extract custom type from elm file

src/compile-testcases.ts

@@ -18,11 +18,99 @@ compile(['Main.elm'], {
 const elmParser = new Parser();
 elmParser.setLanguage(Elm);
 
-const parseElm = (filename: string) => {
+interface ElmVariant {
+  typeName: string;
+  name: string;
+  index: number;
+  slots: [string];
+}
+
+const parseElm = (filename: string): { [id: string]: [ElmVariant] } => {
   const source = fs.readFileSync(filename, 'utf8');
-  console.log(source);
   const tree = elmParser.parse(source);
-  console.log(tree);
+  const found: { [id: string]: [ElmVariant] } = {};
+
+  /*
+      A quick reference for using treesitter.
+      Generally it's pretty easy to see what methods are available here: 
+      https://github.com/tree-sitter/node-tree-sitter/blob/master/index.js
+
+      We usually want these things
+
+        - node.namedChildren 
+            Gives a list of named children for a node.  Unnamed children are things like intermediate characters in the AST.
+            http://tree-sitter.github.io/tree-sitter/using-parsers#named-vs-anonymous-nodes
+        
+        - node.type 
+            The name of the AST node that was parsed.  e.g. upper_case_identifier, or union_variant
+
+        - node.toString()
+            See the s-expression version of the node.  e.g. (union_variant (upper_case_identifier) (type_ref (upper_case_qid (upper_case_identifier))))
+            May look kinda weird, but it's basically describing the AST for that node.
+            http://tree-sitter.github.io/tree-sitter/using-parsers#query-syntax
+
+        - node.text
+            Render the literal text for that node.
+
+  */
+
+  for (let child of tree.rootNode.namedChildren) {
+    if (child.type == 'type_declaration') {
+      let name = '';
+      let index = 0;
+
+      for (let variant of child.namedChildren) {
+        switch (variant.type) {
+          case 'upper_case_identifier': {
+            name = variant.text;
+            break;
+          }
+          case 'union_variant': {
+            let foundVariantName = '';
+            let slots: string[] = [];
+            for (let detail of variant.namedChildren) {
+              switch (detail.type) {
+                case 'upper_case_identifier': {
+                  foundVariantName = detail.text;
+                  break;
+                }
+
+                default: {
+                  slots.push(detail.text);
+                  break;
+                }
+              }
+            }
+
+            if (name in found) {
+              found[name].push({
+                typeName: name,
+                name: foundVariantName,
+                index: index,
+                slots: slots,
+              });
+            } else {
+              found[name] = [
+                {
+                  typeName: name,
+                  name: foundVariantName,
+                  index: index,
+                  slots: slots,
+                },
+              ];
+            }
+
+            index = index + 1;
+            break;
+          }
+          default: {
+            break;
+          }
+        }
+      }
+    }
+  }
+  return found;
 };
 
 const result = parseElm('./testcases/simple/Main.elm');