Better api generation

Things to consider:

• breaking changes (removed imports), so up minor version, because we are still not in 1.0

src/main/jastadd/backend/API.jadd

 aspect BackendAPI {
   public void Relation.generateAPI(StringBuilder sb) {
-    sb.append(ind(1) + "// " + prettyPrint() + "\n");
-    getDirection().generateAPI(sb);
+    sb.append(ind(1) + "// api for " + prettyPrint() + "\n");
+    if (getLeft().isNavigable()) {
+      sb.append(ind(1) + "// left direction for " + prettyPrint() + "\n");
+      getLeft().generateAPI(sb);
+    }
+    if (getRight().isNavigable()) {
+      sb.append(ind(1) + "// right direction for " + prettyPrint() + "\n");
+      getRight().generateAPI(sb);
+    }
     sb.append("\n");
   }
-  public abstract void Direction.generateAPI(StringBuilder sb);
 
+  public void RelationComponent.generateAPI(StringBuilder sb) {
+    if (otherSide().isNavigable()) {
+      if (multiplicityOne() || multiplicityOpt()) {
+        if (otherSide().multiplicityOne() || otherSide().multiplicityOpt()) {
+          generateBiOneOne(sb);
+        } else if (otherSide().multiplicityMany()) {
+          generateBiOneMany(sb);
+        }
+      } else if (multiplicityMany()) {
+        if (otherSide().multiplicityOne() || otherSide().multiplicityOpt()) {
+          generateBiManyOne(sb);
+        } else if (otherSide().multiplicityMany()) {
+          generateBiManyMany(sb);
+        }
+      }
+    } else {
+      if (multiplicityOne() || multiplicityOpt()) {
+        generateDirectedZeroOneAPI(sb);
+      } else if (multiplicityMany()) {
+        generateDirectedManyAPI(sb);
+      }
+    }
+  }
+
+  public void RelationComponent.generateExtraOptAPI(StringBuilder sb) {
+    // has
+    sb.append(ind(1) + "public boolean " + getTypeUse().decl());
+    sb.append(".has" + nameCapitalized() + "() {\n");
+    sb.append(ind(2) + "return ");
+    if (useJastAddNames) {
+      sb.append("get" + nameCapitalized());
+    } else {
+      sb.append(name());
+    }
+    sb.append("() != null;\n");
+    sb.append(ind(1) + "}\n");
+
+    // clear
+    sb.append(ind(1) + "public void " + getTypeUse().decl());
+    sb.append(".clear" + nameCapitalized() + "() {\n");
+    sb.append(ind(2) + "set" + nameCapitalized() + "(null);\n");
+    sb.append(ind(1) + "}\n");
+  }
 
   inh Relation Direction.relation();
+  inh Relation RelationComponent.relation();
   eq Relation.getChild().relation() = this;
   eq Program.getChild().relation() = null;
 
+  inh boolean RelationComponent.isNavigable();
+  eq Relation.getLeft().isNavigable() = getDirection().isNavigableLeftToRight();
+  eq Relation.getRight().isNavigable() = getDirection().isNavigableRightToLeft();
+
+  syn boolean Direction.isNavigableRightToLeft() = true;
+  eq RightDirection.isNavigableRightToLeft() = false;
+  syn boolean Direction.isNavigableLeftToRight() = true;
+  eq LeftDirection.isNavigableLeftToRight() = false;
+
   public String RelationComponent.nameCapitalized() {
     return name().substring(0,1).toUpperCase() + name().substring(1);
   }