#!/bin/bash

# Credit: 
# Mitsuo, GPT4
# 2023年 11月  8日 水曜日 15:46:55 -05

# Check for proper number of command line args.
expected_args=3
if [ $# -ne $expected_args ]; then
    echo "Usage: $1 {prefix} {date in yyyy-mm-dd format} {file extension, e.g., jpg}"
    exit 1
fi

# Assign command line args to variables
prefix=$1
current_date=$2
extension=$3

# Validations
if ! [[ $current_date =~ ^[0-9]{4}-[0-9]{2}-[0-9]{2}$ ]]; then
    echo "Date format is invalid. Please use yyyy-mm-dd format."
    exit 1
fi

if [[ $extension == .* ]]; then
    echo "Please provide the file extension without a leading period."
    exit 1
fi

if [[ -z $prefix ]]; then
    echo "Please provide a non-empty prefix."
    exit 1
fi


# Loop through all files with the given extension in the current directory
# 
# By default, if you use a pattern that doesn't match any filenames (like *.jpg
# when there are no .jpg files), bash will pass the pattern itself as an
# argument to commands. For example, if there are no .jpg files in your
# directory and you use the *.jpg pattern in a loop or command, the loop or
# command will receive *.jpg as an input, which is probably not what you want.
shopt -s nullglob
i=1
for file in *$extension; do
    # Skip if the file is not a regular file
    if [[ ! -f $file ]]; then
        continue
    fi

    # Generate the correlative number with leading zeros
    printf -v suffix "%02d" $i

    # Rename the file (-- is end of command line options)
    mv -- "$file" "${prefix}-${current_date}_${suffix}.${extension}"

    # Increment the counter
    ((i++))
done

shopt -u nullglob
echo "Renaming complete!"