#include "config.h"
#include <stdio.h>
#include <string.h>

/**
 * strgrp - group/cluster similar strings.
 *
 * strgrp clusters similar strings using the Longest Common Subsequence (LCS)
 * algorithm[1]. Clustering is governed by a threshold value, which is compared
 * with the normalised LCS scores calculated from the input string and each
 * existing group.
 *
 * As a coarse and not entirely accurate summary, strgrp takes the following
 * steps:
 *
 * 1. For all known groups, calculate the normalised LCS value against the
 * input string
 *
 * 2. Find the maximum normalised LCS value and associated group
 *
 * 3. If the calculated maximum normalised LCS value exceeds the configured
 * threshold add the input string to the group, otherwise create a new group
 *
 * The clustering operation is expensive; LCS on its own is computationally
 * O(m * n) on its two input strings and optimally requires O(min(m, n))
 * memory. In general each input string should be compared against all known
 * strings, giving O(n^2) behaviour of the clustering algorithm on top of the
 * O(m * n) LCS similarity measurement.
 *
 * strgrp tries to battle this complexity on several fronts:
 *
 * 1. Caching of input strings and their associated group. By incurring the
 * cost of a map's string hash function we may eliminate all further search
 * costs for exact matches, potentially reducing the insertion to a
 * constant-time operation.
 *
 * 2. Coarse reduction of the required comparisons. Each group has a 'key',
 * which is the string that triggered the creation of the group. Input strings
 * are only compared against group keys rather than all known strings, reducing
 * the complexity to the current number of groups rather than all known
 * strings. Note due the pathological case where the number of groups is equal
 * to the number of known strings the algorithm still has O(n^2) computational
 * complexity
 *
 * 3. Whilst the data dependencies of LCS prevent internally parallel
 * implementations, LCS and other filters can be applied in parallel. The code
 * uses OpenMP to automatically distribute scoring of the input string
 * against group keys across a number of threads.
 *
 * 4. Elimination of LCS computations that will never breach the configured
 * threshold. Two measurements are used as rejecting filters (i.e. a failure to
 * exceed the threshold prevents further measurements being made):
 *
 * 4a. Comparison of string lengths: String lengths must be within given bounds
 * to satisfy the user-supplied similarity constraint. A negative result avoids
 * invoking the O(m * n) behaviour of LCS at the cost of O(m + n) in the two
 * strlen() invocations.
 *
 * 4b. Comparison of character distribution: Cosine similarity[2] is used to
 * measure unordered character similarity between the input strings. The
 * implementation is again O(m + n), and avoids the O(m * n) behaviour of LCS.
 *
 * Performance will vary not only with the number of input strings but
 * with their lengths and relative similarities. A large number of long input
 * strings that are relatively similar will give the worst performance.
 * However to provide some context, strgrp can cluster a real-world test set of
 * 3500 strings distributed in length between 20 and 100 characters to 85%
 * similarity on a 4-core 2010-era amd64 laptop in approximately 750ms.
 *
 * [1] https://en.wikipedia.org/wiki/Longest_common_subsequence_problem
 *
 * [2] https://en.wikipedia.org/wiki/Cosine_similarity
 *
 * License: LGPL
 * Author: Andrew Jeffery <andrew@aj.id.au>
 *
 * Example:
 *     FILE *f;
 *     char *buf;
 *     struct strgrp *ctx;
 *     struct strgrp_iter *iter;
 *     const struct strgrp_grp *grp;
 *     struct strgrp_grp_iter *grp_iter;
 *     const struct strgrp_item *item;
 *
 *     f = fdopen(0, "r");
 *     #define BUF_SIZE 512
 *     buf = malloc(BUF_SIZE);
 *     ctx = strgrp_new(0.85);
 *     while(fgets(buf, BUF_SIZE, f)) {
 *         buf[strcspn(buf, "\r\n")] = '\0';
 *         if (!strgrp_add(ctx, buf, NULL)) {
 *             printf("Failed to classify %s\n", buf);
 *         }
 *     }
 *
 *     // Re-implement something similar to strgrp_print() via API as an
 *     // example
 *     iter = strgrp_iter_new(ctx);
 *     while(NULL != (grp = strgrp_iter_next(iter))) {
 *         printf("%s\n", strgrp_grp_key(grp));
 *         grp_iter = strgrp_grp_iter_new(grp);
 *         while(NULL != (item = strgrp_grp_iter_next(grp_iter))) {
 *              printf("\t%s\n", strgrp_item_key(item));
 *         }
 *         strgrp_grp_iter_free(grp_iter);
 *     }
 *
 *     strgrp_iter_free(iter);
 *     strgrp_free(ctx);
 *     free(buf);
 *     fclose(f);
 */
int main(int argc, char *argv[]) {
    if (argc != 2) {
        return 1;
    }

    if (strcmp(argv[1], "depends") == 0) {
        printf("ccan/darray\n");
        printf("ccan/stringmap\n");
        printf("ccan/tal\n");
        printf("ccan/tal/str\n");
        return 0;
    }

    if (strcmp(argv[1], "testdepends") == 0) {
        printf("ccan/str\n");
        return 0;
    }

    if (strcmp(argv[1], "cflags") == 0) {
#if HAVE_OPENMP
        printf("-fopenmp\n");
#endif
        printf("-O2\n");
        return 0;
    }

    if (strcmp(argv[1], "libs") == 0) {
        printf("m\n");
        return 0;
    }

    return 1;
}
