#include <ctype.h>
#include <string.h>
#include "sync/lexer.h"

void lexer_init(Lexer *lexer, const char *source) {
    lexer->source = source;
    lexer->pos = 0;
}

static char peek(Lexer *lexer) {
    return lexer->source[lexer->pos];
}

static char double_peek(Lexer *lexer) {
    return lexer->source[lexer->pos+1];
}

static char advance(Lexer *lexer) {
    return lexer->source[lexer->pos++];
}

static int is_identifier_start(char c) {
    return isalpha(c) || c == '_';
}

static int is_identifier_char(char c) {
    return isalnum(c) || c == '_';
}

Token lexer_next(Lexer *lexer) {
    // Gets the next token from the source

    while (isspace(peek(lexer)) || peek(lexer) == '/') {
        // Skip Comments
        if (peek(lexer) == '/' && double_peek(lexer) == '/')
            while (peek(lexer) != '\n') advance(lexer);
        // Skip whitespace
        while (isspace(peek(lexer))) advance(lexer);
    }

    char c = peek(lexer);
    size_t start = lexer->pos;

    // End of file tokens
    if (c == '\0') {
        return (Token){TOKEN_EOF, &lexer->source[start], 0};
    }

    // Identifiers
    if (is_identifier_start(c)) {
        while (is_identifier_char(peek(lexer))) advance(lexer);
        return (Token){TOKEN_IDENTIFIER, &lexer->source[start], lexer->pos - start};
    }

    // Digits
    if (isdigit(c)) {
        while (isdigit(peek(lexer))) advance(lexer);
        return (Token){TOKEN_NUMBER, &lexer->source[start], lexer->pos - start};
    }

    advance(lexer);
    switch (c) {
        case '=':
            if (peek(lexer) == '=') return (Token){TOKEN_OPERATOR, &lexer->source[start], 2};
        case '+':
        case '-':
        case '*':
        case '/':
            return (Token){TOKEN_OPERATOR, &lexer->source[start], 1};
        case '(': return (Token){TOKEN_LPAREN, &lexer->source[start], 1};
        case ')': return (Token){TOKEN_RPAREN, &lexer->source[start], 1};
        case ';': return (Token){TOKEN_SEMICOLON, &lexer->source[start], 1};
        default: return (Token){TOKEN_UNKNOWN, &lexer->source[start], 1};
    }
}