import { Agent, get } from "node:https";
import * as fs from "node:fs";
import * as path from "node:path";
import { Buffer } from "node:buffer";
import type { ClientRequest } from "node:http";
import LRUCache from "lru-cache";
import { open } from "node:fs/promises";
import { createHash } from "node:crypto";
import { scoped } from "@paperclover/console";
import { escapeUri } from "./format.ts";

declare const Deno: any;

const sourceOfTruth = "https://nas.paperclover.net:43250";
const caCert = fs.readFileSync("src/file-viewer/cert.pem");

const diskCacheRoot = path.join(import.meta.dirname, "../.clover/filecache/");
const diskCacheMaxSize = 14 * 1024 * 1024 * 1024; // 14GB
const ramCacheMaxSize = 1 * 1024 * 1024 * 1024; // 1.5GB
const loadInProgress = new Map<
  string,
  Promise<{ stream: ReadableStream }> | { stream: ReadableStream }
>();
// Disk cache serializes the access times
const diskCacheState: Record<string, [size: number, lastAccess: number]> =
  loadDiskCacheState();
const diskCache = new LRUCache<string, number>({
  maxSize: diskCacheMaxSize,
  ttl: 0,
  sizeCalculation: (value) => value,
  dispose: (_, key) => {
    delete diskCacheState[key];
  },
  onInsert: (size, key) => {
    diskCacheState[key] = [size, Date.now()];
  },
});
const ramCache = new LRUCache<string, Buffer>({
  maxSize: ramCacheMaxSize,
  ttl: 0,
  sizeCalculation: (value) => value.byteLength,
});
let diskCacheFlush: NodeJS.Timeout | undefined;

{
  // Initialize the disk cache by validating all files exist, and then
  // inserting them in last to start order. State is repaired pessimistically.
  const toDelete = new Set(Object.keys(diskCacheState));
  fs.mkdirSync(diskCacheRoot, { recursive: true });
  for (
    const file of fs.readdirSync(diskCacheRoot, {
      recursive: true,
      encoding: "utf-8",
    })
  ) {
    const key = file.split("/").pop()!;
    if (key.length !== 40) continue;
    const entry = diskCacheState[key];
    if (!entry) {
      fs.rmSync(path.join(diskCacheRoot, file), {
        recursive: true,
        force: true,
      });
      delete diskCacheState[key];
      continue;
    }
    toDelete.delete(key);
  }
  for (const key of toDelete) {
    delete diskCacheState[key];
  }
  saveDiskCacheState();
  const sorted = Object.keys(diskCacheState).sort((a, b) =>
    diskCacheState[b][1] - diskCacheState[a][1]
  );
  for (const key of sorted) {
    diskCache.set(key, diskCacheState[key][0]);
  }
}

export type CacheSource = "ram" | "disk" | "miss" | "lan" | "flight";
export type CompressionFormat = "gzip" | "zstd" | "raw";
const compressionFormatMap = {
  gzip: "gz",
  zstd: "zstd",
  raw: "file",
} as const;

const log = scoped("file_cache");

const lanMount = "/Volumes/clover/Published";
const hasLanMount = fs.existsSync(lanMount);

/**
 * Fetches a file with the given compression format.
 * Uncompressed files are never persisted to disk.
 *
 * Returns a promise to either:
 * - Buffer: the data is from RAM cache
 * - ReadableStream: the data is being streamed in from disk/server
 *
 * Additionally, returns a string indicating the source of the data, for debugging.
 *
 * Callers must be able to consume both output types.
 */
export async function fetchFile(
  pathname: string,
  format: CompressionFormat = "raw",
): Promise<
  [Buffer | ReadableStream, encoding: CompressionFormat, src: CacheSource]
> {
  // 1. Ram cache
  const cacheKey = hashKey(`${pathname}:${format}`);
  const ramCacheHit = ramCache.get(cacheKey);
  if (ramCacheHit) {
    log(`ram hit: ${format}${pathname}`);
    return [ramCacheHit, format, "ram"];
  }

  // 2. Tee an existing loading stream.
  const inProgress = loadInProgress.get(cacheKey);
  if (inProgress) {
    const stream = await inProgress;
    const [stream1, stream2] = stream.stream.tee();
    loadInProgress.set(cacheKey, { stream: stream2 });
    log(`in-flight copy: ${format}${pathname}`);
    return [stream1, format, "flight"];
  }

  // 3. Disk cache + Load into ram cache.
  if (format !== "raw") {
    const diskCacheHit = diskCache.get(cacheKey);
    if (diskCacheHit) {
      diskCacheState[cacheKey] = [diskCacheHit, Date.now()];
      saveDiskCacheStateLater();
      log(`disk hit: ${format}/${pathname}`);
      return [
        startInProgress(
          cacheKey,
          new ReadableStream({
            start: async (controller) => {
              const stream = fs.createReadStream(
                path.join(diskCacheRoot, cacheKey),
              );
              const chunks: Buffer[] = [];
              stream.on("data", (chunk) => {
                controller.enqueue(chunk);
                chunks.push(chunk as Buffer);
              });
              stream.on("end", () => {
                controller.close();
                ramCache.set(cacheKey, Buffer.concat(chunks));
                finishInProgress(cacheKey);
              });
              stream.on("error", (error) => {
                controller.error(error);
              });
            },
          }),
        ),
        format,
        "disk",
      ];
    }
  }

  // 4. Lan Mount (access files that prod may not have)
  if (hasLanMount) {
    log(`lan hit: ${format}/${pathname}`);
    return [
      startInProgress(
        cacheKey,
        new ReadableStream({
          start: async (controller) => {
            const stream = fs.createReadStream(
              path.join(lanMount, pathname),
            );
            const chunks: Buffer[] = [];
            stream.on("data", (chunk) => {
              controller.enqueue(chunk);
              chunks.push(chunk as Buffer);
            });
            stream.on("end", () => {
              controller.close();
              ramCache.set(cacheKey, Buffer.concat(chunks));
              finishInProgress(cacheKey);
            });
            stream.on("error", (error) => {
              controller.error(error);
            });
          },
        }),
      ),
      "raw",
      "lan",
    ];
  }

  // 4. Fetch from server
  const url = `${compressionFormatMap[format]}${escapeUri(pathname)}`;
  log(`miss: ${format}${pathname}`);
  const response = await startInProgress(cacheKey, fetchFileUncached(url));
  const [stream1, stream2] = response.tee();
  handleDownload(cacheKey, format, stream2);
  return [stream1, format, "miss"];
}

export async function prefetchFile(
  pathname: string,
  format: CompressionFormat = "zstd",
) {
  const cacheKey = hashKey(`${pathname}:${format}`);
  const ramCacheHit = ramCache.get(cacheKey);
  if (ramCacheHit) {
    return;
  }
  if (hasLanMount) return;
  const url = `${compressionFormatMap[format]}${pathname}`;
  log(`prefetch: ${format}${pathname}`);
  const stream2 = await startInProgress(cacheKey, fetchFileUncached(url));
  handleDownload(cacheKey, format, stream2);
}

async function handleDownload(
  cacheKey: string,
  format: CompressionFormat,
  stream2: ReadableStream,
) {
  let chunks: Buffer[] = [];
  if (format !== "raw") {
    const file = await open(path.join(diskCacheRoot, cacheKey), "w");
    try {
      for await (const chunk of stream2) {
        await file.write(chunk);
        chunks.push(chunk);
      }
    } finally {
      file.close();
    }
  } else {
    for await (const chunk of stream2) {
      chunks.push(chunk);
    }
  }
  const final = Buffer.concat(chunks);
  chunks.length = 0;
  ramCache.set(cacheKey, final);
  if (format !== "raw") {
    diskCache.set(cacheKey, final.byteLength);
  }
  finishInProgress(cacheKey);
}

function hashKey(key: string): string {
  return createHash("sha1").update(key).digest("hex");
}

function startInProgress<T extends Promise<ReadableStream> | ReadableStream>(
  cacheKey: string,
  promise: T,
): T {
  if (promise instanceof Promise) {
    let resolve2: (stream: { stream: ReadableStream }) => void;
    let reject2: (error: Error) => void;
    const stream2Promise = new Promise<{ stream: ReadableStream }>(
      (resolve, reject) => {
        resolve2 = resolve;
        reject2 = reject;
      },
    );
    const stream1Promise = new Promise<ReadableStream>((resolve, reject) => {
      promise.then((stream) => {
        const [stream1, stream2] = stream.tee();
        const stream2Obj = { stream: stream2 };
        resolve2(stream2Obj);
        loadInProgress.set(cacheKey, stream2Obj);
        resolve(stream1);
      }, reject);
    });
    loadInProgress.set(cacheKey, stream2Promise);
    return stream1Promise as T;
  } else {
    const [stream1, stream2] = promise.tee();
    loadInProgress.set(cacheKey, { stream: stream2 });
    return stream1 as T;
  }
}

function loadDiskCacheState(): Record<
  string,
  [size: number, lastAccess: number]
> {
  try {
    const state = JSON.parse(
      fs.readFileSync(path.join(diskCacheRoot, "state.json"), "utf-8"),
    );
    return state;
  } catch (error) {
    return {};
  }
}

function saveDiskCacheStateLater() {
  if (diskCacheFlush) {
    return;
  }
  diskCacheFlush = setTimeout(() => {
    saveDiskCacheState();
  }, 60_000) as NodeJS.Timeout;
  if (diskCacheFlush.unref) {
    diskCacheFlush.unref();
  }
}

process.on("exit", () => {
  saveDiskCacheState();
});

function saveDiskCacheState() {
  fs.writeFileSync(
    path.join(diskCacheRoot, "state.json"),
    JSON.stringify(diskCacheState),
  );
}

function finishInProgress(cacheKey: string) {
  loadInProgress.delete(cacheKey);
}

// Self signed certificate must be trusted to be able to request the above URL.
//
// Unfortunately, Bun and Deno are both not node.js compatible, so those two
// runtimes need fallback implementations. The fallback implementations calls
// fetch with the `agent` value as the RequestInit. Since `fetch` decompresses
// the body for you, it must be disabled.
const agent: any = typeof Bun !== "undefined"
  ? {
    // Bun has two non-standard fetch extensions
    decompress: false,
    tls: {
      ca: caCert,
    },
  }
  // TODO: https://github.com/denoland/deno/issues/12291
  // : typeof Deno !== "undefined"
  // ? {
  //   // Deno configures through the non-standard `client` extension
  //   client: Deno.createHttpClient({
  //     caCerts: [caCert.toString()],
  //   }),
  // }
  // Node.js supports node:http
  : new Agent({
    ca: caCert,
  });

function fetchFileNode(pathname: string): Promise<ReadableStream> {
  return new Promise((resolve, reject) => {
    const request: ClientRequest = get(`${sourceOfTruth}/${pathname}`, {
      agent,
    });
    request.on("response", (response) => {
      if (response.statusCode !== 200) {
        reject(new Error(`Failed to fetch ${pathname}`));
        return;
      }

      const stream = new ReadableStream({
        start(controller) {
          response.on("data", (chunk) => {
            controller.enqueue(chunk);
          });

          response.on("end", () => {
            controller.close();
          });

          response.on("error", (error) => {
            controller.error(error);
            reject(error);
          });
        },
      });

      resolve(stream);
    });

    request.on("error", (error) => {
      reject(error);
    });
  });
}

async function fetchFileDenoBun(pathname: string): Promise<ReadableStream> {
  const req = await fetch(`${sourceOfTruth}/${pathname}`, agent);
  if (!req.ok) {
    throw new Error(`Failed to fetch ${pathname}`);
  }
  return req.body!;
}

const fetchFileUncached =
  typeof Bun !== "undefined" || typeof Deno !== "undefined"
    ? fetchFileDenoBun
    : fetchFileNode;

export async function toBuffer(
  stream: ReadableStream | Buffer,
): Promise<Buffer> {
  if (!(stream instanceof ReadableStream)) {
    return stream;
  }
  const chunks: Buffer[] = [];
  for await (const chunk of stream) {
    chunks.push(chunk);
  }
  return Buffer.concat(chunks);
}