using System;
using System.Collections.Generic;
using System.Linq;
using Jellyfin.Extensions;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Http.Features;
using Microsoft.Extensions.Primitives;

namespace Jellyfin.Api.Middleware
{
    /// <summary>
    /// Defines the <see cref="UrlDecodeQueryFeature"/>.
    /// </summary>
    public class UrlDecodeQueryFeature : IQueryFeature
    {
        private IQueryCollection? _store;

        /// <summary>
        /// Initializes a new instance of the <see cref="UrlDecodeQueryFeature"/> class.
        /// </summary>
        /// <param name="feature">The <see cref="IQueryFeature"/> instance.</param>
        public UrlDecodeQueryFeature(IQueryFeature feature)
        {
            Query = feature.Query;
        }

        /// <summary>
        /// Gets or sets a value indicating the url decoded <see cref="IQueryCollection"/>.
        /// </summary>
        public IQueryCollection Query
        {
            get
            {
                return _store ?? QueryCollection.Empty;
            }

            set
            {
                // Only interested in where the querystring is encoded which shows up as one key with nothing in the value.
                if (value.Count != 1)
                {
                    _store = value;
                    return;
                }

                // Encoded querystrings have no value, so don't process anything if a value is present.
                var (key, stringValues) = value.First();
                if (!string.IsNullOrEmpty(stringValues))
                {
                    _store = value;
                    return;
                }

                if (!key.Contains('=', StringComparison.Ordinal))
                {
                    _store = value;
                    return;
                }

                var pairs = new Dictionary<string, StringValues>();
                foreach (var pair in key.SpanSplit('&'))
                {
                    var i = pair.IndexOf('=');
                    if (i == -1)
                    {
                        // encoded is an equals.
                        // We use TryAdd so duplicate keys get ignored
                        pairs.TryAdd(pair.ToString(), StringValues.Empty);
                        continue;
                    }

                    var k = pair[..i].ToString();
                    var v = pair[(i + 1)..].ToString();
                    if (!pairs.TryAdd(k, new StringValues(v)))
                    {
                        pairs[k] = StringValues.Concat(pairs[k], v);
                    }
                }

                _store = new QueryCollection(pairs);
            }
        }
    }
}