"use strict";

var traverse = require("../../../traverse");
var t        = require("../../../types");

var visitor = {
  enter: function (node, parent, scope, context, state) {
    if (!t.isReferencedIdentifier(node, parent)) return;

    var declared = state.letRefs[node.name];
    if (!declared) return;

    // declared node is different in this scope
    if (scope.getBinding(node.name) !== declared) return;

    var declaredLoc  = declared.loc;
    var referenceLoc = node.loc;

    if (!declaredLoc || !referenceLoc) return;

    // does this reference appear on a line before the declaration?
    var before = referenceLoc.start.line < declaredLoc.start.line;

    if (referenceLoc.start.line === declaredLoc.start.line) {
      // this reference appears on the same line
      // check it appears before the declaration
      before = referenceLoc.start.col < declaredLoc.start.col;
    }

    if (before) {
      throw state.file.errorWithNode(node, "Temporal dead zone - accessing a variable before it's initialized");
    }
  }
};

exports.optional = true;

exports.Loop =
exports.Program =
exports.BlockStatement = function (node, parent, scope, context, file) {
  var letRefs = node._letReferences;
  if (!letRefs) return;

  var state = {
    letRefs: letRefs,
    file:    file
  };

  traverse(node, visitor, scope, state);
};