import { spawn as nodeSpawn, type ChildProcessWithoutNullStreams } from "node:child_process";
import { join } from "node:path";
import type { AppConfig } from "../config.js";
import { RpcClient } from "../rpc/rpc-client.js";
import { SessionBridge } from "../bridge/session-bridge.js";
import type { ThtRunner } from "../tht/tht-runner.js";

export interface SessionRuntime {
  rpc: RpcClient;
  bridge: SessionBridge;
  child: ChildProcessWithoutNullStreams;
}

/** Injected test double signature: produce a child process, no args needed. */
type SpawnFn = () => ChildProcessWithoutNullStreams;

export class PiProcessManager {
  private runtimes = new Map<string, SessionRuntime>();
  private spawnFn: (sessionId: string, author: string) => ChildProcessWithoutNullStreams;

  constructor(private cfg: AppConfig, opts?: { spawnFn?: SpawnFn }) {
    if (opts?.spawnFn) {
      this.spawnFn = () => opts.spawnFn!();
    } else {
      this.spawnFn = (sessionId: string, author: string) => {
        const harnessVenvBin = join(cfg.harnessDir, ".venv", "bin");
        const env: NodeJS.ProcessEnv = {
          ...process.env,
          THT_SESSION: sessionId,
          THT_AUTHOR: author,
          PATH: `${harnessVenvBin}:${process.env.PATH ?? ""}`,
        };
        const child = nodeSpawn(cfg.piBin, ["--mode", "rpc", "--approve"], {
          cwd: cfg.harnessDir,
          env,
        });
        // Drain stderr so the child's stderr buffer never blocks the process.
        child.stderr.resume();
        return child;
      };
    }
  }

  count(): number { return this.runtimes.size; }

  get(id: string): SessionRuntime | undefined { return this.runtimes.get(id); }

  async spawnFor(
    sessionId: string,
    o: { provider?: string; model?: string; thinking?: string; author?: string; mode?: "new" | "resume" },
  ): Promise<SessionRuntime> {
    // Idempotent per session id: tear down any existing runtime for this id
    // first (before the cap check) so a resume/respawn neither leaks the old
    // child nor falsely hits the process cap.
    const existing = this.runtimes.get(sessionId);
    if (existing) {
      existing.child.kill();
      this.runtimes.delete(sessionId);
    }
    if (this.runtimes.size >= this.cfg.maxPiProcesses) {
      throw new Error("max Pi processes reached");
    }
    const author = o.author ?? "dev@local";
    const child = this.spawnFn(sessionId, author);
    const rpc = new RpcClient(child);
    const bridge = new SessionBridge(rpc);
    const rt: SessionRuntime = { rpc, bridge, child };
    this.runtimes.set(sessionId, rt);
    // Identity-checked: a stale child's exit must not evict a newer runtime.
    child.on("exit", () => { if (this.runtimes.get(sessionId) === rt) this.runtimes.delete(sessionId); });

    const provider = o.provider ?? this.cfg.defaults.provider;
    const model = o.model ?? this.cfg.defaults.model;
    const thinking = o.thinking ?? this.cfg.defaults.thinking;

    if (provider && model) {
      await rpc.request({ type: "set_model", provider, modelId: model } as object & { type: string });
    }
    if (thinking) {
      await rpc.request({ type: "set_thinking_level", level: thinking } as object & { type: string });
    }

    const message = o.mode === "resume"
      ? `/riprendi-sessione ${sessionId}`
      : `/nuova-domanda "kickoff"`;
    rpc.send({ type: "prompt", message });
    return rt;
  }

  async resume(sessionId: string, tht: ThtRunner): Promise<SessionRuntime> {
    const manifest = await tht.sessionShow(sessionId) as { provider?: string; model?: string; thinking?: string } | null;
    return this.spawnFor(sessionId, {
      provider: manifest?.provider,
      model: manifest?.model,
      thinking: manifest?.thinking,
      mode: "resume",
    });
  }

  teardown(id: string): void {
    const rt = this.runtimes.get(id);
    if (rt) {
      rt.child.kill();
      this.runtimes.delete(id);
    }
  }
}