*** DONE git: post-commit hook for determining large number of deleted lines in Org-mode :blog:emacs:pim:diy:software:
CLOSED: [2014-08-20 Wed 18:34]
:PROPERTIES:
:CREATED:  [2014-08-20 Wed 18:24]
:ID: 2014-08-20-org-losses-determining-post-commit
:END:
:LOGBOOK:
- State "DONE"       from "DONE"       [2023-09-02 Sat 09:20]
- State "DONE"       from "DONE"       [2020-01-01 Wed 22:41]
- State "DONE"       from "NEXT"       [2014-08-20 Wed 18:34]
:END:

- Updates
  - 2020-01-01: Modified version using =appendorgheading=
  - 2023-09-02: Updated link to gitwatch repository

Maybe you have faced the very same issue: when large [[http://orgmode.org][Org mode]]
hierarchies are folded, it might happen that you overwrite or delete
large parts of your Org mode file without noticing.

This is not a big deal if you happen to have your Org mode files
within a [[http://git-scm.com/][git]] repository. All changes to my Org mode files even get
committed automatically using [[https://github.com/gitwatch/gitwatch][gitwatch]]. Everything that happened to
your Org mode files can be revoked. However, you have to *recognize*
the deleted lines in order to be able to restore them.

And this is where this small trick can help you: using the [[http://git-scm.com/book/en/Customizing-Git-Git-Hooks][post-commit
hook]] below, you get a warning on your daily agenda when you check in a
commit that deleted more than a given number of lines.

**** Implementation

In order to make it work, you have to adopt the script below. Please
change the content of ~OUTFILE~ to a file which is part of your
~org-agenda-files~. Any warning message generated by the script gets
appended to it. With a recurring time-stamp (of the commit), you can
not miss the message: it is placed on your daily agenda.

You might also want to adopt the value of ~THRESHOLD~. Its value
represents the number of lines that might get deleted within a single
file without any warning.

#+BEGIN_EXAMPLE
#!/bin/sh
#
# An example hook script that is called after a successful
# commit is made.
#
# To enable this hook, rename this file to "post-commit".

## current/last commit:
CURRENT_HASH=`git rev-parse HEAD`

## the commit before:
PREVIOUS_HASH=`git rev-parse HEAD^1`

## the file where the message(s) are being written to:
OUTFILE="${HOME}/org/errors_orgmode_commits.org"

## number of lines that are OK to be deleted in one single file:
THRESHOLD=250


MESSAGE="** commit ${CURRENT_HASH} deleted more than ${THRESHOLD} lines in a file!"

DETAILS="#+BEGIN_SRC sh :results output
cd ${HOME}/org
echo \"commit ${CURRENT_HASH}\"
git diff --stat \"${PREVIOUS_HASH}\" \"${CURRENT_HASH}\"
#+END_SRC"


## manual test with:
##  git diff --stat `git rev-parse HEAD^1` `git rev-parse HEAD`

git diff --numstat "${PREVIOUS_HASH}" "${CURRENT_HASH}" | \
	cut -f 2 | \
	while read line
	do test "$line" -gt "${THRESHOLD}" && \
	   echo "${MESSAGE}\n<`date '+%Y-%m-%d %H:%M'` +1d>\n\n${DETAILS}\n" >> \
		"${OUTFILE}"; \
	done

#end
#+END_EXAMPLE

So when you recognize a warning on your agenda, click on it and
optionally do a ~C-c C-c~ on the babel snippet which is below the
heading. It gives your details on the commit.

After you have resolved the issue, just delete the heading of the
resolved error in the error Org mode file manually.

**** Implementation Using =appendorgheading=

Using the method described [[id:2019-12-31-appendorgheading][in this article]], the post-commit hook looks
like this:

: #!/bin/sh
: #
: # An example hook script that is called after a successful
: # commit is made.
: #
: # To enable this hook, rename this file to "post-commit".
:
: ## current/last commit:
: CURRENT_HASH=$(git rev-parse HEAD)
:
: ## the commit before:
: PREVIOUS_HASH=$(git rev-parse HEAD^1)
:
: ## number of lines that are OK to be deleted in one single file:
: THRESHOLD=200
:
: TMPFILE="$(mktemp)"
:
: TITLE="commit ${CURRENT_HASH} deleted more than ${THRESHOLD} lines in a file!"
: echo "#+BEGIN_SRC sh
: gitk ${CURRENT_HASH}
: #+END_SRC
:
: #+BEGIN_EXAMPLE
: `cd ${HOME}/org ; git diff --stat \"${PREVIOUS_HASH}\" \"${CURRENT_HASH}\"`
: #+END_EXAMPLE" > "${TMPFILE}"
:
: ## manual test with:
: ##  git diff --stat `git rev-parse HEAD^1` `git rev-parse HEAD`
:
: git diff --numstat "${PREVIOUS_HASH}" "${CURRENT_HASH}" | \
:         cut -f 2 | \
:         while read line
:         do test "$line" -gt "${THRESHOLD}" && \
:             /usr/local/bin/appendorgheading --title "${TITLE}" --filecontent "${TMPFILE}"
:         done
:
: rm "${TMPFILE}"
: #end