// Copyright 2007 The Closure Library Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS-IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

/**
 * @fileoverview Error handling utilities.
 *
 */

goog.provide('goog.debug.ErrorHandler');
goog.provide('goog.debug.ErrorHandler.ProtectedFunctionError');

goog.require('goog.asserts');
goog.require('goog.debug');
goog.require('goog.debug.EntryPointMonitor');
goog.require('goog.debug.Trace');



/**
 * The ErrorHandler can be used to to wrap functions with a try/catch
 * statement. If an exception is thrown, the given error handler function will
 * be called.
 *
 * When this object is disposed, it will stop handling exceptions and tracing.
 * It will also try to restore window.setTimeout and window.setInterval
 * if it wrapped them. Notice that in the general case, it is not technically
 * possible to remove the wrapper, because functions have no knowledge of
 * what they have been assigned to. So the app is responsible for other
 * forms of unwrapping.
 *
 * @param {Function} handler Handler for exceptions.
 * @constructor
 * @extends {goog.Disposable}
 * @implements {goog.debug.EntryPointMonitor}
 */
goog.debug.ErrorHandler = function(handler) {
  goog.base(this);

  /**
   * Handler for exceptions, which can do logging, reporting, etc.
   * @type {Function}
   * @private
   */
  this.errorHandlerFn_ = handler;
};
goog.inherits(goog.debug.ErrorHandler, goog.Disposable);


/**
 * Whether to add tracers when instrumenting entry points.
 * @type {boolean}
 * @private
 */
goog.debug.ErrorHandler.prototype.addTracersToProtectedFunctions_ = false;


/**
 * Enable tracers when instrumenting entry points.
 * @param {boolean} newVal See above.
 */
goog.debug.ErrorHandler.prototype.setAddTracersToProtectedFunctions =
    function(newVal) {
  this.addTracersToProtectedFunctions_ = newVal;
};


/** @override */
goog.debug.ErrorHandler.prototype.wrap = function(fn) {
  return this.protectEntryPoint(goog.asserts.assertFunction(fn));
};


/** @override */
goog.debug.ErrorHandler.prototype.unwrap = function(fn) {
  goog.asserts.assertFunction(fn);
  return fn[this.getFunctionIndex_(false)] || fn;
};


/**
 * Private helper function to return a span that can be clicked on to display
 * an alert with the current stack trace. Newlines are replaced with a
 * placeholder so that they will not be html-escaped.
 * @param {string} stackTrace The stack trace to create a span for.
 * @return {string} A span which can be clicked on to show the stack trace.
 * @private
 */
goog.debug.ErrorHandler.prototype.getStackTraceHolder_ = function(stackTrace) {
  var buffer = [];
  buffer.push('##PE_STACK_START##');
  buffer.push(stackTrace.replace(/(\r\n|\r|\n)/g, '##STACK_BR##'));
  buffer.push('##PE_STACK_END##');
  return buffer.join('');
};


/**
 * Get the index for a function. Used for internal indexing.
 * @param {boolean} wrapper True for the wrapper; false for the wrapped.
 * @return {string} The index where we should store the function in its
 *     wrapper/wrapped function.
 * @private
 */
goog.debug.ErrorHandler.prototype.getFunctionIndex_ = function(wrapper) {
  return (wrapper ? '__wrapper_' : '__protected_') + goog.getUid(this) + '__';
};


/**
 * Installs exception protection for an entry point function. When an exception
 * is thrown from a protected function, a handler will be invoked to handle it.
 *
 * @param {Function} fn An entry point function to be protected.
 * @return {!Function} A protected wrapper function that calls the entry point
 *     function.
 */
goog.debug.ErrorHandler.prototype.protectEntryPoint = function(fn) {
  var protectedFnName = this.getFunctionIndex_(true);
  if (!fn[protectedFnName]) {
    var wrapper = fn[protectedFnName] = this.getProtectedFunction(fn);
    wrapper[this.getFunctionIndex_(false)] = fn;
  }
  return fn[protectedFnName];
};


/**
 * Helps {@link #protectEntryPoint} by actually creating the protected
 * wrapper function, after {@link #protectEntryPoint} determines that one does
 * not already exist for the given function.  Can be overriden by subclasses
 * that may want to implement different error handling, or add additional
 * entry point hooks.
 * @param {!Function} fn An entry point function to be protected.
 * @return {!Function} protected wrapper function.
 * @protected
 */
goog.debug.ErrorHandler.prototype.getProtectedFunction = function(fn) {
  var that = this;
  var tracers = this.addTracersToProtectedFunctions_;
  if (tracers) {
    var stackTrace = goog.debug.getStacktraceSimple(15);
  }
  var googDebugErrorHandlerProtectedFunction = function() {
    if (that.isDisposed()) {
      return fn.apply(this, arguments);
    }

    if (tracers) {
      var tracer = goog.debug.Trace.startTracer('protectedEntryPoint: ' +
          that.getStackTraceHolder_(stackTrace));
    }
    try {
      return fn.apply(this, arguments);
    } catch (e) {
      that.errorHandlerFn_(e);
      // Re-throw it since this may be expected by the caller.
      throw new goog.debug.ErrorHandler.ProtectedFunctionError(e);
    } finally {
      if (tracers) {
        goog.debug.Trace.stopTracer(tracer);
      }
    }
  };
  googDebugErrorHandlerProtectedFunction[this.getFunctionIndex_(false)] = fn;
  return googDebugErrorHandlerProtectedFunction;
};


/**
 * Installs exception protection for window.setTimeout to handle exceptions.
 */
goog.debug.ErrorHandler.prototype.protectWindowSetTimeout =
    function() {
  this.protectWindowFunctionsHelper_('setTimeout');
};


/**
 * Install exception protection for window.setInterval to handle exceptions.
 */
goog.debug.ErrorHandler.prototype.protectWindowSetInterval =
    function() {
  this.protectWindowFunctionsHelper_('setInterval');
};


/**
 * Helper function for protecting setTimeout/setInterval.
 * @param {string} fnName The name of the function we're protecting. Must
 *     be setTimeout or setInterval.
 * @private
 */
goog.debug.ErrorHandler.prototype.protectWindowFunctionsHelper_ =
    function(fnName) {
  var win = goog.getObjectByName('window');
  var originalFn = win[fnName];
  var that = this;
  win[fnName] = function(fn, time) {
    // Don't try to protect strings. In theory, we could try to globalEval
    // the string, but this seems to lead to permission errors on IE6.
    if (goog.isString(fn)) {
      fn = goog.partial(goog.globalEval, fn);
    }
    fn = that.protectEntryPoint(fn);

    // IE doesn't support .call for setInterval/setTimeout, but it
    // also doesn't care what "this" is, so we can just call the
    // original function directly
    if (originalFn.call) {
      return originalFn.call(this, fn, time);
    } else {
      return originalFn(fn, time);
    }
  };
  win[fnName][this.getFunctionIndex_(false)] = originalFn;
};


/** @override */
goog.debug.ErrorHandler.prototype.disposeInternal = function() {
  // Try to unwrap window.setTimeout and window.setInterval.
  var win = goog.getObjectByName('window');
  win.setTimeout = this.unwrap(win.setTimeout);
  win.setInterval = this.unwrap(win.setInterval);

  goog.base(this, 'disposeInternal');
};



/**
 * Error thrown to the caller of a protected entry point if the entry point
 * throws an error.
 * @param {*} cause The error thrown by the entry point.
 * @constructor
 * @extends {goog.debug.Error}
 */
goog.debug.ErrorHandler.ProtectedFunctionError = function(cause) {
  var message = goog.debug.ErrorHandler.ProtectedFunctionError.MESSAGE_PREFIX +
      (cause && cause.message ? String(cause.message) : String(cause));
  goog.base(this, message);

  /**
   * The error thrown by the entry point.
   * @type {*}
   */
  this.cause = cause;

  var stack = cause && cause.stack;
  if (stack && goog.isString(stack)) {
    this.stack = /** @type {string} */ (stack);
  }
};
goog.inherits(goog.debug.ErrorHandler.ProtectedFunctionError, goog.debug.Error);


/**
 * Text to prefix the message with.
 * @type {string}
 */
goog.debug.ErrorHandler.ProtectedFunctionError.MESSAGE_PREFIX =
    'Error in protected function: ';