From efcc4b981d2a10ac3b10522c596f8bf9ddff6ff9 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Thu, 22 Feb 2024 16:38:14 -0800
Subject: Implement autocs mode.

* cdlog.sh (cdlog_autocs): New variable.
(cdlog.chdir): Implement autocs logic, if enabled.
(cdlog.mcd): Use Bash dynamic scoping to override
the cdlog_autocs variable false; we don't want mcd
to have swapping semantics regardless of autocs
mode; the user must use the distinct command mcs.

* README.md: Documented.
---
 README.md | 10 ++++++++++
 cdlog.sh  | 19 +++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/README.md b/README.md
index c6bf5d8..7c7bd3f 100644
--- a/README.md
+++ b/README.md
@@ -72,6 +72,16 @@ When one or more persisted session are present, `cdlog`'s initialization
 mentions this, suggesting that the `cdr` command may be used to recover
 to one of the sessions.
 
+## `autocs` mode
+
+The variable `cdlog_autocs`, whose default value is `y` (enabled)
+controls `autocs` mode. In `autocs` mode, whenever the
+`cd`/`cdlog.chdir` command successfully changes to a new directory,
+and that directory already occurs in the FIFO, then the previous
+current directory is placed into the FIFO, overwriting that entry.
+Effectively, the original current directory is swapped with the
+FIFO entry as if using the `cs <n>` command.
+
 ## How is this better?
 
 * It's not hard-coded C code inside the shell; it consists of a small amount of
diff --git a/cdlog.sh b/cdlog.sh
index 59368f9..017a9f0 100644
--- a/cdlog.sh
+++ b/cdlog.sh
@@ -1,5 +1,9 @@
 # License at bottom.
 
+# Configuration variables
+
+cdlog_autocs=${cdlog_autocs-y}    # cd behaves like cs if match
+
 # Update after FIFO change.
 cdlog.update()
 {
@@ -142,11 +146,25 @@ cdlog.recover()
 cdlog.chdir()
 {
   local cur=$PWD
+  local i=10
 
   if command cd "$@" && [ "$PWD" != "$cur" ]; then
     # only if we successfully change to a different
     # directory do the following
 
+    if [ $cdlog_autocs ] ; then
+      local d=("" "$c1" "$c2" "$c3" "$c4" "$c5" "$c6" "$c7" "$c8" "$c9")
+      unset d[0]
+
+      for ((i = 1; i <= 9; i++)); do
+        if [ "${d[$i]}" = "$PWD" ] ; then
+          d[$i]=$cur
+          cdlog.args "${d[@]}"
+          return 0
+        fi
+      done
+    fi
+
     c9=$c8; c8=$c7; c7=$c6
     c6=$c5; c5=$c4; c4=$c3
     c3=$c2; c2=$c1
@@ -253,6 +271,7 @@ cdlog.mcd()
   local res=1
   local i
   local d=("" "$c1" "$c2" "$c3" "$c4" "$c5" "$c6" "$c7" "$c8" "$c9")
+  local cdlog_autocs= # override to off; mcd doesn't do autocs
 
   if [ $# -gt 0 ] && [ "$1" = -s ] ; then
     swap=y
-- 
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