#!/bin/bash
# Copyright (C) 2014 Ian Kelling
# This program is under GPL v. 3 or later, see <http://www.gnu.org/licenses/>

appendu() {
    local help="Usage: appendu [OPTION]... FILE [LINE]...
Append unique.
Append each line to FILE if it does not exist in FILE.
Use LINE if specified, else use lines from stdin.
Appended lines are output to the terminal.

  -s      don't try to use sudo when it would help us read or write the file
  --      stop processing arguments
  --help  display this message"

    local dosudo=true
    
    while true; do
        if [[ $1 == --help ]]; then
            echo "$help"
            return
        elif [[ $1 == -s ]]; then
            dosudo=false
            shift
        elif [[ $1 == -- ]]; then
            shift
            break
        else
            break
        fi
    done
    
    if [[ ${#@} == 0 ]]; then
        echo "error: need 1 or more arguments"
        echo "$help"
        return 1
    fi

    local readsudo writesudo x
    local file="$1"
    shift
    
    if [[ -e $file ]]; then
        [[ -r $file ]] || readsudo=sudo
        [[ -w $file ]] || writesudo=sudo
    else 
        local dir="$(dirname "$file")"
        if [[ -d $dir ]]; then
            [[ ! -w $dir ]] && writesudo=sudo
        else
            echo "appendu error: $dir does not exist"
            return 1
        fi
    fi
    if ! $dosudo; then
        readsudo=
        writesudo=
    fi
    if (( $# )); then
        for x in "$@"; do
            [[ -e "$file" ]] && $readsudo grep -q "^$x$" "$file" || $writesudo tee -a "$file"<<<"$x"
        done
    elif [[ ! -t 0 ]]; then
        unset IFS
        while read -r x; do
            # duplicated from above
            [[ -e "$file" ]] && $readsudo grep -q "^$x$" "$file" || $writesudo tee -a "$file"<<<"$x"
        done
    fi
}