using System.Globalization;
using System.Text.Json.Nodes;

namespace RadicadeServer.Radicade.Discord;

public static class DiscordPayloadJson
{
	private const int MaxContentLength = 2000;
	private const int MaxTitleLength = 256;
	private const int MaxDescriptionLength = 4096;
	private const int MaxFieldNameLength = 256;
	private const int MaxFieldValueLength = 1024;
	private const int MaxFieldCount = 25;

	public static string Build(DiscordPayload payload, string? contentOverride = null, string? embedImageUrl = null)
	{
		var embed = new JsonObject();

		if (!string.IsNullOrWhiteSpace(payload.Title))
			embed["title"] = Truncate(payload.Title, MaxTitleLength);
		if (!string.IsNullOrWhiteSpace(payload.Description))
			embed["description"] = Truncate(payload.Description, MaxDescriptionLength);
		embed["color"] = payload.Color;

		var imageUrl = string.IsNullOrWhiteSpace(embedImageUrl) ? payload.ImageUrl : embedImageUrl;
		if (!string.IsNullOrWhiteSpace(imageUrl))
			embed["image"] = new JsonObject { ["url"] = Truncate(imageUrl, MaxTitleLength) };
		if (!string.IsNullOrWhiteSpace(payload.ThumbnailUrl))
			embed["thumbnail"] = new JsonObject { ["url"] = Truncate(payload.ThumbnailUrl, MaxTitleLength) };

		if (!string.IsNullOrWhiteSpace(payload.TimestampUtc)
			&& DateTime.TryParse(payload.TimestampUtc, CultureInfo.InvariantCulture, DateTimeStyles.RoundtripKind, out var parsed))
		{
			embed["timestamp"] = parsed.ToString("O");
		}

		var fields = new JsonArray();
		foreach (var field in (payload.Fields ?? new List<DiscordField>()).Take(MaxFieldCount))
		{
			if (field == null) continue;
			fields.Add(new JsonObject
			{
				["name"] = Truncate(field.Name ?? "", MaxFieldNameLength),
				["value"] = Truncate(field.Value ?? "", MaxFieldValueLength),
				["inline"] = field.Inline
			});
		}
		if (fields.Count > 0)
			embed["fields"] = fields;

		var message = new JsonObject
		{
			["content"] = Truncate(contentOverride ?? payload.Title ?? "", MaxContentLength)
		};
		message["embeds"] = new JsonArray { embed };

		return message.ToJsonString();
	}

	private static string Truncate(string value, int max)
	{
		if (string.IsNullOrEmpty(value)) return "";
		if (value.Length <= max) return value;

		var cut = max;
		if (char.IsHighSurrogate(value[cut - 1]) && cut < value.Length && char.IsLowSurrogate(value[cut]))
			cut--;
		return value[..cut];
	}
}