/*
 * Copyright (C) 2010, Google Inc.
 * and other copyright owners as documented in JGit's IP log.
 *
 * This program and the accompanying materials are made available
 * under the terms of the Eclipse Distribution License v1.0 which
 * accompanies this distribution, is reproduced below, and is
 * available at http://www.eclipse.org/org/documents/edl-v10.php
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials provided
 *   with the distribution.
 *
 * - Neither the name of the Eclipse Foundation, Inc. nor the
 *   names of its contributors may be used to endorse or promote
 *   products derived from this software without specific prior
 *   written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "xinclude.h"
#include "xtypes.h"
#include "xdiff.h"

#define MAX_PTR UINT_MAX
#define MAX_CNT UINT_MAX

#define LINE_END(n) (line##n + count##n - 1)
#define LINE_END_PTR(n) (*line##n + *count##n - 1)

struct histindex {
        struct record {
                unsigned int ptr, cnt;
                struct record *next;
        } **records, /* an ocurrence */
          **line_map; /* map of line to record chain */
        chastore_t rcha;
        unsigned int *next_ptrs;
        unsigned int table_bits,
                     records_size,
                     line_map_size;

        unsigned int max_chain_length,
                     key_shift,
                     ptr_shift;

        unsigned int cnt,
                     has_common;

        xdfenv_t *env;
        xpparam_t const *xpp;
};

struct region {
        unsigned int begin1, end1;
        unsigned int begin2, end2;
};

#define LINE_MAP(i, a) (i->line_map[(a) - i->ptr_shift])

#define NEXT_PTR(index, ptr) \
        (index->next_ptrs[(ptr) - index->ptr_shift])

#define CNT(index, ptr) \
        ((LINE_MAP(index, ptr))->cnt)

#define REC(env, s, l) \
        (env->xdf##s.recs[l - 1])

static int cmp_recs(xpparam_t const *xpp,
        xrecord_t *r1, xrecord_t *r2)
{
        return r1->ha == r2->ha &&
                xdl_recmatch(r1->ptr, r1->size, r2->ptr, r2->size,
                            xpp->flags);
}

#define CMP_ENV(xpp, env, s1, l1, s2, l2) \
        (cmp_recs(xpp, REC(env, s1, l1), REC(env, s2, l2)))

#define CMP(i, s1, l1, s2, l2) \
        (CMP_ENV(i->xpp, i->env, s1, l1, s2, l2))

#define TABLE_HASH(index, side, line) \
        XDL_HASHLONG((REC(index->env, side, line))->ha, index->table_bits)

static int scanA(struct histindex *index, int line1, int count1)
{
        unsigned int ptr, tbl_idx;
        unsigned int chain_len;
        struct record **rec_chain, *rec;

        for (ptr = LINE_END(1); line1 <= ptr; ptr--) {
                tbl_idx = TABLE_HASH(index, 1, ptr);
                rec_chain = index->records + tbl_idx;
                rec = *rec_chain;

                chain_len = 0;
                while (rec) {
                        if (CMP(index, 1, rec->ptr, 1, ptr)) {
                                /*
                                 * ptr is identical to another element. Insert
                                 * it onto the front of the existing element
                                 * chain.
                                 */
                                NEXT_PTR(index, ptr) = rec->ptr;
                                rec->ptr = ptr;
                                /* cap rec->cnt at MAX_CNT */
                                rec->cnt = XDL_MIN(MAX_CNT, rec->cnt + 1);
                                LINE_MAP(index, ptr) = rec;
                                goto continue_scan;
                        }

                        rec = rec->next;
                        chain_len++;
                }

                if (chain_len == index->max_chain_length)
                        return -1;

                /*
                 * This is the first time we have ever seen this particular
                 * element in the sequence. Construct a new chain for it.
                 */
                if (!(rec = xdl_cha_alloc(&index->rcha)))
                        return -1;
                rec->ptr = ptr;
                rec->cnt = 1;
                rec->next = *rec_chain;
                *rec_chain = rec;
                LINE_MAP(index, ptr) = rec;

continue_scan:
                ; /* no op */
        }

        return 0;
}

static int try_lcs(struct histindex *index, struct region *lcs, int b_ptr,
        int line1, int count1, int line2, int count2)
{
        unsigned int b_next = b_ptr + 1;
        struct record *rec = index->records[TABLE_HASH(index, 2, b_ptr)];
        unsigned int as, ae, bs, be, np, rc;
        int should_break;

        for (; rec; rec = rec->next) {
                if (rec->cnt > index->cnt) {
                        if (!index->has_common)
                                index->has_common = CMP(index, 1, rec->ptr, 2, b_ptr);
                        continue;
                }

                as = rec->ptr;
                if (!CMP(index, 1, as, 2, b_ptr))
                        continue;

                index->has_common = 1;
                for (;;) {
                        should_break = 0;
                        np = NEXT_PTR(index, as);
                        bs = b_ptr;
                        ae = as;
                        be = bs;
                        rc = rec->cnt;

                        while (line1 < as && line2 < bs
                                && CMP(index, 1, as - 1, 2, bs - 1)) {
                                as--;
                                bs--;
                                if (1 < rc)
                                        rc = XDL_MIN(rc, CNT(index, as));
                        }
                        while (ae < LINE_END(1) && be < LINE_END(2)
                                && CMP(index, 1, ae + 1, 2, be + 1)) {
                                ae++;
                                be++;
                                if (1 < rc)
                                        rc = XDL_MIN(rc, CNT(index, ae));
                        }

                        if (b_next <= be)
                                b_next = be + 1;
                        if (lcs->end1 - lcs->begin1 < ae - as || rc < index->cnt) {
                                lcs->begin1 = as;
                                lcs->begin2 = bs;
                                lcs->end1 = ae;
                                lcs->end2 = be;
                                index->cnt = rc;
                        }

                        if (np == 0)
                                break;

                        while (np <= ae) {
                                np = NEXT_PTR(index, np);
                                if (np == 0) {
                                        should_break = 1;
                                        break;
                                }
                        }

                        if (should_break)
                                break;

                        as = np;
                }
        }
        return b_next;
}

static int find_lcs(struct histindex *index, struct region *lcs,
        int line1, int count1, int line2, int count2) {
        int b_ptr;

        if (scanA(index, line1, count1))
                return -1;

        index->cnt = index->max_chain_length + 1;

        for (b_ptr = line2; b_ptr <= LINE_END(2); )
                b_ptr = try_lcs(index, lcs, b_ptr, line1, count1, line2, count2);

        return index->has_common && index->max_chain_length < index->cnt;
}

static void reduce_common_start_end(xpparam_t const *xpp, xdfenv_t *env,
        int *line1, int *count1, int *line2, int *count2)
{
        if (*count1 <= 1 || *count2 <= 1)
                return;
        while (*count1 > 1 && *count2 > 1 && CMP_ENV(xpp, env, 1, *line1, 2, *line2)) {
                (*line1)++;
                (*count1)--;
                (*line2)++;
                (*count2)--;
        }
        while (*count1 > 1 && *count2 > 1 && CMP_ENV(xpp, env, 1, LINE_END_PTR(1), 2, LINE_END_PTR(2))) {
                (*count1)--;
                (*count2)--;
        }
}

static int fall_back_to_classic_diff(struct histindex *index,
                int line1, int count1, int line2, int count2)
{
        xpparam_t xpp;
        xpp.flags = index->xpp->flags & ~XDF_HISTOGRAM_DIFF;

        return xdl_fall_back_diff(index->env, &xpp,
                                  line1, count1, line2, count2);
}

static int histogram_diff(xpparam_t const *xpp, xdfenv_t *env,
        int line1, int count1, int line2, int count2)
{
        struct histindex index;
        struct region lcs;
        int sz;
        int result = -1;

        if (count1 <= 0 && count2 <= 0)
                return 0;

        if (LINE_END(1) >= MAX_PTR)
                return -1;

        if (!count1) {
                while(count2--)
                        env->xdf2.rchg[line2++ - 1] = 1;
                return 0;
        } else if (!count2) {
                while(count1--)
                        env->xdf1.rchg[line1++ - 1] = 1;
                return 0;
        }

        memset(&index, 0, sizeof(index));

        index.env = env;
        index.xpp = xpp;

        index.records = NULL;
        index.line_map = NULL;
        /* in case of early xdl_cha_free() */
        index.rcha.head = NULL;

        index.table_bits = xdl_hashbits(count1);
        sz = index.records_size = 1 << index.table_bits;
        sz *= sizeof(struct record *);
        if (!(index.records = (struct record **) xdl_malloc(sz)))
                goto cleanup;
        memset(index.records, 0, sz);

        sz = index.line_map_size = count1;
        sz *= sizeof(struct record *);
        if (!(index.line_map = (struct record **) xdl_malloc(sz)))
                goto cleanup;
        memset(index.line_map, 0, sz);

        sz = index.line_map_size;
        sz *= sizeof(unsigned int);
        if (!(index.next_ptrs = (unsigned int *) xdl_malloc(sz)))
                goto cleanup;
        memset(index.next_ptrs, 0, sz);

        /* lines / 4 + 1 comes from xprepare.c:xdl_prepare_ctx() */
        if (xdl_cha_init(&index.rcha, sizeof(struct record), count1 / 4 + 1) < 0)
                goto cleanup;

        index.ptr_shift = line1;
        index.max_chain_length = 64;

        memset(&lcs, 0, sizeof(lcs));
        if (find_lcs(&index, &lcs, line1, count1, line2, count2))
                result = fall_back_to_classic_diff(&index, line1, count1, line2, count2);
        else {
                if (lcs.begin1 == 0 && lcs.begin2 == 0) {
                        int ptr;
                        for (ptr = 0; ptr < count1; ptr++)
                                env->xdf1.rchg[line1 + ptr - 1] = 1;
                        for (ptr = 0; ptr < count2; ptr++)
                                env->xdf2.rchg[line2 + ptr - 1] = 1;
                        result = 0;
                } else {
                        result = histogram_diff(xpp, env,
                                                line1, lcs.begin1 - line1,
                                                line2, lcs.begin2 - line2);
                        if (result)
                                goto cleanup;
                        result = histogram_diff(xpp, env,
                                                lcs.end1 + 1, LINE_END(1) - lcs.end1,
                                                lcs.end2 + 1, LINE_END(2) - lcs.end2);
                        if (result)
                                goto cleanup;
                }
        }

cleanup:
        xdl_free(index.records);
        xdl_free(index.line_map);
        xdl_free(index.next_ptrs);
        xdl_cha_free(&index.rcha);

        return result;
}

int xdl_do_histogram_diff(mmfile_t *file1, mmfile_t *file2,
        xpparam_t const *xpp, xdfenv_t *env)
{
        int line1, line2, count1, count2;

        if (xdl_prepare_env(file1, file2, xpp, env) < 0)
                return -1;

        line1 = line2 = 1;
        count1 = env->xdf1.nrec;
        count2 = env->xdf2.nrec;

        reduce_common_start_end(xpp, env, &line1, &count1, &line2, &count2);

        return histogram_diff(xpp, env, line1, count1, line2, count2);
}