import { readFile } from 'node:fs/promises';
import path from 'node:path';
import type { CodingConversationV2 } from './conversation-store';
import { validateSessionKey } from './conversation-store';
import type { ConversationSnapshot } from '../../shared/coding-conversation-contracts';
import { getPiManagedPaths } from '../coding-runtime/pi/resource-loader';
import { projectPiSessionSnapshot } from '../coding-runtime/pi/session-projector';

/** Read durable active-branch history without starting or reconfiguring Pi. */
export async function readCodingConversationHistory(
  userDataDir: string,
  projectId: string,
  conversation: CodingConversationV2
): Promise<ConversationSnapshot> {
  const base: ConversationSnapshot = {
    schemaVersion: 1,
    conversation: {
      id: conversation.id,
      projectId,
      agentId: conversation.agentId,
      title: conversation.title,
      model: { model: conversation.model, modelResolution: conversation.modelResolution },
    },
    nodes: [],
    run: { status: 'idle' },
    queue: { items: [] },
    context: { usedTokens: 0, contextWindow: 0, compaction: 'idle' },
    pendingInteractions: [],
    worker: { status: 'stopped', generation: 0 },
    cursor: { workerGeneration: 0, seq: 0 },
  };
  if (!conversation.sessionKey) return base;
  const filename = path.join(
    getPiManagedPaths(userDataDir).sessionsDir,
    projectId,
    validateSessionKey(conversation.sessionKey) + '.jsonl'
  );
  const text = await readFile(filename, 'utf8');
  // Pi 0.84.2 rebuilds its current leaf from the last non-header entry.
  const entries = text
    .split('\n')
    .filter((line) => line.trim())
    .map((line) => JSON.parse(line) as { id: string; type: string })
    .filter((entry) => entry.type !== 'session');
  const snapshot = await projectPiSessionSnapshot({
    snapshot: base,
    workerGeneration: 1,
    state: { isStreaming: false },
    entries: { entries, leafId: entries.at(-1)?.id ?? null },
  });
  return { ...snapshot, worker: { status: 'stopped', generation: 1 } };
}