"use client";

import { useEffect, useId, useRef, useState } from "react";
import { useInView, useReducedMotion } from "motion/react";

type TrainStep = { title: string; text: string; time?: string };

type ProcessTrainProps = {
  /** One station each, in order. */
  steps?: TrainStep[];
  /** Ms the train waits at a station before it runs on by itself. */
  hold?: number;
  /** Called when the train stops at a station. */
  onArrive?: (index: number) => void;
  /** Set the width here. Everything scales with it. */
  className?: string;
};

const STEPS: TrainStep[] = [
  { title: "Enquiry", text: "Tell us what you need. We reply the same day with a plain price.", time: "Day 1" },
  { title: "Plan", text: "We map the work on one page, so you know each stop before we leave.", time: "Day 2" },
  { title: "Build", text: "Your first version comes in a week. You check it, we fix it.", time: "Week 1" },
  { title: "Launch", text: "We go live together and stay on the line for the first month.", time: "Week 2" },
];

const W = 640;
const H = 232;
const RAIL = 192;
const GAP = 560; // track between two stations
const ENGINE = 372; // back of the engine on screen
const START = -470; // the train rolls in from here
const COACH = 104;
const PUFFS = 12;
const BRAKE = 95;

const ROOF = (i: number) => (i * 37 + 11) % 90;

function hills(from: number, to: number, base: number, lift: number, seed: number) {
  let d = `M${from} ${H}`;
  for (let x = from; x <= to; x += 24) {
    const y = base - (Math.sin(x * 0.009 + seed) * lift + Math.sin(x * 0.023 + seed * 2) * lift * 0.45);
    d += ` L${x} ${y.toFixed(1)}`;
  }
  return `${d} L${to} ${H} Z`;
}

function Wheel({ x, r, spokes = 6 }: { x: number; r: number; spokes?: number }) {
  return (
    <g transform={`translate(${x} ${-r})`}>
      <g data-wheel="">
        <circle r={r} fill="#17181d" />
        <circle r={r - 1.8} fill="#a12a24" />
        {Array.from({ length: spokes }, (_, i) => (
          <rect key={i} x={-0.8} y={-(r - 2)} width={1.6} height={(r - 2) * 2} fill="#17181d" transform={`rotate(${(i * 180) / spokes})`} />
        ))}
        <circle r={2.4} fill="#e8c56c" />
      </g>
    </g>
  );
}

function Coach({ x, lit, label }: { x: number; lit: boolean; label: number }) {
  const glow = lit ? "#ffd98a" : "#26395f";
  return (
    <g transform={`translate(${x} 0)`}>
      <rect x="2" y="-70" width="92" height="10" rx="5" fill="#1a2a4c" />
      <rect x="0" y="-62" width="96" height="42" rx="3" fill="#2a4a8c" />
      <rect x="0" y="-45" width="96" height="4" fill="#ecdfc0" />
      {[8, 24, 56, 72].map((wx) => (
        <rect key={wx} x={wx} y="-57" width="12" height="11" rx="1.5" fill={glow} style={{ transition: "fill 500ms" }} />
      ))}
      <rect x="41" y="-59" width="14" height="37" rx="1.5" fill="#1a2a4c" />
      <text x="48" y="-29" textAnchor="middle" fontSize="11" fontWeight="700" fill={lit ? "#ffd98a" : "#7f8fb5"} style={{ transition: "fill 500ms" }}>{label}</text>
      <rect x="0" y="-20" width="96" height="3" fill="#17181d" />
      <rect x="96" y="-27" width="9" height="3" fill="#17181d" />
      <Wheel x={18} r={9} spokes={4} />
      <Wheel x={78} r={9} spokes={4} />
    </g>
  );
}

function Station({ index, title, passed }: { index: number; title: string; passed: boolean }) {
  const wide = Math.max(92, title.length * 10.5 + 40);
  return (
    <g transform={`translate(${index * GAP} 0)`}>
      {/* Platform. */}
      <rect x="170" y={RAIL - 26} width="330" height="26" fill="#c9bfae" />
      <rect x="170" y={RAIL - 26} width="330" height="4" fill="#f4efe2" />
      {Array.from({ length: 11 }, (_, i) => (
        <rect key={i} x={170 + i * 30} y={RAIL - 22} width="15" height="22" fill="#b7ac99" opacity="0.5" />
      ))}
      {/* Shelter. */}
      <path d="M188 70 L392 70 L378 54 L202 54 Z" fill="#7b2f28" />
      <rect x="188" y="70" width="204" height="4" fill="#efe3c6" />
      <rect x="208" y="74" width="5" height="92" fill="#3d4b57" />
      <rect x="367" y="74" width="5" height="92" fill="#3d4b57" />
      {/* Board. */}
      <g transform={`translate(${290 - wide / 2} 84)`}>
        <rect x="14" y="-10" width="2.4" height="10" fill="#3d4b57" />
        <rect x={wide - 16} y="-10" width="2.4" height="10" fill="#3d4b57" />
        <rect width={wide} height="27" rx="1.5" fill="#f7cb1a" stroke="#17181d" strokeWidth="2" />
        <text x={wide / 2} y="19" textAnchor="middle" fontSize="16" fontWeight="800" letterSpacing="0.8" fill="#17181d">{title.toUpperCase()}</text>
      </g>
      {/* Signal past the end of the platform. */}
      <rect x="514" y="118" width="4" height="74" fill="#3d4b57" />
      <rect x="507" y="104" width="18" height="30" rx="4" fill="#17181d" />
      <circle cx="516" cy="112" r="4.2" fill={passed ? "#4a1612" : "#ff5040"} style={{ transition: "fill 300ms" }} />
      <circle cx="516" cy="125" r="4.2" fill={passed ? "#49f08e" : "#123322"} style={{ transition: "fill 300ms" }} />
    </g>
  );
}

/* ProcessTrain: a how-it-works section told as a railway line at dusk. Each step is a station with a yellow name board. The train runs from one to the next as the land slides past on three layers, a coach lights up at each stop, and pressing any stop on the route sends it there, backwards if needed. */
export function ProcessTrain({ steps = STEPS, hold = 3800, onArrive, className = "w-full max-w-3xl" }: ProcessTrainProps) {
  const reduce = useReducedMotion();
  const id = useId().replace(/[^a-zA-Z0-9]/g, "");
  const box = useRef<HTMLDivElement>(null);
  const scene = useRef<SVGSVGElement>(null);
  const seen = useInView(box, { once: true, amount: 0.35 });

  const n = steps.length;
  const end = n * GAP + 700;
  const [at, setAt] = useState(0); // where the train is heading
  const [here, setHere] = useState(-1); // where it stands, -1 while moving
  const [best, setBest] = useState(-1); // the furthest stop so far
  const [auto, setAuto] = useState(true);
  const [paused, setPaused] = useState(false);

  const cam = useRef(START);
  const vel = useRef(0);
  const puffs = useRef(Array.from({ length: PUFFS }, () => ({ x: 0, y: 0, age: 9, life: 1 })));
  const told = useRef(onArrive);

  useEffect(() => {
    told.current = onArrive;
  }, [onArrive]);

  useEffect(() => {
    if (!seen) return;
    const svg = scene.current;
    if (!svg) return;
    const world = svg.querySelector("[data-layer='world']");
    const mid = svg.querySelector("[data-layer='mid']");
    const far = svg.querySelector("[data-layer='far']");
    const rod = svg.querySelector("[data-rod]");
    const wheels = Array.from(svg.querySelectorAll("[data-wheel]"));
    const clouds = Array.from(svg.querySelectorAll("[data-puff]"));
    const target = at * GAP;
    let raf = 0;
    let last = performance.now();
    let chuff = 0;
    let stopped = false;
    // A far stop takes about as long as a near one: it just brakes harder.
    const brake = BRAKE * Math.max(1, Math.abs(target - cam.current) / GAP);

    const tick = (now: number) => {
      const dt = Math.min(0.05, (now - last) / 1000);
      last = now;

      if (reduce) {
        cam.current = target;
        vel.current = 0;
      } else {
        const d = target - cam.current;
        // Brakes at a steady rate, so it stops in a clean line, not by creeping in.
        const top = Math.max(230, Math.abs(d) / 1.2);
        const want = Math.sign(d) * Math.min(top, Math.sqrt(2 * brake * Math.abs(d)));
        const push = brake * 2.4 * dt;
        vel.current += Math.max(-push, Math.min(push, want - vel.current));
        cam.current += vel.current * dt;
        if (Math.abs(d) < 1.2) {
          cam.current = target;
          vel.current = 0;
        }
      }

      const x = cam.current;
      world?.setAttribute("transform", `translate(${-x} 0)`);
      mid?.setAttribute("transform", `translate(${-x * 0.45} 0)`);
      far?.setAttribute("transform", `translate(${-x * 0.14} 0)`);
      const turn = x / 11;
      for (const w of wheels) w.setAttribute("transform", `rotate(${((turn * 180) / Math.PI).toFixed(1)})`);
      rod?.setAttribute("transform", `translate(${(Math.cos(turn) * 5).toFixed(2)} ${(Math.sin(turn) * 5).toFixed(2)})`);

      // Smoke leaves the chimney and is left behind by the speed of the train.
      const speed = Math.abs(vel.current);
      chuff -= dt * (1 + speed / 70);
      if (chuff <= 0 && speed > 5 && !reduce) {
        chuff = 0.3;
        const free = puffs.current.find((p) => p.age >= p.life);
        if (free) {
          free.x = ENGINE + 94;
          free.y = RAIL - 72;
          free.age = 0;
          free.life = 1.1 + Math.random() * 0.7;
        }
      }
      let alive = false;
      puffs.current.forEach((p, i) => {
        const c = clouds[i];
        if (!c) return;
        if (p.age >= p.life) {
          c.setAttribute("opacity", "0");
          return;
        }
        alive = true;
        p.age += dt;
        p.x -= (vel.current * 0.75 + 9) * dt;
        p.y -= (26 - p.age * 10) * dt;
        const t = p.age / p.life;
        c.setAttribute("cx", p.x.toFixed(1));
        c.setAttribute("cy", p.y.toFixed(1));
        c.setAttribute("r", (4 + t * 15).toFixed(1));
        c.setAttribute("opacity", ((1 - t) * 0.62).toFixed(2));
      });

      const still = x === target;
      if (still && !stopped) {
        stopped = true;
        setHere(at);
        setBest((b) => Math.max(b, at));
        told.current?.(at);
      }
      if (!still || alive) raf = requestAnimationFrame(tick);
    };
    raf = requestAnimationFrame(tick);
    return () => cancelAnimationFrame(raf);
  }, [seen, at, reduce]);

  useEffect(() => {
    if (!auto || reduce || paused || here !== at || at >= n - 1) return;
    const t = setTimeout(() => {
      setHere(-1);
      setAt((a) => a + 1);
    }, hold);
    return () => clearTimeout(t);
  }, [auto, reduce, paused, here, at, n, hold]);

  const go = (i: number) => {
    setAuto(false);
    if (i === at) return;
    setHere(-1);
    setAt(i);
  };

  const step = steps[at];

  return (
    <div
      ref={box}
      className={`@container ${className}`}
      onPointerEnter={() => setPaused(true)}
      onPointerLeave={() => setPaused(false)}
      onFocusCapture={() => setPaused(true)}
      onBlurCapture={() => setPaused(false)}
    >
      <div className="overflow-hidden rounded-[2cqw]" style={{ fontSize: "clamp(11.5px, 3.3cqw, 18px)", boxShadow: "0 1.6cqw 4cqw #0008" }}>
        <svg ref={scene} viewBox={`0 0 ${W} ${H}`} className="block w-full" style={{ fontFamily: "system-ui, sans-serif" }} aria-hidden>
          <defs>
            <linearGradient id={`${id}sky`} x1="0" y1="0" x2="0" y2="1">
              <stop offset="0" stopColor="#3b2a6b" />
              <stop offset="0.45" stopColor="#c8506b" />
              <stop offset="0.8" stopColor="#f79f5a" />
            </linearGradient>
            <pattern id={`${id}ties`} x="0" y={RAIL} width="18" height="10" patternUnits="userSpaceOnUse">
              <rect x="3" y="1" width="9" height="7" fill="#4b3324" />
            </pattern>
          </defs>
          <rect width={W} height={H} fill={`url(#${id}sky)`} />
          <circle cx="500" cy="118" r="44" fill="#ffd27a" />
          <circle cx="500" cy="118" r="62" fill="#ffd27a" opacity="0.22" />

          <g data-layer="far" transform={`translate(${-START * 0.14} 0)`}>
            <path d={hills(-900, end, 136, 22, 1.2)} fill="#7b3a70" />
          </g>
          <g data-layer="mid" transform={`translate(${-START * 0.45} 0)`}>
            <path d={hills(-900, end, 166, 11, 3.1)} fill="#44295c" />
            {Array.from({ length: Math.ceil((end + 900) / 170) }, (_, i) => {
              const x = -900 + i * 170 + ROOF(i);
              const tall = 34 + (i % 3) * 9;
              return (
                <g key={i} transform={`translate(${x} ${172})`} fill="#2a1a3f" stroke="#2a1a3f">
                  <path d={`M0 0 Q 3 ${-tall / 2} 7 ${-tall}`} fill="none" strokeWidth="2.6" />
                  <g transform={`translate(7 ${-tall})`} strokeWidth="0">
                    <path d="M0 0 Q -14 -9 -24 3 Q -12 -3 0 0" />
                    <path d="M0 0 Q 13 -10 24 2 Q 12 -3 0 0" />
                    <path d="M0 0 Q -7 -15 -18 -14 Q -7 -8 0 0" />
                    <path d="M0 0 Q 7 -15 18 -15 Q 7 -8 0 0" />
                  </g>
                </g>
              );
            })}
          </g>

          <g data-layer="world" transform={`translate(${-START} 0)`}>
            <rect x="-900" y={RAIL - 12} width={end + 1800} height="60" fill="#2d2130" />
            {steps.map((s, i) => (
              <Station key={s.title} index={i} title={s.title} passed={i <= best && i < at} />
            ))}
            <rect x="-900" y={RAIL + 1} width={end + 1800} height="10" fill={`url(#${id}ties)`} />
            <rect x="-900" y={RAIL} width={end + 1800} height="2.6" fill="#c3c6cc" />
          </g>

          <g transform={`translate(${ENGINE} ${RAIL})`}>
            {/* Engine. Its nose points right. */}
            <rect x="-3" y="-20" width="116" height="4" fill="#a12a24" />
            <rect x="0" y="-64" width="36" height="44" rx="2" fill="#1f3a70" />
            <rect x="-4" y="-69" width="44" height="6" rx="2.5" fill="#17181d" />
            <rect x="9" y="-56" width="18" height="16" rx="1.5" fill="#ffd98a" />
            <rect x="36" y="-53" width="62" height="33" rx="9" fill="#2a4a8c" />
            {[46, 62, 78].map((bx) => (
              <rect key={bx} x={bx} y="-53" width="2.6" height="33" fill="#ecdfc0" opacity="0.75" />
            ))}
            <rect x="96" y="-55" width="12" height="37" rx="3" fill="#17181d" />
            <rect x="88" y="-71" width="11" height="18" fill="#17181d" />
            <rect x="85.5" y="-74" width="16" height="4.5" rx="1.5" fill="#17181d" />
            <circle cx="63" cy="-55" r="7" fill="#e8c56c" />
            <circle cx="104" cy="-38" r="4" fill="#ffefb0" />
            <circle cx="104" cy="-38" r="9" fill="#ffefb0" opacity="0.3" />
            <path d="M108 -16 L128 0 L106 0 Z" fill="#17181d" />
            <rect x="107" y="-26" width="7" height="10" fill="#a12a24" />
            <Wheel x={22} r={11} />
            <Wheel x={50} r={11} />
            <Wheel x={78} r={11} />
            <g data-rod="">
              <rect x="20" y="-13.5" width="60" height="3.2" rx="1.6" fill="#e8c56c" />
            </g>
            {steps.map((_, i) => (
              <Coach key={i} x={-(i + 1) * COACH} lit={i <= best} label={i + 1} />
            ))}
          </g>

          {Array.from({ length: PUFFS }, (_, i) => (
            <circle key={i} data-puff="" r="0" fill="#f3e6dc" opacity="0" />
          ))}
        </svg>

        <div className="flex items-start gap-[0.8em] px-[1em] py-[0.6em]" style={{ background: "#f7cb1a", color: "#17181d", borderTop: "0.16em solid #17181d" }}>
          <span className="grid size-[2.1em] shrink-0 place-items-center rounded-full text-[1.05em] font-extrabold" style={{ background: "#17181d", color: "#f7cb1a" }} aria-hidden>
            {at + 1}
          </span>
          <div className="min-w-0 flex-1" aria-live={auto ? "off" : "polite"}>
            <p className="m-0 flex items-baseline justify-between gap-[0.6em] leading-[1.2]">
              <span className="text-[1.15em] font-extrabold tracking-[0.02em]">{step?.title}</span>
              {step?.time && <span className="font-mono text-[0.85em] font-semibold whitespace-nowrap">{here === at ? step.time : "Arriving"}</span>}
            </p>
            <p className="m-0 mt-[0.15em] leading-[1.28]">{step?.text}</p>
          </div>
        </div>

        <ol className="relative m-0 flex list-none justify-between p-0 px-[1.2em] py-[0.42em]" style={{ background: "#17181d" }} aria-label="Stops on the line">
          <span className="absolute inset-x-[2.2em] top-1/2 h-[0.14em] -translate-y-1/2" style={{ background: "#555a66" }} aria-hidden />
          {steps.map((s, i) => {
            const now = i === at;
            return (
              <li key={s.title} className="relative">
                <button
                  type="button"
                  onClick={() => go(i)}
                  aria-current={now ? "step" : undefined}
                  aria-label={`Stop ${i + 1}, ${s.title}`}
                  className="grid size-[1.9em] min-h-6 min-w-6 cursor-pointer place-items-center rounded-full text-[0.86em] font-bold transition-colors"
                  style={{ background: now ? "#f7cb1a" : i <= best ? "#2a4a8c" : "#2c2e36", color: now ? "#17181d" : "#f1efe8" }}
                >
                  {i + 1}
                </button>
              </li>
            );
          })}
        </ol>
      </div>
    </div>
  );
}