New feature: trigger mode.

Prototype: does substring searching only: no regex.

2 files changed, 119 insertions, 27 deletions

diff --git a/pw.1 b/pw.1
index 23c02a4..5fe9000 100644
--- a/pw.1
+++ b/pw.1
@@ -177,6 +177,34 @@ and
 also terminate colon mode without executing a command. Colon commands
 are documented in the COLON COMMANDS section below.
 
+.IP \fB/\fP\fIpattern\fP
+Activate head trigger mode if a non-empty
+.I pattern
+is specified, or else cancel trigger mode if an empty pattern is
+specified. Under head trigger mode,
+the display refreshes only when the most recent line in the FIFO
+matches the specified
+.IR pattern .
+That line at the head of the FIFO is the one which will appear at
+the bottom of the display, since newer lines appear at the bottom
+and scroll out toward the top.
+In head trigger mode, the status string
+.BI "TRIG (/" pattern ")"
+appears, showing the pattern preceded by a slash.
+
+.IP \fB?\fP\fIpattern\fP
+Activate tail trigger mode if a non-empty
+.I pattern
+is specified, or else cancel trigger mode if an empty pattern is
+specified. Under tail trigger mode,
+the display refreshes only when the least recent line in the FIFO
+matches the specified
+.IR pattern .
+That line at the tail of the FIFO is the one which will appear at
+the top of the display.  In tail trigger mode, the status string
+.BI "TRIG (?" pattern ")"
+appears, showing the pattern preceded by a question mark.
+
 .SH COLON COMMANDS
 
 First, some general remarks. Display refresh doesn't pause during the editing
diff --git a/pw.c b/pw.c
index 7f39674..9e2a64a 100644
--- a/pw.c
+++ b/pw.c
@@ -13,9 +13,12 @@
 #include <sys/time.h>
 
 enum status_flags {
-  stat_dirty = 1,
-  stat_eof = 2,
-  stat_susp = 4
+  stat_dirty = 1,   // display needs refresh
+  stat_eof = 2,     // end of data reached
+  stat_susp = 4,    // display refresh suspended
+  stat_htmode = 8,  // head trigger mode
+  stat_ttmode = 16, // tail trigger mode
+  stat_trgrd = 32   // triggered flag
 };
 
 typedef struct dstr {
@@ -28,6 +31,7 @@ typedef struct dstr {
 
 char **snapshot;
 int snaplines;
+char *trigpat;
 
 static void panic(const char *fmt, ...)
 {
@@ -88,6 +92,14 @@ static char *dsgrow(char *str, size_t len)
   return ds->str;
 }
 
+static char *dsdup(char *str)
+{
+  size_t len = strlen(str);
+  char *copy = dsgrow(0, len);
+  memcpy(copy, str, len);
+  return copy;
+}
+
 static char *addch(char *line, int ch)
 {
   size_t len = line ? dslen(line) : 0;
@@ -178,9 +190,13 @@ static void drawstatus(unsigned stat, char *cmd)
 {
   if (cmd) {
     printf("%s", cmd);
-  } else if ((stat & (stat_eof | stat_susp))) {
+  } else if ((stat & (stat_eof | stat_susp | stat_htmode | stat_ttmode))) {
     if ((stat & stat_eof))
       printf("EOF ");
+    else if ((stat & stat_htmode))
+      printf("TRIG (/%s) ", trigpat);
+    else if ((stat & stat_ttmode))
+      printf("TRIG (?%s) ", trigpat);
     if ((stat & stat_susp))
       printf("SUSPENDED ");
   } else {
@@ -192,7 +208,10 @@ static void drawstatus(unsigned stat, char *cmd)
 static void redraw(char **circbuf, int nlines, int hpos,
                    int columns, unsigned stat, char *cmd)
 {
-  if ((stat & stat_susp) == 0) {
+  if ((stat & stat_susp) == 0 &&
+      (stat & (stat_htmode | stat_trgrd)) != stat_htmode &&
+      (stat & (stat_ttmode | stat_trgrd)) != stat_ttmode)
+  {
     if (snapshot) {
       for (int i = 0; i < snaplines; i++)
        dsdrop(snapshot[i]);
@@ -204,7 +223,9 @@ static void redraw(char **circbuf, int nlines, int hpos,
       snapshot[i] = dsref(circbuf[i]);
     }
   } else {
-    clrline();
+    printf("\r\033[%dA\033[J", snaplines);
+    for (int i = 0; i < snaplines; i++)
+      drawline(snapshot[i], hpos, columns);
   }
   drawstatus(stat, cmd);
 }
@@ -283,10 +304,13 @@ int main(int argc, char **argv)
   struct termios tty_saved, tty_new;
   struct winsize ws = { 0 };
   int columns = 80;
-  enum kbd_state { kbd_cmd, kbd_esc, kbd_bkt, kbd_exit, kbd_colon, kbd_result };
+  enum kbd_state {
+    kbd_cmd, kbd_esc, kbd_bkt, kbd_exit,
+    kbd_colon, kbd_result, kbd_htrig, kbd_ttrig
+  };
   int auto_quit = 1;
   int exit_status = EXIT_FAILURE;
-  char cmdbuf[100], *colcmd = 0;
+  char cmdbuf[100], *curcmd = 0;
 
   if (fd < 0)
     panic("unable to obtain input file descriptor");
@@ -361,11 +385,16 @@ int main(int argc, char **argv)
   for (unsigned stat = stat_dirty, hpos = 0, kbd_state = kbd_cmd, lasttime = ~0U;
        kbd_state != kbd_exit ;)
   {
+    int force = 0;
     struct pollfd pe[2] = {
       { .fd = ttyfd, .events = POLLIN | POLLHUP | POLLERR },
       { .fd = fd, .events = POLLIN | POLLHUP | POLLERR },
     };
 
+    if (stat & stat_trgrd)
+      force = 1;
+
+    if (!force)
     {
       struct timeval tv;
       unsigned now;
@@ -374,38 +403,49 @@ int main(int argc, char **argv)
       now = (((unsigned) tv.tv_sec)%1000000)*1000 + tv.tv_usec/1000;
       if (lasttime == ~0U || now - lasttime > (unsigned) long_interval) {
         if ((stat & stat_dirty) && nlines == maxlines)
-          redraw(circbuf, nlines, hpos, columns, stat, colcmd);
+          force = 1;
         lasttime = now;
         stat &= ~stat_dirty;
       }
     }
 
+    if (force) {
+      redraw(circbuf, nlines, hpos, columns, stat, curcmd);
+      stat &= ~(stat_dirty | stat_trgrd);
+    }
+
     if (poll(pe, ((stat & stat_eof)) ? 1 : 2, poll_interval) <= 0) {
       if ((stat & stat_dirty) && nlines == maxlines) {
-        redraw(circbuf, nlines, hpos, columns, stat, colcmd);
+        redraw(circbuf, nlines, hpos, columns, stat, curcmd);
         stat &= ~stat_dirty;
       }
       if (kbd_state == kbd_esc || kbd_state == kbd_result) {
         kbd_state = kbd_cmd;
-        colcmd = 0;
+        curcmd = 0;
         clrline();
-        drawstatus(stat, colcmd);
+        drawstatus(stat, curcmd);
       }
     } else {
       if ((stat & stat_eof) == 0 && pe[1].revents) {
         if ((line = getln(stdin))) {
+          if ((stat & stat_htmode))
+            if (strstr(line, trigpat))
+              stat |= stat_trgrd;
           if (nlines == maxlines) {
             dsdrop(circbuf[0]);
             memmove(circbuf, circbuf + 1, (nlines - 1) * sizeof *circbuf);
             circbuf[nlines - 1] = line;
             stat |= stat_dirty;
+            if ((stat & stat_ttmode))
+              if (strstr(circbuf[0], trigpat))
+                stat |= stat_trgrd;
           } else {
             circbuf[nlines++] = line;
             if ((stat & stat_susp) == 0) {
               snapshot[snaplines++] = dsref(line);
               clrline();
               drawline(line, hpos, columns);
-              drawstatus(stat, colcmd);
+              drawstatus(stat, curcmd);
             }
           }
         } else {
@@ -413,7 +453,7 @@ int main(int argc, char **argv)
             kbd_state = kbd_exit;
           else
             stat |= stat_eof;
-          redraw(circbuf, nlines, hpos, columns, stat, colcmd);
+          redraw(circbuf, nlines, hpos, columns, stat, curcmd);
           stat |= stat_eof;
           stat &= ~stat_dirty;
           if (!ferror(stdin))
@@ -431,7 +471,7 @@ int main(int argc, char **argv)
           switch (ch) {
           case 'q': case 3:
             kbd_state = kbd_exit;
-            if ((stat & (stat_eof | stat_susp))) {
+            if ((stat & (stat_eof | stat_susp | stat_htmode | stat_ttmode))) {
               clrline();
               fflush(stdout);
             }
@@ -467,7 +507,19 @@ int main(int argc, char **argv)
             kbd_state = kbd_colon;
             cmdbuf[0] = ch;
             cmdbuf[1] = 0;
-            colcmd = cmdbuf;
+            curcmd = cmdbuf;
+            break;
+          case '/':
+            kbd_state = kbd_htrig;
+            cmdbuf[0] = ch;
+            cmdbuf[1] = 0;
+            curcmd = cmdbuf;
+            break;
+          case '?':
+            kbd_state = kbd_ttrig;
+            cmdbuf[0] = ch;
+            cmdbuf[1] = 0;
+            curcmd = cmdbuf;
             break;
           }
           break;
@@ -491,24 +543,35 @@ int main(int argc, char **argv)
           }
           break;
         case kbd_colon:
+        case kbd_htrig:
+        case kbd_ttrig:
           switch (ch) {
           case 27: case 13: case 3:
             kbd_state = kbd_cmd;
             stat |= stat_dirty;
-            if (ch == 13 && cmdbuf[1]) {
-              execute(cmdbuf);
-              stat &= ~stat_dirty;
-              kbd_state = kbd_result;
-              break;
+            if (ch == 13) {
+              if (kbd_state == kbd_colon && cmdbuf[1]) {
+                execute(cmdbuf);
+                stat &= ~stat_dirty;
+                kbd_state = kbd_result;
+                break;
+              } else if (cmdbuf[1]) {
+                dsdrop(trigpat);
+                trigpat = dsdup(cmdbuf + 1);
+                stat &= ~(stat_htmode | stat_ttmode);
+                stat |= (kbd_state == kbd_htrig) ? stat_htmode : stat_ttmode;
+              } else {
+                stat &= ~(stat_htmode | stat_ttmode);
+              }
             }
-            colcmd = 0;
+            curcmd = 0;
             break;
           case 8: case 127:
             {
               size_t len = strlen(cmdbuf);
               if (len == 1) {
                 kbd_state = kbd_cmd;
-                colcmd = 0;
+                curcmd = 0;
                 stat |= stat_dirty;
               } else {
                 cmdbuf[--len] = 0;
@@ -543,18 +606,19 @@ int main(int argc, char **argv)
         case kbd_result:
           kbd_state = kbd_cmd;
           stat |= stat_dirty;
-          colcmd = 0;
+          curcmd = 0;
           break;
         case kbd_exit:
           break;
         }
 
         if ((stat & stat_dirty)) {
-          redraw(circbuf, nlines, hpos, columns, stat, colcmd);
+          redraw(circbuf, nlines, hpos, columns, stat, curcmd);
           stat &= ~stat_dirty;
-        } else if (kbd_state == kbd_colon || kbd_state == kbd_result) {
+        } else switch (kbd_state) {
+        case kbd_colon: case kbd_htrig: case kbd_ttrig: case kbd_result:
           clrline();
-          drawstatus(stat, colcmd);
+          drawstatus(stat, curcmd);
         }
       }
     }