using System.Text.Json.Nodes;

using static PrivaPub.Federation.Objects.ActivityJson;

namespace PrivaPub.Federation.Objects
{
	public static class ObjectFeatures
	{
		public static List<string> Detect(JsonObject raw)
		{
			var found = new List<string>();
			if (raw == default)
				return found;
			void When(bool condition, string feature)
			{
				if (condition)
					found.Add(feature);
			}

			When(raw.ContainsKey("quote"), "fep-044f-quote");
			When(raw.ContainsKey("quoteAuthorization"), "fep-044f-authorization");
			When(raw.ContainsKey("_misskey_quote") || raw.ContainsKey("quoteUrl") || raw.ContainsKey("quoteUri"), "legacy-quote");
			When(raw.ContainsKey("interactionPolicy"), "interaction-policy");
			When(raw.ContainsKey("context"), "context");
			When(raw.ContainsKey("proof"), "fep-8b32-proof");
			When(raw.Any(p => p.Key.StartsWith("_misskey_", StringComparison.Ordinal)), "misskey");
			When(raw["source"] is JsonObject, "source:" + (Value(raw["source"], "mediaType") ?? "unknown"));
			When(raw["source"] is JsonValue, "source:url");
			When(raw.ContainsKey("htmlMfm"), "fep-c16b-mfm");
			When(raw.ContainsKey("formerRepresentations"), "former-representations");
			When(raw.ContainsKey("searchableBy"), "fep-268d-searchable-by");
			When(raw.ContainsKey("audience"), "fep-1b12-audience");
			When(Items(raw["attachment"]).Any(a => Value(a, "type") == "Link"), "fep-8967-link");
			When(Items(raw["tag"]).Any(t => Value(t, "type") == "Emoji"), "custom-emoji");
			When(Value(raw, "type") == "Question", "poll");
			When(raw["contentMap"] is JsonObject, "content-map");
			When(raw["url"] is JsonArray, "url-variants");
			var contentType = Value(raw, "mediaType");
			When(contentType is not (null or "text/html"), "content:" + contentType);
			return found;
		}

		public static List<string> Namespaces(JsonObject raw, string activityContext = default) =>
			Namespaces(raw?["@context"] ?? (activityContext == default ? default : JsonNode.Parse(activityContext)));

		static List<string> Namespaces(JsonNode context) => context switch
		{
			JsonValue single when single.TryGetValue<string>(out var url) => new List<string> { url },
			JsonArray array => array.SelectMany(entry => entry switch
				{
					JsonValue value when value.TryGetValue<string>(out var url) => new[] { url },
					JsonObject terms => terms.Where(t => t.Value is JsonValue v && v.TryGetValue<string>(out var target) && target.EndsWith('#'))
						.Select(t => t.Key + "=" + t.Value!.GetValue<string>()),
					_ => Enumerable.Empty<string>()
				})
				.Take(32)
				.ToList(),
			_ => new List<string>()
		};

		static IEnumerable<JsonObject> Items(JsonNode node) => node switch
		{
			JsonArray array => array.OfType<JsonObject>(),
			JsonObject single => new[] { single },
			_ => Enumerable.Empty<JsonObject>()
		};
	}
}