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

#include "speller.h"

const char idchars[] = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_";

/**************************************************
 * Looks for correct spelling.
 * Currently only looks a 'distance' of one from the seed[].
 * This does an exhaustive search, so can potentially be very slow.
 * Input:
 *seedwrongly spelled word
 *fpsearch function
 *fpargargument to search function
 *charsetcharacter set
 * Returns:
 *NULLno correct spellings found
 *void*value returned by fp() for first possible correct spelling
 */

void *speller(const char *seed, fp_speller_t fp, void *fparg, const char *charset)
{
    size_t seedlen = strlen(seed);
    if (!seedlen)
        return NULL;

    char *buf = (char *)alloca(seedlen + 2);// leave space for extra char
    if (!buf)
        return NULL;// no matches

    /* Deletions */
    memcpy(buf, seed + 1, seedlen);
    for (int i = 0; i < seedlen; i++)
        {
            //printf("del buf = '%s'\n", buf);
            void *p = (*fp)(fparg, buf);
            if (p)
                return p;

            buf[i] = seed[i];
        }

    /* Transpositions */
    memcpy(buf, seed, seedlen + 1);
    for (int i = 0; i + 1 < seedlen; i++)
        {
            // swap [i] and [i + 1]
            buf[i] = seed[i + 1];
            buf[i + 1] = seed[i];

            //printf("tra buf = '%s'\n", buf);
            void *p = (*fp)(fparg, buf);
            if (p)
                return p;

            buf[i] = seed[i];
        }

    if (charset && *charset)
        {
            /* Substitutions */
            memcpy(buf, seed, seedlen + 1);
            for (int i = 0; i < seedlen; i++)
                {
                    for (const char *s = charset; *s; s++)
                        {
                            buf[i] = *s;

                            //printf("sub buf = '%s'\n", buf);
                            void *p = (*fp)(fparg, buf);
                            if (p)
                                return p;
                        }
                    buf[i] = seed[i];
                }

            /* Insertions */
            memcpy(buf + 1, seed, seedlen + 1);
            for (int i = 0; i <= seedlen; i++)// yes, do seedlen+1 iterations
                {
                    for (const char *s = charset; *s; s++)
                        {
                            buf[i] = *s;

                            //printf("ins buf = '%s'\n", buf);
                            void *p = (*fp)(fparg, buf);
                            if (p)
                                return p;
                        }
                    buf[i] = seed[i];// going past end of seed[] is ok, as we hit the 0
                }
        }

    return NULL;// didn't find any corrections
}