/*
 * High level routines dealing with getting lines of input
 * from the file being viewed.
 *
 * When we speak of "lines" here, we mean PRINTABLE lines;
 * lines processed with respect to the screen width.
 * We use the term "raw line" to refer to lines simply
 * delimited by newlines; not processed with respect to screen width.
 */

#include "less.h"


extern int squeeze;
extern char *line;

/*
 * Get the next line.
 * A "current" position is passed and a "new" position is returned.
 * The current position is the position of the first character of
 * a line.  The new position is the position of the first character
 * of the NEXT line.  The line obtained is the line starting at curr_pos.
 */
#ifdef __STDC__
POSITION forw_line (POSITION curr_pos)
#else
        public POSITION
forw_line(curr_pos)
        POSITION curr_pos;
#endif
{
        POSITION new_pos;
        register int c;

        if (curr_pos == NULL_POSITION || ch_seek(curr_pos))
                return (NULL_POSITION);

        c = ch_forw_get();
        if (c == EOF)
                return (NULL_POSITION);

        prewind();
        for (;;)
        {
                if (c == '\n' || c == EOF)
                {
                        /*
                         * End of the line.
                         */
                        new_pos = ch_tell();
                        break;
                }

                /*
                 * Append the char to the line and get the next char.
                 */
                if (pappend(c))
                {
                        /*
                         * The char won't fit in the line; the line
                         * is too long to print in the screen width.
                         * End the line here.
                         */
                        new_pos = ch_tell() - 1;
                        break;
                }
                c = ch_forw_get();
        }
        (void) pappend('\0');

        if (squeeze && *line == '\0')
        {
                /*
                 * This line is blank.
                 * Skip down to the last contiguous blank line
                 * and pretend it is the one which we are returning.
                 */
                while ((c = ch_forw_get()) == '\n')
                        ;
                if (c != EOF)
                        (void) ch_back_get();
                new_pos = ch_tell();
        }

        return (new_pos);
}

/*
 * Get the previous line.
 * A "current" position is passed and a "new" position is returned.
 * The current position is the position of the first character of
 * a line.  The new position is the position of the first character
 * of the PREVIOUS line.  The line obtained is the one starting at new_pos.
 */
#ifdef __STDC__
POSITION back_line (POSITION curr_pos)
#else
        public POSITION
back_line(curr_pos)
        POSITION curr_pos;
#endif
{
        POSITION new_pos, begin_new_pos;
        int c;

        if (curr_pos == NULL_POSITION || curr_pos <= (POSITION)0 ||
                ch_seek(curr_pos-1))
                return (NULL_POSITION);

        if (squeeze)
        {
                /*
                 * Find out if the "current" line was blank.
                 */
                (void) ch_forw_get();   /* Skip the newline */
                c = ch_forw_get();      /* First char of "current" line */
                (void) ch_back_get();   /* Restore our position */
                (void) ch_back_get();

                if (c == '\n')
                {
                        /*
                         * The "current" line was blank.
                         * Skip over any preceeding blank lines,
                         * since we skipped them in forw_line().
                         */
                        while ((c = ch_back_get()) == '\n')
                                ;
                        if (c == EOF)
                                return (NULL_POSITION);
                        (void) ch_forw_get();
                }
        }

        /*
         * Scan backwards until we hit the beginning of the line.
         */
        for (;;)
        {
                c = ch_back_get();
                if (c == '\n')
                {
                        /*
                         * This is the newline ending the previous line.
                         * We have hit the beginning of the line.
                         */
                        new_pos = ch_tell() + 1;
                        break;
                }
                if (c == EOF)
                {
                        /*
                         * We have hit the beginning of the file.
                         * This must be the first line in the file.
                         * This must, of course, be the beginning of the line.
                         */
                        new_pos = ch_tell();
                        break;
                }
        }

        /*
         * Now scan forwards from the beginning of this line.
         * We keep discarding "printable lines" (based on screen width)
         * until we reach the curr_pos.
         *
         * {{ This algorithm is pretty inefficient if the lines
         *    are much longer than the screen width,
         *    but I don't know of any better way. }}
         */
        if (ch_seek(new_pos))
                return (NULL_POSITION);
    loop:
        begin_new_pos = new_pos;
        prewind();

        do
        {
                c = ch_forw_get();
                new_pos++;
                if (c == '\n')
                        break;
                if (pappend(c))
                {
                        /*
                         * Got a full printable line, but we haven't
                         * reached our curr_pos yet.  Discard the line
                         * and start a new one.
                         */
                        (void) pappend('\0');
                        (void) ch_back_get();
                        new_pos--;
                        goto loop;
                }
        } while (new_pos < curr_pos);

        (void) pappend('\0');

        return (begin_new_pos);
}