using Godot;
using System;
using System.IO;

namespace IslaApocalypse.Core
{
	/// <summary>
	/// Writes a WorldBlueprint to disk in the v2 tagged-section container
	/// (layout: Core/Scripts/BLUEPRINT_FORMAT.md; constants: BlueprintFormat).
	///
	/// Deliberately written against the blueprint data types, not the generator's
	/// internal arrays, so it is callable outside a generation run — the map generator
	/// and the round-trip harness are both just callers.
	///
	/// Provenance (timestamp, git hash) is stamped at write time — it describes the
	/// file being written, not whatever was in blueprint.Params. If blueprint.Params is
	/// null (a re-encode of a legacy v1 file), the sentinel values from BlueprintFormat
	/// are written instead of real generation inputs.
	/// </summary>
	public static class BlueprintWriter
	{
		public static void WriteV2(string absolutePath, WorldBlueprint bp)
		{
			ulong started = Time.GetTicksMsec();

			using (FileStream stream = File.Open(absolutePath, FileMode.Create))
			using (BinaryWriter writer = new BinaryWriter(stream))
			{
				// Header: raw "ISLA" magic + u32 version. Little-endian throughout.
				writer.Write(BlueprintFormat.MAGIC);
				writer.Write(BlueprintFormat.VERSION);

				WriteSection(writer, BlueprintFormat.TAG_PARAMS, w => WriteParams(w, bp));
				WriteSection(writer, BlueprintFormat.TAG_HEIGHTS, w => WriteHeights(w, bp));
				WriteSection(writer, BlueprintFormat.TAG_BIOMES, w => WriteBiomes(w, bp));
				WriteSection(writer, BlueprintFormat.TAG_TOWNS, w => WriteTowns(w, bp));
				WriteSection(writer, BlueprintFormat.TAG_ROADS_HIGHWAY, w => WriteRoadTier(w, bp.Highways));
				WriteSection(writer, BlueprintFormat.TAG_ROADS_BRANCH, w => WriteRoadTier(w, bp.BranchRoads));
				WriteSection(writer, BlueprintFormat.TAG_ROADS_RUGGED, w => WriteRoadTier(w, bp.RuggedRoads));
				WriteSection(writer, BlueprintFormat.TAG_ROADS_TRAIL, w => WriteRoadTier(w, bp.TrailRoads));
			}

			double seconds = (Time.GetTicksMsec() - started) / 1000.0;
			Vector2 impact = bp.Params?.ImpactCenter
				?? new Vector2(BlueprintFormat.SENTINEL_IMPACT_CENTER, BlueprintFormat.SENTINEL_IMPACT_CENTER);
			GD.Print($"[BlueprintWriter] v2 blueprint written in {seconds:F1}s to: {absolutePath} " +
				$"(seed {bp.Params?.WorldSeed ?? BlueprintFormat.SENTINEL_WORLD_SEED}, " +
				$"MapSize {bp.MapSize}, impactCenter ({impact.X:F1},{impact.Y:F1}))");
		}

		/// <summary>
		/// Frames one section: [u32 tag][u64 payload-length][payload]. The length is
		/// back-patched after the payload is written, so payload writers never have to
		/// pre-compute their own size.
		/// </summary>
		private static void WriteSection(BinaryWriter writer, uint tag, Action<BinaryWriter> payload)
		{
			writer.Write(tag);
			long lengthPos = writer.BaseStream.Position;
			writer.Write((ulong)0);
			long payloadStart = writer.BaseStream.Position;

			payload(writer);

			long payloadEnd = writer.BaseStream.Position;
			writer.BaseStream.Position = lengthPos;
			writer.Write((ulong)(payloadEnd - payloadStart));
			writer.BaseStream.Position = payloadEnd;
		}

		private static void WriteParams(BinaryWriter writer, WorldBlueprint bp)
		{
			BlueprintParams p = bp.Params;
			writer.Write(p?.WorldSeed ?? BlueprintFormat.SENTINEL_WORLD_SEED);
			writer.Write(bp.MapSize); // always real — the blueprint knows its own size
			writer.Write(p?.CraterRadius ?? BlueprintFormat.SENTINEL_CRATER_RADIUS);
			writer.Write(p?.DensityMultiplier ?? BlueprintFormat.SENTINEL_DENSITY_MULTIPLIER);
			Vector2 impact = p?.ImpactCenter
				?? new Vector2(BlueprintFormat.SENTINEL_IMPACT_CENTER, BlueprintFormat.SENTINEL_IMPACT_CENTER);
			writer.Write(impact.X);
			writer.Write(impact.Y);

			// Provenance, stamped now (length-prefixed .NET strings — fine inside a
			// length-framed section; only the file HEADER must avoid them).
			writer.Write(DateTime.UtcNow.ToString("yyyy-MM-ddTHH:mm:ssZ"));
			writer.Write(TryGetGitShortHash());
		}

		private static void WriteHeights(BinaryWriter writer, WorldBlueprint bp)
		{
			// X outer / Y inner — the v1 convention, kept: the second index is the map's
			// north/south axis and the server consumes it as world Z.
			int n = bp.MapSize;
			for (int x = 0; x < n; x++)
				for (int y = 0; y < n; y++)
					writer.Write(bp.HeightMap[x, y]);
		}

		private static void WriteBiomes(BinaryWriter writer, WorldBlueprint bp)
		{
			int n = bp.MapSize;
			for (int x = 0; x < n; x++)
			{
				for (int y = 0; y < n; y++)
				{
					int ordinal = (int)bp.BiomeMap[x, y];
					if (ordinal < 0 || ordinal > byte.MaxValue)
						throw new InvalidDataException(
							$"[BlueprintWriter] Biome ordinal {ordinal} at ({x},{y}) does not fit in a byte.");
					writer.Write((byte)ordinal);
				}
			}
		}

		private static void WriteTowns(BinaryWriter writer, WorldBlueprint bp)
		{
			writer.Write(bp.Towns.Count);
			foreach (TownLocation town in bp.Towns)
			{
				int tier = (int)town.Tier;
				if (tier < 0 || tier > byte.MaxValue)
					throw new InvalidDataException(
						$"[BlueprintWriter] TownTier ordinal {tier} does not fit in a byte.");
				writer.Write(town.Position.X);
				writer.Write(town.Position.Y);
				writer.Write((byte)tier);
				writer.Write(town.IsHighwayNode ? (byte)1 : (byte)0);
			}
		}

		private static void WriteRoadTier(BinaryWriter writer, System.Collections.Generic.List<Vector2[]> paths)
		{
			writer.Write(paths.Count);
			foreach (Vector2[] path in paths)
			{
				writer.Write(path.Length);
				foreach (Vector2 p in path) { writer.Write(p.X); writer.Write(p.Y); }
			}
		}

		/// <summary>
		/// Best-effort short hash of the generator repo (reads res://.git directly, no
		/// git invocation). Returns "" when unavailable — e.g. an exported build.
		/// </summary>
		private static string TryGetGitShortHash()
		{
			try
			{
				string gitDir = Path.Combine(ProjectSettings.GlobalizePath("res://"), ".git");
				string head = File.ReadAllText(Path.Combine(gitDir, "HEAD")).Trim();
				if (head.StartsWith("ref: "))
				{
					string refPath = Path.Combine(gitDir, head.Substring(5));
					if (!File.Exists(refPath)) return "";
					head = File.ReadAllText(refPath).Trim();
				}
				return head.Length >= 8 ? head.Substring(0, 8) : head;
			}
			catch
			{
				return "";
			}
		}
	}
}