42sh/src/lexer/lexer.c

#include "lexer.h"

#include <ctype.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "../io_backend/io_backend.h"
#include "../utils/string_utils/string_utils.h"
#include "lexer_utils.h"

/* @brief: sets the ctx->current_token to [tok].
 *        this function is called by token_peek().
 */
static void update_current_token(struct token *tok, struct lexer_context *ctx)
{
    ctx->current_token = tok;
}

/* @brief: frees the last token and sets it to [tok].
 *        Also sets ctx->current_token to NULL.
 *        this function is called by token_pop().
 */
static void update_previous_token(struct token *tok, struct lexer_context *ctx)
{
    free_token(&ctx->previous_token);
    ctx->previous_token = tok;
}
/* @brief: updates the current position in the stream.
 *          [stream] += [i]
 *        Also frees the last sent token, and sets it to ctx->current_token.
 *        Current token is then set to NULL.
 *        This function is called by token_pop().
 */
static void save_state(char *stream, ssize_t i, struct lexer_context *ctx)
{
    ctx->remaining_chars -= i;
    ctx->end_previous_token = stream + i;

    update_previous_token(ctx->current_token, ctx);
    update_current_token(NULL, ctx);
}

/*
 * @brief: Updates the lexing_mode to LEXER_NORMAL
 *         if the SECOND quote is found at stream[i].
 *         Updates the lexing_mode to the corresponding quote type
 *         if the FIRST quote of any type is found.
 *
 * @return: true if an update was done. false otherwise.
 */
static bool update_lexing_mode(char *stream, ssize_t i,
                               enum lexing_mode *lexing_mode)
{
    enum lexing_mode mode_before_update = *lexing_mode;

    // FIRST quote
    if (*lexing_mode == LEXER_NORMAL)
    {
        if (stream[i] == '"')
            *lexing_mode = LEXER_DOUBLE_QUOTE;

        if (stream[i] == '\'')
            *lexing_mode = LEXER_QUOTE;
    }

    // SECOND quote
    else
    {
        if (*lexing_mode == LEXER_QUOTE && stream[i] == '\'')
            *lexing_mode = LEXER_NORMAL;
        if (*lexing_mode == LEXER_DOUBLE_QUOTE && stream[i] == '"')
            *lexing_mode = LEXER_NORMAL;
    }

    return *lexing_mode != mode_before_update;
}

/* @brief: updates the flags only_digits and equal_count
 *         according to the character at stream[i].
 */
static void update_flags(char *stream, ssize_t i, struct lexer_context *ctx)
{
    if (stream[i] == '=')
    {
        ctx->equal_count++;
    }
    else if (!isdigit(stream[i]) && ctx->only_digits)
    {
        ctx->only_digits = false;
    }
}

struct token *peek_token(struct lexer_context *ctx)
{
    // we already created the upcoming token during the previous call to peek()
    if (ctx->current_token != NULL)
    {
        return ctx->current_token;
    }

    stream_init(ctx);
    char *stream = ctx->end_previous_token;
    ssize_t i = 0;

    // Usefull to know if we are inside a quote or double quote
    enum lexing_mode lexing_mode = LEXER_NORMAL;

    while (i < ctx->remaining_chars)
    {
        // true if we didn't encounter a quote of any type at stream[i]
        // AND we are not inside quotes
        if (!update_lexing_mode(stream, i, &lexing_mode)
            && lexing_mode == LEXER_NORMAL)
        {
            update_flags(stream, i, ctx);
            if (is_special_char(stream, i))
            {
                if (i == 0) // where we create spe_char token
                    i += len_op_sepchar(stream, i);
                break;
            }
            if (isblank(stream[i]))
            {
                break;
            }
        }
        else if (stream[i] == EOF)
        {
            fprintf(stderr, "Lexing error: unmatched quote\n");

            // error handling
            return NULL;
        }
        i++;
    }

    struct token *tok = new_token(stream, i, ctx->only_digits, ctx->equal_count);
    // if token is comment, we don't want it

    if (tok->type == TOKEN_COMMENT)
    {
        // Find next newline or EOF.
        go_end_of_line(ctx);

        free_token(&tok);
        tok = peek_token(ctx);
    }
    update_current_token(tok, ctx);
    return tok;
}

struct token *pop_token(struct lexer_context *ctx)
{
    if (ctx->current_token != NULL && ctx->current_token->type == TOKEN_EOF)
    {
        // we reached end of input, frees all the token still allocated.
        free_token(&ctx->previous_token);
        free_token(&ctx->current_token);
        return NULL;
    }
    stream_init(ctx);
    char *stream = ctx->end_previous_token;
    ssize_t i = 0;

    // Usefull to know if we are inside a quote or double quote
    enum lexing_mode lexing_mode = LEXER_NORMAL;

    while (i < ctx->remaining_chars)
    {
        // true if we didn't encounter a quote of any type at stream[i]
        // AND we are not inside quotes
        if (!update_lexing_mode(stream, i, &lexing_mode)
            && lexing_mode == LEXER_NORMAL)
        {
            if (is_special_char(stream, i))
            {
                if (i == 0) // where we create spe_char token
                    i += len_op_sepchar(stream, i);
                break;
            }
            if (isblank(stream[i]))
            {
                break;
            }
        }
        else if (stream[i] == EOF)
        {
            fprintf(stderr, "Lexing error: unmatched quote\n");

            // error handling
            return NULL;
        }
        i++;
    }

    // just in case peek() was not called before poping.
    // (this should never happen)
    if (ctx->current_token == NULL)
    {
        ctx->current_token = new_token(stream, i, ctx->only_digits);
    }
    save_state(stream, i, ctx);

    return ctx->previous_token;
}