// SOLARGOD sky-events layer (Wave 2 · SYZYGY) — the almanac learns to predict.
// Pure geometry on the ephemeris: heliocentric longitude λ(body)=atan2(y,x) and
// the geocentric elongation angle give oppositions, conjunctions and greatest
// elongations with no network at all. Two plain exports (findEvents / nextEvent)
// so verify.html and node can gate the MATH directly; the default factory paints
// diamond marks on the time bar and jumps the clock on click.
//
// Longitude alignment (heliocentric, Earth E, planet P, both from the Sun):
//   opposition (outer): normDegPM180(λp − λe) crosses 0   — Sun·Earth·planet in line
//   solar conj (outer): the same crosses 180
//   inferior conj (inner): crosses 0 ;  superior conj (inner): crosses 180
//   greatest elongation (inner): local max of acos( (−E·(P−E)) / (|E||P−E|) )

import * as ephem from '../ephem.js';
import { BODIES } from '../bodies.js';
import { normDegPM180, RAD, unixMsFromJd, formatUTCDate, fmtDuration } from '../lib.js';

// Bodies that show an opposition (outer) vs an elongation (inner). Pluto rides the
// small-body element set; every other id is an ephem.js planet key.
export const OUTER = ['mars', 'jupiter', 'saturn', 'uranus', 'neptune', 'pluto'];
export const INNER = ['mercury', 'venus'];
export function isOuter(id) { return OUTER.includes(id); }
export function isInner(id) { return INNER.includes(id); }

const PLUTO_EL = BODIES.pluto.elements;
const STEP_DAYS = 5;      // coarse scan step; finest synodic (Mercury) still safe
const HOUR = 1 / 24;      // bisection tolerance — refine crossings to < 1 hour

// ---- position helpers (scratch objects; all calls are sequential) ----
const _h = {}, _E = {}, _P = {};
function helioAt(id, jd, out) {
  return id === 'pluto' ? ephem.smallBodyEcl(PLUTO_EL, jd, out) : ephem.helioEcl(id, jd, out);
}
function lonDeg(id, jd) {
  helioAt(id, jd, _h);
  return Math.atan2(_h.y, _h.x) * RAD;
}
// signed longitude gap planet−Earth, wrapped to (−180,180]; 0 = opp/inferior conj.
function deltaLon(id, jd) { return normDegPM180(lonDeg(id, jd) - lonDeg('earth', jd)); }
// shifted so a zero marks the 180° alignment (solar / superior conjunction).
function deltaLon180(id, jd) { return normDegPM180(lonDeg(id, jd) - lonDeg('earth', jd) - 180); }

// Geocentric elongation angle (Sun–Earth–planet), degrees.
function elongationDeg(id, jd) {
  ephem.helioEcl('earth', jd, _E);
  helioAt(id, jd, _P);
  const sx = -_E.x, sy = -_E.y, sz = -_E.z;                 // Earth→Sun
  const px = _P.x - _E.x, py = _P.y - _E.y, pz = _P.z - _E.z; // Earth→planet
  const ns = Math.hypot(sx, sy, sz), np = Math.hypot(px, py, pz);
  let c = (sx * px + sy * py + sz * pz) / (ns * np);
  c = c > 1 ? 1 : c < -1 ? -1 : c;
  return Math.acos(c) * RAD;
}
// East (evening star) when the planet leads the Sun in geocentric ecliptic longitude.
function elongSide(id, jd) {
  ephem.helioEcl('earth', jd, _E);
  helioAt(id, jd, _P);
  const lonSun = Math.atan2(-_E.y, -_E.x) * RAD;
  const lonP = Math.atan2(_P.y - _E.y, _P.x - _E.x) * RAD;
  return normDegPM180(lonP - lonSun) >= 0 ? 'E' : 'W';
}

// ---- root finding ----
// Bisect a continuous angle fn(id,·) with opposite signs at [a,b] to < 1 hour.
function bisect(id, a, b, fn) {
  let fa = fn(id, a);
  for (let i = 0; i < 40 && b - a > HOUR; i++) {
    const m = 0.5 * (a + b), fm = fn(id, m);
    if (fa * fm <= 0) b = m; else { a = m; fa = fm; }
  }
  return 0.5 * (a + b);
}
// Coarse-scan fn for sign changes; the |Δf|<90 guard rejects the ±180 wrap of a
// wrapped angle (a real crossing steps only a few degrees per 5 days).
function scanZeros(id, jdStart, jdEnd, fn, onCross) {
  let ja = jdStart, fa = fn(id, ja);
  for (let jb = jdStart + STEP_DAYS; jb <= jdEnd + 1e-9; jb += STEP_DAYS) {
    const fb = fn(id, jb);
    if (fa !== 0 && fa * fb < 0 && Math.abs(fa - fb) < 90) onCross(bisect(id, ja, jb, fn));
    ja = jb; fa = fb;
  }
}
// Local maxima of elongation: numeric derivative flips + → −, then bisect it to 0.
function scanElongMax(id, jdStart, jdEnd, onMax) {
  const h = 0.5;
  const der = (jd) => elongationDeg(id, jd + h) - elongationDeg(id, jd - h);
  let ja = jdStart, da = der(ja);
  for (let jb = jdStart + STEP_DAYS; jb <= jdEnd + 1e-9; jb += STEP_DAYS) {
    const db = der(jb);
    if (da > 0 && db < 0) {
      let a = ja, b = jb;
      for (let i = 0; i < 40 && b - a > HOUR; i++) { const m = 0.5 * (a + b); if (der(m) > 0) a = m; else b = m; }
      onMax(0.5 * (a + b));
    }
    ja = jb; da = db;
  }
}

// ---- event construction ----
function makeEvent(id, jd, kind) {
  const name = BODIES[id].name;
  if (kind === 'opposition') return { jd, type: 'opposition', bodies: [id], label: `${name} at opposition` };
  if (kind === 'solar') return { jd, type: 'conjunction', bodies: [id], label: `${name} at solar conjunction` };
  if (kind === 'inferior') return { jd, type: 'conjunction', bodies: [id], label: `${name} at inferior conjunction` };
  if (kind === 'superior') return { jd, type: 'conjunction', bodies: [id], label: `${name} at superior conjunction` };
  // greatest elongation — carry side + angle
  const side = elongSide(id, jd), ang = elongationDeg(id, jd);
  return { jd, type: side === 'E' ? 'elongation-east' : 'elongation-west', bodies: [id],
    label: `${name} greatest elongation ${side === 'E' ? 'east' : 'west'} (${ang.toFixed(0)}°)` };
}

function scanBody(id, jdStart, jdEnd) {
  const out = [];
  const outer = isOuter(id);
  scanZeros(id, jdStart, jdEnd, deltaLon, (jd) => out.push(makeEvent(id, jd, outer ? 'opposition' : 'inferior')));
  scanZeros(id, jdStart, jdEnd, deltaLon180, (jd) => out.push(makeEvent(id, jd, outer ? 'solar' : 'superior')));
  if (!outer) scanElongMax(id, jdStart, jdEnd, (jd) => out.push(makeEvent(id, jd, 'elongation')));
  return out;
}

// PLAIN API — pure math, importable with zero Three.js in scope.
// All sky events in [jdStart, jdEnd], chronological.
export function findEvents(jdStart, jdEnd) {
  const all = [];
  for (const id of [...OUTER, ...INNER]) for (const e of scanBody(id, jdStart, jdEnd)) all.push(e);
  all.sort((a, b) => a.jd - b.jd);
  return all;
}
// Next headline event for a body strictly after jd — opposition (outer) or
// greatest elongation (inner). Widens the search span until one is found.
export function nextEvent(bodyId, jd) {
  const outer = isOuter(bodyId);
  const want = outer ? (e) => e.type === 'opposition' : (e) => e.type.startsWith('elongation');
  let span = outer ? 820 : 500;
  for (let tries = 0; tries < 4; tries++) {
    const hit = scanBody(bodyId, jd, jd + span).filter((e) => e.jd > jd + 1e-6 && want(e)).sort((a, b) => a.jd - b.jd)[0];
    if (hit) return hit;
    span *= 2;
  }
  return null;
}

// ---- default factory: timeline diamonds + HUD row ----
const WINDOW_DAYS = 730; // ±2 years, computed lazily around the current sim date
function cssKind(type) { return type === 'opposition' ? 'opp' : type.startsWith('elongation') ? 'elong' : 'conj'; }

export default function create(ctx) {
  const { CONFIG, ui, clock } = ctx;
  const strip = document.getElementById('timeline-outer');
  if (!strip) return null; // no time bar (e.g. headless) — plain exports still work

  const marks = document.createElement('div');
  marks.id = 'event-marks';
  strip.appendChild(marks);

  const minMs = CONFIG.time.minMs, maxMs = CONFIG.time.maxMs, spanMs = maxMs - minMs;
  let on = true, events = [];
  let winStart = 0, winEnd = 0;      // computed window in JD
  let queue = null, pending = [];    // chunked-scan state
  let lastCheck = 0;

  ui.addLayer('events', 'Sky events', true, (v) => { on = v; marks.style.display = v ? '' : 'none'; });
  startScan(clock.jd);

  // Kick off a fresh ±2 yr scan centred on jd; bodies are processed one-per-tick.
  function startScan(centerJd) {
    winStart = centerJd - WINDOW_DAYS; winEnd = centerJd + WINDOW_DAYS;
    queue = [...OUTER, ...INNER]; pending = [];
    ui.setStatus('events', 'computing…', 'warn');
  }

  function step() {
    if (!queue) return;
    const id = queue.shift();
    for (const e of scanBody(id, winStart, winEnd)) pending.push(e);
    if (queue.length) { ui.setStatus('events', `computing… ${8 - queue.length}/8`, 'warn'); return; }
    queue = null;
    pending.sort((a, b) => a.jd - b.jd);
    events = pending; pending = [];
    render();
    ui.setStatus('events', `${events.length} events ±2 yr · computed`, on ? 'ok' : 'off');
  }

  function render() {
    marks.textContent = '';
    for (const e of events) {
      const ms = unixMsFromJd(e.jd);
      const f = (ms - minMs) / spanMs;
      if (f < 0 || f > 1) continue;
      const d = document.createElement('div');
      d.className = `ev-mark ev-${cssKind(e.type)}`;
      d.style.left = `${(f * 100).toFixed(4)}%`;
      d.title = `${e.label} · ${formatUTCDate(ms)}`;
      d.addEventListener('pointerdown', (ev) => {
        ev.stopPropagation(); // don't let the strip's scrub-capture hijack the jump
        clock.simMs = Math.max(minMs, Math.min(maxMs, ms));
      });
      marks.appendChild(d);
    }
  }

  return {
    id: 'events',
    onClockTick(simMs, jd) {
      if (queue) { step(); return; } // finish the current scan before anything else
      const now = performance.now();
      if (now - lastCheck < 250) return; // window check ≤4 Hz
      lastCheck = now;
      if (jd < winStart || jd > winEnd) startScan(jd); // clock left the window → recompute
    },
  };
}