import { MOTION } from './design-tokens.js';
import { routePoints } from './geometry.js';

// Timing follows actual path length, so a piece beside an exit has no fixed
// wait. Cruising speed is one constant for every piece — until the knee. Past
// it the piece accelerates instead of taking longer, because uncapped linear
// timing ran a single departure to seventeen seconds and reads as a stall
// rather than as a journey. Callers may override the ceiling to compare
// settings; labs/exit-timing does exactly that.
export function exitTiming(route,{knee=MOTION.exitMaxTravelMs,maxMs=MOTION.exitLongMaxMs}={}) {
  const points=routePoints({...route,end:null},{size:1,ox:0,oy:0});
  const distance=points.slice(1).reduce((sum,p,i)=>sum+Math.hypot(p.x-points[i].x,p.y-points[i].y),0);
  const linear=distance*MOTION.exitMsPerUnit;
  // Below the knee nothing changes: same speed as before, same feel.
  const base=linear<=knee?linear
    :Math.min(maxMs,knee+(linear-knee)*Math.max(0,(maxMs-knee))/Math.max(1,linear-knee)*(1-Math.exp(-(linear-knee)/Math.max(1,maxMs-knee))));
  const rampMs=Math.min(MOTION.exitRampMs,base/3);
  const travelMs=base+rampMs;
  const duration=travelMs+MOTION.exitEffectMs;
  return {duration,travelMs,distance,travelFraction:travelMs/duration,capped:linear>knee};
}

// Zero endpoint velocity: a soft launch and a settled finish, without overshoot.
export function smoothMotion(value) {
  const t=Math.max(0,Math.min(1,value));
  return t*t*(3-2*t);
}

// Fixed-duration acceleration and braking; the middle travels at a shared speed.
export function travelProgress(progress,travelMs){
  const t=Math.max(0,Math.min(1,progress))*travelMs;
  const ramp=Math.min(MOTION.exitRampMs,travelMs/4),area=travelMs-ramp;
  if(t<ramp)return t*t/(2*ramp*area);
  if(t>travelMs-ramp)return 1-(travelMs-t)**2/(2*ramp*area);
  return (t-ramp/2)/area;
}