/*
 *	PNG Extractor
 */

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

unsigned long swap_endian(unsigned long x)
{
#ifdef BIG_ENDIAN
	return x;
#else
	return x << 24 | (x << 8 & 0xFF0000) | (x >> 8 & 0xFF00) | x >> 24;
#endif
}

size_t min(size_t a, size_t b)
{
	return a < b ? a : b;
}

void fcopy(FILE *dest, FILE *src, size_t len)
{
	int buf[1024];
	size_t n;
	for ( ; (n = fread(buf, 1, min(len, sizeof buf), src)) != 0; len -= n)
		fwrite(buf, 1, n, dest);
}

void png_extract(const char *filename)
{
	int out_i;
	FILE *fin;
	long type;
	if ((fin = fopen(filename, "rb")) == NULL)
		return;
	for (out_i = 0; fread(&type, 1, 4, fin) == 4; out_i++) {
		char outname[FILENAME_MAX];
		FILE *fout;
		int x;
		int idat;
		while (type != *(const long *)"IHDR") {
			if ((x = fgetc(fin)) == EOF)
				goto end;
			memmove(&type, (char *)&type + 1, 3);
			((char *)&type)[3] = (char)x;
		}
		sprintf(outname, "%s.%04d.png", filename, out_i);
		printf("\rExtracting: %s -> %d", filename, out_i);
		if ((fout = fopen(outname, "wb")) == NULL) {
			printf("\n  Failed to create file !!\n");
			abort();
		}
		fwrite("\x89PNG\r\n\x1A\n", 1, 8, fout);
		fwrite("\0\0\0\x0D" "IHDR", 1, 8, fout);
		fcopy(fout, fin, 0x0D + 4);
		for (idat = 0; ; ) {
			unsigned long size;
			if (fread(&size, 1, 4, fin) != 4 ||
				fread(&type, 1, 4, fin) != 4)
				goto end;
			if (!idat) {
				if (type == *(const long *)"IDAT")
					idat = 1;
				else {
					fwrite(&size, 1, 4, fout);
					fwrite(&type, 1, 4, fout);
					fcopy(fout, fin, swap_endian(size) + 4);
					continue;
				}
			} else {
				if (type != *(const long *)"IDAT")
					break;
			}
			fwrite(&size, 1, 4, fout);
			fwrite(&type, 1, 4, fout);
			fcopy(fout, fin, swap_endian(size) + 4);
		}
		fwrite("\0\0\0\0" "IEND"
			"\xAE\x42\x60\x82", 1, 12, fout);
		fclose(fout);
	}
end:
	fclose(fin);
	printf("\n");
}

int main(int argc, char *argv[])
{
	int i;
	for (i = 1; i < argc; i++)
		png_extract(argv[i]);
	return 0;
}