import { spawn, SpawnOptions } from "node:child_process";
import fs from "node:fs";
import net from "node:net";
import path from "node:path";

import { AppRuntimeConfig } from "../config/runtime-config";
import { NODE_RUNTIME_NAME } from "../constants";
import { killProcessTree } from "./process-killer";

type NodecgProcessManagerConfig = {
  isDev: boolean;
  nodecgRootPath: string;
  nodecgBaseUrl: string;
  appConfig: AppRuntimeConfig;
  log: (...args: unknown[]) => void;
  deps?: Partial<NodecgProcessManagerDeps>;
};

type NodecgProcessManagerDeps = {
  spawnProcess: (command: string, args: string[], options: SpawnOptions) => NodecgChildProcess;
  pathExists: (candidatePath: string) => boolean;
  fetchUrl: typeof fetch;
  platform: NodeJS.Platform;
  execPath: string;
  env: NodeJS.ProcessEnv;
  killProcess: (pid: number, signal: NodeJS.Signals) => void;
  setTimer: (handler: () => void, timeoutMs: number) => unknown;
  stdoutWrite: (chunk: string) => void;
  stderrWrite: (chunk: string) => void;
  probePortAvailable: (port: number) => Promise<boolean>;
  hasReadWriteAccess: (candidatePath: string) => boolean;
};

type NodecgChildProcess = {
  pid?: number;
  killed: boolean;
  exitCode: number | null;
  signalCode: NodeJS.Signals | null;
  stdout?: ProcessOutputStream | null;
  stderr?: ProcessOutputStream | null;
  on(event: "exit", listener: (code: number | null, signal: NodeJS.Signals | null) => void): unknown;
  on(event: "error", listener: (error: Error) => void): unknown;
  once(event: "exit", listener: () => void): unknown;
};

type ProcessOutputStream = {
  on(event: "data", listener: (chunk: unknown) => void): unknown;
};

export type NodecgProcessManager = {
  startNodecgProcess: () => Promise<void>;
  waitForNodecgReady: (startTime: number) => Promise<void>;
  stopNodecgProcessGracefully: () => Promise<void>;
  getState: () => NodecgProcessState;
};

type NodecgProcessState = "idle" | "starting" | "running" | "stopping" | "stopped" | "failed";

export function createNodecgProcessManager({
  isDev,
  nodecgRootPath,
  nodecgBaseUrl,
  appConfig,
  log,
  deps,
}: NodecgProcessManagerConfig): NodecgProcessManager {
  const resolvedDeps = resolveDeps(deps);

  let nodecgProcess: NodecgChildProcess | null = null;
  let nodecgState: NodecgProcessState = "idle";
  let startNodecgPromise: Promise<void> | null = null;
  let stopNodecgPromise: Promise<void> | null = null;
  let lastExit: { code: number | null; signal: NodeJS.Signals | null } | null = null;
  let lastStderrLine: string | null = null;

  const startNodecgProcess = (): Promise<void> => {
    if (nodecgProcess && nodecgState === "running") {
      return Promise.resolve();
    }

    if (startNodecgPromise) {
      return startNodecgPromise;
    }

    if (nodecgState === "stopping") {
      return Promise.reject(new Error("Cannot start NodeCG while shutdown is in progress."));
    }

    nodecgState = "starting";
    startNodecgPromise = (async () => {
      // Fail fast with actionable errors before spawning child processes.
      validateNodecgInstall(
        nodecgRootPath,
        appConfig.bundleName,
        resolvedDeps.pathExists,
        resolvedDeps.hasReadWriteAccess,
      );

      const portAsNumber = Number.parseInt(appConfig.nodecgPort, 10);
      const isPortAvailable = await resolvedDeps.probePortAvailable(portAsNumber);
      if (!isPortAvailable) {
        throw new Error(
          `Port ${appConfig.nodecgPort} is already in use. Stop the process using it or set NODECG_PORT before starting.`,
        );
      }

      const indexPath = path.join(nodecgRootPath, "index.js");
      const child = resolvedDeps.spawnProcess(resolvedDeps.execPath, [indexPath], {
        cwd: nodecgRootPath,
        env: {
          ...resolvedDeps.env,
          NODE_ENV: isDev ? "development" : "production",
          NODECG_PORT: appConfig.nodecgPort,
          ELECTRON_RUN_AS_NODE: "1",
        },
        stdio: ["ignore", "pipe", "pipe"],
        detached: resolvedDeps.platform !== "win32",
        shell: false,
        windowsHide: true,
      });

      child.stdout?.on("data", (chunk) => {
        resolvedDeps.stdoutWrite(String(chunk));
      });

      child.stderr?.on("data", (chunk) => {
        const line = String(chunk);
        lastStderrLine = line.trim().length > 0 ? line.trim() : lastStderrLine;
        resolvedDeps.stderrWrite(line);
      });

      log(`NodeCG started with pid=${child.pid} using ${NODE_RUNTIME_NAME}`);

      child.on("exit", (code, signal) => {
        log(`NodeCG exited code=${code} signal=${signal ?? "none"}`);
        lastExit = { code, signal };

        if (nodecgProcess === child) {
          nodecgProcess = null;
        }

        if (nodecgState !== "stopping") {
          nodecgState = code === 0 ? "stopped" : "failed";
        }
      });

      lastExit = null;
      lastStderrLine = null;
      nodecgProcess = child;
      nodecgState = "running";
    })()
      .catch((error: unknown) => {
        nodecgState = "failed";
        throw error;
      })
      .finally(() => {
        startNodecgPromise = null;
      });

    return startNodecgPromise;
  };

  const waitForNodecgReady = async (startTime: number): Promise<void> => {
    // Poll the local NodeCG URL until it answers or we hit the configured timeout.
    while (Date.now() - startTime < appConfig.startupTimeoutMs) {
      if (!nodecgProcess) {
        const exitDetails = lastExit
          ? `Last recorded exit: code=${lastExit.code ?? "null"}, signal=${lastExit.signal ?? "none"}.`
          : "No NodeCG process exit code was recorded.";
        const stderrDetails = lastStderrLine ? `Last stderr: ${lastStderrLine}` : "No stderr output captured.";
        throw new Error(
          [
            "NodeCG exited before becoming ready.",
            exitDetails,
            stderrDetails,
            `NodeCG path: ${nodecgRootPath}`,
            "Check that the packaged runtime was installed correctly and the bundle exists.",
          ].join("\n"),
        );
      }

      try {
        const response = await resolvedDeps.fetchUrl(nodecgBaseUrl, { method: "GET" });
        if (response.ok || response.status === 404) {
          return;
        }
      } catch {
        // retry until timeout
      }

      await sleep(500, resolvedDeps.setTimer);
    }

    throw new Error(`Timeout waiting for NodeCG at ${nodecgBaseUrl} (${appConfig.startupTimeoutMs}ms).`);
  };

  const stopNodecgProcessGracefully = (): Promise<void> => {
    // Reuse the same stop promise to avoid sending multiple kill signals during app shutdown.
    if (stopNodecgPromise) {
      return stopNodecgPromise;
    }

    if (!nodecgProcess || nodecgProcess.killed) {
      nodecgState = "stopped";
      return Promise.resolve();
    }

    const processToStop = nodecgProcess;
    const pid = processToStop.pid;

    if (typeof pid !== "number") {
      log("NodeCG pid unavailable, skipping graceful stop");
      nodecgProcess = null;
      nodecgState = "stopped";
      return Promise.resolve();
    }

    nodecgState = "stopping";
    log(`Stopping NodeCG pid=${pid}`);
    killProcessTree(pid, "SIGTERM", {
      platform: resolvedDeps.platform,
      spawnProcess: resolvedDeps.spawnProcess,
      killProcess: resolvedDeps.killProcess,
      log,
    });

    stopNodecgPromise = new Promise((resolve) => {
      let completed = false;

      const complete = () => {
        if (completed) {
          return;
        }

        completed = true;

        if (nodecgProcess === processToStop) {
          nodecgProcess = null;
        }

        nodecgState = "stopped";
        stopNodecgPromise = null;
        resolve();
      };

      processToStop.once("exit", () => {
        complete();
      });

      resolvedDeps.setTimer(
        () => {
          if (processToStop.exitCode === null && processToStop.signalCode === null) {
            log(`NodeCG did not exit after SIGTERM, forcing SIGKILL pid=${pid}`);
            killProcessTree(pid, "SIGKILL", {
              platform: resolvedDeps.platform,
              spawnProcess: resolvedDeps.spawnProcess,
              killProcess: resolvedDeps.killProcess,
              log,
            });
            complete();
          }
        },
        Math.max(0, appConfig.nodecgKillTimeoutMs),
      );
    });

    return stopNodecgPromise;
  };

  return {
    startNodecgProcess,
    waitForNodecgReady,
    stopNodecgProcessGracefully,
    getState: () => nodecgState,
  };
}

function resolveDeps(deps?: Partial<NodecgProcessManagerDeps>): NodecgProcessManagerDeps {
  return {
    spawnProcess: deps?.spawnProcess ?? spawn,
    pathExists: deps?.pathExists ?? fs.existsSync,
    fetchUrl: deps?.fetchUrl ?? fetch,
    platform: deps?.platform ?? process.platform,
    execPath: deps?.execPath ?? process.execPath,
    env: deps?.env ?? process.env,
    killProcess: deps?.killProcess ?? process.kill,
    setTimer: deps?.setTimer ?? setTimeout,
    stdoutWrite: deps?.stdoutWrite ?? ((chunk) => process.stdout.write(chunk)),
    stderrWrite: deps?.stderrWrite ?? ((chunk) => process.stderr.write(chunk)),
    probePortAvailable: deps?.probePortAvailable ?? probePortAvailable,
    hasReadWriteAccess: deps?.hasReadWriteAccess ?? hasReadWriteAccess,
  };
}

function validateNodecgInstall(
  nodecgRootPath: string,
  bundleName: string,
  pathExists: (candidatePath: string) => boolean,
  hasReadWriteAccessToPath: (candidatePath: string) => boolean,
): void {
  const indexPath = path.join(nodecgRootPath, "index.js");
  const nodecgBootstrapPath = path.join(nodecgRootPath, "node_modules", "nodecg", "dist", "server", "bootstrap.js");
  const bundlePath = path.join(nodecgRootPath, "bundles", bundleName);

  if (!pathExists(nodecgRootPath)) {
    throw new Error(`NodeCG folder does not exist: ${nodecgRootPath}`);
  }

  if (!hasReadWriteAccessToPath(nodecgRootPath)) {
    throw new Error(`No read/write permissions on NodeCG: ${nodecgRootPath}`);
  }

  if (!pathExists(indexPath)) {
    throw new Error(`${indexPath} was not found. Build the packaged NodeCG runtime before starting Electron.`);
  }

  if (!pathExists(nodecgBootstrapPath)) {
    throw new Error(
      [
        "NodeCG is present but internal dependencies are missing.",
        `Not found: ${nodecgBootstrapPath}`,
        "Solution: rebuild the packaged runtime:",
        "  npm run prepare:runtime",
      ].join("\n"),
    );
  }

  if (!pathExists(bundlePath)) {
    throw new Error(
      [
        `Bundle '${bundleName}' was not found.`,
        `Expected path: ${bundlePath}`,
        "Build and package the Scoreko bundle before running Electron.",
      ].join("\n"),
    );
  }
}

function hasReadWriteAccess(candidatePath: string): boolean {
  try {
    fs.accessSync(candidatePath, fs.constants.R_OK | fs.constants.W_OK);
    return true;
  } catch {
    return false;
  }
}

function probePortAvailable(port: number): Promise<boolean> {
  return new Promise((resolve) => {
    // A successful TCP connection means some process is already listening on the port.
    const socket = net.createConnection({ host: "127.0.0.1", port });
    let resolved = false;

    const complete = (isAvailable: boolean): void => {
      if (resolved) {
        return;
      }

      resolved = true;
      socket.destroy();
      resolve(isAvailable);
    };

    socket.setTimeout(1000);

    socket.once("connect", () => {
      complete(false);
    });

    socket.once("timeout", () => {
      complete(true);
    });

    socket.once("error", (error: NodeJS.ErrnoException) => {
      if (error.code === "ECONNREFUSED" || error.code === "EHOSTUNREACH") {
        complete(true);
        return;
      }

      complete(false);
    });
  });
}

function sleep(ms: number, setTimer: (handler: () => void, timeoutMs: number) => unknown): Promise<void> {
  return new Promise((resolve) => {
    setTimer(resolve, ms);
  });
}