#!/bin/env bash
# dab - delete all but
# Craig Jennings <c@cjennings.net>
# deletes all files in current directory that are NOT of a specific extension

# default switch values
recurse=""
del_dirs=""

# help function
show_help() {
    echo "Usage: $0 [extension] [OPTION]"
    echo "Deletes all files that do not match the given extension from the current directory."
    echo ""
    echo "Options:"
    echo "-r  Delete files in directories recursively."
    echo "-d  Delete directories if they become empty after deletions."
    echo "-h  Display this help message and exit."
    echo ""
    echo "Example: $0 txt -r -d"
    echo "This would delete all non-text files in the current directory and subdirectories. Any directories emptied by this process will also be deleted."
    echo ""
    echo "Note: Directories that were previously empty will remain untouched."
}

# if help was requested, show it and exit
if [[ $1 = "-h" ]] || [[ $2 = "-h" ]] || [[ $3 = "-h" ]]; then
    show_help
    exit
fi

# error if nothing or * was passed
if [[ -z $1 ]] || [[ $1 = "*" ]]; then
    echo "ERROR: No file extension was provided or invalid extension ('*')."
    show_help
    exit
fi

# identify rest of arguments
ext=$1
if [[ $2 == *"-r"* ]] || [[ $3 == *"-r"* ]]; then
    recurse="-R"
fi

if [[ $2 == *"-d"* ]] || [[ $3 == *"-d"* ]]; then
    del_dirs="true"
fi

# Save empty directories into an array before deleting the files
empty_dirs=()
while IFS=  read -r -d $'\0'; do
    empty_dirs+=("$REPLY")
done < <(find . -type d -empty -print0)

shopt -s globstar nullglob extglob

# remove non-matching files
for file in **; do
    if [[ -f "$file" ]] && [[ "$file" != *".$ext" ]]; then
        rm "$file"
    fi
done

# remove directories emptied by this operation
if [[ $del_dirs == "true" ]]; then
    for dir in **/; do
        if [[ ! -n "$(ls -A $dir)" ]] && [[ ! "${empty_dirs[*]}" =~ $dir ]]; then
            rmdir "$dir"
        fi
    done
fi