import {
  type MediaChunkAckDto,
  type MediaUploadCreateDto,
  type MediaUploadSessionDto,
  type UploadCategory,
  type UploadSurface,
  MEDIA_UPLOAD_CHUNK_SIZE_BYTES,
  MediaUploadCanceledError,
  MediaUploadExpiredError,
  MediaUploadRejectedError,
  MediaUploadScanTimeoutError,
  isTerminalMediaUploadState,
} from "@/api/media-upload-contracts";
import {
  type MediaUploadEndpointSet,
  computeSha256Hex,
  isAbortError,
  isNetworkUploadError,
} from "@/api/media-upload-client";

const MAX_CREATE_ATTEMPTS = 2;
const MAX_CHUNK_RECOVERY_ATTEMPTS = 3;
const CHUNK_RECOVERY_BACKOFF_MS = 200;
const MAX_COMMIT_ATTEMPTS = 2;
const MAX_POLL_ATTEMPTS = 120;
const DEFAULT_POLL_DELAY_MS = 1_500;

export interface ResumableUploadArgs {
  file: File;
  endpoints: MediaUploadEndpointSet;
  surface: UploadSurface;
  category?: UploadCategory;
  signal?: AbortSignal;
  onProgress?: (percent: number) => void;
  /** Defaults to a fresh random UUID per attempt. */
  idempotencyKey?: string;
  digest?: (buffer: ArrayBuffer) => Promise<string>;
  pollDelayMs?: number;
}

export function chunkCountFor(sizeBytes: number, chunkSizeBytes: number): number {
  if (sizeBytes <= 0) return 1;
  return Math.ceil(sizeBytes / chunkSizeBytes);
}

export function missingChunkIndices(received: readonly number[], total: number): number[] {
  const acked = new Set(received);
  const missing: number[] = [];
  for (let index = 0; index < total; index += 1) {
    if (!acked.has(index)) {
      missing.push(index);
    }
  }
  return missing;
}

function acknowledgedBytes(
  received: readonly number[],
  totalBytes: number,
  chunkSize: number,
): number {
  let bytes = 0;
  for (const index of received) {
    if (index >= 0 && index < chunkCountFor(totalBytes, chunkSize)) {
      bytes += Math.min(chunkSize, totalBytes - index * chunkSize);
    }
  }
  return bytes;
}

function reportProgress(
  args: ResumableUploadArgs,
  received: readonly number[],
  totalBytes: number,
  chunkSize: number,
): void {
  if (!args.onProgress || totalBytes <= 0) return;
  const percent = Math.min(
    100,
    Math.round((acknowledgedBytes(received, totalBytes, chunkSize) / totalBytes) * 100),
  );
  args.onProgress(percent);
}

function assertNotAborted(signal: AbortSignal | undefined): void {
  if (signal?.aborted) {
    throw new DOMException("The upload was aborted.", "AbortError");
  }
}

function throwForTerminalState(state: MediaUploadSessionDto["state"]): void {
  if (state === "Rejected") throw new MediaUploadRejectedError();
  if (state === "Expired") throw new MediaUploadExpiredError();
  if (state === "Canceled") throw new MediaUploadCanceledError();
}

/** Idempotent create: a network failure retries the same idempotency key, never a new session. */
async function createSessionIdempotent(
  endpoints: MediaUploadEndpointSet,
  dto: MediaUploadCreateDto,
  signal: AbortSignal | undefined,
): Promise<MediaUploadSessionDto> {
  let lastError: unknown;
  for (let attempt = 0; attempt < MAX_CREATE_ATTEMPTS; attempt += 1) {
    try {
      return await endpoints.create(dto, signal);
    } catch (error) {
      if (!isNetworkUploadError(error)) throw error;
      lastError = error;
    }
  }
  throw lastError;
}

/**
 * Network failure recovery: re-read the session; terminal states settle here,
 * otherwise the returned receivedChunks define what still needs sending.
 */
async function recoverSession(
  endpoints: MediaUploadEndpointSet,
  uploadId: string,
  signal: AbortSignal | undefined,
): Promise<MediaUploadSessionDto> {
  let session: MediaUploadSessionDto;
  try {
    session = await endpoints.getStatus(uploadId, signal);
  } catch (error) {
    if (isAbortError(error)) throw error;
    if (isNetworkUploadError(error)) {
      // Still offline — bubble so the attempt surfaces as retryable failure.
      throw error;
    }
    throw error;
  }
  if (isTerminalMediaUploadState(session.state)) {
    throwForTerminalState(session.state);
    return session;
  }
  return session;
}

async function waitForScanTerminal(
  args: ResumableUploadArgs,
  uploadId: string,
): Promise<MediaUploadSessionDto> {
  const delayMs = args.pollDelayMs ?? DEFAULT_POLL_DELAY_MS;
  for (let attempt = 0; attempt < MAX_POLL_ATTEMPTS; attempt += 1) {
    assertNotAborted(args.signal);
    await new Promise((resolve) => setTimeout(resolve, delayMs));
    assertNotAborted(args.signal);
    let session: MediaUploadSessionDto;
    try {
      session = await args.endpoints.getStatus(uploadId, args.signal);
    } catch (error) {
      if (isAbortError(error)) throw error;
      continue; // Transient poll failure — keep polling until the deadline.
    }
    if (isTerminalMediaUploadState(session.state)) {
      throwForTerminalState(session.state);
      return session;
    }
  }
  throw new MediaUploadScanTimeoutError();
}

async function commitAndObserve(
  args: ResumableUploadArgs,
  uploadId: string,
): Promise<MediaUploadSessionDto> {
  let lastError: unknown;
  for (let attempt = 0; attempt < MAX_COMMIT_ATTEMPTS; attempt += 1) {
    try {
      const committed = await args.endpoints.commit(uploadId, args.signal);
      return committed.state === "Scanning" ? waitForScanTerminal(args, uploadId) : committed;
    } catch (error) {
      if (!isNetworkUploadError(error)) throw error;
      lastError = error;
      const observed = await args.endpoints.getStatus(uploadId, args.signal);
      if (observed.state === "Completed") return observed;
      if (isTerminalMediaUploadState(observed.state)) {
        throwForTerminalState(observed.state);
      }
      if (observed.state === "Scanning") return waitForScanTerminal(args, uploadId);
      if (attempt + 1 < MAX_COMMIT_ATTEMPTS) {
        continue; // Commit is idempotent for this uploadId.
      }
    }
  }
  throw lastError;
}

async function sendChunk(
  args: ResumableUploadArgs,
  uploadId: string,
  index: number,
  chunkSize: number,
): Promise<MediaChunkAckDto> {
  const { file } = args;
  const start = index * chunkSize;
  const end = Math.min(start + chunkSize, file.size);
  const blob = file.slice(start, end);
  const buffer = await blob.arrayBuffer();
  const digest = args.digest ?? computeSha256Hex;
  const sha256 = await digest(buffer);
  return args.endpoints.putChunk({
    uploadId,
    index,
    blob,
    start,
    end,
    totalBytes: file.size,
    sha256,
    signal: args.signal,
  });
}

/**
 * Upload one file through the resumable session API: create → chunks → commit → poll.
 * One in-flight chunk request per file; durable progress counts only acknowledged parts.
 */
export async function uploadFileResumable(
  args: ResumableUploadArgs,
): Promise<MediaUploadSessionDto> {
  assertNotAborted(args.signal);
  const createDto: MediaUploadCreateDto = {
    idempotencyKey: args.idempotencyKey ?? crypto.randomUUID(),
    fileName: args.file.name,
    contentType: args.file.type,
    sizeBytes: args.file.size,
    surface: args.surface,
    ...(args.category ? { category: args.category } : {}),
  };

  let session = await createSessionIdempotent(args.endpoints, createDto, args.signal);
  const uploadId = session.uploadId;
  const chunkSize =
    Number.isFinite(session.chunkSizeBytes) && session.chunkSizeBytes > 0
      ? session.chunkSizeBytes
      : MEDIA_UPLOAD_CHUNK_SIZE_BYTES;
  const totalChunks = chunkCountFor(args.file.size, chunkSize);
  reportProgress(args, session.receivedChunks, args.file.size, chunkSize);

  try {
    const recoveryAttempts = new Map<number, number>();
    for (;;) {
      assertNotAborted(args.signal);
      const missing = missingChunkIndices(session.receivedChunks, totalChunks);
      if (missing.length === 0) break;
      for (const index of missing) {
        assertNotAborted(args.signal);
        try {
          const ack = await sendChunk(args, session.uploadId, index, chunkSize);
          const acked = Array.isArray(ack?.receivedChunks) ? ack.receivedChunks : [];
          if (!acked.includes(index)) {
            // Treat a malformed ack as not-yet-acked so the loop cannot spin forever.
            throw new Error("Chunk acknowledgement missing from server response.");
          }
          session = { ...session, receivedChunks: acked };
        } catch (error) {
          if (!isNetworkUploadError(error)) throw error;
          session = await recoverSession(args.endpoints, session.uploadId, args.signal);
          if (session.receivedChunks.includes(index)) {
            recoveryAttempts.delete(index);
          } else {
            const attempts = (recoveryAttempts.get(index) ?? 0) + 1;
            recoveryAttempts.set(index, attempts);
            if (attempts >= MAX_CHUNK_RECOVERY_ATTEMPTS) throw error;
            await new Promise((resolve) =>
              setTimeout(resolve, CHUNK_RECOVERY_BACKOFF_MS * attempts),
            );
            assertNotAborted(args.signal);
          }
          break; // Re-derive missing indices from the recovered server state.
        }
        reportProgress(args, session.receivedChunks, args.file.size, chunkSize);
      }
    }

    assertNotAborted(args.signal);
    session = await commitAndObserve(args, uploadId);
  } catch (error) {
    // Cancellation aborts the in-flight request and DELETEs the known session.
    if (isAbortError(error)) {
      await args.endpoints.cancel(uploadId);
    }
    throw error;
  }

  throwForTerminalState(session.state);
  reportProgress(args, session.receivedChunks, args.file.size, chunkSize);
  return session;
}

/** Upload a queue of files with at most `maxConcurrent` files in flight. */
export async function runMediaUploadQueue<T>(
  items: readonly T[],
  runner: (item: T) => Promise<void>,
  maxConcurrent = 2,
): Promise<void> {
  let cursor = 0;
  const workers = Array.from({ length: Math.min(maxConcurrent, items.length) }, async () => {
    while (cursor < items.length) {
      const item = items[cursor];
      cursor += 1;
      await runner(item);
    }
  });
  await Promise.all(workers);
}