#include <cairo/cairo.h>
#include <pango/pangocairo.h>
#include <stdio.h>
#include <stdlib.h>

#define FONT "Monospace 10"

// struct for storing dimensions used for calculations, movement, etc.
struct dimensions {
   // Multiplication factors
   int row_count;	/* rows */
   int column_count;	/* columns */

   // All of these are in units chosen by width in "calp.c"
   // Most likely milimeters (mm)
   double paper_width; 	/* paper width */
   double paper_height;	/* paper height */
   double month_width;	/* month width */
   double month_height;	/* month height */
   double month_top_corner_x;
   double month_top_corner_y;
   double day_width;	/* day box width */
   double day_height;	/* day box height */
   double margin;	/* margin */
};




// Fill entire background with current color 
// Function name is changed for clarity
int fill_bg(cairo_t *c) {
   cairo_paint(c);
   return 0;
}



// Draw text at a certain point.
// Needn't be a string pointer, can be fixed array of chars
// Creates and destroys layout within the scope of the function
// Is that performant when looped over 365 operations?
int draw_text (cairo_t *c, double x, double y, char *text) {
   PangoLayout *layout;
   PangoFontDescription *desc;

   // Create a PangoLayout, setting font & text
   layout = pango_cairo_create_layout(c);
   desc = pango_font_description_from_string(FONT);
   pango_layout_set_font_description(layout, desc);
   pango_font_description_free(desc);

   pango_layout_set_text(layout, text, -1);
   //printf("text: %s\n", text);

   cairo_move_to (c, x, y);
   pango_cairo_show_layout (c, layout);
   g_object_unref(layout);
   return 0;
}



// Calculate dimenions for one page and stores it in the dimensions struct
int calculate_dimensions(double pw, double ph, struct dimensions *d) {
   // Percentage of page that should be margin
   double margin = 0.1 * pw;

   // Everything other than margin
   double month_width = 0.8 * pw; 

   // width of day is 1/7th of total width
   double box_width = month_width / 7.0;

   // Width = Height; Day Box is a square
   double box_height = box_width;

   // Height is based on how tall # of weeks are 
   double month_height = box_height * 6.0;

   // Set items in struct to calculated values
   d->row_count = 6;
   d->column_count = 7;
   d->paper_width = pw;
   d->paper_height = ph;
   d->margin = margin;
   d->month_width = month_width;
   d->month_top_corner_x = margin;
   d->month_top_corner_y = ph - margin - month_height;
   d->month_height = month_height;
   d->day_width = box_width;
   d->day_height = box_height;
   return 0;
}


int print_dimensions(struct dimensions *d) {
   printf("row count:    %d\n", d->row_count);
   printf("column count:   %d\n", d->column_count);
   printf("paper width:    %.2f\n", d->paper_width);
   printf("paper height:   %.2f\n", d->paper_height);
   printf("margin:         %.2f\n", d->margin);
   printf("month width:    %.2f\n", d->month_width);
   printf("month height:   %.2f\n", d->month_height);
   printf("month_top_corner_x: %f\n", d->month_top_corner_x);
   printf("month_top_corner_y: %f\n", d->month_top_corner_y);
   printf("day width:      %.2f\n", d->day_width);
   printf("day height:     %.2f\n", d->day_height);
   return 0;
}


// Draws the lines for a month
//int draw_month_grid (cairo_t *c, int month, int start_day) {
//int draw_month_grid (cairo_t *c, struct dimensions *d) {
//   cairo_move_to (c, d->month_top_corner_x, d->month_top_corner_y);
//   return 0;
//}



// Draws one month using daybox sub-surface & context, main context, and dimension struct
int draw_month (cairo_t *c, cairo_t *cd, cairo_surface_t *s, struct dimensions *d, int days_in_month, int start_day) {
   double cursor_x = d->month_top_corner_x;
   if (start_day != 0) cursor_x = cursor_x + (d->day_width * start_day);
   printf("%d\n", start_day);
   double cursor_y = d->month_top_corner_y;

   int current_day = start_day;

   int increment = 0;

   char str[20];

   for (int i = 0; i < d->row_count; i++) {
      for (int k = current_day; k < d->column_count; k++) {
         // When the increment reached the end of the month, end
         // the function.
         if (increment >= days_in_month) return 0;

         // Fill bg with color
         cairo_set_source_rgb (cd, 0.0, 0.0, 255.0);
         fill_bg(cd);

         // Change text color
         cairo_set_source_rgb (cd, 255.0, 255.0, 255.0);

         // draw_text(), and by extension pango_layout_set_text(), needs a 
         // string as input, so the current day's date is converted.
         snprintf(str, sizeof(str), "%d", increment + 1);


         // Position within cd is arbitrary: (0,0) is too close to edge
         draw_text(cd, 4.0, 4.0, str);


         // Position sub-surface on main surface
         cairo_set_source_surface (c, s, cursor_x, cursor_y);
         cairo_paint(c);

         // Move cursor one box over 
         cursor_x = cursor_x + d->day_width;
         increment++;
      } 
      current_day = 0;
   

   cursor_x = d->month_top_corner_x;
   cursor_y = cursor_y + d->day_height;
   }

   cairo_stroke(cd);
   return 0;
}

// Get the day of the week for a given day
// Mostly used for calculating when the start of a month is
// Relative to "Su Mo ... Sa" frame, not when Su and Sa are together
// Range is 0 -> 6
// https://wiki.c2.com/?PerpetualCalendarAlgorithm
int day_of_week (int d, int m, int y) {
   return((d += m < 3 ? y-- : y - 2, 23*m/9 + d + 4 + y/4- y/100 + y/400)%7);
}