audio-ui/components/tracks/TrackFader.tsx

'use client';

import * as React from 'react';
import { cn } from '@/lib/utils/cn';

export interface TrackFaderProps {
  value: number;
  peakLevel: number;
  rmsLevel: number;
  onChange: (value: number) => void;
  onTouchStart?: () => void;
  onTouchEnd?: () => void;
  className?: string;
}

export function TrackFader({
  value,
  peakLevel,
  rmsLevel,
  onChange,
  onTouchStart,
  onTouchEnd,
  className,
}: TrackFaderProps) {
  const [isDragging, setIsDragging] = React.useState(false);
  const containerRef = React.useRef<HTMLDivElement>(null);

  // Convert linear 0-1 to dB scale for display
  const linearToDb = (linear: number): number => {
    if (linear === 0) return -60;
    const db = 20 * Math.log10(linear);
    return Math.max(-60, Math.min(0, db));
  };

  const valueDb = linearToDb(value);
  const peakDb = linearToDb(peakLevel);
  const rmsDb = linearToDb(rmsLevel);

  // Calculate bar widths (0-100%)
  const peakWidth = ((peakDb + 60) / 60) * 100;
  const rmsWidth = ((rmsDb + 60) / 60) * 100;

  const handleMouseDown = (e: React.MouseEvent) => {
    e.preventDefault();
    setIsDragging(true);
    onTouchStart?.();
    updateValue(e.clientY);
  };

  const handleMouseMove = React.useCallback(
    (e: MouseEvent) => {
      if (!isDragging) return;
      updateValue(e.clientY);
    },
    [isDragging]
  );

  const handleMouseUp = React.useCallback(() => {
    setIsDragging(false);
    onTouchEnd?.();
  }, [onTouchEnd]);

  const handleTouchStart = (e: React.TouchEvent) => {
    e.preventDefault();
    const touch = e.touches[0];
    setIsDragging(true);
    onTouchStart?.();
    updateValue(touch.clientY);
  };

  const handleTouchMove = React.useCallback(
    (e: TouchEvent) => {
      if (!isDragging || e.touches.length === 0) return;
      const touch = e.touches[0];
      updateValue(touch.clientY);
    },
    [isDragging]
  );

  const handleTouchEnd = React.useCallback(() => {
    setIsDragging(false);
    onTouchEnd?.();
  }, [onTouchEnd]);

  const updateValue = (clientY: number) => {
    if (!containerRef.current) return;

    const rect = containerRef.current.getBoundingClientRect();
    const y = clientY - rect.top;

    // Track has 32px (2rem) padding on top and bottom (top-8 bottom-8)
    const trackPadding = 32;
    const trackHeight = rect.height - (trackPadding * 2);

    // Clamp y to track bounds
    const clampedY = Math.max(trackPadding, Math.min(rect.height - trackPadding, y));

    // Inverted: top = max (1), bottom = min (0)
    // Map clampedY from [trackPadding, height-trackPadding] to [1, 0]
    const percentage = 1 - ((clampedY - trackPadding) / trackHeight);
    onChange(Math.max(0, Math.min(1, percentage)));
  };

  React.useEffect(() => {
    if (isDragging) {
      window.addEventListener('mousemove', handleMouseMove);
      window.addEventListener('mouseup', handleMouseUp);
      window.addEventListener('touchmove', handleTouchMove);
      window.addEventListener('touchend', handleTouchEnd);
      return () => {
        window.removeEventListener('mousemove', handleMouseMove);
        window.removeEventListener('mouseup', handleMouseUp);
        window.removeEventListener('touchmove', handleTouchMove);
        window.removeEventListener('touchend', handleTouchEnd);
      };
    }
  }, [isDragging, handleMouseMove, handleMouseUp, handleTouchMove, handleTouchEnd]);

  return (
    <div className={cn('flex gap-3', className)} style={{ marginLeft: '16px' }}>
      {/* dB Labels (Left) */}
      <div className="flex flex-col justify-between text-[10px] font-mono text-muted-foreground py-1">
        <span>0</span>
        <span>-12</span>
        <span>-24</span>
        <span>-60</span>
      </div>

      {/* Fader Container */}
      <div
        ref={containerRef}
        className="relative w-12 h-40 bg-background/50 rounded-md border border-border/50 cursor-pointer"
        onMouseDown={handleMouseDown}
        onTouchStart={handleTouchStart}
      >
        {/* Peak Meter (Horizontal Bar - Top) */}
        <div className="absolute inset-x-2 top-2 h-3 bg-background/80 rounded-sm overflow-hidden border border-border/30">
          <div
            className="absolute left-0 top-0 bottom-0 transition-all duration-75 ease-out"
            style={{ width: `${Math.max(0, Math.min(100, peakWidth))}%` }}
          >
            <div className={cn(
              'w-full h-full',
              peakDb > -3 ? 'bg-red-500' :
              peakDb > -6 ? 'bg-yellow-500' :
              'bg-green-500'
            )} />
          </div>
        </div>

        {/* RMS Meter (Horizontal Bar - Bottom) */}
        <div className="absolute inset-x-2 bottom-2 h-3 bg-background/80 rounded-sm overflow-hidden border border-border/30">
          <div
            className="absolute left-0 top-0 bottom-0 transition-all duration-150 ease-out"
            style={{ width: `${Math.max(0, Math.min(100, rmsWidth))}%` }}
          >
            <div className={cn(
              'w-full h-full',
              rmsDb > -3 ? 'bg-red-500' :
              rmsDb > -6 ? 'bg-yellow-500' :
              'bg-green-500'
            )} />
          </div>
        </div>

        {/* Fader Track */}
        <div className="absolute top-8 bottom-8 left-1/2 -translate-x-1/2 w-1.5 bg-muted/50 rounded-full" />

        {/* Fader Handle */}
        <div
          className="absolute left-1/2 -translate-x-1/2 w-10 h-4 bg-primary/80 border-2 border-primary rounded-md shadow-lg cursor-grab active:cursor-grabbing pointer-events-none transition-all"
          style={{
            // Inverted: value 1 = top of track (20%), value 0 = bottom of track (80%)
            // Track has top-8 bottom-8 padding (20% and 80% of h-40 container)
            // Handle moves within 60% range (from 20% to 80%)
            top: `calc(${20 + (1 - value) * 60}% - 0.5rem)`,
          }}
        >
          {/* Handle grip lines */}
          <div className="absolute inset-0 flex items-center justify-center gap-0.5">
            <div className="h-2 w-px bg-primary-foreground/30" />
            <div className="h-2 w-px bg-primary-foreground/30" />
            <div className="h-2 w-px bg-primary-foreground/30" />
          </div>
        </div>

        {/* dB Scale Markers */}
        <div className="absolute inset-0 px-2 py-8 pointer-events-none">
          <div className="relative h-full">
            {/* -12 dB */}
            <div className="absolute left-0 right-0 h-px bg-border/20" style={{ top: '50%' }} />
            {/* -6 dB */}
            <div className="absolute left-0 right-0 h-px bg-yellow-500/20" style={{ top: '20%' }} />
            {/* -3 dB */}
            <div className="absolute left-0 right-0 h-px bg-red-500/30" style={{ top: '10%' }} />
          </div>
        </div>
      </div>

      {/* Value and Level Display (Right) */}
      <div className="flex flex-col justify-between items-start text-[9px] font-mono py-1 w-[36px]">
        {/* Current dB Value */}
        <div className={cn(
          'font-bold text-[11px]',
          valueDb > -3 ? 'text-red-500' :
          valueDb > -6 ? 'text-yellow-500' :
          'text-green-500'
        )}>
          {valueDb > -60 ? `${valueDb.toFixed(1)}` : '-∞'}
        </div>

        {/* Spacer */}
        <div className="flex-1" />

        {/* Peak Level */}
        <div className="flex flex-col items-start">
          <span className="text-muted-foreground/60">PK</span>
          <span className={cn(
            'font-mono text-[10px]',
            peakDb > -3 ? 'text-red-500' :
            peakDb > -6 ? 'text-yellow-500' :
            'text-green-500'
          )}>
            {peakDb > -60 ? `${peakDb.toFixed(1)}` : '-∞'}
          </span>
        </div>

        {/* RMS Level */}
        <div className="flex flex-col items-start">
          <span className="text-muted-foreground/60">RM</span>
          <span className={cn(
            'font-mono text-[10px]',
            rmsDb > -3 ? 'text-red-500' :
            rmsDb > -6 ? 'text-yellow-500' :
            'text-green-500'
          )}>
            {rmsDb > -60 ? `${rmsDb.toFixed(1)}` : '-∞'}
          </span>
        </div>

        {/* dB Label */}
        <span className="text-muted-foreground/60 text-[8px]">dB</span>
      </div>
    </div>
  );
}