/**
 * redDwarf ember field — a slow drift of tiny warm sparks behind the art.
 *
 * Content layer (world-space sprites), NOT a filter: it works in the
 * Canvas fallback and can never touch the HUD (it is a sprite at depth 3,
 * like the starfield, so the camera split is irrelevant to it). The sparks
 * are small, warm, additively blended (they glow like embers) and sit at a
 * parallax BETWEEN the starfield (0.15–0.85) and the ship — dust in the
 * air, closer than the stars, farther than you.
 *
 * The field FILLs the view and parallaxes like the starfield (the proven
 * pattern in Starfield.js): embers start in a window around the CURRENT
 * camera, each frame they shift by (1 − p) of the camera delta (so on
 * screen they stream opposite to travel, near sparks faster than far
 * ones) plus their own slow drift, and are wrapped back into the current
 * view. That keeps them on screen no matter how far the ship flies.
 *
 * Config: data/systems.json → types.redDwarf.effect.particles.
 * Node-testable color/shape math is inline (this file imports Phaser and
 * is exercised in the browser via dev/server.mjs).
 */
import Phaser from '../vendor/phaser.js';
import { canvasTexture } from '../utils/Textures.js';
import { toColor } from '../utils/Color.js';

const DEPTH = 3; // behind the art (planets 5, ship 10), in front of starfield
const MARGIN = 80; // embers may start/exit this far past the viewport

/** A small, bright, soft dot — an ember. White so a tint reads as color. */
function drawSpark(ctx, size) {
  const c = size / 2;
  const g = ctx.createRadialGradient(c, c, 0, c, c, c);
  g.addColorStop(0.0, 'rgba(255,255,255,1.0)');
  g.addColorStop(0.35, 'rgba(255,255,255,0.85)');
  g.addColorStop(1.0, 'rgba(255,255,255,0.0)');
  ctx.fillStyle = g;
  ctx.fillRect(0, 0, size, size);
}

/** Maps any coordinate into [left, left + span) — safe for huge deltas too. */
function wrapIn(v, left, span) {
  return left + ((((v - left) % span) + span) % span);
}

/**
 * The ember layer.
 *
 * @param {object} scene Phaser scene (add / camera / renderer / scale)
 * @param {string} color ember color (CSS hex)
 * @param {object} cfg data/systems.json → effect.particles
 * @param {{phase?:number, angle?:number, drift?:number}} fx per-system seeded 0..1 variation
 */
export class EmberField {
  constructor(scene, color, cfg, fx = {}) {
    this.scene = scene;
    this.color = toColor(color, 0xff8a4a);
    this.cfg = cfg ?? {};
    this.fx = fx ?? {};
    this.sprites = [];
    this.lastScrollX = 0;
    this.lastScrollY = 0;
  }

  /** Build the spark texture + one sprite per ember (idempotent). */
  create() {
    const scene = this.scene;
    if (this.sprites.length) return;
    const {
      count = 40,
      size = [2, 6],
      alpha = [0.4, 0.9],
      parallax = [0.25, 0.5],
      speed = [8, 25],
    } = this.cfg;

    const texKey = canvasTexture(scene, 'fx-ember-spark', 32, 32, (ctx) => drawSpark(ctx, 32));
    const w = scene.scale.width;
    const h = scene.scale.height;
    const cam = scene.cameras.main;

    // Embers start in a window around the CURRENT camera view (like the
    // starfield); update() keeps them wrapped into it as the camera flies.
    const left = cam.scrollX - MARGIN;
    const top = cam.scrollY - MARGIN;

    // Seeded per-ember variation (xorshift32 from the system fx, so the
    // same system looks the same every run).
    let s = (Math.imul(0x9e3779b1, 2654435761) ^ Math.round((this.fx.angle ?? 0.5) * 1e9)) >>> 0;
    const rand = () => {
      s ^= s << 13; s >>>= 0;
      s ^= s >> 17; s >>>= 0;
      s ^= s << 5; s >>>= 0;
      return (s >>> 0) / 4294967296;
    };
    const range = (a, b) => a + (b - a) * rand();

    for (let i = 0; i < count; i++) {
      const bx = left + rand() * (w + 2 * MARGIN);
      const by = top + rand() * (h + 2 * MARGIN);
      const ang = rand() * Math.PI * 2;
      const spd = range(speed[0], speed[1]);
      const sp = scene.add
        .image(bx, by, texKey)
        .setDepth(DEPTH)
        .setTint(this.color)
        .setAlpha(range(alpha[0], alpha[1]))
        .setBlendMode(Phaser.BlendModes.ADD);
      const sz = range(size[0], size[1]);
      sp.setScale(sz / 16); // 32px texture, scale to ~size px
      this.sprites.push({
        sp,
        vx: Math.cos(ang) * spd,
        vy: Math.sin(ang) * spd,
        p: range(parallax[0], parallax[1]),
      });
    }
    this.lastScrollX = cam.scrollX;
    this.lastScrollY = cam.scrollY;
  }

  /** Per-frame: parallax (opposite the camera, like the starfield) + drift. */
  update(nowMs, dtMs) {
    if (!this.sprites.length) return;
    const dt = (dtMs || 0) / 1000;
    const cam = this.scene.cameras.main;
    const dx = cam.scrollX - this.lastScrollX;
    const dy = cam.scrollY - this.lastScrollY;
    this.lastScrollX = cam.scrollX;
    this.lastScrollY = cam.scrollY;

    const w = this.scene.scale.width;
    const h = this.scene.scale.height;
    const spanX = w + 2 * MARGIN;
    const spanY = h + 2 * MARGIN;
    const left = cam.scrollX - MARGIN;
    const top = cam.scrollY - MARGIN;

    for (const e of this.sprites) {
      // Move by (1 − p) of the camera delta (→ on screen −p of it, opposite
      // to travel, near sparks faster), plus the ember's own slow drift.
      e.sp.x += dx * (1 - e.p) + e.vx * dt;
      e.sp.y += dy * (1 - e.p) + e.vy * dt;
      // Keep the field full: wrap into the current camera window.
      e.sp.x = wrapIn(e.sp.x, left, spanX);
      e.sp.y = wrapIn(e.sp.y, top, spanY);
    }
  }

  /** Tear down. */
  destroy() {
    for (const e of this.sprites) e.sp.destroy();
    this.sprites = [];
  }
}