/**
   * @fileoverview A rule to suggest using arrow functions as callbacks.
   * @author Toru Nagashima
   * @copyright 2015 Toru Nagashima. All rights reserved.
   */
  
  "use strict";
  
  //------------------------------------------------------------------------------
  // Helpers
  //------------------------------------------------------------------------------
  
  /**
   * Checks whether or not a given variable is a function name.
   * @param {escope.Variable} variable - A variable to check.
   * @returns {boolean} `true` if the variable is a function name.
   */
  function isFunctionName(variable) {
      return variable && variable.defs[0].type === "FunctionName";
  }
  
  /**
   * Checks whether or not a given MetaProperty node equals to a given value.
   * @param {ASTNode} node - A MetaProperty node to check.
   * @param {string} metaName - The name of `MetaProperty.meta`.
   * @param {string} propertyName - The name of `MetaProperty.property`.
   * @returns {boolean} `true` if the node is the specific value.
   */
  function checkMetaProperty(node, metaName, propertyName) {
      // TODO: Remove this if block after https://github.com/eslint/espree/issues/206 was fixed.
      if (typeof node.meta === "string") {
          return node.meta === metaName && node.property === propertyName;
      }
      return node.meta.name === metaName && node.property.name === propertyName;
  }
  
  /**
   * Gets the variable object of `arguments` which is defined implicitly.
   * @param {escope.Scope} scope - A scope to get.
   * @returns {escope.Variable} The found variable object.
   */
  function getVariableOfArguments(scope) {
      var variables = scope.variables;
      for (var i = 0; i < variables.length; ++i) {
          var variable = variables[i];
          if (variable.name === "arguments") {
              // If there was a parameter which is named "arguments", the implicit "arguments" is not defined.
              // So does fast return with null.
              return (variable.identifiers.length === 0) ? variable : null;
          }
      }
  
      /* istanbul ignore next */
      return null;
  }
  
  /**
   * Checkes whether or not a given node is a callback.
   * @param {ASTNode} node - A node to check.
   * @returns {object}
   *   {boolean} retv.isCallback - `true` if the node is a callback.
   *   {boolean} retv.isLexicalThis - `true` if the node is with `.bind(this)`.
   */
  function getCallbackInfo(node) {
      var retv = {isCallback: false, isLexicalThis: false};
      var parent = node.parent;
      while (node) {
          switch (parent.type) {
              // Checks parents recursively.
              case "LogicalExpression":
              case "ConditionalExpression":
                  break;
  
              // Checks whether the parent node is `.bind(this)` call.
              case "MemberExpression":
                  if (parent.object === node &&
                      !parent.property.computed &&
                      parent.property.type === "Identifier" &&
                      parent.property.name === "bind" &&
                      parent.parent.type === "CallExpression" &&
                      parent.parent.callee === parent
                  ) {
                      retv.isLexicalThis = (
                          parent.parent.arguments.length === 1 &&
                          parent.parent.arguments[0].type === "ThisExpression"
                      );
                      node = parent;
                      parent = parent.parent;
                  } else {
                      return retv;
                  }
                  break;
  
              // Checks whether the node is a callback.
              case "CallExpression":
              case "NewExpression":
                  if (parent.callee !== node) {
                      retv.isCallback = true;
                  }
                  return retv;
  
              default:
                  return retv;
          }
  
          node = parent;
          parent = parent.parent;
      }
  
      /* istanbul ignore next */
      throw new Error("unreachable");
  }
  
  //------------------------------------------------------------------------------
  // Rule Definition
  //------------------------------------------------------------------------------
  
  module.exports = function(context) {
      // {Array<{this: boolean, super: boolean, meta: boolean}>}
      // - this - A flag which shows there are one or more ThisExpression.
      // - super - A flag which shows there are one or more Super.
      // - meta - A flag which shows there are one or more MethProperty.
      var stack = [];
  
      /**
       * Pushes new function scope with all `false` flags.
       * @returns {void}
       */
      function enterScope() {
          stack.push({this: false, super: false, meta: false});
      }
  
      /**
       * Pops a function scope from the stack.
       * @returns {{this: boolean, super: boolean, meta: boolean}} The information of the last scope.
       */
      function exitScope() {
          return stack.pop();
      }
  
      return {
          // Reset internal state.
          Program: function() {
              stack = [];
          },
  
          // If there are below, it cannot replace with arrow functions merely.
          ThisExpression: function() {
              var info = stack[stack.length - 1];
              if (info) {
                  info.this = true;
              }
          },
          Super: function() {
              var info = stack[stack.length - 1];
              if (info) {
                  info.super = true;
              }
          },
          MetaProperty: function(node) {
              var info = stack[stack.length - 1];
              if (info && checkMetaProperty(node, "new", "target")) {
                  info.meta = true;
              }
          },
  
          // To skip nested scopes.
          FunctionDeclaration: enterScope,
          "FunctionDeclaration:exit": exitScope,
  
          // Main.
          FunctionExpression: enterScope,
          "FunctionExpression:exit": function(node) {
              var scopeInfo = exitScope();
  
              // Skip generators.
              if (node.generator) {
                  return;
              }
  
              // Skip recursive functions.
              var nameVar = context.getDeclaredVariables(node)[0];
              if (isFunctionName(nameVar) && nameVar.references.length > 0) {
                  return;
              }
  
              // Skip if it's using arguments.
              var variable = getVariableOfArguments(context.getScope());
              if (variable && variable.references.length > 0) {
                  return;
              }
  
              // Reports if it's a callback which can replace with arrows.
              var callbackInfo = getCallbackInfo(node);
              if (callbackInfo.isCallback &&
                  (!scopeInfo.this || callbackInfo.isLexicalThis) &&
                  !scopeInfo.super &&
                  !scopeInfo.meta
              ) {
                  context.report(node, "Unexpected function expression.");
              }
          }
      };
  };
  
  module.exports.schema = [];