/*
 *
 * (c) Copyright Ascensio System Limited 2010-2018
 *
 * This program is freeware. You can redistribute it and/or modify it under the terms of the GNU 
 * General Public License (GPL) version 3 as published by the Free Software Foundation (https://www.gnu.org/copyleft/gpl.html). 
 * In accordance with Section 7(a) of the GNU GPL its Section 15 shall be amended to the effect that 
 * Ascensio System SIA expressly excludes the warranty of non-infringement of any third-party rights.
 *
 * THIS PROGRAM IS DISTRIBUTED WITHOUT ANY WARRANTY; WITHOUT EVEN THE IMPLIED WARRANTY OF MERCHANTABILITY OR
 * FITNESS FOR A PARTICULAR PURPOSE. For more details, see GNU GPL at https://www.gnu.org/copyleft/gpl.html
 *
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 *
 * The interactive user interfaces in modified source and object code versions of ONLYOFFICE must display 
 * Appropriate Legal Notices, as required under Section 5 of the GNU GPL version 3.
 *
 * Pursuant to Section 7 § 3(b) of the GNU GPL you must retain the original ONLYOFFICE logo which contains 
 * relevant author attributions when distributing the software. If the display of the logo in its graphic 
 * form is not reasonably feasible for technical reasons, you must include the words "Powered by ONLYOFFICE" 
 * in every copy of the program you distribute. 
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*/

namespace ASC.Web.Core.Helpers
{
    /// <summary>
    /// Defines a type converter for enum values that converts enum values to 
    /// and from string representations using resources
    /// </summary>
    /// <remarks>
    /// This class makes localization of display values for enums in a project easy.  Simply
    /// derive a class from this class and pass the ResourceManagerin the constructor.  
    /// 
    /// Then define the enum values in the resource editor.   The names of
    /// the resources are simply the enum value prefixed by the enum type name with an
    /// underscore separator eg MyEnum_MyValue.  You can then use the TypeConverter attribute
    /// to make the LocalizedEnumConverter the default TypeConverter for the enums in your
    /// project.
    /// </remarks>
    public class ResourceEnumConverter : System.ComponentModel.EnumConverter
    {
        private class LookupTable : Dictionary<string, object> { }
        private readonly Dictionary<CultureInfo, LookupTable> _lookupTables = new Dictionary<CultureInfo, LookupTable>();
        private readonly System.Resources.ResourceManager _resourceManager;
        private readonly bool _isFlagEnum = false;
        private readonly Array _flagValues;

        /// <summary>
        /// Get the lookup table for the given culture (creating if necessary)
        /// </summary>
        /// <param name="culture"></param>
        /// <returns></returns>
        private LookupTable GetLookupTable(CultureInfo culture)
        {
            if (culture == null)
                culture = CultureInfo.CurrentCulture;

            if (!_lookupTables.TryGetValue(culture, out var result))
            {
                result = new LookupTable();
                foreach (var value in GetStandardValues())
                {
                    var text = GetValueText(culture, value);
                    if (text != null)
                    {
                        result.Add(text, value);
                    }
                }
                _lookupTables.Add(culture, result);
            }
            return result;
        }

        /// <summary>
        /// Return the text to display for a simple value in the given culture
        /// </summary>
        /// <param name="culture">The culture to get the text for</param>
        /// <param name="value">The enum value to get the text for</param>
        /// <returns>The localized text</returns>
        private string GetValueText(CultureInfo culture, object value)
        {
            var type = value.GetType();
            var resourceName = $"{type.Name}_{value}";
            var result = _resourceManager.GetString(resourceName, culture);
            if (result == null)
                result = resourceName;
            return result;
        }

        /// <summary>
        /// Return true if the given value is can be represented using a single bit
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        private bool IsSingleBitValue(ulong value)
        {
            return value switch
            {
                0 => false,
                1 => true,
                _ => (value & (value - 1)) == 0,
            };
        }

        /// <summary>
        /// Return the text to display for a flag value in the given culture
        /// </summary>
        /// <param name="culture">The culture to get the text for</param>
        /// <param name="value">The flag enum value to get the text for</param>
        /// <returns>The localized text</returns>
        private string GetFlagValueText(CultureInfo culture, object value)
        {
            // if there is a standard value then use it
            //
            if (Enum.IsDefined(value.GetType(), value))
            {
                return GetValueText(culture, value);
            }

            // otherwise find the combination of flag bit values
            // that makes up the value
            //
            ulong lValue = Convert.ToUInt32(value);
            string result = null;
            foreach (var flagValue in _flagValues)
            {
                ulong lFlagValue = Convert.ToUInt32(flagValue);
                if (IsSingleBitValue(lFlagValue))
                {
                    if ((lFlagValue & lValue) == lFlagValue)
                    {
                        var valueText = GetValueText(culture, flagValue);
                        if (result == null)
                        {
                            result = valueText;
                        }
                        else
                        {
                            result = $"{result}, {valueText}";
                        }
                    }
                }
            }
            return result;
        }

        /// <summary>
        /// Return the Enum value for a simple (non-flagged enum)
        /// </summary>
        /// <param name="culture">The culture to convert using</param>
        /// <param name="text">The text to convert</param>
        /// <returns>The enum value</returns>
        private object GetValue(CultureInfo culture, string text)
        {
            var lookupTable = GetLookupTable(culture);
            lookupTable.TryGetValue(text, out var result);
            return result;
        }

        /// <summary>
        /// Return the Enum value for a flagged enum
        /// </summary>
        /// <param name="culture">The culture to convert using</param>
        /// <param name="text">The text to convert</param>
        /// <returns>The enum value</returns>
        private object GetFlagValue(CultureInfo culture, string text)
        {
            var lookupTable = GetLookupTable(culture);
            var textValues = text.Split(',');
            ulong result = 0;
            foreach (var textValue in textValues)
            {
                var trimmedTextValue = textValue.Trim();
                if (!lookupTable.TryGetValue(trimmedTextValue, out var value))
                {
                    return null;
                }
                result |= Convert.ToUInt32(value);
            }
            return Enum.ToObject(EnumType, result);
        }

        /// <summary>
        /// Create a new instance of the converter using translations from the given resource manager
        /// </summary>
        /// <param name="type"></param>
        /// <param name="resourceManager"></param>
        public ResourceEnumConverter(Type type, System.Resources.ResourceManager resourceManager)
            : base(type)
        {
            _resourceManager = resourceManager;
            var flagAttributes = type.GetCustomAttributes(typeof(FlagsAttribute), true);
            _isFlagEnum = flagAttributes.Length > 0;
            if (_isFlagEnum)
            {
                _flagValues = Enum.GetValues(type);
            }
        }

        /// <summary>
        /// Convert string values to enum values
        /// </summary>
        /// <param name="context"></param>
        /// <param name="culture"></param>
        /// <param name="value"></param>
        /// <returns></returns>
        public override object ConvertFrom(System.ComponentModel.ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value)
        {
            if (value is string @string)
            {
                var result = _isFlagEnum ?
                    GetFlagValue(culture, @string) : GetValue(culture, @string);
                if (result == null)
                {
                    result = base.ConvertFrom(context, culture, value);
                }
                return result;
            }
            else
            {
                return base.ConvertFrom(context, culture, value);
            }
        }

        /// <summary>
        /// Convert the enum value to a string
        /// </summary>
        /// <param name="context"></param>
        /// <param name="culture"></param>
        /// <param name="value"></param>
        /// <param name="destinationType"></param>
        /// <returns></returns>
        public override object ConvertTo(System.ComponentModel.ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value, Type destinationType)
        {
            if (value != null && destinationType == typeof(string))
            {
                object result = _isFlagEnum ?
                    GetFlagValueText(culture, value) : GetValueText(culture, value);
                return result;
            }
            else
            {
                return base.ConvertTo(context, culture, value, destinationType);
            }
        }

        /// <summary>
        /// Convert the given enum value to string using the registered type converter
        /// </summary>
        /// <param name="value">The enum value to convert to string</param>
        /// <returns>The localized string value for the enum</returns>
        static public string ConvertToString(Enum value)
        {
            var converter = TypeDescriptor.GetConverter(value.GetType());
            return converter.ConvertToString(value);
        }

        /// <summary>
        /// Return a list of the enum values and their associated display text for the given enum type
        /// </summary>
        /// <param name="enumType">The enum type to get the values for</param>
        /// <param name="culture">The culture to get the text for</param>
        /// <returns>
        /// A list of KeyValuePairs where the key is the enum value and the value is the text to display
        /// </returns>
        /// <remarks>
        /// This method can be used to provide localized binding to enums in ASP.NET applications.   Unlike 
        /// windows forms the standard ASP.NET controls do not use TypeConverters to convert from enum values
        /// to the displayed text.   You can bind an ASP.NET control to the list returned by this method by setting
        /// the DataValueField to "Key" and theDataTextField to "Value". 
        /// </remarks>
        static public List<KeyValuePair<Enum, string>> GetValues(Type enumType, CultureInfo culture)
        {
            var result = new List<KeyValuePair<Enum, string>>();
            var converter = TypeDescriptor.GetConverter(enumType);
            foreach (Enum value in Enum.GetValues(enumType))
            {
                var pair = new KeyValuePair<Enum, string>(value, converter.ConvertToString(null, culture, value));
                result.Add(pair);
            }
            return result;
        }

        /// <summary>
        /// Return a list of the enum values and their associated display text for the given enum type in the current UI Culture
        /// </summary>
        /// <param name="enumType">The enum type to get the values for</param>
        /// <returns>
        /// A list of KeyValuePairs where the key is the enum value and the value is the text to display
        /// </returns>
        /// <remarks>
        /// This method can be used to provide localized binding to enums in ASP.NET applications.   Unlike 
        /// windows forms the standard ASP.NET controls do not use TypeConverters to convert from enum values
        /// to the displayed text.   You can bind an ASP.NET control to the list returned by this method by setting
        /// the DataValueField to "Key" and theDataTextField to "Value". 
        /// </remarks>
        static public List<KeyValuePair<Enum, string>> GetValues(Type enumType)
        {
            return GetValues(enumType, CultureInfo.CurrentUICulture);
        }
    }
}