import { $hook, $inject, Alepha } from "alepha";
import { $cache } from "alepha/cache";
import { CryptoProvider } from "alepha/crypto";
import { DateTimeProvider, type DurationLike } from "alepha/datetime";
import { $logger } from "alepha/logger";
import type { ServerRequest, ServerRoute } from "alepha/server";
import type { EtagMiddlewareOptionsResolved } from "../primitives/$etag.ts";

// ---------------------------------------------------------------------------------------------------------------------

export class ServerEtagProvider {
  protected readonly log = $logger();
  protected readonly alepha = $inject(Alepha);
  protected readonly crypto = $inject(CryptoProvider);
  protected readonly time = $inject(DateTimeProvider);
  protected readonly cache = $cache<RouteCacheEntry>({
    provider: "memory",
    name: "http:server",
  });

  public generateETag(content: string | Buffer): string {
    const data = typeof content === "string" ? content : content.toString();
    return `"${this.crypto.hash(data, "md5")}"`;
  }

  public async invalidate(route: ServerRoute) {
    await this.cache.invalidate(this.createCacheKey(route));
  }

  /**
   * Check cache for a stored response. Returns the cached body if found, undefined otherwise.
   * Called by the $etag() middleware before the handler runs.
   */
  public async checkCache(
    request: ServerRequest,
    options: EtagMiddlewareOptionsResolved,
  ): Promise<any> {
    if (!this.shouldStore(options)) {
      return undefined;
    }

    // Build key from route metadata (set by ServerRouterProvider before handler)
    // or from action request context (for .run() direct calls)
    const actionRequest = this.alepha.store.get("alepha.action.request");

    const keySource = {
      method:
        request.metadata?.routeMethod ??
        actionRequest?.method ??
        request.method ??
        "GET",
      path:
        request.metadata?.routePath ??
        String(actionRequest?.url ?? request.url ?? ""),
    } as ServerRoute;

    const key = this.createCacheKey(keySource, actionRequest ?? request);
    const cached = await this.cache.get(key);

    if (!cached) {
      this.log.trace("Cache miss", { key });
      return undefined;
    }

    this.log.trace("Cache hit", { key });

    // Mark as cache hit in request metadata
    request.metadata ??= {} as any;
    request.metadata.etagHit = true;

    // For HTTP routes, set reply headers
    if (request.reply) {
      // Check if client has matching ETag - return 304
      if (
        request.headers?.["if-none-match"] === cached.hash ||
        request.headers?.["if-modified-since"] === cached.lastModified
      ) {
        request.reply.status = 304;
        request.reply.setHeader("etag", cached.hash);
        request.reply.setHeader("last-modified", cached.lastModified);
        this.log.trace("ETag match, returning 304", {
          key,
          etag: cached.hash,
        });
        return request.reply.body;
      }

      request.reply.body = cached.body;
      request.reply.status = cached.status ?? 200;

      if (cached.contentType) {
        request.reply.setHeader("Content-Type", cached.contentType);
      }

      request.reply.setHeader("etag", cached.hash);
      request.reply.setHeader("last-modified", cached.lastModified);
    }

    // For action direct invocations, return body
    const body =
      cached.contentType === "application/json"
        ? JSON.parse(cached.body)
        : cached.body;

    return body;
  }

  // -------------------------------------------------------------------------------------------------------------------
  // Hooks (post-handler, read from request.metadata)
  // -------------------------------------------------------------------------------------------------------------------

  /**
   * After an action response, store it in cache if store is enabled.
   */
  protected readonly onActionResponse = $hook({
    on: "action:onResponse",
    handler: async ({ action, request, response }) => {
      const options = request.metadata
        ?.etagOptions as EtagMiddlewareOptionsResolved;
      if (!options || !this.shouldStore(options)) {
        return;
      }

      // Skip if this was a cache hit (don't re-store)
      if (request.metadata?.etagHit) {
        return;
      }

      // Don't cache error responses (status >= 400)
      if (request.reply.status && request.reply.status >= 400) {
        return;
      }

      if (!response) {
        return;
      }

      const contentType =
        typeof response === "string" ? "text/plain" : "application/json";
      const body =
        contentType === "text/plain" ? response : JSON.stringify(response);

      const generatedEtag = this.generateETag(body);
      const lastModified = this.time.toISOString();

      const key = this.createCacheKey(action.route, request);

      this.log.trace("Storing action response", {
        key,
        action: action.name,
      });

      await this.cache.set(key, {
        body: body,
        lastModified,
        contentType: contentType,
        hash: generatedEtag,
      });

      // Set Cache-Control header if configured
      const cacheControl = this.buildCacheControlHeader(options);
      if (cacheControl) {
        request.reply.setHeader("cache-control", cacheControl);
      }
    },
  });

  /**
   * Before sending the response, check ETag for etag-only routes.
   * This handles the case where etag is enabled but store is not.
   */
  protected readonly onSend = $hook({
    on: "server:onSend",
    handler: ({ request }) => {
      const options = request.metadata
        ?.etagOptions as EtagMiddlewareOptionsResolved;
      if (!options) {
        return;
      }

      const shouldStore = this.shouldStore(options);
      const shouldUseEtag = this.shouldUseEtag(options);

      if (request.reply.headers.etag) {
        // ETag already set, skip
        return;
      }

      if (
        !shouldStore &&
        shouldUseEtag &&
        request.reply.body != null &&
        (typeof request.reply.body === "string" ||
          Buffer.isBuffer(request.reply.body))
      ) {
        const generatedEtag = this.generateETag(request.reply.body);

        if (request.headers["if-none-match"] === generatedEtag) {
          request.reply.status = 304;
          request.reply.body = undefined;
          request.reply.setHeader("etag", generatedEtag);
          this.log.trace("ETag match on send, returning 304", {
            route: request.url,
            etag: generatedEtag,
          });
          return;
        }
      }
    },
  });

  /**
   * After the response is generated, store it and set ETag headers.
   */
  protected readonly onResponse = $hook({
    on: "server:onResponse",
    priority: "first",
    handler: async ({ route, request, response }) => {
      const options = request.metadata
        ?.etagOptions as EtagMiddlewareOptionsResolved;
      if (!options) {
        return;
      }

      // Set Cache-Control header if configured
      const cacheControl = this.buildCacheControlHeader(options);
      if (cacheControl) {
        response.headers["cache-control"] = cacheControl;
      }

      const shouldStore = this.shouldStore(options);
      const shouldUseEtag = this.shouldUseEtag(options);

      // Skip if neither cache nor etag is enabled
      if (!shouldStore && !shouldUseEtag) {
        return;
      }

      // Skip if this was a cache hit (don't re-store)
      if (request.metadata?.etagHit) {
        return;
      }

      // Don't cache error responses (status >= 400)
      if (response.status && response.status >= 400) {
        return;
      }

      // Initialize headers if not present
      response.headers ??= {};

      const key = this.createCacheKey(route, request);

      // Handle ReadableStream responses (e.g., SSR streaming)
      if (response.body instanceof ReadableStream && shouldStore) {
        // Tee the stream: one for client, one for cache collection
        const [clientStream, cacheStream] = (
          response.body as ReadableStream<Uint8Array>
        ).tee();

        // Replace response body with client stream (continues streaming to client)
        response.body = clientStream as typeof response.body;

        // Collect cache stream in background (non-blocking)
        this.collectStreamForCache(
          cacheStream,
          key,
          response.status,
          response.headers?.["content-type"],
          shouldUseEtag,
        )
          .then((hash) => {
            if (shouldUseEtag && hash) {
              this.log.trace("Stream cached with hash", { key, hash });
            }
          })
          .catch((err) => {
            this.log.warn("Failed to cache stream", { key, error: err });
          });

        return;
      }

      // Only process string responses (text, html, json, etc.)
      if (typeof response.body !== "string") {
        return;
      }

      const generatedEtag = this.generateETag(response.body);
      const lastModified = this.time.toISOString();

      // Store response if storing is enabled
      if (shouldStore) {
        this.log.trace("Storing response", {
          key,
          route: route.path,
          etag: shouldUseEtag,
        });

        await this.cache.set(key, {
          body: response.body,
          status: response.status,
          contentType: response.headers?.["content-type"],
          lastModified,
          hash: generatedEtag,
        });
      }

      // Set ETag headers if etag is enabled
      if (shouldUseEtag) {
        response.headers.etag = generatedEtag;
        response.headers["last-modified"] = lastModified;
      }
    },
  });

  // -------------------------------------------------------------------------------------------------------------------
  // Public helpers
  // -------------------------------------------------------------------------------------------------------------------

  public buildCacheControlHeader(
    options?: EtagMiddlewareOptionsResolved,
  ): string | undefined {
    if (!options) {
      return undefined;
    }

    const control = options.control;
    if (!control) {
      return undefined;
    }

    // If control is a string, return it directly
    if (typeof control === "string") {
      return control;
    }

    // If control is true, return default Cache-Control
    if (control === true) {
      return "public, max-age=300";
    }

    // Build Cache-Control from object directives
    const directives: string[] = [];

    if (control.public) {
      directives.push("public");
    }
    if (control.private) {
      directives.push("private");
    }
    if (control.noCache) {
      directives.push("no-cache");
    }
    if (control.noStore) {
      directives.push("no-store");
    }
    if (control.maxAge !== undefined) {
      const maxAgeSeconds = this.durationToSeconds(control.maxAge);
      directives.push(`max-age=${maxAgeSeconds}`);
    }
    if (control.sMaxAge !== undefined) {
      const sMaxAgeSeconds = this.durationToSeconds(control.sMaxAge);
      directives.push(`s-maxage=${sMaxAgeSeconds}`);
    }
    if (control.mustRevalidate) {
      directives.push("must-revalidate");
    }
    if (control.proxyRevalidate) {
      directives.push("proxy-revalidate");
    }
    if (control.immutable) {
      directives.push("immutable");
    }
    if (control.staleWhileRevalidate !== undefined) {
      const seconds = this.durationToSeconds(control.staleWhileRevalidate);
      directives.push(`stale-while-revalidate=${seconds}`);
    }

    return directives.length > 0 ? directives.join(", ") : undefined;
  }

  public shouldStore(options?: EtagMiddlewareOptionsResolved): boolean {
    if (!options) return false;
    if (options.store) return true;
    return false;
  }

  public shouldUseEtag(options?: EtagMiddlewareOptionsResolved): boolean {
    if (!options) return false;
    if (options.etag) return true;
    return false;
  }

  // -------------------------------------------------------------------------------------------------------------------
  // Protected helpers
  // -------------------------------------------------------------------------------------------------------------------

  protected durationToSeconds(duration: number | DurationLike): number {
    if (typeof duration === "number") {
      return duration;
    }

    return this.time.duration(duration).asSeconds();
  }

  protected createCacheKey(route: ServerRoute, config?: ServerRequest): string {
    const params: string[] = [];
    for (const [key, value] of Object.entries(config?.params ?? {})) {
      params.push(`${key}=${value}`);
    }
    for (const [key, value] of Object.entries(config?.query ?? {})) {
      params.push(`${key}=${value}`);
    }

    return `${route.method}:${(route.path ?? "").replaceAll(":", "")}:${params.join(",").replaceAll(":", "")}`;
  }

  /**
   * Collect a ReadableStream into a string and store it in the cache.
   * This runs in the background while the original stream is sent to the client.
   */
  protected async collectStreamForCache(
    stream: ReadableStream<Uint8Array>,
    key: string,
    status: number | undefined,
    contentType: string | undefined,
    generateEtag: boolean,
  ): Promise<string | undefined> {
    const chunks: Uint8Array[] = [];
    const reader = stream.getReader();

    try {
      while (true) {
        const { done, value } = await reader.read();
        if (done) break;
        chunks.push(value);
      }

      // Combine chunks into a single string
      const decoder = new TextDecoder();
      const body =
        chunks
          .map((chunk) => decoder.decode(chunk, { stream: true }))
          .join("") + decoder.decode(); // Flush remaining

      const hash = this.generateETag(body);
      const lastModified = this.time.toISOString();

      this.log.trace("Storing streamed response", { key });

      await this.cache.set(key, {
        body,
        status,
        contentType,
        lastModified,
        hash,
      });

      return generateEtag ? hash : undefined;
    } finally {
      reader.releaseLock();
    }
  }
}

// ---------------------------------------------------------------------------------------------------------------------

interface RouteCacheEntry {
  contentType?: string;
  body: any;
  status?: number;
  lastModified: string;
  hash: string;
}