#!/bin/bash
# git-backup - Stash work in progress and push it as a timestamped backup tag
#
# Usage:
#   git-backup [--dry-run] <repo_directory> [remote]
#   git-backup -h
#
# Options:
#   -n, --dry-run    Print the commands that would run; make no changes
#   repo_directory   Path to the git repository
#   remote           Remote name (default: origin)
#   -h, --help       Show help message

_git_backup() (
    local SCRIPT_NAME; SCRIPT_NAME="$(basename "${BASH_SOURCE[0]}")"
    case "${BASH_SOURCE[0]}" in /dev/*|/proc/*) SCRIPT_NAME="" ;; esac
    case "$SCRIPT_NAME" in ""|bash|sh|zsh|dash) SCRIPT_NAME="git-backup" ;; esac

    _show_help() {
        local s; [ -t 1 ] && s=$'\033[4m'
        local r; [ -t 1 ] && r=$'\033[24m'
        cat <<EOF
NAME
  $SCRIPT_NAME - back up git changes to a timestamped remote tag
SYNOPSIS
  $SCRIPT_NAME [--dry-run] ${s}repo_directory${r} [${s}remote${r}]
  $SCRIPT_NAME -h
DESCRIPTION
  Stashes all tracked and untracked changes, detaches HEAD, commits
  everything, tags it backup-YYYY-MM-DD-HHMM.SS (UTC), pushes the tag
  to the remote, then restores the original branch and working state.
  The local tag is deleted after pushing; the remote tag persists.

  Pushes immediately without confirmation -- the backup tag is named
  uniquely by timestamp and won't overwrite or interfere with your main
  work. Use --dry-run first if you want to see what would happen.

  If \`git stash apply\` hits conflicts, the script auto-resolves them by
  keeping the stashed version (\`git checkout --theirs\`). See CAVEATS.
OPTIONS
  -n, --dry-run      Print the commands that would run, make no changes
  ${s}repo_directory${r}   Path to the git repository (e.g. . for CWD)
  ${s}remote${r}           Remote name (default: origin)
  -h, --help         Show this help message
PRECONDITIONS
  - ${s}repo_directory${r} is an accessible git working tree
  - ${s}remote${r} is configured in that repo and you have push access
EXIT STATUS
  0   Success
  1   Runtime failure (git command failed)
  2   Usage / precondition error (remote missing, bad args)
DEPENDENCIES
  git
CAVEATS
  Conflict auto-resolution uses \`git checkout --theirs\` (keep stashed
  side). This is destructive for the 'ours' side of any conflict --
  review the backup tag after a conflict-resolved run.

  Backup tags persist on the remote and are not auto-pruned. Clean
  them up periodically with:
    git push ${s}remote${r} :refs/tags/backup-YYYY-...
EOF
    }

    _error() { echo "[ERR][$SCRIPT_NAME] $*" >&2; }

    _failed() { _error "\`$1\` failed"; }

    _expand_short_opts() {
        # $1 = string of short-opt letters that take a value (e.g. "nXHd"); "" for flag-only scripts
        # $2..$N = "$@"
        # Populates _EXPANDED; caller does: set -- "${_EXPANDED[@]}"; unset _EXPANDED
        local value_opts="$1"; shift
        _EXPANDED=()
        local passthru=""
        local arg
        local rest
        local c
        for arg in "$@"; do
            if [ -n "$passthru" ]; then _EXPANDED+=("$arg"); continue; fi
            case "$arg" in
                --)          passthru=1; _EXPANDED+=("$arg") ;;
                --*|-|"")    _EXPANDED+=("$arg") ;;
                -[a-zA-Z]?*)
                    rest="${arg#-}"
                    while [ -n "$rest" ]; do
                        c="${rest%"${rest#?}"}"; rest="${rest#?}"
                        _EXPANDED+=("-$c")
                        case "$value_opts" in *"$c"*)
                            [ -n "$rest" ] && _EXPANDED+=("$rest")
                            rest="" ;;
                        esac
                    done ;;
                *)        _EXPANDED+=("$arg") ;;
            esac
        done
    }

    # Parse args: collect flags, then positional
    local dry_run=0
    local positional=()

    _expand_short_opts "" "$@"
    set -- "${_EXPANDED[@]}"; unset _EXPANDED

    while [ $# -gt 0 ]; do
        case "$1" in
            -h|--help) _show_help; return 0 ;;
            -n|--dry-run) dry_run=1; shift ;;
            --) shift; while [ $# -gt 0 ]; do positional+=("$1"); shift; done ;;
            -*)
                _error "Unknown argument '$1'. Run \`$SCRIPT_NAME -h\` for usage"
                return 2
                ;;
            *) positional+=("$1"); shift ;;
        esac
    done

    if [ "${#positional[@]}" -eq 0 ]; then
        _error "Must provide a directory. Run \`$SCRIPT_NAME -h\` for usage"
        return 2
    fi

    # Directory of the Git repository
    local repo_dir="${positional[0]}"
    # Name of remote to push to - git defaults to "origin" so we do too
    local remote="${positional[1]:-"origin"}"

    local timestamp; timestamp="$(TZ=Etc/UTC date +"%Y-%m-%d-%H%M.%S")"
    local backup_name="backup-$timestamp"

    if [ "$dry_run" -eq 1 ]; then
        echo "[DRY RUN] would back up $repo_dir to $remote as tag $backup_name"
        echo "[DRY RUN] cd \"$repo_dir\""
        echo "[DRY RUN] git remote get-url \"$remote\"   # (pre-flight check)"
        echo "[DRY RUN] git stash save --include-untracked \"$backup_name\""
        echo "[DRY RUN] git checkout --detach"
        echo "[DRY RUN] git stash apply   # (auto-resolves conflicts with --theirs)"
        echo "[DRY RUN] git add ."
        echo "[DRY RUN] git commit -m \"Backup $timestamp\""
        echo "[DRY RUN] git tag \"$backup_name\""
        echo "[DRY RUN] git push \"$remote\" \"refs/tags/$backup_name\""
        echo "[DRY RUN] git checkout -"
        echo "[DRY RUN] git stash apply"
        echo "[DRY RUN] git tag -d \"$backup_name\""
        return 0
    fi

    echo "Starting git repo backup $timestamp"

    # Change to the repository directory
    if ! cd "$repo_dir"; then
        _error "Failed to change to directory \"$repo_dir\""
        return 1
    fi

    # Pre-flight: the named remote must exist. Without this, `git push` later
    # produces a raw git error that doesn't say which side (tooling or config)
    # is at fault
    if ! git remote get-url "$remote" >/dev/null 2>&1; then
        _error "Remote '$remote' not configured in '$repo_dir'. Run \`$SCRIPT_NAME -h\` for usage"
        return 2
    fi

    # Stash any uncommitted changes and untracked files
    if ! git stash save --include-untracked "$backup_name"; then
        _failed "git stash save --include-untracked \"$backup_name\""
        return 1
    fi

    # Detach HEAD so the backup commit lands on no branch
    if ! git checkout --detach; then
        _failed "git checkout --detach"
        return 1
    fi

    # Apply the changes from stash, overwriting any conflicts
    local stash_apply_output
    if ! stash_apply_output="$(git stash apply 2>&1)"; then
        _failed "git stash apply"
        return 1
    fi
    if echo "$stash_apply_output" | tee /dev/stdout | grep -q 'CONFLICT'; then
        echo "Conflicts detected during 'git stash apply'. Attempting to resolve conflicts by keeping stashed changes."
        git status --short | grep '^U' | cut -c 4- \
        | while read -r file; do
            echo "Resolving conflict in $file"
            if ! git checkout --theirs "$file"; then
                _failed "git checkout --theirs \"$file\""
                return 1
            fi
            git add "$file"
        done
        echo "Conflicts resolved. Committing the changes."
    fi

    # Add all changes to the index
    if ! git add .; then
        _failed "git add ."
        return 1
    fi

    # Commit the changes
    if ! git commit -m "Backup $timestamp"; then
        _failed "git commit -m \"Backup $timestamp\""
        return 1
    fi

    # Tag the commit; the tag is what gets pushed and persists on the remote
    if ! git tag "$backup_name"; then
        _failed "git tag \"$backup_name\""
        return 1
    fi

    # Push the tag to the remote repository
    if ! git push "$remote" "refs/tags/$backup_name"; then
        _failed "git push \"$remote\" \"refs/tags/$backup_name\""
        return 1
    fi

    # Switch back to the original branch
    if ! git checkout -; then
       _failed "git checkout -"
       return 1
    fi

    # Restore changes to original branch
    if ! git stash apply; then
        _failed "git stash apply"
        return 1
    fi

    # Delete the local tag, now that it has been pushed to the remote
    if ! git tag -d "$backup_name"; then
        _failed "git tag -d \"$backup_name\""
        return 1
    fi
)

_git_backup "$@"
__git_backup_rc=$?
unset -f _git_backup
if [ -n "${BASH_SOURCE[0]}" ] && [ "${BASH_SOURCE[0]}" != "$0" ]; then
    eval "unset __git_backup_rc; return $__git_backup_rc"
fi
eval "unset __git_backup_rc; exit $__git_backup_rc"