/**
 * subagent-mode.ts — subagent sessions are read-only for memory and skill
 * writes. All automatic write-related work (background review, correction
 * detection, session flushes, session indexing) is skipped as well.
 *
 * A child session is identified by the `<active_agent name="..."/>` identity
 * tag that pi-subagents stamps into every child prompt
 * (permission-system-bridge.ts): the tag arrives via
 * `systemPromptOptions.customPrompt`. The tag is only trusted on that field —
 * never in the rendered system prompt, which a main session can legitimately
 * contain through project docs.
 *
 * Membership is tracked per session by its sessionManager identity: the same
 * process hosts the parent and its children concurrently, so a global boolean
 * would let a child's turn flip the parent's session into read-only mid-turn.
 */
import type { BeforeAgentStartEvent, ExtensionContext } from "@earendil-works/pi-coding-agent";

/** pi-subagents `<active_agent name="X"/>` identity tag contract. */
const ACTIVE_AGENT_TAG = /<active_agent\s+name=["'][^"']+["'][^>]*>/i;
const LEADING_ACTIVE_AGENT_TAG = /^\s*<active_agent\s+name=["'][^"']+["'][^>]*>/i;

export const SUBAGENT_WRITE_DISABLED_MESSAGE =
  "Memory and skill writes are disabled in subagent sessions; include this in your final report so the delegating agent can decide.";

const subagentSessionManagers = new WeakSet<object>();

/** Same regex as the pi-subagents `<active_agent>` contract, applied only to customPrompt. */
export function isSubagentCustomPrompt(customPrompt: string | undefined | null): boolean {
  return typeof customPrompt === "string" && ACTIVE_AGENT_TAG.test(customPrompt);
}

/**
 * before_agent_start hook: authoritative detection via the event's
 * systemPromptOptions.customPrompt.
 */
export function markSubagentSession(event: BeforeAgentStartEvent, ctx: ExtensionContext): void {
  if (isSubagentCustomPrompt(event.systemPromptOptions?.customPrompt)) {
    subagentSessionManagers.add(ctx.sessionManager);
  }
}

/**
 * session_start runs before before_agent_start; detect tag-leading prompts
 * early so session_start writes (skill migration, root setup) can be skipped.
 * A main prompt cannot lead with the tag — without customPrompt the rendered
 * prompt always opens with the base preamble.
 */
export function markSubagentSessionFromPrompt(systemPrompt: string, ctx: ExtensionContext): void {
  if (LEADING_ACTIVE_AGENT_TAG.test(systemPrompt)) {
    subagentSessionManagers.add(ctx.sessionManager);
  }
}

export function isSubagentSession(ctx: unknown): boolean {
  const sm = (ctx as { sessionManager?: unknown } | undefined | null)?.sessionManager;
  return typeof sm === "object" && sm !== null && subagentSessionManagers.has(sm);
}