import * as pfs from './pfs';
import os from 'os';
import path from 'path';
import {env} from 'process';

const WindowsPowerShell64BitLabel = 'Windows PowerShell';
const WindowsPowerShell32BitLabel = 'Windows PowerShell (x86)';

// This is required, since parseInt("7-preview") will return 7.
const IntRegex: RegExp = /^\d+$/;

const PwshMsixRegex: RegExp = /^Microsoft.PowerShell_.*/;
const PwshPreviewMsixRegex: RegExp = /^Microsoft.PowerShellPreview_.*/;

// The platform details descriptor for the platform we're on
const isProcess64Bit: boolean = process.arch === 'x64';
const isOS64Bit: boolean = isProcess64Bit || os.arch() === 'x64';

export interface IPowerShellExeDetails {
  readonly displayName: string;
  readonly exePath: string;
}

export interface IPossiblePowerShellExe extends IPowerShellExeDetails {
  exists(): Promise<boolean>;
}

class PossiblePowerShellExe implements IPossiblePowerShellExe {
  constructor(
    public readonly exePath: string,
    public readonly displayName: string,
    private knownToExist?: boolean
  ) {}

  public async exists(): Promise<boolean> {
    if (this.knownToExist === undefined) {
      this.knownToExist = await pfs.fileExists(this.exePath);
    }
    return this.knownToExist!;
  }
}

function getProgramFilesPath({useAlternateBitness = false}: {useAlternateBitness?: boolean} = {}):
  | string
  | null {
  if (!useAlternateBitness) {
    // Just use the native system bitness
    return env.ProgramFiles || null;
  }

  // We might be a 64-bit process looking for 32-bit program files
  if (isProcess64Bit) {
    return env['ProgramFiles(x86)'] || null;
  }

  // We might be a 32-bit process looking for 64-bit program files
  if (isOS64Bit) {
    return env.ProgramW6432 || null;
  }

  // We're a 32-bit process on 32-bit Windows, there is no other Program Files dir
  return null;
}

function getSystem32Path({
  useAlternateBitness = false
}: {useAlternateBitness?: boolean} = {}): string {
  const windir: string = env.windir!;

  if (!useAlternateBitness) {
    // Just use the native system bitness
    return path.join(windir, 'System32');
  }

  // We might be a 64-bit process looking for 32-bit system32
  if (isProcess64Bit) {
    return path.join(windir, 'SysWOW64');
  }

  // We might be a 32-bit process looking for 64-bit system32
  if (isOS64Bit) {
    return path.join(windir, 'Sysnative');
  }

  // We're on a 32-bit Windows, so no alternate bitness
  return path.join(windir, 'System32');
}

async function findPSCoreWindowsInstallation({
  useAlternateBitness = false,
  findPreview = false
}: {
  useAlternateBitness?: boolean;
  findPreview?: boolean;
} = {}): Promise<IPossiblePowerShellExe | null> {
  const programFilesPath = getProgramFilesPath({useAlternateBitness});
  if (!programFilesPath) {
    return null;
  }

  const powerShellInstallBaseDir = path.join(programFilesPath, 'PowerShell');

  // Ensure the base directory exists
  if (!(await pfs.dirExists(powerShellInstallBaseDir))) {
    return null;
  }

  let highestSeenVersion: number = -1;
  let pwshExePath: string | null = null;
  for (const item of await pfs.readdir(powerShellInstallBaseDir)) {
    let currentVersion: number = -1;
    if (findPreview) {
      // We are looking for something like "7-preview"

      // Preview dirs all have dashes in them
      const dashIndex = item.indexOf('-');
      if (dashIndex < 0) {
        continue;
      }

      // Verify that the part before the dash is an integer
      // and that the part after the dash is "preview"
      const intPart: string = item.substring(0, dashIndex);
      if (!IntRegex.test(intPart) || item.substring(dashIndex + 1) !== 'preview') {
        continue;
      }

      currentVersion = parseInt(intPart, 10);
    } else {
      // Search for a directory like "6" or "7"
      if (!IntRegex.test(item)) {
        continue;
      }

      currentVersion = parseInt(item, 10);
    }

    // Ensure we haven't already seen a higher version
    if (currentVersion <= highestSeenVersion) {
      continue;
    }

    // Now look for the file
    const exePath = path.join(powerShellInstallBaseDir, item, 'pwsh.exe');
    if (!(await pfs.fileExists(exePath))) {
      continue;
    }

    pwshExePath = exePath;
    highestSeenVersion = currentVersion;
  }

  if (!pwshExePath) {
    return null;
  }

  const bitness: string = programFilesPath.includes('x86') ? ' (x86)' : '';
  const preview: string = findPreview ? ' Preview' : '';

  return new PossiblePowerShellExe(pwshExePath, `PowerShell${preview}${bitness}`, true);
}

async function findPSCoreMsix({
  findPreview
}: {findPreview?: boolean} = {}): Promise<IPossiblePowerShellExe | null> {
  // We can't proceed if there's no LOCALAPPDATA path
  if (!env.LOCALAPPDATA) {
    return null;
  }

  // Find the base directory for MSIX application exe shortcuts
  const msixAppDir = path.join(env.LOCALAPPDATA, 'Microsoft', 'WindowsApps');

  if (!(await pfs.dirExists(msixAppDir))) {
    return null;
  }

  // Define whether we're looking for the preview or the stable
  const {pwshMsixDirRegex, pwshMsixName} = findPreview
    ? {pwshMsixDirRegex: PwshPreviewMsixRegex, pwshMsixName: 'PowerShell Preview (Store)'}
    : {pwshMsixDirRegex: PwshMsixRegex, pwshMsixName: 'PowerShell (Store)'};

  // We should find only one such application, so return on the first one
  for (const subdir of await pfs.readdir(msixAppDir)) {
    if (pwshMsixDirRegex.test(subdir)) {
      const pwshMsixPath = path.join(msixAppDir, subdir, 'pwsh.exe');
      return new PossiblePowerShellExe(pwshMsixPath, pwshMsixName);
    }
  }

  // If we find nothing, return null
  return null;
}

function findPSCoreDotnetGlobalTool(): IPossiblePowerShellExe {
  const dotnetGlobalToolExePath: string = path.join(os.homedir(), '.dotnet', 'tools', 'pwsh.exe');

  return new PossiblePowerShellExe(dotnetGlobalToolExePath, '.NET Core PowerShell Global Tool');
}

function findWinPS({
  useAlternateBitness = false
}: {useAlternateBitness?: boolean} = {}): IPossiblePowerShellExe | null {
  // x86 and ARM only have one WinPS on them
  if (!isOS64Bit && useAlternateBitness) {
    return null;
  }

  const systemFolderPath = getSystem32Path({useAlternateBitness});

  const winPSPath = path.join(systemFolderPath, 'WindowsPowerShell', 'v1.0', 'powershell.exe');

  let displayName: string;
  if (isProcess64Bit) {
    displayName = useAlternateBitness ? WindowsPowerShell32BitLabel : WindowsPowerShell64BitLabel;
  } else if (isOS64Bit) {
    displayName = useAlternateBitness ? WindowsPowerShell64BitLabel : WindowsPowerShell32BitLabel;
  } else {
    // NOTE: ARM Windows devices also have Windows PowerShell x86 on them. There is no
    // "ARM Windows PowerShell".
    displayName = WindowsPowerShell32BitLabel;
  }

  return new PossiblePowerShellExe(winPSPath, displayName, true);
}

/**
 * Iterates through all the possible well-known PowerShell installations on a machine.
 * Returned values may not exist, but come with an .exists property
 * which will check whether the executable exists.
 */
async function* enumerateDefaultPowerShellInstallations(): AsyncIterable<IPossiblePowerShellExe> {
  // Find PSCore stable first
  let pwshExe = await findPSCoreWindowsInstallation();
  if (pwshExe) {
    yield pwshExe;
  }

  // Windows may have a 32-bit pwsh.exe
  pwshExe = await findPSCoreWindowsInstallation({useAlternateBitness: true});
  if (pwshExe) {
    yield pwshExe;
  }

  // Also look for the MSIX/UWP installation
  pwshExe = await findPSCoreMsix();
  if (pwshExe) {
    yield pwshExe;
  }

  // Look for the .NET global tool
  // Some older versions of PowerShell have a bug in this where startup will fail,
  // but this is fixed in newer versions
  pwshExe = findPSCoreDotnetGlobalTool();
  if (pwshExe) {
    yield pwshExe;
  }

  // Look for PSCore preview
  pwshExe = await findPSCoreWindowsInstallation({findPreview: true});
  if (pwshExe) {
    yield pwshExe;
  }

  // Find a preview MSIX
  pwshExe = await findPSCoreMsix({findPreview: true});
  if (pwshExe) {
    yield pwshExe;
  }

  // Look for pwsh-preview with the opposite bitness
  pwshExe = await findPSCoreWindowsInstallation({useAlternateBitness: true, findPreview: true});
  if (pwshExe) {
    yield pwshExe;
  }

  // Finally, get Windows PowerShell

  // Get the natural Windows PowerShell for the process bitness
  pwshExe = findWinPS();
  if (pwshExe) {
    yield pwshExe;
  }

  // Get the alternate bitness Windows PowerShell
  pwshExe = findWinPS({useAlternateBitness: true});
  if (pwshExe) {
    yield pwshExe;
  }
}

/**
 * Iterates through PowerShell installations on the machine according
 * to configuration passed in through the constructor.
 * PowerShell items returned by this object are verified
 * to exist on the filesystem.
 */
export async function* enumeratePowerShellInstallations(): AsyncIterable<IPowerShellExeDetails> {
  // Get the default PowerShell installations first
  for await (const defaultPwsh of enumerateDefaultPowerShellInstallations()) {
    if (await defaultPwsh.exists()) {
      yield defaultPwsh;
    }
  }
}