#!/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. Duplicate
LINE_SETs are treated the same.

  --           stop processing arguments
  [-h|--help]  display this message"

    
    while true; do
        if [[ $1 == --help || $1 == -h ]]; then
            echo "$help"
            return
        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 new_file=true
    if [[ -e $file ]]; then
        new_file=false
    else
        local dir="$(dirname "$file")"
        if [[ ! -d $dir ]]; then
            echo "appendu error: $dir does not exist"
            return 1
        fi
    fi
    if ! $new_file; then
        if [[ ! -r $file ]]; then
            echo "appendu error: cannot read or write $file"
            return 1
        fi
        if [[ ! -w $file ]]; then
            echo "appendu error: cannot read or write $file"
            return 1
        fi            
    fi
    
    if (( $# == 0 )); then
        unset IFS
        while read -r x; do
            strings+=( "$x" )
        done
    else
        strings=( "$@" )
    fi

    # fix files with no newline at the end.
    # the following command won't work right on them otherwise.
    # 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\' "$file"
    # command substitution removes any trailing newlines, so we have to add
    # a non-newline ending, we randomly chose "b", then remove it.
    content=$(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="
*"
    local return_code
    for string in "${strings[@]}"; do
        if $new_file || [[ $content != $start"$string"$end ]]; then
            if ! tee -a "$file"<<<"$string"; then
                return_code=$?
                echo "appendu error: error writing to $file"
                return $return_code
            fi
        fi
    done
    return 0
}
appendu "$@"