#include <fcntl.h> /* open */
#include <stdio.h> /* printf, fprintf */
#include <stdlib.h> /* malloc */
#include <sys/stat.h> /* fstat */
#include <unistd.h> /* read */

#include <cairo.h>
#include <svgtiny.h>

/* Convenient typedefs for libsvgtiny */
typedef struct svgtiny_diagram diagram_t;


/**
 * Render an svgtiny path using cairo.
 */
void render_path(cairo_t *cr, struct svgtiny_shape *path) {
  unsigned int j;

  cairo_new_path(cr);
  for (j = 0; j != path->path_length; ) {
    switch ((int) path->path[j]) {
    case svgtiny_PATH_MOVE:
      cairo_move_to(cr,
		    path->path[j + 1],
		    path->path[j + 2]);
      j += 3;
      break;
    case svgtiny_PATH_CLOSE:
      cairo_close_path(cr);
      j += 1;
      break;
    case svgtiny_PATH_LINE:
      cairo_line_to(cr,
		    path->path[j + 1],
		    path->path[j + 2]);
      j += 3;
      break;
    case svgtiny_PATH_BEZIER:
      cairo_curve_to(cr,
		     path->path[j + 1],
		     path->path[j + 2],
		     path->path[j + 3],
		     path->path[j + 4],
		     path->path[j + 5],
		     path->path[j + 6]);
      j += 7;
      break;
    default:
      printf("error ");
      j += 1;
    }
  }
  if (path->fill != svgtiny_TRANSPARENT) {
    cairo_set_source_rgb(cr,
			 svgtiny_RED(path->fill) / 255.0,
			 svgtiny_GREEN(path->fill) / 255.0,
			 svgtiny_BLUE(path->fill) / 255.0);
    cairo_fill_preserve(cr);
  }
  if (path->stroke != svgtiny_TRANSPARENT) {
    cairo_set_source_rgb(cr,
			 svgtiny_RED(path->stroke) / 255.0,
			 svgtiny_GREEN(path->stroke) / 255.0,
			 svgtiny_BLUE(path->stroke) / 255.0);
    cairo_set_line_width(cr, path->stroke_width);
    cairo_stroke_preserve(cr);
  }
}

/*
 * @brief Parse an SVG file into a diagram_t structure.
 *
 * @param path
 *   The path to the SVG file.
 *
 * @return If successful, a pointer to a @c diagram_t structure is
 *   returned; if not, @c NULL is returned. You are expected to @c
 *   svgtiny_free the result if it is valid.
 */
diagram_t* svgtiny_diagram_from_path(char* path, int width, int height) {
  diagram_t *diagram;

  int fd;
  size_t bytecount;
  char *buffer;
  size_t bytesread;
  struct stat sb;
  svgtiny_code code;

  /* load file into memory buffer */
  fd = open(path, O_RDONLY);
  if (fd == -1) {
    perror(path);
    return NULL;
  }

  if (fstat(fd, &sb)) {
    perror(path);
    return NULL;
  }
  bytecount = sb.st_size;

  buffer = malloc(bytecount);
  if (!buffer) {
    fprintf(stderr, "Unable to allocate %zd bytes\n", bytecount);
    return NULL;
  }

  bytesread = read(fd, buffer, bytecount);
  if (bytesread != bytecount) {
    perror(path);
    return NULL;
  }
  close(fd);


  /* create svgtiny object */
  diagram = svgtiny_create();
  if (!diagram) {
    fprintf(stderr, "svgtiny_create() failed\n");
    return NULL;
  }

  code = svgtiny_parse(diagram, buffer, bytecount, path, width, height);
  free(buffer);

  if (code != svgtiny_OK) {
    fprintf(stderr, "svgtiny_parse failed: ");
    switch (code) {
    case svgtiny_OUT_OF_MEMORY:
      fprintf(stderr, "svgtiny_OUT_OF_MEMORY");
      break;
    case svgtiny_LIBDOM_ERROR:
      fprintf(stderr, "svgtiny_LIBDOM_ERROR");
      break;
    case svgtiny_NOT_SVG:
      fprintf(stderr, "svgtiny_NOT_SVG");
      break;
    case svgtiny_SVG_ERROR:
      fprintf(stderr, "svgtiny_SVG_ERROR: line %i: %s",
	      diagram->error_line,
	      diagram->error_message);
      break;
    default:
      fprintf(stderr, "unknown svgtiny_code %i", code);
      break;
    }
    fprintf(stderr, "\n");
    return NULL;
  }

  return diagram;
}


/*
 * @brief Create a cairo context from a libsvgtiny diagram.
 *
 * @param diagram
 *   A pointer to a valid libsvgtiny diagram.
 *
 * @return If successful, a pointer to a @c cairo_t context structure
 *   is returned; if not, @c NULL is returned. You are expected to @c
 *   cairo_destroy the result if it is valid.
 */
cairo_t* cairo_context_from_diagram(diagram_t* diagram) {
  cairo_t* cr;
  cairo_surface_t* surface;
  cairo_status_t crs;
  unsigned int i;

  surface = cairo_image_surface_create(CAIRO_FORMAT_RGB24,
				       diagram->width,
				       diagram->height);

  crs = cairo_surface_status(surface);
  if (crs != CAIRO_STATUS_SUCCESS) {
    fprintf(stderr,
	    "cairo_image_surface_create failed: %s\n",
	    cairo_status_to_string(crs));
    cairo_surface_destroy(surface);
    return NULL;
  }

  cr = cairo_create(surface);
  crs = cairo_status(cr);

  /* Immediately destroy the surface which is now accessible as
     cr->target */
  cairo_surface_destroy(surface);

  if (crs != CAIRO_STATUS_SUCCESS) {
    fprintf(stderr,
	    "cairo_create failed: %s\n",
	    cairo_status_to_string(crs));
    cairo_destroy(cr);
    return NULL;
  }

  cairo_set_source_rgb(cr, 1, 1, 1);
  cairo_paint(cr);

  /* Loop through the shapes in the diagram... */
  for (i = 0; i != diagram->shape_count; i++) {

    /* If this shape is a path, just render it. */
    if (diagram->shape[i].path) {
      render_path(cr, &diagram->shape[i]);
    }

    /* If this shape is text... */
    if (diagram->shape[i].text) {
      /* Figure out what color to use from the R/G/B components of the
	 shape's stroke. */
      cairo_set_source_rgb(cr,
			   svgtiny_RED(diagram->shape[i].stroke) / 255.0,
			   svgtiny_GREEN(diagram->shape[i].stroke) / 255.0,
			   svgtiny_BLUE(diagram->shape[i].stroke) / 255.0);
      /* Then move to the actual position of the text within the
	 shape... */
      cairo_move_to(cr,
		    diagram->shape[i].text_x,
		    diagram->shape[i].text_y);

      /* and draw it. */
      cairo_show_text(cr, diagram->shape[i].text);
    }
  }


  /* Check the status again just for good measure? */
  crs = cairo_status(cr);
  if (crs != CAIRO_STATUS_SUCCESS) {
    fprintf(stderr,
	    "cairo error: %s\n",
	    cairo_status_to_string(crs));
    cairo_destroy(cr);
    return NULL;
  }

  return cr;
}


int main(int argc, char** argv) {
  int exit_code = 0;

  char* svgpath;
  char* pngpath;
  int pngwidth = 1024, pngheight = 1024;

  diagram_t* diagram;
  cairo_surface_t *surface;
  cairo_t *cr = 0;
  cairo_status_t crs;

  /* Parse arguments, and maybe print usage */
  if (argc < 3) {
    printf("Usage: %s INPUT OUTPUT\n", argv[0]);
    printf("Convert an SVG file (INPUT) to a PNG file (OUTPUT)\n");
    return 2;
  }

  svgpath = argv[1];
  pngpath = argv[2];

  diagram = svgtiny_diagram_from_path(svgpath, pngwidth, pngheight);
  if (!diagram) {
    return 1;
  }

  cr = cairo_context_from_diagram(diagram);
  if (!cr) {
    svgtiny_free(diagram);
    return 1;
  }

  crs = cairo_surface_write_to_png(cairo_get_target(cr), pngpath);
  if (crs != CAIRO_STATUS_SUCCESS) {
    fprintf(stderr,
	    "cairo_surface_write_to_png failed: %s\n",
	    cairo_status_to_string(crs));
    svgtiny_free(diagram);
    cairo_destroy(cr);
    return 1;
  }

  return 0;
}