/**
 * Instances Route Handler
 *
 * Endpoint for querying instance types with filtering, sorting, and pagination.
 * Integrates with cache service for performance optimization.
 */

import type { Env, InstanceQueryParams } from '../types';
import { QueryService } from '../services/query';
import { getGlobalCacheService } from '../services/cache';
import { logger } from '../utils/logger';
import {
  SUPPORTED_PROVIDERS,
  type SupportedProvider,
  VALID_SORT_FIELDS,
  INSTANCE_FAMILIES,
  PAGINATION,
  CACHE_TTL,
  HTTP_STATUS,
} from '../constants';

/**
 * Worker-level service singleton cache
 * Performance optimization: Reuse service instances across requests within same Worker instance
 *
 * Benefits:
 * - Reduces GC pressure by avoiding object creation per request
 * - Maintains service state (e.g., logger initialization) across requests
 * - Safe for Cloudflare Workers as Worker instances are isolated and stateless
 *
 * Note: Worker instances are recreated periodically, preventing memory leaks
 */
let cachedQueryService: QueryService | null = null;
let cachedDb: D1Database | null = null;

/**
 * Get or create QueryService singleton
 * Lazy initialization on first request, then reused for subsequent requests
 * Invalidates cache if database binding changes (rolling deploy scenario)
 */
function getQueryService(db: D1Database, env: Env): QueryService {
  // Invalidate cache if db binding changed (rolling deploy scenario)
  if (!cachedQueryService || cachedDb !== db) {
    cachedQueryService = new QueryService(db, env);
    cachedDb = db;
    logger.debug('[Instances] QueryService singleton initialized/refreshed');
  }
  return cachedQueryService;
}

/**
 * Parsed and validated query parameters
 */
interface ParsedQueryParams {
  provider?: string;
  region?: string;
  min_vcpu?: number;
  max_vcpu?: number;
  min_memory_gb?: number;
  max_memory_gb?: number;
  max_price?: number;
  instance_family?: string;
  has_gpu?: boolean;
  sort_by?: string;
  order?: 'asc' | 'desc';
  limit: number;
  offset: number;
}

/**
 * Validate provider name
 */
function isSupportedProvider(provider: string): provider is SupportedProvider {
  return SUPPORTED_PROVIDERS.includes(provider as SupportedProvider);
}

/**
 * Validate sort field
 */
function isValidSortField(field: string): boolean {
  return VALID_SORT_FIELDS.includes(field as typeof VALID_SORT_FIELDS[number]);
}

/**
 * Validate instance family
 */
function isValidFamily(family: string): boolean {
  return INSTANCE_FAMILIES.includes(family as typeof INSTANCE_FAMILIES[number]);
}

/**
 * Parse and validate query parameters
 */
function parseQueryParams(url: URL): {
  params?: ParsedQueryParams;
  error?: { code: string; message: string; parameter?: string };
} {
  const searchParams = url.searchParams;
  const params: ParsedQueryParams = {
    limit: PAGINATION.DEFAULT_LIMIT,
    offset: PAGINATION.DEFAULT_OFFSET,
  };

  // Provider validation
  const provider = searchParams.get('provider');
  if (provider !== null) {
    if (!isSupportedProvider(provider)) {
      return {
        error: {
          code: 'INVALID_PARAMETER',
          message: `Invalid provider: ${provider}. Supported providers: ${SUPPORTED_PROVIDERS.join(', ')}`,
          parameter: 'provider',
        },
      };
    }
    params.provider = provider;
  }

  // Region (no validation, passed as-is)
  const region = searchParams.get('region');
  if (region !== null) {
    params.region = region;
  }

  // Numeric parameter validation helper
  function parsePositiveNumber(
    name: string,
    value: string | null
  ): number | undefined | { error: { code: string; message: string; parameter: string } } {
    if (value === null) return undefined;

    const parsed = Number(value);
    if (isNaN(parsed) || parsed < 0) {
      return {
        error: {
          code: 'INVALID_PARAMETER',
          message: `Invalid value for ${name}: must be a positive number`,
          parameter: name,
        },
      };
    }
    return parsed;
  }

  // Parse min_vcpu
  const minVcpuResult = parsePositiveNumber('min_vcpu', searchParams.get('min_vcpu'));
  if (minVcpuResult && typeof minVcpuResult === 'object' && 'error' in minVcpuResult) {
    return minVcpuResult;
  }
  if (typeof minVcpuResult === 'number') {
    params.min_vcpu = minVcpuResult;
  }

  // Parse max_vcpu
  const maxVcpuResult = parsePositiveNumber('max_vcpu', searchParams.get('max_vcpu'));
  if (maxVcpuResult && typeof maxVcpuResult === 'object' && 'error' in maxVcpuResult) {
    return maxVcpuResult;
  }
  if (typeof maxVcpuResult === 'number') {
    params.max_vcpu = maxVcpuResult;
  }

  // Parse min_memory_gb
  const minMemoryResult = parsePositiveNumber('min_memory_gb', searchParams.get('min_memory_gb'));
  if (minMemoryResult && typeof minMemoryResult === 'object' && 'error' in minMemoryResult) {
    return minMemoryResult;
  }
  if (typeof minMemoryResult === 'number') {
    params.min_memory_gb = minMemoryResult;
  }

  // Parse max_memory_gb
  const maxMemoryResult = parsePositiveNumber('max_memory_gb', searchParams.get('max_memory_gb'));
  if (maxMemoryResult && typeof maxMemoryResult === 'object' && 'error' in maxMemoryResult) {
    return maxMemoryResult;
  }
  if (typeof maxMemoryResult === 'number') {
    params.max_memory_gb = maxMemoryResult;
  }

  // Parse max_price
  const maxPriceResult = parsePositiveNumber('max_price', searchParams.get('max_price'));
  if (maxPriceResult && typeof maxPriceResult === 'object' && 'error' in maxPriceResult) {
    return maxPriceResult;
  }
  if (typeof maxPriceResult === 'number') {
    params.max_price = maxPriceResult;
  }

  // Instance family validation
  const family = searchParams.get('instance_family');
  if (family !== null) {
    if (!isValidFamily(family)) {
      return {
        error: {
          code: 'INVALID_PARAMETER',
          message: `Invalid instance_family: ${family}. Valid values: ${INSTANCE_FAMILIES.join(', ')}`,
          parameter: 'instance_family',
        },
      };
    }
    params.instance_family = family;
  }

  // GPU filter (boolean)
  const hasGpu = searchParams.get('has_gpu');
  if (hasGpu !== null) {
    if (hasGpu !== 'true' && hasGpu !== 'false') {
      return {
        error: {
          code: 'INVALID_PARAMETER',
          message: 'Invalid value for has_gpu: must be "true" or "false"',
          parameter: 'has_gpu',
        },
      };
    }
    params.has_gpu = hasGpu === 'true';
  }

  // Sort by validation
  const sortBy = searchParams.get('sort_by');
  if (sortBy !== null) {
    if (!isValidSortField(sortBy)) {
      return {
        error: {
          code: 'INVALID_PARAMETER',
          message: `Invalid sort_by: ${sortBy}. Valid values: ${VALID_SORT_FIELDS.join(', ')}`,
          parameter: 'sort_by',
        },
      };
    }
    params.sort_by = sortBy;
  }

  // Sort order validation
  const order = searchParams.get('order');
  if (order !== null) {
    if (order !== 'asc' && order !== 'desc') {
      return {
        error: {
          code: 'INVALID_PARAMETER',
          message: 'Invalid order: must be "asc" or "desc"',
          parameter: 'order',
        },
      };
    }
    params.order = order;
  }

  // Limit validation
  const limitStr = searchParams.get('limit');
  if (limitStr !== null) {
    const limit = Number(limitStr);
    if (isNaN(limit) || limit < 1 || limit > PAGINATION.MAX_LIMIT) {
      return {
        error: {
          code: 'INVALID_PARAMETER',
          message: `Invalid limit: must be between 1 and ${PAGINATION.MAX_LIMIT}`,
          parameter: 'limit',
        },
      };
    }
    params.limit = limit;
  }

  // Offset validation
  const offsetStr = searchParams.get('offset');
  if (offsetStr !== null) {
    const offset = Number(offsetStr);
    if (isNaN(offset) || offset < 0) {
      return {
        error: {
          code: 'INVALID_PARAMETER',
          message: 'Invalid offset: must be a non-negative number',
          parameter: 'offset',
        },
      };
    }
    params.offset = offset;
  }

  // Range consistency validation
  if (params.min_vcpu !== undefined && params.max_vcpu !== undefined) {
    if (params.min_vcpu > params.max_vcpu) {
      return {
        error: {
          code: 'INVALID_RANGE',
          message: 'min_vcpu cannot be greater than max_vcpu',
          parameter: 'min_vcpu',
        },
      };
    }
  }

  if (params.min_memory_gb !== undefined && params.max_memory_gb !== undefined) {
    if (params.min_memory_gb > params.max_memory_gb) {
      return {
        error: {
          code: 'INVALID_RANGE',
          message: 'min_memory_gb cannot be greater than max_memory_gb',
          parameter: 'min_memory_gb',
        },
      };
    }
  }

  return { params };
}


/**
 * Handle GET /instances endpoint
 *
 * @param request - HTTP request object
 * @param env - Cloudflare Worker environment bindings
 * @returns JSON response with instance query results
 *
 * @example
 * GET /instances?provider=linode&min_vcpu=2&max_price=20&sort_by=price&order=asc&limit=50
 */
export async function handleInstances(
  request: Request,
  env: Env
): Promise<Response> {
  const startTime = Date.now();

  logger.info('[Instances] Request received', { url: request.url });

  try {
    // Parse URL and query parameters
    const url = new URL(request.url);
    const parseResult = parseQueryParams(url);

    // Handle validation errors
    if (parseResult.error) {
      logger.error('[Instances] Validation error', parseResult.error);
      return Response.json(
        {
          success: false,
          error: parseResult.error,
        },
        { status: HTTP_STATUS.BAD_REQUEST }
      );
    }

    const params = parseResult.params!;
    logger.info('[Instances] Query params validated', params as unknown as Record<string, unknown>);

    // Get global cache service singleton (shared across all routes)
    const cacheService = getGlobalCacheService(CACHE_TTL.INSTANCES, env.RATE_LIMIT_KV);

    // Generate cache key from query parameters
    const cacheKey = cacheService.generateKey(params as unknown as Record<string, unknown>);
    logger.info('[Instances] Cache key generated', { cacheKey });

    // Check cache first
    interface CachedData {
      instances: unknown[];
      pagination: {
        total: number;
        limit: number;
        offset: number;
        has_more: boolean;
      };
      metadata: {
        cached: boolean;
        last_sync: string;
        query_time_ms: number;
        filters_applied: unknown;
      };
    }

    const cached = await cacheService.get<CachedData>(cacheKey);

    if (cached) {
      logger.info('[Instances] Cache hit', {
        cacheKey,
        age: cached.cache_age_seconds,
      });

      return Response.json(
        {
          success: true,
          data: {
            ...cached.data,
            metadata: {
              ...cached.data.metadata,
              cached: true,
              cache_age_seconds: cached.cache_age_seconds,
              cached_at: cached.cached_at,
            },
          },
        },
        {
          status: HTTP_STATUS.OK,
          headers: {
            'Cache-Control': `public, max-age=${CACHE_TTL.INSTANCES}`,
          },
        }
      );
    }

    logger.info('[Instances] Cache miss');

    // Map route parameters to QueryService parameters
    const queryParams: InstanceQueryParams = {
      provider: params.provider,
      region_code: params.region,
      family: params.instance_family as 'general' | 'compute' | 'memory' | 'storage' | 'gpu' | undefined,
      min_vcpu: params.min_vcpu,
      max_vcpu: params.max_vcpu,
      min_memory: params.min_memory_gb ? params.min_memory_gb * 1024 : undefined, // Convert GB to MB
      max_memory: params.max_memory_gb ? params.max_memory_gb * 1024 : undefined, // Convert GB to MB
      min_price: undefined, // Route doesn't expose min_price
      max_price: params.max_price,
      has_gpu: params.has_gpu,
      sort_by: params.sort_by,
      sort_order: params.order,
      page: Math.floor(params.offset / params.limit) + 1, // Convert offset to page
      limit: params.limit,
    };

    // Get QueryService singleton (reused across requests)
    const queryService = getQueryService(env.DB, env);
    const result = await queryService.queryInstances(queryParams);

    const queryTime = Date.now() - startTime;

    logger.info('[Instances] Query executed', {
      queryTime,
      results: result.data.length,
      total: result.pagination.total_results,
    });

    // Prepare response data
    const responseData = {
      instances: result.data,
      pagination: {
        total: result.pagination.total_results,
        limit: params.limit,
        offset: params.offset,
        has_more: result.pagination.has_next,
      },
      metadata: {
        cached: false,
        last_sync: new Date().toISOString(),
        query_time_ms: queryTime,
        filters_applied: result.meta.filters_applied,
      },
    };

    // Store result in cache
    try {
      await cacheService.set(cacheKey, responseData, CACHE_TTL.INSTANCES);
    } catch (error) {
      // Graceful degradation: log error but don't fail the request
      logger.error('[Instances] Cache write failed',
        error instanceof Error ? { message: error.message } : { error: String(error) });
    }

    return Response.json(
      {
        success: true,
        data: responseData,
      },
      {
        status: HTTP_STATUS.OK,
        headers: {
          'Cache-Control': `public, max-age=${CACHE_TTL.INSTANCES}`,
        },
      }
    );

  } catch (error) {
    logger.error('[Instances] Unexpected error', { error });

    return Response.json(
      {
        success: false,
        error: {
          code: 'QUERY_FAILED',
          message: 'Instance query failed. Please try again later.',
          request_id: crypto.randomUUID(),
        },
      },
      { status: HTTP_STATUS.INTERNAL_ERROR }
    );
  }
}