import syntaxPipelines from "babel-plugin-syntax-pipelines";

export default function({ types: t }) {
  return {
    inherits: syntaxPipelines,

    visitor: {
      BinaryExpression(path) {
        if (path.node.operator === "|>") {
          //
          // Transform the pipeline!
          //
          const tempVar = getTempId(path.scope);
          const assignments = pipe(t, tempVar, path.node.left).concat([
            t.callExpression(
              path.node.right,
              [tempVar]
            )
          ]);

          path.replaceWith( t.sequenceExpression(assignments) );
        }
      },
    },
  };
}

//
// Limits the variable generation to one per scope
//
function getTempId(scope) {
  let id = scope.path.getData("pipelineOp");
  if (id) return id;

  id = scope.generateDeclaredUidIdentifier("tmp");
  return scope.path.setData("pipelineOp", id);
}

//
// Converts:
//    10 |> obj.f |> g;
// To:
//    (_x = 10, _x = obj.f(_x), _x = g(_x));
//
function pipe(t, tempVar, node) {

  if (node.operator === "|>" && node.type === "BinaryExpression") {
    const decl = t.assignmentExpression(
      '=',
      tempVar,
      t.callExpression( node.right, [tempVar]),
    );
    return pipe(t, tempVar, node.left).concat([decl]);
  } else {
    return [t.assignmentExpression('=', tempVar, node)];
  }
}