#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>

#include <kernel/tty.h>
#include <kernel/utils.h>

static const size_t TERM_WIDTH=80;
static const size_t TERM_HEIGHT=25;

static size_t terminal_row;
static size_t terminal_column;

static uint8_t current_color;
static uint16_t* term_buffer;
static uint16_t* const vga_buffer = (uint16_t*) 0xB8000;

void screen_initialize(void) {
	
	terminal_row = 0;
	terminal_column = 0;
	current_color = vga_color_set(LIGHT_GREY, BLACK);
	term_buffer = vga_buffer;
	
	for (size_t y = 0; y < TERM_HEIGHT; y++) {
		for(size_t x = 0; x < TERM_WIDTH; x++) {
			const size_t offset = y * TERM_WIDTH + x;
			term_buffer[offset] = vga_entry(' ', current_color);
		}
	}
}

void term_setcolor(enum vga_colors color) {
	current_color = color;
}

void term_putentryat (char c, uint8_t color, size_t x, size_t y) {
	const size_t offset = y * TERM_WIDTH + x;
	term_buffer[offset] = vga_entry(c, color);
}

void term_putchar(char c) {
	unsigned char uc = c;
	
	//Handle escaped characters, such as newline, and crtn.
	switch (uc) {
		case '\n':
			terminal_column = 0;
			terminal_row += 1;
			break;
		default:
			term_putentryat(uc, current_color, terminal_column, terminal_row);
			break;
	}
	
	if(++terminal_column == TERM_WIDTH) 
	{
		terminal_column = 0;
		if(++terminal_row == TERM_HEIGHT){
			term_scroll(false);
			terminal_row = 0;
		}
	}
}

void term_write(const char* data, size_t size) {
	for(size_t i = 0; i < size; i++) {
		//Begin handling ANSI escape codes.
		if(data[i] == 0x1B) { //The current character is ESC - the start of ANSI codes.
			term_writes("ANSI Code encountered: ");
			
			bool string_terminated = false; //Flag used in some of the escape codes
			switch(data[i+1]) {
				case 0x9b/*[*/: //CSI - Control Sequence Introducer (The most common one, hence it comes first)
					char* controlSequence;
					if(data[i+2] == NULL) {
						controlSequence = '\0';
					for(size_t j = 0; j < (strlen(data) - (i+2); j++) {
						if(data[j] == ' ') 
							break;
						controlSequence += data[j];
					}
					handleControlSequence(controlSequence); //Send it off to our handler function to keep this part clean
					break;
					
				//Single shifts are not handled, so just print them and exit
				case 0x8e/*N*/: //SS2 - Single Shift Two
					term_writes("Single Shift Two\n");
					break;
				case 0x8f/*O*/: //SS3 - Single Shift Three
					term_writes("Single Shift Three\n");
					break;
				
				//Control Strings
				case 0x90/*P*/: //DCS - Device Control String
					term_writes("Device Control String");
					string_terminated = false;
					break;
				case 0x9c/*\*/: //ST - String Terminator 
					term_writes("String Terminator\n");
					string_terminated = true;
					break;
				case 0x9d/*]*/: //OSC - Operating System Command
					term_writes("Operating System Command\n");
					string_terminated = false;
					break;
				case 0x98/*X*/: //SOS - Start Of String
					term_writes("Start of String");
					string_terminated = false;
					break;
				case 0x9e/*^*/: //PM - Privacy Message
					term_writes("Privacy Message\n");
					break;
				case 0x9f/*_*/: //APC - Application Program Command
					term_writes("Application Program Command\n");
					break;
			}
			
		}
		
		term_putchar(data[i]);
	}
}

void term_writes(const char* data) {
	term_write(data, strlen(data));
}

void puts(const char* string) { 
	term_write(string, strlen(string));
	term_putchar('\n');
}

void handleControlSequence(const char* sequence) {
	//Check for our failsafes
	if(sequence) {
		if(sequence != '\0') {
			int n = 0; //Default of the flag used for a few items
			
			bool nPresent = false;
			bool terminated = false;
			for(size_t i = 0; i < strlen(sequence); i++) {
				if(isDigit(sequence[i])) {
						nPresent = true;
						n = (n*10) + sequence[i];
					} else if(n > 80) {
						n = 80;
						break;
					}
				}
				
				if(n == 0)
					n = 1;
				
				switch(sequence[i]) {
					case ';':
						terminated = true;
						int m = 0; 
						for(size_t j = 0; j < strlen(sequence - i); j++) {
							if(sequence[j] == 'H' ||sequence[j] == 'f') 
								break;
							
							if(isDigit(sequence[j])) {
									m = (m*10) + sequence[j];
							} else if(j > 80) break;
						}
						
						if(m == 0)
							m = 1;
						cursor_pos(n, m);
						
						break;
					case 'A': //CUU - Cursor Up
						//cursor_pos(x, y)
						
						cursor_pos(terminal_column, terminal_row + n);
						break;
					case 'B': //CUD - Cursor Down
						cursor_pos(terminal_column, terminal_row - n);
						break;
					case 'C': //CUF - Cursor Forward
						cursor_pos(terminal_column + n, terminal_row);
						break;
					case 'D': //CUB - Cursor Back
						cursor_pos(terminal_column - n, terminal_row);
						break;
					case 'E': //CNL - Cursor Next Line
						cursor_pos(0, terminal_row + n);
						break;
					case 'F': //CPL - Cursor Previous Line
						cursor_pos(0, terminal_row - n);
						break;
					case 'G': //CHA - Cursor Horizontal Absolute
						cursor_pos(n, terminal_row);
					case 'J': //ED - Erase in Display
						//current cursor pos = y * width + x
						int pos = terminal_row * 80 + terminal_column;
						if(!nPresent) {
							for(pos < (25 * 80); pos++) {
								vga_buffer[pos] = '\0';
							}
							n = 0;
						} else if(nPresent && n == 1) {
							for(pos > 0; pos--) {
								vga_buffer[pos] = '\0';
							}
						} else if(n == 2 || n == 3) {
							for(int i = 0; i < (25*80); i++) {
								vga_buffer[0] = '\0';
							}
						} 
						break;
					case 'K': //EL - Erase in Line
					
						int pos = terminal_row * 80 + terminal_column;
						if(!nPresent) { //From cursor to end of line
							int endPos = (terminal_row + 1) * 80 - 1; //End of line = current row + 25 columns = current row + 1
							for(pos < endPos; pos++) {
								vga_buffer[pos] = '\0';
							}
						} else if(nPresent && n == 1) { //From cursor to start of line
							int endPos = terminal_row * 80; //Start of line = end of previous line + 1 == current line
							for(pos > endPos; pos--) {
								vga_buffer[pos] = '\0';
							}
						} else if(nPresent && n == 2) { //Entire current line
							pos = terminal_row * 80;
							int endPos = (terminal_row + 1) * 80 - 1;
							for(pos < endPos; pos++) {
								vga_buffer[pos] = '\0';
							}
						}
						break;
					case 'S': //SU - Scroll Up
						term_scroll(true);
						break;
					case 'T': //SD - Scroll Down
						term_scroll(false);
						break;
				}
			}
		}
	}
	
}

bool isDigit(const char c) {
	return c == '0' || c == '1' || c == '2' || c == '3' ||
			c == '4' || c == '5' || c == '6' || c == '7' ||
			c == '8' || c == '9';
}

void term_scroll(bool down) {

	int current_pos;
	if(down) {
		current_pos = 25 * 80; //Start of the last line.
	} else {
		current_pos = 160; //Start of the second line.
	}
	
	unsigned char* term_buffer = (unsigned char*) vga_buffer;
	
	if(down) { //To scroll down, move every character into the one below it, or "pull" every character down
		while(current_pos > 80) {
			term_buffer[current_pos + 160] = vga_buffer[current_pos];
			term_buffer[current_pos + 159] = vga_buffer[current_pos - 1];
			current_pos -= 2;
	} else {
		while (current_pos <= 4000) {
			term_buffer[current_pos - 160 /*The character immediately below it*/] = vga_buffer[current_pos];      //Move each character up a line
			term_buffer[current_pos - 159 /*The color of the character below*/] = vga_buffer[current_pos + 1];    //As well as its color
			current_pos += 2; //Move to next char
		}
	}
	
	if(down) {
		current_pos = 0; //Start of first line
		for(current_pos < 80; current_pos++) {
			term_buffer[current_pos] = '\0';
			current_pos += 2;
	} else {
		; //Start of the last line
		//Wipe out the bottom line
		for(current_pos = 3840; current_pos <= 3920; i++) {
			term_buffer[current_pos] = 0;
			current_pos += 2;
		}
	}
	
	terminal_row = 24; //Start writing on the last line
	terminal_column = 0;
}