#include "lexer.h"
#include "slice.h"
#include "token.h"
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>

static int
iswordy(int c)
{
	if (isalpha(c) || c == '_')
		return 1;
	return 0;
}

static unsigned int
simple_token(char c)
{
	switch (c) {
	case '{': return TOK_OPEN_CURL;
	case '}': return TOK_CLOS_CURL;
	case '(': return TOK_OPEN_PAREN;
	case ')': return TOK_CLOS_PAREN;
	case '[': return TOK_OPEN_SQUAR;
	case ']': return TOK_CLOS_SQUAR;
	case '=': return TOK_ASSIGN;
	case ';': return TOK_END;
	default:  return TOK_NONE;
	}
}

static Slice
slice_match(Slice slice, int (*isfun)(int c))
{
	for (int i = slice.begin; i < slice.end; i++)
		if (!isfun(slice.str[i]))
			return slice_sub(slice, slice.begin, i);
	return slice;
}

Token *
lexer(Slice slice)
{
	Token *toks = NULL;
	int i = slice.begin;
	while (i < slice.end) {
		// Skip whitespaces.
		if (isspace(slice.str[i])) {
			i += 1;
			continue;
		}

		// Ignore comments.
		if (slice.str[i] == '/' && slice.str[i + 1] == '/') {
			while (i < slice.end && slice.str[i] != '\n')
				i += 1;
			continue;
		}

		// Single character tokens.
		if (simple_token(slice.str[i]) != TOK_NONE) {
			Slice sub = slice_sub(slice, i, i + 1);
			token_append(&toks, token_create(sub,
			             simple_token(slice.str[i])));
			if (slice.str[i] == '}')
				token_append(&toks,
				             token_create(sub, TOK_END));
			i += 1;
			continue;
		}

		// Number token.
		if (isdigit(slice.str[i])) {
			Slice number;
			number = slice_match(slice_sub(slice, i, slice.end),
			                     isdigit);
			token_append(&toks, token_create(number, TOK_NUMBER));
			i = number.end;
			continue;
		}

		// Word token, and keywords by extension.
		if (iswordy(slice.str[i])) {
			Slice word = slice_match(slice_sub(slice, i, slice.end),
			                         iswordy);

			// Keywords.
			unsigned int type = TOK_WORD;
			if (slice_equal(word, slice_from_str("while")))
				type = TOK_KW_WHILE;
			else if (slice_equal(word, slice_from_str("if")))
				type = TOK_KW_IF;
			else if (slice_equal(word, slice_from_str("else")))
				type = TOK_KW_ELSE;
			else if (slice_equal(word, slice_from_str("let")))
				type = TOK_KW_LET;
			else if (slice_equal(word, slice_from_str("return")))
				type = TOK_KW_RETURN;

			token_append(&toks, token_create(word, type));
			i = word.end;
			continue;
		}

		// String token.
		if (slice.str[i] == '"') {
			int close = i + 1;
			while (close < slice.end && slice.str[close] != '"')
				close += 1;
			if (slice.str[close] != '"') {
				// XXX: Streamline this kind of error handling.
				fprintf(stderr, "unclosed string\n");
				token_destroy(toks);
				return NULL;
			}
			Slice string = slice_sub(slice, i + 1, close);
			token_append(&toks, token_create(string, TOK_STRING));
			i = close + 1;
			continue;
		}

		// Character token.
		if (slice.str[i] == '\'') {
			if (slice.str[i + 1] == '\0' ||
			    slice.str[i + 2] != '\'') {
				fprintf(stderr, "unclosed character\n");
				token_destroy(toks);
				return NULL;
			}
			Slice character = slice_sub(slice, i + 1, i + 2);
			token_append(&toks, token_create(character, TOK_CHAR));
			i += 3;
			continue;
		}

		printf("skipping '%c'\n", slice.str[i]);
		i += 1;
	}
	return toks;
}