#!/usr/bin/env bash

# author: Frank Steinmetzger
# version: 2022-11-23

# Helper functions ------------------------------------------------------------

# oops, something occured and the script must exit with an error message
die() {
    echo "$PROGNAME error: ${@}" > /dev/stderr
    exit 1
}

# move a file after printing an info text
move() {
    echo "  Moving '${1##*/}' -> '$2'"
    mv -f "$1" "$2"
}

# print help text
usage() {
    cat <<-EOF
	$PROGNAME: replace files in one dir with files from another, but keeping the extension

	Synposis: $PROGNAME [-h|-s DIR]
	  -h      show this help and exit
	  -s      the source directory from which to pick files. Default: ./$SRC_DIR
	EOF
}

# Preamble --------------------------------------------------------------------

PROGNAME="$(basename "$0")"

# halt script on any uncaught error
set -e

# the default directory
SRC_DIR="temp"

# parse arguments
while getopts "hs:" OPTION; do
    case $OPTION in
        h) usage; exit 0 ;;
        s) SRC_DIR="$OPTARG" ;;
        *) die "Unknown option '$OPTION'" ;;
    esac
done

# input sanitisation
[ -d "$SRC_DIR" ] || die "'$SRC_DIR' is not a directory or does not exist."
[ "$(readlink -m "$SRC_DIR")" = "$(readlink -m .)" ] && die 'Source dir equals destination dir.'

# generate list of possible destination files
declare -A DST_FILES
for DST_FILE in *; do
    [ -f "$DST_FILE" ] || continue
    DST_FILES["$DST_FILE"]=''
done

# Main part -------------------------------------------------------------------

# loop over all files in the source dir
for SRC_PATH in "$SRC_DIR"/*; do
    [ "$SRC_PATH" = "$SRC_DIR/*" ] && die 'Source dir is empty.'

    SRC_FILE="${SRC_PATH##*/}"

    # selection of destination file
    echo
    echo "Select destination for file '$SRC_FILE':"
    unset DST_FILE
    select DST_FILE in '[-skip-]' '[-keep as is-]' "${!DST_FILES[@]}"; do
        [ "$DST_FILE" ] && break
    done

    # don't do anything with the file
    if [ ! "$DST_FILE" ] || [ "$DST_FILE" = "[-skip-]" ]; then
        echo "  Skipping '$SRC_FILE'"
        continue
    fi

    # move the file to destination without renaming
    if [ "$DST_FILE" = "[-keep as is-]" ]; then
        if [ -f "$SRC_FILE" ]; then
            echo -n "The file '$SRC_FILE' already exists. Overwrite? [y/N] "
            read INPUT
            if [ "$INPUT" != "y" ] && [ "$INPUT" != "Y" ]; then
                echo "  Skipping '$SRC_FILE'"
                continue
            fi
        fi
        move "$SRC_PATH" "./$SRC_FILE"
    else
        # replace destination with source file
        SRC_EXT="${SRC_FILE##*.}"
        DST_BASE="${DST_FILE%.*}"
        NEW_DST_FILE="${DST_BASE}.${SRC_EXT}"
        if [ "$DST_FILE" != "$NEW_DST_FILE" ]; then
            echo "  Removing '$DST_FILE'"
            rm -f "$DST_FILE"
        fi
        move "$SRC_PATH" "./$NEW_DST_FILE"

        # remove the destination file from future selections
        unset DST_FILES["$DST_FILE"]
    fi
done