#!/bin/bash
if [[ "$1" == "--help" || "$1" == "-h" ]]
then
    echo "Usage:"
    echo "    git force"
    echo "    git force <remote>"
    echo "    git force <remote> <branch>"
    exit 0
fi
REMOTE=""
BRANCH=""
PRETTY="--pretty=format:%h, %an <%ae>, %ar: %s"
if [[ "$#" == "0" ]]
then
    BRANCH="$(git branch --show-current)"
    if [[ "$BRANCH" == "" ]]
    then
        echo "error: currently in detached HEAD state" >&2
        exit 1
    fi
fi
if [[ "$#" -gt "0" ]]
then
    REMOTE="$1"
    git config "remote.$REMOTE.url" > /dev/null 2>&1
    if [[ "$?" != "0" ]]
    then
        echo "error: specified remote is invalid" >&2
        exit 2
    fi
fi
if [[ "$#" -gt "1" ]]
then
    BRANCH="$2"
    git rev-parse --verify "$BRANCH" > /dev/null 2>&1
    if [[ "$?" != "0" ]]
    then
        echo "error: specified branch is invalid" >&2
        exit 3
    fi
fi
if [[ "$REMOTE" == "" ]]
then
    REMOTE=$(git config "branch.$BRANCH.remote")
    if [[ "$?" != "0" ]]
    then
        echo "error: current branch does not have a remote and no remote was specified" >&2
        echo "see: git force --help"
        exit 4
    fi
fi
if [[ "$REMOTE" == "" || "$BRANCH" == "" ]]
then
    echo "assertion failed: remote or branch is blank" >&2
    exit 5
fi
REMOTE_BRANCH="$REMOTE/$BRANCH"
REMOTE_HASH="$(git rev-parse "$REMOTE_BRANCH")" # later used to throw errors if something changes remote or local
if [[ "$?" != "0" || "$REMOTE_HASH" == "" ]]
then
    echo "internal error: failed to fetch remote hash" >&2
    exit 5
fi
LOCAL_HASH="$(git rev-parse "$BRANCH")"         # as that may cause the user unintentionally pushing/overwriting unwanted things
if [[ "$?" != "0" || "$LOCAL_HASH" == "" ]]
then
    echo "internal error: failed to fetch local hash" >&2
    exit 5
fi

if [[ "$REMOTE_HASH" == "$LOCAL_HASH" ]]
then
    echo "error: the branches are already the same" >&2
    exit 8
fi

if [[ "$REMOTE_HASH" == "$FORK_POINT" ]]
then
    echo "error: the branches have not diverged" >&2
    exit 9
fi

FORK_POINT="$(git merge-base "$BRANCH" "$REMOTE_BRANCH")"
if [[ "$?" != "0" ]]
then
echo "The branches do not have a common ancestor, the latest commits for each are listed below:"
echo ""
echo "remote:"
git show -s "$PRETTY" "$REMOTE_HASH"
echo ""
echo "remote:"
git show -s "$PRETTY" "$REMOTE_HASH"
else
echo "The following commits will be OVERWRITTEN:"
git log "$PRETTY" "$FORK_POINT..$REMOTE_HASH"
echo ""
echo "The following commits will overwrite the above commits:"
git log "$PRETTY" "$FORK_POINT..$LOCAL_HASH"
fi
echo ""
read -p "Continue? [y/N] " SHOULD_CONTINUE
if [[ "$SHOULD_CONTINUE" != "y" ]]
then
echo "Abort." >&2
exit 6
fi
REMOTE_HASH_2="$(git rev-parse "$REMOTE_BRANCH")"
LOCAL_HASH_2="$(git rev-parse "$BRANCH")"
if [[ "$REMOTE_HASH_2" != "$REMOTE_HASH" ]]
then
echo "@@@@@@@@@@@@@@@@@@@@@@@@@" >&2
echo "@  REMOTE HAS UPDATED!  @" >&2
echo "@@@@@@@@@@@@@@@@@@@@@@@@@" >&2
echo "" >&2
echo "The remote updated from $REMOTE_HASH"
echo "to $REMOTE_HASH_2 while you were confirming."
echo "Please re-run this command and check again."
exit 7
fi
if [[ "$LOCAL_HASH_2" != "$LOCAL_HASH" ]]
then
echo "@@@@@@@@@@@@@@@@@@@@@@@@" >&2
echo "@  LOCAL HAS UPDATED!  @" >&2
echo "@@@@@@@@@@@@@@@@@@@@@@@@" >&2
echo "" >&2
echo "The local updated from $LOCAL_HASH"
echo "to $LOCAL_HASH_2 while you were confirming."
echo "Please re-run this command and check again."
exit 7
fi
git push --force-with-lease "$REMOTE" "$BRANCH"