/**
 * Typed localStorage read/write helpers for the health-marketing-compliance-rag frontend.
 *
 * Keys:
 *   hmc-conversations    — array of Conversation objects (max 20, sorted by last_active_at desc)
 *   hmc-saved-responses  — array of SavedResponse objects (max 50, sorted by saved_at desc)
 */

import type { Conversation, Message, SavedResponse } from "../types";

const CONVERSATIONS_KEY = "hmc-conversations";
const SAVED_RESPONSES_KEY = "hmc-saved-responses";
const CONVERSATIONS_CAP = 20;
const SAVED_RESPONSES_CAP = 50;
const TITLE_MAX_LENGTH = 80;

// ---------------------------------------------------------------------------
// Conversations
// ---------------------------------------------------------------------------

/**
 * Reads the stored conversations array from localStorage.
 * Returns an empty array on missing key or JSON parse error.
 */
export function readConversations(): Conversation[] {
  try {
    const raw = localStorage.getItem(CONVERSATIONS_KEY);
    if (raw === null) return [];
    return JSON.parse(raw) as Conversation[];
  } catch {
    return [];
  }
}

/**
 * Writes conversations to localStorage, enforcing a cap of 20 entries.
 * Entries are sorted by `last_active_at` descending before the cap is applied,
 * so the oldest entry is always the one evicted.
 *
 * On `QuotaExceededError`: evicts the oldest conversation and retries once.
 * If the retry also fails, emits a console warning and swallows the error.
 */
export function writeConversations(conversations: Conversation[]): void {
  // Sort descending by last_active_at, then cap at 20.
  const sorted = [...conversations].sort(
    (a, b) =>
      new Date(b.last_active_at).getTime() -
      new Date(a.last_active_at).getTime()
  );
  const capped = sorted.slice(0, CONVERSATIONS_CAP);

  try {
    localStorage.setItem(CONVERSATIONS_KEY, JSON.stringify(capped));
  } catch (err) {
    if (isQuotaError(err)) {
      // Evict the oldest entry (last in the sorted array) and retry once.
      const evicted = capped.slice(0, capped.length - 1);
      try {
        localStorage.setItem(CONVERSATIONS_KEY, JSON.stringify(evicted));
      } catch (retryErr) {
        console.warn(
          "[storage] Failed to write conversations after quota eviction:",
          retryErr
        );
      }
    }
  }
}

// ---------------------------------------------------------------------------
// Saved responses
// ---------------------------------------------------------------------------

/**
 * Reads the stored saved-responses array from localStorage.
 * Returns an empty array on missing key or JSON parse error.
 */
export function readSavedResponses(): SavedResponse[] {
  try {
    const raw = localStorage.getItem(SAVED_RESPONSES_KEY);
    if (raw === null) return [];
    return JSON.parse(raw) as SavedResponse[];
  } catch {
    return [];
  }
}

/**
 * Writes saved responses to localStorage, enforcing a cap of 50 entries.
 * Entries are sorted by `saved_at` descending before the cap is applied,
 * so the oldest entry is always the one evicted.
 *
 * On `QuotaExceededError`: evicts the oldest response and retries once.
 * If the retry also fails, emits a console warning and swallows the error.
 */
export function writeSavedResponses(responses: SavedResponse[]): void {
  // Sort descending by saved_at, then cap at 50.
  const sorted = [...responses].sort(
    (a, b) =>
      new Date(b.saved_at).getTime() - new Date(a.saved_at).getTime()
  );
  const capped = sorted.slice(0, SAVED_RESPONSES_CAP);

  try {
    localStorage.setItem(SAVED_RESPONSES_KEY, JSON.stringify(capped));
  } catch (err) {
    if (isQuotaError(err)) {
      // Evict the oldest entry (last in the sorted array) and retry once.
      const evicted = capped.slice(0, capped.length - 1);
      try {
        localStorage.setItem(SAVED_RESPONSES_KEY, JSON.stringify(evicted));
      } catch (retryErr) {
        console.warn(
          "[storage] Failed to write saved responses after quota eviction:",
          retryErr
        );
      }
    }
  }
}

// ---------------------------------------------------------------------------
// Utility helpers
// ---------------------------------------------------------------------------

/**
 * Derives a conversation title from a message array.
 * Finds the first message with role "user" and truncates its content to 80
 * characters, appending the Unicode ellipsis character (U+2026) if truncated.
 * Returns "New conversation" when no user message is present.
 */
export function titleFromMessages(messages: Message[]): string {
  const userMessage = messages.find((m) => m.role === "user");
  if (!userMessage) return "New conversation";

  const { content } = userMessage;
  if (content.length > TITLE_MAX_LENGTH) {
    return content.slice(0, TITLE_MAX_LENGTH) + "\u2026";
  }
  return content;
}

/**
 * Returns the stable ID for a saved response: `"{conversationId}:{msgIndex}"`.
 */
export function savedResponseId(
  conversationId: string,
  msgIndex: number
): string {
  return `${conversationId}:${msgIndex}`;
}

// ---------------------------------------------------------------------------
// Internal helpers
// ---------------------------------------------------------------------------

function isQuotaError(err: unknown): boolean {
  if (err instanceof DOMException) {
    // Standard name across modern browsers.
    return (
      err.name === "QuotaExceededError" ||
      // Legacy Firefox name.
      err.name === "NS_ERROR_DOM_QUOTA_REACHED"
    );
  }
  return false;
}