#!/usr/bin/env bash
# Version: 0.0.2
# Copyright (c) 2023:
#   Darren 'Tadgy' Austin <darren (at) afterdark.org.uk>
# Licensed under the terms of the GNU General Public License version 3.

# Defaults.
DB_FILE=".gitattributsdb"		# Database file, relative to the repository root.
DB_EXTRA=".gitattributsdb-extra"	# List of base64 encoded filenames (one per line) to also store/restore attributes for.
					# To add entries to this file, use: printf "%s" "<filename>" | base64 -w 0 >>.gitattributsdb-extra
					# Where '<filename>' is relative to the repository root.

# Variables.
declare -A DB_ACLS DB_ATIMES DB_MODES DB_MTIMES DB_OWNERSHIPS
# shellcheck disable=SC2155
declare PLATFORM="$(uname -s)"

# Function to output a log/info message.
log() {
  printf "%s: %s\\n" "${0##*/}" "$*"
}

# Function to output a warning message to stderr.
warn() {
  log "Warning:" "$*" >&2
}

# Function to output an error message to stderr and die.
error() {
  log "Error:" "$*" >&2
  exit 1
}

# Function to display help.
show_help() {
  local SCRIPT="${0##*/}"

	#........1.........2.........3.........4.........5.........6.........7.........8
  cat <<-EOF
	Usage: $SCRIPT [options] <hook name>
	Store and restore file attributes for files within the git repository from a
	database stored within the repository itself.

	This program is intended to be called from git hooks, rather than directly.

	# FIXME: Write some info about using as a submodule and as a hook in .githooks/.
	EOF
}

# Function to read the database into an array.
read_db() {
  local ACL ATIME FILENAME MODE MTIME OWNERSHIP

  # Do nothing if the DB file doesn't exist.
  [[ ! -e "$DB_FILE" ]] && return 0

  # Read the file.
  while read -r FILENAME MTIME ATIME OWNERSHIP MODE ACL; do
    # Store the attributes in arrays.
    DB_MTIMES[$FILENAME]="$MTIME"
    DB_ATIMES[$FILENAME]="$ATIME"
    DB_OWNERSHIPS[$FILENAME]="$OWNERSHIP"
    DB_MODES[$FILENAME]="$MODE"
    DB_ACLS[$FILENAME]="$ACL"
  done < <(grep -Ev '^(#|$)' "$DB_FILE")

  return 0
}

# Function to store file attributes into the database.
store_attributes() {
  local COUNT=0 DB_TMP FILE X

  # Informational message.
  log "Storing file attributes into database"

  # Use a temporary file for the new database.
  DB_TMP="$(mktemp "$DB_FILE.XXXXXX" 2>/dev/null)" || error "Failed to create temporary database file"

  # While Darwin supports ACLs, there is no standard output and input format for them - don't even try.
  [[ "$PLATFORM" == "Darwin" ]] && warn "Not storing ACLs on Darwin"

  # File header.
  printf "# %s\\n" "This is the gitattributsdb database file." >"$DB_TMP"
  printf "# %s\\n\\n" "Do not manually edit this file - any changes will be overwritten." >>"$DB_TMP"

  # Create the database.
  while read -r -d $'\0' FILE; do
    # No need to process the database files themselves.
    [[ "$FILE" == "$DB_FILE" ]] || [[ "$FILE" == "$DB_EXTRA" ]] && continue

    if [[ "$PLATFORM" == "Linux" ]]; then
      # On Linux, we can handle ACLs too.
      printf "%s %s %s\\n" "$(printf "%s" "$FILE" | base64 -w 0 2>/dev/null)" "$(stat --printf '%.9Y %.9X %U:%G %.4a' -- "$FILE" 2>/dev/null)" \
          "$(getfacl -cEsp -- "$FILE" 2>/dev/null | base64 -w 0 2>/dev/null)" >>"$DB_TMP"
    elif [[ "$PLATFORM" == "Darwin" ]]; then
      # Darwin just has to be different.
      # Use the full path to Darwin's stat, in case there's a macports/brew/etc version installed.
      printf "%s %s\\n" "$(printf "%s" "$FILE" | base64 -b 0 2>/dev/null)" "$(/usr/bin/stat -f '%Fm %Fa %Su:%Sg %Mp%Lp' -- "$FILE" 2>/dev/null)" >>"$DB_TMP"
    fi

    (( COUNT++ ))
  done < <(git ls-files -z --full-name -- . 2>/dev/null; while read -r X; do printf "%s\\0" "$(printf "%s" "$X" | base64 -d 2>/dev/null)"; done < \
      <(grep -Ev '^(#|$)' "$DB_EXTRA" 2>/dev/null))

  # Move the temporary file into place.
  mv -- "$DB_TMP" "$DB_FILE" 2>/dev/null || { rm -f -- "$DB_TMP"; error "Failed to move database temporary file into place"; }

  log "$COUNT entries stored"

  # Add the databases themselves to the commit.
  git add --all -f -- "$DB_EXTRA" 2>/dev/null	# OK to fail silently.
  git add --all -f -- "$DB_FILE" 2>/dev/null || error "Failed to add database files to commit"

  return 0
}

# Function to restore file attributes from the database.
restore_attributes() {
  local COUNT=0 FILE ID

  # Informational message.
  log "Restoring file attributes from database"

  # Read the database.
  read_db

  # While Darwin supports ACLs, there is no standard output and input format for them - don't even try.
  [[ "$PLATFORM" == "Darwin" ]] && warn "Not restoring ACLs on Darwin"

  # Restore from the read database.
  while read -r ID; do
    # Decode the filename from the array ID.
    FILE="$(printf "%s" "$ID" | base64 -d 2>/dev/null)" || { warn "Failed to decode filename: $ID"; continue; }

    # Ignore empty filenames, or non-existant files.
    [[ -z "$FILE" ]] || [[ ! -e "$FILE" ]] && continue

    # Don't restore attributes for symlinks.
    [[ -L "$FILE" ]] && warn "Not restoring attributes for symlink: $FILE" && continue

    # Restore ownerships.
    chown -- "${DB_OWNERSHIPS[$ID]}" "$FILE" 2>/dev/null || warn "Failed to restore ownership: $FILE"

    # Store mode.
    chmod -- "${DB_MODES[$ID]}" "$FILE" 2>/dev/null || warn "Failed to restore permissions: $FILE"

    # Restore ACLs on Linux.
    if [[ "$PLATFORM" == "Linux" ]]; then
      touch -m --date="$(date --date="19700101 00:00:00 + ${DB_MTIMES[$ID]} seconds" +'%Y/%m/%d %H:%M:%S.%N' 2>/dev/null)" -- "$FILE" 2>/dev/null || \
          warn "Failed to restore mtime: $FILE"
      touch -a --date="$(date --date="19700101 00:00:00 + ${DB_ATIMES[$ID]} seconds" +'%Y/%m/%d %H:%M:%S.%N' 2>/dev/null)" -- "$FILE" 2>/dev/null || \
          warn "Failed to restore atime: $FILE"
      printf "%s" "${DB_ACLS[$ID]}" | base64 -d 2>/dev/null | setfacl -M - -- "$FILE" 2>/dev/null || warn "Failed to restore ACLs: $FILE"
    elif [[ "$PLATFORM" == "Darwin" ]]; then
      touch -m -d "$(date -j -r "${DB_MTIMES[$ID]%.*}" +"%Y-%m-%dT%H:%M:%S.${DB_MTIMES[$ID]#*.}")" -- "$FILE" 2>/dev/null || \
          warn "Failed to restore mtime: $FILE"
      touch -a -d "$(date -j -r "${DB_MTIMES[$ID]%.*}" +"%Y-%m-%dT%H:%M:%S.${DB_MTIMES[$ID]#*.}")" -- "$FILE" 2>/dev/null || \
          warn "Failed to restore atime: $FILE"
    fi

    (( COUNT++ ))
  done < <(printf "%s\\n" "${!DB_OWNERSHIPS[@]}")

  log "$COUNT entries restored"

  return 0
}

# Exit if bash isn't v4+.
(( BASH_VERSINFO[0] < 4 )) && error "Bash v4 or later is required"

# Change to the root directory of the repository.
REPO_ROOT="$(git rev-parse --show-toplevel 2>/dev/null)"
[[ -z "$REPO_ROOT" ]] && error "Could not determine git repository root"
pushd -- "$REPO_ROOT" >/dev/null 2>&1 || error "Failed to switch to git repository root"

# Parse command line.
(( $# == 0 )) && {
  printf "%s: %s\\n" "${0##*/}" "missing argument" >&2
  printf "%s: %s %s\\n" "Try" "${0##*/}" "--help" >&2
  exit 1
}
case "$1" in
  '-h'|'--h'|'--help')
    show_help
    ;;
  'post-checkout'|'post-merge')
    # Restore the file attributes from the database.
    restore_attributes
    ;;
  'pre-commit')
    # Store the file attributes into the database.
    store_attributes
    ;;
  *)
    printf "%s: %s: %s\\n" "${0##*/}" "invalid option" "$1" >&2
    printf "%s: %s %s\\n" "Try" "${0##*/}" "--help" >&2
    exit 1
    ;;
esac

exit 0