GH-477 Environment Variable Default Provider

Signed-off-by: Markus KARG <[email protected]>

src/main/java/com/beust/jcommander/defaultprovider/EnvironmentVariableDefaultProvider.java

@@ -0,0 +1,103 @@
+/**
+ * Copyright (C) 2019 the original author or authors.
+ * See the notice.md file distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.beust.jcommander.defaultprovider;
+
+import static java.util.Objects.requireNonNull;
+
+import java.util.function.Function;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import com.beust.jcommander.IDefaultProvider;
+
+/**
+ * A default provider that reads its default values from an environment
+ * variable.
+ * 
+ * A prefix pattern can be provided to indicate how options are identified.
+ * The default pattern {@code -/} mandates that options MUST start with either a dash or a slash.
+ * Options can have values separated by whitespace.
+ * Values can contain whitespace as long as they are single-quoted or double-quoted.
+ * Otherwhise whitespace identifies the end of a value.
+ *
+ * @author Markus KARG ([email protected])
+ */
+public final class EnvironmentVariableDefaultProvider implements IDefaultProvider {
+
+    private static final String DEFAULT_VARIABLE_NAME = "JCOMMANDER_OPTS";
+
+    private static final String DEFAULT_PREFIXES_PATTERN = "-/";
+
+    private final String environmentVariableValue;
+
+    private final String optionPrefixesPattern;
+
+    /**
+     * Creates a default provider reading the environment variable {@code JCOMMANDER_OPTS} using the prefixes pattern {@code -/}.
+     */
+    public EnvironmentVariableDefaultProvider() {
+        this(DEFAULT_VARIABLE_NAME, DEFAULT_PREFIXES_PATTERN);
+    }
+
+    /**
+     * Creates a default provider reading the specified environment variable using the specified prefixes pattern.
+     *  
+     * @param environmentVariableName
+     *            The name of the environment variable to read (e. g. {@code "JCOMMANDER_OPTS"}). Must not be {@code null}.
+     * @param optionPrefix
+     *            A set of characters used to indicate the start of an option (e. g. {@code "-/"} if option names may start with either dash or slash). Must not be {@code null}.
+     */
+    public EnvironmentVariableDefaultProvider(final String environmentVariableName, final String optionPrefixes) {
+        this(requireNonNull(environmentVariableName), requireNonNull(optionPrefixes), System::getenv);
+    }
+
+    /**
+     * For Unit Tests Only: Allows to mock the resolver, as Java cannot set environment variables.
+     *
+     * @param environmentVariableName
+     *            The name of the environment variable to read. May be {@code null} if the passed resolver doesn't use it (e. g. Unit Test).
+     * @param optionPrefix
+     *            A set of characters used to indicate the start of an option (e. g. {@code "-/"} if option names may start with either dash or slash). Must not be {@code null}.
+     * @param resolver
+     *            Reads the value from the environment variable (e. g. {@code System::getenv}). Must not be {@code null}.
+     */
+    EnvironmentVariableDefaultProvider(final String environmentVariableName, final String optionPrefixes, final Function<String, String> resolver) {
+        this.environmentVariableValue = resolver.apply(environmentVariableName);
+        this.optionPrefixesPattern = requireNonNull(optionPrefixes);
+    }
+
+    @Override
+    public final String getDefaultValueFor(final String optionName) {
+        if (this.environmentVariableValue == null)
+            return null;
+        final Matcher matcher = Pattern
+                .compile("(?:(?:.*\\s+)|(?:^))(" + Pattern.quote(optionName) + ")\\s*((?:'[^']*(?='))|(?:\"[^\"]*(?=\"))|(?:[^" + this.optionPrefixesPattern + "\\s]+))?.*")
+                .matcher(this.environmentVariableValue);
+        if (!matcher.matches())
+            return null;
+        String value = matcher.group(2);
+        if (value == null)
+            return "true";
+        final char firstCharacter = value.charAt(0);
+        if (firstCharacter == '\'' || firstCharacter == '"')
+            value = value.substring(1);
+        return value;
+    }
+
+}

src/test/java/com/beust/jcommander/defaultprovider/EnvironmentVariableDefaultProviderTest.java

@@ -0,0 +1,53 @@
+/**
+ * Copyright (C) 2019 the original author or authors.
+ * See the notice.md file distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.beust.jcommander.defaultprovider;
+
+import static org.testng.Assert.assertEquals;
+import static org.testng.Assert.assertNull;
+
+import java.util.function.Function;
+
+import org.testng.annotations.Test;
+
+import com.beust.jcommander.IDefaultProvider;
+
+public final class EnvironmentVariableDefaultProviderTest {
+
+	@Test
+	public final void shouldParseEnvironmentVariable() {
+        // given
+		final Function<String, String> variableResolver = name -> "--some-option --simple-value ABC --quoted-value 'A BC' --double-quoted-value \"AB C\"";
+		final IDefaultProvider defaultProvider = new EnvironmentVariableDefaultProvider(null, "-", variableResolver);
+
+		// when
+		final String nonExistentValue = defaultProvider.getDefaultValueFor("--non-existent-option");
+		final String someOption = defaultProvider.getDefaultValueFor("--some-option");
+		final String simpleValue = defaultProvider.getDefaultValueFor("--simple-value");
+		final String quotedValue = defaultProvider.getDefaultValueFor("--quoted-value");
+		final String doubleQuotedValue = defaultProvider.getDefaultValueFor("--double-quoted-value");
+
+		// then
+		assertNull(nonExistentValue);
+		assertEquals(someOption, "true");
+		assertEquals(simpleValue, "ABC");
+		assertEquals(quotedValue, "A BC");
+		assertEquals(doubleQuotedValue, "AB C");
+	}
+
+}

src/test/resources/testng.xml

@@ -20,6 +20,7 @@
       <class name="com.beust.jcommander.DefaultUsageFormatterTest" />
       <class name="com.beust.jcommander.UnixStyleUsageFormatterTest" />
       <class name="com.beust.jcommander.StringsTest" />
+      <class name="com.beust.jcommander.defaultprovider.EnvironmentVariableDefaultProviderTest" />
     </classes>
   </test>