import type { TaskDetails } from "../tool/types.js";
import { EMPTY_STATE, type TaskState } from "./state.js";

/**
 * Discriminator for `details` envelopes that match the persisted `TaskDetails`
 * shape. Defensive — branch entries from older or corrupt sessions are
 * skipped silently.
 */
export function isTaskDetails(value: unknown): value is TaskDetails {
	if (!value || typeof value !== "object") return false;
	const v = value as Record<string, unknown>;
	return Array.isArray(v.tasks) && typeof v.nextId === "number";
}

/**
 * Walk the current branch in chronological order; the LAST `toolResult` whose
 * `toolName === "todo"` and whose `details` shape matches `TaskDetails` wins
 * (last-write-wins). When no matching entry exists, returns `EMPTY_STATE`.
 *
 * Pure of module state — `index.ts` writes the returned snapshot into the
 * store after this returns. The function explicitly does NOT touch the store
 * cell.
 */
export function replayFromBranch(ctx: { sessionManager: { getBranch(): Iterable<unknown> } }): TaskState {
	let result: TaskState = { tasks: [...EMPTY_STATE.tasks], nextId: EMPTY_STATE.nextId };
	for (const entry of ctx.sessionManager.getBranch()) {
		const e = entry as { type?: string; message?: { role?: string; toolName?: string; details?: unknown } };
		if (e.type !== "message") continue;
		const msg = e.message;
		if (msg?.role !== "toolResult" || msg.toolName !== "todo") continue;
		if (!isTaskDetails(msg.details)) continue;
		result = {
			tasks: msg.details.tasks.map((t) => ({ ...t })),
			nextId: msg.details.nextId,
		};
	}
	return result;
}