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

#define CHUNK 4096
#define MAX_PDF_SIZE (100LL * 1024 * 1024)  // 100 MB

int valid_pdf_header(const unsigned char *buf, size_t len) {
    if (len < 9) return 0;

    if (memcmp(buf, "%PDF-", 5) != 0)
        return 0;

    if (buf[5] < '0' || buf[5] > '9') return 0;
    if (buf[6] != '.') return 0;
    if (buf[7] < '0' || buf[7] > '9') return 0;

    size_t i = 8;

    if (buf[i] >= '0' && buf[i] <= '9') i++;

    if (buf[i] == '\r' && buf[i + 1] == '\n') return 1;
    if (buf[i] == '\n') return 1;

    return 0;
}

size_t find_eof(const unsigned char *buf, size_t len) {
    for (size_t i = 0; i + 5 <= len; i++) {
        if (memcmp(buf + i, "%%EOF", 5) == 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);

		if (strcmp(infile, "-") == 0) {
				infile = "/dev/stdin";
		}
    FILE *f = fopen(infile, "rb");
    if (!f) {
        perror("open input");
        return 1;
    }

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

    unsigned char *pdf_buf = NULL;
    size_t pdf_size = 0;

    int collecting = 0;
    int pdf_count = 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 + 10 < buf_len && valid_pdf_header(buf + i, buf_len - i)) {
                    collecting = 1;
                    pdf_buf = malloc(1024);
                    pdf_size = 0;
                }
            }

            if (collecting) {

                // HARD SIZE LIMIT CHECK
                if (pdf_size >= MAX_PDF_SIZE) {
                    free(pdf_buf);
                    pdf_buf = NULL;
                    pdf_size = 0;
                    collecting = 0;
                    continue;
                }

                if (pdf_size % 1024 == 0) {
                    pdf_buf = realloc(pdf_buf, pdf_size + 1024);
                }

                pdf_buf[pdf_size++] = buf[i];

                size_t eof_pos = find_eof(pdf_buf, pdf_size);
                if (eof_pos != (size_t)-1) {
                    size_t end = eof_pos + 5;

                    write_pdf(pdf_buf, end, pdf_count++, outdir);

                    free(pdf_buf);
                    pdf_buf = NULL;
                    pdf_size = 0;
                    collecting = 0;
                }
            }

            i++;
        }

        buf_len = 0;
    }

    free(buf);
    fclose(f);

    return 0;
}