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

    const rect = containerRef.current.getBoundingClientRect();
    const y = clientY - rect.top;
    // Inverted: top = max (1), bottom = min (0)
    const percentage = Math.max(0, Math.min(1, 1 - (y / rect.height)));
    onChange(percentage);
  };

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

  return (
    <div className={cn('flex gap-2', className)}>
      {/* dB Labels (Left) */}
      <div className="flex flex-col justify-between text-[9px] 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-10 h-32 bg-background/50 rounded-md border border-border/50 cursor-pointer"
        onMouseDown={handleMouseDown}
      >
        {/* Peak Meter (Horizontal Bar - Top) */}
        <div className="absolute inset-x-1.5 top-1.5 h-2.5 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-1.5 bottom-1.5 h-2.5 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-400' :
              rmsDb > -6 ? 'bg-yellow-400' :
              'bg-green-400'
            )} />
          </div>
        </div>

        {/* Fader Track */}
        <div className="absolute top-6 bottom-6 left-1/2 -translate-x-1/2 w-1 bg-muted/50 rounded-full" />

        {/* Fader Handle */}
        <div
          className="absolute left-1/2 -translate-x-1/2 w-9 h-3.5 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, value 0 = bottom
            top: `calc(${(1 - value) * 100}% - 0.4375rem)`,
          }}
        >
          {/* Handle grip lines */}
          <div className="absolute inset-0 flex items-center justify-center gap-0.5">
            <div className="h-1.5 w-px bg-primary-foreground/30" />
            <div className="h-1.5 w-px bg-primary-foreground/30" />
            <div className="h-1.5 w-px bg-primary-foreground/30" />
          </div>
        </div>

        {/* dB Scale Markers */}
        <div className="absolute inset-0 px-1.5 py-6 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 Display (Right) */}
      <div className="flex flex-col justify-center items-start text-[9px] font-mono">
        {/* Current dB Value */}
        <div className={cn(
          'font-bold text-[10px]',
          valueDb > -3 ? 'text-red-500' :
          valueDb > -6 ? 'text-yellow-500' :
          'text-green-500'
        )}>
          {valueDb > -60 ? `${valueDb.toFixed(1)}` : '-∞'}
        </div>
      </div>
    </div>
  );
}