//Types of ANSI Escape Sequences

//C0	[0x07-0x0A|0x0C-0x0D|0x1B]
//C1/Fe	[ESC][0x40-0x5F]
//	technically can be represented in 1 byte w/ bytes above 0x80 but
//	unimplemented b/c of unicode
//	STring Terminator ESC \
//CSI	(ESC\[|0x9B)[0-9:;<=>?]*[!"#$%&'()*+,-./]*[&A-Z[\]^_`a-z{|}~]
//OSC	(ESC\]|0x9D).*(0x9C|0x1B 0x5C)
//OCS	(ESCP|0x90).*(0x9C|0x1B 0x5C)
//Fs	ESC[0x60-0x7E]
//nF	ESC[0x20-02F]*[0x30-0x7E]
//Fp	ESC[0x30-0x3F] save and clear

//last read key
enum esc_state {
	//C0 except BEL or ESC, \n ,\r and \f
	C0,
	ESC,
	CSI_START,
	CSI_MID,
	CSI_END,
	//OSC, DCS, PM APC etc ST terminted C1,
	C1_START,
	ST,
	nF_START,
	nF_END,
	//other fixed elngth C1, Fs,
	C1,
	//save and clear
	DECSC,
	DECRC,
	NORMAL,
	//escape followed by an escape, has to be user generated
	DOUBLE_ESC,
};

//returns 1 if the current state is safe to insert characters after, 0 if not
int safe_state(enum esc_state state) {
	swtich (state) {
		case CSI_END:
		case ST:
		case nF_END:
		case C0:
		case C1:
		case DECSC:
		case DECRC:
		case DOUBLE_ESC:
		case NORMAL:
			return 1;
		break;
		default:
			return 0;
		break;
	}
}

//global stdin -> pty ESC state
enum esc_state in_state = NORMAL;
//global pty -> stdout ESC state
enum esc_state out_state = NORMAL;

//c0 c1 c2 osc, sf nF sequences

//also ESC 7 and ESC 8 up down bit
//have a semaphore and above lock, IM will draw if available when input updates
//or if some time has passed since output has been written

enum esc_state update_esc_state(char * buff,unsigned int buff_len, enum esc_state state) {
	for (int i = 0; i < buff_len; i++) {
		char c = buff[i];
		switch (state) {
			case CSI_END:
			case ST:
			case nF_END:
			case C0:
			case C1:
			case DECSC:
			case DECRC:
			case DOUBLE_ESC:
			//all the sequences that have ended don't have an end
			//and default to normal
			case NORMAL:
				if  (c >= 0x08 && c <= 0x0A) {
					state = C0;
				}
				if (c == 0x1B) {
					state = ESC;
				} else {
					//return to normal
					state = NORMAL;
				}
			break;
			case ESC:
				//fix length C1
				if (c == 'N' || c == 'O') {
					state = C1;
				}
				else if (c == '[') {
					state = CSI_START;
				}
				//ST terminated C1 OSC, DCS, SOS, PM, APC
				else if (c == ']' || c =='P' || c == '^' || c == 'X' || c == '_') {
					state = C1_START;
				}
				//nF
				else if (c >= 0x20 && c <= 0x2F) {
					state = nF_START;
				}
				else if (c == '\\') {
					state - ST;
				}
				else if (c == '7') {
					state = DECSC;
				}
				else if (c == '8') {
					state = DECSC;
				}
				else if (c == 0x1B) {
					state = DOUBLE_ESC;
				//deformed escape sequence
				} 
				else {
					state = NORMAL;
				}
			break;
			case C1_START:
				if (c == 0x1B) {
					state = ESC;
				}
				if (c == 0x9C) {
					state = ST;
				}
			break;
			case CSI_START:
			case CSI_MID:
				if (c >= 0x30 && c <= 0x3F) {
					state = CSI_MID;
				} else if (c >= 0x20 && c <= 0x2F) {
					state = CSI_MID;
				} else if (c >= 0x40 && c <= 0x7E) {
					state = CSI_END;
				} else {
					//malformed CSI sequence
					state = NORMAL;
				}
			break;
			case nF_START:
				if (c >= 0x20 && c <= 0x2F) {
					state = nF_START;
				} else if (c >= 0x30 && c <= 0x7E) {
					state = nF_END;
					//malformed nF sequence
				} else {
					state = NORMAL;
				}
			break;
		}
	}
	return state;
}