/**
 * Object Store helpers. Wraps `@nats-io/obj` with the v0.4 `obj://` URI codec
 * used by `messages.materializePart` to offload >1 MB Part payloads.
 *
 * The SDK never opens its own ObjectStore — the caller (adapter) passes an
 * already-opened handle. Bucket naming is sesh-ops's concern.
 */

import type { ObjectStore } from "@nats-io/obj";
import { ObjectURLError } from "./errors.ts";

export const OBJ_URI_SCHEME = "obj" as const;

/**
 * obj:// URI shape: `obj://<scope-kind>/<scope-id>/<task-id>/<artifact-id>`
 * - scope-kind ∈ { "task" | "session" | "machine" }  (mirrors sesh-ops/scope)
 * - scope-id   — bucket-name-safe sesh-ops scope id (8 or 32 hex typically)
 * - task-id    — ULID
 * - artifact-id — ULID OR a part-id when used for Part offload
 */
export interface ObjectURLParts {
  scopeKind: "task" | "session" | "machine";
  scopeId: string;
  taskId: string;
  artifactId: string;
}

const SCOPE_ID_RE = /^[A-Za-z0-9_-]+$/;
const SEG_RE = /^[A-Za-z0-9_.-]+$/;

export function objectURL(p: ObjectURLParts): string {
  if (!SCOPE_ID_RE.test(p.scopeId)) {
    throw new ObjectURLError(`invalid scopeId for obj:// URL: ${p.scopeId}`);
  }
  if (!SEG_RE.test(p.taskId)) {
    throw new ObjectURLError(`invalid taskId for obj:// URL: ${p.taskId}`);
  }
  if (!SEG_RE.test(p.artifactId)) {
    throw new ObjectURLError(`invalid artifactId for obj:// URL: ${p.artifactId}`);
  }
  return `${OBJ_URI_SCHEME}://${p.scopeKind}/${p.scopeId}/${p.taskId}/${p.artifactId}`;
}

export function parseObjectURL(url: string): ObjectURLParts {
  let u: URL;
  try {
    u = new URL(url);
  } catch (e) {
    throw new ObjectURLError(`invalid URL: ${url}`, e);
  }
  if (u.protocol !== `${OBJ_URI_SCHEME}:`) {
    throw new ObjectURLError(`expected ${OBJ_URI_SCHEME}:// scheme, got ${u.protocol}`);
  }
  const scopeKind = u.hostname;
  if (scopeKind !== "task" && scopeKind !== "session" && scopeKind !== "machine") {
    throw new ObjectURLError(`invalid scope kind: ${scopeKind}`);
  }
  const segments = u.pathname.split("/").filter(Boolean);
  if (segments.length !== 3) {
    throw new ObjectURLError(`expected 3 path segments, got ${segments.length}: ${url}`);
  }
  const scopeId = segments[0] as string;
  const taskId = segments[1] as string;
  const artifactId = segments[2] as string;
  return { scopeKind, scopeId, taskId, artifactId };
}

/**
 * Compose the Object Store key for an obj:// URL. The store itself is
 * per-scope; the key is `<task-id>/<artifact-id>`. Bucket choice is the
 * caller's concern — the SDK doesn't open or name buckets.
 */
export function objectKey(p: Pick<ObjectURLParts, "taskId" | "artifactId">): string {
  return `${p.taskId}/${p.artifactId}`;
}

export async function putObject(
  os: ObjectStore,
  key: string,
  bytes: Uint8Array,
): Promise<void> {
  await os.putBlob({ name: key }, bytes);
}

export async function getObject(
  os: ObjectStore,
  key: string,
): Promise<Uint8Array | null> {
  return await os.getBlob(key);
}