SocialPub/PrivaPub/Api/Mastodon/Infrastructure/MastodonParams.cs

using Microsoft.AspNetCore.Http.Features;

using System.Text.Json;

namespace PrivaPub.Api.Mastodon.Infrastructure
{
	public sealed class MastodonParams
	{
		readonly Dictionary<string, List<string>> _values;

		MastodonParams(Dictionary<string, List<string>> values)
		{
			_values = values;
		}

		public static async Task<MastodonParams> Read(HttpRequest request, CancellationToken token)
		{
			var values = new Dictionary<string, List<string>>(StringComparer.Ordinal);
			foreach (var pair in request.Query)
				foreach (var value in pair.Value)
					Add(values, pair.Key, value);

			if (request.HasFormContentType)
			{
				var form = await request.ReadFormAsync(token);
				foreach (var pair in form)
					foreach (var value in pair.Value)
						Add(values, pair.Key, value);
			}
			else if (request.ContentType?.Contains("json", StringComparison.OrdinalIgnoreCase) == true && request.ContentLength != 0)
			{
				try
				{
					using var document = await JsonDocument.ParseAsync(request.Body, cancellationToken: token);
					Flatten(values, default, document.RootElement);
				}
				catch (JsonException)
				{
				}
			}
			return new MastodonParams(values);
		}

		public static MastodonParams From(IEnumerable<KeyValuePair<string, string>> pairs)
		{
			var values = new Dictionary<string, List<string>>(StringComparer.Ordinal);
			foreach (var pair in pairs)
				Add(values, pair.Key, pair.Value);
			return new MastodonParams(values);
		}

		public bool Has(string name) => _values.ContainsKey(name);

		public string Get(string name) => _values.TryGetValue(name, out var list) && list.Count > 0 ? list[^1] : default;

		public IReadOnlyList<string> List(string name) => _values.TryGetValue(name, out var list) ? list : (IReadOnlyList<string>)Array.Empty<string>();

		public bool? Bool(string name) => Get(name)?.ToLowerInvariant() switch
		{
			"true" or "1" or "on" or "yes" => true,
			"false" or "0" or "off" or "no" or "" => false,
			_ => (bool?)null
		};

		public int? Int(string name) => int.TryParse(Get(name), out var value) ? value : (int?)null;

		static void Add(Dictionary<string, List<string>> values, string key, string value)
		{
			key = key.EndsWith("[]", StringComparison.Ordinal) ? key[..^2] : key;
			if (!values.TryGetValue(key, out var list))
				values[key] = list = new List<string>();
			list.Add(value);
		}

		static void Flatten(Dictionary<string, List<string>> values, string prefix, JsonElement element)
		{
			switch (element.ValueKind)
			{
				case JsonValueKind.Object:
					foreach (var property in element.EnumerateObject())
						Flatten(values, prefix == default ? property.Name : $"{prefix}[{property.Name}]", property.Value);
					break;
				case JsonValueKind.Array:
					foreach (var item in element.EnumerateArray())
					{
						if (item.ValueKind is JsonValueKind.Object or JsonValueKind.Array)
							Flatten(values, prefix + "[]", item);
						else
							Add(values, prefix, Scalar(item));
					}
					break;
				case JsonValueKind.Null or JsonValueKind.Undefined:
					break;
				default:
					if (prefix != default)
						Add(values, prefix, Scalar(element));
					break;
			}
		}

		static string Scalar(JsonElement element) => element.ValueKind switch
		{
			JsonValueKind.String => element.GetString(),
			JsonValueKind.True => "true",
			JsonValueKind.False => "false",
			_ => element.GetRawText()
		};
	}
}