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export interface Environment {  /** Gets an environment variable. */  env(key: string): string | undefined;  /** Resolves the `Deno.FileInfo` for the specified   * path following symlinks.   */  stat(filePath: string): Promise<Pick<Deno.FileInfo, "isFile">>;  /** Synchronously resolves the `Deno.FileInfo` for   * the specified path following symlinks.   */  statSync(filePath: string): Pick<Deno.FileInfo, "isFile">;  /** Gets the current operating system. */  os: typeof Deno.build.os;}
export class RealEnvironment implements Environment {  env(key: string): string | undefined {    return Deno.env.get(key);  }
  stat(path: string): Promise<Deno.FileInfo> {    return Deno.stat(path);  }
  statSync(path: string): Deno.FileInfo {    return Deno.statSync(path);  }
  get os() {    return Deno.build.os;  }}
/** Finds the path to the specified command asynchronously. */export async function which(  command: string,  environment: Omit<Environment, "statSync"> = new RealEnvironment(),) {  const systemInfo = getSystemInfo(command, environment);  if (systemInfo == null) {    return undefined;  }
  for (const pathItem of systemInfo.pathItems) {    const filePath = pathItem + command;    if (systemInfo.pathExts) {      for (const pathExt of systemInfo.pathExts) {        const filePath = pathItem + command + pathExt;        if (await pathMatches(environment, filePath)) {          return filePath;        }      }    } else {      if (await pathMatches(environment, filePath)) {        return filePath;      }    }  }
  return undefined;}
async function pathMatches(  environment: Omit<Environment, "statSync">,  path: string,): Promise<boolean> {  try {    const result = await environment.stat(path);    return result.isFile;  } catch (err) {    if (err instanceof Deno.errors.PermissionDenied) {      throw err;    }    return false;  }}
/** Finds the path to the specified command synchronously. */export function whichSync(  command: string,  environment: Omit<Environment, "stat"> = new RealEnvironment(),) {  const systemInfo = getSystemInfo(command, environment);  if (systemInfo == null) {    return undefined;  }
  for (const pathItem of systemInfo.pathItems) {    const filePath = pathItem + command;    if (pathMatchesSync(environment, filePath)) {      return filePath;    }    if (systemInfo.pathExts) {      for (const pathExt of systemInfo.pathExts) {        const filePath = pathItem + command + pathExt;        if (pathMatchesSync(environment, filePath)) {          return filePath;        }      }    }  }
  return undefined;}
function pathMatchesSync(  environment: Omit<Environment, "stat">,  path: string,): boolean {  try {    const result = environment.statSync(path);    return result.isFile;  } catch (err) {    if (err instanceof Deno.errors.PermissionDenied) {      throw err;    }    return false;  }}
interface SystemInfo {  pathItems: string[];  pathExts: string[] | undefined;  isNameMatch: (a: string, b: string) => boolean;}
function getSystemInfo(  command: string,  environment: Omit<Environment, "stat" | "statSync">,): SystemInfo | undefined {  const isWindows = environment.os === "windows";  const envValueSeparator = isWindows ? ";" : ":";  const path = environment.env("PATH");  const pathSeparator = isWindows ? "\\" : "/";  if (path == null) {    return undefined;  }
  return {    pathItems: splitEnvValue(path).map((item) => normalizeDir(item)),    pathExts: getPathExts(),    isNameMatch: isWindows      ? (a, b) => a.toLowerCase() === b.toLowerCase()      : (a, b) => a === b,  };
  function getPathExts() {    if (!isWindows) {      return undefined;    }
    const pathExtText = environment.env("PATHEXT") ?? ".EXE;.CMD;.BAT;.COM";    const pathExts = splitEnvValue(pathExtText);    const lowerCaseCommand = command.toLowerCase();
    for (const pathExt of pathExts) {      // Do not use the pathExts if someone has provided a command      // that ends with the extenion of an executable extension      if (lowerCaseCommand.endsWith(pathExt.toLowerCase())) {        return undefined;      }    }
    return pathExts;  }
  function splitEnvValue(value: string) {    return value      .split(envValueSeparator)      .map((item) => item.trim())      .filter((item) => item.length > 0);  }
  function normalizeDir(dirPath: string) {    if (!dirPath.endsWith(pathSeparator)) {      dirPath += pathSeparator;    }    return dirPath;  }}