import { ChildProcess, 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";

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) => ChildProcess;
  pathExists: (candidatePath: string) => boolean;
  fetchUrl: typeof fetch;
  platform: NodeJS.Platform;
  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;
};

export type NodecgProcessManager = {
  startNodecgProcess: () => Promise<ChildProcess>;
  waitForNodecgReady: (startTime: number) => Promise<void>;
  stopNodecgProcessGracefully: () => Promise<void>;
  getProcess: () => ChildProcess | null;
};

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

  let nodecgProcess: ChildProcess | 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 = async (): Promise<ChildProcess> => {
    validateNodecgInstall(nodecgRootPath, resolvedDeps.platform, 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 command = resolvedDeps.platform === "win32" ? "npx.cmd" : "npx";
    const child = resolvedDeps.spawnProcess(command, ["nodecg", "start"], {
      cwd: nodecgRootPath,
      env: {
        ...resolvedDeps.env,
        NODE_ENV: isDev ? "development" : "production",
        NODECG_PORT: appConfig.nodecgPort,
      },
      stdio: ["ignore", "pipe", "pipe"],
      detached: resolvedDeps.platform !== "win32",
      shell: false,
    });

    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 };
      nodecgProcess = null;
    });

    lastExit = null;
    lastStderrLine = null;
    nodecgProcess = child;
    return child;
  };

  const waitForNodecgReady = async (startTime: number): Promise<void> => {
    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 lib/scoreko-dev dependencies are installed 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> => {
    if (stopNodecgPromise) {
      return stopNodecgPromise;
    }

    if (!nodecgProcess || nodecgProcess.killed) {
      return Promise.resolve();
    }

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

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

    log(`Stopping NodeCG pid=${pid}`);
    killNodecgProcessTree(pid, "SIGTERM", log, resolvedDeps);

    stopNodecgPromise = new Promise((resolve) => {
      const complete = () => {
        if (nodecgProcess === processToStop) {
          nodecgProcess = null;
        }

        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}`);
            killNodecgProcessTree(pid, "SIGKILL", log, resolvedDeps);
          }
        },
        Math.max(0, appConfig.nodecgKillTimeoutMs),
      );
    });

    return stopNodecgPromise;
  };

  return {
    startNodecgProcess,
    waitForNodecgReady,
    stopNodecgProcessGracefully,
    getProcess: () => nodecgProcess,
  };
}

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,
    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,
  platform: NodeJS.Platform,
  pathExists: (candidatePath: string) => boolean,
  hasReadWriteAccessToPath: (candidatePath: string) => boolean,
): void {
  const packageJsonPath = path.join(nodecgRootPath, "package.json");
  const nodecgDependencyPath = path.join(nodecgRootPath, "node_modules", "nodecg", "package.json");
  const nodecgCliPath = path.join(nodecgRootPath, "node_modules", ".bin", platform === "win32" ? "nodecg.cmd" : "nodecg");
  const bundleAssetDirs = ["dashboard", "graphics", "extension", "extensions"].map((dir) =>
    path.join(nodecgRootPath, dir),
  );

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

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

  if (!pathExists(packageJsonPath)) {
    throw new Error(`${packageJsonPath} was not found. Expected a NodeCG bundle app at lib/scoreko-dev.`);
  }

  if (!pathExists(nodecgDependencyPath) || !pathExists(nodecgCliPath)) {
    throw new Error(
      [
        "NodeCG dependency is missing in lib/scoreko-dev.",
        `Not found: ${nodecgDependencyPath} and/or ${nodecgCliPath}`,
        "Solution: enter lib/scoreko-dev and install dependencies:",
        "  npm install",
      ].join("\n"),
    );
  }

  if (!bundleAssetDirs.some((candidatePath) => pathExists(candidatePath))) {
    throw new Error(
      [
        "scoreko-dev bundle appears incomplete.",
        `Expected one of: ${bundleAssetDirs.join(", ")}`,
        "Ensure extensions/dashboard/graphics assets exist inside lib/scoreko-dev.",
      ].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) => {
    const server = net.createServer();

    server.once("error", () => {
      resolve(false);
    });

    server.once("listening", () => {
      server.close(() => resolve(true));
    });

    server.listen(port, "127.0.0.1");
  });
}

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

function killNodecgProcessTree(
  pid: number,
  signal: NodeJS.Signals,
  log: (...args: unknown[]) => void,
  deps: Pick<NodecgProcessManagerDeps, "platform" | "killProcess">,
): void {
  if (deps.platform === "win32") {
    try {
      deps.killProcess(pid, signal);
    } catch (error) {
      log(`Error sending ${signal} to pid=${pid}`, error);
    }

    return;
  }

  try {
    deps.killProcess(-pid, signal);
  } catch {
    try {
      deps.killProcess(pid, signal);
    } catch (error) {
      log(`Error sending ${signal} to pid=${pid}`, error);
    }
  }
}