/* (C) Copyright 2008 Nick Mudge <mudgen@gmail.com>
 * This code can be freely copied and modified.
 */
#include "symbol_table.c"
#include <stdio.h>

/* Chars */
#define ALPHA 0
#define DIGIT 1
#define WHITE_SPACE 3
#define ERROR_CHAR 127

/* Tokens */
#define IDENTIFIER 1
#define NUM 2
#define KEYWORD 3
#define TOKEN_END 126
#define ERROR_TOKEN 127

#define INITIALIZE_TABLE(table, function) if(table[0] == 0) function(table)

/*
variable:
a(ad)*
a = a-z, A-Z, _
d = 0-9
operators:
+ -
* /
=
numbers:
0-9
*/

typedef struct token {
	char value;
	Entry *symbol_entry;
} Token;

extern char *input;
extern char *input_beginning;
extern Token token;
extern Token look_ahead_token;
Symbol_table *symbol_table;

Token return_token(void);

void initialize_char_set(char char_set[]) {
	int i;
	for(i = 0; i < 127; i++) {
		if((i > 64 && i < 91) || (i > 96 && i < 123))
			char_set[i] = ALPHA;
		else if (i > 47 && i < 58)
			char_set[i] = DIGIT;
		else if (i == ' ' || i == '\t' || i == '\n')
			char_set[i] = WHITE_SPACE;
		else
			char_set[i] = ERROR_CHAR;
	}
}
void la(void) {
	if(token.value == 0 && token.symbol_entry == NULL) {
		token = return_token();
		look_ahead_token = return_token();
	}
	else {
		token = look_ahead_token;
		look_ahead_token = return_token();
	}
}

Token return_token(void) {
	static char char_set[128];
	int state;
	char *lexeme_end;
	char *possible_identifier_beginning;
	char string_symbol_table_buffer;
	Token token;
	state = 0;
	possible_identifier_beginning = NULL;
	INITIALIZE_TABLE(char_set, initialize_char_set);
	
	if(input < input_beginning) {
		token.symbol_entry = NULL;
		token.value = TOKEN_END;
		return token;
	}
	
	for(; input >= input_beginning; input--) {		
		if(state == 0 && char_set[(int)*input] == WHITE_SPACE) {
			continue;
		}
		if(state == 0 && (char_set[(int)*input] == ALPHA || char_set[(int)*input] == DIGIT)) {
			lexeme_end = input + 1;			
			string_symbol_table_buffer = *lexeme_end;
			state = 1;
		}
		if(state == 2 || char_set[(int)*input] == ALPHA) {
			if(possible_identifier_beginning == NULL) {
				possible_identifier_beginning = input;
				state = 2;
			}
			if(input-1 < input_beginning || (char_set[(int)*(input-1)] != ALPHA && char_set[(int)*(input-1)] != DIGIT)) {
				if(char_set[(int)*input] == DIGIT)
					input = possible_identifier_beginning;
				*lexeme_end = '\0';
				token.symbol_entry = add_to_symbol_table(input);
				*lexeme_end = string_symbol_table_buffer;
				if(token.symbol_entry->keyword == TRUE)
					token.value = KEYWORD;
				else					
					token.value = IDENTIFIER;
				input--;
				return token;
			}
		}		
		else if(char_set[(int)*input] == DIGIT) {
			if(input-1<input_beginning || (char_set[(int)*(input-1)] != DIGIT && char_set[(int)*(input-1)] != ALPHA)) {
				*lexeme_end = '\0';				
				token.symbol_entry = add_to_symbol_table(input);
				*lexeme_end = string_symbol_table_buffer;
				token.value = NUM;
				input--;
				return token;
			}
		}
		else if(*input == '+') {
			token.value = '+';
			token.symbol_entry = NULL;
			input--;
			return token;
		}
		else if(*input == '-') {
			token.value = '-';
			token.symbol_entry = NULL;
			input--;
			return token;
		}
		else if(*input == '*') {
			token.value = '*';
			token.symbol_entry = NULL;
			input--;
			return token;
		}
		else if(*input == '/') {
			token.value = '/';
			token.symbol_entry = NULL;
			input--;
			return token;
		}
		else if(*input == ')') {
			token.value = ')';
			token.symbol_entry = NULL;
			input--;
			return token;
		}
		else if(*input == '(') {
			token.value = '(';
			token.symbol_entry = NULL;
			input--;
			return token;
		}
		else if(*input == '=') {
			token.value = '=';
			token.symbol_entry = NULL;
			input--;
			return token;			
		}
		else if(*input == ';') {
			token.value = ';';
			token.symbol_entry = NULL;
			input--;
			return token;
		}
		else {
			token.value = ERROR_TOKEN;
			token.symbol_entry = NULL;
			input--;
			return token;
		}
	}
	token.symbol_entry = NULL;
	token.value = ERROR_TOKEN;
	return token;
}