import React, { useMemo } from 'react';
import { SeasonalOverlayProps } from '../types';
import {
  animSnowFall,
  animSnowSway,
  animBulbBreathe,
  animAurora,
  animFrostPulse,
} from './Christmas.css';

// Deterministic pseudo-random so the scene is identical every mount (no React
// state per frame). Large primes keep the distribution well spread.
const rand = (seed: number) => {
  const x = Math.sin(seed * 127.1 + 311.7) * 43758.5453;
  return x - Math.floor(x);
};

// Warm incandescent string-light hues in oklch — gold, soft red, cool white,
// pine green, icy blue. Kept luminous and gentle so they read as bokeh glow.
const BULB_COLORS = [
  'oklch(0.85 0.12 85)', // warm gold
  'oklch(0.72 0.15 28)', // soft red
  'oklch(0.95 0.03 230)', // icy white
  'oklch(0.78 0.13 150)', // pine green
  'oklch(0.8 0.1 235)', // cool blue
];

type Flake = {
  left: number;
  size: number;
  duration: number;
  delay: number;
  swayDuration: number;
  opacity: number;
  blur: number;
};

type Bulb = {
  left: number;
  top: number;
  size: number;
  color: string;
  duration: number;
  delay: number;
};

export function ChristmasOverlay({ reduced }: SeasonalOverlayProps) {
  // Three parallax bands of snow: far (small/slow/dim) -> near (large/fast).
  const flakes = useMemo<Flake[]>(() => {
    const bands = [
      { count: 12, size: [1.5, 2.5], dur: [16, 22], op: [0.35, 0.55], blur: 0.6 },
      { count: 10, size: [2.5, 4], dur: [11, 15], op: [0.55, 0.8], blur: 0.3 },
      { count: 8, size: [4, 6.5], dur: [8, 11], op: [0.7, 0.95], blur: 0 },
    ];
    const out: Flake[] = [];
    let s = 1;
    bands.forEach((b) => {
      for (let i = 0; i < b.count; i += 1) {
        const r1 = rand(s);
        const r2 = rand(s + 0.37);
        const r3 = rand(s + 0.71);
        const r4 = rand(s + 0.91);
        out.push({
          left: r1 * 100,
          size: b.size[0] + r2 * (b.size[1] - b.size[0]),
          duration: b.dur[0] + r3 * (b.dur[1] - b.dur[0]),
          delay: -r4 * (b.dur[1] + 4),
          swayDuration: 4 + r2 * 5,
          opacity: b.op[0] + r3 * (b.op[1] - b.op[0]),
          blur: b.blur,
        });
        s += 1;
      }
    });
    return out;
  }, []);

  // Bokeh string lights strung along the very top edge, gently sagging.
  const bulbs = useMemo<Bulb[]>(() => {
    const count = 9;
    const out: Bulb[] = [];
    for (let i = 0; i < count; i += 1) {
      const t = i / (count - 1);
      // Two-segment garland sag so the lights drape rather than sit in a line.
      const sag = Math.sin(t * Math.PI * 2) * 3.2;
      out.push({
        left: 4 + t * 92,
        top: 2.5 + Math.abs(Math.sin(t * Math.PI)) * 2 + sag,
        size: 12 + rand(i + 5) * 8,
        color: BULB_COLORS[i % BULB_COLORS.length],
        duration: 3.4 + rand(i + 2) * 2.6,
        delay: -rand(i + 9) * 3,
      });
    }
    return out;
  }, []);

  return (
    <>
      {/* Deep night-blue ambient wash — layered radial + linear oklch gradients
          for depth. Kept low-opacity so chat text stays legible (WCAG-AA). */}
      <div
        aria-hidden="true"
        style={{
          position: 'absolute',
          inset: 0,
          contain: 'layout paint style',
          backgroundImage: [
            'radial-gradient(120% 80% at 50% -10%, oklch(0.25 0.07 250 / 0.16) 0%, transparent 55%)',
            'radial-gradient(90% 60% at 85% 110%, oklch(0.3 0.06 255 / 0.1) 0%, transparent 60%)',
            'linear-gradient(180deg, oklch(0.95 0.03 230 / 0.05) 0%, transparent 22%, transparent 80%, oklch(0.22 0.07 255 / 0.08) 100%)',
          ].join(','),
        }}
      />

      {/* Frosted vignette frame — cold edges, clear center. backdrop-filter on a
          single cheap layer for a faint icy haze around the rim. */}
      <div
        aria-hidden="true"
        style={{
          position: 'absolute',
          inset: 0,
          contain: 'layout paint style',
          backdropFilter: 'blur(0.4px) saturate(1.04)',
          WebkitBackdropFilter: 'blur(0.4px) saturate(1.04)',
          backgroundImage:
            'radial-gradient(135% 120% at 50% 42%, transparent 52%, oklch(0.9 0.04 225 / 0.07) 74%, oklch(0.28 0.07 250 / 0.16) 100%)',
          animation: reduced ? 'none' : `${animFrostPulse} 12s ease-in-out infinite`,
          willChange: reduced ? undefined : 'opacity',
        }}
      />

      {/* Aurora shimmer band high up — soft conic-ish wash of icy blue/green. */}
      <div
        aria-hidden="true"
        style={{
          position: 'absolute',
          top: '-6%',
          left: '-10%',
          right: '-10%',
          height: '40%',
          contain: 'layout paint style',
          mixBlendMode: 'screen',
          filter: 'blur(26px)',
          opacity: reduced ? 0.6 : undefined,
          backgroundImage: [
            'radial-gradient(60% 100% at 30% 0%, oklch(0.85 0.12 165 / 0.18) 0%, transparent 70%)',
            'radial-gradient(55% 100% at 68% 0%, oklch(0.8 0.1 235 / 0.16) 0%, transparent 72%)',
            'radial-gradient(50% 100% at 50% 0%, oklch(0.9 0.06 280 / 0.1) 0%, transparent 75%)',
          ].join(','),
          animation: reduced ? 'none' : `${animAurora} 18s ease-in-out infinite`,
          willChange: reduced ? undefined : 'transform, opacity',
        }}
      />

      {/* String-light wire — a faint catenary line the bulbs hang from. */}
      <div
        aria-hidden="true"
        style={{
          position: 'absolute',
          top: 0,
          left: 0,
          right: 0,
          height: '14%',
          contain: 'layout paint style',
          backgroundImage:
            'radial-gradient(140% 60% at 50% -30%, oklch(0.3 0.04 250 / 0.14) 0%, transparent 70%)',
        }}
      />

      {/* Bokeh string lights — soft blurred orbs that breathe. */}
      {bulbs.map((b, i) => (
        <div
          key={`bulb-${i}`}
          aria-hidden="true"
          style={{
            position: 'absolute',
            left: `${b.left}%`,
            top: `${b.top}%`,
            width: `${b.size}px`,
            height: `${b.size}px`,
            marginLeft: `${-b.size / 2}px`,
            borderRadius: '50%',
            background: `radial-gradient(circle at 38% 34%, oklch(0.98 0.02 95 / 0.95) 0%, ${b.color} 38%, transparent 72%)`,
            boxShadow: `0 0 ${b.size}px ${b.size * 0.45}px ${b.color.replace(')', ' / 0.45)')}`,
            filter: 'blur(0.5px)',
            opacity: reduced ? 0.9 : undefined,
            animation: reduced
              ? 'none'
              : `${animBulbBreathe} ${b.duration}s ease-in-out ${b.delay}s infinite`,
            willChange: reduced ? undefined : 'transform, opacity',
          }}
        />
      ))}

      {/* Snowfall (motion only) — three parallax bands. Static dusting below. */}
      {!reduced &&
        flakes.map((f, i) => (
          <div
            key={`snow-${i}`}
            aria-hidden="true"
            style={{
              position: 'absolute',
              top: 0,
              left: `${f.left}%`,
              width: `${f.size}px`,
              height: `${f.size}px`,
              animation: `${animSnowSway} ${f.swayDuration}s ease-in-out ${f.delay}s infinite`,
              willChange: 'transform',
            }}
          >
            <div
              style={{
                width: '100%',
                height: '100%',
                borderRadius: '50%',
                background:
                  'radial-gradient(circle at 35% 35%, oklch(0.99 0.01 230 / 0.95) 0%, oklch(0.95 0.03 230 / 0.7) 60%, transparent 100%)',
                boxShadow: '0 0 4px oklch(0.9 0.05 235 / 0.55)',
                opacity: f.opacity,
                filter: f.blur ? `blur(${f.blur}px)` : undefined,
                animation: `${animSnowFall} ${f.duration}s linear ${f.delay}s infinite`,
                willChange: 'transform, opacity',
              }}
            />
          </div>
        ))}

      {/* Static dusting of snow for the reduced-motion / preview scene — a
          sparse scatter so the thumbnail still reads as snowfall. */}
      {reduced &&
        flakes.map((f, i) => {
          const fy = rand(i + 0.5) * 96 + 2;
          return (
            <div
              key={`snow-static-${i}`}
              aria-hidden="true"
              style={{
                position: 'absolute',
                left: `${f.left}%`,
                top: `${fy}%`,
                width: `${f.size}px`,
                height: `${f.size}px`,
                borderRadius: '50%',
                background:
                  'radial-gradient(circle at 35% 35%, oklch(0.99 0.01 230 / 0.95) 0%, oklch(0.95 0.03 230 / 0.7) 60%, transparent 100%)',
                boxShadow: '0 0 4px oklch(0.9 0.05 235 / 0.5)',
                opacity: f.opacity,
                filter: f.blur ? `blur(${f.blur}px)` : undefined,
              }}
            />
          );
        })}
    </>
  );
}