/**
 * Memento MCP Server - Metrics & Observability
 *
 * Collects and exports metrics for monitoring and observability.
 * Compatible with Prometheus scraping format.
 */

import config from './config.js';

/**
 * Metrics storage
 */
const metrics = {
  // Request metrics
  requests: {
    total: 0,
    byTool: {},
    byStatus: {},
    byMethod: {},
  },
  // Response time metrics (in milliseconds)
  latency: {
    values: [],
    p50: 0,
    p95: 0,
    p99: 0,
    avg: 0,
  },
  // Error metrics
  errors: {
    total: 0,
    byCategory: {},
    byCode: {},
  },
  // Authentication metrics
  auth: {
    successes: 0,
    failures: 0,
    byMethod: {},
  },
  // Database metrics
  database: {
    queries: 0,
    errors: 0,
    slowQueries: 0,
    avgQueryTime: 0,
    activeConnections: 0,
  },
  // Session metrics
  sessions: {
    active: 0,
    created: 0,
    expired: 0,
    total: 0,
  },
  // Rate limiting metrics
  rateLimit: {
    blocked: 0,
    byUser: {},
  },
  // Cache metrics
  cache: {
    hits: 0,
    misses: 0,
    size: 0,
  },
  // Tool-specific metrics
  tools: {
    calls: {},
    failures: {},
    avgExecutionTime: {},
  },
};

// Latency samples (keep last 1000 for percentile calculation)
const latencySamples = [];
const MAX_LATENCY_SAMPLES = 1000;

/**
 * Record a request
 */
export function recordRequest(tool, status, method = 'unknown', latency = 0) {
  metrics.requests.total++;

  // By tool
  if (!metrics.requests.byTool[tool]) {
    metrics.requests.byTool[tool] = 0;
  }
  metrics.requests.byTool[tool]++;

  // By status
  if (!metrics.requests.byStatus[status]) {
    metrics.requests.byStatus[status] = 0;
  }
  metrics.requests.byStatus[status]++;

  // By method
  if (!metrics.requests.byMethod[method]) {
    metrics.requests.byMethod[method] = 0;
  }
  metrics.requests.byMethod[method]++;

  // Record latency
  if (latency > 0) {
    recordLatency(latency);
  }
}

/**
 * Record latency sample
 */
function recordLatency(ms) {
  latencySamples.push(ms);

  // Keep only recent samples
  if (latencySamples.length > MAX_LATENCY_SAMPLES) {
    latencySamples.shift();
  }

  // Update percentiles
  updateLatencyMetrics();
}

/**
 * Update latency percentiles
 */
function updateLatencyMetrics() {
  if (latencySamples.length === 0) return;

  const sorted = [...latencySamples].sort((a, b) => a - b);
  const len = sorted.length;

  metrics.latency.p50 = sorted[Math.floor(len * 0.5)] || 0;
  metrics.latency.p95 = sorted[Math.floor(len * 0.95)] || 0;
  metrics.latency.p99 = sorted[Math.floor(len * 0.99)] || 0;
  metrics.latency.avg = sorted.reduce((a, b) => a + b, 0) / len;
}

/**
 * Record an error
 */
export function recordError(category, code, context = {}) {
  metrics.errors.total++;

  // By category
  if (!metrics.errors.byCategory[category]) {
    metrics.errors.byCategory[category] = 0;
  }
  metrics.errors.byCategory[category]++;

  // By code
  if (!metrics.errors.byCode[code]) {
    metrics.errors.byCode[code] = 0;
  }
  metrics.errors.byCode[code]++;
}

/**
 * Record authentication event
 */
export function recordAuth(success, method = 'unknown') {
  if (success) {
    metrics.auth.successes++;
  } else {
    metrics.auth.failures++;
  }

  // By method
  if (!metrics.auth.byMethod[method]) {
    metrics.auth.byMethod[method] = { successes: 0, failures: 0 };
  }
  if (success) {
    metrics.auth.byMethod[method].successes++;
  } else {
    metrics.auth.byMethod[method].failures++;
  }
}

/**
 * Record database query
 */
export function recordDbQuery(success, duration = 0) {
  metrics.database.queries++;

  if (duration > 0) {
    // Update average query time
    const currentAvg = metrics.database.avgQueryTime;
    const count = metrics.database.queries;
    metrics.database.avgQueryTime = (currentAvg * (count - 1) + duration) / count;

    // Track slow queries (> 1 second)
    if (duration > 1000) {
      metrics.database.slowQueries++;
    }
  }

  if (!success) {
    metrics.database.errors++;
  }
}

/**
 * Record session event
 */
export function recordSession(event, count = 1) {
  switch (event) {
    case 'create':
      metrics.sessions.created += count;
      metrics.sessions.total += count;
      break;
    case 'expire':
      metrics.sessions.expired += count;
      metrics.sessions.total -= count;
      break;
    case 'active':
      metrics.sessions.active = count;
      break;
  }
}

/**
 * Record rate limit block
 */
export function recordRateLimitBlocked(identifier) {
  metrics.rateLimit.blocked++;

  if (!metrics.rateLimit.byUser[identifier]) {
    metrics.rateLimit.byUser[identifier] = 0;
  }
  metrics.rateLimit.byUser[identifier]++;
}

/**
 * Record cache hit/miss
 */
export function recordCacheHit(hit) {
  if (hit) {
    metrics.cache.hits++;
  } else {
    metrics.cache.misses++;
  }
}

/**
 * Update cache size
 */
export function updateCacheSize(size) {
  metrics.cache.size = size;
}

/**
 * Record tool execution
 */
export function recordToolExecution(tool, success, duration = 0) {
  // Record call
  if (!metrics.tools.calls[tool]) {
    metrics.tools.calls[tool] = 0;
  }
  metrics.tools.calls[tool]++;

  // Record failure
  if (!success) {
    if (!metrics.tools.failures[tool]) {
      metrics.tools.failures[tool] = 0;
    }
    metrics.tools.failures[tool]++;
  }

  // Update average execution time
  if (duration > 0) {
    const currentAvg = metrics.tools.avgExecutionTime[tool] || 0;
    const callCount = metrics.tools.calls[tool];
    metrics.tools.avgExecutionTime[tool] = (currentAvg * (callCount - 1) + duration) / callCount;
  }
}

/**
 * Get current metrics snapshot
 */
export function getMetrics() {
  return {
    ...metrics,
    uptime: process.uptime(),
    memory: process.memoryUsage(),
    timestamp: new Date().toISOString(),
  };
}

/**
 * Get metrics in Prometheus format
 */
export function getPrometheusMetrics() {
  const lines = [];
  const timestamp = Date.now();

  // Helper to format metric line
  const metricLine = (name, value, labels = {}) => {
    const labelStr = Object.keys(labels).length > 0
      ? `{${Object.entries(labels).map(([k, v]) => `${k}="${v}"`).join(',')}}`
      : '';
    return `mcp_${name}${labelStr} ${value} ${timestamp}`;
  };

  // Request metrics
  lines.push(`# HELP mcp_requests_total Total number of requests`);
  lines.push(`# TYPE mcp_requests_total counter`);
  lines.push(metricLine('requests_total', metrics.requests.total));

  for (const [tool, count] of Object.entries(metrics.requests.byTool)) {
    lines.push(metricLine('requests_total', count, { tool }));
  }

  for (const [status, count] of Object.entries(metrics.requests.byStatus)) {
    lines.push(metricLine('requests_total', count, { status }));
  }

  // Latency metrics
  lines.push(`# HELP mcp_latency_ms Request latency in milliseconds`);
  lines.push(`# TYPE mcp_latency_ms gauge`);
  lines.push(metricLine('latency_ms', metrics.latency.p50, { quantile: '0.5' }));
  lines.push(metricLine('latency_ms', metrics.latency.p95, { quantile: '0.95' }));
  lines.push(metricLine('latency_ms', metrics.latency.p99, { quantile: '0.99' }));
  lines.push(metricLine('latency_ms', metrics.latency.avg, { quantile: 'avg' }));

  // Error metrics
  lines.push(`# HELP mcp_errors_total Total number of errors`);
  lines.push(`# TYPE mcp_errors_total counter`);
  lines.push(metricLine('errors_total', metrics.errors.total));

  for (const [category, count] of Object.entries(metrics.errors.byCategory)) {
    lines.push(metricLine('errors_total', count, { category }));
  }

  // Auth metrics
  lines.push(`# HELP mcp_auth_total Authentication attempts`);
  lines.push(`# TYPE mcp_auth_total counter`);
  lines.push(metricLine('auth_total', metrics.auth.successes, { result: 'success' }));
  lines.push(metricLine('auth_total', metrics.auth.failures, { result: 'failure' }));

  // Database metrics
  lines.push(`# HELP mcp_db_queries_total Total database queries`);
  lines.push(`# TYPE mcp_db_queries_total counter`);
  lines.push(metricLine('db_queries_total', metrics.database.queries));
  lines.push(metricLine('db_errors_total', metrics.database.errors));
  lines.push(metricLine('db_slow_queries_total', metrics.database.slowQueries));
  lines.push(metricLine('db_query_latency_ms', metrics.database.avgQueryTime));

  // Session metrics
  lines.push(`# HELP mcp_sessions_active Active sessions`);
  lines.push(`# TYPE mcp_sessions_active gauge`);
  lines.push(metricLine('sessions_active', metrics.sessions.active));
  lines.push(metricLine('sessions_created_total', metrics.sessions.created));
  lines.push(metricLine('sessions_expired_total', metrics.sessions.expired));

  // Rate limit metrics
  lines.push(`# HELP mcp_rate_limit_blocked_total Rate limit blocks`);
  lines.push(`# TYPE mcp_rate_limit_blocked_total counter`);
  lines.push(metricLine('rate_limit_blocked_total', metrics.rateLimit.blocked));

  // Cache metrics
  lines.push(`# HELP mcp_cache_operations_total Cache operations`);
  lines.push(`# TYPE mcp_cache_operations_total counter`);
  lines.push(metricLine('cache_operations_total', metrics.cache.hits, { result: 'hit' }));
  lines.push(metricLine('cache_operations_total', metrics.cache.misses, { result: 'miss' }));
  lines.push(metricLine('cache_size', metrics.cache.size));

  // Tool metrics
  lines.push(`# HELP mcp_tool_calls_total Tool calls`);
  lines.push(`# TYPE mcp_tool_calls_total counter`);
  for (const [tool, count] of Object.entries(metrics.tools.calls)) {
    lines.push(metricLine('tool_calls_total', count, { tool }));
  }

  lines.push(`# HELP mcp_tool_failures_total Tool failures`);
  lines.push(`# TYPE mcp_tool_failures_total counter`);
  for (const [tool, count] of Object.entries(metrics.tools.failures)) {
    lines.push(metricLine('tool_failures_total', count, { tool }));
  }

  lines.push(`# HELP mcp_tool_duration_ms Tool execution duration`);
  lines.push(`# TYPE mcp_tool_duration_ms gauge`);
  for (const [tool, avg] of Object.entries(metrics.tools.avgExecutionTime)) {
    lines.push(metricLine('tool_duration_ms', avg, { tool }));
  }

  // Process metrics
  lines.push(`# HELP mcp_process_memory_bytes Process memory usage`);
  lines.push(`# TYPE mcp_process_memory_bytes gauge`);
  lines.push(metricLine('process_memory_bytes', process.memoryUsage().rss, { type: 'rss' }));
  lines.push(metricLine('process_memory_bytes', process.memoryUsage().heapUsed, { type: 'heap_used' }));
  lines.push(metricLine('process_memory_bytes', process.memoryUsage().heapTotal, { type: 'heap_total' }));

  lines.push(`# HELP mcp_process_uptime_seconds Process uptime`);
  lines.push(`# TYPE mcp_process_uptime_seconds gauge`);
  lines.push(metricLine('process_uptime_seconds', process.uptime()));

  return lines.join('\n') + '\n';
}

/**
 * Reset all metrics (useful for testing)
 */
export function resetMetrics() {
  metrics.requests.total = 0;
  metrics.requests.byTool = {};
  metrics.requests.byStatus = {};
  metrics.requests.byMethod = {};

  metrics.latency.values = [];
  metrics.latency.p50 = 0;
  metrics.latency.p95 = 0;
  metrics.latency.p99 = 0;
  metrics.latency.avg = 0;

  metrics.errors.total = 0;
  metrics.errors.byCategory = {};
  metrics.errors.byCode = {};

  metrics.auth.successes = 0;
  metrics.auth.failures = 0;
  metrics.auth.byMethod = {};

  metrics.database.queries = 0;
  metrics.database.errors = 0;
  metrics.database.slowQueries = 0;
  metrics.database.avgQueryTime = 0;

  metrics.sessions.active = 0;
  metrics.sessions.created = 0;
  metrics.sessions.expired = 0;
  metrics.sessions.total = 0;

  metrics.rateLimit.blocked = 0;
  metrics.rateLimit.byUser = {};

  metrics.cache.hits = 0;
  metrics.cache.misses = 0;
  metrics.cache.size = 0;

  metrics.tools.calls = {};
  metrics.tools.failures = {};
  metrics.tools.avgExecutionTime = {};

  latencySamples.length = 0;
}

/**
 * Get metrics summary for health endpoint
 */
export function getMetricsSummary() {
  return {
    uptime: process.uptime(),
    requests: metrics.requests.total,
    errors: metrics.errors.total,
    errorRate: metrics.requests.total > 0 ? metrics.errors.total / metrics.requests.total : 0,
    avgLatency: metrics.latency.avg,
    sessions: metrics.sessions.active,
    cacheHitRate:
      metrics.cache.hits + metrics.cache.misses > 0
        ? metrics.cache.hits / (metrics.cache.hits + metrics.cache.misses)
        : 0,
  };
}

export default metrics;