#include <stdio.h>
#include <stdlib.h>
#include <libpng12/png.h>

#include <errno.h>
#include <string.h>

#include <assert.h>
#include <math.h>

#include "readpng.h"
#include "writepng.h"

//#define DEBUG_SCALER

void usage(char * s)
{
	fprintf(stderr, "Usage:\n");
	fprintf(stderr, "\t%s filename [width height]\n", s);
	exit(1);
}

unsigned char ** scale_image(int wo, int ho, int w, int h, unsigned char ** data)
{
	unsigned char ** ret;
	int i, j, k;
	double ofs_x, ofs_y;
	double xod, yod;
	double p, q;
	int xo, yo;
	
	double a, b, d;
	double c1, c2, c3, c4;
	
	int nx, ny;
	
	p = (double) w / (double) wo;
	q = (double) h / (double) ho;
	printf("p = %f, q = %f\n", p, q);

	ret = malloc(h * sizeof(char *)); /* alokacja wskaznikow dla poszczegolnych linii */
	assert(ret);
	for (i = 0; i < h ; i++) {
		ret[i] = malloc(w * 3); /* alokacja linii */
		assert(ret[i]);
	}
		/* alokacja pamieci dla obrazka docelowego */

	for (i = 0; i < h; i++) {
		for (j = 0; j < w; j++) {
			xod = (double) j / p;
			yod = (double) i / q;
				/* punkty obrazka zrodlowego */
				
			ofs_x = xod - floor(xod);
			ofs_y = yod - floor(yod);
				/* czesci ulamkowe punktow obrazka zrodlowego */

			xo = floor(xod);
			yo = floor(yod);
				/* czesci calkowiete punktow obrazka zrodlowego */
#ifdef DEBUG_SCALER
			printf("(%d, %d) -> (%f, %f) offsets: (%f, %f)\n", j, i, xod, yod, ofs_x, ofs_y);
#endif
			for (k = 0; k < 3; k++) {
#if 1
				nx = xo + 1;
				if (nx == wo)
					nx--;
				ny = yo + 1;
				if (ny == ho)
					ny--;
					/* "zabezpieczenie" przed pobieraniem probek spoza obrazka zrodlowego */

				c1 = data[yo][xo * 3 + k];
				c2 = data[yo][nx * 3 + k];
				c3 = data[ny][xo * 3 + k];
				c4 = data[ny][nx * 3 + k];
#ifdef DEBUG_SCALER
				printf("%f %f %f %f\n", c1, c2, c3, c4);
				fflush(stdout);
#endif
				a = c1 + (c2 - c1) * ofs_x;
				b = c3 + (c4 - c3) * ofs_x;
				d = a + (b - a) * ofs_y;
#endif
				ret[i][j * 3 + k] = d;
			}
		}
	}
	return ret;
}

int main(int ac, char ** av)
{
	int rv;
	FILE * fp;
	FILE * fpw;

	int w, h;
	unsigned char ** data;

	if (ac < 2) {
		usage(av[0]);
	}
	printf("Processing file: %s\n", av[1]);

	if ((fp = fopen(av[1], "rb")) == NULL) {
		fprintf(stderr, "%s: %s\n", av[1], strerror(errno));
		return 1;
	}
	rv=read_png(fp);
	printf("File read with status %d\n", rv);
	if (rv != 0) {
		fprintf(stderr, "Error while reading file!\n");
		return 1;
	}
	printf("Image info:\n");
	printf("%ldx%ld, %d bits per channel\n", info_ptr->width, info_ptr->height, info_ptr->bit_depth);
	printf("color type: %d\n", info_ptr->color_type);
	printf("%d channels, %d bits per pixel\n", info_ptr->channels, info_ptr->pixel_depth);
	
	if (ac < 4) {
		close_png();
		fclose(fp);
		if (ac > 2) {
			fprintf(stderr, "warning: extra arguments!\n");
			usage(av[0]);
		}
		return 1;
	}


	if (info_ptr->color_type != PNG_COLOR_TYPE_RGB || info_ptr->bit_depth != 8 || info_ptr->channels != 3) {
		fprintf(stderr, "Only RGB, 8 bits per channel, 3 channel images are supported!\n");
		close_png();
		fclose(fp);
		return 1;
	}
	printf("Checking image validity...\n");
	if (!(info_ptr->valid & PNG_INFO_IDAT)) {
		fprintf(stderr, "image invalid!\n");
		close_png();
		fclose(fp);
		return 1;
	}
	printf("Image is valid and loaded correctly!\n");

	w = atoi(av[2]);
	h = atoi(av[3]);
	printf("Requested resolution: %dx%d\n", w, h);
	if (w <= 0 || h <= 0) {
		fprintf(stderr, "Invalid resolution requested!\n");
		close_png();
		fclose(fp);
		return 1;
	}

	printf("Scaling...\n");
	data = scale_image(info_ptr->width, info_ptr->height, w, h, info_ptr->row_pointers);
	printf("Done\n");
	
	printf("Closing source file...\n");
	close_png();
	fclose(fp);
	printf("Done.\n");

	printf("Writing destination file...\n");
	fpw = fopen("output_scaled.png", "wb+");
	if (!fpw) {
		fprintf(stderr, "Cannot open file output_scaled.png for writing: %s\n", strerror(errno));
		return 1;
	}

	rv = write_png(fpw, w, h, data);
	printf("PNG write returned: %d\n", rv);
	if (rv) {
		printf("PNG write erred!\n");
		fclose(fpw);
		return 1;
	}
	fclose(fpw);
	printf("Success!\n");

	return 0;
}