/*
 * Copyright (C) 1984-2012  Mark Nudelman
 * Modified for use with illumos by Garrett D'Amore.
 * Copyright 2014 Garrett D'Amore <garrett@damore.org>
 *
 * You may distribute under the terms of either the GNU General Public
 * License or the Less License, as specified in the README file.
 *
 * For more information, see the README file.
 */

/*
 * Routines to search a file for a pattern.
 */

#include "charset.h"
#include "less.h"
#include "pattern.h"
#include "position.h"

#define MINPOS(a, b)    (((a) < (b)) ? (a) : (b))
#define MAXPOS(a, b)    (((a) > (b)) ? (a) : (b))

extern int how_search;
extern int caseless;
extern int linenums;
extern int sc_height;
extern int jump_sline;
extern int bs_mode;
extern int ctldisp;
extern int status_col;
extern void *const ml_search;
extern off_t start_attnpos;
extern off_t end_attnpos;
extern int utf_mode;
extern int screen_trashed;
extern int hilite_search;
extern int size_linebuf;
extern int squished;
extern int can_goto_line;
static int hide_hilite;
static off_t prep_startpos;
static off_t prep_endpos;
static int is_caseless;
static int is_ucase_pattern;

struct hilite {
        struct hilite *hl_next;
        off_t hl_startpos;
        off_t hl_endpos;
};
static struct hilite hilite_anchor = { NULL, -1, -1 };
static struct hilite filter_anchor = { NULL, -1, -1 };
#define hl_first        hl_next

/*
 * These are the static variables that represent the "remembered"
 * search pattern and filter pattern.
 */
struct pattern_info {
        regex_t *compiled;
        char *text;
        int search_type;
};

#define info_compiled(info) ((info)->compiled)

static struct pattern_info search_info;
static struct pattern_info filter_info;

/*
 * Are there any uppercase letters in this string?
 */
static int
is_ucase(char *str)
{
        wchar_t ch;
        int len;

        for (; *str != '\0'; str += len) {
                if ((len = mbtowc(&ch, str, MB_CUR_MAX)) == -1) {
                        mbtowc(NULL, NULL, MB_CUR_MAX);
                        len = 1;
                } else if (iswupper(ch))
                        return (1);
        }
        return (0);
}

/*
 * Compile and save a search pattern.
 */
static int
set_pattern(struct pattern_info *info, char *pattern, int search_type)
{
        if (pattern == NULL)
                info->compiled = NULL;
        else if (compile_pattern(pattern, search_type, &info->compiled) < 0)
                return (-1);
        /* Pattern compiled successfully; save the text too. */
        free(info->text);
        info->text = NULL;
        if (pattern != NULL)
                info->text = estrdup(pattern);
        info->search_type = search_type;

        /*
         * Ignore case if -I is set OR
         * -i is set AND the pattern is all lowercase.
         */
        is_ucase_pattern = is_ucase(pattern);
        if (is_ucase_pattern && caseless != OPT_ONPLUS)
                is_caseless = 0;
        else
                is_caseless = caseless;
        return (0);
}

/*
 * Discard a saved pattern.
 */
static void
clear_pattern(struct pattern_info *info)
{
        free(info->text);
        info->text = NULL;
        uncompile_pattern(&info->compiled);
}

/*
 * Initialize saved pattern to nothing.
 */
static void
init_pattern(struct pattern_info *info)
{
        info->compiled = NULL;
        info->text = NULL;
        info->search_type = 0;
}

/*
 * Initialize search variables.
 */
void
init_search(void)
{
        init_pattern(&search_info);
        init_pattern(&filter_info);
}

/*
 * Determine which text conversions to perform before pattern matching.
 */
static int
get_cvt_ops(void)
{
        int ops = 0;
        if (is_caseless || bs_mode == BS_SPECIAL) {
                if (is_caseless)
                        ops |= CVT_TO_LC;
                if (bs_mode == BS_SPECIAL)
                        ops |= CVT_BS;
                if (bs_mode != BS_CONTROL)
                        ops |= CVT_CRLF;
        } else if (bs_mode != BS_CONTROL) {
                ops |= CVT_CRLF;
        }
        if (ctldisp == OPT_ONPLUS)
                ops |= CVT_ANSI;
        return (ops);
}

/*
 * Is there a previous (remembered) search pattern?
 */
static int
prev_pattern(struct pattern_info *info)
{
        if ((info->search_type & SRCH_NO_REGEX) == 0)
                return (info->compiled != NULL);
        return (info->text != NULL);
}

/*
 * Repaint the hilites currently displayed on the screen.
 * Repaint each line which contains highlighted text.
 * If on==0, force all hilites off.
 */
void
repaint_hilite(int on)
{
        int slinenum;
        off_t pos;
        int save_hide_hilite;

        if (squished)
                repaint();

        save_hide_hilite = hide_hilite;
        if (!on) {
                if (hide_hilite)
                        return;
                hide_hilite = 1;
        }

        if (!can_goto_line) {
                repaint();
                hide_hilite = save_hide_hilite;
                return;
        }

        for (slinenum = TOP; slinenum < TOP + sc_height-1; slinenum++) {
                pos = position(slinenum);
                if (pos == -1)
                        continue;
                (void) forw_line(pos);
                goto_line(slinenum);
                put_line();
        }
        lower_left();
        hide_hilite = save_hide_hilite;
}

/*
 * Clear the attn hilite.
 */
void
clear_attn(void)
{
        int slinenum;
        off_t old_start_attnpos;
        off_t old_end_attnpos;
        off_t pos;
        off_t epos;
        int moved = 0;

        if (start_attnpos == -1)
                return;
        old_start_attnpos = start_attnpos;
        old_end_attnpos = end_attnpos;
        start_attnpos = end_attnpos = -1;

        if (!can_goto_line) {
                repaint();
                return;
        }
        if (squished)
                repaint();

        for (slinenum = TOP; slinenum < TOP + sc_height-1; slinenum++) {
                pos = position(slinenum);
                if (pos == -1)
                        continue;
                epos = position(slinenum+1);
                if (pos < old_end_attnpos &&
                    (epos == -1 || epos > old_start_attnpos)) {
                        (void) forw_line(pos);
                        goto_line(slinenum);
                        put_line();
                        moved = 1;
                }
        }
        if (moved)
                lower_left();
}

/*
 * Hide search string highlighting.
 */
void
undo_search(void)
{
        if (!prev_pattern(&search_info)) {
                error("No previous regular expression", NULL);
                return;
        }
        hide_hilite = !hide_hilite;
        repaint_hilite(1);
}

/*
 * Clear the hilite list.
 */
static void
clr_hlist(struct hilite *anchor)
{
        struct hilite *hl;
        struct hilite *nexthl;

        for (hl = anchor->hl_first; hl != NULL; hl = nexthl) {
                nexthl = hl->hl_next;
                free(hl);
        }
        anchor->hl_first = NULL;
        prep_startpos = prep_endpos = -1;
}

void
clr_hilite(void)
{
        clr_hlist(&hilite_anchor);
}

static void
clr_filter(void)
{
        clr_hlist(&filter_anchor);
}

/*
 * Should any characters in a specified range be highlighted?
 */
        static int
is_hilited_range(off_t pos, off_t epos)
{
        struct hilite *hl;

        /*
         * Look at each highlight and see if any part of it falls in the range.
         */
        for (hl = hilite_anchor.hl_first; hl != NULL; hl = hl->hl_next) {
                if (hl->hl_endpos > pos &&
                    (epos == -1 || epos > hl->hl_startpos))
                        return (1);
        }
        return (0);
}

/*
 * Is a line "filtered" -- that is, should it be hidden?
 */
int
is_filtered(off_t pos)
{
        struct hilite *hl;

        if (ch_getflags() & CH_HELPFILE)
                return (0);

        /*
         * Look at each filter and see if the start position
         * equals the start position of the line.
         */
        for (hl = filter_anchor.hl_first; hl != NULL; hl = hl->hl_next) {
                if (hl->hl_startpos == pos)
                        return (1);
        }
        return (0);
}

/*
 * Should any characters in a specified range be highlighted?
 * If nohide is nonzero, don't consider hide_hilite.
 */
int
is_hilited(off_t pos, off_t epos, int nohide, int *p_matches)
{
        int match;

        if (p_matches != NULL)
                *p_matches = 0;

        if (!status_col &&
            start_attnpos != -1 &&
            pos < end_attnpos &&
            (epos == -1 || epos > start_attnpos))
                /*
                 * The attn line overlaps this range.
                 */
                return (1);

        match = is_hilited_range(pos, epos);
        if (!match)
                return (0);

        if (p_matches != NULL)
                /*
                 * Report matches, even if we're hiding highlights.
                 */
                *p_matches = 1;

        if (hilite_search == 0)
                /*
                 * Not doing highlighting.
                 */
                return (0);

        if (!nohide && hide_hilite)
                /*
                 * Highlighting is hidden.
                 */
                return (0);

        return (1);
}

/*
 * Add a new hilite to a hilite list.
 */
static void
add_hilite(struct hilite *anchor, struct hilite *hl)
{
        struct hilite *ihl;

        /*
         * Hilites are sorted in the list; find where new one belongs.
         * Insert new one after ihl.
         */
        for (ihl = anchor; ihl->hl_next != NULL; ihl = ihl->hl_next)
        {
                if (ihl->hl_next->hl_startpos > hl->hl_startpos)
                        break;
        }

        /*
         * Truncate hilite so it doesn't overlap any existing ones
         * above and below it.
         */
        if (ihl != anchor)
                hl->hl_startpos = MAXPOS(hl->hl_startpos, ihl->hl_endpos);
        if (ihl->hl_next != NULL)
                hl->hl_endpos = MINPOS(hl->hl_endpos,
                    ihl->hl_next->hl_startpos);
        if (hl->hl_startpos >= hl->hl_endpos) {
                /*
                 * Hilite was truncated out of existence.
                 */
                free(hl);
                return;
        }
        hl->hl_next = ihl->hl_next;
        ihl->hl_next = hl;
}

/*
 * Highlight every character in a range of displayed characters.
 */
static void
create_hilites(off_t linepos, int start_index, int end_index, int *chpos)
{
        struct hilite *hl;
        int i;

        /* Start the first hilite. */
        hl = ecalloc(1, sizeof (struct hilite));
        hl->hl_startpos = linepos + chpos[start_index];

        /*
         * Step through the displayed chars.
         * If the source position (before cvt) of the char is one more
         * than the source pos of the previous char (the usual case),
         * just increase the size of the current hilite by one.
         * Otherwise (there are backspaces or something involved),
         * finish the current hilite and start a new one.
         */
        for (i = start_index+1; i <= end_index; i++) {
                if (chpos[i] != chpos[i-1] + 1 || i == end_index) {
                        hl->hl_endpos = linepos + chpos[i-1] + 1;
                        add_hilite(&hilite_anchor, hl);
                        /* Start new hilite unless this is the last char. */
                        if (i < end_index) {
                                hl = ecalloc(1, sizeof (struct hilite));
                                hl->hl_startpos = linepos + chpos[i];
                        }
                }
        }
}

/*
 * Make a hilite for each string in a physical line which matches
 * the current pattern.
 * sp,ep delimit the first match already found.
 */
static void
hilite_line(off_t linepos, char *line, int line_len, int *chpos,
    char *sp, char *ep)
{
        char *searchp;
        char *line_end = line + line_len;

        /*
         * sp and ep delimit the first match in the line.
         * Mark the corresponding file positions, then
         * look for further matches and mark them.
         * {{ This technique, of calling match_pattern on subsequent
         *    substrings of the line, may mark more than is correct
         *    if the pattern starts with "^".  This bug is fixed
         *    for those regex functions that accept a notbol parameter
         *    (currently POSIX, PCRE and V8-with-regexec2). }}
         */
        searchp = line;
        do {
                if (sp == NULL || ep == NULL)
                        return;

                create_hilites(linepos, (intptr_t)sp - (intptr_t)line,
                    (intptr_t)ep - (intptr_t)line, chpos);
                /*
                 * If we matched more than zero characters,
                 * move to the first char after the string we matched.
                 * If we matched zero, just move to the next char.
                 */
                if (ep > searchp)
                        searchp = ep;
                else if (searchp != line_end)
                        searchp++;
                else /* end of line */
                        break;
        } while (match_pattern(info_compiled(&search_info), search_info.text,
            searchp, (intptr_t)line_end - (intptr_t)searchp, &sp, &ep, 1,
            search_info.search_type));
}

/*
 * Change the caseless-ness of searches.
 * Updates the internal search state to reflect a change in the -i flag.
 */
void
chg_caseless(void)
{
        if (!is_ucase_pattern)
                /*
                 * Pattern did not have uppercase.
                 * Just set the search caselessness to the global caselessness.
                 */
                is_caseless = caseless;
        else
                /*
                 * Pattern did have uppercase.
                 * Discard the pattern; we can't change search caselessness now.
                 */
                clear_pattern(&search_info);
}

/*
 * Find matching text which is currently on screen and highlight it.
 */
static void
hilite_screen(void)
{
        struct scrpos scrpos;

        get_scrpos(&scrpos);
        if (scrpos.pos == -1)
                return;
        prep_hilite(scrpos.pos, position(BOTTOM_PLUS_ONE), -1);
        repaint_hilite(1);
}

/*
 * Change highlighting parameters.
 */
void
chg_hilite(void)
{
        /*
         * Erase any highlights currently on screen.
         */
        clr_hilite();
        hide_hilite = 0;

        if (hilite_search == OPT_ONPLUS)
                /*
                 * Display highlights.
                 */
                hilite_screen();
}

/*
 * Figure out where to start a search.
 */
static off_t
search_pos(int search_type)
{
        off_t pos;
        int linenum;

        if (empty_screen()) {
                /*
                 * Start at the beginning (or end) of the file.
                 * The empty_screen() case is mainly for
                 * command line initiated searches;
                 * for example, "+/xyz" on the command line.
                 * Also for multi-file (SRCH_PAST_EOF) searches.
                 */
                if (search_type & SRCH_FORW) {
                        pos = ch_zero();
                } else {
                        pos = ch_length();
                        if (pos == -1) {
                                (void) ch_end_seek();
                                pos = ch_length();
                        }
                }
                linenum = 0;
        } else {
                int add_one = 0;

                if (how_search == OPT_ON) {
                        /*
                         * Search does not include current screen.
                         */
                        if (search_type & SRCH_FORW)
                                linenum = BOTTOM_PLUS_ONE;
                        else
                                linenum = TOP;
                } else if (how_search == OPT_ONPLUS &&
                    !(search_type & SRCH_AFTER_TARGET)) {
                        /*
                         * Search includes all of displayed screen.
                         */
                        if (search_type & SRCH_FORW)
                                linenum = TOP;
                        else
                                linenum = BOTTOM_PLUS_ONE;
                } else {
                        /*
                         * Search includes the part of current screen beyond
                         * the jump target.
                         * It starts at the jump target (if searching
                         * backwards), or at the jump target plus one
                         * (if forwards).
                         */
                        linenum = jump_sline;
                        if (search_type & SRCH_FORW)
                                add_one = 1;
                }
                linenum = adjsline(linenum);
                pos = position(linenum);
                if (add_one)
                        pos = forw_raw_line(pos, NULL, NULL);
        }

        /*
         * If the line is empty, look around for a plausible starting place.
         */
        if (search_type & SRCH_FORW) {
                while (pos == -1) {
                        if (++linenum >= sc_height)
                                break;
                        pos = position(linenum);
                }
        } else {
                while (pos == -1) {
                        if (--linenum < 0)
                                break;
                        pos = position(linenum);
                }
        }
        return (pos);
}

/*
 * Search a subset of the file, specified by start/end position.
 */
static int
search_range(off_t pos, off_t endpos, int search_type, int matches,
    int maxlines, off_t *plinepos, off_t *pendpos)
{
        char *line;
        char *cline;
        int line_len;
        off_t linenum;
        char *sp, *ep;
        int line_match;
        int cvt_ops;
        int cvt_len;
        int *chpos;
        off_t linepos, oldpos;

        linenum = find_linenum(pos);
        oldpos = pos;
        for (;;) {
                /*
                 * Get lines until we find a matching one or until
                 * we hit end-of-file (or beginning-of-file if we're
                 * going backwards), or until we hit the end position.
                 */
                if (abort_sigs()) {
                        /*
                         * A signal aborts the search.
                         */
                        return (-1);
                }

                if ((endpos != -1 && pos >= endpos) ||
                    maxlines == 0) {
                        /*
                         * Reached end position without a match.
                         */
                        if (pendpos != NULL)
                                *pendpos = pos;
                        return (matches);
                }
                if (maxlines > 0)
                        maxlines--;

                if (search_type & SRCH_FORW) {
                        /*
                         * Read the next line, and save the
                         * starting position of that line in linepos.
                         */
                        linepos = pos;
                        pos = forw_raw_line(pos, &line, &line_len);
                        if (linenum != 0)
                                linenum++;
                } else {
                        /*
                         * Read the previous line and save the
                         * starting position of that line in linepos.
                         */
                        pos = back_raw_line(pos, &line, &line_len);
                        linepos = pos;
                        if (linenum != 0)
                                linenum--;
                }

                if (pos == -1) {
                        /*
                         * Reached EOF/BOF without a match.
                         */
                        if (pendpos != NULL)
                                *pendpos = oldpos;
                        return (matches);
                }

                /*
                 * If we're using line numbers, we might as well
                 * remember the information we have now (the position
                 * and line number of the current line).
                 * Don't do it for every line because it slows down
                 * the search.  Remember the line number only if
                 * we're "far" from the last place we remembered it.
                 */
                if (linenums && abs((int)(pos - oldpos)) > 2048)
                        add_lnum(linenum, pos);
                oldpos = pos;

                if (is_filtered(linepos))
                        continue;

                /*
                 * If it's a caseless search, convert the line to lowercase.
                 * If we're doing backspace processing, delete backspaces.
                 */
                cvt_ops = get_cvt_ops();
                cvt_len = cvt_length(line_len);
                cline = ecalloc(1, cvt_len);
                chpos = cvt_alloc_chpos(cvt_len);
                cvt_text(cline, line, chpos, &line_len, cvt_ops);

                /*
                 * Check to see if the line matches the filter pattern.
                 * If so, add an entry to the filter list.
                 */
                if ((search_type & SRCH_FIND_ALL) &&
                    prev_pattern(&filter_info)) {
                        int line_filter =
                            match_pattern(info_compiled(&filter_info),
                            filter_info.text, cline, line_len, &sp, &ep, 0,
                            filter_info.search_type);
                        if (line_filter) {
                                struct hilite *hl =
                                    ecalloc(1, sizeof (struct hilite));
                                hl->hl_startpos = linepos;
                                hl->hl_endpos = pos;
                                add_hilite(&filter_anchor, hl);
                        }
                }

                /*
                 * Test the next line to see if we have a match.
                 * We are successful if we either want a match and got one,
                 * or if we want a non-match and got one.
                 */
                if (prev_pattern(&search_info)) {
                        line_match = match_pattern(info_compiled(&search_info),
                            search_info.text, cline, line_len, &sp, &ep, 0,
                            search_type);
                        if (line_match) {
                                /*
                                 * Got a match.
                                 */
                                if (search_type & SRCH_FIND_ALL) {
                                        /*
                                         * We are supposed to find all matches
                                         * in the range.
                                         * Just add the matches in this line
                                         * to the hilite list and keep
                                         * searching.
                                         */
                                        hilite_line(linepos, cline, line_len,
                                            chpos, sp, ep);
                                } else if (--matches <= 0) {
                                        /*
                                         * Found the one match we're looking
                                         * for.  Return it.
                                         */
                                        if (hilite_search == OPT_ON) {
                                                /*
                                                 * Clear the hilite list and
                                                 * add only
                                                 * the matches in this one line.
                                                 */
                                                clr_hilite();
                                                hilite_line(linepos, cline,
                                                    line_len, chpos, sp, ep);
                                        }
                                        free(cline);
                                        free(chpos);
                                        if (plinepos != NULL)
                                                *plinepos = linepos;
                                        return (0);
                                }
                        }
                }
                free(cline);
                free(chpos);
        }
}

/*
 * search for a pattern in history. If found, compile that pattern.
 */
static int
hist_pattern(int search_type)
{
        char *pattern;

        set_mlist(ml_search, 0);
        pattern = cmd_lastpattern();
        if (pattern == NULL)
                return (0);

        if (set_pattern(&search_info, pattern, search_type) < 0)
                return (0);

        if (hilite_search == OPT_ONPLUS && !hide_hilite)
                hilite_screen();

        return (1);
}

/*
 * Search for the n-th occurrence of a specified pattern,
 * either forward or backward.
 * Return the number of matches not yet found in this file
 * (that is, n minus the number of matches found).
 * Return -1 if the search should be aborted.
 * Caller may continue the search in another file
 * if less than n matches are found in this file.
 */
int
search(int search_type, char *pattern, int n)
{
        off_t pos;

        if (pattern == NULL || *pattern == '\0') {
                /*
                 * A null pattern means use the previously compiled pattern.
                 */
                search_type |= SRCH_AFTER_TARGET;
                if (!prev_pattern(&search_info) && !hist_pattern(search_type)) {
                        error("No previous regular expression", NULL);
                        return (-1);
                }
                if ((search_type & SRCH_NO_REGEX) !=
                    (search_info.search_type & SRCH_NO_REGEX)) {
                        error("Please re-enter search pattern", NULL);
                        return (-1);
                }
                if (hilite_search == OPT_ON) {
                        /*
                         * Erase the highlights currently on screen.
                         * If the search fails, we'll redisplay them later.
                         */
                        repaint_hilite(0);
                }
                if (hilite_search == OPT_ONPLUS && hide_hilite) {
                        /*
                         * Highlight any matches currently on screen,
                         * before we actually start the search.
                         */
                        hide_hilite = 0;
                        hilite_screen();
                }
                hide_hilite = 0;
        } else {
                /*
                 * Compile the pattern.
                 */
                if (set_pattern(&search_info, pattern, search_type) < 0)
                        return (-1);
                if (hilite_search) {
                        /*
                         * Erase the highlights currently on screen.
                         * Also permanently delete them from the hilite list.
                         */
                        repaint_hilite(0);
                        hide_hilite = 0;
                        clr_hilite();
                }
                if (hilite_search == OPT_ONPLUS) {
                        /*
                         * Highlight any matches currently on screen,
                         * before we actually start the search.
                         */
                        hilite_screen();
                }
        }

        /*
         * Figure out where to start the search.
         */
        pos = search_pos(search_type);
        if (pos == -1) {
                /*
                 * Can't find anyplace to start searching from.
                 */
                if (search_type & SRCH_PAST_EOF)
                        return (n);
                /* repaint(); -- why was this here? */
                error("Nothing to search", NULL);
                return (-1);
        }

        n = search_range(pos, -1, search_type, n, -1, &pos, NULL);
        if (n != 0) {
                /*
                 * Search was unsuccessful.
                 */
                if (hilite_search == OPT_ON && n > 0)
                        /*
                         * Redisplay old hilites.
                         */
                        repaint_hilite(1);
                return (n);
        }

        if (!(search_type & SRCH_NO_MOVE)) {
                /*
                 * Go to the matching line.
                 */
                jump_loc(pos, jump_sline);
        }

        if (hilite_search == OPT_ON)
                /*
                 * Display new hilites in the matching line.
                 */
                repaint_hilite(1);
        return (0);
}


/*
 * Prepare hilites in a given range of the file.
 *
 * The pair (prep_startpos,prep_endpos) delimits a contiguous region
 * of the file that has been "prepared"; that is, scanned for matches for
 * the current search pattern, and hilites have been created for such matches.
 * If prep_startpos == -1, the prep region is empty.
 * If prep_endpos == -1, the prep region extends to EOF.
 * prep_hilite asks that the range (spos,epos) be covered by the prep region.
 */
void
prep_hilite(off_t spos, off_t epos, int maxlines)
{
        off_t nprep_startpos = prep_startpos;
        off_t nprep_endpos = prep_endpos;
        off_t new_epos;
        off_t max_epos;
        int result;
        int i;

/*
 * Search beyond where we're asked to search, so the prep region covers
 * more than we need.  Do one big search instead of a bunch of small ones.
 */
#define SEARCH_MORE (3*size_linebuf)

        if (!prev_pattern(&search_info) && !is_filtering())
                return;

        /*
         * If we're limited to a max number of lines, figure out the
         * file position we should stop at.
         */
        if (maxlines < 0) {
                max_epos = -1;
        } else {
                max_epos = spos;
                for (i = 0; i < maxlines; i++)
                        max_epos = forw_raw_line(max_epos, NULL, NULL);
        }

        /*
         * Find two ranges:
         * The range that we need to search (spos,epos); and the range that
         * the "prep" region will then cover (nprep_startpos,nprep_endpos).
         */

        if (prep_startpos == -1 ||
            (epos != -1 && epos < prep_startpos) ||
            spos > prep_endpos) {
                /*
                 * New range is not contiguous with old prep region.
                 * Discard the old prep region and start a new one.
                 */
                clr_hilite();
                clr_filter();
                if (epos != -1)
                        epos += SEARCH_MORE;
                nprep_startpos = spos;
        } else {
                /*
                 * New range partially or completely overlaps old prep region.
                 */
                if (epos != -1) {
                        if (epos > prep_endpos) {
                                /*
                                 * New range ends after old prep region.
                                 * Extend prep region to end at end of new
                                 * range.
                                 */
                                epos += SEARCH_MORE;

                        } else {
                                /*
                                 * New range ends within old prep region.
                                 * Truncate search to end at start of old prep
                                 * region.
                                 */
                                epos = prep_startpos;
                        }
                }

                if (spos < prep_startpos) {
                        /*
                         * New range starts before old prep region.
                         * Extend old prep region backwards to start at
                         * start of new range.
                         */
                        if (spos < SEARCH_MORE)
                                spos = 0;
                        else
                                spos -= SEARCH_MORE;
                        nprep_startpos = spos;
                } else { /* (spos >= prep_startpos) */
                        /*
                         * New range starts within or after old prep region.
                         * Trim search to start at end of old prep region.
                         */
                        spos = prep_endpos;
                }
        }

        if (epos != -1 && max_epos != -1 &&
            epos > max_epos)
                /*
                 * Don't go past the max position we're allowed.
                 */
                epos = max_epos;

        if (epos == -1 || epos > spos) {
                int search_type = SRCH_FORW | SRCH_FIND_ALL;
                search_type |= (search_info.search_type & SRCH_NO_REGEX);
                result = search_range(spos, epos, search_type, 0,
                    maxlines, NULL, &new_epos);
                if (result < 0)
                        return;
                if (prep_endpos == -1 || new_epos > prep_endpos)
                        nprep_endpos = new_epos;
        }
        prep_startpos = nprep_startpos;
        prep_endpos = nprep_endpos;
}

/*
 * Set the pattern to be used for line filtering.
 */
void
set_filter_pattern(char *pattern, int search_type)
{
        clr_filter();
        if (pattern == NULL || *pattern == '\0')
                clear_pattern(&filter_info);
        else
                (void) set_pattern(&filter_info, pattern, search_type);
        screen_trashed = 1;
}

/*
 * Is there a line filter in effect?
 */
int
is_filtering(void)
{
        if (ch_getflags() & CH_HELPFILE)
                return (0);
        return (prev_pattern(&filter_info));
}