Refactor pandoc download code

Also fixing downloads on macOS

(Closes #1429)

Co-authored-by: Michael Lasevich <michael.lasevich@bhnetwork.com>
Co-authored-by: Alexander Schwartz <alexander.schwartz@gmx.net>

config/checkstyle/checkstyle.xml

@@ -166,7 +166,10 @@
         <!--
         <module name="InterfaceIsType"/>
         -->
-        <module name="VisibilityModifier"/>
+        <module name="VisibilityModifier">
+          <property name="allowPublicImmutableFields" value="true"/>
+          <property name="immutableClassCanonicalNames" value="java.lang.String, java.lang.Integer, java.lang.Byte, java.lang.Character, java.lang.Short, java.lang.Boolean, java.lang.Long, java.lang.Double, java.lang.Float, java.lang.StackTraceElement, java.math.BigInteger, java.math.BigDecimal, java.io.File, java.util.Locale, java.util.UUID, java.net.URL, java.net.URI, java.net.Inet4Address, java.net.Inet6Address, java.net.InetSocketAddress, org.asciidoc.intellij.arch.OS, org.asciidoc.intellij.arch.Arch" />
+        </module>
 
         <!-- Miscellaneous other checks.                   -->
         <!-- See http://checkstyle.sf.net/config_misc.html -->

src/main/java/org/asciidoc/intellij/arch/Arch.java

@@ -0,0 +1,16 @@
+package org.asciidoc.intellij.arch;
+
+import java.util.Locale;
+
+public enum Arch {
+  ARM,
+  INTEL;
+
+  static Arch identify() {
+    String osArch = System.getProperty("os.arch").toLowerCase(Locale.ROOT);
+    if (osArch.contains("arm") || osArch.contains("aarch64")) {
+      return Arch.ARM;
+    }
+    return Arch.INTEL;
+  }
+}

src/main/java/org/asciidoc/intellij/arch/OS.java

@@ -0,0 +1,28 @@
+package org.asciidoc.intellij.arch;
+
+import com.intellij.openapi.util.SystemInfoRt;
+
+public enum OS {
+  LINUX(SystemInfoRt.isLinux),
+  MAC(SystemInfoRt.isMac),
+  WINDOWS(SystemInfoRt.isWindows),
+  OTHER(true);
+
+  public final boolean active;
+
+  OS(boolean active) {
+    this.active = active;
+  }
+
+  /**
+   * Get active OS.
+   */
+  public static OS identfy() {
+    for (OS os : OS.values()) {
+      if (os.active) {
+        return os;
+      }
+    }
+    return OS.OTHER;
+  }
+}

src/main/java/org/asciidoc/intellij/arch/Platform.java

@@ -0,0 +1,30 @@
+package org.asciidoc.intellij.arch;
+
+public enum Platform {
+  LINUX_ARM(OS.LINUX, Arch.ARM, "arm64"),
+  LINUX_INTEL_64(OS.LINUX, Arch.INTEL, "amd64"),
+  WINDOWS_INTEL_64(OS.WINDOWS, Arch.INTEL, "x86_64"),
+  MAC_ARM64(OS.MAC, Arch.ARM, "arm64"),
+  MAC_INTEL_64(OS.MAC, Arch.INTEL, "x86_64"),
+  OTHER(null, null, "");
+  public final String archName;
+  public final OS os;
+  public final Arch arch;
+
+  Platform(OS os, Arch arch, String archName) {
+    this.arch = arch;
+    this.os = os;
+    this.archName = archName;
+  }
+
+  public static Platform identify() {
+    OS os = OS.identfy();
+    Arch arch = Arch.identify();
+    for (Platform platform : Platform.values()) {
+      if ((platform.os == os) && (platform.arch == arch)) {
+        return platform;
+      }
+    }
+    return Platform.OTHER;
+  }
+}