#!/usr/bin/env bash
#
# health-check.sh
# Polls the app's /health endpoint every 30 seconds, logs status + response
# time to a CSV file that the dashboard (dashboard.html) can read, and
# alerts (stderr + log) if the app is unhealthy for 3 consecutive checks.
#
# Usage:
#   ./health-check.sh https://your-app.ghaymah.systems
#
# Run in the background on the host, or as a sidecar container, or as a
# systemd service (recommended for production on Ghaymah).

set -uo pipefail

APP_URL="${1:-http://localhost:8080}"
HEALTH_ENDPOINT="${APP_URL%/}/health"
CHECK_INTERVAL=30          # seconds
LOG_FILE="./metrics.csv"
FAIL_THRESHOLD=3
consecutive_failures=0

# Create CSV header if the file doesn't exist yet
if [[ ! -f "$LOG_FILE" ]]; then
    echo "timestamp,status,http_code,response_time_ms" > "$LOG_FILE"
fi

log() {
    echo "[$(date '+%Y-%m-%d %H:%M:%S')] $1"
}

log "Starting health monitor for: $HEALTH_ENDPOINT (interval: ${CHECK_INTERVAL}s)"

while true; do
    start_ms=$(date +%s%3N)

    # -o /dev/null discards body, -w prints http_code, -s silent, -m 5 timeout 5s
    http_code=$(curl -s -o /dev/null -w "%{http_code}" -m 5 "$HEALTH_ENDPOINT")
    curl_exit=$?

    end_ms=$(date +%s%3N)
    response_time_ms=$((end_ms - start_ms))
    timestamp=$(date '+%Y-%m-%d %H:%M:%S')

    if [[ $curl_exit -eq 0 && "$http_code" == "200" ]]; then
        status="UP"
        consecutive_failures=0
        log "OK  - ${HEALTH_ENDPOINT} - ${http_code} - ${response_time_ms}ms"
    else
        status="DOWN"
        consecutive_failures=$((consecutive_failures + 1))
        log "FAIL - ${HEALTH_ENDPOINT} - http_code=${http_code:-none} curl_exit=${curl_exit} - failure #${consecutive_failures}"

        if [[ $consecutive_failures -ge $FAIL_THRESHOLD ]]; then
            log "ALERT: ${consecutive_failures} consecutive failures! Application appears DOWN." >&2
            # In production: send this to Slack/Email/PagerDuty/Ghaymah alerting webhook, e.g.:
            # curl -s -X POST -H "Content-Type: application/json" \
            #   -d "{\"text\":\"ALERT: ${APP_URL} is down (${consecutive_failures} consecutive failures)\"}" \
            #   "$ALERT_WEBHOOK_URL"
        fi
    fi

    echo "${timestamp},${status},${http_code:-0},${response_time_ms}" >> "$LOG_FILE"

    sleep "$CHECK_INTERVAL"
done