import type { ConversationSnapshot, ConversationSummary } from "./types";

const MAX_CONVERSATIONS = 20;

function isSnapshot(value: unknown): value is ConversationSnapshot {
  const snapshot = value as ConversationSnapshot;

  return (
    snapshot?.schemaVersion === 1 &&
    typeof snapshot.sessionId === "string" &&
    snapshot.sessionId.length > 0 &&
    typeof snapshot.title === "string" &&
    Array.isArray(snapshot.messages) &&
    typeof snapshot.createdAt === "number" &&
    typeof snapshot.updatedAt === "number"
  );
}

export function parseArchive(raw: string | null): ConversationSnapshot[] {
  if (!raw) {
    return [];
  }

  try {
    const parsed = JSON.parse(raw) as unknown;
    if (!Array.isArray(parsed)) {
      return [];
    }

    return parsed.filter(isSnapshot);
  } catch {
    return [];
  }
}

export function serializeArchive(snapshots: ConversationSnapshot[]): string {
  return JSON.stringify(limitArchive(snapshots));
}

export function upsertSnapshot(
  snapshots: ConversationSnapshot[],
  snapshot: ConversationSnapshot,
): ConversationSnapshot[] {
  const next = snapshots.filter(
    (item) => item.sessionId !== snapshot.sessionId,
  );
  next.push(snapshot);

  return limitArchive(next);
}

export function findSnapshot(
  snapshots: ConversationSnapshot[],
  sessionId: string | null,
): ConversationSnapshot | null {
  if (!sessionId) {
    return null;
  }

  return snapshots.find((item) => item.sessionId === sessionId) ?? null;
}

export function listArchivedConversations(
  snapshots: ConversationSnapshot[],
  activeSessionId: string | null,
): ConversationSummary[] {
  return snapshots
    .filter((snapshot) => snapshot.sessionId !== activeSessionId)
    .sort((a, b) => b.updatedAt - a.updatedAt)
    .map((snapshot) => ({
      sessionId: snapshot.sessionId,
      title: snapshot.title,
      updatedAt: snapshot.updatedAt,
    }));
}

export function clearArchived(
  snapshots: ConversationSnapshot[],
  activeSessionId: string | null,
): ConversationSnapshot[] {
  return snapshots.filter((snapshot) => snapshot.sessionId === activeSessionId);
}

function limitArchive(
  snapshots: ConversationSnapshot[],
): ConversationSnapshot[] {
  return [...snapshots]
    .sort((a, b) => b.updatedAt - a.updatedAt)
    .slice(0, MAX_CONVERSATIONS);
}