/**
 * Client Agent-scope primitive: mint a Cordis context tagged with the owning
 * Agent's identity. The mechanism mirrors the host `dsh-scope` architecture
 * (no-op plugin fiber + context tag + `Context.filter` routing predicate);
 * the shape deliberately diverges: the filter lives on the actx itself
 * instead of a separate carrier object, so scoped dispatch is plain cordis —
 * `actx.bail(actx, event, payload)` / `actx.emit(actx, ...)` — with no
 * wrapper. The host needs a detached carrier because its dispatch subject is
 * the business Agent object; client scope events carry only ids, so the
 * actx is the natural subject. The second divergence stands: the scope key
 * is the branded `SessionId` (value compared), not an object identity — the
 * agent and its session share one id (1:1, same axis; no separate AgentId
 * brand), and a client scope's identity IS that wire id. Third divergence,
 * deliberate: the client scopes the Agent IDENTITY, not a live Agent object
 * — a cold session's host Agent is already disposed while its client actx
 * stays alive for history viewing.
 */
import { Context as CordisContext } from 'cordis'
import type { Context, Fiber } from 'cordis'
import type { SessionId } from '@deepseek-ai/dsh-client-connection/client'
import type { TypeRTRemoteContextApi } from '@deepseek-ai/dsh-type-meta'

/** Context tag written by {@link createScope}. */
const kScope = Symbol('dsh.client.scope')

/** A minted Agent scope and its disposal boundary. */
export interface AgentScopeHandle {
  /**
   * Tagged context: scope-owned registrations and scoped dispatch both go
   * through it (passing it as the dispatch subject routes to this agent's
   * tagged listeners plus every untagged one).
   */
  ctx: Context & TypeRTRemoteContextApi<'agent'>
  /** Backing fiber (dispose tears down every scope-owned registration). */
  fiber: Fiber
}

/** Shared no-op plugin backing each Agent scope fiber. */
function agentScope(): void {}

/**
 * Mint an Agent scope under `ctx`: a no-op plugin fiber whose context
 * carries the agent tag and the dispatch filter — untagged listeners are
 * admitted globally, tagged listeners only for a matching agent.
 * Registrations through the returned ctx dispose with the fiber.
 * @param ctx - client root context the scope fiber mounts under.
 * @param key - owning agent identity (the routing tag; agent id === session id).
 * @returns the tagged context and its backing fiber.
 */
export function createScope(ctx: Context, key: SessionId): AgentScopeHandle {
  const fiber = ctx.plugin(agentScope)
  const scoped = fiber.ctx.extend({
    [kScope]: key,
    [CordisContext.filter](listenerCtx: Context): boolean {
      const tag = scopeOf(listenerCtx)
      return tag === undefined || tag === key
    },
  }) as Context & TypeRTRemoteContextApi<'agent'>
  return {
    fiber,
    ctx: scoped,
  }
}

/**
 * Read the nearest agent tag inherited by a context.
 * @param ctx - any client context.
 * @returns its agent identity (the session id), or undefined for root contexts.
 */
export function scopeOf(ctx: Context): SessionId | undefined {
  return (ctx as Context & { [kScope]?: SessionId })[kScope]
}
