#!/usr/bin/env bash
# SPDX-License-Identifier: Apache-2.0
# Copyright (C) 2021 Arm Limited or its affiliates and Contributors. All rights reserved.

[[ "$TRACE" ]] && set -x
set -euo pipefail

print_help() {
    echo 'Usage: git-checkout-worktree [SRC] [DEST] [COMMIT] [PATHSPEC]...'
    echo ''
    echo 'Uses reflink copies to reduce the storage requirements of a git worktree add operation.'
}

main() {
    # Path to source worktree
    SRC_WORKTREE="$1"
    # Path to new worktree
    DEST_WORKTREE="$2"
    # Optional; Commit to checkout at dest
    COMMIT="${3-}"
    # Required if COMMIT is specified; Pathspec to checkout
    CHECKOUT_PATHSPEC=("${*:4}")

    # Copy SRC_WORKTREE to DEST_WORKTREE, and checkout COMMIT on the second.
    git worktree add --no-checkout -B "$DEST_WORKTREE" "$DEST_WORKTREE"
    cp --reflink=auto -a "$SRC_WORKTREE"/* "$DEST_WORKTREE"
    OLD_IDX="$(cd "$SRC_WORKTREE" && git rev-parse --git-path index)"
    NEW_IDX="$(cd "$DEST_WORKTREE" && git rev-parse --git-path index)"
    cp --reflink=auto "$OLD_IDX" "$NEW_IDX"

    if [ -n "$COMMIT" ]; then
        git reset --soft "$COMMIT"
        git -c core.checkStat=minimal -c advice.detachedHead=false checkout --no-overlay --progress "$COMMIT" -- "${CHECKOUT_PATHSPEC[@]}"
    else
        git reset --soft "$(cd "$SRC_WORKTREE" && git rev-parse HEAD)"
    fi
}

case "${1:--h}" in
    -h | --help)
        print_help
        [ $# -ne 0 ]
        exit $?
        ;;
    *)
        main "$@"
        ;;
esac