// XXX docs

// Things we explicitly do NOT support:
//    - heterogenous arrays

var currentArgumentChecker = new Meteor.EnvironmentVariable;

/**
 * @summary Check that a value matches a [pattern](#matchpatterns).
 * If the value does not match the pattern, throw a `Match.Error`.
 *
 * Particularly useful to assert that arguments to a function have the right
 * types and structure.
 * @locus Anywhere
 * @param {Any} value The value to check
 * @param {MatchPattern} pattern The pattern to match
 * `value` against
 */
check = function (value, pattern) {
  // Record that check got called, if somebody cared.
  //
  // We use getOrNullIfOutsideFiber so that it's OK to call check()
  // from non-Fiber server contexts; the downside is that if you forget to
  // bindEnvironment on some random callback in your method/publisher,
  // it might not find the argumentChecker and you'll get an error about
  // not checking an argument that it looks like you're checking (instead
  // of just getting a "Node code must run in a Fiber" error).
  var argChecker = currentArgumentChecker.getOrNullIfOutsideFiber();
  if (argChecker)
    argChecker.checking(value);
  try {
    checkSubtree(value, pattern);
  } catch (err) {
    if ((err instanceof Match.Error) && err.path)
      err.message += " in field " + err.path;
    throw err;
  }
};

/**
 * @namespace Match
 * @summary The namespace for all Match types and methods.
 */
Match = {
  Optional: function (pattern) {
    return new Optional(pattern);
  },
  OneOf: function (/*arguments*/) {
    return new OneOf(_.toArray(arguments));
  },
  Any: ['__any__'],
  Where: function (condition) {
    return new Where(condition);
  },
  ObjectIncluding: function (pattern) {
    return new ObjectIncluding(pattern);
  },
  ObjectWithValues: function (pattern) {
    return new ObjectWithValues(pattern);
  },
  // Matches only signed 32-bit integers
  Integer: ['__integer__'],

  // XXX matchers should know how to describe themselves for errors
  Error: Meteor.makeErrorType("Match.Error", function (msg) {
    this.message = "Match error: " + msg;
    // The path of the value that failed to match. Initially empty, this gets
    // populated by catching and rethrowing the exception as it goes back up the
    // stack.
    // E.g.: "vals[3].entity.created"
    this.path = "";
    // If this gets sent over DDP, don't give full internal details but at least
    // provide something better than 500 Internal server error.
    this.sanitizedError = new Meteor.Error(400, "Match failed");
  }),

  // Tests to see if value matches pattern. Unlike check, it merely returns true
  // or false (unless an error other than Match.Error was thrown). It does not
  // interact with _failIfArgumentsAreNotAllChecked.
  // XXX maybe also implement a Match.match which returns more information about
  //     failures but without using exception handling or doing what check()
  //     does with _failIfArgumentsAreNotAllChecked and Meteor.Error conversion

  /**
   * @summary Returns true if the value matches the pattern.
   * @locus Anywhere
   * @param {Any} value The value to check
   * @param {MatchPattern} pattern The pattern to match `value` against
   */
  test: function (value, pattern) {
    try {
      checkSubtree(value, pattern);
      return true;
    } catch (e) {
      if (e instanceof Match.Error)
        return false;
      // Rethrow other errors.
      throw e;
    }
  },

  // Runs `f.apply(context, args)`. If check() is not called on every element of
  // `args` (either directly or in the first level of an array), throws an error
  // (using `description` in the message).
  //
  _failIfArgumentsAreNotAllChecked: function (f, context, args, description) {
    var argChecker = new ArgumentChecker(args, description);
    var result = currentArgumentChecker.withValue(argChecker, function () {
      return f.apply(context, args);
    });
    // If f didn't itself throw, make sure it checked all of its arguments.
    argChecker.throwUnlessAllArgumentsHaveBeenChecked();
    return result;
  }
};

var Optional = function (pattern) {
  this.pattern = pattern;
};

var OneOf = function (choices) {
  if (_.isEmpty(choices))
    throw new Error("Must provide at least one choice to Match.OneOf");
  this.choices = choices;
};

var Where = function (condition) {
  this.condition = condition;
};

var ObjectIncluding = function (pattern) {
  this.pattern = pattern;
};

var ObjectWithValues = function (pattern) {
  this.pattern = pattern;
};

var typeofChecks = [
  [String, "string"],
  [Number, "number"],
  [Boolean, "boolean"],
  // While we don't allow undefined in EJSON, this is good for optional
  // arguments with OneOf.
  [undefined, "undefined"]
];

var checkSubtree = function (value, pattern) {
  // Match anything!
  if (pattern === Match.Any)
    return;

  // Basic atomic types.
  // Do not match boxed objects (e.g. String, Boolean)
  for (var i = 0; i < typeofChecks.length; ++i) {
    if (pattern === typeofChecks[i][0]) {
      if (typeof value === typeofChecks[i][1])
        return;
      throw new Match.Error("Expected " + typeofChecks[i][1] + ", got " +
                            typeof value);
    }
  }
  if (pattern === null) {
    if (value === null)
      return;
    throw new Match.Error("Expected null, got " + EJSON.stringify(value));
  }

  // Strings and numbers match literally.  Goes well with Match.OneOf.
  if (typeof pattern === "string" || typeof pattern === "number") {
    if (value === pattern)
      return;
    throw new Match.Error("Expected " + pattern + ", got " +
                          EJSON.stringify(value));
  }

  // Match.Integer is special type encoded with array
  if (pattern === Match.Integer) {
    // There is no consistent and reliable way to check if variable is a 64-bit
    // integer. One of the popular solutions is to get reminder of division by 1
    // but this method fails on really large floats with big precision.
    // E.g.: 1.348192308491824e+23 % 1 === 0 in V8
    // Bitwise operators work consistantly but always cast variable to 32-bit
    // signed integer according to JavaScript specs.
    if (typeof value === "number" && (value | 0) === value)
      return
    throw new Match.Error("Expected Integer, got "
                + (value instanceof Object ? EJSON.stringify(value) : value));
  }

  // "Object" is shorthand for Match.ObjectIncluding({});
  if (pattern === Object)
    pattern = Match.ObjectIncluding({});

  // Array (checked AFTER Any, which is implemented as an Array).
  if (pattern instanceof Array) {
    if (pattern.length !== 1)
      throw Error("Bad pattern: arrays must have one type element" +
                  EJSON.stringify(pattern));
    if (!_.isArray(value) && !_.isArguments(value)) {
      throw new Match.Error("Expected array, got " + EJSON.stringify(value));
    }

    _.each(value, function (valueElement, index) {
      try {
        checkSubtree(valueElement, pattern[0]);
      } catch (err) {
        if (err instanceof Match.Error) {
          err.path = _prependPath(index, err.path);
        }
        throw err;
      }
    });
    return;
  }

  // Arbitrary validation checks. The condition can return false or throw a
  // Match.Error (ie, it can internally use check()) to fail.
  if (pattern instanceof Where) {
    if (pattern.condition(value))
      return;
    // XXX this error is terrible
    throw new Match.Error("Failed Match.Where validation");
  }


  if (pattern instanceof Optional)
    pattern = Match.OneOf(undefined, pattern.pattern);

  if (pattern instanceof OneOf) {
    for (var i = 0; i < pattern.choices.length; ++i) {
      try {
        checkSubtree(value, pattern.choices[i]);
        // No error? Yay, return.
        return;
      } catch (err) {
        // Other errors should be thrown. Match errors just mean try another
        // choice.
        if (!(err instanceof Match.Error))
          throw err;
      }
    }
    // XXX this error is terrible
    throw new Match.Error("Failed Match.OneOf or Match.Optional validation");
  }

  // A function that isn't something we special-case is assumed to be a
  // constructor.
  if (pattern instanceof Function) {
    if (value instanceof pattern)
      return;
    throw new Match.Error("Expected " + (pattern.name ||
                                         "particular constructor"));
  }

  var unknownKeysAllowed = false;
  var unknownKeyPattern;
  if (pattern instanceof ObjectIncluding) {
    unknownKeysAllowed = true;
    pattern = pattern.pattern;
  }
  if (pattern instanceof ObjectWithValues) {
    unknownKeysAllowed = true;
    unknownKeyPattern = [pattern.pattern];
    pattern = {};  // no required keys
  }

  if (typeof pattern !== "object")
    throw Error("Bad pattern: unknown pattern type");

  // An object, with required and optional keys. Note that this does NOT do
  // structural matches against objects of special types that happen to match
  // the pattern: this really needs to be a plain old {Object}!
  if (typeof value !== 'object')
    throw new Match.Error("Expected object, got " + typeof value);
  if (value === null)
    throw new Match.Error("Expected object, got null");
  if (value.constructor !== Object)
    throw new Match.Error("Expected plain object");

  var requiredPatterns = {};
  var optionalPatterns = {};
  _.each(pattern, function (subPattern, key) {
    if (subPattern instanceof Optional)
      optionalPatterns[key] = subPattern.pattern;
    else
      requiredPatterns[key] = subPattern;
  });

  _.each(value, function (subValue, key) {
    try {
      if (_.has(requiredPatterns, key)) {
        checkSubtree(subValue, requiredPatterns[key]);
        delete requiredPatterns[key];
      } else if (_.has(optionalPatterns, key)) {
        checkSubtree(subValue, optionalPatterns[key]);
      } else {
        if (!unknownKeysAllowed)
          throw new Match.Error("Unknown key");
        if (unknownKeyPattern) {
          checkSubtree(subValue, unknownKeyPattern[0]);
        }
      }
    } catch (err) {
      if (err instanceof Match.Error)
        err.path = _prependPath(key, err.path);
      throw err;
    }
  });

  _.each(requiredPatterns, function (subPattern, key) {
    throw new Match.Error("Missing key '" + key + "'");
  });
};

var ArgumentChecker = function (args, description) {
  var self = this;
  // Make a SHALLOW copy of the arguments. (We'll be doing identity checks
  // against its contents.)
  self.args = _.clone(args);
  // Since the common case will be to check arguments in order, and we splice
  // out arguments when we check them, make it so we splice out from the end
  // rather than the beginning.
  self.args.reverse();
  self.description = description;
};

_.extend(ArgumentChecker.prototype, {
  checking: function (value) {
    var self = this;
    if (self._checkingOneValue(value))
      return;
    // Allow check(arguments, [String]) or check(arguments.slice(1), [String])
    // or check([foo, bar], [String]) to count... but only if value wasn't
    // itself an argument.
    if (_.isArray(value) || _.isArguments(value)) {
      _.each(value, _.bind(self._checkingOneValue, self));
    }
  },
  _checkingOneValue: function (value) {
    var self = this;
    for (var i = 0; i < self.args.length; ++i) {
      // Is this value one of the arguments? (This can have a false positive if
      // the argument is an interned primitive, but it's still a good enough
      // check.)
      // (NaN is not === to itself, so we have to check specially.)
      if (value === self.args[i] || (_.isNaN(value) && _.isNaN(self.args[i]))) {
        self.args.splice(i, 1);
        return true;
      }
    }
    return false;
  },
  throwUnlessAllArgumentsHaveBeenChecked: function () {
    var self = this;
    if (!_.isEmpty(self.args))
      throw new Error("Did not check() all arguments during " +
                      self.description);
  }
});

var _jsKeywords = ["do", "if", "in", "for", "let", "new", "try", "var", "case",
  "else", "enum", "eval", "false", "null", "this", "true", "void", "with",
  "break", "catch", "class", "const", "super", "throw", "while", "yield",
  "delete", "export", "import", "public", "return", "static", "switch",
  "typeof", "default", "extends", "finally", "package", "private", "continue",
  "debugger", "function", "arguments", "interface", "protected", "implements",
  "instanceof"];

// Assumes the base of path is already escaped properly
// returns key + base
var _prependPath = function (key, base) {
  if ((typeof key) === "number" || key.match(/^[0-9]+$/))
    key = "[" + key + "]";
  else if (!key.match(/^[a-z_$][0-9a-z_$]*$/i) || _.contains(_jsKeywords, key))
    key = JSON.stringify([key]);

  if (base && base[0] !== "[")
    return key + '.' + base;
  return key + base;
};