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line.c

/*
 * Copyright (C) 1984-2000  Mark Nudelman
 *
 * 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 about less, or for information on how to 
 * contact the author, see the README file.
 */


/*
 * Routines to manipulate the "line buffer".
 * The line buffer holds a line of output as it is being built
 * in preparation for output to the screen.
 */

#include "less.h"

#define IS_CONT(c)  (((c) & 0xC0) == 0x80)
#define LINENUM_WIDTH   8       /* Chars to use for line number */

/* Buffer which holds the current output line */
public char linebuf[LINEBUF_SIZE];
public int size_linebuf = sizeof(linebuf);

public int cshift;            /* Current left-shift of output line buffer */
public int hshift;            /* Desired left-shift of output line buffer */

static char attr[LINEBUF_SIZE];     /* Extension of linebuf to hold attributes */
static int curr;        /* Index into linebuf */
static int column;            /* Printable length, accounting for
                           backspaces, etc. */
static int overstrike;        /* Next char should overstrike previous char */
static int is_null_line;      /* There is no current line */
static int lmargin;           /* Left margin */
static char pendc;
static POSITION pendpos;
static char *end_ansi_chars;

static int do_append();

extern int bs_mode;
extern int tabstop;
extern int linenums;
extern int ctldisp;
extern int twiddle;
extern int binattr;
extern int status_col;
extern int auto_wrap, ignaw;
extern int bo_s_width, bo_e_width;
extern int ul_s_width, ul_e_width;
extern int bl_s_width, bl_e_width;
extern int so_s_width, so_e_width;
extern int sc_width, sc_height;
extern int utf_mode;
extern POSITION start_attnpos;
extern POSITION end_attnpos;

/*
 * Initialize from environment variables.
 */
      public void
init_line()
{
      end_ansi_chars = lgetenv("LESSANSIENDCHARS");
      if (end_ansi_chars == NULL || *end_ansi_chars == '\0')
            end_ansi_chars = "m";
}

/*
 * Rewind the line buffer.
 */
      public void
prewind()
{
      curr = 0;
      column = 0;
      overstrike = 0;
      is_null_line = 0;
      pendc = '\0';
      lmargin = 0;
      if (status_col)
            lmargin += 1;
      if (linenums == OPT_ONPLUS)
            lmargin += LINENUM_WIDTH+1;
}

/*
 * Insert the line number (of the given position) into the line buffer.
 */
      public void
plinenum(pos)
      POSITION pos;
{
      register int lno;
      register int i;

      if (linenums == OPT_ONPLUS)
      {
            /*
             * Get the line number and put it in the current line.
             * {{ Note: since find_linenum calls forw_raw_line,
             *    it may seek in the input file, requiring the caller 
             *    of plinenum to re-seek if necessary. }}
             * {{ Since forw_raw_line modifies linebuf, we must
             *    do this first, before storing anything in linebuf. }}
             */
            lno = find_linenum(pos);
      }

      /*
       * Display a status column if the -J option is set.
       */
      if (status_col)
      {
            linebuf[curr] = ' ';
            if (start_attnpos != NULL_POSITION &&
                pos >= start_attnpos && pos < end_attnpos)
                  attr[curr] = AT_STANDOUT;
            else
                  attr[curr] = 0;
            curr++;
            column++;
      }
      /*
       * Display the line number at the start of each line
       * if the -N option is set.
       */
      if (linenums == OPT_ONPLUS)
      {
            sprintf(&linebuf[curr], "%*d", LINENUM_WIDTH, lno);
            column += LINENUM_WIDTH;
            for (i = 0;  i < LINENUM_WIDTH;  i++)
                  attr[curr++] = 0;
      }
      /*
       * Append enough spaces to bring us to the lmargin.
       */
      while (column < lmargin)
      {
            linebuf[curr] = ' ';
            attr[curr++] = AT_NORMAL;
            column++;
      }
}

/*
 *
 */
      static int
utf_len(char *s, int len)
{
      int ulen = 0;

      while (*s != '\0' && len > 0)
      {
            if (!IS_CONT(*s))
                  len--;
            s++;
            ulen++;
      }
      while (IS_CONT(*s))
      {
            s++;
            ulen++;
      }
      return (ulen);
}

/*
 * Shift the input line left.
 * This means discarding N printable chars at the start of the buffer.
 */
      static void
pshift(shift)
      int shift;
{
      int i;
      int real_shift;

      if (shift > column - lmargin)
            shift = column - lmargin;
      if (shift > curr - lmargin)
            shift = curr - lmargin;

      if (!utf_mode)
            real_shift = shift;
      else
      {
            real_shift = utf_len(linebuf + lmargin, shift);
            if (real_shift > curr)
                  real_shift = curr;
      }
      for (i = 0;  i < curr - real_shift;  i++)
      {
            linebuf[lmargin + i] = linebuf[lmargin + i + real_shift];
            attr[lmargin + i] = attr[lmargin + i + real_shift];
      }
      column -= shift;
      curr -= real_shift;
      cshift += shift;
}

/*
 * Return the printing width of the start (enter) sequence
 * for a given character attribute.
 */
      static int
attr_swidth(a)
      int a;
{
      switch (a)
      {
      case AT_BOLD:           return (bo_s_width);
      case AT_UNDERLINE:      return (ul_s_width);
      case AT_BLINK:          return (bl_s_width);
      case AT_STANDOUT: return (so_s_width);
      }
      return (0);
}

/*
 * Return the printing width of the end (exit) sequence
 * for a given character attribute.
 */
      static int
attr_ewidth(a)
      int a;
{
      switch (a)
      {
      case AT_BOLD:           return (bo_e_width);
      case AT_UNDERLINE:      return (ul_e_width);
      case AT_BLINK:          return (bl_e_width);
      case AT_STANDOUT: return (so_e_width);
      }
      return (0);
}

/*
 * Return the printing width of a given character and attribute,
 * if the character were added to the current position in the line buffer.
 * Adding a character with a given attribute may cause an enter or exit
 * attribute sequence to be inserted, so this must be taken into account.
 */
      static int
pwidth(c, a)
      int c;
      int a;
{
      register int w;

      if (utf_mode && IS_CONT(c))
            return (0);

      if (c == '\b')
            /*
             * Backspace moves backwards one position.
             */
            return (-1);

      if (control_char(c))
            /*
             * Control characters do unpredicatable things,
             * so we don't even try to guess; say it doesn't move.
             * This can only happen if the -r flag is in effect.
             */
            return (0);

      /*
       * Other characters take one space,
       * plus the width of any attribute enter/exit sequence.
       */
      w = 1;
      if (curr > 0 && attr[curr-1] != a)
            w += attr_ewidth(attr[curr-1]);
      if (a && (curr == 0 || attr[curr-1] != a))
            w += attr_swidth(a);
      return (w);
}

/*
 * Delete the previous character in the line buffer.
 */
      static void
backc()
{
      curr--;
      column -= pwidth(linebuf[curr], attr[curr]);
}

/*
 * Are we currently within a recognized ANSI escape sequence?
 */
      static int
in_ansi_esc_seq()
{
      int i;

      /*
       * Search backwards for either an ESC (which means we ARE in a seq);
       * or an end char (which means we're NOT in a seq).
       */
      for (i = curr-1;  i >= 0;  i--)
      {
            if (linebuf[i] == ESC)
                  return (1);
            if (strchr(end_ansi_chars, linebuf[i]) != NULL)
                  return (0);
      }
      return (0);
}

/*
 * Append a character and attribute to the line buffer.
 */
      static int
storec(c, a, pos)
      int c;
      int a;
      POSITION pos;
{
      register int w;

#if HILITE_SEARCH
      if (is_hilited(pos, pos+1, 0))
            /*
             * This character should be highlighted.
             * Override the attribute passed in.
             */
            a = AT_STANDOUT;
#endif
      if (ctldisp == OPT_ONPLUS && in_ansi_esc_seq())
            w = 0;
      else
            w = pwidth(c, a);
      if (ctldisp != OPT_ON && column + w + attr_ewidth(a) > sc_width)
            /*
             * Won't fit on screen.
             */
            return (1);

      if (curr >= sizeof(linebuf)-2)
            /*
             * Won't fit in line buffer.
             */
            return (1);

      /*
       * Special handling for "magic cookie" terminals.
       * If an attribute enter/exit sequence has a printing width > 0,
       * and the sequence is adjacent to a space, delete the space.
       * We just mark the space as invisible, to avoid having too
       * many spaces deleted.
       * {{ Note that even if the attribute width is > 1, we
       *    delete only one space.  It's not worth trying to do more.
       *    It's hardly worth doing this much. }}
       */
      if (curr > 0 && a != AT_NORMAL && 
            linebuf[curr-1] == ' ' && attr[curr-1] == AT_NORMAL &&
            attr_swidth(a) > 0)
      {
            /*
             * We are about to append an enter-attribute sequence
             * just after a space.  Delete the space.
             */
            attr[curr-1] = AT_INVIS;
            column--;
      } else if (curr > 0 && attr[curr-1] != AT_NORMAL && 
            attr[curr-1] != AT_INVIS && c == ' ' && a == AT_NORMAL &&
            attr_ewidth(attr[curr-1]) > 0)
      {
            /*
             * We are about to append a space just after an 
             * exit-attribute sequence.  Delete the space.
             */
            a = AT_INVIS;
            column--;
      }
      /* End of magic cookie handling. */

      linebuf[curr] = c;
      attr[curr] = a;
      column += w;
      return (0);
}

/*
 * Append a character to the line buffer.
 * Expand tabs into spaces, handle underlining, boldfacing, etc.
 * Returns 0 if ok, 1 if couldn't fit in buffer.
 */
      public int
pappend(c, pos)
      register int c;
      POSITION pos;
{
      int r;

      if (pendc)
      {
            if (do_append(pendc, pendpos))
                  /*
                   * Oops.  We've probably lost the char which
                   * was in pendc, since caller won't back up.
                   */
                  return (1);
            pendc = '\0';
      }

      if (c == '\r' && bs_mode == BS_SPECIAL)
      {
            /*
             * Don't put the CR into the buffer until we see 
             * the next char.  If the next char is a newline,
             * discard the CR.
             */
            pendc = c;
            pendpos = pos;
            return (0);
      }

      r = do_append(c, pos);
      /*
       * If we need to shift the line, do it.
       * But wait until we get to at least the middle of the screen,
       * so shifting it doesn't affect the chars we're currently
       * pappending.  (Bold & underline can get messed up otherwise.)
       */
      if (cshift < hshift && column > sc_width / 2)
            pshift(hshift - cshift);
      return (r);
}

      static int
do_append(c, pos)
      int c;
      POSITION pos;
{
      register char *s;
      register int a;

#define     STOREC(c,a) \
      if (storec((c),(a),pos)) return (1); else curr++

      if (c == '\b')
      {
            switch (bs_mode)
            {
            case BS_NORMAL:
                  STOREC(c, AT_NORMAL);
                  break;
            case BS_CONTROL:
                  goto do_control_char;
            case BS_SPECIAL:
                  if (curr == 0)
                        break;
                  backc();
                  overstrike = 1;
                  break;
            }
      } else if (overstrike)
      {
            /*
             * Overstrike the character at the current position
             * in the line buffer.  This will cause either 
             * underline (if a "_" is overstruck), 
             * bold (if an identical character is overstruck),
             * or just deletion of the character in the buffer.
             */
            overstrike = 0;
            if ((char)c == linebuf[curr])
                  STOREC(linebuf[curr], AT_BOLD);
            else if (c == '_')
                  STOREC(linebuf[curr], AT_UNDERLINE);
            else if (linebuf[curr] == '_')
                  STOREC(c, AT_UNDERLINE);
            else if (control_char(c))
                  goto do_control_char;
            else
                  STOREC(c, AT_NORMAL);
      } else if (c == '\t') 
      {
            /*
             * Expand a tab into spaces.
             */
            if (tabstop == 0)
                  tabstop = 1;
            switch (bs_mode)
            {
            case BS_CONTROL:
                  goto do_control_char;
            case BS_NORMAL:
            case BS_SPECIAL:
                  do
                  {
                        STOREC(' ', AT_NORMAL);
                  } while (((column + cshift - lmargin) % tabstop) != 0);
                  break;
            }
      } else if (control_char(c))
      {
      do_control_char:
            if (ctldisp == OPT_ON || (ctldisp == OPT_ONPLUS && c == ESC))
            {
                  /*
                   * Output as a normal character.
                   */
                  STOREC(c, AT_NORMAL);
            } else 
            {
                  /*
                   * Convert to printable representation.
                   */
                  s = prchar(c);  
                  a = binattr;

                  /*
                   * Make sure we can get the entire representation
                   * of the character on this line.
                   */
                  if (column + (int) strlen(s) + 
                      attr_swidth(a) + attr_ewidth(a) > sc_width)
                        return (1);

                  for ( ;  *s != 0;  s++)
                        STOREC(*s, a);
            }
      } else
      {
            STOREC(c, AT_NORMAL);
      }

      return (0);
}

/*
 * Terminate the line in the line buffer.
 */
      public void
pdone(endline)
      int endline;
{
      if (pendc && (pendc != '\r' || !endline))
            /*
             * If we had a pending character, put it in the buffer.
             * But discard a pending CR if we are at end of line
             * (that is, discard the CR in a CR/LF sequence).
             */
            (void) do_append(pendc, pendpos);

      /*
       * Make sure we've shifted the line, if we need to.
       */
      if (cshift < hshift)
            pshift(hshift - cshift);

      /*
       * Add a newline if necessary,
       * and append a '\0' to the end of the line.
       */
      if (column < sc_width || !auto_wrap || ignaw || ctldisp == OPT_ON)
      {
            linebuf[curr] = '\n';
            attr[curr] = AT_NORMAL;
            curr++;
      }
      linebuf[curr] = '\0';
      attr[curr] = AT_NORMAL;
      /*
       * If we are done with this line, reset the current shift.
       */
      if (endline)
            cshift = 0;
}

/*
 * Get a character from the current line.
 * Return the character as the function return value,
 * and the character attribute in *ap.
 */
      public int
gline(i, ap)
      register int i;
      register int *ap;
{
      char *s;
      
      if (is_null_line)
      {
            /*
             * If there is no current line, we pretend the line is
             * either "~" or "", depending on the "twiddle" flag.
             */
            *ap = AT_BOLD;
            s = (twiddle) ? "~\n" : "\n";
            return (s[i]);
      }

      *ap = attr[i];
      return (linebuf[i] & 0377);
}

/*
 * Indicate that there is no current line.
 */
      public void
null_line()
{
      is_null_line = 1;
      cshift = 0;
}

/*
 * Analogous to forw_line(), but deals with "raw lines":
 * lines which are not split for screen width.
 * {{ This is supposed to be more efficient than forw_line(). }}
 */
      public POSITION
forw_raw_line(curr_pos, linep)
      POSITION curr_pos;
      char **linep;
{
      register char *p;
      register int c;
      POSITION new_pos;

      if (curr_pos == NULL_POSITION || ch_seek(curr_pos) ||
            (c = ch_forw_get()) == EOI)
            return (NULL_POSITION);

      p = linebuf;

      for (;;)
      {
            if (c == '\n' || c == EOI)
            {
                  new_pos = ch_tell();
                  break;
            }
            if (p >= &linebuf[sizeof(linebuf)-1])
            {
                  /*
                   * Overflowed the input buffer.
                   * Pretend the line ended here.
                   * {{ The line buffer is supposed to be big
                   *    enough that this never happens. }}
                   */
                  new_pos = ch_tell() - 1;
                  break;
            }
            *p++ = c;
            c = ch_forw_get();
      }
      *p = '\0';
      if (linep != NULL)
            *linep = linebuf;
      return (new_pos);
}

/*
 * Analogous to back_line(), but deals with "raw lines".
 * {{ This is supposed to be more efficient than back_line(). }}
 */
      public POSITION
back_raw_line(curr_pos, linep)
      POSITION curr_pos;
      char **linep;
{
      register char *p;
      register int c;
      POSITION new_pos;

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

      p = &linebuf[sizeof(linebuf)];
      *--p = '\0';

      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 == EOI)
            {
                  /*
                   * 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_zero();
                  break;
            }
            if (p <= linebuf)
            {
                  /*
                   * Overflowed the input buffer.
                   * Pretend the line ended here.
                   */
                  new_pos = ch_tell() + 1;
                  break;
            }
            *--p = c;
      }
      if (linep != NULL)
            *linep = p;
      return (new_pos);
}

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