#!/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_SET]...

Append unique.

A LINE_SET is one or more lines. Append LINE_SET to FILE if it does not exist in
FILE.  If no LINE_SET argument is given, read lines from stdin, and treat each
as a single LINE_SET. Appended text is 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 readsudo writesudo x strings string content
    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 file="$1"
    shift

    local file_exists=false
    if [[ -e $file ]]; then
        file_exists=true
        [[ -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 (( $# == 0 )); then
        unset IFS
        while read -r x; do
            strings+=( "$x" )
        done
    else
        strings=( "$@" )
    fi

    if $file_exists; then
        # fix files with no newline at the end.
        # the following command won't work right on them.
        # e = run script, $a\ means append following text, but there is none,
        # so sed only does what it always does when it was supposed to modify a file,
        # which is append a newline if there was none.
        sed -ie '$a\' "$file"
        # command substitution removes any trailing newlines, so we have to add
        # a non-newline ending, we randomly chose "b", then remove it.
        content=$($readsudo cat "$file"; echo b) content=${content%b}
        
        # we aren't using regex because we want to match strings,
        # but we also want our match to start at the beginning of a line,
        # or the beginning of the file, and to end at a line ending.
        # So we do some slick bash to match this.
        local start="?(*
)"
        local end="
*"
        for string in "${strings[@]}"; do
            [[ $content != $start"$string"$end ]] && $writesudo tee -a "$file"<<<"$string"
        done
    else
        for string in "${strings[@]}"; do
            $writesudo tee -a "$file"<<<"${strings[@]}"
        done
    fi
    return 0
}