/*

 * 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"

#include "common.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 occurrence */

	  **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_recs(i->xpp, REC(i->env, s1, l1), REC(i->env, 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, unsigned int line1, unsigned int count1)

{

	unsigned int ptr;

	unsigned int 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, unsigned int b_ptr,

	unsigned int line1, unsigned int count1,

	unsigned int line2, unsigned 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,

	unsigned int line1, unsigned int count1,

	unsigned int line2, unsigned int count2)

{

	unsigned 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 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_DIFF_ALGORITHM_MASK;

	return xdl_fall_back_diff(index->env, &xpp,

				  line1, count1, line2, count2);

}

static int histogram_diff(

	xpparam_t const *xpp, xdfenv_t *env,

	unsigned int line1, unsigned int count1,

	unsigned int line2, unsigned int count2)

{

	struct histindex index;

	struct region lcs;

	size_t 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;

	GITERR_CHECK_ALLOC_MULTIPLY(&sz, 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) {

			while (count1--)

				env->xdf1.rchg[line1++ - 1] = 1;

			while (count2--)

				env->xdf2.rchg[line2++ - 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)

{

	if (xdl_prepare_env(file1, file2, xpp, env) < 0)

		return -1;

	return histogram_diff(xpp, env,

		env->xdf1.dstart + 1, env->xdf1.dend - env->xdf1.dstart + 1,

		env->xdf2.dstart + 1, env->xdf2.dend - env->xdf2.dstart + 1);

}