// lib/metrics.ts
import { Counter, Histogram, Gauge, Registry } from "prom-client";

const registry = new Registry();

// Request metrics
export const linearRequestsTotal = new Counter({
  name: "linear_api_requests_total",
  help: "Total Linear API requests",
  labelNames: ["operation", "status"],
  registers: [registry],
});

export const linearRequestDuration = new Histogram({
  name: "linear_api_request_duration_seconds",
  help: "Linear API request duration in seconds",
  labelNames: ["operation"],
  buckets: [0.1, 0.25, 0.5, 1, 2.5, 5, 10],
  registers: [registry],
});

export const linearComplexityCost = new Histogram({
  name: "linear_api_complexity_cost",
  help: "Linear API query complexity cost",
  labelNames: ["operation"],
  buckets: [10, 50, 100, 250, 500, 1000, 2500],
  registers: [registry],
});

// Rate limit metrics
export const linearRateLimitRemaining = new Gauge({
  name: "linear_rate_limit_remaining",
  help: "Remaining Linear API rate limit",
  registers: [registry],
});

export const linearComplexityRemaining = new Gauge({
  name: "linear_complexity_remaining",
  help: "Remaining Linear complexity quota",
  registers: [registry],
});

// Webhook metrics
export const linearWebhooksReceived = new Counter({
  name: "linear_webhooks_received_total",
  help: "Total Linear webhooks received",
  labelNames: ["type", "action"],
  registers: [registry],
});

export const linearWebhookProcessingDuration = new Histogram({
  name: "linear_webhook_processing_duration_seconds",
  help: "Linear webhook processing duration",
  labelNames: ["type"],
  buckets: [0.01, 0.05, 0.1, 0.25, 0.5, 1, 2.5],
  registers: [registry],
});

// Cache metrics
export const linearCacheHits = new Counter({
  name: "linear_cache_hits_total",
  help: "Total Linear cache hits",
  registers: [registry],
});

export const linearCacheMisses = new Counter({
  name: "linear_cache_misses_total",
  help: "Total Linear cache misses",
  registers: [registry],
});

export { registry };

// lib/instrumented-client.ts
import { LinearClient } from "@linear/sdk";
import {
  linearRequestsTotal,
  linearRequestDuration,
  linearRateLimitRemaining,
  linearComplexityRemaining,
} from "./metrics";

export function createInstrumentedClient(apiKey: string): LinearClient {
  const client = new LinearClient({
    apiKey,
    fetch: async (url, init) => {
      const operation = extractOperationName(init?.body);
      const timer = linearRequestDuration.startTimer({ operation });

      try {
        const response = await fetch(url, init);

        // Record rate limit headers
        const remaining = response.headers.get("x-ratelimit-remaining");
        const complexity = response.headers.get("x-complexity-remaining");

        if (remaining) linearRateLimitRemaining.set(parseInt(remaining));
        if (complexity) linearComplexityRemaining.set(parseInt(complexity));

        // Record success/failure
        const status = response.ok ? "success" : "error";
        linearRequestsTotal.inc({ operation, status });

        timer();
        return response;
      } catch (error) {
        linearRequestsTotal.inc({ operation, status: "error" });
        timer();
        throw error;
      }
    },
  });

  return client;
}

function extractOperationName(body: BodyInit | undefined): string {
  if (!body || typeof body !== "string") return "unknown";

  try {
    const parsed = JSON.parse(body);
    // Extract operation name from GraphQL query
    const match = parsed.query?.match(/(?:query|mutation)\s+(\w+)/);
    return match?.[1] || "anonymous";
  } catch {
    return "unknown";
  }
}

// lib/logger.ts
import pino from "pino";

export const logger = pino({
  level: process.env.LOG_LEVEL || "info",
  formatters: {
    level: (label) => ({ level: label }),
  },
  base: {
    service: "linear-integration",
    environment: process.env.NODE_ENV,
  },
});

// Linear-specific logger
export const linearLogger = logger.child({ component: "linear" });

// Log API calls
export function logApiCall(operation: string, duration: number, success: boolean) {
  linearLogger.info({
    event: "api_call",
    operation,
    duration_ms: duration,
    success,
  });
}

// Log webhook events
export function logWebhook(type: string, action: string, id: string) {
  linearLogger.info({
    event: "webhook_received",
    webhook_type: type,
    webhook_action: action,
    entity_id: id,
  });
}

// Log errors with context
export function logError(error: Error, context: Record<string, unknown>) {
  linearLogger.error({
    event: "error",
    error_message: error.message,
    error_stack: error.stack,
    ...context,
  });
}

// api/health.ts
import { LinearClient } from "@linear/sdk";
import { registry } from "../lib/metrics";

interface HealthStatus {
  status: "healthy" | "degraded" | "unhealthy";
  checks: {
    linear_api: { status: string; latency_ms?: number; error?: string };
    cache: { status: string; hit_rate?: number };
    rate_limit: { status: string; remaining?: number; percentage?: number };
  };
  timestamp: string;
}

export async function healthCheck(client: LinearClient): Promise<HealthStatus> {
  const checks: HealthStatus["checks"] = {
    linear_api: { status: "unknown" },
    cache: { status: "unknown" },
    rate_limit: { status: "unknown" },
  };

  // Check Linear API
  const start = Date.now();
  try {
    await client.viewer;
    checks.linear_api = {
      status: "healthy",
      latency_ms: Date.now() - start,
    };
  } catch (error) {
    checks.linear_api = {
      status: "unhealthy",
      error: error instanceof Error ? error.message : "Unknown error",
    };
  }

  // Check rate limit status
  const metrics = await registry.getMetricsAsJSON();
  const rateLimitMetric = metrics.find(m => m.name === "linear_rate_limit_remaining");
  if (rateLimitMetric) {
    const remaining = (rateLimitMetric as any).values?.[0]?.value || 0;
    const percentage = (remaining / 1500) * 100;
    checks.rate_limit = {
      status: percentage > 10 ? "healthy" : percentage > 5 ? "degraded" : "unhealthy",
      remaining,
      percentage: Math.round(percentage),
    };
  }

  // Determine overall status
  const statuses = Object.values(checks).map(c => c.status);
  let status: HealthStatus["status"] = "healthy";
  if (statuses.includes("unhealthy")) status = "unhealthy";
  else if (statuses.includes("degraded")) status = "degraded";

  return {
    status,
    checks,
    timestamp: new Date().toISOString(),
  };
}

# prometheus/alerts.yml
groups:
  - name: linear-integration
    rules:
      # High error rate
      - alert: LinearHighErrorRate
        expr: |
          sum(rate(linear_api_requests_total{status="error"}[5m]))
          / sum(rate(linear_api_requests_total[5m])) > 0.05
        for: 5m
        labels:
          severity: warning
        annotations:
          summary: High Linear API error rate
          description: "Linear API error rate is {{ $value | humanizePercentage }}"

      # Rate limit approaching
      - alert: LinearRateLimitLow
        expr: linear_rate_limit_remaining < 100
        for: 2m
        labels:
          severity: warning
        annotations:
          summary: Linear rate limit running low
          description: "Only {{ $value }} requests remaining in rate limit window"

      # Slow API responses
      - alert: LinearSlowResponses
        expr: |
          histogram_quantile(0.95, rate(linear_api_request_duration_seconds_bucket[5m])) > 2
        for: 5m
        labels:
          severity: warning
        annotations:
          summary: Slow Linear API responses
          description: "95th percentile response time is {{ $value }}s"

      # Webhook processing errors
      - alert: LinearWebhookErrors
        expr: |
          sum(rate(linear_webhooks_received_total{status="error"}[5m])) > 0.1
        for: 5m
        labels:
          severity: critical
        annotations:
          summary: Linear webhook processing errors
          description: "Webhook error rate: {{ $value }} per second"

{
  "dashboard": {
    "title": "Linear Integration",
    "panels": [
      {
        "title": "API Request Rate",
        "type": "graph",
        "targets": [
          {
            "expr": "sum(rate(linear_api_requests_total[5m])) by (status)",
            "legendFormat": "{{ status }}"
          }
        ]
      },
      {
        "title": "Request Latency (p95)",
        "type": "gauge",
        "targets": [
          {
            "expr": "histogram_quantile(0.95, rate(linear_api_request_duration_seconds_bucket[5m]))"
          }
        ]
      },
      {
        "title": "Rate Limit Remaining",
        "type": "stat",
        "targets": [
          {
            "expr": "linear_rate_limit_remaining"
          }
        ]
      },
      {
        "title": "Webhooks by Type",
        "type": "piechart",
        "targets": [
          {
            "expr": "sum(linear_webhooks_received_total) by (type)"
          }
        ]
      }
    ]
  }
}