#!/bin/bash

# Desc: Template function to write data supplied as argument

yell() { echo "$0: $*" >&2; } # Yell, Die, Try Three-Fingered Claw technique; # Ref/Attrib: https://stackoverflow.com/a/25515370
die() { yell "$*"; exit 111; }
try() { "$@" || die "cannot $*"; }
appendArgTar(){
    # Desc: Writes first argument to temporary file with arguments as options, then appends file to tar
    # Usage: appendArgTar "$(echo "Data to be written.")" [name of file to be inserted] [tar path] [temp dir] ([cmd1] [cmd2] [cmd3] [cmd4]...)
    # Version: 1.0.3
    # Input: arg1: data to be written
    #        arg2: file name of file to be inserted into tar
    #        arg3: tar archive path (must exist first)
    #        arg4: temporary working dir
    #        arg5+: command strings (ex: "gpsbabel -i nmea -f - -o kml -F - ")
    # Output: file written to disk
    # Example: decrypt multiple large files in parallel
    #          appendArgTar "$(cat /tmp/largefile1.gpg)" "largefile1" $HOME/archive.tar /tmp "gpg --decrypt" &
    #          appendArgTar "$(cat /tmp/largefile2.gpg)" "largefile2" $HOME/archive.tar /tmp "gpg --decrypt" &
    #          appendArgTar "$(cat /tmp/largefile3.gpg)" "largefile3" $HOME/archive.tar /tmp "gpg --decrypt" &
    # Depends: bash 5
    # Ref/Attrib: Using 'eval' to construct command strings https://askubuntu.com/a/476533

    # Save function name
    local FN="${FUNCNAME[0]}";
    #yell "DEBUG:STATUS:$FN:Finished appendArgTar()."
    
    # Set file name
    if ! [ -z "$2" ]; then FILENAME="$2"; else yell "ERROR:$FN:Not enough arguments."; exit 1; fi
    
    # Check tar path is a file
    if [ -f "$3" ]; then TAR_PATH="$3"; else yell "ERROR:$FN:Tar archive arg not a file."; exit 1; fi
	
    # Check temp dir arg
    if ! [ -z "$4" ]; then TMP_DIR="$4"; else yell "ERROR:$FN:No temporary working dir set."; exit 1; fi
    
    # Set command strings
    if ! [ -z "$5" ]; then CMD1="$5"; else CMD1="tee /dev/null "; fi # command string 1
    if ! [ -z "$6" ]; then CMD2="$6"; else CMD2="tee /dev/null "; fi # command string 2
    if ! [ -z "$7" ]; then CMD3="$7"; else CMD3="tee /dev/null "; fi # command string 3
    if ! [ -z "$8" ]; then CMD4="$8"; else CMD4="tee /dev/null "; fi # command string 4

    # Input command
    CMD0="echo \"\$1\""

    # # Debug
    # yell "DEBUG:STATUS:$FN:CMD0:$CMD0"
    # yell "DEBUG:STATUS:$FN:CMD1:$CMD1"
    # yell "DEBUG:STATUS:$FN:CMD2:$CMD2"
    # yell "DEBUG:STATUS:$FN:CMD3:$CMD3"
    # yell "DEBUG:STATUS:$FN:CMD4:$CMD4"
    # yell "DEBUG:STATUS:$FN:FILENAME:$FILENAME"
    # yell "DEBUG:STATUS:$FN:TAR_PATH:$TAR_PATH"
    # yell "DEBUG:STATUS:$FN:TMP_DIR:$TMP_DIR"
    
    # Write to temporary working dir
    eval "$CMD0"" | ""$CMD1"" | ""$CMD2"" | ""$CMD3"" | ""$CMD4" > "$TMP_DIR"/"$FILENAME";

    # Append to tar
    try tar --append --directory="$TMP_DIR" --file="$TAR_PATH" "$FILENAME";
    #yell "DEBUG:STATUS:$FN:Finished appendArgTar()."
} # Append Bash var to file appended to Tar archive

#==BEGIN sample code==
myTar="/tmp/$(date +%s).tar";
try tar --create --file="$myTar" --files-from=/dev/null ;
myVar="how are you doing?"
appendArgTar "$myVar" "$(date +%s)..LOUD_insidetar" "$myTar" "/dev/shm" "tee /tmp/$(date +%s)..outsidetar " "tr '[:lower:]' '[:upper:]'"
#==END sample code==

# Author: Steven Baltakatei Sandoval
# License: GPLv3+