/* ============================================================
   qft/palette.js — per-field hue gradients + substrate variants.
   Each FIELD (one lattice) is parameterised as a slider:
     hueStart, hueEnd, saturation, lightness, opacity
   The renderer asks for the colour at a t∈[0,1] along an edge (or
   at an (x,y) position when the gradient mode is radial/linear).
   "Hue gradient over time" = per-edge progression, the QFT analog
   of the bubble-chamber lifecycle palette.

   Self-contained: no dependency on the bubble-chamber palette
   registry. Reuses only the generic hslToRgb util.
   ============================================================ */
import { hslToRgb } from '../render/palette.js';

const clamp = (v, lo, hi) => Math.max(lo, Math.min(hi, v));

/* Substrate variants — the "chemistry" the lattices sit on. */
export const SUBSTRATES = {
  vintage:  { paper: { flat: [42, 32, 22],   glowIn: [62, 48, 32],   glowOut: [22, 16, 10] },
              vign: [10, 7, 4],    feature: [178, 138, 78] },
  void:     { paper: { flat: [10, 10, 14],   glowIn: [22, 22, 30],   glowOut: [3, 3, 6] },
              vign: [0, 0, 0],     feature: [150, 150, 180] },
  cream:    { paper: { flat: [207, 200, 180], glowIn: [226, 219, 199], glowOut: [179, 170, 146] },
              vign: [56, 46, 32],  feature: [42, 30, 20] },
  selenium: { paper: { flat: [190, 181, 197], glowIn: [210, 201, 217], glowOut: [156, 146, 166] },
              vign: [42, 38, 54],  feature: [58, 50, 72] },
  cyanotype:{ paper: { flat: [22, 48, 82],   glowIn: [38, 70, 110],  glowOut: [10, 22, 44] },
              vign: [6, 12, 22],   feature: [180, 210, 235] },
};

export function resolveSubstrate(id = 'vintage') {
  return SUBSTRATES[id] || SUBSTRATES.vintage;
}

/* Sample the gradient parameter s ∈ [0, 1] for a point on an edge.
   - along-edge: s = t (the per-edge t the renderer passes in)
   - radial:     s = min(1, |(x, y)|)         (centre → 0, corners → 1)
   - linear-x:   s = (x + 1) / 2              (left → 0, right → 1)
   - linear-y:   s = (y + 1) / 2              (top  → 0, bottom → 1) */
export function gradientS(t, x, y, mode = 'along-edge') {
  switch (mode) {
    case 'radial':   return clamp(Math.hypot(x, y), 0, 1);
    case 'linear-x': return clamp((x + 1) / 2, 0, 1);
    case 'linear-y': return clamp((y + 1) / 2, 0, 1);
    case 'along-edge':
    default:         return clamp(t, 0, 1);
  }
}

/* Compute the colour for a field at gradient parameter s. Hue rotates from
   hueStart → hueEnd by the SHORT way around the circle (so a small Δ stays
   small even when crossing 1.0). */
export function fieldColor(field, s) {
  let dh = field.hueEnd - field.hueStart;
  // wrap to shortest-path delta (-0.5 .. +0.5)
  if (dh > 0.5)  dh -= 1;
  if (dh < -0.5) dh += 1;
  const h = field.hueStart + s * dh;
  return hslToRgb(h, field.saturation, field.lightness);
}