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

#define CHUNK (1024 * 1024)  // 1 MB buffer
#define MAX_PDF_SIZE (100LL * 1024 * 1024)

typedef enum {
	SCANNING,
	IN_PDF
} State;

static int valid_pdf_header(const unsigned char *p, size_t len) {
	if (len < 10) return 0;
	if (p[0] != '%' || p[1] != 'P' || p[2] != 'D' || p[3] != 'F' || p[4] != '-')
		return 0;
	if (p[5] < '0' || p[5] > '9') return 0;
	if (p[6] != '.') return 0;
	if (p[7] < '0' || p[7] > '9') return 0;
	size_t i = 8;
	if (p[i] >= '0' && p[i] <= '9') i++;
	return (p[i] == '\n' || (p[i] == '\r' && p[i + 1] == '\n'));
}

static void make_outfile(char *path, size_t sz, const char *dir, int idx) {
	snprintf(path, sz, "%s/pdf_%04d.pdf", dir, idx);
}

int main(int argc, char **argv) {
	if (argc != 3) {
		fprintf(stderr, "Usage: %s <image_file> <output_dir>\n", argv[0]);
		return 1;
	}
	char *infile = argv[1];
		if (infile[0] == '-' && infile[1] == '\0') {
				infile = "/dev/stdin";
		}
	const char *outdir = argv[2];
	mkdir(outdir, 0755);
	FILE *in = fopen(infile, "rb");
	if (!in) {
		perror("open input");
		return 1;
	}
	unsigned char *buf = malloc(CHUNK);
	if (!buf) return 1;
	State state = SCANNING;
	FILE *out = NULL;
	unsigned char eof_win[5] = {0};  // rolling "%%EOF"
	size_t pdf_size = 0;
	int pdf_count = 0;
	// overlap buffer to catch split headers across chunks
	unsigned char overlap[16];
	size_t overlap_len = 0;
	while (1) {
		size_t r = fread(buf, 1, CHUNK, in);
		if (r == 0) break;
		size_t i = 0;
		// prepend overlap
		unsigned char *data = buf;
		size_t len = r;
		unsigned char temp[CHUNK + 16];
		if (overlap_len > 0) {
			memcpy(temp, overlap, overlap_len);
			memcpy(temp + overlap_len, buf, r);
			data = temp;
			len = r + overlap_len;
			i = 0;
		}
		overlap_len = 0;
		for (; i < len; i++) {
			if (state == SCANNING) {
				// only attempt match on '%'
				if (data[i] == '%' && i + 10 < len) {
					if (valid_pdf_header(&data[i], len - i)) {
						char path[512];
						make_outfile(path, sizeof(path), outdir, pdf_count++);
						out = fopen(path, "wb");
						if (!out) {
							state = SCANNING;
							continue;
						}
						state = IN_PDF;
						pdf_size = 0;

						memset(eof_win, 0, sizeof(eof_win));
					}
				}
			}
			else if (state == IN_PDF) {
				if (pdf_size >= MAX_PDF_SIZE) {
					fclose(out);
					out = NULL;
					state = SCANNING;
					continue;
				}
				fputc(data[i], out);
				pdf_size++;
				// rolling EOF detector
				eof_win[0] = eof_win[1];
				eof_win[1] = eof_win[2];
				eof_win[2] = eof_win[3];
				eof_win[3] = eof_win[4];
				eof_win[4] = data[i];
				if (eof_win[0] == '%' &&
					eof_win[1] == '%' &&
					eof_win[2] == 'E' &&
					eof_win[3] == 'O' &&
					eof_win[4] == 'F') {
					fclose(out);
					out = NULL;
					state = SCANNING;
				}
			}
		}
		// save last 16 bytes for boundary-safe matching
		overlap_len = (len < 16) ? len : 16;
		memcpy(overlap, data + (len - overlap_len), overlap_len);
	}
	if (out) fclose(out);
	free(buf);
	fclose(in);

	return 0;
}