/**
   * @fileoverview A rule to suggest using arrow functions as callbacks.
   * @author Toru Nagashima
   */
  
  "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) {
      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) {
      const variables = scope.variables;
  
      for (let i = 0; i < variables.length; ++i) {
          const 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) {
      const retv = { isCallback: false, isLexicalThis: false };
      let 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");
  }
  
  /**
  * Checks whether a simple list of parameters contains any duplicates. This does not handle complex
  parameter lists (e.g. with destructuring), since complex parameter lists are a SyntaxError with duplicate
  parameter names anyway. Instead, it always returns `false` for complex parameter lists.
  * @param {ASTNode[]} paramsList The list of parameters for a function
  * @returns {boolean} `true` if the list of parameters contains any duplicates
  */
  function hasDuplicateParams(paramsList) {
      return paramsList.every(param => param.type === "Identifier") && paramsList.length !== new Set(paramsList.map(param => param.name)).size;
  }
  
  //------------------------------------------------------------------------------
  // Rule Definition
  //------------------------------------------------------------------------------
  
  module.exports = {
      meta: {
          docs: {
              description: "require arrow functions as callbacks",
              category: "ECMAScript 6",
              recommended: false
          },
  
          schema: [
              {
                  type: "object",
                  properties: {
                      allowNamedFunctions: {
                          type: "boolean"
                      },
                      allowUnboundThis: {
                          type: "boolean"
                      }
                  },
                  additionalProperties: false
              }
          ],
  
          fixable: "code"
      },
  
      create(context) {
          const options = context.options[0] || {};
  
          const allowUnboundThis = options.allowUnboundThis !== false;  // default to true
          const allowNamedFunctions = options.allowNamedFunctions;
          const sourceCode = context.getSourceCode();
  
          /*
           * {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.
           */
          let 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() {
                  stack = [];
              },
  
              // If there are below, it cannot replace with arrow functions merely.
              ThisExpression() {
                  const info = stack[stack.length - 1];
  
                  if (info) {
                      info.this = true;
                  }
              },
  
              Super() {
                  const info = stack[stack.length - 1];
  
                  if (info) {
                      info.super = true;
                  }
              },
  
              MetaProperty(node) {
                  const 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"(node) {
                  const scopeInfo = exitScope();
  
                  // Skip named function expressions
                  if (allowNamedFunctions && node.id && node.id.name) {
                      return;
                  }
  
                  // Skip generators.
                  if (node.generator) {
                      return;
                  }
  
                  // Skip recursive functions.
                  const nameVar = context.getDeclaredVariables(node)[0];
  
                  if (isFunctionName(nameVar) && nameVar.references.length > 0) {
                      return;
                  }
  
                  // Skip if it's using arguments.
                  const variable = getVariableOfArguments(context.getScope());
  
                  if (variable && variable.references.length > 0) {
                      return;
                  }
  
                  // Reports if it's a callback which can replace with arrows.
                  const callbackInfo = getCallbackInfo(node);
  
                  if (callbackInfo.isCallback &&
                      (!allowUnboundThis || !scopeInfo.this || callbackInfo.isLexicalThis) &&
                      !scopeInfo.super &&
                      !scopeInfo.meta
                  ) {
                      context.report({
                          node,
                          message: "Unexpected function expression.",
                          fix(fixer) {
                              if ((!callbackInfo.isLexicalThis && scopeInfo.this) || hasDuplicateParams(node.params)) {
  
                                  // If the callback function does not have .bind(this) and contains a reference to `this`, there
                                  // is no way to determine what `this` should be, so don't perform any fixes.
                                  // If the callback function has duplicates in its list of parameters (possible in sloppy mode),
                                  // don't replace it with an arrow function, because this is a SyntaxError with arrow functions.
                                  return null;
                              }
  
                              const paramsLeftParen = node.params.length ? sourceCode.getTokenBefore(node.params[0]) : sourceCode.getTokenBefore(node.body, 1);
                              const paramsRightParen = sourceCode.getTokenBefore(node.body);
                              const asyncKeyword = node.async ? "async " : "";
                              const paramsFullText = sourceCode.text.slice(paramsLeftParen.range[0], paramsRightParen.range[1]);
  
                              if (callbackInfo.isLexicalThis) {
  
                                  // If the callback function has `.bind(this)`, replace it with an arrow function and remove the binding.
                                  return fixer.replaceText(node.parent.parent, `${asyncKeyword}${paramsFullText} => ${sourceCode.getText(node.body)}`);
                              }
  
                              // Otherwise, only replace the `function` keyword and parameters with the arrow function parameters.
                              return fixer.replaceTextRange([node.start, node.body.start], `${asyncKeyword}${paramsFullText} => `);
                          }
                      });
                  }
              }
          };
      }
  };