import { mkdir, readFile, rename, rmdir, stat } from "node:fs/promises";
import { dirname, join, resolve } from "node:path";
import { type Context, type JsonlSessionMetadata, JsonlSessionRepo, type Session } from "@earendil-works/pi-agent-core";
import { NodeExecutionEnv } from "@earendil-works/pi-agent-core/harness/env/nodejs";

export interface OpenedSession {
  session: Session<JsonlSessionMetadata>;
  repo: JsonlSessionRepo;
  path: string;
  created: boolean;
}

const SAFE_RUN_ID = /^[A-Za-z0-9][A-Za-z0-9._-]{0,127}$/;

export function sessionPathFor(sessionDir: string, runId: string): string {
  if (!SAFE_RUN_ID.test(runId) || runId.includes("..")) throw new Error(`runId 不能用作文件名: ${runId}`);
  return join(resolve(sessionDir), `${runId}.jsonl`);
}

/**
 * 打开/创建 sessionDir/<runId>.jsonl。
 * JsonlSessionRepo 默认会把文件放到 `<root>/--cwd--/<时间戳>_<id>.jsonl`;这里创建后把空会话文件
 * (只有 header)移到固定路径,再按元数据打开,之后所有写入都追加到固定路径。
 * NodeExecutionEnv 只当作会话目录的 FileSystem 使用,它的 exec/shell 从不暴露给模型。
 */
export async function openRunSession(sessionDir: string, runId: string, ctx: Context): Promise<OpenedSession> {
  const root = resolve(sessionDir);
  await mkdir(root, { recursive: true });
  const target = sessionPathFor(root, runId);
  const fileSystem = new NodeExecutionEnv({ cwd: root });
  const repo = new JsonlSessionRepo({ fileSystem, sessionsRoot: root });

  const existing = await stat(target).catch(() => undefined);
  if (existing) {
    const firstLine = (await readFile(target, "utf8")).split("\n", 1)[0] ?? "";
    const header = JSON.parse(firstLine) as { id: string; createdAt: number; storageVersion: number; cwd: string };
    if (header.id !== runId) throw new Error(`会话文件 ${target} 属于 ${header.id},不是 ${runId}`);
    const metadata: JsonlSessionMetadata = {
      id: header.id,
      createdAt: header.createdAt,
      storageVersion: header.storageVersion,
      cwd: header.cwd,
      path: target,
      modifiedAt: existing.mtimeMs,
    };
    const session = await repo.open(metadata, ctx);
    return { session, repo, path: target, created: false };
  }

  const draft = await repo.create({ id: runId, cwd: root }, ctx);
  const draftPath = draft.metadata.path;
  await draft.close(ctx);
  await rename(draftPath, target);
  await rmdir(dirname(draftPath)).catch(() => undefined);
  const info = await stat(target);
  const session = await repo.open({ ...draft.metadata, path: target, modifiedAt: info.mtimeMs }, ctx);
  return { session, repo, path: target, created: true };
}