/**
 * Completion notice: pure functions only (AGENTS.md 硬约束 5, D4).
 * Lane decision, notice text, and the single sendMessage touchpoint.
 * Pattern: pi-subagents/src/runs/background/notify.ts.
 */

import type { ExtensionAPI } from "@earendil-works/pi-coding-agent";
import { statusLine, type JobSnapshot } from "./jobs.ts";

export type Lane = "wake" | "steer" | "drop";
export type Delivery = "wakeup" | "quiet";

export interface LaneInput {
	reported: boolean;
	idle: boolean;
	spentWakes: number;
	budget: number;
	delivery: Delivery;
}

/** D2 contract: notice carries only id/kind/label/status + where to read output. */
export function formatNotice(job: JobSnapshot): string {
	return `background job ${job.id} (${job.kind}: ${job.label}) finished ${statusLine(job)}. Read its output with job_output.`;
}

/**
 * Lane decision (dsh onJobDone):
 * - reported (model already knows via kill/terminal read) -> drop
 * - quiet delivery -> never wake, always steer
 * - idle with wake budget left -> wake (followUp + triggerTurn)
 * - anything else -> steer (inject into the current/next turn)
 */
export function decideLane(input: LaneInput): Lane {
	if (input.reported) return "drop";
	if (input.delivery === "quiet") return "steer";
	if (input.idle && input.spentWakes < input.budget) return "wake";
	return "steer";
}

/**
 * Replay-only notice variant: at session_start the job and its output are gone
 * (they died with the old session), so the collection instruction must not
 * point at a job that no longer exists. Swap the tail for an honest note.
 */
export function formatReplayNotice(content: string): string {
	const marker = " Read its output with job_output.";
	if (!content.endsWith(marker)) return content;
	return `${content.slice(0, -marker.length)} The session ended before this notice was delivered; the job's output is no longer available.`;
}

/** The only place touching pi.sendMessage (D4). Accepted = did not throw; Phase 4 persists on false. */
export function sendCompletion(
	send: Pick<ExtensionAPI, "sendMessage">,
	content: string,
	wake: boolean,
): boolean {
	try {
		send.sendMessage(
			{
				customType: "nightshift",
				content,
				display: true,
			},
			wake
				? { deliverAs: "followUp", triggerTurn: true }
				: { deliverAs: "steer" },
		);
		return true;
	} catch {
		return false;
	}
}

/** Ceiling for one completion notice; longer batches degrade (multi-byte safe). */
export const NOTICE_MAX_BYTES = 4096;

const encoder = new TextEncoder();

/**
 * Batch notice text. One job keeps the D2 single-line form; several become a
 * bulleted list. Over the byte ceiling the labels are dropped for ids only;
 * at pathological sizes it degrades to the count + job_list pointer.
 */
export function formatBatch(items: Array<{ job: JobSnapshot }>): string {
	if (items.length === 1) return formatNotice(items[0]!.job);

	const full = [
		`background jobs finished (${items.length}):`,
		...items.map(({ job }) => `- ${job.id} (${job.kind}: ${job.label}) ${statusLine(job)}`),
		"Read their output with job_output.",
	].join("\n");
	if (encoder.encode(full).byteLength <= NOTICE_MAX_BYTES) return full;

	const ids = `${items.length} background jobs finished: ${items.map(({ job }) => job.id).join(", ")}. Read their output with job_output.`;
	if (encoder.encode(ids).byteLength <= NOTICE_MAX_BYTES) return ids;

	return `${items.length} background jobs finished. Use job_list to see them and job_output to read output.`;
}