From 0afacf7ddcc21280db0812b50df5e605ee74f3da Mon Sep 17 00:00:00 2001
From: Riccardo Azzolini <riccardo4096@gmail.com>
Date: Sat, 6 Oct 2018 14:27:06 +0200
Subject: [PATCH] Implement NegativePattern

---
 .../rules/dsl/patterns/NegativePattern.java   | 33 +++++++++++++++++++
 .../warppi/math/rules/dsl/PatternTest.java    | 20 +++++++++++
 2 files changed, 53 insertions(+)
 create mode 100644 core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/NegativePattern.java

diff --git a/core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/NegativePattern.java b/core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/NegativePattern.java
new file mode 100644
index 00000000..d71d5a56
--- /dev/null
+++ b/core/src/main/java/it/cavallium/warppi/math/rules/dsl/patterns/NegativePattern.java
@@ -0,0 +1,33 @@
+package it.cavallium.warppi.math.rules.dsl.patterns;
+
+import it.cavallium.warppi.math.Function;
+import it.cavallium.warppi.math.functions.Negative;
+import it.cavallium.warppi.math.rules.dsl.Pattern;
+import it.cavallium.warppi.math.rules.dsl.VisitorPattern;
+
+import java.util.Map;
+import java.util.Optional;
+
+/**
+ * Matches and generates the negative of another pattern.
+ */
+public class NegativePattern extends VisitorPattern {
+    private final Pattern inner;
+
+    public NegativePattern(Pattern inner) {
+        this.inner = inner;
+    }
+
+    @Override
+    public Optional<Map<String, Function>> visit(Negative negative) {
+        return inner.match(negative.getParameter());
+    }
+
+    @Override
+    public Function replace(Map<String, Function> subFunctions) {
+        return new Negative(
+                null,
+                inner.replace(subFunctions)
+        );
+    }
+}
diff --git a/core/src/test/java/it/cavallium/warppi/math/rules/dsl/PatternTest.java b/core/src/test/java/it/cavallium/warppi/math/rules/dsl/PatternTest.java
index 37f188fa..c0d75568 100644
--- a/core/src/test/java/it/cavallium/warppi/math/rules/dsl/PatternTest.java
+++ b/core/src/test/java/it/cavallium/warppi/math/rules/dsl/PatternTest.java
@@ -1,9 +1,11 @@
 package it.cavallium.warppi.math.rules.dsl;
 
 import it.cavallium.warppi.math.Function;
+import it.cavallium.warppi.math.functions.Negative;
 import it.cavallium.warppi.math.functions.Number;
 import it.cavallium.warppi.math.functions.Subtraction;
 import it.cavallium.warppi.math.functions.Sum;
+import it.cavallium.warppi.math.rules.dsl.patterns.NegativePattern;
 import it.cavallium.warppi.math.rules.dsl.patterns.NumberPattern;
 import it.cavallium.warppi.math.rules.dsl.patterns.SubFunctionPattern;
 import it.cavallium.warppi.math.rules.dsl.patterns.SumPattern;
@@ -92,4 +94,22 @@ public class PatternTest {
         assertTrue(subFunctions.isPresent());
         assertEquals(shouldMatch, pattern.replace(subFunctions.get()));
     }
+
+    @Test
+    public void negativePattern() {
+        final Pattern pattern = new NegativePattern(
+                new SubFunctionPattern("x")
+        );
+
+        final Function shouldNotMatch = new Number(null, 1);
+        assertFalse(pattern.match(shouldNotMatch).isPresent());
+
+        final Function shouldMatch = new Negative(
+                null,
+                new Number(null, 2)
+        );
+        final Optional<Map<String, Function>> subFunctions = pattern.match(shouldMatch);
+        assertTrue(subFunctions.isPresent());
+        assertEquals(shouldMatch, pattern.replace(subFunctions.get()));
+    }
 }
\ No newline at end of file