#!/bin/sh

PATH=/sbin:/bin:/usr/sbin:/usr/bin:/usr/local/sbin:/usr/local/bin
CONFIG=$1

WEIGHT=2 #Weight value of non-200 responses

#Alias DB command for easy future adjustments
SQL='sqlite3'

# Check for dependencies
if ! which $SQL >/dev/null 2>&1; then
    printf '%s\n' "ERROR 12: Missing dependency -- '$SQL' command not found." >&2
    exit 12
fi
if ! which curl >/dev/null 2>&1; then
    printf '%s\n' "ERROR 12: Missing dependency -- 'curl' command not found." >&2
    exit 12
fi

# BEGIN CONFIG CHECK
### Provides KEY, CHATID, CHKLIST
if [ -n "$CONFIG" ]; then
    if [ -f "$CONFIG" ]; then
        . $CONFIG #Source config file
    else
        printf '%s\n' "$CONFIG: File does not exist." >&2
        exit 10
    fi
else
    if [ -f ".httpcheck_telegram" ]; then
        . .httpcheck_telegram #Source config file
    else
        printf '%s\n' "No configuration file found." >&2
        exit 10
    fi
fi

W_MAX=$(( $WEIGHT * $MAX_COUNT ))

# Check if config was loaded by examining all configuration variables, exit if not
if [ -z "$KEY" ]; then
    printf '%s\n' "Configuration not set correctly: KEY not set" >&2
    ERROR11=true
fi
if [ -z "$CHATID" ]; then
    printf '%s\n' "Configuration not set correctly: CHATID not set" >&2
    ERROR11=true
fi
if [ -z "$CHKLIST" ]; then
    printf '%s\n' "Configuration not set correctly: CHKLIST not set" >&2
    ERROR11=true
fi
if [ -z "$DB" ]; then
    printf '%s\n' "Configuration not set correctly: DB not set" >&2
    ERROR11=true
fi
if [ -z "$MAX_COUNT" ]; then
    printf '%s\n' "Configuration not set correctly: MAX_COUNT not set" >&2
    ERROR11=true
fi
[ "$ERROR11" = "true" ] && exit 11
# END CONFIG CHECK

#DB functions
db_create() {
    $SQL $DB "CREATE TABLE problem (
                site TEXT UNIQUE NOT NULL,
                count INT NOT NULL DEFAULT 0,
                alert INT NOT NULL DEFAULT 0,
                sent INT NOT NULL DEFAULT 0
              );" || return 1
}
db_addsite() {
    $SQL $DB "INSERT OR IGNORE INTO problem (site) VALUES('$1');"
}
db_rmsite() {
    $SQL $DB "DELETE FROM problem WHERE site = '$1';"
}
db_inc() {
    $SQL $DB "UPDATE problem SET count = count + $WEIGHT WHERE site = '$1' AND count < $W_MAX;"
    if [ $($SQL $DB "SELECT count FROM problem WHERE site = '$1';") -ge $W_MAX ]; then
       $SQL $DB "UPDATE problem SET alert = 1 WHERE site = '$1';"
    fi

    # Correct values above $W_MAX, possible due to the implementation of weight.
    if [ $($SQL $DB "SELECT count FROM problem WHERE site = '$1';") -gt $W_MAX ]; then
        $SQL $DB "UPDATE problem SET count = $W_MAX WHERE site = '$1';"
    fi
}
db_dec() {
    # Add weight only if alert state is active, allowing alerts to clear in the expected time frame.
    if [ $($SQL $DB "SELECT alert FROM problem WHERE site = '$1';") -eq 1 ]; then
        $SQL $DB "UPDATE problem SET count = count - $WEIGHT WHERE site = '$1' AND count > 0;"
    else
        $SQL $DB "UPDATE problem SET count = count - 1 WHERE site = '$1' AND count > 0;"
    fi

    if [ $($SQL $DB "SELECT count FROM problem WHERE site = '$1';") -le 0 ]; then
       $SQL $DB "UPDATE problem SET alert = 0 WHERE site = '$1';"
    fi

    # Correct values below zero, possible due to the implementation of weight.
    if [ $($SQL $DB "SELECT count FROM problem WHERE site = '$1';") -lt 0 ]; then
        $SQL $DB "UPDATE problem SET count = 0 WHERE site = '$1';"
    fi
}


TIME="10"
URL="https://api.telegram.org/bot$KEY/sendMessage"

#Telegram message function
send_message() {
    curl -s --max-time $TIME -d "chat_id=${CHATID}&disable_web_page_preview=1&text=$1" $URL >/dev/null
}

get_http_code() {
    if host $(printf '%s\n' $1 | awk '{gsub("https?://|/.*","")}1') 2>&1 >/dev/null; then
        curl -sILk --max-time $TIME $1 | grep HTTP | tail -n 1 | grep -Eo '[0-9]{3}' || printf '%s\n' 999
    else
        printf '%s\n' 000
    fi
}

read_checklist() {
    grep -v "^#\|^$" $CHKLIST | sort | uniq || return 1
}

print_time() {
    date '+%Y-%m-%d %H:%M:%S'
}

# Prepare message header
#MSG="${HEADER}%0AProblems Found:"
FAILURE=false

# Create database if it doesn't exist
if [ -f $DB ]; then
    printf '%s\n' "Database found: $DB"
    # Remove stale entries in DB no longer found in check list
    printf '%s\n' "Pruning database..."
    for row in $($SQL $DB "SELECT site FROM problem;"); do
        if ! read_checklist | grep $row >/dev/null 2>&1; then
            db_rmsite "$row" && printf '%s\n' "Removing old record: $row"
        fi
    done
    printf '%s\n' "Database pruning complete."
else
    printf '%s' "Database not found at '$DB'\nCreating DB ... "
    if db_create; then
        printf '%s\n' "DONE"
    else
        printf '%s\n' "FAILED"
        printf '%s\n' "Database creation failed!" >&2
        exit 13
    fi
fi

# Check HTTP codes
for site in $(read_checklist); do
    db_addsite $site
    respcode=$(get_http_code $site)
    case $respcode in
        000)
            printf '%s\n' "[$(print_time)]: PROBLEM -- $site: DNS record not found" >&2
            db_inc $site
            #MSG="${MSG}%0A%0A %2B ${site}%0A    DNS record not found"
            #FAILURE=true
            ;;
        200)
            printf '%s\n' "[$(print_time)]: OK -- $site returns $respcode"
            db_dec $site
            ;;
        999)
            printf '%s\n' "[$(print_time)]: PROBLEM -- $site caused general cURL failure" >&2
            db_inc $site
            ;;
        *)
            printf '%s\n' "[$(print_time)]: PROBLEM -- $site returns $respcode" >&2
            db_inc $site
            #MSG="${MSG}%0A%0A %2B ${site}%0A    Responding ${respcode}"
            #FAILURE=true
            ;;
    esac
done || exit 2

# Find down sites without sent alerts
unsent=$($SQL $DB "SELECT count(*) FROM problem WHERE alert = 1 AND sent = 0;")
cleared=$($SQL $DB "SELECT count(*) FROM problem WHERE alert = 0 AND sent = 1;")
down=$($SQL $DB "SELECT count(*) FROM problem WHERE alert = 1;")
downlist=$($SQL $DB "SELECT site FROM problem WHERE alert = 1;" | perl -p -e 's/\n/%0A/g')

# If ANY sites have unsent alerts, send a list of ALL sites in 'alert' state
if [ $unsent -gt 0 ]; then
    ALERT="${HEADER}%0ASites Down:%0A${downlist}"
    send_message "$ALERT" && printf '%s\n' "Problems found. Message sent via Telegram bot" >&2 || printf '%s\n' "Problems found. Message sending has failed"
    $SQL $DB "UPDATE problem SET sent = 1 WHERE sent = 0 AND alert = 1;" #Prevents resending messages
fi

# If ALL sites have cleared alerts, send an all-clear
if [ $cleared -gt 0 ]; then
    clearlist=$($SQL $DB "SELECT site FROM problem WHERE alert = 0 AND sent = 1;" | perl -p -e 's/\n/%0A/g')
    CLEARED="${HEADER}%0AThese HTTP alerts have cleared:%0A${clearlist}"
    if [ $down -gt 0 ]; then
        CLEARED="${CLEARED}%0ASites still down:%0A${downlist}"
    fi
    send_message "$CLEARED" && printf '%s\n' "A site's alert status has cleared. Message sent via Telegram bot" >&2 || printf '%s\n' "A site's alert status has cleared. Message sending has failed"
    $SQL $DB "UPDATE problem SET sent = 0 WHERE sent = 1 AND alert = 0;" #Prevents resending messages
fi

exit 0