'use client';

import { useState } from 'react';
import { motion, useMotionValueEvent, useScroll, useSpring, useTransform } from 'framer-motion';
import { usePrefersReducedMotion } from '@/lib/motion';
import { BARRAS_SIMBOLO, VIEWBOX_SIMBOLO } from '@/lib/simbolo';

// The gold spine of the page: one continuous line down the vertical centre,
// drawing itself as the reader scrolls and resolving into the ≡ at the close.
// It is what turns ten sections into a single route — *claridad · dirección ·
// crecimiento* made visible, per the Manual de Identidad Visual.
//
// Centred, never in a side gutter: the brand's through-line belongs in the
// middle, on every breakpoint. It sits ABOVE the section backgrounds (z-10)
// but BELOW the text, which `Container` lifts to z-20 — so the thread reads
// as a faint watermark spine behind the reading, never crossing it.
//
// Page-level useScroll() with no target ref on purpose: no element measuring,
// no "container has a static position" warnings, one listener for the page.

const TRAMOS = 4;
const ALTO = 1200;
const PASO = ALTO / TRAMOS;

// A band, not a thread. Held in real pixels by vector-effect below, so it never
// again collapses to a hairline when the viewBox scale changes.
const GROSOR = 14;

// Four long swells rather than one page-long curve or ten short ones. Stretched
// over the whole document with preserveAspectRatio="none", a single swell reads
// as a straight rule and ten read as a fidget; four put roughly one screen's
// worth of travel — some 180px across the column — into every viewport.
const TRAZO = Array.from({ length: TRAMOS }, (_, i) => {
  const y = i * PASO;
  const x = i % 2 === 0 ? 72 : 28;
  // The final bend straightens as it lands so the thread enters the ≡ vertically.
  const salida = i === TRAMOS - 1 ? 50 : x;
  return `C ${x} ${y + PASO * 0.25}, ${salida} ${y + PASO * 0.75}, 50 ${y + PASO}`;
}).reduce((d, tramo) => `${d} ${tramo}`, 'M50 0');

// The draw finishes at 85% of the document instead of at the very bottom:
// scrollYProgress only reaches 1 past the footer, so tying the thread to it
// left the tip trailing in mid-screen and the ending never seen.
const FIN = 0.85;

export function HiloConductor({ className = '' }: { className?: string }) {
  const reduced = usePrefersReducedMotion();
  const { scrollYProgress } = useScroll();
  const recorrido = useTransform(scrollYProgress, [0, FIN], [0, 1], { clamp: true });
  const avance = useSpring(recorrido, { stiffness: 90, damping: 30, restDelta: 0.001 });

  const [dibujado, setDibujado] = useState(false);
  useMotionValueEvent(avance, 'change', (v) => {
    if (v > 0.98) setDibujado(true);
  });
  const resuelto = reduced || dibujado;

  const wrapper = `pointer-events-none absolute inset-0 z-10 ${className}`;

  // Plain <path> for reduced motion: motion.path applies dash scaffolding even
  // without initial/animate and would leave the thread invisible.
  // vector-effect keeps the stroke at its declared width — the non-uniform
  // viewBox scale squeezes a vertical line's stroke by the x factor alone.
  const trazo = reduced ? (
    <path
      d={TRAZO}
      fill="none"
      stroke="currentColor"
      strokeWidth={GROSOR}
      strokeLinecap="round"
      vectorEffect="non-scaling-stroke"
    />
  ) : (
    <motion.path
      d={TRAZO}
      fill="none"
      stroke="currentColor"
      strokeWidth={GROSOR}
      strokeLinecap="round"
      vectorEffect="non-scaling-stroke"
      style={{ pathLength: avance }}
    />
  );

  return (
    <div className={wrapper}>
      {/* Mirrors Container's own centring (`mx-auto max-w-content`) so the
          thread is measured from the real column edge and stays centred in it. */}
      <div className="relative mx-auto h-full w-full max-w-content">
        <svg
          className="absolute top-0 bottom-20 left-1/2 w-full -translate-x-1/2 text-dorado/25"
          viewBox={`0 0 100 ${ALTO}`}
          preserveAspectRatio="none"
          aria-hidden="true"
          focusable="false"
        >
          {trazo}
        </svg>
        {/* The ending. The line arrives and becomes the mark — same geometry as
            the wordmark's ≡, never a lookalike. Uniformly scaled in its own
            svg, because the band's stretch would flatten the bars. */}
        <svg
          className="absolute bottom-4 left-1/2 w-24 -translate-x-1/2 text-dorado"
          viewBox={VIEWBOX_SIMBOLO}
          aria-hidden="true"
          focusable="false"
        >
          {BARRAS_SIMBOLO.map((barra, i) =>
            reduced ? (
              <rect key={i} {...barra} rx={1.5} fill="currentColor" />
            ) : (
              <motion.rect
                key={i}
                {...barra}
                rx={1.5}
                fill="currentColor"
                initial={{ opacity: 0 }}
                animate={{ opacity: resuelto ? 1 : 0 }}
                transition={{ duration: 0.5, delay: i * 0.12, ease: [0.22, 1, 0.36, 1] }}
              />
            ),
          )}
        </svg>
      </div>
    </div>
  );
}