/** 上下文检查点（A3.8）：平台保存「发给模型的上下文」的摘要与来源，权威在平台（实施设计 1.5） */
import type { Database } from './db.js';

export interface ContextCheckpoint {
  sessionId: string;
  summary: string;
  summarySourceIds: string[];
  includedMessageIds: string[];
  lastMessageId: string | null;
  pinned: string[];
  estimatedChars: number;
  updatedAt: number;
}

interface CheckpointRow {
  session_id: string;
  summary: string;
  summary_source_ids: string;
  included_message_ids: string;
  last_message_id: string | null;
  pinned: string;
  estimated_chars: number;
  updated_at: number;
}

const parseIds = (raw: string): string[] => {
  try {
    const parsed = JSON.parse(raw) as unknown;
    return Array.isArray(parsed) ? parsed.filter((item): item is string => typeof item === 'string') : [];
  } catch {
    return [];
  }
};

export class ContextRepository {
  constructor(private readonly db: Database) {}

  save(checkpoint: Omit<ContextCheckpoint, 'updatedAt'>): void {
    this.db
      .prepare(
        `insert into context_checkpoints (session_id, summary, summary_source_ids, included_message_ids, last_message_id, pinned, estimated_chars, updated_at)
         values (?, ?, ?, ?, ?, ?, ?, ?)
         on conflict(session_id) do update set
           summary = excluded.summary,
           summary_source_ids = excluded.summary_source_ids,
           included_message_ids = excluded.included_message_ids,
           last_message_id = excluded.last_message_id,
           pinned = excluded.pinned,
           estimated_chars = excluded.estimated_chars,
           updated_at = excluded.updated_at`,
      )
      .run(
        checkpoint.sessionId,
        checkpoint.summary,
        JSON.stringify(checkpoint.summarySourceIds),
        JSON.stringify(checkpoint.includedMessageIds),
        checkpoint.lastMessageId,
        JSON.stringify(checkpoint.pinned),
        checkpoint.estimatedChars,
        Date.now(),
      );
  }

  get(sessionId: string): ContextCheckpoint | undefined {
    const row = this.db.prepare('select * from context_checkpoints where session_id = ?').get(sessionId) as unknown as CheckpointRow | undefined;
    if (!row) return undefined;
    return {
      sessionId: row.session_id,
      summary: row.summary,
      summarySourceIds: parseIds(row.summary_source_ids),
      includedMessageIds: parseIds(row.included_message_ids),
      lastMessageId: row.last_message_id,
      pinned: parseIds(row.pinned),
      estimatedChars: row.estimated_chars,
      updatedAt: row.updated_at,
    };
  }
}