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

#define DELTA 0x9E3779B9

void xtea_encrypt_block(uint32_t *v, const uint32_t key[4]) {
    uint32_t v0 = v[0], v1 = v[1], sum = 0;
    for (unsigned i = 0; i < 32; i++) {
        v0 += (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + key[sum & 3]);
        sum += DELTA;
        v1 += (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + key[(sum >> 11) & 3]);
    }
    v[0] = v0;
    v[1] = v1;
}

void xtea_decrypt_block(uint32_t *v, const uint32_t key[4]) {
    uint32_t v0 = v[0], v1 = v[1];
    uint32_t sum = DELTA * 32;
    for (unsigned i = 0; i < 32; i++) {
        v1 -= (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + key[(sum >> 11) & 3]);
        sum -= DELTA;
        v0 -= (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + key[sum & 3]);
    }
    v[0] = v0;
    v[1] = v1;
}

void xtea_process(int encrypt, const char *keyfile, const char *infile, const char *outfile) {
    uint32_t key[4];

    FILE *fk = fopen(keyfile, "rb");
    if (!fk || fread(key, sizeof *key, 4, fk) != 4) {
        fprintf(stderr, "Erreur lecture clé\n");
        exit(1);
    }
    fclose(fk);

    FILE *fin  = fopen(infile,  "rb");
    FILE *fout = fopen(outfile, "wb");
    if (!fin || !fout) {
        fprintf(stderr, "Erreur ouverture fichiers\n");
        exit(1);
    }

    uint8_t block[8];
    size_t  n;

    while ((n = fread(block, 1, 8, fin)) == 8) {
        xtea_encrypt_block((uint32_t*)block, key);
        if (!encrypt)
            xtea_decrypt_block((uint32_t*)block, key);
        fwrite(block, 1, 8, fout);
    }

    if (encrypt) {
        for (size_t i = n; i < 8 - 1; i++) {
            block[i] = 0;
        }
        block[8 - 1] = 8 - n;
        xtea_encrypt_block((uint32_t*)block, key);
        fwrite(block, 1, 8, fout);
    } else if (n > 0) {
        fprintf(stderr, "Erreur : fichier chiffré mal aligné\n");
        exit(1);
    }

    fclose(fin);
    fclose(fout);
}

int main(int argc, char *argv[])
{
    if (argc != 5) {
        fprintf(stderr, "Usage : %s -e|-d keyfile infile outfile\n", argv[0]);
        return 1;
    }
    int enc = (strcmp(argv[1], "-e") == 0);
    xtea_process(enc, argv[2], argv[3], argv[4]);
    return 0;
}