#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>

#define CHUNK 4096

int match_at(const unsigned char *buf, size_t len, const char *pat) {
    size_t p = strlen(pat);
    if (len < p) return 0;
    return memcmp(buf, pat, p) == 0;
}

size_t find_in_buffer(const unsigned char *buf, size_t len, const char *pat) {
    size_t p = strlen(pat);
    for (size_t i = 0; i + p <= len; i++) {
        if (memcmp(buf + i, pat, p) == 0)
            return i;
    }
    return (size_t)-1;
}

void write_pdf(const unsigned char *data, size_t len, int idx, const char *outdir) {
    char path[512];
    snprintf(path, sizeof(path), "%s/pdf_%04d.pdf", outdir, idx);

    FILE *f = fopen(path, "wb");
    if (!f) return;

    fwrite(data, 1, len, f);
    fclose(f);
}

int main(int argc, char **argv) {
    if (argc != 3) {
        fprintf(stderr, "Usage: %s <image_file> <output_dir>\n", argv[0]);
        return 1;
    }

    const char *infile = argv[1];
    const char *outdir = argv[2];

    mkdir(outdir, 0755);

    FILE *f = fopen(infile, "rb");
    if (!f) {
        perror("open input");
        return 1;
    }

    unsigned char *buf = malloc(CHUNK * 2);
    size_t buf_len = 0;
    int pdf_count = 0;

    unsigned char *file_data = NULL;
    size_t file_size = 0;
    int collecting = 0;

    while (!feof(f)) {
        size_t r = fread(buf + buf_len, 1, CHUNK, f);
        buf_len += r;

        size_t i = 0;

        while (i < buf_len) {

            if (!collecting) {
                if (i + 5 < buf_len && memcmp(buf + i, "%PDF-", 5) == 0) {
                    collecting = 1;
                    file_data = malloc(1024);
                    file_size = 0;
                }
            }

            if (collecting) {
                if (file_size % 1024 == 0) {
                    file_data = realloc(file_data, file_size + 1024);
                }

                file_data[file_size++] = buf[i];

                if (file_size > 6) {
                    if (memmem(file_data, file_size, "%%EOF", 5)) {
                        write_pdf(file_data, file_size, pdf_count++, outdir);
                        free(file_data);
                        file_data = NULL;
                        file_size = 0;
                        collecting = 0;
                    }
                }
            }

            i++;
        }

        buf_len = 0;
    }

    free(buf);
    fclose(f);

    return 0;
}