/**
 * The background task registry seam (`ctx.tasks`). It owns the contract for
 * task ids, session-scoped access, lifecycle state, completion listeners, and
 * owner cleanup while producers retain their execution resources. The
 * process-local registry lives in `@deepseek-ai/dsh-tasks-local`.
 * @module @deepseek-ai/dsh-tasks
 */

import { Context, Service } from 'cordis'
import type { Agent } from '@deepseek-ai/dsh-agent'
import type { TaskDoneListener, TaskId, TaskRead, TaskSnapshot, TaskStart } from './types.ts'

export { TaskId } from './types.ts'
export type {
  TaskDoneListener,
  TaskHooks,
  TaskKind,
  TaskKindMap,
  TaskOutcome,
  TaskRead,
  TaskSnapshot,
  TaskStart,
  TaskStatus,
} from './types.ts'

declare module 'cordis' {
  interface Context {
    tasks: TaskService
  }
}

/**
 * Abstract background task registry. Subclass, implement the abstract methods,
 * and load the subclass as a plugin — it registers as `ctx.tasks` (one
 * implementation per context; loading a second throws, which is cordis'
 * standard duplicate-service behavior).
 *
 * Implementations must honor these semantics:
 * - Registrations outlive producer and control-surface fibers. Owner and
 *   service disposal cancel live work and await compliant producers; a
 *   throwing teardown cancel force-fails only the record.
 * - Owned-task access is fenced by the owner's session id. Ids are
 *   predictable, so authorization — not secrecy — is the boundary.
 * - Settlement is first-wins: one terminal record, one round of contained
 *   listener notification, and released waiters, even against a late
 *   producer outcome.
 * - {@link start} refuses work while no control surface is attached, so a
 *   producer cannot start work that callers cannot collect or stop.
 */
export abstract class TaskService extends Service {
  constructor(ctx: Context) {
    // `abstract` erases at runtime, and this package name used to be the
    // mountable concrete registry — a stale composition row would otherwise
    // register a ctx.tasks with no method implementations and fail far from
    // the misconfiguration. Fail loud at load instead.
    if (new.target === TaskService) {
      throw new Error('@deepseek-ai/dsh-tasks is the abstract task registry seam; load an implementation such as @deepseek-ai/dsh-tasks-local instead')
    }
    super(ctx, 'tasks')
  }

  /**
   * Preflight access, validation, and owner cleanup before starting and
   * atomically registering work. A throwing starter leaves nothing registered;
   * after it returns, registration cannot fail. Settlement records the outcome,
   * notifies listeners, and releases waiters.
   * @param spec - task identity, owner, and synchronous starter.
   * @returns the registry-issued `<kind>-N` id.
   */
  abstract start(spec: TaskStart): TaskId

  /**
   * List caller-owned and unowned tasks in registration order without exposing
   * another session's labels.
   * @param caller - reading agent; a non-agent caller sees only unowned tasks.
   * @returns fresh snapshots.
   */
  abstract list(caller?: Agent): TaskSnapshot[]

  /**
   * Return a non-consuming snapshot without changing its read cursor or notice
   * state. Throws for an unknown or foreign task.
   * @param id - task to look up.
   * @param caller - reading agent checked against the owner.
   * @returns a fresh snapshot.
   */
  abstract get(id: TaskId, caller?: Agent): TaskSnapshot

  /**
   * Read the next stream delta, or the idempotent final output after settlement.
   * A terminal read marks the task reported. Throws for an unknown or foreign
   * task.
   * @param id - task to read.
   * @param caller - reading agent checked against the owner.
   * @returns output text and the post-read snapshot.
   */
  abstract read(id: TaskId, caller?: Agent): TaskRead

  /**
   * Request cancellation, then mark the task stopping and reported. A producer
   * throw propagates without changing task state. Throws for an unknown or
   * foreign task.
   * @param id - task to cancel.
   * @param caller - killing agent checked against the owner.
   * @param reason - logged reason forwarded to the producer.
   * @returns `requested` for live work, otherwise `already-finished`.
   */
  abstract kill(id: TaskId, caller?: Agent, reason?: string): 'requested' | 'already-finished'

  /**
   * Wait for settlement or timeout without cancelling the task. Caller abort
   * rejects only while the task is live; after settlement the terminal
   * snapshot wins so a notice suppressed for this waiter is still delivered.
   * Throws for invalid, unknown, or foreign input.
   * @param id - task to wait for.
   * @param timeoutMs - positive finite wait bound in milliseconds.
   * @param caller - waiting agent checked against the owner.
   * @param signal - optional cancellation of the wait itself.
   * @returns snapshot at settlement or timeout.
   */
  abstract wait(id: TaskId, timeoutMs: number, caller?: Agent, signal?: AbortSignal): Promise<TaskSnapshot>

  /**
   * Register an effect-scoped completion listener. Each listener is contained;
   * returned promises are observed but not awaited. No listener runs after
   * service disposal.
   * @param listener - receives each terminal snapshot and its exact owner.
   * @returns disposer that unregisters the listener.
   */
  abstract onTaskDone(listener: TaskDoneListener): () => void

  /**
   * Attach an effect-scoped surface that can read and stop tasks. {@link start}
   * refuses work while none is attached.
   * @param name - diagnostic label; duplicate names remain independent.
   * @returns disposer that detaches this surface.
   */
  abstract attachSurface(name: string): () => void
}

export default TaskService