/*	$Id: db.c,v 1.1 2011/11/09 01:24:23 kristaps Exp $ */
/*
 * Copyright (c) 2011 Kristaps Dzonsons <kristaps@bsd.lv>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
#include <assert.h>
#include <fcntl.h>
#include <regex.h>
#include <stdarg.h>
#include <stdlib.h>
#include <string.h>

#ifdef __linux__
# include <db_185.h>
#else
# include <db.h>
#endif

#include "apropos.h"
#include "mandoc.h"

static	DB	*btree_open(void);
static	int	 btree_read(const DBT *, const struct mchars *, char **);
static	DB	*index_open(void);
static	int	 index_read(const DBT *, const DBT *, 
			const struct mchars *, struct rec *);
static	void	 norm_string(const char *,
			const struct mchars *, char **);
static	size_t	 norm_utf8(unsigned int, char[7]);

/*
 * Open the keyword mandoc-db database.
 */
static DB *
btree_open(void)
{
	BTREEINFO	 info;
	DB		*db;

	memset(&info, 0, sizeof(BTREEINFO));
	info.flags = R_DUP;

	db = dbopen("mandoc.db", O_RDONLY, 0, DB_BTREE, &info);
	if (NULL != db) 
		return(db);

	return(NULL);
}

/*
 * Read a keyword from the database and normalise it.
 * Return 0 if the database is insane, else 1.
 */
static int
btree_read(const DBT *v, const struct mchars *mc, char **buf)
{

	/* Sanity: are we nil-terminated? */

	assert(v->size > 0);
	if ('\0' != ((char *)v->data)[(int)v->size - 1])
		return(0);

	norm_string((char *)v->data, mc, buf);
	return(1);
}

/*
 * Take a Unicode codepoint and produce its UTF-8 encoding.
 * This isn't the best way to do this, but it works.
 * The magic numbers are from the UTF-8 packaging.  
 * They're not as scary as they seem: read the UTF-8 spec for details.
 */
static size_t
norm_utf8(unsigned int cp, char out[7])
{
	size_t		 rc;

	rc = 0;

	if (cp <= 0x0000007F) {
		rc = 1;
		out[0] = (char)cp;
	} else if (cp <= 0x000007FF) {
		rc = 2;
		out[0] = (cp >> 6  & 31) | 192;
		out[1] = (cp       & 63) | 128;
	} else if (cp <= 0x0000FFFF) {
		rc = 3;
		out[0] = (cp >> 12 & 15) | 224;
		out[1] = (cp >> 6  & 63) | 128;
		out[2] = (cp       & 63) | 128;
	} else if (cp <= 0x001FFFFF) {
		rc = 4;
		out[0] = (cp >> 18 & 7) | 240;
		out[1] = (cp >> 12 & 63) | 128;
		out[2] = (cp >> 6  & 63) | 128;
		out[3] = (cp       & 63) | 128;
	} else if (cp <= 0x03FFFFFF) {
		rc = 5;
		out[0] = (cp >> 24 & 3) | 248;
		out[1] = (cp >> 18 & 63) | 128;
		out[2] = (cp >> 12 & 63) | 128;
		out[3] = (cp >> 6  & 63) | 128;
		out[4] = (cp       & 63) | 128;
	} else if (cp <= 0x7FFFFFFF) {
		rc = 6;
		out[0] = (cp >> 30 & 1) | 252;
		out[1] = (cp >> 24 & 63) | 128;
		out[2] = (cp >> 18 & 63) | 128;
		out[3] = (cp >> 12 & 63) | 128;
		out[4] = (cp >> 6  & 63) | 128;
		out[5] = (cp       & 63) | 128;
	} else
		return(0);

	out[rc] = '\0';
	return(rc);
}

/*
 * Normalise strings from the index and database.
 * These strings are escaped as defined by mandoc_char(7) along with
 * other goop in mandoc.h (e.g., soft hyphens).
 * This function normalises these into a nice UTF-8 string.
 * Returns 0 if the database is fucked.
 */
static void
norm_string(const char *val, const struct mchars *mc, char **buf)
{
	size_t		  sz, bsz;
	char		  utfbuf[7];
	const char	 *seq, *cpp;
	int		  len, u, pos;
	enum mandoc_esc	  esc;
	static const char res[] = { '\\', '\t', 
				ASCII_NBRSP, ASCII_HYPH, '\0' };

	/* Pre-allocate by the length of the input */

	bsz = strlen(val) + 1;
	*buf = mandoc_realloc(*buf, bsz);
	pos = 0;

	while ('\0' != *val) {
		/*
		 * Halt on the first escape sequence.
		 * This also halts on the end of string, in which case
		 * we just copy, fallthrough, and exit the loop.
		 */
		if ((sz = strcspn(val, res)) > 0) {
			memcpy(&(*buf)[pos], val, sz);
			pos += (int)sz;
			val += (int)sz;
		}

		if (ASCII_HYPH == *val) {
			(*buf)[pos++] = '-';
			val++;
			continue;
		} else if ('\t' == *val || ASCII_NBRSP == *val) {
			(*buf)[pos++] = ' ';
			val++;
			continue;
		} else if ('\\' != *val)
			break;

		/* Read past the slash. */

		val++;
		u = 0;

		/*
		 * Parse the escape sequence and see if it's a
		 * predefined character or special character.
		 */

		esc = mandoc_escape(&val, &seq, &len);
		if (ESCAPE_ERROR == esc)
			break;

		/* 
		 * XXX - this just does UTF-8, but we need to know
		 * beforehand whether we should do text substitution.
		 */

		switch (esc) {
		case (ESCAPE_SPECIAL):
			if (0 != (u = mchars_spec2cp(mc, seq, len)))
				break;
			/* FALLTHROUGH */
		default:
			continue;
		}

		/*
		 * If we have a Unicode codepoint, try to convert that
		 * to a UTF-8 byte string.
		 */

		cpp = utfbuf;
		if (0 == (sz = norm_utf8(u, utfbuf)))
			continue;

		/* Copy the rendered glyph into the stream. */

		sz = strlen(cpp);
		bsz += sz;

		*buf = mandoc_realloc(*buf, bsz);

		memcpy(&(*buf)[pos], cpp, sz);
		pos += (int)sz;
	}

	(*buf)[pos] = '\0';
}

/*
 * Open the filename-index mandoc-db database.
 * Returns NULL if opening failed.
 */
static DB *
index_open(void)
{
	DB		*db;

	db = dbopen("mandoc.index", O_RDONLY, 0, DB_RECNO, NULL);
	if (NULL != db)
		return(db);

	return(NULL);
}

/*
 * Safely unpack from an index file record into the structure.
 * Returns 1 if an entry was unpacked, 0 if the database is insane.
 */
static int
index_read(const DBT *key, const DBT *val, 
		const struct mchars *mc, struct rec *rec)
{
	size_t		 left;
	char		*np, *cp;

#define	INDEX_BREAD(_dst) \
	do { \
		if (NULL == (np = memchr(cp, '\0', left))) \
			return(0); \
		norm_string(cp, mc, &(_dst)); \
		left -= (np - cp) + 1; \
		cp = np + 1; \
	} while (/* CONSTCOND */ 0)

	left = val->size;
	cp = (char *)val->data;

	rec->rec = *(recno_t *)key->data;

	INDEX_BREAD(rec->file);
	INDEX_BREAD(rec->cat);
	INDEX_BREAD(rec->title);
	INDEX_BREAD(rec->arch);
	INDEX_BREAD(rec->desc);
	return(1);
}

/*
 * Search the mandocdb database for the regular expression "q".
 * Filter out by "opts".
 * Call "res" with the results, which may be zero.
 */
void
apropos_search(const struct opts *opts, const char *q, void *arg, 
		void (*res)(struct rec *, size_t, void *))
{
	int		 i, len, root, leaf;
	regex_t		 reg;
	DBT		 key, val;
	DB		*btree, *idx;
	struct mchars	*mc;
	int		 ch;
	char		*buf;
	recno_t		 rec;
	struct rec	*recs;
	struct rec	 srec;

	root	= -1;
	leaf	= -1;
	btree	= NULL;
	idx	= NULL;
	mc	= NULL;
	buf	= NULL;
	recs	= NULL;
	len	= 0;

	memset(&srec, 0, sizeof(struct rec));

	if (NULL != q && '\0' == *q)
		q = NULL;

	ch = REG_EXTENDED | REG_NOSUB | 
		(OPTS_INSENS & opts->flags ? REG_ICASE : 0);

	/* XXX: error out with bad regexp? */

	if (NULL == q || regcomp(&reg, q, ch)) {
		(*res)(NULL, 0, arg);
		return;
	}

	mc = mchars_alloc();

	/* XXX: return fact that we've errored? */

	if (NULL == (btree = btree_open())) 
		goto out;
	if (NULL == (idx = index_open())) 
		goto out;

	while (0 == (ch = (*btree->seq)(btree, &key, &val, R_NEXT))) {
		/* 
		 * Low-water mark for key and value.
		 * The key must have something in it, and the value must
		 * have the correct tags/recno mix.
		 */
		if (key.size < 2 || 8 != val.size) 
			break;

		if ( ! (*(int32_t *)val.data & opts->types))
			continue;

		if ( ! btree_read(&key, mc, &buf))
			break;
		if (regexec(&reg, buf, 0, NULL, 0))
			continue;

		memcpy(&rec, val.data + 4, sizeof(recno_t));

		/*
		 * O(log n) scan for prior records.  Since a record
		 * number is unbounded, this has decent performance over
		 * a complex hash function.
		 */

		for (leaf = root; leaf >= 0; )
			if (rec > recs[leaf].rec && recs[leaf].rhs >= 0)
				leaf = recs[leaf].rhs;
			else if (rec < recs[leaf].rec && recs[leaf].lhs >= 0)
				leaf = recs[leaf].lhs;
			else 
				break;

		if (leaf >= 0 && recs[leaf].rec == rec)
			continue;

		/*
		 * Now we actually extract the manpage's metadata from
		 * the index database.
		 */

		key.data = &rec;
		key.size = sizeof(recno_t);

		if (0 != (*idx->get)(idx, &key, &val, 0))
			break;

		srec.lhs = srec.rhs = -1;
		if ( ! index_read(&key, &val, mc, &srec))
			break;

		if (opts->cat && strcasecmp(opts->cat, srec.cat))
			continue;
		if (opts->arch && strcasecmp(opts->arch, srec.arch))
			continue;

		recs = mandoc_realloc
			(recs, (len + 1) * sizeof(struct rec));

		memcpy(&recs[len], &srec, sizeof(struct rec));

		/* Append to our tree. */

		if (leaf >= 0) {
			if (rec > recs[leaf].rec)
				recs[leaf].rhs = len;
			else
				recs[leaf].lhs = len;
		} else
			root = len;
		
		memset(&srec, 0, sizeof(struct rec));
		len++;
	}

	if (1 == ch)
		(*res)(recs, len, arg);

	/* XXX: else?  corrupt database error? */
out:
	for (i = 0; i < len; i++) {
		free(recs[i].file);
		free(recs[i].cat);
		free(recs[i].title);
		free(recs[i].arch);
		free(recs[i].desc);
	}

	free(srec.file);
	free(srec.cat);
	free(srec.title);
	free(srec.arch);
	free(srec.desc);

	if (mc)
		mchars_free(mc);
	if (btree)
		(*btree->close)(btree);
	if (idx)
		(*idx->close)(idx);

	free(buf);
	free(recs);
	regfree(&reg);
}