import { createHash, randomBytes } from "node:crypto";
import { createReadStream, readFileSync } from "node:fs";
import { mkdir, open, readFile, rm } from "node:fs/promises";
import path from "node:path";
import { rootPath } from "./config";
import type { ParsedSshInvocation, ParsedSshRoute, SshCaptureResult } from "./ssh";

export interface SshRemoteCommandStreamHandlers {
  onStdout(chunk: Buffer): Promise<void> | void;
  onStderr?(chunk: Buffer): Promise<void> | void;
}

export interface SshRemoteCommandExecutor {
  streamInactivityTimeoutMs: number;
  runRemoteCommand(remoteCommand: string, input?: string, options?: { runtimeTimeoutMs?: number }): Promise<SshCaptureResult>;
  streamRemoteCommand?(
    remoteCommand: string,
    handlers: SshRemoteCommandStreamHandlers,
    input?: string,
    options?: { inactivityTimeoutMs?: number },
  ): Promise<SshCaptureResult>;
}

export interface SshFileTransferCommandBuilders {
  buildRouteCommand(route: ParsedSshRoute, command: string[], options?: { stdin?: boolean }): string;
  buildWindowsPowerShellCommand(script: string): string;
}

type SshFileTransferOperation =
  | "stat"
  | "write-b64-argv"
  | "write-b64-stdin"
  | "write-b64-begin"
  | "write-b64-block-stdin"
  | "write-b64-abort"
  | "write-b64-commit";

interface SshFileTransferCliOptions {
  action: "upload" | "download";
  localPath: string;
  remotePath: string;
  inactivityTimeoutMs?: number;
  allowTextTransfer: boolean;
}

interface SshFileTransferStat {
  bytes: number;
  sha256: string;
}

interface SshFileTransferEndpointStat extends SshFileTransferStat {
  side: "local" | "remote";
  path: string;
}

interface SshFileTransferWriteResult {
  strategy: "argv" | "stdin" | "parallel-chunked-stdin";
  chunks: number;
  concurrency: number;
}

interface SshFileTransferDownloadResult {
  remote: SshFileTransferStat;
  local: SshFileTransferStat;
  strategy: "tcp-pool-parallel-range-stream";
  transport: "host.ssh.tcp-pool";
  sourceRoute: string;
  sourcePath: string;
  chunks: number;
  concurrency: number;
  elapsedMs: number;
  throughputBytesPerSecond: number;
  remainingBytes: number;
}

export interface SshVerifiedDownloadResult {
  remotePath: string;
  localPath: string;
  bytes: number;
  sha256: string;
  verified: true;
  verification: Record<string, unknown>;
  transfer: {
    strategy: SshFileTransferDownloadResult["strategy"];
    transport: SshFileTransferDownloadResult["transport"];
    sourceRoute: string;
    sourcePath: string;
    chunks: number;
    concurrency: number;
    elapsedMs: number;
    throughputBytesPerSecond: number;
    remainingBytes: number;
  };
}

class SshFileTransferError extends Error {
  constructor(message: string, public readonly details: Record<string, unknown> = {}) {
    super(message);
    this.name = "SshFileTransferError";
  }
}

const fileTransferWriteB64ArgvLimit = 48_000;
const fileTransferWriteRawChunkBytes = 3 * 1024 * 1024;
const fileTransferDownloadMinimumRangeBytes = 1024 * 1024;
const fileTransferDownloadRangeAlignment = 64 * 1024;
const fileTransferConfigPath = "config/unidesk-cli.yaml";
const fileTransferWriteB64ChunkChars = 1_398_104;
const fileTransferUploadProgressEveryChunks = 16;
const fileTransferDownloadProgressEveryChunks = 256;

interface SshFileTransferSettings {
  concurrency: number;
  transportOpenRetries: number;
  transportRetryDelayMs: number;
}

const knownTextExtensions = new Set([
  ".bat", ".bib", ".c", ".cc", ".cfg", ".cmd", ".conf", ".cpp", ".css", ".csv", ".cts", ".cxx",
  ".diff", ".env", ".go", ".h", ".hpp", ".htm", ".html", ".ini", ".java", ".js", ".json", ".jsonl",
  ".jsx", ".less", ".log", ".md", ".markdown", ".mts", ".mjs", ".patch", ".ps1", ".py", ".rs", ".scss",
  ".sh", ".sql", ".svg", ".tex", ".text", ".toml", ".ts", ".tsv", ".tsx", ".txt", ".xml", ".yaml", ".yml",
]);

const knownTextBasenames = new Set([
  ".editorconfig", ".gitattributes", ".gitignore", "agents.md", "dockerfile", "license", "makefile", "mdtodo", "readme",
]);

const fileTransferUsageHint = {
  code: "prefer-remote-text-operations",
  message: "已知文本路径会在传输前被拦截；读取使用 cat/head/tail/rg，修改直接使用 apply-patch quoted heredoc。upload/download 仅用于必要的二进制文件或生成物。",
  preferredOperations: {
    read: ["cat", "head", "tail", "rg"],
    edit: ["apply-patch <<'PATCH'"],
  },
};

function readFileTransferSettings(configPath = rootPath(fileTransferConfigPath)): SshFileTransferSettings {
  const source = `${fileTransferConfigPath}#trans.fileTransfer`;
  const root = Bun.YAML.parse(readFileSync(configPath, "utf8")) as unknown;
  if (typeof root !== "object" || root === null || Array.isArray(root)) {
    throw new Error(`${fileTransferConfigPath} must be an object`);
  }
  const trans = (root as Record<string, unknown>).trans;
  if (typeof trans !== "object" || trans === null || Array.isArray(trans)) {
    throw new Error(`${fileTransferConfigPath}#trans must be an object`);
  }
  const transfer = (trans as Record<string, unknown>).fileTransfer;
  if (typeof transfer !== "object" || transfer === null || Array.isArray(transfer)) {
    throw new Error(`${fileTransferConfigPath}#trans.fileTransfer must be an object`);
  }
  const values = transfer as Record<string, unknown>;
  const concurrency = values.concurrency;
  if (!Number.isInteger(concurrency) || Number(concurrency) < 1) {
    throw new Error(`${source}.concurrency must be a positive integer`);
  }
  const transportOpenRetries = values.transportOpenRetries;
  if (!Number.isInteger(transportOpenRetries) || Number(transportOpenRetries) < 0) {
    throw new Error(`${source}.transportOpenRetries must be a non-negative integer`);
  }
  const transportRetryDelayMs = values.transportRetryDelayMs;
  if (!Number.isInteger(transportRetryDelayMs) || Number(transportRetryDelayMs) < 0) {
    throw new Error(`${source}.transportRetryDelayMs must be a non-negative integer`);
  }
  return {
    concurrency: Number(concurrency),
    transportOpenRetries: Number(transportOpenRetries),
    transportRetryDelayMs: Number(transportRetryDelayMs),
  };
}

export function readFileTransferConcurrency(configPath = rootPath(fileTransferConfigPath)): number {
  return readFileTransferSettings(configPath).concurrency;
}

function isPreDispatchTransportFailure(result: SshCaptureResult): boolean {
  return /timed out waiting for provider session|provider ssh tcp data pool has no idle channel|requested ssh tcp data channel is not ready|provider-data-pool-exhausted/iu.test(result.stderr);
}

function emitTransportRetry(
  invocation: ParsedSshInvocation,
  operation: string,
  attempt: number,
  retry: SshFileTransferSettings,
): void {
  process.stderr.write(`${JSON.stringify({
    event: "unidesk.ssh.file-transfer.transport-retry",
    route: invocation.route.raw,
    providerId: invocation.providerId,
    operation,
    attempt: attempt + 1,
    nextAttempt: attempt + 2,
    maxAttempts: retry.transportOpenRetries + 1,
    delayMs: retry.transportRetryDelayMs,
  })}\n`);
}

async function waitForTransportRetry(retry: SshFileTransferSettings): Promise<void> {
  if (retry.transportRetryDelayMs > 0) await Bun.sleep(retry.transportRetryDelayMs);
}

export function isSshFileTransferOperation(args: string[]): boolean {
  const subcommand = args[0] ?? "";
  return subcommand === "upload" || subcommand === "download";
}

export async function runSshFileTransferOperation(
  invocation: ParsedSshInvocation,
  args: string[],
  executor: SshRemoteCommandExecutor,
  builders: SshFileTransferCommandBuilders,
): Promise<number> {
  const options = parseSshFileTransferCliOptions(args);
  const localPath = path.resolve(options.localPath);
  const transferPolicy = enforceTextTransferPolicy(invocation, options, localPath);
  if (options.action === "upload") {
    const content = await readFile(localPath);
    const expected = { bytes: content.length, sha256: sha256HexBuffer(content) };
    const write = await writeRemoteFileVerified(invocation, executor, builders, options.remotePath, content, options.inactivityTimeoutMs);
    const remote = await statRemoteFile(invocation, executor, builders, options.remotePath);
    assertTransferStat("upload final remote verification", options.remotePath, expected, remote);
    const verification = buildTransferVerification(
      { side: "local", path: localPath, ...expected },
      { side: "remote", path: options.remotePath, ...remote },
    );
    process.stdout.write(`${JSON.stringify({
      ok: true,
      command: "ssh upload",
      route: invocation.route.raw,
      providerId: invocation.providerId,
      localPath,
      remotePath: options.remotePath,
      bytes: expected.bytes,
      sha256: expected.sha256,
      verified: true,
      transferPolicy,
      hint: fileTransferUsageHint,
      verification,
      transfer: write,
    }, null, 2)}\n`);
    return 0;
  }

  const download = await downloadSshFileVerified(invocation, executor, builders, options.remotePath, localPath, options.inactivityTimeoutMs);
  process.stdout.write(`${JSON.stringify({
    ok: true,
    command: "ssh download",
    route: invocation.route.raw,
    providerId: invocation.providerId,
    remotePath: options.remotePath,
    localPath,
    bytes: download.bytes,
    sha256: download.sha256,
    verified: true,
    transferPolicy,
    hint: fileTransferUsageHint,
    verification: download.verification,
    transfer: download.transfer,
  }, null, 2)}\n`);
  return 0;
}

export async function downloadSshFileVerified(
  invocation: ParsedSshInvocation,
  executor: SshRemoteCommandExecutor,
  builders: SshFileTransferCommandBuilders,
  remotePath: string,
  localPath: string,
  inactivityTimeoutMs?: number,
): Promise<SshVerifiedDownloadResult> {
  const read = await downloadRemoteFileVerified(invocation, executor, builders, remotePath, localPath, inactivityTimeoutMs);
  const verification = buildTransferVerification(
    { side: "remote", path: remotePath, ...read.remote },
    { side: "local", path: localPath, ...read.local },
  );
  return {
    remotePath,
    localPath,
    bytes: read.remote.bytes,
    sha256: read.remote.sha256,
    verified: true,
    verification,
    transfer: {
      strategy: read.strategy,
      transport: read.transport,
      sourceRoute: read.sourceRoute,
      sourcePath: read.sourcePath,
      chunks: read.chunks,
      concurrency: read.concurrency,
      elapsedMs: read.elapsedMs,
      throughputBytesPerSecond: read.throughputBytesPerSecond,
      remainingBytes: read.remainingBytes,
    },
  };
}

function parseSshFileTransferCliOptions(args: string[]): SshFileTransferCliOptions {
  const action = args[0];
  if (action !== "upload" && action !== "download") throw new Error("ssh file transfer requires upload or download");
  const positionals: string[] = [];
  let inactivityTimeoutMs: number | undefined;
  let allowTextTransfer = false;
  for (let index = 1; index < args.length; index += 1) {
    const arg = args[index] ?? "";
    if (arg === "--") {
      positionals.push(...args.slice(index + 1));
      break;
    }
    if (arg === "--chunk-bytes" || arg === "--block-bytes") {
      throw new Error(`unsupported ssh ${action} option: ${arg}; downloads use host.ssh.tcp-pool stdout streaming and no longer support the legacy base64 block reader`);
    }
    if (arg === "--allow-text-transfer") {
      allowTextTransfer = true;
      continue;
    }
    if (arg === "--inactivity-timeout-ms" || arg === "--runtime-timeout-ms") {
      const value = args[index + 1];
      if (value === undefined) throw new Error(`ssh ${action} ${arg} requires a positive integer value`);
      index += 1;
      inactivityTimeoutMs = parsePositiveRuntimeTimeoutMs(value, `ssh ${action} ${arg}`);
      continue;
    }
    if (arg.startsWith("--inactivity-timeout-ms=")) {
      inactivityTimeoutMs = parsePositiveRuntimeTimeoutMs(arg.slice("--inactivity-timeout-ms=".length), `ssh ${action} --inactivity-timeout-ms`);
      continue;
    }
    if (arg.startsWith("--runtime-timeout-ms=")) {
      inactivityTimeoutMs = parsePositiveRuntimeTimeoutMs(arg.slice("--runtime-timeout-ms=".length), `ssh ${action} --runtime-timeout-ms`);
      continue;
    }
    if (arg === "--help" || arg === "-h" || arg === "help") {
      throw new Error(`ssh ${action} usage: trans <route> ${action} ${action === "upload" ? "<local-file> <remote-file>" : "<remote-file> <local-file>"}`);
    }
    if (arg.startsWith("-")) throw new Error(`unsupported ssh ${action} option: ${arg}`);
    positionals.push(arg);
  }
  if (positionals.length !== 2) {
    throw new Error(`ssh ${action} requires exactly two paths: ${action === "upload" ? "<local-file> <remote-file>" : "<remote-file> <local-file>"}`);
  }
  const [first, second] = positionals;
  if (!first || !second) throw new Error(`ssh ${action} paths must be non-empty`);
  return action === "upload"
    ? { action, localPath: first, remotePath: second, inactivityTimeoutMs, allowTextTransfer }
    : { action, remotePath: first, localPath: second, inactivityTimeoutMs, allowTextTransfer };
}

function enforceTextTransferPolicy(
  invocation: ParsedSshInvocation,
  options: SshFileTransferCliOptions,
  resolvedLocalPath: string,
): Record<string, unknown> {
  const knownTextPaths = [
    knownTextPath(options.remotePath),
    knownTextPath(resolvedLocalPath),
  ].filter((item): item is { path: string; reason: string } => item !== null);
  if (knownTextPaths.length > 0 && !options.allowTextTransfer) {
    const readCommand = `trans ${invocation.route.raw} cat ${JSON.stringify(options.remotePath)}`;
    const editCommand = `trans ${invocation.route.raw} apply-patch <<'PATCH'`;
    throw new SshFileTransferError("remote text transfer is discouraged; use the native text operation", {
      code: "text-transfer-discouraged",
      action: options.action,
      route: invocation.route.raw,
      knownTextPaths,
      preferred: options.action === "download"
        ? { operation: "cat", command: readCommand }
        : { operation: "apply-patch", command: editCommand },
      alternatives: options.action === "download"
        ? [readCommand, `trans ${invocation.route.raw} head -n 80 ${JSON.stringify(options.remotePath)}`, `trans ${invocation.route.raw} rg <pattern> ${JSON.stringify(options.remotePath)}`]
        : [editCommand],
      override: {
        option: "--allow-text-transfer",
        purpose: "仅用于确需整体搬运的生成物；成功结果会记录 overrideRequested=true。",
      },
      targetCreated: false,
      remoteOperationStarted: false,
    });
  }
  return {
    code: "binary-or-generated-artifact-transfer",
    knownTextPaths,
    overrideRequested: options.allowTextTransfer,
    overrideUsed: knownTextPaths.length > 0 && options.allowTextTransfer,
  };
}

function knownTextPath(rawPath: string): { path: string; reason: string } | null {
  const normalized = rawPath.trim().replace(/\\/gu, "/").replace(/\/+$/gu, "");
  const basename = normalized.slice(normalized.lastIndexOf("/") + 1).toLowerCase();
  if (knownTextBasenames.has(basename)) return { path: rawPath, reason: `basename:${basename}` };
  const extension = path.posix.extname(basename);
  return knownTextExtensions.has(extension) ? { path: rawPath, reason: `extension:${extension}` } : null;
}

function parsePositiveRuntimeTimeoutMs(value: string, label: string): number {
  const parsed = Number(value);
  if (!Number.isFinite(parsed) || parsed <= 0 || !Number.isInteger(parsed)) {
    throw new Error(`${label} must be a positive integer number of milliseconds`);
  }
  return parsed;
}

async function writeRemoteFileVerified(
  invocation: ParsedSshInvocation,
  executor: SshRemoteCommandExecutor,
  builders: SshFileTransferCommandBuilders,
  remotePath: string,
  content: Buffer,
  runtimeTimeoutMs?: number,
): Promise<SshFileTransferWriteResult> {
  const expectedBytes = String(content.length);
  const expectedSha256 = sha256HexBuffer(content);
  const encoded = content.length <= fileTransferWriteB64ArgvLimit
    ? content.toString("base64")
    : "";
  if (invocation.route.plane !== "win" && encoded.length > 0 && encoded.length <= fileTransferWriteB64ArgvLimit) {
    await checkedFileTransfer(invocation, executor, builders, "write-b64-argv", [remotePath, expectedBytes, expectedSha256, ...chunkString(encoded, fileTransferWriteB64ChunkChars)], undefined, runtimeTimeoutMs);
    return {
      strategy: "argv",
      chunks: encoded.length === 0 ? 0 : Math.ceil(encoded.length / fileTransferWriteB64ChunkChars),
      concurrency: 1,
    };
  }
  if (content.length <= fileTransferWriteRawChunkBytes) {
    try {
      await checkedFileTransfer(invocation, executor, builders, "write-b64-stdin", [remotePath, expectedBytes, expectedSha256], content.toString("base64"), runtimeTimeoutMs);
      return { strategy: "stdin", chunks: 1, concurrency: 1 };
    } catch {
      // Fall through to chunked upload with per-block base64 encoding.
    }
  }
  const token = `${process.pid}-${Date.now()}-${randomBytes(4).toString("hex")}-${expectedSha256.slice(0, 12)}`;
  const startedAtMs = Date.now();
  const blocks = byteRanges(content.length, fileTransferWriteRawChunkBytes);
  const concurrency = readFileTransferConcurrency();
  let completedChunks = 0;
  let completedBytes = 0;
  await checkedFileTransfer(invocation, executor, builders, "write-b64-begin", [remotePath, token, expectedBytes], undefined, runtimeTimeoutMs);
  try {
    await runConcurrent(blocks, concurrency, async ({ offset, length }) => {
      const block = content.subarray(offset, offset + length);
      await checkedFileTransfer(
        invocation,
        executor,
        builders,
        "write-b64-block-stdin",
        [remotePath, token, String(offset), String(length), sha256HexBuffer(block)],
        block.toString("base64"),
        runtimeTimeoutMs,
      );
      completedChunks += 1;
      completedBytes += length;
      emitUploadProgress(
        invocation,
        remotePath,
        completedChunks,
        completedBytes,
        content.length,
        length,
        startedAtMs,
      );
    });
    await checkedFileTransfer(invocation, executor, builders, "write-b64-commit", [remotePath, token, expectedBytes, expectedSha256], undefined, runtimeTimeoutMs);
  } catch (error) {
    await checkedFileTransfer(invocation, executor, builders, "write-b64-abort", [remotePath, token], undefined, runtimeTimeoutMs).catch(() => undefined);
    throw error;
  }
  emitUploadProgress(invocation, remotePath, Math.max(1, completedChunks), content.length, content.length, 0, startedAtMs, true);
  return {
    strategy: "parallel-chunked-stdin",
    chunks: blocks.length,
    concurrency: Math.min(concurrency, blocks.length),
  };
}

async function downloadRemoteFileVerified(
  invocation: ParsedSshInvocation,
  executor: SshRemoteCommandExecutor,
  builders: SshFileTransferCommandBuilders,
  remotePath: string,
  localPath: string,
  inactivityTimeoutMs?: number,
): Promise<SshFileTransferDownloadResult> {
  if (executor.streamRemoteCommand === undefined) {
    throw new SshFileTransferError("ssh download requires a tcp-pool stdout stream sink", {
      route: invocation.route.raw,
      providerId: invocation.providerId,
      remotePath,
      localPath,
      requiredTransport: "host.ssh.tcp-pool",
      blocker: "streamRemoteCommand unavailable",
    });
  }
  const streamSource = invocation.route.plane === "win"
    ? {
        route: invocation.route,
        path: resolveWindowsTransferPath(remotePath, invocation.route.workspace),
      }
    : { route: invocation.route, path: remotePath };
  if (invocation.route.plane === "win") {
    process.stderr.write(`${JSON.stringify({
      event: "unidesk.ssh.download.win-native-stream",
      at: new Date().toISOString(),
      route: invocation.route.raw,
      providerId: invocation.providerId,
      remotePath,
      sourceRoute: streamSource.route.raw,
      sourcePath: streamSource.path,
      transport: "host.ssh.tcp-pool",
    })}\n`);
  }
  const remote = await statRemoteFile(invocation, executor, builders, remotePath);
  await mkdir(path.dirname(localPath), { recursive: true });
  const concurrency = readFileTransferConcurrency();
  const ranges = parallelDownloadRanges(remote.bytes, concurrency);
  const startedAtMs = Date.now();
  const output = await open(localPath, "w", 0o600);
  await output.truncate(remote.bytes);
  const retry = readFileTransferSettings();
  let actualBytes = 0;
  let chunkCount = 0;
  try {
    await runConcurrent(ranges, concurrency, async (range) => {
      const remoteCommand = buildStreamDownloadRemoteCommand(
        streamSource.route,
        builders,
        streamSource.path,
        range.offset,
        range.length,
      );
      let rangeBytes = 0;
      let result: SshCaptureResult;
      for (let attempt = 0; ; attempt += 1) {
        result = await executor.streamRemoteCommand!(remoteCommand, {
          onStdout: async (chunk) => {
            if (rangeBytes + chunk.length > range.length) {
              throw new SshFileTransferError("remote ssh download range exceeded expected bytes", {
                remotePath,
                offset: range.offset,
                expectedBytes: range.length,
                actualBytes: rangeBytes + chunk.length,
              });
            }
            const chunkOffset = rangeBytes;
            rangeBytes += chunk.length;
            actualBytes += chunk.length;
            chunkCount += 1;
            await writeFileHandleChunk(output, chunk, range.offset + chunkOffset);
            emitDownloadProgress(invocation, remotePath, chunkCount, actualBytes, remote.bytes, chunk.length, startedAtMs);
          },
        }, undefined, { inactivityTimeoutMs: inactivityTimeoutMs ?? executor.streamInactivityTimeoutMs });
        if (result.exitCode === 0 || rangeBytes > 0 || !isPreDispatchTransportFailure(result) || attempt >= retry.transportOpenRetries) break;
        emitTransportRetry(invocation, "download-range", attempt, retry);
        await waitForTransportRetry(retry);
      }
      if (result.exitCode !== 0 || rangeBytes !== range.length) {
        throw new SshFileTransferError("remote ssh download range failed", {
          route: invocation.route.raw,
          providerId: invocation.providerId,
          remotePath,
          localPath,
          offset: range.offset,
          expectedBytes: range.length,
          actualBytes: rangeBytes,
          exitCode: result.exitCode,
          stdout: transferTextSnapshot(result.stdout, { headChars: 120, tailChars: 500 }),
          stderr: transferTextSnapshot(result.stderr, { headChars: 120, tailChars: 1000 }),
        });
      }
    });
    await output.close();
    const local = {
      bytes: actualBytes,
      sha256: await sha256File(localPath),
    };
    if (actualBytes !== remote.bytes) {
      throw new SshFileTransferError("remote ssh download ranges returned incomplete data", {
        remotePath,
        expectedBytes: remote.bytes,
        actualBytes,
      });
    }
    const elapsedMs = Math.max(1, Date.now() - startedAtMs);
    assertTransferStat("download tcp-pool stdout stream verification", localPath, remote, local);
    emitDownloadProgress(invocation, remotePath, Math.max(1, chunkCount), actualBytes, remote.bytes, 0, startedAtMs, true);
    return {
      remote,
      local,
      strategy: "tcp-pool-parallel-range-stream",
      transport: "host.ssh.tcp-pool",
      sourceRoute: streamSource.route.raw,
      sourcePath: streamSource.path,
      chunks: chunkCount,
      concurrency: Math.min(concurrency, ranges.length),
      elapsedMs,
      throughputBytesPerSecond: Math.round((actualBytes * 1000) / elapsedMs),
      remainingBytes: Math.max(0, remote.bytes - actualBytes),
    };
  } catch (error) {
    await output.close().catch(() => undefined);
    await rm(localPath, { force: true }).catch(() => undefined);
    throw error;
  }
}

function resolveWindowsTransferPath(rawPath: string, basePath: string | null): string {
  const normalizedRaw = stripWindowsLongPathPrefix(rawPath.trim()).replace(/\//gu, "\\");
  if (normalizedRaw.length === 0) {
    throw new SshFileTransferError("ssh win download requires a non-empty remote path");
  }
  if (/^\\\\/u.test(normalizedRaw)) {
    throw new SshFileTransferError("ssh win download cannot auto-map UNC paths to WSL /mnt/<drive>", {
      remotePath: rawPath,
      fallback: "copy the file to a drive-letter path such as D:\\tmp, then retry download",
    });
  }
  if (/^[A-Za-z]:/u.test(normalizedRaw)) return normalizeWindowsAbsolutePath(normalizedRaw);
  const base = basePath === null ? "" : stripWindowsLongPathPrefix(basePath.trim()).replace(/\//gu, "\\");
  const baseMatch = base.match(/^([A-Za-z]):\\?(.*)$/u);
  if (baseMatch === null) {
    throw new SshFileTransferError("ssh win download with a relative path requires a drive-letter route workspace", {
      remotePath: rawPath,
      routeWorkspace: basePath,
      example: "trans D518:win/d/tmp download image.png /tmp/image.png",
    });
  }
  const drive = baseMatch[1]!;
  const baseRest = baseMatch[2] ?? "";
  return normalizeWindowsAbsolutePath(`${drive}:\\${[baseRest, normalizedRaw].filter((part) => part.length > 0).join("\\")}`);
}

function stripWindowsLongPathPrefix(value: string): string {
  if (value.startsWith("\\\\?\\")) return value.slice(4);
  return value;
}

function normalizeWindowsAbsolutePath(value: string): string {
  const match = value.match(/^([A-Za-z]):\\?(.*)$/u);
  if (match === null) return value;
  const drive = match[1]!.toUpperCase();
  const segments = normalizeWindowsPathSegments((match[2] ?? "").split(/[\\/]+/u));
  return `${drive}:\\${segments.join("\\")}`;
}

function normalizeWindowsPathSegments(segments: string[]): string[] {
  const normalized: string[] = [];
  for (const segment of segments) {
    if (segment.length === 0 || segment === ".") continue;
    if (segment === "..") {
      if (normalized.length === 0) throw new SshFileTransferError("ssh win download path escapes the drive root");
      normalized.pop();
      continue;
    }
    normalized.push(segment);
  }
  return normalized;
}

interface FileTransferRange {
  offset: number;
  length: number;
}

function byteRanges(totalBytes: number, rangeBytes: number): FileTransferRange[] {
  const ranges: FileTransferRange[] = [];
  for (let offset = 0; offset < totalBytes; offset += rangeBytes) {
    ranges.push({ offset, length: Math.min(rangeBytes, totalBytes - offset) });
  }
  return ranges;
}

function parallelDownloadRanges(totalBytes: number, concurrency: number): FileTransferRange[] {
  if (totalBytes === 0) return [];
  const rangeCount = Math.min(concurrency, Math.max(1, Math.ceil(totalBytes / fileTransferDownloadMinimumRangeBytes)));
  const unalignedBytes = Math.ceil(totalBytes / rangeCount);
  const rangeBytes = Math.ceil(unalignedBytes / fileTransferDownloadRangeAlignment) * fileTransferDownloadRangeAlignment;
  return byteRanges(totalBytes, rangeBytes);
}

async function runConcurrent<T>(
  items: T[],
  concurrency: number,
  worker: (item: T) => Promise<void>,
): Promise<void> {
  let nextIndex = 0;
  let firstError: unknown = null;
  const runners = Array.from({ length: Math.min(concurrency, items.length) }, async () => {
    while (firstError === null) {
      const index = nextIndex;
      nextIndex += 1;
      if (index >= items.length) return;
      try {
        await worker(items[index]!);
      } catch (error) {
        firstError ??= error;
      }
    }
  });
  await Promise.all(runners);
  if (firstError !== null) throw firstError;
}

function emitDownloadProgress(
  invocation: ParsedSshInvocation,
  remotePath: string,
  chunkCount: number,
  actualBytes: number,
  expectedBytes: number,
  lastChunkBytes: number,
  startedAtMs: number,
  force = false,
): void {
  if (!force && chunkCount !== 1 && actualBytes < expectedBytes && chunkCount % fileTransferDownloadProgressEveryChunks !== 0) return;
  const elapsedMs = Math.max(1, Date.now() - startedAtMs);
  process.stderr.write(`${JSON.stringify({
    event: "unidesk.ssh.download.progress",
    at: new Date().toISOString(),
    route: invocation.route.raw,
    providerId: invocation.providerId,
    remotePath,
    strategy: "tcp-pool-parallel-range-stream",
    transport: "host.ssh.tcp-pool",
    chunks: chunkCount,
    bytes: actualBytes,
    totalBytes: expectedBytes,
    actualBytes,
    expectedBytes,
    lastChunkBytes,
    remainingBytes: Math.max(0, expectedBytes - actualBytes),
    elapsedMs,
    throughputBytesPerSecond: Math.round((actualBytes * 1000) / elapsedMs),
  })}\n`);
}

function emitUploadProgress(
  invocation: ParsedSshInvocation,
  remotePath: string,
  chunkCount: number,
  actualBytes: number,
  expectedBytes: number,
  lastChunkBytes: number,
  startedAtMs: number,
  force = false,
): void {
  if (!force && chunkCount !== 1 && actualBytes < expectedBytes && chunkCount % fileTransferUploadProgressEveryChunks !== 0) return;
  const elapsedMs = Math.max(1, Date.now() - startedAtMs);
  process.stderr.write(`${JSON.stringify({
    event: "unidesk.ssh.upload.progress",
    at: new Date().toISOString(),
    route: invocation.route.raw,
    providerId: invocation.providerId,
    remotePath,
    strategy: "parallel-chunked-stdin",
    chunks: chunkCount,
    bytes: actualBytes,
    totalBytes: expectedBytes,
    actualBytes,
    expectedBytes,
    lastChunkBytes,
    remainingBytes: Math.max(0, expectedBytes - actualBytes),
    elapsedMs,
    throughputBytesPerSecond: Math.round((actualBytes * 1000) / elapsedMs),
  })}\n`);
}

async function statRemoteFile(
  invocation: ParsedSshInvocation,
  executor: SshRemoteCommandExecutor,
  builders: SshFileTransferCommandBuilders,
  remotePath: string,
): Promise<SshFileTransferStat> {
  const stat = await checkedFileTransfer(invocation, executor, builders, "stat", [remotePath]);
  return parseFileTransferStat(stat.stdout, stat.stderr, remotePath);
}

function buildStreamDownloadRemoteCommand(
  route: ParsedSshRoute,
  builders: SshFileTransferCommandBuilders,
  remotePath: string,
  offset: number,
  length: number,
): string {
  if (route.plane === "win") {
    return builders.buildWindowsPowerShellCommand(windowsStreamDownloadScript(route.workspace, remotePath, offset, length));
  }
  return builders.buildRouteCommand(route, [
    "sh",
    "-c",
    "dd if=\"$1\" bs=65536 skip=\"$2\" count=\"$3\" 2>/dev/null | head -c \"$4\"",
    "unidesk-download",
    remotePath,
    String(offset / fileTransferDownloadRangeAlignment),
    String(Math.ceil(length / fileTransferDownloadRangeAlignment)),
    String(length),
  ]);
}

function windowsStreamDownloadScript(basePath: string | null, remotePath: string, offset: number, length: number): string {
  return [
    "$ErrorActionPreference = 'Stop';",
    "$ProgressPreference = 'SilentlyContinue';",
    `$basePath = ${powerShellSingleQuote(basePath ?? "")};`,
    `$targetArg = ${powerShellSingleQuote(remotePath)};`,
    `$offset = [Int64]${offset};`,
    `$length = [Int64]${length};`,
    "if ([System.IO.Path]::IsPathRooted($targetArg)) { $target = [System.IO.Path]::GetFullPath($targetArg) } elseif (-not [string]::IsNullOrWhiteSpace($basePath)) { $target = [System.IO.Path]::GetFullPath([System.IO.Path]::Combine($basePath, $targetArg)) } else { $target = [System.IO.Path]::GetFullPath($targetArg) };",
    "if (-not [System.IO.File]::Exists($target)) { [Console]::Error.WriteLine('file not found: ' + $target); exit 1 };",
    "$inputStream = [System.IO.File]::Open($target, [System.IO.FileMode]::Open, [System.IO.FileAccess]::Read, [System.IO.FileShare]::ReadWrite);",
    "try { [void]$inputStream.Seek($offset, [System.IO.SeekOrigin]::Begin); $outputStream = [Console]::OpenStandardOutput(); $buffer = [byte[]]::new(65536); $remaining = $length; while ($remaining -gt 0) { $requested = [Math]::Min([Int64]$buffer.Length, $remaining); $count = $inputStream.Read($buffer, 0, [int]$requested); if ($count -le 0) { break }; $outputStream.Write($buffer, 0, $count); $outputStream.Flush(); $remaining -= $count }; if ($remaining -ne 0) { [Console]::Error.WriteLine('download range ended early: remaining=' + $remaining); exit 26 } } finally { $inputStream.Dispose() }",
  ].join(" ");
}

async function writeFileHandleChunk(
  file: Awaited<ReturnType<typeof open>>,
  chunk: Buffer,
  position: number,
): Promise<void> {
  let written = 0;
  while (written < chunk.length) {
    const result = await file.write(chunk, written, chunk.length - written, position + written);
    if (result.bytesWritten <= 0) throw new Error("local parallel download write made no progress");
    written += result.bytesWritten;
  }
}

async function sha256File(filePath: string): Promise<string> {
  const hash = createHash("sha256");
  for await (const chunk of createReadStream(filePath)) hash.update(chunk as Buffer);
  return hash.digest("hex");
}

async function checkedFileTransfer(
  invocation: ParsedSshInvocation,
  executor: SshRemoteCommandExecutor,
  builders: SshFileTransferCommandBuilders,
  operation: SshFileTransferOperation,
  args: string[],
  input?: string,
  runtimeTimeoutMs?: number,
): Promise<SshCaptureResult> {
  const remoteCommand = buildFileTransferRemoteCommand(invocation.route, builders, operation, args, input !== undefined);
  const retry = readFileTransferSettings();
  for (let attempt = 0; ; attempt += 1) {
    const result = await executor.runRemoteCommand(remoteCommand, input, { runtimeTimeoutMs });
    if (result.exitCode === 0) return result;
    const preDispatchFailure = isPreDispatchTransportFailure(result);
    if (!preDispatchFailure || attempt >= retry.transportOpenRetries) {
      throw new SshFileTransferError("remote ssh file transfer operation failed", {
        route: invocation.route.raw,
        operation,
        args: args.slice(0, 4),
        attempt: attempt + 1,
        exitCode: result.exitCode,
        stdout: transferTextSnapshot(result.stdout, { headChars: operation === "stat" ? 500 : 120, tailChars: 500 }),
        stderr: transferTextSnapshot(result.stderr, { headChars: 120, tailChars: 1000 }),
      });
    }
    emitTransportRetry(invocation, operation, attempt, retry);
    await waitForTransportRetry(retry);
  }
}

function buildFileTransferRemoteCommand(
  route: ParsedSshRoute,
  builders: SshFileTransferCommandBuilders,
  operation: SshFileTransferOperation,
  args: string[],
  hasInput: boolean,
): string {
  if (route.plane === "win") return buildWindowsFileTransferCommand(route, builders, operation, args);
  return builders.buildRouteCommand(route, ["sh", "-c", posixFileTransferScript(), "unidesk-file-transfer", operation, ...args], { stdin: hasInput });
}

function parseFileTransferStat(stdout: string, stderr: string, remotePath: string): SshFileTransferStat {
  const lines = stdout.split(/\r?\n/u).map((line) => line.trim()).filter((line) => line.length > 0);
  for (const line of lines) {
    const [bytesText, sha256, extra] = line.split(/\s+/u);
    const bytes = Number(bytesText);
    if (extra === undefined && Number.isSafeInteger(bytes) && bytes >= 0 && /^[0-9a-f]{64}$/u.test(sha256 ?? "")) {
      return { bytes, sha256: sha256! };
    }
  }
  {
    throw new SshFileTransferError("remote file transfer stat returned invalid metadata", {
      remotePath,
      expected: "<bytes> <sha256>",
      stdout: transferTextSnapshot(stdout, { headChars: 500, tailChars: 500 }),
      stderr: transferTextSnapshot(stderr, { headChars: 120, tailChars: 1000 }),
      candidateLines: lines.slice(0, 8).map((line) => line.slice(0, 200)),
      candidateLineCount: lines.length,
    });
  }
}

function transferTextSnapshot(value: string, limits: { headChars: number; tailChars: number }): Record<string, unknown> {
  return {
    bytes: Buffer.byteLength(value, "utf8"),
    chars: value.length,
    head: value.slice(0, limits.headChars),
    tail: value.slice(Math.max(0, value.length - limits.tailChars)),
    truncated: value.length > limits.headChars + limits.tailChars,
  };
}

function assertTransferStat(label: string, pathName: string, expected: SshFileTransferStat, actual: SshFileTransferStat): void {
  if (expected.bytes === actual.bytes && expected.sha256 === actual.sha256) return;
  throw new SshFileTransferError(`${label} failed`, {
    path: pathName,
    expected,
    actual,
  });
}

function buildTransferVerification(source: SshFileTransferEndpointStat, target: SshFileTransferEndpointStat): Record<string, unknown> {
  return {
    automatic: true,
    algorithm: "sha256",
    checked: ["bytes", "sha256"],
    verified: source.bytes === target.bytes && source.sha256 === target.sha256,
    source,
    target,
    match: {
      bytes: source.bytes === target.bytes,
      sha256: source.sha256 === target.sha256,
    },
  };
}

function sha256HexBuffer(value: Buffer): string {
  return createHash("sha256").update(value).digest("hex");
}

function chunkString(value: string, chunkSize: number): string[] {
  const chunks: string[] = [];
  for (let index = 0; index < value.length; index += chunkSize) {
    chunks.push(value.slice(index, index + chunkSize));
  }
  return chunks.length > 0 ? chunks : [""];
}

function posixFileTransferScript(): string {
  return [
    "set -eu",
    "sha256_file() {",
    "  if command -v sha256sum >/dev/null 2>&1; then sha256sum -- \"$1\" | awk '{print $1}'; return; fi",
    "  if command -v shasum >/dev/null 2>&1; then shasum -a 256 -- \"$1\" | awk '{print $1}'; return; fi",
    "  if command -v openssl >/dev/null 2>&1; then openssl dgst -sha256 -- \"$1\" | awk '{print $NF}'; return; fi",
    "  printf 'missing sha256 tool\\n' >&2; return 127",
    "}",
    "ensure_parent() { case \"$1\" in */*) parent=${1%/*}; mkdir -p -- \"$parent\";; esac; }",
    "verify_tmp() {",
    "  target=$1; tmp=$2; expected_bytes=$3; expected_sha256=$4",
    "  actual_bytes=$(wc -c < \"$tmp\" | tr -d '[:space:]')",
    "  if [ \"$actual_bytes\" != \"$expected_bytes\" ]; then rm -f -- \"$tmp\"; printf 'transfer byte count mismatch for %s: expected=%s actual=%s\\n' \"$target\" \"$expected_bytes\" \"$actual_bytes\" >&2; exit 23; fi",
    "  actual_sha256=$(sha256_file \"$tmp\")",
    "  if [ \"$actual_sha256\" != \"$expected_sha256\" ]; then rm -f -- \"$tmp\"; printf 'transfer sha256 mismatch for %s: expected=%s actual=%s\\n' \"$target\" \"$expected_sha256\" \"$actual_sha256\" >&2; exit 24; fi",
    "}",
    "set_tmp_paths() {",
    "  target=$1; token=$2",
    "  case \"$token\" in ''|*[!a-zA-Z0-9_.-]*) printf 'invalid transfer temp token\\n' >&2; exit 2;; esac",
    "  base=${target##*/}; dir=.",
    "  case \"$target\" in */*) dir=${target%/*};; esac",
    "  tmp=\"$dir/.${base}.unidesk-transfer-${token}.tmp\"",
    "  tmp_b64=\"$tmp.b64\"",
    "}",
    "op=$1; shift",
    "case \"$op\" in",
    "  stat)",
    "    target=$1; bytes=$(wc -c < \"$target\" | tr -d '[:space:]'); digest=$(sha256_file \"$target\"); printf '%s %s\\n' \"$bytes\" \"$digest\"",
    "    ;;",
    "  write-b64-argv)",
    "    target=$1; expected_bytes=$2; expected_sha256=$3; shift 3",
    "    ensure_parent \"$target\"; base=${target##*/}; dir=.; case \"$target\" in */*) dir=${target%/*};; esac",
    "    tmp=\"$dir/.${base}.unidesk-transfer-$$.tmp\"; tmp_b64=\"$tmp.b64\"; : > \"$tmp_b64\"",
    "    for chunk in \"$@\"; do printf '%s' \"$chunk\" >> \"$tmp_b64\"; done",
    "    if ! base64 -d < \"$tmp_b64\" > \"$tmp\"; then rm -f -- \"$tmp\" \"$tmp_b64\"; printf 'transfer base64 decode failed for %s\\n' \"$target\" >&2; exit 22; fi",
    "    rm -f -- \"$tmp_b64\"; verify_tmp \"$target\" \"$tmp\" \"$expected_bytes\" \"$expected_sha256\"; mv -f -- \"$tmp\" \"$target\"",
    "    actual_sha256=$(sha256_file \"$target\"); if [ \"$actual_sha256\" != \"$expected_sha256\" ]; then printf 'transfer final sha256 mismatch for %s\\n' \"$target\" >&2; exit 25; fi",
    "    ;;",
    "  write-b64-stdin)",
    "    target=$1; expected_bytes=$2; expected_sha256=$3",
    "    ensure_parent \"$target\"; base=${target##*/}; dir=.; case \"$target\" in */*) dir=${target%/*};; esac",
    "    tmp=\"$dir/.${base}.unidesk-transfer-$$.tmp\"",
    "    if ! base64 -d > \"$tmp\"; then rm -f -- \"$tmp\"; printf 'transfer base64 decode failed for %s\\n' \"$target\" >&2; exit 22; fi",
    "    verify_tmp \"$target\" \"$tmp\" \"$expected_bytes\" \"$expected_sha256\"; mv -f -- \"$tmp\" \"$target\"",
    "    actual_sha256=$(sha256_file \"$target\"); if [ \"$actual_sha256\" != \"$expected_sha256\" ]; then printf 'transfer final sha256 mismatch for %s\\n' \"$target\" >&2; exit 25; fi",
    "    ;;",
    "  write-b64-begin)",
    "    target=$1; token=$2; expected_bytes=$3; ensure_parent \"$target\"; set_tmp_paths \"$target\" \"$token\"",
    "    if command -v truncate >/dev/null 2>&1; then truncate -s \"$expected_bytes\" \"$tmp\"; else dd if=/dev/zero of=\"$tmp\" bs=1 count=0 seek=\"$expected_bytes\" 2>/dev/null; fi",
    "    ;;",
    "  write-b64-block-stdin)",
    "    target=$1; token=$2; offset=$3; expected_block_bytes=$4; expected_block_sha256=$5; set_tmp_paths \"$target\" \"$token\"; part=\"$tmp.$offset.part\"",
    "    if ! base64 -d > \"$part\"; then rm -f -- \"$part\"; printf 'transfer base64 block decode failed for %s at %s\\n' \"$target\" \"$offset\" >&2; exit 22; fi",
    "    actual_block_bytes=$(wc -c < \"$part\" | tr -d '[:space:]'); actual_block_sha256=$(sha256_file \"$part\")",
    "    if [ \"$actual_block_bytes\" != \"$expected_block_bytes\" ] || [ \"$actual_block_sha256\" != \"$expected_block_sha256\" ]; then rm -f -- \"$part\"; printf 'transfer block verification failed for %s at %s\\n' \"$target\" \"$offset\" >&2; exit 24; fi",
    "    if ! dd if=\"$part\" of=\"$tmp\" bs=1 seek=\"$offset\" conv=notrunc 2>/dev/null; then rm -f -- \"$part\"; printf 'transfer block write failed for %s at %s\\n' \"$target\" \"$offset\" >&2; exit 27; fi",
    "    rm -f -- \"$part\"",
    "    ;;",
    "  write-b64-abort)",
    "    target=$1; token=$2; set_tmp_paths \"$target\" \"$token\"; rm -f -- \"$tmp\" \"$tmp\".*.part",
    "    ;;",
    "  write-b64-commit)",
    "    target=$1; token=$2; expected_bytes=$3; expected_sha256=$4; set_tmp_paths \"$target\" \"$token\"",
    "    verify_tmp \"$target\" \"$tmp\" \"$expected_bytes\" \"$expected_sha256\"; mv -f -- \"$tmp\" \"$target\"",
    "    actual_sha256=$(sha256_file \"$target\"); if [ \"$actual_sha256\" != \"$expected_sha256\" ]; then printf 'transfer final sha256 mismatch for %s\\n' \"$target\" >&2; exit 25; fi",
    "    ;;",
    "  *) printf 'unsupported transfer op: %s\\n' \"$op\" >&2; exit 2;;",
    "esac",
  ].join("\n");
}

function buildWindowsFileTransferCommand(
  route: ParsedSshRoute,
  builders: SshFileTransferCommandBuilders,
  operation: SshFileTransferOperation,
  args: string[],
): string {
  return builders.buildWindowsPowerShellCommand(windowsFileTransferScript(route.workspace, operation, args));
}

function windowsFileTransferScript(basePath: string | null, operation: SshFileTransferOperation, args: string[]): string {
  const target = args[0] ?? "";
  const tokenOrBlock = args[1] ?? "";
  const third = args[2] ?? "";
  const fourth = args[3] ?? "";
  const fifth = args[4] ?? "";
  const argvChunks = args.slice(3).map(powerShellSingleQuote).join(", ");
  return [
    "$ErrorActionPreference = 'Stop';",
    "$ProgressPreference = 'SilentlyContinue';",
    "[Console]::InputEncoding = [System.Text.UTF8Encoding]::new();",
    "[Console]::OutputEncoding = [System.Text.UTF8Encoding]::new();",
    "$OutputEncoding = [System.Text.UTF8Encoding]::new();",
    `$basePath = ${powerShellSingleQuote(basePath ?? "")};`,
    `$operation = ${powerShellSingleQuote(operation)};`,
    `$targetArg = ${powerShellSingleQuote(target)};`,
    `$arg1 = ${powerShellSingleQuote(tokenOrBlock)};`,
    `$arg2 = ${powerShellSingleQuote(third)};`,
    `$arg3 = ${powerShellSingleQuote(fourth)};`,
    `$arg4 = ${powerShellSingleQuote(fifth)};`,
    `$argvChunks = @(${argvChunks});`,
    "function Fail([string]$Message, [int]$Code) { [Console]::Error.WriteLine($Message); exit $Code }",
    "function Resolve-UnideskPath([string]$Raw) { if ([string]::IsNullOrWhiteSpace($Raw)) { Fail 'empty transfer path' 2 }; if ([System.IO.Path]::IsPathRooted($Raw)) { return [System.IO.Path]::GetFullPath($Raw) }; if (-not [string]::IsNullOrWhiteSpace($basePath)) { return [System.IO.Path]::GetFullPath([System.IO.Path]::Combine($basePath, $Raw)) }; return [System.IO.Path]::GetFullPath($Raw) }",
    "function Ensure-Parent([string]$Target) { $parent = [System.IO.Path]::GetDirectoryName($Target); if (-not [string]::IsNullOrWhiteSpace($parent)) { [System.IO.Directory]::CreateDirectory($parent) | Out-Null } }",
    "function Get-Sha256([string]$Path) { return (Get-FileHash -LiteralPath $Path -Algorithm SHA256).Hash.ToLowerInvariant() }",
    "function Set-TmpPaths([string]$Target, [string]$Token) { if ($Token -notmatch '^[A-Za-z0-9_.-]+$') { Fail 'invalid transfer temp token' 2 }; $dir = [System.IO.Path]::GetDirectoryName($Target); if ([string]::IsNullOrWhiteSpace($dir)) { $dir = (Get-Location).ProviderPath }; $base = [System.IO.Path]::GetFileName($Target); $script:tmp = [System.IO.Path]::Combine($dir, '.' + $base + '.unidesk-transfer-' + $Token + '.tmp'); $script:tmpB64 = $script:tmp + '.b64' }",
    "function Verify-Temp([string]$Target, [string]$Tmp, [Int64]$ExpectedBytes, [string]$ExpectedSha256) { $actualBytes = ([System.IO.FileInfo]$Tmp).Length; if ($actualBytes -ne $ExpectedBytes) { Remove-Item -LiteralPath $Tmp -Force -ErrorAction SilentlyContinue; Fail ('transfer byte count mismatch for ' + $Target + ': expected=' + $ExpectedBytes + ' actual=' + $actualBytes) 23 }; $actualSha256 = Get-Sha256 $Tmp; if ($actualSha256 -ne $ExpectedSha256) { Remove-Item -LiteralPath $Tmp -Force -ErrorAction SilentlyContinue; Fail ('transfer sha256 mismatch for ' + $Target + ': expected=' + $ExpectedSha256 + ' actual=' + $actualSha256) 24 } }",
    "function Decode-ToTarget([string]$Target, [string]$Encoded, [Int64]$ExpectedBytes, [string]$ExpectedSha256) { Ensure-Parent $Target; Set-TmpPaths $Target ([guid]::NewGuid().ToString('N')); try { $bytes = [Convert]::FromBase64String(($Encoded -replace '\\s','')) } catch { Fail ('transfer base64 decode failed for ' + $Target + ': ' + $_.Exception.Message) 22 }; [System.IO.File]::WriteAllBytes($script:tmp, $bytes); Verify-Temp $Target $script:tmp $ExpectedBytes $ExpectedSha256; Move-Item -LiteralPath $script:tmp -Destination $Target -Force; $actualSha256 = Get-Sha256 $Target; if ($actualSha256 -ne $ExpectedSha256) { Fail ('transfer final sha256 mismatch for ' + $Target) 25 } }",
    "$target = Resolve-UnideskPath $targetArg;",
    "switch ($operation) {",
    "  'stat' { if (-not (Test-Path -LiteralPath $target -PathType Leaf)) { Fail ('file not found: ' + $target) 1 }; $bytes = ([System.IO.FileInfo]$target).Length; $digest = Get-Sha256 $target; [Console]::Out.WriteLine(([string]$bytes) + ' ' + $digest); break }",
    "  'write-b64-argv' { Decode-ToTarget $target ([string]::Concat($argvChunks)) ([Int64]$arg1) $arg2; break }",
    "  'write-b64-stdin' { Decode-ToTarget $target ([Console]::In.ReadToEnd()) ([Int64]$arg1) $arg2; break }",
    "  'write-b64-begin' { Ensure-Parent $target; Set-TmpPaths $target $arg1; $stream = [System.IO.File]::Open($script:tmp, [System.IO.FileMode]::Create, [System.IO.FileAccess]::Write, [System.IO.FileShare]::ReadWrite); try { $stream.SetLength([Int64]$arg2) } finally { $stream.Dispose() }; break }",
    "  'write-b64-block-stdin' { Set-TmpPaths $target $arg1; try { $bytes = [Convert]::FromBase64String((([Console]::In.ReadToEnd()) -replace '\\s','')) } catch { Fail ('transfer base64 block decode failed for ' + $target + ' at ' + $arg2 + ': ' + $_.Exception.Message) 22 }; $sha = [System.Security.Cryptography.SHA256]::Create(); try { $blockSha256 = ([System.BitConverter]::ToString($sha.ComputeHash($bytes))).Replace('-', '').ToLowerInvariant() } finally { $sha.Dispose() }; if ($bytes.Length -ne [Int64]$arg3 -or $blockSha256 -ne $arg4) { Fail ('transfer block verification failed for ' + $target + ' at ' + $arg2) 24 }; $stream = [System.IO.File]::Open($script:tmp, [System.IO.FileMode]::Open, [System.IO.FileAccess]::Write, [System.IO.FileShare]::ReadWrite); try { [void]$stream.Seek([Int64]$arg2, [System.IO.SeekOrigin]::Begin); $stream.Write($bytes, 0, $bytes.Length); $stream.Flush() } finally { $stream.Dispose() }; break }",
    "  'write-b64-abort' { Set-TmpPaths $target $arg1; Remove-Item -LiteralPath $script:tmp -Force -ErrorAction SilentlyContinue; break }",
    "  'write-b64-commit' { Set-TmpPaths $target $arg1; Verify-Temp $target $script:tmp ([Int64]$arg2) $arg3; Move-Item -LiteralPath $script:tmp -Destination $target -Force; $actualSha256 = Get-Sha256 $target; if ($actualSha256 -ne $arg3) { Fail ('transfer final sha256 mismatch for ' + $target) 25 }; break }",
    "  default { Fail ('unsupported transfer op: ' + $operation) 2 }",
    "}",
  ].join(" ");
}

function powerShellSingleQuote(value: string): string {
  return `'${value.replace(/'/g, "''")}'`;
}