Add isEquivalentTo method to COSBase and COSObject

src/main/java/org/verapdf/cos/COSArray.java

@@ -189,6 +189,49 @@ private COSObject _at(final int i) {
         return this.entries.get(i);
     }
 
+    @Override
+    public boolean isEquivalentTo(COSBase o) {
+        if (this == o) return true;
+        if (o == null) return false;
+
+        if (o.isIndirect()) {
+            return this.isEquivalentTo(o.getDirectBase());
+        }
+
+        if (!(o instanceof COSArray)) return false;
+        List<COSBasePair> checkedObjects = new LinkedList<>();
+        return isEquivalentTo(o, checkedObjects);
+    }
+
+    @Override
+    boolean isEquivalentTo(COSBase o, List<COSBasePair> checkedObjects) {
+        if (this == o) return true;
+        if (o == null) return false;
+
+        if (!(o instanceof COSArray)) return false;
+
+        COSArray that = (COSArray) o;
+        if (COSBasePair.listContainsPair(checkedObjects, this, that)) {
+            return true;
+        }
+        COSBasePair.addPairToList(checkedObjects, this, that);
+
+        if (!Objects.equals(this.size(), that.size())) return false;
+
+        for (int i = 0; i < this.size(); ++i) {
+            COSBase thisElem = this.at(i).getDirectBase();
+            COSBase thatElem = that.at(i).getDirectBase();
+
+            if (thisElem == null && thatElem == null) continue;
+            if (thisElem == null || thatElem == null) return false;
+
+            if (!thisElem.isEquivalentTo(thatElem, checkedObjects)) {
+                return false;
+            }
+        }
+        return true;
+    }
+
     @Override
     public boolean equals(Object obj) {
         if (this == obj) {

src/main/java/org/verapdf/cos/COSBase.java

@@ -140,6 +140,12 @@ public void setObjectKey(COSKey indirectKey) {
 
 	public abstract void mark();
 
+    public abstract boolean isEquivalentTo(COSBase obj);
+
+    boolean isEquivalentTo(COSBase o, List<COSBasePair> checkedObjects) {
+        return isEquivalentTo(o);
+    }
+
 	boolean equals(Object obj, List<COSBasePair> checkedObjects) {
 		return this.equals(obj);
 	}

src/main/java/org/verapdf/cos/COSBoolean.java

@@ -71,6 +71,23 @@ public boolean setBoolean(final boolean value) {
         return true;
     }
 
+    @Override
+    public boolean isEquivalentTo(COSBase o) {
+        if (this == o) return true;
+        if (o == null) return false;
+
+        if (o.isIndirect()) {
+            return isEquivalentTo(o.getDirectBase());
+        }
+
+        if (!(o instanceof COSBoolean)) return false;
+
+        COSBoolean that = (COSBoolean) o;
+
+        return value == that.value;
+
+    }
+
     public boolean get() {
         return this.value;
     }

src/main/java/org/verapdf/cos/COSDictionary.java

@@ -299,6 +299,73 @@ public Collection<COSObject> getValues() {
         return this.entries.values();
     }
 
+    private Set<ASAtom> getNonNullKeySet() {
+        Set<ASAtom> nonNullKeys = new HashSet<>();
+        for (ASAtom key : getKeySet()) {
+            COSBase value = getKey(key).getDirectBase();
+            if (value != null) {
+                nonNullKeys.add(key);
+            }
+        }
+        return nonNullKeys;
+    }
+
+    @Override
+    public boolean isEquivalentTo(COSBase o) {
+        if (this == o) return true;
+        if (o == null) return false;
+
+        if (o.isIndirect()) {
+            return isEquivalentTo(o.getDirectBase());
+        }
+
+        if (!(o instanceof COSDictionary)) return false;
+
+        List<COSBasePair> checkedObjects = new LinkedList<>();
+        return isEquivalentTo(o, checkedObjects);
+    }
+
+    /**
+     * Internal recursive comparison with cycle detection.
+     */
+    boolean isEquivalentTo(COSBase o, List<COSBasePair> checkedObjects) {
+        if (this == o) return true;
+        if (o == null) return false;
+        if (!(o instanceof COSDictionary)) return false;
+
+        COSDictionary that = (COSDictionary) o;
+
+        if (COSBasePair.listContainsPair(checkedObjects, this, that)) {
+            return true;
+        }
+        COSBasePair.addPairToList(checkedObjects, this, that);
+
+        Set<ASAtom> thisKeys = this.getNonNullKeySet();
+        Set<ASAtom> thatKeys = that.getNonNullKeySet();
+
+        if (!thisKeys.equals(thatKeys)) {
+            return false;
+        }
+
+        return isEquivalentKeys(that, thisKeys, checkedObjects);
+    }
+
+    protected boolean isEquivalentKeys(COSDictionary that, Set<ASAtom> thisKeys, List<COSBasePair> checkedObjects) {
+        for (ASAtom key : thisKeys) {
+            COSBase thisVal = this.getKey(key).getDirectBase();
+            COSBase thatVal = that.getKey(key).getDirectBase();
+
+            if (thisVal == null && thatVal == null) continue;
+            if (thisVal == null || thatVal == null) return false;
+
+            if (!thisVal.isEquivalentTo(thatVal, checkedObjects)) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
     @Override
     public boolean equals(Object obj) {
         if (this == obj) {

src/main/java/org/verapdf/cos/COSIndirect.java

@@ -480,6 +480,17 @@ public void mark() {
         }
     }
 
+    @Override
+    public boolean isEquivalentTo(COSBase o) {
+        if (this == o) return true;
+
+        COSBase thisBase = this.getDirectBase();
+        if (thisBase == null && o == null) return true;
+        if (thisBase == null || o == null) return false;
+
+        return thisBase.isEquivalentTo(o.getDirectBase());
+    }
+
     @Override
     public boolean equals(Object o) {
         if (this == o) return true;

src/main/java/org/verapdf/cos/COSInteger.java

@@ -23,6 +23,8 @@
 import org.verapdf.cos.visitor.ICOSVisitor;
 import org.verapdf.cos.visitor.IVisitor;
 
+import java.math.BigDecimal;
+
 /**
  * @author Timur Kamalov
  */
@@ -75,6 +77,27 @@ public boolean setReal(final double value) {
         return true;
     }
 
+    @Override
+    public boolean isEquivalentTo(COSBase o) {
+        if (this == o) return true;
+        if (o == null) return false;
+
+        if (o.isIndirect()) {
+            return isEquivalentTo(o.getDirectBase());
+        }
+
+        if (o instanceof COSInteger) {
+            return this.value == ((COSInteger) o).value;
+        }
+
+        if (o instanceof COSReal) {
+            COSReal thatReal = (COSReal) o;
+            return BigDecimal.valueOf(this.value).compareTo(thatReal.getDecimalValue()) == 0;
+        }
+
+        return false;
+    }
+
     public long get() {
         return this.value;
     }
@@ -97,4 +120,9 @@ public boolean equals(Object o) {
         return value == that.value;
 
     }
+
+    @Override
+    public BigDecimal getDecimalValue() {
+        return BigDecimal.valueOf(value);
+    }
 }

src/main/java/org/verapdf/cos/COSName.java

@@ -25,6 +25,7 @@
 import org.verapdf.cos.visitor.IVisitor;
 
 import java.nio.charset.StandardCharsets;
+import java.util.Arrays;
 import java.util.Objects;
 
 /**
@@ -91,6 +92,22 @@ public boolean setName(final ASAtom value) {
         return true;
     }
 
+    @Override
+    public boolean isEquivalentTo(COSBase o) {
+        if (this == o) return true;
+        if (o == null) return false;
+
+        if (o.isIndirect()) {
+            return isEquivalentTo(o.getDirectBase());
+        }
+
+        if (!(o instanceof COSName)) return false;
+
+        COSName that = (COSName) o;
+
+        return Objects.equals(value, that.value);
+    }
+
     public ASAtom get() {
         return value;
     }

src/main/java/org/verapdf/cos/COSNull.java

@@ -51,6 +51,11 @@ public Object accept(final ICOSVisitor visitor) {
         return visitor.visitFromNull(this);
     }
 
+    @Override
+    public boolean isEquivalentTo(COSBase o) {
+        return equals(o);
+    }
+
     @Override
     public boolean equals(Object o) {
         if (this == o) return true;

src/main/java/org/verapdf/cos/COSNumber.java

@@ -20,6 +20,8 @@
  */
 package org.verapdf.cos;
 
+import java.math.BigDecimal;
+
 /**
  * @author Timur Kamalov
  */
@@ -29,4 +31,6 @@ public COSNumber() {
         super();
     }
 
+    public abstract BigDecimal getDecimalValue();
+
 }

src/main/java/org/verapdf/cos/COSObject.java

@@ -494,6 +494,18 @@ public void setIsHeaderFormatComplyPDFA(Boolean isHeaderFormatComplyPDFA) {
 		this.isHeaderFormatComplyPDFA = isHeaderFormatComplyPDFA;
 	}
 
+    public boolean isEquivalentTo(COSObject o) {
+        if (o == this) return true;
+        if (o == null) return false;
+
+        COSBase thisBase = this.getDirectBase();
+        COSBase otherBase = o.getDirectBase();
+        if (thisBase == null && otherBase == null) return true;
+        if (thisBase == null || otherBase == null) return false;
+
+        return thisBase.isEquivalentTo(otherBase);
+    }
+
 	@Override
 	public boolean equals(Object o) {
 		if (this == o) return true;

src/main/java/org/verapdf/cos/COSReal.java

@@ -23,6 +23,7 @@
 import org.verapdf.cos.visitor.ICOSVisitor;
 import org.verapdf.cos.visitor.IVisitor;
 
+import java.math.BigDecimal;
 import java.text.DecimalFormat;
 import java.text.DecimalFormatSymbols;
 
@@ -45,6 +46,11 @@ public class COSReal extends COSNumber {
     protected COSReal() {
     }
 
+    @Override
+    public BigDecimal getDecimalValue() {
+        return BigDecimal.valueOf(value);
+    }
+
     protected COSReal(final double value) {
         this.value = value;
     }
@@ -88,6 +94,27 @@ public boolean setReal(final double value) {
         return true;
     }
 
+    @Override
+    public boolean isEquivalentTo(COSBase o) {
+        if (this == o) return true;
+
+        if (o.isIndirect()) {
+            return isEquivalentTo(o.getDirectBase());
+        }
+
+        if (o instanceof COSReal) {
+            COSReal thatReal = (COSReal) o;
+            return this.getDecimalValue().compareTo(thatReal.getDecimalValue()) == 0;
+        }
+
+        if (o instanceof COSInteger) {
+            COSInteger thatInt = (COSInteger) o;
+            return this.getDecimalValue().compareTo(thatInt.getDecimalValue()) == 0;
+        }
+
+        return false;
+    }
+
     public double get() {
         return this.value;
     }