#include "lexer.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct lexer *lexer_new(const char *input)
{
    struct lexer *new = malloc(sizeof(struct lexer));
    new->input = input;
    new->pos = 0;
    return new;
}

void lexer_free(struct lexer *lexer)
{
    free(lexer);
}

struct template
{
    char value;
    enum token_type type;
};

struct template templates[] = {
    { '+', TOKEN_PLUS }, { '-', TOKEN_MINUS },    { '*', TOKEN_MUL },
    { '/', TOKEN_DIV },  { '(', TOKEN_LEFT_PAR }, { ')', TOKEN_RIGHT_PAR },
    { '\0', TOKEN_EOF }, { 0, TOKEN_ERROR }
};

static ssize_t parse_number(struct lexer *l)
{
    union
    {
        const char *cc;
        char *c;
    } cast;
    cast.cc = l->input + l->pos;
    char *in = cast.c;
    size_t t = 0;
    while (in[t] && in[t] >= '0' && in[t] <= '9')
        t++;
    char tmp = in[t];
    in[t] = '\0';
    ssize_t res = atoi(in);
    in[t] = tmp;
    return res;
}

struct token lexer_next_token(struct lexer *lexer)
{
    for (; lexer->input[lexer->pos] && lexer->input[lexer->pos] == ' ';
         lexer->pos++)
        continue;
    for (int i = 0; i < 7; i++)
    {
        if (lexer->input[lexer->pos] == templates[i].value)
        {
            lexer->current_tok.type = templates[i].type;
            return lexer->current_tok;
        }
    }
    if (lexer->input[lexer->pos] > '9' || lexer->input[lexer->pos] < '0')
    {
        lexer->current_tok.type = TOKEN_ERROR;
        fprintf(stderr, "lexer: invalid token %c\n", lexer->input[lexer->pos]);
        return lexer->current_tok;
    }
    else
    {
        lexer->current_tok.type = TOKEN_NUMBER;
        lexer->current_tok.value = parse_number(lexer);
        return lexer->current_tok;
    }
}

struct token lexer_peek(struct lexer *lexer)
{
    return lexer_next_token(lexer);
}

static size_t count_numbers(ssize_t value)
{
    if (value == 0)
        return 1;
    size_t size = 0;
    while (value)
    {
        size++;
        value /= 10;
    }
    return size;
}

struct token lexer_pop(struct lexer *lexer)
{
    struct token res = lexer_next_token(lexer);
    if (res.type == TOKEN_NUMBER)
        lexer->pos += count_numbers(res.value);
    else
        lexer->pos++;
    return res;
}