#!/bin/bash
# Copyright (C) 2016 Ian Kelling

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at

#     http://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

append() {
    cat >> "$1"
}
log-once() {
    local help="Usage: log-once [OPTION]... LOG_NAME [LOG_MESSAGE]

For cronjobs, email only once for repeated failures, and for success after failure.

Meant for use in cronjobs where LOG_MESSAGE or STDIN represents an error,
but we only want to output that to STDOUT if we've seen this type of
error ERRORS(default 3) number of times in a row, then we don't
want to output anything again until we've seen a success (an empty LOG_MESSAGE).

Logs LOG_MESSAGE or STDIN to ~/.cron_errors/LOG_NAME, and keeps
state in the same directory.

-e ERRORS:  ERRORS is the number of errors to accumulate before outputing the error"
    local cbase c c1 c2 log x i out file
    errors=3
    while true; do
        if [[ $1 == --help ]]; then
            echo "$help"
            return
        elif [[ $1 == -[0-9]* ]]; then
            errors={$1#-}
            shift
        elif [[ $1 == -- ]]; then
            shift
            break
        else
            break
        fi
    done
    log_name=$1
    # todo, make option & make them overridable based on command line or env variable
    cbase=$HOME/.cron-errors
    [[ -d $cbase ]] || mkdir -p $cbase
    c=$cbase/$log_name
    # http://stackoverflow.com/questions/2456750/detect-presence-of-stdin-contents-in-shell-script
    log=false
    if [[ $2 ]]; then
        log=true
        # read stdin for anything which is not just a newline
    elif [[ ! -t 0 ]]; then
        while read -r x; do
            output+=( $x )
            [[ $x ]] && log=true
        done
    fi
    if $log; then
        file=
        if [[ -f $c$((errors-1)) ]]; then
            out="tee -a"
        else
            out=append
        fi
        for ((i=errors; i>=1; i--)); do
            if [[ -f $c$((i-1)) ]]; then
                file=$c$i
                mv $c$((i-1)) $file
                break
            fi
        done
        if [[ ! $file ]]; then
            if [[ -f $c$errors ]]; then
                file=$c$errors
            else
                file=${c}1
            fi
        fi
        $out $file <<<"log-once: $(date "+%A, %B %d, %r")"
        if [[ $2 ]]; then
            $out $file <<<"$2"
        else
            $out $file <<<"${output[@]}"
            $out $file
        fi
        exit 1
    elif [[ -f $c$errors ]]; then
        echo "log-once success after failure for $c"
        rm -f $c$errors
    else
        rm -f $c[0-9]* # assuming  no one is putting crazy files names, as this is not exact
    fi
}