Manually find powershell.exe or pwsh.exe on path

Some windows systems have pwsh.exe but not powershell.exe. For the
purpose of this library, both executables have interchangeable
functionality so we can fall back to pwsh.exe when powershell.exe is not
present. It is also possible that neither powershell.exe nor pwsh.exe is
availble on the path. When that is the case, we can fall back to looking
them up in the default system locations: C:\Program Files\PowerShell\*
and C:\\Windows\\System32\\WindowsPowerShell\\v1.0.

On my windows vm, powershell.exe and pwsh.exe are both available but
powershell.exe is noticeably faster to execute this command (running
test takes about 3 seconds with pwsh.exe and 1 seconds with
powershell.exe). For this reason, I made it so that powershell.exe is
preferred over pwsh.exe if it is available.

src/main/java/dev/dirs/Util.java

@@ -3,6 +3,7 @@
 import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStreamReader;
+import java.io.File;
 import java.lang.reflect.Method;
 import java.nio.charset.Charset;
 import java.util.Locale;
@@ -134,7 +135,11 @@ static String[] getXDGUserDirs(String... dirs) {
       buf.append(';');
     }
     commands[2] = buf.toString();
-    return runCommands(dirsLength, Charset.defaultCharset(), commands);
+    try {
+      return runCommands(dirsLength, Charset.defaultCharset(), commands);
+    } catch (IOException e) {
+      throw new RuntimeException(e);
+    }
   }
 
   static String[] getWinDirs(String... guids) {
@@ -148,13 +153,15 @@ static String[] getWinDirs(String... guids) {
     }
 
     String encodedCommand = SCRIPT_START_BASE64 + toUTF16LEBase64(buf.toString() + "}");
-
-    return runCommands(guidsLength, Charset.forName("UTF-8"),
-        "powershell.exe",
-        "-NoProfile",
-        "-EncodedCommand",
-        encodedCommand
-    );
+    String path = System.getenv("Path");
+    String[] dirs = path == null ? new String[0] : path.split(File.pathSeparator);
+    Charset utf8 = Charset.forName("UTF-8");
+    if (dirs.length == 0) return windowsFallback(guidsLength, utf8, encodedCommand);
+    try {
+      return runWinCommands(guidsLength, utf8, dirs, encodedCommand);
+    } catch (IOException e) {
+      return windowsFallback(guidsLength, utf8, encodedCommand);
+    }
   }
 
   private static String toUTF16LEBase64(String script) {
@@ -183,27 +190,20 @@ private static void initBase64Encoding() {
     }
   }
 
-  private static String[] runCommands(int expectedResultLines, Charset charset, String... commands) {
-    final ProcessBuilder processBuilder = new ProcessBuilder(commands);
-    Process process;
-    try {
-      process = processBuilder.start();
-    } catch (IOException e) {
-      throw new RuntimeException(e);
-    }
+  private static String[] runCommands(int expectedResultLines, Charset charset, String... commands) throws IOException {
+    final Process process = new ProcessBuilder(commands).start();
 
     String[] results = new String[expectedResultLines];
     BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream(), charset));
     try {
       for (int i = 0; i < expectedResultLines; i++) {
         String line = reader.readLine();
+        if (line == null) throw new IOException("no output from process");
         if (i == 0 && operatingSystem == 'w' && line != null && line.startsWith(UTF8_BOM))
           line = line.substring(UTF8_BOM.length());
         results[i] = line;
       }
       return results;
-    } catch (IOException e) {
-      throw new RuntimeException(e);
     } finally {
       process.destroy();
       try {
@@ -214,6 +214,51 @@ private static String[] runCommands(int expectedResultLines, Charset charset, St
     }
   }
 
+  private static String[] runWinCommands(int guidsLength, Charset charset, String[] dirs, String encodedCommand) throws IOException {
+    // legacy powershell.exe seems to run faster than pwsh.exe so prefer it if available
+    String[] commands = new String[] { "powershell.exe", "pwsh.exe" };
+    IOException firstException = null;
+    for (String dir : dirs) {
+      File dirFile = new File(dir);
+      for (String command : commands) {
+        File commandFile = new File(dir, command);
+        if (commandFile.exists()) {
+          try {
+            return runCommands(guidsLength, Charset.forName("UTF-8"),
+                commandFile.toString(),
+                "-NoProfile",
+                "-EncodedCommand",
+                encodedCommand
+            );
+          } catch (IOException e) {
+            firstException = firstException == null ? e : firstException;
+          }
+        }
+      }
+    }
+    if (firstException != null) throw firstException;
+    else throw new IOException("no directories");
+  }
+
+  private static String[] windowsFallback(int guidsLength, Charset charset, String encodedCommand) {
+    File powerShellBase = new File("C:\\Program Files\\Powershell");
+    String[] powerShellDirs = powerShellBase.list();
+    if (powerShellDirs == null) powerShellDirs = new String[0];
+    String[] allPowerShellDirs = new String[powerShellDirs.length + 1];
+
+    // legacy powershell.exe seems to run faster than pwsh.exe so prefer it if available
+    String systemRoot = System.getenv("SystemRoot");
+    if (systemRoot == null) systemRoot = "C:\\Windows";
+    allPowerShellDirs[0] = systemRoot + "\\System32\\WindowsPowerShell\\v1.0\\";
+
+    for (int i = 0; i < powerShellDirs.length; ++i) allPowerShellDirs[i + 1] = new File(powerShellBase, powerShellDirs[i]).toString();
+    try {
+      return runWinCommands(guidsLength, Charset.forName("UTF-8"), allPowerShellDirs, encodedCommand);
+    } catch (final IOException ex) {
+      throw new RuntimeException("Couldn't find pwsh.exe or powershell.exe on path or in default system locations", ex);
+    }
+  }
+
   static String macOSApplicationPath(String qualifier, String organization, String application) {
     StringBuilder buf = new StringBuilder(Math.max(stringLength(qualifier) + stringLength(organization) + stringLength(application), 0));
     boolean qualPresent = !isNullOrEmpty(qualifier);