import { createHash } from "node:crypto";
import type { FileHandle } from "node:fs/promises";
import { assertArtifactReadActive } from "../artifacts/ArtifactFileOperation.js";
import { ArtifactReaderFailure } from "../artifacts/ArtifactReader.js";
import {
  BinaryFormatFailure,
  BinaryResourceFailure,
} from "../native/metadata/BinaryContainer.js";
import type {
  NativeReadRequest,
  NativeSectionDirectory,
} from "../native/metadata/NativeSectionDirectory.js";
export const GPU_OBJECT_BYTES = 128 * 1024 * 1024;
export const GPU_REPORT_BYTES = 16 * 1024 * 1024;
/** A retained-facts refusal aborts discovery; it is never downgraded to one opaque payload. */
export class GpuReportCapacityFailure extends BinaryResourceFailure {
  constructor() {
    super(
      "structure",
      GPU_REPORT_BYTES,
      "GPU facts exceed the 16 MiB retained report budget",
    );
  }
}
export const rejectGpu = (message: string): never => {
  throw new BinaryFormatFailure("malformed", message);
};
export const gpuCount = (value: bigint): number => {
  if (value < 0n || value > BigInt(Number.MAX_SAFE_INTEGER))
    rejectGpu("GPU range exceeds exact host offset precision");
  return Number(value);
};
export interface GpuSource {
  readonly size: number;
  readonly containerId: string | null;
  read(offset: number, size: number): Promise<Buffer>;
}
export const checkGpuRange = (
  length: number,
  offset: number,
  size: number,
): void => {
  if (
    !Number.isSafeInteger(offset) ||
    !Number.isSafeInteger(size) ||
    offset < 0 ||
    size < 0 ||
    offset > length ||
    size > length - offset
  )
    rejectGpu("GPU byte range is outside its containing object");
  if (size > GPU_OBJECT_BYTES)
    throw new BinaryResourceFailure(
      "structure",
      GPU_OBJECT_BYTES,
      "GPU object exceeds the 128 MiB decoding budget",
    );
};
export class GpuFileSource implements GpuSource {
  readonly containerId = null;
  bytesRead = 0;
  constructor(
    readonly file: FileHandle,
    readonly size: number,
    readonly signal?: AbortSignal,
  ) {}
  async read(offset: number, size: number): Promise<Buffer> {
    checkGpuRange(this.size, offset, size);
    const bytes = Buffer.alloc(size);
    let position = 0;
    while (position < size) {
      assertArtifactReadActive(this.signal);
      const result = await this.file.read(
        bytes,
        position,
        size - position,
        offset + position,
      );
      if (result.bytesRead === 0)
        throw new ArtifactReaderFailure(
          "integrity",
          "GPU source was truncated during inspection",
        );
      position += result.bytesRead;
      this.bytesRead += result.bytesRead;
    }
    return bytes;
  }
  async digest(): Promise<string> {
    const hash = createHash("sha256");
    for (let position = 0; position < this.size;) {
      const bytes = await this.read(
        position,
        Math.min(1024 * 1024, this.size - position),
      );
      hash.update(bytes);
      position += bytes.length;
    }
    return hash.digest("hex");
  }
}
export class GpuBufferSource implements GpuSource {
  readonly size: number;
  constructor(
    readonly bytes: Buffer,
    readonly containerId: string | null,
  ) {
    this.size = bytes.length;
  }
  async read(offset: number, size: number): Promise<Buffer> {
    checkGpuRange(this.size, offset, size);
    return this.bytes.subarray(offset, offset + size);
  }
}
export const readGpuNativeDirectory = async (
  source: GpuSource,
  steps: Generator<NativeReadRequest, NativeSectionDirectory, Buffer>,
): Promise<NativeSectionDirectory> => {
  let next = steps.next();
  while (!next.done) {
    const { offset, size } = next.value;
    next = steps.next(await source.read(offset, size));
  }
  return next.value;
};
export const gpuSha256 = (bytes: Buffer): string =>
  createHash("sha256").update(bytes).digest("hex");

export const nextGpuContainerOffset = async (
  source: GpuSource,
  start: number,
): Promise<number> => {
  let width = 64;
  for (let position = start; position < source.size;) {
    const bytes = await source.read(
      position,
      Math.min(width, source.size - position),
    );
    const index = bytes.findIndex((byte) => byte !== 0);
    if (index >= 0) return position + index;
    position += bytes.length;
    width = 65536;
  }
  return source.size;
};