#!/bin/sh

## General information on Git post-checkout hooks:
#
# This hook is invoked when a git checkout is run after having updated
# the worktree. The hook is given three parameters: the ref of the
# previous HEAD, the ref of the new HEAD (which may or may not have
# changed), and a flag indicating whether the checkout was a branch
# checkout (changing branches, flag=1) or a file checkout (retrieving
# a file from the index, flag=0). This hook cannot affect the outcome
# of git checkout.
#
# It is also run after git clone, unless the --no-checkout (-n) option
# is used. The first parameter given to the hook is the null-ref, the
# second the ref of the new HEAD and the flag is always 1.
#
# This hook can be used to perform repository validity checks,
# auto-display differences from the previous HEAD if different, or set
# working dir metadata properties.

head_old=$1
head_new=$2
flag=$3

# We are interested only in branch checkouts.
if [ "$flag" != "1" ]; then
    exit 0
fi

# n.b. pwd will be this working copy's root directory.
root=$(pwd)

# printf "$0: %s - %s - %s\n" "$@"
# ls -l "$root"/.git/BISECT*

if [ -f "$root/.git/BISECT_LOG" ]; then
    # Currently bisecting.  If the ONLY thing which has happened so
    # far is the "git bisect start" command, then mark our always-good
    # commits as "good".  (This will append to the log, after which
    # the following test will fail.)
    tail -1 "$root/.git/BISECT_LOG" | grep -q '^git bisect .*\bstart\b' \
        && [ -f "$root/etc/git-bisect-good-refs" ] \
        && cp "$root/etc/git-bisect-good-refs" "$root/.git/BISECT_EMACS_GOOD_REFS" \
        && printf %s\\n "Marking known-good references in Emacs repository." \
        && cat "$root/.git/BISECT_EMACS_GOOD_REFS" | xargs git bisect good \
        && git bisect log
else
    # Not currently bisecting; just tidy up.
    [ -f "$root/.git/BISECT_EMACS_GOOD_REFS" ] \
        && rm "$root/.git/BISECT_EMACS_GOOD_REFS"
fi

exit 0

# etc/git-bisect-good-refs is a file containing this commit ref:
# 806734c1b1f433de43d59d9a5e3a1e89d64315f6