#!/usr/bin/env bash

find . -type d | while read -r dir; do
    name=$(basename "$dir")

    # Match Disc1, Disc01, disc02, CD1, cd01, etc.
    if [[ $name =~ (^|[[:space:]._-])([Dd]isc|[Cc][Dd])0*([0-9]+)$ ]]; then

        cdnum="${BASH_REMATCH[3]}"    
        parent=$(dirname "$dir")
        parentname=$(basename "$parent")

        find "$dir" -maxdepth 1 -type f | while read -r file; do
            filename=$(basename "$file")
            ext="${filename##*.}"
            base="${filename%.*}"

            # If there's only one file in the folder, omit the original basename.
            if [[ $(find "$dir" -maxdepth 1 -type f | wc -l) -eq 1 ]]; then
                newname="CD${cdnum}.${ext}"
            else
                newname="CD${cdnum}.${base}.${ext}"
            fi
            echo "$file" "$parent/$newname"
            cp "$file" "$parent/$newname"
        done
    else
        echo "$name"
    fi
done