#!/bin/bash

###############################################################################
# Script Name: rename-images-by-date.sh
#
# Description:
#   Renames image files using their original capture timestamp.
#
#   The script:
#     1. Scans the target directory for image files.
#     2. Reads the EXIF DateTimeOriginal tag using exiftool.
#     3. Falls back to the file modification timestamp if EXIF data
#        is unavailable.
#     4. Renames files to the format:
#
#            IMG_YYYYMMDD_HHMMSS.ext
#
#     5. Automatically resolves filename collisions by appending a
#        numeric suffix.
#
# Requirements:
#   - Bash
#   - exiftool
#
# Usage:
#
#   Process current directory:
#       ./rename-images-by-date.sh
#
#   Process a specific directory:
#       ./rename-images-by-date.sh /path/to/images
#
# Examples:
#
#   ./rename-images-by-date.sh ~/Pictures
#
# Result:
#
#   Before:
#       DSC00123.JPG
#       Vacation.png
#
#   After:
#       IMG_20230821_143210.JPG
#       IMG_20240106_094533.png
#
# Notes:
#   - Uses EXIF DateTimeOriginal when available.
#   - Falls back to the file modification time when EXIF metadata is
#     missing.
#   - Preserves the original file extension.
#   - Prevents overwriting existing files.
#
###############################################################################

# Change to target directory
TARGET_DIR="./"

if [[ -n "$1" ]]; then
    TARGET_DIR="$1"
fi

cd "$TARGET_DIR" || exit 1

for file in *.{jpg,jpeg,JPG,JPEG,png,PNG}; do

    # Skip non-existing matches
    [ -f "$file" ] || continue

    # Extract original capture timestamp from EXIF metadata
    datetime=$(exiftool -DateTimeOriginal -s3 "$file")

    if [[ -n "$datetime" ]]; then

        # Convert:
        # 2023:08:21 14:32:10
        # into:
        # 20230821_143210
        formatted=$(
            echo "$datetime" |
            sed 's/://g' |
            sed 's/ /_/g' |
            cut -c1-15
        )

        echo "$formatted"

    else

        # Fallback: use file modification timestamp
        formatted=$(date -r "$file" +"%Y%m%d_%H%M%S")

    fi

    extension="${file##*.}"

    newname="IMG_${formatted}.${extension}"

    # Prevent overwriting existing files
    if [[ -e "$newname" ]]; then

        i=1

        while [[ -e "IMG_${formatted}_$i.${extension}" ]]; do
            ((i++))
        done

        newname="IMG_${formatted}_$i.${extension}"
    fi

    echo "Renaming: '$file' -> '$newname'"

    mv "$file" "$newname"

done