/* Shennong */


#include "u8g2.h"
#include <stdio.h>

u8g2_t u8g2;

/*

The Farmer God Shen Nong Tastes All the Plants 

http://chinesereadingpractice.com/2012/08/22/the-farmer-god-shen-nong-tastes-all-the-plants/



All his life, Shen Nong had a crystal abdomen, and one could 
clearly see all of his internal organs. At that time, humans were 
often getting sick and even dying because they ate things 
indiscriminately [not knowing if they were good or bad]. Shen 
Nong determinedly tasted everything everywhere; the 
good-tasting things he put in a bag on his left side, those were 
for people to eat; the bad-tasting things he put in a bag on his 
right side, and those were used for medicine.

The first time, Shen Nong tasted a small fresh leaf. As this leaf 
fell into his stomach, it cleaned every inch of his insides so that 
every organ top and bottom was fresh and cool, as if [the leaf] 
was somehow on patrol [making the rounds], so Shen Nong 
called it “chá” [to investigate / check], and later generations of 
men called it “chá” [tea]. Shen Nong put it in the bag on the 
right. The second time, Shen Nong tasted a little light red flower 
that looked like a butterfly, which was sweet and delicious, with 
an exotic smell that filled his nostrils, so he called it “licorice”. He 
put it in the bag on the left. In this way, Shen Nong diligently 
tasted all manner of flora, and every time he was poisoned, he 
used tea to rescue himself. Before long, the bag on his left 
contained 47,000 kinds of flowers, grasses, roots and leaves, 
and the right side had 398,000 kinds.

But one day, Shen Nong tasted “heartbreak grass”, and this 
poison was too terrible, so there wasn’t enough time to eat the 
tea leaves to detoxify and he died. He sacrificed himself to save 
humanity, so people call him the “Bodhisattva of Medicine”, and 
people forever commemorate him through this story. 
*/

/* The Farmer God Shen Nong Tastes All the Plants  */
const char c_str[] = 
"Shen Nong\n\n"
"神农一生下来就是\n"
"个水晶肚子，五脏\n"
"六腑全都能看得一\n"
"清二楚。那时侯，\n"
"人们经常因为乱吃\n"
"东西而生病，甚至\n"
"丧命。神农决心尝\n"
"遍所有的东西，好\n"
"吃的放在身边左边\n"
"的袋子里，给人吃\n"
"；\n"
"不好吃的就放在身\n"
"子右边的袋子里，\n"
"作药用。\n"
"第一次，神农尝了\n"
"一片小嫩叶。这叶\n"
"片一落进肚里，就\n"
"上上下下地把里面\n"
"各器官擦洗得清清\n"
"爽爽，\n"
"象巡查似的，\n"
"神农把它叫做\n"
"“查”，\n"
"就是后人所称的\n"
"“茶”。\n"
"神农将它放进右边\n"
"袋子里。第二次，\n"
"神农尝了朵蝴蝶样\n"
"的淡红小花，甜津\n"
"津的，香味扑鼻，\n"
"这是“甘草”。他把\n"
"它放进了左边袋子\n"
"里。就这样，神农\n"
"辛苦地尝遍百草，\n"
"每次中毒，都靠茶\n"
"来解救。后来，\n"
"他左边的袋子里花\n"
"草根叶有四万七千\n"
"种，右边有三十九\n"
"万八千种。\n"
"但有一天，神农尝\n"
"到了“断肠草”，这\n"
"种毒草太厉害了，\n"
"他还来不及吃茶解\n"
"毒就死了。\n"
"他是为了拯救人们\n"
"而牺牲的，人们称\n"
"他为“药王菩萨”，\n"
"人间以这个神话故\n"
"事永远地纪念他。\n";

#define SCROLL_DELTA 4

/* return number of unkown glyphs */

/*
uint16_t check_str(const char *str)
{
  uint16_t e, cnt;
  
  u8g2.u8x8.next_cb = u8x8_utf8_next;
  u8x8_utf8_init(u8g2_GetU8x8(&u8g2));
  
  cnt = 0;
  for(;;)
  {
    e = u8g2.u8x8.next_cb(u8g2_GetU8x8(&u8g2), (uint8_t)*str);
    if ( e == 0x0ffff )
      break;
    str++;
    if ( e != 0x0fffe )
    {
      if ( u8g2_IsGlyph(&u8g2, e) != 0 )
      {
	cnt++;
      }
    }
  }
  return cnt;      
}
*/


int main(void)
{
  int k;
  static char buf[128];
   
  uint8_t total_lines;	// the total number of lines in the story
  uint8_t i;		// loop variable for the lines
  uint8_t line_cnt;	// number of lines to draw, usually equal to lines_per_draw
  uint8_t start_line;	// topmost visible line, derived from top_window_pos
  uint8_t lines_per_draw;	// how many lines to draw on the screen, derived from font and display height
  uint16_t glyph_height;	// height of the glyphs
  
  uint16_t top_window_pos;		// defines the display position in pixel within the text
  uint16_t total_height;			// total height in pixel, derived from font height and total_lines
  u8g2_uint_t top_offset;			// offset between the first visible line and the display
  
  u8g2_SetupBuffer_SDL_128x64_4(&u8g2, &u8g2_cb_r0);
  u8x8_InitDisplay(u8g2_GetU8x8(&u8g2));
  u8x8_SetPowerSave(u8g2_GetU8x8(&u8g2), 0);  
  u8g2_SetFont(&u8g2, u8g2_font_wqy12_t_chinese1);	// two unknown glyphs
 //u8g2_SetFont(&u8g2, u8g2_font_wqy12_t_chinese3);	// two unknown glyphs

  //u8g2_SetFont(&u8g2, u8g2_font_wqy12_t_gb2312a);	// ";" is missing
  //u8g2_SetFont(&u8g2, u8g2_font_wqy12_t_gb2312b);	// all glyphs available

  /* calculate the length of the text in lines */
  total_lines = u8x8_GetStringLineCnt(c_str);
  
  /* get the height of the glyphs */
  glyph_height = u8g2_GetMaxCharHeight(&u8g2);

  /* calculate the height of the text in pixel */
  total_height = (uint16_t)total_lines * (uint16_t)glyph_height;
  

  /* calculate how many lines must be drawn on the screen */
  lines_per_draw = u8g2_GetDisplayHeight(&u8g2) / glyph_height;
  lines_per_draw += 2;
  
  printf("Total lines: %d\n", (int)total_lines);
  printf("Glyph height: %d\n", (int)glyph_height);
  printf("Number of lines to draw: %d\n", (int)lines_per_draw);
  
  top_window_pos = 0;
  for(;;)
  {
    
    printf("Pos: %d\n", (int)top_window_pos);
    
    start_line = top_window_pos / glyph_height;
    top_offset = top_window_pos % glyph_height;
    
    line_cnt = total_lines - start_line;
    if ( line_cnt > lines_per_draw )
      line_cnt = lines_per_draw;
    
    u8g2_FirstPage(&u8g2);
    do
    {
      u8g2_SetFontDirection(&u8g2, 0); 

      for( i = 0; i < line_cnt; i++ )
      {
	u8x8_CopyStringLine(buf, i+start_line, c_str);
	u8g2_DrawUTF8(&u8g2, 0, i*glyph_height-top_offset +glyph_height, buf);
      }
      

    } while( u8g2_NextPage(&u8g2) );
    
    do
    {
      k = u8g_sdl_get_key();
    } while( k < 0 );
    
    /* up */
    if ( k == 273 )
    {
      if ( top_window_pos > 0 )
      {
	top_window_pos-=SCROLL_DELTA;
      }
    }
    
    /* down */
    if ( k == 274 ) 
    {
      if ( top_window_pos < total_height )
      {
	top_window_pos+=SCROLL_DELTA;
      }
      else
      {
	top_window_pos = 0;
      }
    }
    
    if ( k == 'q' ) break;
    
  }
  
  
  return 0;
}