1 files changed, 90 insertions, 0 deletions
diff --git a/src/main/java/org/zwobble/couscous/transforms/DesugarSwitchToIfElse.java b/src/main/java/org/zwobble/couscous/transforms/DesugarSwitchToIfElse.java
new file mode 100644
index 0000000..3ffaad5
--- /dev/null
+++ b/src/main/java/org/zwobble/couscous/transforms/DesugarSwitchToIfElse.java
@@ -0,0 +1,90 @@
+package org.zwobble.couscous.transforms;
+
+import org.zwobble.couscous.ast.LocalVariableDeclarationNode;
+import org.zwobble.couscous.ast.NodeTypes;
+import org.zwobble.couscous.ast.StatementNode;
+import org.zwobble.couscous.ast.sugar.SwitchCaseNode;
+import org.zwobble.couscous.ast.sugar.SwitchNode;
+import org.zwobble.couscous.ast.visitors.NodeTransformer;
+import org.zwobble.couscous.frontends.java.Scope;
+import org.zwobble.couscous.types.Types;
+import org.zwobble.couscous.util.ExtraLists;
+
+import java.util.List;
+import java.util.Optional;
+
+import static com.google.common.collect.Iterables.tryFind;
+import static org.zwobble.couscous.ast.IfStatementNode.ifStatement;
+import static org.zwobble.couscous.ast.MethodCallNode.methodCall;
+import static org.zwobble.couscous.ast.TypeCoercionNode.coerce;
+import static org.zwobble.couscous.ast.VariableReferenceNode.reference;
+import static org.zwobble.couscous.ast.sugar.SwitchCaseNode.switchCase;
+import static org.zwobble.couscous.util.ExtraIterables.lazyFlatMap;
+import static org.zwobble.couscous.util.ExtraLists.*;
+import static org.zwobble.couscous.util.Fold.foldRight;
+import static org.zwobble.couscous.util.Tails.tails;
+import static org.zwobble.couscous.util.UpToAndIncludingIterable.upToAndIncluding;
+
+public class DesugarSwitchToIfElse {
+    // TODO: ensure globally unique IDs, and locally unique variable names
+
+    public static NodeTransformer transformer(Scope scope) {
+        return NodeTransformer.builder()
+            .transformStatement(statement -> {
+                if (statement.type() == NodeTypes.SWITCH) {
+                    return Optional.of(desugar(scope, ((SwitchNode) statement)));
+                } else {
+                    return Optional.empty();
+                }
+            })
+            .build();
+    }
+
+    public static List<StatementNode> desugar(Scope scope, SwitchNode switchNode) {
+        LocalVariableDeclarationNode switchValueAssignment = scope.temporaryVariable(switchNode.getValue());
+
+        List<StatementNode> handleDefault = tryFind(switchNode.getCases(), SwitchCaseNode::isDefault)
+            .transform(SwitchCaseNode::getStatements)
+            .or(list());
+
+        List<SwitchCaseNode> cases = eagerMap(
+            tails(switchNode.getCases()),
+            remainingCases -> readSwitchCase(remainingCases.get(0), remainingCases)
+        );
+
+        return cons(
+            switchValueAssignment,
+            foldRight(cases, handleDefault, (handle, currentCase) ->
+                currentCase.getValue()
+                    .map(value -> list(ifStatement(
+                        methodCall(
+                            reference(switchValueAssignment),
+                            "equals",
+                            list(coerce(value, Types.OBJECT)),
+                            Types.BOOLEAN
+                        ),
+                        currentCase.getStatements(),
+                        handle
+                    )))
+                    .orElse(handle)
+            )
+        );
+    }
+
+    private static SwitchCaseNode readSwitchCase(SwitchCaseNode caseStatement, List<SwitchCaseNode> cases)
+    {
+        Iterable<StatementNode> statementsForCase = upToAndIncluding(
+            lazyFlatMap(cases, SwitchCaseNode::getStatements),
+            DesugarSwitchToIfElse::isEndOfCase
+        );
+        return switchCase(
+            caseStatement.getValue(),
+            ExtraLists.copyOf(statementsForCase)
+        );
+    }
+
+    private static boolean isEndOfCase(StatementNode statement) {
+        // TODO: add attribute onto statement node to detect exit
+        return statement.type() == NodeTypes.RETURN;
+    }
+}