yavsc/Yavsc/GoogleApiSupport/Google.Apis.Core/Util/Utilities.cs

/*
Copyright 2010 Google Inc

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.
*/

using Google.Apis.Testing;
using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Reflection;
using System.Text.RegularExpressions;

namespace Google.Apis.Util
{
    /// <summary>A utility class which contains helper methods and extension methods.</summary>
    public static class Utilities
    {
        /// <summary>Returns the version of the core library.</summary>
        [VisibleForTestOnly]
        public static string GetLibraryVersion()
        {
            return Regex.Match(typeof(Utilities).GetTypeInfo().Assembly.FullName, "Version=([\\d\\.]+)").Groups[1].ToString();
        }

        /// <summary>
        /// A Google.Apis utility method for throwing an <see cref="System.ArgumentNullException"/> if the object is
        /// <c>null</c>.
        /// </summary>
        public static T ThrowIfNull<T>(this T obj, string paramName)
        {
            if (obj == null)
            {
                throw new ArgumentNullException(paramName);
            }

            return obj;
        }

        /// <summary>
        /// A Google.Apis utility method for throwing an <see cref="System.ArgumentNullException"/> if the string is
        /// <c>null</c> or empty.
        /// </summary>
        /// <returns>The original string.</returns>
        public static string ThrowIfNullOrEmpty(this string str, string paramName)
        {
            if (string.IsNullOrEmpty(str))
            {
                throw new ArgumentException("Parameter was empty", paramName);
            }
            return str;
        }

        /// <summary>Returns <c>true</c> in case the enumerable is <c>null</c> or empty.</summary>
        internal static bool IsNullOrEmpty<T>(this IEnumerable<T> coll)
        {
            return coll == null || coll.Count() == 0;
        }

        /// <summary>
        /// A Google.Apis utility method for returning the first matching custom attribute (or <c>null</c>) of the specified member.
        /// </summary>
        public static T GetCustomAttribute<T>(this MemberInfo info) where T : Attribute
        {
            object[] results = info.GetCustomAttributes(typeof(T), false).ToArray();
            return results.Length == 0 ? null : (T)results[0];
        }

        /// <summary>Returns the defined string value of an Enum.</summary>
        internal static string GetStringValue(this Enum value)
        {
            FieldInfo entry = value.GetType().GetField(value.ToString());
            entry.ThrowIfNull("value");

            // If set, return the value.
            var attribute = entry.GetCustomAttribute<StringValueAttribute>();
            if (attribute != null)
            {
                return attribute.Text;
            }

            // Otherwise, throw an exception.
            throw new ArgumentException(
                string.Format("Enum value '{0}' does not contain a StringValue attribute", entry), "value");
        }

        /// <summary>
        /// Returns the defined string value of an Enum. Use for test purposes or in other Google.Apis projects.
        /// </summary>
        public static string GetEnumStringValue(Enum value)
        {
            return value.GetStringValue();
        }

        /// <summary>
        /// Tries to convert the specified object to a string. Uses custom type converters if available.
        /// Returns null for a null object.
        /// </summary>
        [VisibleForTestOnly]
        public static string ConvertToString(object o)
        {
            if (o == null)
            {
                return null;
            }

            if (o.GetType().GetTypeInfo().IsEnum)
            {
                // Try to convert the Enum value using the StringValue attribute.
                var enumType = o.GetType();
                FieldInfo field = enumType.GetField(o.ToString());
                StringValueAttribute attribute = field.GetCustomAttribute<StringValueAttribute>();
                return attribute != null ? attribute.Text : o.ToString();
            }

            if (o is DateTime)
            {
                // Honor RFC3339.
                return ConvertToRFC3339((DateTime)o);
            }

            if (o is bool)
            {
                return o.ToString().ToLowerInvariant();
            }

            return o.ToString();
        }

        /// <summary>Converts the input date into a RFC3339 string (http://www.ietf.org/rfc/rfc3339.txt).</summary>
        internal static string ConvertToRFC3339(DateTime date)
        {
            if (date.Kind == DateTimeKind.Unspecified)
            {
                date = date.ToUniversalTime();
            }
            return date.ToString("yyyy-MM-dd'T'HH:mm:ss.fffK", DateTimeFormatInfo.InvariantInfo);
        }

        /// <summary>
        /// Parses the input string and returns <see cref="System.DateTime"/> if the input is a valid 
        /// representation of a date. Otherwise it returns <c>null</c>.
        /// </summary>
        public static DateTime? GetDateTimeFromString(string raw)
        {
            DateTime result;
            if (!DateTime.TryParse(raw, out result))
            {
                return null;
            }
            return result;
        }

        /// <summary>Returns a string (by RFC3339) form the input <see cref="DateTime"/> instance.</summary>
        public static string GetStringFromDateTime(DateTime? date)
        {
            if (!date.HasValue)
            {
                return null;
            }
            return ConvertToRFC3339(date.Value);
        }
    }
}