import type { MediaUpload } from "@rakazo/contracts";
import { Sha256 } from "./media-sha256";

/*
 * Resumable chunked upload of one device original (spec 2.7). The server owns
 * the protocol: `uploads.begin` opens or resumes an upload for the same asset
 * and content, chunks go to `PUT /api/media/uploads/:id/chunks/:index` with
 * their exact length, `uploads.status.receivedChunks` says what already
 * arrived, and an upload idle for too long answers 409 "Upload expired" and
 * must begin again. This module is the driver; the native glue injects I/O.
 */

/** A failed byte route or RPC with the HTTP status the server answered. */
export class MediaUploadHttpError extends Error {
  constructor(
    readonly status: number,
    message: string,
  ) {
    super(message);
    this.name = "MediaUploadHttpError";
  }
}

/** The local original no longer matches what the upload was opened for. */
export class MediaFileChangedError extends Error {
  constructor() {
    super("The file changed while reading it");
    this.name = "MediaFileChangedError";
  }
}

export function chunkCount(sizeBytes: number, chunkBytes: number): number {
  if (!Number.isSafeInteger(sizeBytes) || sizeBytes <= 0) throw new Error("Invalid upload size");
  if (!Number.isSafeInteger(chunkBytes) || chunkBytes <= 0) throw new Error("Invalid chunk size");
  return Math.ceil(sizeBytes / chunkBytes);
}

/** Byte range of chunk `index`: every chunk is full except the last. */
export function chunkRange(
  index: number,
  sizeBytes: number,
  chunkBytes: number,
): { start: number; length: number } {
  const count = chunkCount(sizeBytes, chunkBytes);
  if (!Number.isInteger(index) || index < 0 || index >= count) {
    throw new Error("Chunk index out of range");
  }
  const start = index * chunkBytes;
  return { start, length: Math.min(chunkBytes, sizeBytes - start) };
}

/** Chunk indexes the server has not confirmed yet, in upload order. */
export function missingChunks(
  upload: Pick<MediaUpload, "sizeBytes" | "chunkBytes" | "receivedChunks">,
) {
  const received = new Set(upload.receivedChunks);
  const missing: number[] = [];
  for (let index = 0; index < chunkCount(upload.sizeBytes, upload.chunkBytes); index++) {
    if (!received.has(index)) missing.push(index);
  }
  return missing;
}

export function isUploadExpired(error: unknown): boolean {
  return (
    error instanceof MediaUploadHttpError && error.status === 409 && /expired/i.test(error.message)
  );
}

/** Network failures and server hiccups are worth another try; client errors are not. */
export function isRetryableUploadError(error: unknown): boolean {
  if (error instanceof MediaUploadHttpError) {
    return error.status === 408 || error.status === 429 || error.status >= 500;
  }
  if (error instanceof MediaFileChangedError) return false;
  return !(error instanceof Error && error.name === "AbortError");
}

/** Bytes of one chunk, backed by a plain ArrayBuffer so fetch can send them. */
export type ChunkBytes = Uint8Array<ArrayBuffer>;

/** Reads `length` bytes at `start` from the original. */
export type ReadChunk = (start: number, length: number) => Promise<ChunkBytes> | ChunkBytes;

export async function hashOriginal(
  sizeBytes: number,
  read: ReadChunk,
  options: {
    readBytes?: number;
    signal?: AbortSignal;
    onProgress?: (fraction: number) => void;
  } = {},
): Promise<string> {
  const step = options.readBytes ?? 4 * 1024 * 1024;
  const hash = new Sha256();
  for (let start = 0; start < sizeBytes; start += step) {
    options.signal?.throwIfAborted();
    const length = Math.min(step, sizeBytes - start);
    const bytes = await read(start, length);
    if (bytes.byteLength !== length) throw new MediaFileChangedError();
    hash.update(bytes);
    options.onProgress?.(Math.min(1, (start + length) / sizeBytes));
  }
  return hash.hex();
}

export type UploadTransport = {
  begin(input: {
    assetId: string;
    sizeBytes: number;
    sha256: string;
    fileName: string;
  }): Promise<MediaUpload>;
  status(uploadId: string): Promise<MediaUpload>;
  putChunk(
    uploadId: string,
    index: number,
    bytes: ChunkBytes,
    signal?: AbortSignal,
  ): Promise<MediaUpload>;
  complete(uploadId: string): Promise<MediaUpload>;
};

export type UploadOriginalInput = {
  assetId: string;
  fileName: string;
  sizeBytes: number;
  sha256: string;
  read: ReadChunk;
  transport: UploadTransport;
  signal?: AbortSignal;
  /** Fraction of bytes the server confirmed, 0..1. */
  onProgress?: (fraction: number) => void;
  /** Consecutive failed attempts before giving up. */
  maxAttempts?: number;
  /** How often an expired upload may start over. */
  maxRestarts?: number;
  wait?: (ms: number, signal?: AbortSignal) => Promise<void>;
};

const defaultWait = (ms: number, signal?: AbortSignal) =>
  new Promise<void>((resolve, reject) => {
    const timer = setTimeout(resolve, ms);
    signal?.addEventListener(
      "abort",
      () => {
        clearTimeout(timer);
        reject(signal.reason);
      },
      { once: true },
    );
  });

export function retryDelayMs(attempt: number): number {
  return Math.min(30_000, 1_000 * 2 ** Math.max(0, attempt - 1));
}

function confirmedFraction(upload: MediaUpload): number {
  const count = chunkCount(upload.sizeBytes, upload.chunkBytes);
  let bytes = 0;
  for (const index of new Set(upload.receivedChunks)) {
    if (index >= 0 && index < count) {
      bytes += chunkRange(index, upload.sizeBytes, upload.chunkBytes).length;
    }
  }
  return bytes / upload.sizeBytes;
}

/**
 * Upload one original and complete it. Resumes from the server's
 * `receivedChunks` after any failure, begins again when the upload expired,
 * and backs off between retries. Returns the completed upload.
 */
export async function uploadOriginal(input: UploadOriginalInput): Promise<MediaUpload> {
  const { transport, signal } = input;
  const maxAttempts = input.maxAttempts ?? 5;
  const maxRestarts = input.maxRestarts ?? 2;
  const wait = input.wait ?? defaultWait;
  const begin = () =>
    transport.begin({
      assetId: input.assetId,
      sizeBytes: input.sizeBytes,
      sha256: input.sha256,
      fileName: input.fileName,
    });

  let restarts = 0;
  let failures = 0;
  let upload = await begin();
  for (;;) {
    signal?.throwIfAborted();
    try {
      if (upload.status === "complete") {
        input.onProgress?.(1);
        return upload;
      }
      if (upload.status === "failed") {
        throw new MediaUploadHttpError(409, "Upload expired");
      }
      if (upload.sizeBytes !== input.sizeBytes) throw new MediaFileChangedError();
      input.onProgress?.(confirmedFraction(upload));
      for (const index of missingChunks(upload)) {
        signal?.throwIfAborted();
        const range = chunkRange(index, upload.sizeBytes, upload.chunkBytes);
        const bytes = await input.read(range.start, range.length);
        if (bytes.byteLength !== range.length) throw new MediaFileChangedError();
        upload = await transport.putChunk(upload.id, index, bytes, signal);
        failures = 0;
        input.onProgress?.(confirmedFraction(upload));
      }
      upload = await transport.complete(upload.id);
      if (upload.status !== "complete") throw new Error("Upload did not complete");
      input.onProgress?.(1);
      return upload;
    } catch (error) {
      if (signal?.aborted) throw signal.reason ?? error;
      if (isUploadExpired(error)) {
        if (restarts >= maxRestarts) throw error;
        restarts += 1;
        failures = 0;
        upload = await begin();
        continue;
      }
      if (!isRetryableUploadError(error)) throw error;
      failures += 1;
      if (failures >= maxAttempts) throw error;
      await wait(retryDelayMs(failures), signal);
      // Ask the server what arrived; a chunk may have landed before the error.
      try {
        upload = await transport.status(upload.id);
      } catch (statusError) {
        if (isUploadExpired(statusError)) {
          if (restarts >= maxRestarts) throw statusError;
          restarts += 1;
          upload = await begin();
        } else if (!isRetryableUploadError(statusError)) {
          throw statusError;
        }
      }
    }
  }
}

/** Overall progress of several uploads, weighted by size. */
export function combinedProgress(items: Array<{ sizeBytes: number; fraction: number }>): number {
  const total = items.reduce((sum, item) => sum + item.sizeBytes, 0);
  if (total === 0) return 0;
  return items.reduce((sum, item) => sum + item.sizeBytes * item.fraction, 0) / total;
}