/**
 * Conversation persistence for @geepers/chat
 * localStorage-backed with max 20 conversations, sorted by updatedAt.
 */

import type { ConversationRecord, Message, Provider } from '../types/index.js';

const DEFAULT_KEY = 'gchat_conversations';
const MAX_CONVOS = 20;

export class ConversationStorage {
  private readonly key: string;

  constructor(storageKey = DEFAULT_KEY) {
    this.key = storageKey;
  }

  private read(): Record<string, ConversationRecord> {
    try {
      return JSON.parse(localStorage.getItem(this.key) || '{}');
    } catch {
      return {};
    }
  }

  private write(data: Record<string, ConversationRecord>): void {
    try {
      localStorage.setItem(this.key, JSON.stringify(data));
    } catch {
      // Storage full or unavailable — skip silently
    }
  }

  all(): ConversationRecord[] {
    const data = this.read();
    return Object.values(data).sort((a, b) => b.updatedAt - a.updatedAt);
  }

  get(id: string): ConversationRecord | undefined {
    return this.read()[id];
  }

  save(record: ConversationRecord): void {
    const data = this.read();
    data[record.id] = record;

    // Trim to max
    const sorted = Object.keys(data).sort(
      (a, b) => data[b].updatedAt - data[a].updatedAt
    );
    if (sorted.length > MAX_CONVOS) {
      sorted.slice(MAX_CONVOS).forEach(k => delete data[k]);
    }

    this.write(data);
  }

  delete(id: string): void {
    const data = this.read();
    delete data[id];
    this.write(data);
  }

  /** Create a new ConversationRecord from the given messages */
  static build(
    id: string,
    messages: Message[],
    provider: Provider,
    systemPrompt: string
  ): ConversationRecord {
    const first = messages.find(m => m.role === 'user');
    const title = first
      ? first.content.slice(0, 50) + (first.content.length > 50 ? '…' : '')
      : 'New conversation';

    return {
      id,
      title,
      messages,
      provider,
      systemPrompt,
      createdAt: Date.now(),
      updatedAt: Date.now(),
    };
  }
}