feat(fancy-ctrl-z): Toggle between last two suspended jobs in every case

Allows using the fancy-ctrl-z functionality of toggling between the last
two suspended jobs (`%+` and `%-`, respectively) even if there are more
than two jobs suspended.

Made the whole implementation more robust, especially in case Ctrl-Z is
pressed with an existing non-empty prompt buffer.

Fixed a bug where jobs with multiple different working directories would
cause the back-and-forth functionality to not work.

plugins/fancy-ctrl-z/README.md

@@ -1,8 +1,8 @@
 # fancy-ctrl-z
 
-Allows pressing Ctrl-Z again to switch back to the most recently backgrounded
-job. If there are precisely two backgrounded jobs, Ctrl-Z will toggle between
-them, bringing the other one back.
+Allows pressing <kbd>Ctrl</kbd>-<kbd>Z</kbd> is an empty prompt to bring to the
+foreground the only suspended job, or, if there are more than one such jobs, to
+switch between the two most recently suspended ones.
 
 To use it, add `fancy-ctrl-z` to the `plugins` array in your `.zshrc` file:
 
@@ -12,15 +12,29 @@ plugins=(... fancy-ctrl-z)
 
 ## Motivation
 
-I frequently need to execute random commands in my shell. To achieve it I pause
-Vim by pressing Ctrl-Z, type command and press fg<Enter> to switch back to Vim.
-The fg part really hurts me. I just wanted to hit Ctrl-Z once again to get back
-to Vim. I could not find a solution, so I developed one on my own that
-works wonderfully with ZSH.
+I frequently need to execute random commands in my shell.
+To achieve it, I often pause Vim by pressing <kbd>Ctrl</kbd>-<kbd>Z</kbd>, type
+a command and then would use `fg`<kbd>↵ Enter</kbd> to switch back to Vim.
+Having to type in the `fg` part really hurt me.
+I just wanted to hit <kbd>Ctrl</kbd>-<kbd>Z</kbd> once again to get back to Vim.
+I could not find a solution, so I developed one on my own that works wonderfully
+with Zsh.
 
-Source: http://sheerun.net/2014/03/21/how-to-boost-your-vim-productivity/
+Switching between the last two suspended jobs is motivated by both TV remotes
+that had such feature, and tools like `cd -` and `git checkout -` that switch
+between the current and the second most recent state (directory, branch, etc.).
+Sometimes, you have your Vim where code is changed, and another longer-running
+process (e.g., a `tail` on some logs, or a Python interpreter) where you want
+to test or observe your changes.
+There is no point in time where you would "have the editor open" and "have the
+program open" together, and the workflow clearly mandates always switching
+back and forth between the two.
+That's why the original version of _fancy-ctrl-z_ was extended with this "even
+fancier" behaviour, because the original version would've opened Vim back again
+and again.
 
-Credits:
-- original idea by [@sheerun](https://github.com/sheerun)
-- added to OMZ by [@mbologna](https://github.com/mbologna)
-- two-job switching added by [@Whisperity](https://github.com/Whisperity)
+## Credits
+
+- Original idea by [@sheerun](https://github.com/sheerun), http://sheerun.net/2014/03/21/how-to-boost-your-vim-productivity
+- Added to OMZ by [@mbologna](https://github.com/mbologna)
+- Two-job switching added by [@Whisperity](https://github.com/Whisperity)

plugins/fancy-ctrl-z/fancy-ctrl-z.plugin.zsh

@@ -1,16 +1,38 @@
 fancy-ctrl-z () {
-  if [[ $#BUFFER -eq 0 ]]; then
-    BUFFER="fg"
+  local -i hascmd=$(( ${#BUFFER} > 0 ))
+  local -a sjobs=("${(@f)$(jobs -s)}")
+  local -a opts=("${(@f)$(setopt)}")
+  local -i isverbose=$opts[(Ie)verbose]
+  # In Zsh, arrays are 1-indexed, and an empty array has size 1, not 0.
+  # So we must check the first element's length to see whether it describes a
+  # suspended job.
+  local -i nsjobs="${#${(@)sjobs}}"
+  local -i hassjob=$(( ${#sjobs[1]} > 0 ))
+  local -i hassjobs=$(( nsjobs >= 2 ))
+  # Whether the ^Z action will result in a side effect to the terminal.
+  local -i sideeffect=$(( hassjob || hassjobs || isverbose ))
 
-    IFS=$'\n' local num_jobs=($(jobs))
-    if [[ "${#num_jobs[@]}" -eq 2 ]]; then
-      BUFFER="fg %-"
-    fi
-
-    zle accept-line -w
-  else
+  if (( hascmd && sideeffect )); then
+    # Save the current command.
+    # It will be restored after the side-effect is over, e.g., if the
+    # foregrounded job is put to the background again.
     zle push-input -w
-    zle clear-screen -w
+  fi
+
+  if (( hassjobs )); then
+    # Multiple suspended jobs: foreground the second-to-last suspended job.
+    BUFFER="fg %-"
+    zle accept-line -w
+  elif (( hassjob )); then
+    # Single suspended job: foreground it.
+    # "fg %-" would result in an error as the only suspended job is the
+    # last one, which is referenced by "fg" or "fg %+".
+    BUFFER="fg %+"
+    zle accept-line -w
+  elif (( isverbose )); then
+    # No suspended jobs, but verbose mode, let show the "fg: no current job".
+    BUFFER="fg"
+    zle accept-line -w
   fi
 }