#include <assert.h>
#include <setjmp.h>
#include <stdio.h>
#include <stdlib.h>
#include <png.h>
#include <string.h>
#include "image.h"

#define LINE_THICKNESS 3
#define BLOCK_SIZE 32
#define MARGIN 20

typedef struct {
    char* data;
    int w, h;
} img_data_t;

static void setPixel(img_data_t* img, int x, int y, char v) {
    //fprintf(stderr, "setPixel(img, %d, %d, %d)\n", x, y, v);
    assert((x < img->w) && (y < img->h));
    img->data[y * img->w + x] = v;
}

static void setBox(img_data_t* img, int x, int y, int w, int h, char v) {
    //fprintf(stderr, "setBox(img, %d, %d, %d, %d, %d)\n", x, y, w, h, v);
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            setPixel(img, x + j, y + i, v);
        }
    }
}

static img_data_t* gridToImageData(mazegrid_t const* g) {
    img_data_t* result = malloc(sizeof(img_data_t));
    result->w  = LINE_THICKNESS + g->width  * BLOCK_SIZE + 2 * MARGIN;
    result->h = LINE_THICKNESS + g->height * BLOCK_SIZE + 2 * MARGIN;
    result->data = malloc(result->w * result->h);
    //fprintf(stderr, "Box dimensions: %d x %d\n", result->w, result->h);

    // white background
    memset(result->data, 0, result->w * result->h);

    // draw basic outline
    setBox(result, MARGIN, MARGIN, result->w - 2 * MARGIN, LINE_THICKNESS, 1);
    setBox(result, MARGIN, MARGIN + LINE_THICKNESS, LINE_THICKNESS, (g->height - 1) * BLOCK_SIZE, 1);
    setBox(result, MARGIN, result->h - MARGIN - 1 - LINE_THICKNESS, result->w - 2 * MARGIN, LINE_THICKNESS, 1);
    setBox(result, result->w - MARGIN - LINE_THICKNESS, MARGIN + LINE_THICKNESS + BLOCK_SIZE, LINE_THICKNESS, (g->height - 1) * BLOCK_SIZE, 1);

    // partitions
    for (int i = 0; i < g->height; i++) {
        for (int j = 0; j < g->width; j++) {
            //fprintf(stderr, "Drawing (%d, %d) -> %d, %d\n", j, i, mazegrid_get_edge(g, j, i, EDGE_UP), mazegrid_get_edge(g, j, i, EDGE_RIGHT));
            int x = MARGIN + LINE_THICKNESS + BLOCK_SIZE * j, y = result->h - MARGIN - LINE_THICKNESS - BLOCK_SIZE * i;
            if (i < g->height - 1) {
                if (mazegrid_get_edge(g, j, i, EDGE_UP) == 0)
                    setBox(result, x - LINE_THICKNESS, y - BLOCK_SIZE, BLOCK_SIZE + LINE_THICKNESS, LINE_THICKNESS, 1);
            }
            if (j < g->width - 1) {
                if (mazegrid_get_edge(g, j, i, EDGE_RIGHT) == 0)
                    setBox(result, x + BLOCK_SIZE - LINE_THICKNESS, y - BLOCK_SIZE, LINE_THICKNESS, BLOCK_SIZE, 1);
            }
        }
    }

    return result;
}

static void writeImageData(img_data_t const* img, png_structp png_ptr) {
    for (int i = 0; i < img->h; i++) {
        png_byte row[3 * img->w];
        for (int j = 0; j < img->w; j++) {
            if (img->data[i * img->w + j]) {
                // black
                row[3 * j] = row[3 * j + 1] = row[3 * j + 2] = 0;
            } else {
                // white
                row[3 * j] = row[3 * j + 1] = row[3 * j + 2] = 255;
            }
        }
        png_write_row(png_ptr, row);
    }
}

static void freeImageData(img_data_t* img) {
    free(img->data);
    free(img);
}

int writePNG(mazegrid_t const* g, char const* filename) {
    int code = 1;
    img_data_t* img = gridToImageData(g);
    FILE *f = NULL;
    png_structp png_ptr = NULL;
    png_infop info_ptr  = NULL;
    
    if (strcmp(filename, "-") == 0) {
        f = stdout;
    } else {
        f = fopen(filename, "wb");
        if (NULL == f) {
            fprintf(stderr, "Could not open %s for writing.\n", filename);
            code = 0;
            goto exit;
        }
    }

    png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    if (png_ptr == NULL) {
        fprintf(stderr, "Could not allocate PNG write struct.\n");
        code = 0;
        goto exit;
    }

    info_ptr = png_create_info_struct(png_ptr);
    if (info_ptr == NULL) {
        fprintf(stderr, "Could not allocate PNG info struct.\n");
        code = 0;
        goto exit;
    }

    if (setjmp(png_jmpbuf(png_ptr))) {
        fprintf(stderr, "Error during PNG creation.\n");
        code = 0;
        goto exit;
    }

    png_init_io(png_ptr, f);

    // Write header (8 bit color depth)
    png_set_IHDR(png_ptr, info_ptr, img->w, img->h,
                 8, PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE,
                 PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);

    png_write_info(png_ptr, info_ptr);

    writeImageData(img, png_ptr);

    png_write_end(png_ptr, NULL);

exit:
    if (strcmp(filename, "-") != 0) {
        if (f != NULL) fclose(f);
    }
	if (info_ptr != NULL) {
        png_free_data(png_ptr, info_ptr, PNG_FREE_ALL, -1);
        png_destroy_info_struct(png_ptr, &info_ptr);
    }
    if (png_ptr != NULL) png_destroy_write_struct(&png_ptr, (png_infopp)NULL);
    if (img != NULL) freeImageData(img);
    return code;
}