#!/usr/bin/env bash
#
# Seek the working tree to a given commit.
# Copyright (c) Petr Baudis, 2005
#
# Seeking will bring the working tree from its current 'HEAD' to a given
# commit. Note that it changes just the 'HEAD' of the working tree, not
# the branch it is corresponding to. It will return to the 'HEAD' of
# the appropriate branch if passed no arguments.
#
# Therefore, for a quick excurse to the past of the 'master' branch:
#
#	$ cg-seek git-pasky-0.1
#	$ cg-diff this master	# will do the correct thing
#	$ cg-seek		# will restore what we had before
#
# For intuitiveness, specifying the branch name (`cg-seek master`) will do
# the right thing too. If you want to migrate your working tree to _another_
# branch, use `cg-clone` to create a new tree for the new branch, or
# `cg-switch` to also change your current tree to use the new branch.
#
# Note that during the time you are seeked out, commits, merges, and some
# other operations are blocked, since the next `cg-seek` or `cg-reset`
# invocation will happily wipe out their products silently. You can override
# this in the `cg-commit` command by passing it a '-f' parameter - this
# can be useful e.g. when you seeked to a commit which cannot be compiled
# and you want to commit a compilation fix, as long as you are aware that
# the commit of the fix will be rendered unreachable (you will be able to
# get back to it only if you remember its ID) at the moment you do next
# seek or a reset. If you want to save the commit, you can save it to
# a separate branch using `cg-switch -n`.
#
# Takes the target commit ID to seek to as an argument.
#
# NOTES
# -----
# The `cg-admin-uncommit` command is meant only for temporary excursions
# to the commit history. If you want to permanently switch your branch
# to a different commit id (forgetting its current contents), you can use
# the `cg-switch` command:
#
#	$ cg-switch -f -r COMMIT_ID CURRENT_HEAD_NAME
#
# Note that this command has some serious caveats! Please read the
# `cg-switch` documentation for details.

USAGE="cg-seek [COMMIT_ID]"
_git_requires_root=1

. "${COGITO_LIB}"cg-Xlib || exit 1

dstcommit="${ARGS[0]}"


[ -s "$_git/blocked" ] && grep -vq '^seeked from ' "$_git/blocked" && die "action blocked: $(cat "$_git/blocked")"

curcommit="$(cg-object-id -c)" || exit 1

if [ "$dstcommit" ] && [ "$dstcommit" != "$_git_head" ]; then
	seek_mode=away
	[ -s "$_git/head-name" ] && [ "$(git-symbolic-ref HEAD)" != "refs/heads/cg-seek-point" ] &&
		die "seeked away by some other tool, refusing to meddle (you can still use cg-seek without any arguments to unseek)"
	[ -s "$_git/refs/heads/$dstcommit" ] &&
		warn "seeking to a branch head; this is not for permanent switching, please see cg-switch"
else
	seek_mode=back
	dstcommit="$(cg-object-id -c "$_git_head")" || exit 1
fi

dstcommit="$(cg-object-id -c "$dstcommit")" || exit 1
if [ "$curcommit" != "$dstcommit" ]; then
	tree_timewarp --no-head-update "along" "please rollback" "$curcommit" "$dstcommit"
fi

if [ "$seek_mode" = "away" ]; then
	echo "$_git_head" >"$_git/head-name"
	[ -s "$_git/blocked" ] || echo "seeked from $_git_head (some commands can be still forced)" >"$_git/blocked"
	# We hold this in a temporary branch so that some of the core
	# GIT tools (git checkout and git-fsck-objects) don't get confused.
	echo "$dstcommit" >"$_git/refs/heads/cg-seek-point"
	git-symbolic-ref HEAD "refs/heads/cg-seek-point"
else
	git-symbolic-ref HEAD "refs/heads/$_git_head"
	rm -f "$_git/refs/heads/cg-seek-point" "$_git/head-name"
	rm -f "$_git/blocked"
fi

echo "On commit $dstcommit"