using Godot;

/// <summary>
/// The terrain DETAIL passes (terrain-water task 10) — pure numeric functions
/// (D-035; a named future C++ candidate, kept standalone):
///
///   PASS A — shelf micro-relief: a medium-frequency noise skin (±ShelfReliefAmp,
///   default 3 m) weighted by shelf-ness, so the compressed shelves get their
///   rolling texture back while risers and peaks stay untouched.
///
/// Output-height only; the classify map never sees it.
///
/// NOTE — what this file deliberately no longer contains: the task-10 draft's D8
/// steepest-descent flow routing, accumulation and drainage incision. It shipped,
/// and it produced the canonical grid artifact — thousands of straight,
/// disconnected, pooling scratches running along the eight D8 neighbour
/// directions, because per-cell steepest descent on a regular grid can only ever
/// route along those eight headings. It is reverted whole. Rivers and erosion are
/// Phase C work: a hydraulic-erosion pass over FINAL terrain, not a routing carve
/// on a grid mid-pipeline.
/// </summary>
public static class TerrainDetailPass
{
	// The TDTL body version is owned by the format (Core); the pass just stamps it.
	public const ushort VERSION = IslaApocalypse.Core.BlueprintFormat.TDTL_VERSION;

	// Pass A — micro-relief.
	public const float RELIEF_AMP_DEFAULT_M = 3f;    // config dial: ShelfReliefAmp (metres)
	public const float RELIEF_FREQ_ISLANDS = 40f;    // ~40 undulations per island width (~200 m features)
	public const int RELIEF_SEED_OFFSET = 7409;

	/// <summary>
	/// Shelf-ness weight from the RAW input height: 1 mid-shelf, feathering to 0
	/// through the risers (feather extends 30 % of the band half-width past each
	/// shelf edge). Covers both shelves.
	/// </summary>
	public static float ShelfWeight(float raw, CurveKnots k)
	{
		return Mathf.Max(BandBump(raw, k.K3, k.K4), BandBump(raw, k.K5, k.K6));
	}

	private static float BandBump(float h, float lo, float hi)
	{
		float half = (hi - lo) * 0.5f;
		float t = Mathf.Abs(h - (lo + half)) / half;   // 0 centre, 1 at band edge
		// full inside 60 % of the band, linear feather to zero at 130 %
		return Mathf.Clamp(1f - (t - 0.6f) / 0.7f, 0f, 1f);
	}
}