#!/usr/bin/env sh

# Extracts the archive. 
# The process can vary depending on the file extension. 
# Usage: $0 ARCHIVE_FILE

# Dependencies:
# * xxd V1.10 27oct98 by Juergen Weigert
# * UnZip 6.00 of 20 April 2009
# * tar (GNU tar) 1.32
# * printf (GNU coreutils 8.31)

function get_bytes() {
    local file=$1
    local length=${2:-20}

    # Getting the file signature.
    # At most, we will just get the first 20 bytes of the file.
    local file_sig=$(xxd -l "$length" -ps "$file")
    printf "$file_sig"
}

function extract_path_without_ext() {
    local path=$1

    local filename=$(basename -- "$path")

    # Return the filename without the file extension. 
    # For more information, you can look up the parameter expansion in 
    # https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html. 
    # Even if the filename has no extension, it will print the whole filename. 
    printf "${filename%.*}"
}

function extract_file() {
    local file=$1
    local length=$2

    # Checking the file signatures. 
    # The reference is at https://en.wikipedia.org/wiki/List_of_file_signatures. 
    local file_sig=$(get_bytes "$file" "$length")

    # Extracting the extension out of the given file and creating a directory out of it. 
    local file_without_ext=$(extract_path_without_ext "$file")
    mkdir -p "$file_without_ext"

    # Checking if the file signature matches of a zip
    if [[ $(printf "$file_sig" | head -c 4) == "504b" ]]; then
        cd "$file_without_ext" && unzip "../$file"
    else
        tar xf "$file" --directory "$file_without_ext"
    fi
}

extract_file $1