#!/bin/bash
# screenshot-rename - watch for new macOS screenshots and rename them to a timestamp-only format
#
# Usage:
#   screenshot-rename [-p|--path PATH] [-F|--format FORMAT] [--utc]
#   screenshot-rename -h
#
# Options:
#   -p, --path PATH      Directory to watch (default: macOS configured screenshot
#                        location from `defaults read com.apple.screencapture location`,
#                        falling back to ~/Desktop)
#   -F, --format FORMAT  strftime format for the new filename (default: "%Y-%m-%d %H.%M.%S")
#   -u, --utc            Use UTC timezone instead of local time
#   -h, --help           Show help message

_screenshot_rename() (
    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="screenshot-rename" ;; esac

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

    _show_help() {
        local s; [ -t 1 ] && s=$'\033[4m'
        local r; [ -t 1 ] && r=$'\033[24m'
        cat <<EOF
NAME
  $SCRIPT_NAME - watch for new macOS screenshots and rename them
SYNOPSIS
  $SCRIPT_NAME [-p|--path ${s}path${r}] [-F|--format ${s}format${r}] [--utc]
  $SCRIPT_NAME -h
DESCRIPTION
  Runs as a watcher indefinitely (Ctrl-C to stop). Monitors the
  configured directory (default: ~/Desktop, or the macOS screenshot
  location if different) for new Screenshot files and renames them
  to a timestamp-only format.

  Before: Screenshot 2025-08-04 at 12.05.57.png
  After:  2025-08-04 12.05.57.png

  The timestamp is captured at the moment of rename, not parsed from
  the original filename. If a file with the same timestamp already
  exists, a counter is appended (-1, -2, ...).
OPTIONS
  -p, --path ${s}path${r}      Directory to watch
                       (default: macOS screenshot location, or ~/Desktop)
  -F, --format ${s}format${r}  strftime format for new filenames
                       (default: "%Y-%m-%d %H.%M.%S")
  -u, --utc            Use UTC instead of local time
  -h, --help           Show this help message
EXAMPLES
  $SCRIPT_NAME
  $SCRIPT_NAME --utc
  $SCRIPT_NAME --path ~/Pictures/Screenshots
  $SCRIPT_NAME --format "%Y%m%d-%H%M%S"
EXIT STATUS
  0  Clean shutdown
  2  Usage error (unknown argument, missing flag value)
  3  Dependency error (fswatch missing)
DEPENDENCIES
  fswatch, defaults (macOS)
EOF
    }

    _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
    }

    local use_utc=false
    local watch_dir=""
    local fmt="%Y-%m-%d %H.%M.%S"

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

    while [ "$#" -gt 0 ]; do
        case "$1" in
            --utc|-u) use_utc=true; shift ;;
            -p|--path)
                shift
                if [ $# -eq 0 ] || [ -z "$1" ]; then
                    _error "--path requires a directory. Run \`$SCRIPT_NAME -h\` for usage"
                    return 2
                fi
                watch_dir="$1"
                shift
                ;;
            --path=*)
                watch_dir="${1#*=}"
                [ -n "$watch_dir" ] || { _error "--path requires a directory. Run \`$SCRIPT_NAME -h\` for usage"; return 2; }
                shift
                ;;
            -F|--format)
                shift
                if [ $# -eq 0 ] || [ -z "$1" ]; then
                    _error "--format requires a strftime pattern. Run \`$SCRIPT_NAME -h\` for usage"
                    return 2
                fi
                fmt="$1"
                shift
                ;;
            --format=*)
                fmt="${1#*=}"
                [ -n "$fmt" ] || { _error "--format requires a strftime pattern. Run \`$SCRIPT_NAME -h\` for usage"; return 2; }
                shift
                ;;
            --help|-h) _show_help; return 0 ;;
            --) shift; break ;;
            -*) _error "Unknown argument '$1'. Run \`$SCRIPT_NAME -h\` for usage"; return 2 ;;
            *) _error "Unknown argument '$1'. Run \`$SCRIPT_NAME -h\` for usage"; return 2 ;;
        esac
    done

    if ! command -v fswatch >/dev/null 2>&1; then
        _error "fswatch is required"
        return 3
    fi

    # Determine watch directory: --path wins. Otherwise, try the macOS-configured
    # screenshot location; fall back to ~/Desktop if that fails or isn't a dir
    if [ -z "$watch_dir" ]; then
        watch_dir="$(defaults read com.apple.screencapture location 2>/dev/null)"
        # Expand ~/ if present (defaults may return "~/Desktop" literally)
        watch_dir="${watch_dir/#\~/$HOME}"
        if [ -z "$watch_dir" ] || [ ! -d "$watch_dir" ]; then
            watch_dir="$HOME/Desktop"
        fi
    fi

    echo "Watching for new screenshots in: $watch_dir"
    local path
    fswatch -0 "$watch_dir" | while IFS= read -r -d '' path; do
        case "$path" in
            "$watch_dir"/Screenshot\ *.png)
                # We get multiple lines for a single screenshot, so the file may already be moved
                [ -f "$path" ] || continue
                printf %s "Renaming screenshot: $path"

                # Choose time zone
                local timestamp
                if [ "$use_utc" = true ]; then
                    timestamp="$(TZ=Etc/UTC date "+$fmt")"
                else
                    timestamp="$(TZ=/etc/localtime date "+$fmt")"
                fi

                local dest="$watch_dir/$timestamp.png"
                # In case two renames are attempted at the same time, ensure unique names
                local i=1
                while [ -e "$dest" ]; do
                    dest="$watch_dir/$timestamp-$i.png"
                    i=$((i + 1))
                done
                echo " -> $(basename "$dest")"
                mv "$path" "$dest"
                ;;
        esac
    done
)

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