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

// Simplified frame length calculation (MPEG1 Layer3 only)
uint32_t calc_frame_len(uint32_t header) {
    const int bitrates[] = {0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320};
    const int samplerates[] = {44100, 48000, 32000};
    
    int br_idx = (header >> 12) & 0xF;
    int sr_idx = (header >> 10) & 0x3;
    int padding = (header >> 9) & 0x1;
    
    int bitrate = bitrates[br_idx] * 1000;
    int samplerate = samplerates[sr_idx];
    
    return 144 * bitrate / samplerate + padding;
}

int main(int argc, char** argv) {
    if(argc != 2) return fprintf(stderr, "Usage: %s <input_file>\n", argv[0]), 1;

    FILE* fin = fopen(argv[1], "rb");
    if(!fin) return perror("fopen"), 1;

    FILE* fout = NULL;
    long file_count = 0;
    uint32_t pos = 0;
    uint32_t header;
    uint8_t buf[4];

    while(fread(buf, 1, 4, fin) == 4) {
        header = (buf[0] << 24) | (buf[1] << 16) | (buf[2] << 8) | buf[3];
        
        // Check for valid MP3 header: 0xFF 0xE? (sync + version)
        if(buf[0] == 0xFF && (buf[1] & 0xE0) == 0xE0) {
            uint32_t frame_len = calc_frame_len(header >> 8);
            
            if(frame_len > 0 && frame_len < (10*1024*1024)) { // Sanity check
                if(!fout) {
                    char fname[128];
                    snprintf(fname, sizeof(fname), "output_%ld.mp3", file_count++);
                    fout = fopen(fname, "wb");
                    if(!fout) { perror("fopen output"); break; }
                    printf("Extracting %s\n", fname);
                }
                
                // Save header
                fwrite(buf, 1, 4, fout);
                // Save frame data
                for(uint32_t i = 4; i < frame_len; i++) {
                    int c = fgetc(fin);
                    if(c == EOF) break;
                    fputc(c, fout);
                }
                pos = ftell(fin);
                continue;
            }
        }
        
        if(fout) {
            fclose(fout);
            fout = NULL;
        }
        
        // Rewind 3 bytes to allow overlapping frames
        fseek(fin, ++pos, SEEK_SET);
    }

    if(fout) fclose(fout);
    fclose(fin);
    return 0;
}