using System.Collections.Generic;
using System.Linq;
using Microsoft.Extensions.Configuration;
using Umbraco.Cms.Core;
using Umbraco.Cms.Core.Configuration.Models;
using Umbraco.Cms.Core.Configuration.UmbracoSettings;

namespace Umbraco.Extensions
{
    /// <summary>
    /// Get concatenated user and default character replacements
    /// taking into account <see cref="RequestHandlerSettings.EnableDefaultCharReplacements"/>
    /// </summary>
    public static class RequestHandlerSettingsExtension
    {
        /// <summary>
        /// Get concatenated user and default character replacements
        /// taking into account <see cref="RequestHandlerSettings.EnableDefaultCharReplacements"/>
        /// </summary>
        public static IEnumerable<CharItem> GetCharReplacements(this RequestHandlerSettings requestHandlerSettings)
        {
            if (requestHandlerSettings.EnableDefaultCharReplacements is false)
            {
                return requestHandlerSettings.UserDefinedCharCollection ?? Enumerable.Empty<CharItem>();
            }

            if (requestHandlerSettings.UserDefinedCharCollection == null || requestHandlerSettings.UserDefinedCharCollection.Any() is false)
            {
                return RequestHandlerSettings.DefaultCharCollection;
            }

            return MergeUnique(requestHandlerSettings.UserDefinedCharCollection, RequestHandlerSettings.DefaultCharCollection);
        }

        /// <summary>
        /// Merges CharCollection and UserDefinedCharCollection, prioritizing UserDefinedCharCollection
        /// </summary>
        internal static void MergeReplacements(this RequestHandlerSettings requestHandlerSettings, IConfiguration configuration)
        {
            string sectionKey = $"{Constants.Configuration.ConfigRequestHandler}:";

            IEnumerable<CharItem> charCollection = GetReplacements(
                configuration,
                $"{sectionKey}{nameof(RequestHandlerSettings.CharCollection)}");

            IEnumerable<CharItem> userDefinedCharCollection = GetReplacements(
                configuration,
                $"{sectionKey}{nameof(requestHandlerSettings.UserDefinedCharCollection)}");

            IEnumerable<CharItem> mergedCollection = MergeUnique(userDefinedCharCollection, charCollection);

            requestHandlerSettings.UserDefinedCharCollection = mergedCollection;
        }

        private static IEnumerable<CharItem> GetReplacements(IConfiguration configuration, string key)
        {
            var replacements = new List<CharItem>();
            IEnumerable<IConfigurationSection> config = configuration.GetSection(key).GetChildren();

            foreach (IConfigurationSection section in config)
            {
                var @char = section.GetValue<string>(nameof(CharItem.Char));
                var replacement = section.GetValue<string>(nameof(CharItem.Replacement));
                replacements.Add(new CharItem { Char = @char, Replacement = replacement });
            }

            return replacements;
        }

        /// <summary>
        /// Merges two IEnumerable of CharItem without any duplicates, items in priorityReplacements will override those in alternativeReplacements
        /// </summary>
        private static IEnumerable<CharItem> MergeUnique(
            IEnumerable<CharItem> priorityReplacements,
            IEnumerable<CharItem> alternativeReplacements)
        {
            var priorityReplacementsList = priorityReplacements.ToList();
            var alternativeReplacementsList = alternativeReplacements.ToList();

            foreach (CharItem alternativeReplacement in alternativeReplacementsList)
            {
                foreach (CharItem priorityReplacement in priorityReplacementsList)
                {
                    if (priorityReplacement.Char == alternativeReplacement.Char)
                    {
                        alternativeReplacement.Replacement = priorityReplacement.Replacement;
                    }
                }
            }

            return priorityReplacementsList.Union<CharItem>(
                alternativeReplacementsList,
                new CharacterReplacementEqualityComparer());
        }
    }
}