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.
///
///   PASS B — shelf-edge variation: a per-column shift of the shelf/riser KNOT
///   BLOCK (K3/K4/K5) by a low-frequency noise field, so the boundary where a
///   shelf meets its riser wanders in and out instead of tracing a clean height
///   contour — organic notches, coves and peninsulas at the shelf edge.
///
/// Both are output-height only; the classify map never sees either of them.
///
/// NOTE — what this file deliberately does NOT contain: the task-10 draft's D8
/// flow routing / accumulation / drainage incision. It shipped, produced the
/// canonical grid artifact (thousands of straight, disconnected, pooling
/// scratches along the D8 neighbour directions) and was reverted whole. Rivers
/// and erosion are Phase C work — a hydraulic-erosion pass over FINAL terrain,
/// not a per-cell steepest-descent carve on a grid.
/// </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;

	// Pass B — shelf-edge variation. The amplitude is stated in metres of INPUT
	// height (raw × 251): it is how far, in raw-height terms, a shelf boundary
	// contour is displaced — not an output elevation change. Lateral wander on
	// the map is that displacement divided by the local raw gradient.
	public const float EDGE_AMP_DEFAULT_M = 5f;      // config dial: ShelfEdgeVariation (metres of input height)
	public const float EDGE_FREQ_ISLANDS = 12f;      // ~12 undulations per island width — a handful of notches
	public const int EDGE_SEED_OFFSET = 7507;        //   per shelf perimeter, not hundreds of teeth
	public const float EDGE_SAFETY_FRACTION = 0.5f;  // shift ≤ half the smallest margin to a fixed knot

	/// <summary>
	/// The largest per-column knot shift this preset can take while keeping the
	/// knot set strictly ordered (K2 &lt; K3+d, K5+d &lt; K6) with margin to spare.
	/// K1/K2/K6 never move, so the toe, the orange/red bands and the summit spike
	/// are bit-identical whatever the warp does — which is what makes the
	/// red-ceiling and peak-height guarantees exact rather than statistical.
	/// </summary>
	public static float MaxEdgeShift(CurveKnots k)
	{
		return EDGE_SAFETY_FRACTION * Mathf.Min(k.K3 - k.K2, k.K6 - k.K5);
	}

	/// <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. <paramref name="edgeShift"/> is the same
	/// per-column warp the curve is evaluated with, so the micro-relief skin
	/// follows the shelf wherever pass B has moved its boundary.
	/// </summary>
	public static float ShelfWeight(float raw, CurveKnots k, float edgeShift)
	{
		return Mathf.Max(BandBump(raw, k.K3 + edgeShift, k.K4 + edgeShift),
						 BandBump(raw, k.K5 + edgeShift, 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);
	}
}