#!/bin/bash

# Check status of a list of servers
#
# Any servers in urls that yield a bad response are collated and sent via email
# to all recipients.
# recipients are sourced from a separate file in the cwd; it is expected to
# have a single email address per line.
#
# If WATCHDOG_LOG is set, all output will be redirected there.
#
# Dependencies
# - curl:  Polling the servers
# - msmtp: Sending email; requires separate configuration
# NOTE: Currently only useful for services running over HTTP

#set -eux

main()
{
    local recipients_file="./recipients"
    local urls_file="./urls"
    # TODO: How to check these sensibly?
    #local services_file="./services"

    if [ ! -f ${recipients_file} ]; then
        echo "[ERROR] Please create a file '${recipients_file}'"
        exit 1
    fi
    if [ ! -f ${urls_file} ]; then
        echo "[ERROR] Please create a file '${urls_file}'"
        exit 1
    fi
    # See above TODO
    #if [ ! -f ${services_file} ]; then
    #    echo "[ERROR] Please create a file '${services_file}'"
    #    exit 1
    #fi

    # Source array contents from files, ignoring commented lines
    local recipients=($(cat ${recipients_file} | sed 's/^#.*$//'))
    local urls=($(cat ${urls_file} | sed 's/^#.*$//'))
    # See above TODO
    #local services=($(cat ${services_file} | sed 's/^#.*$//'))

    declare -A FLAGGED

    if [ -n "${WATCHDOG_LOG}" ]; then
        rotate_log WATCHDOG_LOG
        # Redirect all output to WATCHDOG_LOG but preserve a link to stdout should we
        # still want to use it
        exec 3>&1 1>>${WATCHDOG_LOG} 2>&1
    fi

    echo ">> $(date)"
    echo "== Checking:"

    for uri in "${urls[@]}"; do \
        full_uri="https://${uri}"
        echo -n "  ${full_uri} ... ";
        stat="$(curl -s -o /dev/null -w "%{http_code}%{stdout}" ${full_uri})"
        echo "${stat}"

        # All other HTTP responses should not technically be errors
        if ((${stat} >= 400 && ${stat} <= 599)); then
            FLAGGED[${full_uri}]=${stat}
        fi
    done

    ret=0

    if ((${#FLAGGED[@]} > 0)); then
        echo "== Error(s) detected. Sending mail to:"
        for rcp in ${recipients[@]}; do
            echo "  ${rcp}"
        done

        send_mail FLAGGED
        ret=1

    else
        echo "== OK"
    fi

    exit ${ret}
}

rotate_log()
{
    local -n log=$1
    local max_log=4096 # 4M as we get size in K below

    touch ${log}

    local log_size=$(du -k "${log}" | cut -f 1)

    if ((${log_size} > ${max_log})); then
        # Clobber any previous backup
        mv -f ${log} ${log}.1
        touch ${log}
    fi

}

send_mail()
{
    local -n error_list=$1
    local error_string=""

    for i in "${!error_list[@]}"; do
        # Use bash's awful syntax to escape any / in the server string
        code=${i//\//\\\/}
        server=${error_list[$i]}
        error_string+="  ${code}: ${server}\n"
    done

    cat mail_template \
        | sed "s/{ERR_LIST}/${error_string}/g" \
        | msmtp -a omn_server_watch ${recipients[@]} \
        || echo "[ERROR] Failed to send mail!"
}

main