namespace IslaApocalypse.Core
{
	/// <summary>
	/// The single registry of constants for the v2 blueprint container — magic, version,
	/// section tags, validation bounds, and the sentinel values used when a v2 file is
	/// re-encoded from a v1 source that cannot supply real generation parameters.
	///
	/// The byte-accurate layout lives in Core/Scripts/BLUEPRINT_FORMAT.md. Writer:
	/// BlueprintWriter.WriteV2. Reader: MapDataParser (v2 branch). Tags are FourCC codes
	/// stored as little-endian u32, so the raw bytes on disk read as ASCII ("PRMS", "HGTS",
	/// ...) in a hex dump.
	/// </summary>
	public static class BlueprintFormat
	{
		// "ISLA" as raw bytes 'I','S','L','A' == little-endian u32 0x414C5349.
		// Deliberately NOT a length-prefixed .NET string: the v1 header starts with the
		// 7-bit length prefix 0x07, so the first byte alone (0x49 vs 0x07) identifies the
		// format and the reader can dispatch without ambiguity.
		public const uint MAGIC = 0x414C5349;
		public const uint VERSION = 2;

		// Section tags (FourCC, little-endian). Reader rule: known tag -> parse,
		// unknown tag -> skip by length and continue. Never reuse a retired tag value.
		public const uint TAG_PARAMS        = 0x534D5250; // "PRMS"
		public const uint TAG_HEIGHTS       = 0x53544748; // "HGTS"
		public const uint TAG_BIOMES        = 0x4D4F4942; // "BIOM"
		public const uint TAG_TOWNS         = 0x4E574F54; // "TOWN"
		public const uint TAG_ROADS_HIGHWAY = 0x57484452; // "RDHW"
		public const uint TAG_ROADS_BRANCH  = 0x52424452; // "RDBR"
		public const uint TAG_ROADS_RUGGED  = 0x47524452; // "RDRG"
		public const uint TAG_ROADS_TRAIL   = 0x4C544452; // "RDTL"

		// MapSize sanity bounds, checked before any allocation on read.
		public const int MIN_MAP_SIZE = 256;
		public const int MAX_MAP_SIZE = 32768;

		// Sentinels written into the params section when the source blueprint came from a
		// v1 file (a re-encode cannot know the original generation inputs). WorldSeed 0 is
		// also the config "randomize" sentinel, which no real resolved seed ever is.
		public const int SENTINEL_WORLD_SEED = 0;
		public const float SENTINEL_CRATER_RADIUS = -1f;
		public const float SENTINEL_DENSITY_MULTIPLIER = -1f;
		public const float SENTINEL_IMPACT_CENTER = -1f; // both components

		/// <summary>Renders a tag as its 4 ASCII characters, for log messages.</summary>
		public static string TagToString(uint tag)
		{
			return new string(new[] {
				(char)(tag & 0xFF), (char)((tag >> 8) & 0xFF),
				(char)((tag >> 16) & 0xFF), (char)((tag >> 24) & 0xFF)
			});
		}
	}
}