#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <getopt.h>

// Таблица CRC32 для полинома 0xEDB88320 (IEEE 802.3)
static const uint32_t crc32_table[256] = {
        0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA, 0x076DC419, 0x706AF48F,
        0xE963A535, 0x9E6495A3, 0x0EDB8832, 0x79DCB8A4, 0xE0D5E91E, 0x97D2D988,
        0x09B64C2B, 0x7EB17CBD, 0xE7B82D07, 0x90BF1D91, 0x1DB71064, 0x6AB020F2,
        0xF3B97148, 0x84BE41DE, 0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7,
        0x136C9856, 0x646BA8C0, 0xFD62F97A, 0x8A65C9EC, 0x14015C4F, 0x63066CD9,
        0xFA0F3D63, 0x8D080DF5, 0x3B6E20C8, 0x4C69105E, 0xD56041E4, 0xA2677172,
        0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B, 0x35B5A8FA, 0x42B2986C,
        0xDBBBC9D6, 0xACBCF940, 0x32D86CE3, 0x45DF5C75, 0xDCD60DCF, 0xABD13D59,
        0x26D930AC, 0x51DE003A, 0xC8D75180, 0xBFD06116, 0x21B4F4B5, 0x56B3C423,
        0xCFBA9599, 0xB8BDA50F, 0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924,
        0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D, 0x76DC4190, 0x01DB7106,
        0x98D220BC, 0xEFD5102A, 0x71B18589, 0x06B6B51F, 0x9FBFE4A5, 0xE8B8D433,
        0x7807C9A2, 0x0F00F934, 0x9609A88E, 0xE10E9818, 0x7F6A0DBB, 0x086D3D2D,
        0x91646C97, 0xE6635C01, 0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E,
        0x6C0695ED, 0x1B01A57B, 0x8208F4C1, 0xF50FC457, 0x65B0D9C6, 0x12B7E950,
        0x8BBEB8EA, 0xFCB9887C, 0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3, 0xFBD44C65,
        0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2, 0x4ADFA541, 0x3DD895D7,
        0xA4D1C46D, 0xD3D6F4FB, 0x4369E96A, 0x346ED9FC, 0xAD678846, 0xDA60B8D0,
        0x44042D73, 0x33031DE5, 0xAA0A4C5F, 0xDD0D7CC9, 0x5005713C, 0x270241AA,
        0xBE0B1010, 0xC90C2086, 0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F,
        0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4, 0x59B33D17, 0x2EB40D81,
        0xB7BD5C3B, 0xC0BA6CAD, 0xEDB88320, 0x9ABFB3B6, 0x03B6E20C, 0x74B1D29A,
        0xEAD54739, 0x9DD277AF, 0x04DB2615, 0x73DC1683, 0xE3630B12, 0x94643B84,
        0x0D6D6A3E, 0x7A6A5AA8, 0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1,
        0xF00F9344, 0x8708A3D2, 0x1E01F268, 0x6906C2FE, 0xF762575D, 0x806567CB,
        0x196C3671, 0x6E6B06E7, 0xFED41B76, 0x89D32BE0, 0x10DA7A5A, 0x67DD4ACC,
        0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5, 0xD6D6A3E8, 0xA1D1937E,
        0x38D8C2C4, 0x4FDFF252, 0xD1BB67F1, 0xA6BC5767, 0x3FB506DD, 0x48B2364B,
        0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6, 0x41047A60, 0xDF60EFC3, 0xA867DF55,
        0x316E8EEF, 0x4669BE79, 0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236,
        0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F, 0xC5BA3BBE, 0xB2BD0B28,
        0x2BB45A92, 0x5CB36A04, 0xC2D7FFA7, 0xB5D0CF31, 0x2CD99E8B, 0x5BDEAE1D,
        0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A, 0x9C0906A9, 0xEB0E363F,
        0x72076785, 0x05005713, 0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38,
        0x92D28E9B, 0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21, 0x86D3D2D4, 0xF1D4E242,
        0x68DDB3F8, 0x1FDA836E, 0x81BE16CD, 0xF6B9265B, 0x6FB077E1, 0x18B74777,
        0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C, 0x8F659EFF, 0xF862AE69,
        0x616BFFD3, 0x166CCF45, 0xA00AE278, 0xD70DD2EE, 0x4E048354, 0x3903B3C2,
        0xA7672661, 0xD06016F7, 0x4969474D, 0x3E6E77DB, 0xAED16A4A, 0xD9D65ADC,
        0x40DF0B66, 0x37D83BF0, 0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9,
        0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6, 0xBAD03605, 0xCDD70693,
        0x54DE5729, 0x23D967BF, 0xB3667A2E, 0xC4614AB8, 0x5D681B02, 0x2A6F2B94,
        0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D
};

// Структура для параметров командной строки
typedef struct {
    char *filename;
    int write_crc;      // Флаг: записывать CRC в файл
    int verify_crc;     // Флаг: проверять CRC
    int show_only;      // Флаг: только показать CRC без записи
    int verbose;        // Флаг: подробный вывод
} ProgramOptions;

// Прототипы функций
void print_usage(const char *program_name);
int parse_arguments(int argc, char *argv[], ProgramOptions *options);
uint32_t calculate_crc32(const uint8_t *data, uint32_t len);
uint32_t calculate_file_crc32_without_last4(const char *filename, int verbose);
uint32_t calculate_file_crc32_full(const char *filename, int verbose);
int write_crc32_to_file(const char *filename, uint32_t crc_value, int verbose);
int verify_crc32(const char *filename, int verbose);

/**
 * @brief Вычисляет CRC32 (IEEE 802.3) для блока данных в памяти
 */
uint32_t calculate_crc32(const uint8_t *data, uint32_t len) {
    uint32_t crc = 0xFFFFFFFF;

    for (uint32_t i = 0; i < len; i++) {
        crc = (crc >> 8) ^ crc32_table[(crc ^ data[i]) & 0xFF];
    }

    return crc ^ 0xFFFFFFFF;
}

/**
 * @brief Вычисляет CRC32 для файла, исключая последние 4 байта
 * Используется для записи и проверки CRC
 */
uint32_t calculate_file_crc32_without_last4(const char *filename, int verbose) {
    FILE *file = NULL;
    uint8_t *buffer = NULL;
    long file_size = 0;
    uint32_t crc = 0;

    file = fopen(filename, "rb");
    if (file == NULL) {
        perror("Failed to open file");
        return 0;
    }

    // Получаем размер файла
    if (fseek(file, 0, SEEK_END) != 0) {
        perror("Failed to seek to end");
        fclose(file);
        return 0;
    }

    file_size = ftell(file);

    if (file_size < 4) {
        fprintf(stderr, "File size (%ld bytes) is less than 4 bytes\n", file_size);
        fclose(file);
        return 0;
    }

    long data_size = file_size - 4; // Размер данных без последних 4 байт

    if (verbose) {
        printf("File size: %ld bytes\n", file_size);
        printf("Data size for CRC calculation (without last 4 bytes): %ld bytes\n", data_size);
    }

    // Выделяем память под данные
    buffer = (uint8_t*)malloc(data_size);
    if (buffer == NULL && data_size > 0) {
        perror("Failed to allocate memory");
        fclose(file);
        return 0;
    }

    // Возвращаемся в начало
    if (fseek(file, 0, SEEK_SET) != 0) {
        perror("Failed to seek to beginning");
        free(buffer);
        fclose(file);
        return 0;
    }

    // Читаем данные (все, кроме последних 4 байт)
    if (data_size > 0) {
        size_t bytes_read = fread(buffer, 1, data_size, file);
        if (bytes_read != data_size) {
            fprintf(stderr, "Failed to read file data. Read %zu bytes, expected %ld bytes\n",
                    bytes_read, data_size);
            free(buffer);
            fclose(file);
            return 0;
        }
    }

    // Вычисляем CRC
    if (data_size > 0) {
        crc = calculate_crc32(buffer, data_size);
    } else {
        crc = calculate_crc32(NULL, 0);
    }

    free(buffer);
    fclose(file);

    return crc;
}

/**
 * @brief Вычисляет CRC32 для всего файла (включая последние 4 байта)
 * Используется только для показа CRC
 */
uint32_t calculate_file_crc32_full(const char *filename, int verbose) {
    FILE *file = NULL;
    uint8_t *buffer = NULL;
    long file_size = 0;
    uint32_t crc = 0;

    file = fopen(filename, "rb");
    if (file == NULL) {
        perror("Failed to open file");
        return 0;
    }

    if (fseek(file, 0, SEEK_END) != 0) {
        perror("Failed to seek to end");
        fclose(file);
        return 0;
    }

    file_size = ftell(file);
    if (verbose) {
        printf("File size: %ld bytes\n", file_size);
    }

    if (file_size <= 0) {
        fprintf(stderr, "File is empty\n");
        fclose(file);
        return 0;
    }

    buffer = (uint8_t*)malloc(file_size);
    if (buffer == NULL) {
        perror("Failed to allocate memory");
        fclose(file);
        return 0;
    }

    if (fseek(file, 0, SEEK_SET) != 0) {
        perror("Failed to seek to beginning");
        free(buffer);
        fclose(file);
        return 0;
    }

    size_t bytes_read = fread(buffer, 1, file_size, file);
    if (bytes_read != file_size) {
        fprintf(stderr, "Failed to read entire file\n");
        free(buffer);
        fclose(file);
        return 0;
    }

    crc = calculate_crc32(buffer, file_size);

    free(buffer);
    fclose(file);

    return crc;
}

/**
 * @brief Записывает CRC32 в последние 4 байта файла
 */
int write_crc32_to_file(const char *filename, uint32_t crc_value, int verbose) {
    FILE *file = NULL;
    long file_size;

    file = fopen(filename, "rb+");
    if (file == NULL) {
        perror("Failed to open file for writing");
        return -1;
    }

    if (fseek(file, 0, SEEK_END) != 0) {
        perror("Failed to seek to end");
        fclose(file);
        return -1;
    }

    file_size = ftell(file);
    if (file_size < 4) {
        fprintf(stderr, "File size (%ld bytes) is less than 4 bytes\n", file_size);
        fclose(file);
        return -1;
    }

    // Перемещаемся на позицию последних 4 байт
    if (fseek(file, file_size - 4, SEEK_SET) != 0) {
        perror("Failed to seek to CRC position");
        fclose(file);
        return -1;
    }

    // Записываем CRC в little-endian порядке
    uint8_t crc_bytes[4];
    crc_bytes[0] = (crc_value >> 0) & 0xFF;
    crc_bytes[1] = (crc_value >> 8) & 0xFF;
    crc_bytes[2] = (crc_value >> 16) & 0xFF;
    crc_bytes[3] = (crc_value >> 24) & 0xFF;

    size_t bytes_written = fwrite(crc_bytes, 1, 4, file);
    if (bytes_written != 4) {
        fprintf(stderr, "Failed to write CRC to file\n");
        fclose(file);
        return -1;
    }

    fclose(file);

    if (verbose) {
        printf("CRC32 value written: 0x%08X (%u)\n", crc_value, crc_value);
        printf("Written to bytes: %ld-%ld\n", file_size - 4, file_size - 1);
        printf("Byte order: little-endian (LSB first)\n");
    }

    return 0;
}

/**
 * @brief Проверяет CRC32, сравнивая вычисленное значение с сохраненным
 */
int verify_crc32(const char *filename, int verbose) {
    FILE *file = NULL;
    long file_size;
    uint32_t calculated_crc = 0;
    uint32_t stored_crc = 0;

    file = fopen(filename, "rb");
    if (file == NULL) {
        perror("Failed to open file");
        return -1;
    }

    if (fseek(file, 0, SEEK_END) != 0) {
        perror("Failed to seek to end");
        fclose(file);
        return -1;
    }

    file_size = ftell(file);
    if (file_size < 4) {
        fprintf(stderr, "File size (%ld bytes) is less than 4 bytes\n", file_size);
        fclose(file);
        return -1;
    }

    if (verbose) {
        printf("File size: %ld bytes\n", file_size);
    }

    // Читаем сохраненный CRC из последних 4 байт
    if (fseek(file, file_size - 4, SEEK_SET) != 0) {
        perror("Failed to seek to stored CRC");
        fclose(file);
        return -1;
    }

    uint8_t crc_bytes[4];
    size_t bytes_read = fread(crc_bytes, 1, 4, file);
    if (bytes_read != 4) {
        fprintf(stderr, "Failed to read stored CRC\n");
        fclose(file);
        return -1;
    }

    stored_crc = (uint32_t)crc_bytes[0] << 0 |
                 (uint32_t)crc_bytes[1] << 8 |
                 (uint32_t)crc_bytes[2] << 16 |
                 (uint32_t)crc_bytes[3] << 24;

    fclose(file);

    // Вычисляем CRC для данных (без последних 4 байт)
    calculated_crc = calculate_file_crc32_without_last4(filename, verbose);
    if (calculated_crc == 0) {
        fprintf(stderr, "Failed to calculate CRC\n");
        return -1;
    }

    // Всегда выводим значения CRC при проверке
    printf("\n╔════════════════════════════════════════╗\n");
    printf("║         CRC32 Verification             ║\n");
    printf("╠════════════════════════════════════════╣\n");
    printf("║ Stored CRC     : 0x%08X (%10u) ║\n", stored_crc, stored_crc);
    printf("║ Calculated CRC : 0x%08X (%10u) ║\n", calculated_crc, calculated_crc);
    printf("╚════════════════════════════════════════╝\n");

    if (calculated_crc == stored_crc) {
        printf("\n✓ VERIFIED: CRC matches! File integrity check passed.\n");
        return 0;
    } else {
        printf("\n✗ MISMATCH: File is corrupted or CRC was not written correctly!\n");
        printf("  Difference: 0x%08X\n", calculated_crc ^ stored_crc);
        return 1;
    }
}

/**
 * @brief Выводит справку
 */
void print_usage(const char *program_name) {
    printf("\nCRC32 Tool for BIN files\n");
    printf("========================\n\n");
    printf("Usage: %s [OPTIONS] <filename>\n\n", program_name);
    printf("Options:\n");
    printf("  -w, --write          Calculate CRC32 from all except last 4 bytes\n");
    printf("                       and write it to last 4 bytes\n");
    printf("  -c, --check          Verify CRC32 by comparing with stored value\n");
    printf("  -s, --show-only      Calculate and display CRC32 of entire file\n");
    printf("  -v, --verbose        Show detailed information\n");
    printf("  -h, --help           Show this help\n");
    printf("\nExamples:\n");
    printf("  %s -s firmware.bin        # Show CRC32 of entire file\n", program_name);
    printf("  %s -w firmware.bin        # Write CRC32 to last 4 bytes\n", program_name);
    printf("  %s -c firmware.bin        # Verify CRC32\n", program_name);
    printf("  %s -v -w firmware.bin     # Write with verbose output\n", program_name);
    printf("\nNote:\n");
    printf("  For -w and -c operations, CRC is calculated from the first\n");
    printf("  (file_size - 4) bytes, ignoring the last 4 bytes.\n");
    printf("\n");
}

/**
 * @brief Разбирает аргументы командной строки
 */
int parse_arguments(int argc, char *argv[], ProgramOptions *options) {
    int option_index = 0;
    int c;

    static struct option long_options[] = {
            {"write",      no_argument, 0, 'w'},
            {"check",      no_argument, 0, 'c'},
            {"show-only",  no_argument, 0, 's'},
            {"verbose",    no_argument, 0, 'v'},
            {"help",       no_argument, 0, 'h'},
            {0, 0, 0, 0}
    };

    memset(options, 0, sizeof(ProgramOptions));

    while ((c = getopt_long(argc, argv, "wcsvh", long_options, &option_index)) != -1) {
        switch (c) {
            case 'w':
                options->write_crc = 1;
                break;
            case 'c':
                options->verify_crc = 1;
                break;
            case 's':
                options->show_only = 1;
                break;
            case 'v':
                options->verbose = 1;
                break;
            case 'h':
                print_usage(argv[0]);
                return -1;
            case '?':
                return -1;
        }
    }

    if (optind >= argc) {
        fprintf(stderr, "Error: No filename specified.\n");
        print_usage(argv[0]);
        return -1;
    }

    options->filename = argv[optind];

    if (!options->write_crc && !options->verify_crc && !options->show_only) {
        options->show_only = 1;
    }

    int mode_count = options->write_crc + options->verify_crc + options->show_only;
    if (mode_count > 1) {
        fprintf(stderr, "Error: Cannot use multiple modes\n");
        return -1;
    }

    return 0;
}

/**
 * @brief Главная функция
 */
int main(int argc, char *argv[]) {
    ProgramOptions options;
    uint32_t crc_value;
    int result = 0;

    if (parse_arguments(argc, argv, &options) != 0) {
        return 1;
    }

    if (options.show_only) {
        // Показать CRC всего файла
        printf("\n--- CRC32 of %s ---\n", options.filename);
        crc_value = calculate_file_crc32_full(options.filename, options.verbose);
        if (crc_value == 0) {
            fprintf(stderr, "Failed to calculate CRC32\n");
            return 1;
        }
        printf("\nCRC32 (full file): 0x%08X (%u)\n", crc_value, crc_value);

    }
    else if (options.write_crc) {
        // Записать CRC
        printf("\n--- Writing CRC32 to %s ---\n", options.filename);

        if (options.verbose) {
            printf("\nStep 1: Calculating CRC32 from first (file_size - 4) bytes...\n");
        }

        crc_value = calculate_file_crc32_without_last4(options.filename, options.verbose);
        if (crc_value == 0) {
            fprintf(stderr, "Failed to calculate CRC32\n");
            return 1;
        }

        // Всегда выводим вычисленное CRC при записи
        printf("\n╔════════════════════════════════════════╗\n");
        printf("║         CRC32 Calculation              ║\n");
        printf("╠════════════════════════════════════════╣\n");
        printf("║ Calculated CRC : 0x%08X (%10u) ║\n", crc_value, crc_value);
        printf("╚════════════════════════════════════════╝\n");

        if (options.verbose) {
            printf("\nStep 2: Writing to last 4 bytes...\n");
        }

        result = write_crc32_to_file(options.filename, crc_value, options.verbose);
        if (result != 0) {
            fprintf(stderr, "Failed to write CRC32\n");
            return 1;
        }

        printf("\n✓ CRC32 successfully written to file\n");

        // Опционально: проверим сразу после записи
        if (options.verbose) {
            printf("\n--- Verifying after write ---\n");
            verify_crc32(options.filename, 0);
        }

    }
    else if (options.verify_crc) {
        // Проверить CRC
        printf("\n--- Verifying CRC32 for %s ---\n", options.filename);
        result = verify_crc32(options.filename, options.verbose);
    }

    return result;
}