'use strict';
// SHADES — Lane C — wind field core.
//
// Pure math. Zero imports: no THREE, no DOM, no Date.now, no rAF. Everything is
// a closed-form function of (pos, t) given a storm def + seed, which buys us:
//   - selftest can fast-forward a 90 s storm and get identical numbers every run
//   - consumers can sample any t, in any order, as often as they like
//   - the determinism rule (PLAN3D §4) is structural, not a promise
//
// weather.js wraps this to expose the contracts.js surface (Vector3 in/out).
// The prototype scheduled gusts by INTEGRATING (wind.gustT += dt). We can't —
// sample(pos,t) is called by everyone at arbitrary t. So gusts are precomputed
// into a timeline from a seeded PRNG at storm load; the envelope shape below is
// a faithful port of prototype/game.js, just read from t instead of accumulated.

// ---------- gust envelope (ported from prototype/game.js windVec) ----------
// telegraph: wind hasn't risen yet, but you can SEE it coming (grass, band, audio)
export const GUST = Object.freeze({
  TELEGRAPH: 1.5,   // gt < 1.5        → 0        "it's coming"
  RAMP: 0.8,        // 1.5 .. 2.3      → 0 → pow
  HOLD: 1.7,        // 2.3 .. 4.0      → pow
  FADE: 1.0,        // 4.0 .. 5.0      → pow → 0
  TOTAL: 5.0,
});
const RAMP_AT = GUST.TELEGRAPH;                 // 1.5
const HOLD_AT = RAMP_AT + GUST.RAMP;            // 2.3
const FADE_AT = HOLD_AT + GUST.HOLD;            // 4.0
const END_AT = FADE_AT + GUST.FADE;             // 5.0

/** Gust strength at local gust time gt (seconds since telegraph began). */
export function gustEnvelope(gt, pow) {
  if (gt <= 0 || gt >= END_AT) return 0;
  if (gt < RAMP_AT) return 0;                              // telegraph window
  if (gt < HOLD_AT) return pow * (gt - RAMP_AT) / GUST.RAMP;
  if (gt < FADE_AT) return pow;
  return pow * (END_AT - gt) / GUST.FADE;
}

// ---------- deterministic noise ----------
// mulberry32 — small, fast, good enough, and identical in every JS engine.
export function mulberry32(seed) {
  let a = seed >>> 0;
  return function () {
    a = (a + 0x6D2B79F5) | 0;
    let t = Math.imul(a ^ (a >>> 15), 1 | a);
    t = (t + Math.imul(t ^ (t >>> 7), 61 | t)) ^ t;
    return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
  };
}

// int32 hash — Math.imul keeps it exact (plain * would drift past 2^31 as a double)
function hash2(ix, iz, seed) {
  let h = (Math.imul(ix, 374761393) + Math.imul(iz, 668265263) + Math.imul(seed, 1274126177)) | 0;
  h = Math.imul(h ^ (h >>> 13), 1274126177);
  h ^= h >>> 16;
  return (h >>> 0) / 4294967296;
}

const smooth = (f) => f * f * (3 - 2 * f);

/**
 * Value noise, 0..1, C1-continuous (smoothstep interp) so wind never steps.
 *
 * @param {number} [period] Wrap the lattice at this many cells, making the noise
 *   tile seamlessly over [0, period). The wind doesn't want this (the yard would
 *   repeat); a scrolling cloud texture does, or every wrap boundary is a visible
 *   straight edge in the sky. Pass an integer that matches your frequency.
 */
export function valueNoise2(x, z, seed, period = 0) {
  const ix = Math.floor(x), iz = Math.floor(z);
  const ux = smooth(x - ix), uz = smooth(z - iz);
  // branch, not a closure: this is the wind's hot path (the cloth alone samples
  // it thousands of times a second) and a per-call allocation would show up.
  let x0 = ix, x1 = ix + 1, z0 = iz, z1 = iz + 1;
  if (period > 0) {
    x0 = ((x0 % period) + period) % period;
    x1 = ((x1 % period) + period) % period;
    z0 = ((z0 % period) + period) % period;
    z1 = ((z1 % period) + period) % period;
  }
  const a = hash2(x0, z0, seed), b = hash2(x1, z0, seed);
  const c = hash2(x0, z1, seed), d = hash2(x1, z1, seed);
  return (a + (b - a) * ux) * (1 - uz) + (c + (d - c) * ux) * uz;
}

export function smoothstep(e0, e1, x) {
  if (e0 === e1) return x < e0 ? 0 : 1;
  const f = Math.min(1, Math.max(0, (x - e0) / (e1 - e0)));
  return smooth(f);
}

// ---------- curves ----------
/** Piecewise-linear [[t,v],...] lookup, clamped at both ends. */
export function sampleCurve(curve, t) {
  if (!curve || curve.length === 0) return 0;
  if (t <= curve[0][0]) return curve[0][1];
  const last = curve[curve.length - 1];
  if (t >= last[0]) return last[1];
  for (let i = 1; i < curve.length; i++) {
    if (t <= curve[i][0]) {
      const [ta, va] = curve[i - 1], [tb, vb] = curve[i];
      const span = tb - ta;
      return span <= 0 ? vb : va + (vb - va) * ((t - ta) / span);
    }
  }
  return last[1];
}

/** Shortest-arc angle lerp — so a curve crossing ±π doesn't spin the long way. */
export function lerpAngle(a, b, k) {
  const TAU = Math.PI * 2;
  let d = ((b - a + Math.PI) % TAU + TAU) % TAU - Math.PI;
  return a + d * k;
}

function sampleAngleCurve(curve, t) {
  if (!curve || curve.length === 0) return 0;
  if (t <= curve[0][0]) return curve[0][1];
  const last = curve[curve.length - 1];
  if (t >= last[0]) return last[1];
  for (let i = 1; i < curve.length; i++) {
    if (t <= curve[i][0]) {
      const [ta, va] = curve[i - 1], [tb, vb] = curve[i];
      const span = tb - ta;
      return span <= 0 ? vb : lerpAngle(va, vb, (t - ta) / span);
    }
  }
  return last[1];
}

// ---------- gust timeline ----------
// Prototype: pow = 12 + rand*16 + 10*p, next = t + 5 + rand*7. Same shape, from JSON.
export const DEFAULT_DOWNDRAFT = 0.22;

export function buildGustTimeline(def, seed) {
  const g = def.gusts || {};
  const rng = mulberry32(seed >>> 0);
  const minGap = g.minGap ?? 5, maxGap = g.maxGap ?? 12;
  const out = [];
  let t = g.firstAt ?? 3;
  // hard cap: a malformed gap can't spin us forever
  while (t < def.duration && out.length < 512) {
    const p = def.duration > 0 ? t / def.duration : 0;
    const pow = (g.powBase ?? 12) + rng() * (g.powRand ?? 16) + (g.powRamp ?? 10) * p;
    out.push({ t0: t, pow, rampAt: t + GUST.TELEGRAPH, endAt: t + GUST.TOTAL });
    t += minGap + rng() * Math.max(0, maxGap - minGap);
  }
  return out;
}

// ---------- the field ----------
/**
 * @param {object} def   parsed storm JSON (see data/storms/*.json)
 * @param {object} [opts] {seed}
 */
export function createWindField(def, opts = {}) {
  const seed = (opts.seed ?? def.seed ?? 1) >>> 0;
  const duration = def.duration ?? 90;
  const gusts = buildGustTimeline(def, seed);
  const sp = def.spatial || {};
  const amp = sp.amp ?? 0.18;          // ±18% speed across the yard
  const scale = sp.scale ?? 12;        // metres per noise cell — yard is 30×20
  const advect = sp.advect ?? 0.5;     // noise drifts downwind (frozen turbulence)
  const wander = def.dirWander || {};
  const wAmp = wander.amp ?? 0.25, wRate = wander.rate ?? 0.13;
  const nSeed = (seed ^ 0x9e3779b9) | 0;
  // SPRINT3 decision 8: the downdraft is a fraction of TOTAL wind speed, not of
  // gust power. `downdraftOfTotal` is the field name; `downdraft` is read as a
  // legacy alias so an un-migrated storm doesn't silently lose its vertical.
  const gd = def.gusts || {};
  const downFrac = gd.downdraftOfTotal ?? gd.downdraft ?? DEFAULT_DOWNDRAFT;

  let shelters = [];

  /** Spatially-uniform part: base curve + every gust envelope live at t. */
  function uniformSpeed(t) {
    let s = sampleCurve(def.baseCurve, t);
    for (let i = 0; i < gusts.length; i++) {
      const g = gusts[i];
      if (t <= g.t0) break;            // sorted — nothing later can be live
      if (t < g.endAt) s += gustEnvelope(t - g.t0, g.pow);
    }
    return s;
  }

  function gustOnly(t) {
    let s = 0;
    for (let i = 0; i < gusts.length; i++) {
      const g = gusts[i];
      if (t <= g.t0) break;
      if (t < g.endAt) s += gustEnvelope(t - g.t0, g.pow);
    }
    return s;
  }

  function dirAt(t) {
    return sampleAngleCurve(def.dirCurve, t) + wAmp * Math.sin(t * wRate);
  }

  /** Local horizontal wind speed (m/s) — base+gusts, spatial noise, tree shadow.
   *  The one place the local-speed maths lives; speedAt/vecAt/verticalAt share it. */
  function localHoriz(x, z, t) {
    const uni = uniformSpeed(t);
    const d = dirAt(t);
    const s = uni * spatialFactor(x, z, t) * shelterFactor(x, z, Math.cos(d), Math.sin(d));
    return s > 0 ? s : 0;
  }

  /**
   * Vertical wind, m/s. NEGATIVE = downward. A fraction of the LOCAL horizontal
   * speed at this point and time.
   *
   * Why a horizontal sail must pay: cloth pressure goes with dot(wind, normal),
   * a flat panel's normal points at the sky, so in a purely horizontal wind the
   * dot is ~0 and "lie it flat and ignore the storm" wins — the opposite of the
   * game. A descending component hits a flat panel square on.
   *
   * SPRINT3 decision 8 — fraction of TOTAL, not of gust power. Under gust-only
   * semantics the downdraft peaked exactly at the gust peak, where the horizontal
   * ALSO peaked, so a flat sail could never reach 60% of a pitched one's load
   * (B measured 34%) without a downdraft so violent it also killed the twisted
   * rig the §7 gate needs to survive. The two gates pincered. Riding total speed
   * instead spreads the load across the whole storm: a flat roof is pressed
   * steadily (peak total 32.6 m/s dwarfs peak gust power 12.6), so the ratio
   * clears 60% at a gentle fraction, without a spike at the gust peak. It follows
   * the LOCAL speed, so a tree's wind shadow shelters from falling air too.
   */
  function verticalAt(x, z, t) {
    if (downFrac <= 0) return 0;
    return -downFrac * localHoriz(x, z, t);
  }

  // ---- noise drift ----
  // The noise pattern rides downwind with the mean flow (Taylor's frozen
  // turbulence), so a gust visibly travels ACROSS the yard instead of blinking on
  // everywhere at once. That displacement is an integral, D(t) = ∫ advect·U·dir dτ,
  // and it has to be integrated as one: the obvious closed form `U(t)·advect·t`
  // is not the integral, and it whips the whole accumulated field sideways the
  // instant U or dir moves — a 6.8 m/s single-frame jump at the southerly change,
  // which the continuity assert caught. So integrate once at build time into an
  // immutable table; sampling stays a pure function of t.
  // Mean flow only (base curve, no gusts): eddies are carried by the wind, they
  // don't surf their own gust, and it keeps the drift rate smooth.
  const DRIFT_DT = 0.25;
  const driftX = [], driftZ = [];
  {
    let dx = 0, dz = 0;
    const n = Math.ceil((duration + 2) / DRIFT_DT) + 2;
    for (let i = 0; i < n; i++) {
      driftX.push(dx); driftZ.push(dz);
      const tt = i * DRIFT_DT;
      const u = sampleCurve(def.baseCurve, tt) * advect;
      const d = dirAt(tt);
      dx += Math.cos(d) * u * DRIFT_DT;
      dz += Math.sin(d) * u * DRIFT_DT;
    }
  }
  const drift = { x: 0, z: 0 };
  function driftAt(t) {
    if (t <= 0) { drift.x = 0; drift.z = 0; return drift; }
    const f = t / DRIFT_DT;
    let i = Math.floor(f);
    if (i > driftX.length - 2) i = driftX.length - 2;   // past the end: extrapolate
    const k = f - i;
    drift.x = driftX[i] + (driftX[i + 1] - driftX[i]) * k;
    drift.z = driftZ[i] + (driftZ[i + 1] - driftZ[i]) * k;
    return drift;
  }

  /** Speed multiplier: smooth noise, carried downwind. */
  function spatialFactor(x, z, t) {
    if (amp <= 0) return 1;
    const d = driftAt(t);
    const nx = (x - d.x) / scale;
    const nz = (z - d.z) / scale;
    const n = 0.65 * valueNoise2(nx, nz, nSeed)
            + 0.35 * valueNoise2(nx * 2.2 + 31.7, nz * 2.2 + 11.3, nSeed ^ 0x51ed270b);
    return 1 + (n - 0.5) * 2 * amp;
  }

  /** Trees knock a hole downwind of themselves. Cheap, and very juicy. */
  function shelterFactor(x, z, dirX, dirZ) {
    let f = 1;
    for (let i = 0; i < shelters.length; i++) {
      const s = shelters[i];
      const rx = x - s.x, rz = z - s.z;
      const along = rx * dirX + rz * dirZ;          // >0 = downwind of the tree
      if (along <= 0 || along >= s.length) continue;
      const perp = Math.abs(rx * dirZ - rz * dirX);
      if (perp >= s.radius) continue;
      // ramp in over the first half-radius so the shadow can't snap on at along=0
      const fAlong = smoothstep(0, s.radius * 0.5, along) * (1 - smoothstep(0, s.length, along));
      const fPerp = 1 - smoothstep(0, s.radius, perp);
      f *= 1 - s.strength * fAlong * fPerp;
    }
    return f;
  }

  const field = {
    def,
    seed,
    gusts,
    duration,

    /**
     * Trees/house register wind shadows. Lane A calls this after building the
     * yard; unset = no shadows, so nothing breaks before world.js lands.
     * @param {Array<{x,z,radius,strength,length}>} list
     */
    setShelters(list) {
      shelters = (list || []).map((s) => ({
        x: s.x, z: s.z,
        radius: s.radius ?? 2.5,
        strength: Math.min(1, Math.max(0, s.strength ?? 0.45)),
        length: s.length ?? (s.radius ?? 2.5) * 4,
      }));
      return field;
    },
    get shelters() { return shelters; },

    /**
     * Scalar wind speed (m/s) at a point — HORIZONTAL only, which is what an
     * anemometer reads and what the HUD, rain and grass want. The gust downdraft
     * is deliberately not in here: a wind meter jumping because air is falling
     * past it would read as a bug. Use vecAt/sample for the full 3D vector.
     * The cheap path — no allocation.
     */
    speedAt(x, z, t) {
      return localHoriz(x, z, t);
    },

    dirAt,
    uniformSpeed,
    gustOnly,
    verticalAt,
    get downFrac() { return downFrac; },

    /** Writes wind velocity (m/s) into out {x,y,z}. Ground plane is XZ, +Y up. */
    vecAt(x, z, t, out) {
      const d = dirAt(t);
      const dirX = Math.cos(d), dirZ = Math.sin(d);
      const s = localHoriz(x, z, t);
      out.x = dirX * s;
      out.y = -downFrac * s;           // the downdraft rides the local speed — see verticalAt()
      out.z = dirZ * s;
      return out;
    },

    /**
     * The next gust that has been telegraphed but hasn't started ramping.
     * eta = seconds until the wind actually rises. Null when nothing's inbound.
     */
    telegraph(t) {
      for (let i = 0; i < gusts.length; i++) {
        const g = gusts[i];
        if (t < g.t0) return null;     // sorted — next one hasn't telegraphed yet
        if (t < g.rampAt) {
          return { eta: g.rampAt - t, dir: dirAt(g.rampAt), power: g.pow };
        }
      }
      return null;
    },

    /** Storm events (windchange/debris) fired in (a, b]. Pure — replayable. */
    eventsBetween(a, b) {
      const evs = def.events || [];
      const out = [];
      for (let i = 0; i < evs.length; i++) {
        if (evs[i].t > a && evs[i].t <= b) out.push(evs[i]);
      }
      return out;
    },

    /** 0..1 rain intensity for skyfx. */
    rainAt(t) {
      const r = def.rain;
      if (!r) return 0;
      if (r.curve) return Math.min(1, Math.max(0, sampleCurve(r.curve, t)));
      return Math.min(1, Math.max(0, r.intensity ?? 0));
    },
  };

  return field;
}

// ---------- storm JSON validator ----------
// Storms are data so design can tune without code (PLAN3D §4) — which means a
// typo is a data bug, and data bugs should fail loud, not silently blow calm.
export function validateStorm(def, name = 'storm') {
  const errors = [];
  const bad = (m) => errors.push(`${name}: ${m}`);
  const isCurve = (c) => Array.isArray(c) && c.length > 0
    && c.every((p) => Array.isArray(p) && p.length === 2 && p.every(Number.isFinite));
  const monotonic = (c) => c.every((p, i) => i === 0 || p[0] >= c[i - 1][0]);

  if (!def || typeof def !== 'object') { bad('not an object'); return { ok: false, errors }; }
  if (!Number.isFinite(def.duration) || def.duration <= 0) bad('duration must be a positive number');

  if (!isCurve(def.baseCurve)) bad('baseCurve must be [[t,speed],...] of finite numbers');
  else {
    if (!monotonic(def.baseCurve)) bad('baseCurve t must be non-decreasing');
    if (def.baseCurve.some((p) => p[1] < 0)) bad('baseCurve speed must be >= 0');
    const end = def.baseCurve[def.baseCurve.length - 1][0];
    if (Number.isFinite(def.duration) && end < def.duration) {
      bad(`baseCurve ends at t=${end} but storm runs to ${def.duration} — tail would flatline`);
    }
  }

  if (!isCurve(def.dirCurve)) bad('dirCurve must be [[t,radians],...] of finite numbers');
  else if (!monotonic(def.dirCurve)) bad('dirCurve t must be non-decreasing');

  const g = def.gusts;
  if (!g || typeof g !== 'object') bad('gusts block missing');
  else {
    const minGap = g.minGap ?? 5, maxGap = g.maxGap ?? 12;
    if (!(minGap > 0)) bad('gusts.minGap must be > 0 (else the timeline never advances)');
    if (maxGap < minGap) bad('gusts.maxGap must be >= minGap');
    // Overlapping gusts stack, and a stacked telegraph is unreadable to the player.
    if (minGap < GUST.TOTAL) bad(`gusts.minGap (${minGap}) < gust length ${GUST.TOTAL}s — gusts would overlap`);
    if ((g.powBase ?? 12) < 0) bad('gusts.powBase must be >= 0');
    // `downdraft` (gust-only, pre-SPRINT3) is still accepted but flagged, so an
    // un-migrated storm loads visibly wrong rather than silently at a third power.
    if (g.downdraft != null && g.downdraftOfTotal == null) {
      bad('gusts.downdraft is the old gust-only field — rename to downdraftOfTotal (SPRINT3 decision 8); it now means a fraction of TOTAL wind speed');
    }
    const dd = g.downdraftOfTotal ?? g.downdraft ?? DEFAULT_DOWNDRAFT;
    if (!Number.isFinite(dd) || dd < 0 || dd > 1) {
      bad(`gusts.downdraftOfTotal must be 0..1 — the fraction of TOTAL wind speed that blows DOWN — got ${dd}`);
    }
  }

  for (const e of def.events || []) {
    if (!Number.isFinite(e.t)) bad(`event ${JSON.stringify(e)} has no finite t`);
    if (!e.type) bad(`event at t=${e.t} has no type`);
    if (e.type === 'debris' && !e.model) bad(`debris event at t=${e.t} has no model`);
    // A windchange event is HUD metadata; dirCurve is the physics. If they drift
    // apart the player gets warned about a swing that never comes.
    if (e.type === 'windchange' && isCurve(def.dirCurve)) {
      const before = sampleAngleCurve(def.dirCurve, e.t - 0.5);
      const after = sampleAngleCurve(def.dirCurve, e.t + (e.over ?? 6));
      const swing = Math.abs(lerpAngle(before, after, 1) - before);
      if (swing < 0.5) {
        bad(`windchange at t=${e.t} promises a swing but dirCurve only turns ${swing.toFixed(2)} rad by t=${e.t + (e.over ?? 6)}`);
      }
    }
  }

  if (def.rain && def.rain.curve && !isCurve(def.rain.curve)) bad('rain.curve must be [[t,intensity],...]');

  return { ok: errors.length === 0, errors };
}