
        return true;
    }
    return false;
}

static double output_elapsed_time(double prev_tstamp, bool first_char_seen, bool verbose) {
    // How much time has passed since the previous char was received in microseconds.
    double now = timef();
    long long int delta_tstamp_us = 1000000 * (now - prev_tstamp);

    if (verbose) {
        if (delta_tstamp_us >= 200000 && first_char_seen) std::fputwc(L'\n', stderr);
        if (delta_tstamp_us >= 1000000) {
            std::fwprintf(stderr, L"              ");
        } else {
            std::fwprintf(stderr, L"(%3lld.%03lld ms)  ", delta_tstamp_us / 1000,
                          delta_tstamp_us % 1000);
        }
    }
    return now;
}

/// Process the characters we receive as the user presses keys.
static void process_input(bool continuous_mode, bool verbose) {
    bool first_char_seen = false;
    double prev_tstamp = 0.0;
    input_event_queue_t queue;
    std::vector<wchar_t> bind_chars;

    std::fwprintf(stderr, L"Press a key:\n");
    for (;;) {
        maybe_t<char_event_t> evt{};
        if (reader_test_and_clear_interrupted()) {
            evt = char_event_t{shell_modes.c_cc[VINTR]};
        } else {
            evt = queue.readch_timed();
        }
        if (!evt || !evt->is_char()) {
            output_bind_command(bind_chars);
            if (first_char_seen && !continuous_mode) {
                return;
            }
            continue;
        }

        wchar_t wc = evt->get_char();
        prev_tstamp = output_elapsed_time(prev_tstamp, first_char_seen, verbose);
        // Hack for #3189. Do not suggest \c@ as the binding for nul, because a string containing
        // nul cannot be passed to builtin_bind since it uses C strings. We'll output the name of
        // this key (nul) elsewhere.
        if (wc) {
            add_char_to_bind_command(wc, bind_chars);
        }
        if (verbose) {
            output_info_about_char(wc);
        }
        if (output_matching_key_name(wc)) {
            output_bind_command(bind_chars);
        }

        if (continuous_mode && should_exit(wc)) {
            std::fwprintf(stderr, L"\nExiting at your request.\n");
            break;
        }

        first_char_seen = true;
    }
}

/// Setup our environment (e.g., tty modes), process key strokes, then reset the environment.
[[noreturn]] static void setup_and_process_keys(bool continuous_mode, bool verbose) {
    set_interactive_session(true);
    set_main_thread();
    setup_fork_guards();
    env_init();
    reader_init();
    parser_t &parser = parser_t::principal_parser();
    scoped_push<bool> interactive{&parser.libdata().is_interactive, true};
    signal_set_handlers(true);
    // We need to set the shell-modes for ICRNL,
    // in fish-proper this is done once a command is run.
    tcsetattr(STDIN_FILENO, TCSANOW, &shell_modes);

    if (continuous_mode) {
        std::fwprintf(stderr, L"\n");
        std::fwprintf(stderr,
                      L"To terminate this program type \"exit\" or \"quit\" in this window,\n");
        std::fwprintf(stderr, L"or press [ctrl-%c] or [ctrl-%c] twice in a row.\n",
                      shell_modes.c_cc[VINTR] + 0x40, shell_modes.c_cc[VEOF] + 0x40);
        std::fwprintf(stderr, L"\n");
    }

    process_input(continuous_mode, verbose);
    restore_term_mode();
    _exit(0);
}

static bool parse_flags(int argc, char **argv, bool *continuous_mode, bool *verbose) {
    const char *short_opts = "+chvV";
    const struct option long_opts[] = {{"continuous", no_argument, nullptr, 'c'},
                                       {"help", no_argument, nullptr, 'h'},
                                       {"version", no_argument, nullptr, 'v'},
                                       {"verbose", no_argument, nullptr, 'V'},
                                       {}};
    int opt;
    bool error = false;
    while (!error && (opt = getopt_long(argc, argv, short_opts, long_opts, nullptr)) != -1) {
        switch (opt) {
            case 'c': {
                *continuous_mode = true;
                break;
            }
            case 'h': {
                print_help("fish_key_reader", 1);
                exit(0);
            }
            case 'v': {
                std::fwprintf(stdout, _(L"%ls, version %s\n"), program_name, get_fish_version());
                exit(0);
            }
            case 'V': {
                *verbose = true;
                break;
            }
            default: {
                // We assume getopt_long() has already emitted a diagnostic msg.
                error = true;
                break;
            }
        }
    }

    if (error) return false;

    argc -= optind;
    if (argc != 0) {
        std::fwprintf(stderr, L"Expected no arguments, got %d\n", argc);
        return false;
    }

    return true;
}

int main(int argc, char **argv) {
    program_name = L"fish_key_reader";
    bool continuous_mode = false;
    bool verbose = false;

    if (!parse_flags(argc, argv, &continuous_mode, &verbose)) return 1;

    if (!isatty(STDIN_FILENO)) {
        std::fwprintf(stderr, L"Stdin must be attached to a tty.\n");
        return 1;
    }

    setup_and_process_keys(continuous_mode, verbose);
    exit_without_destructors(0);
    return EXIT_FAILURE;  // above should exit
}
