interface ColorRGB {
  r: number;
  g: number;
  b: number;
}

interface ContrastResult {
  passes: boolean;
  ratio: number;
  requiredRatio: number;
}

function hexToRgb(hex: string): ColorRGB {
  const cleanHex = hex.replace('#', '');
  const r = parseInt(cleanHex.substring(0, 2), 16);
  const g = parseInt(cleanHex.substring(2, 4), 16);
  const b = parseInt(cleanHex.substring(4, 6), 16);
  return { r, g, b };
}

function getLuminance(rgb: ColorRGB): number {
  const { r, g, b } = rgb;
  const values = [r, g, b].map(v => {
    const normalized = v / 255;
    return normalized <= 0.03928 ? normalized / 12.92 : Math.pow((normalized + 0.055) / 1.055, 2.4);
  });
  return values[0]! * 0.2126 + values[1]! * 0.7152 + values[2]! * 0.0722;
}

export function calculateContrastRatio(foreground: string, background: string): number {
  const fgRgb = hexToRgb(foreground);
  const bgRgb = hexToRgb(background);
  
  const fgLuminance = getLuminance(fgRgb);
  const bgLuminance = getLuminance(bgRgb);
  
  const lighter = Math.max(fgLuminance, bgLuminance);
  const darker = Math.min(fgLuminance, bgLuminance);
  
  return (lighter + 0.05) / (darker + 0.05);
}

export function meetsWCAGStandard(
  foreground: string,
  background: string,
  level: 'AA' | 'AAA' = 'AA',
  textSize: 'normal' | 'large' = 'normal'
): ContrastResult {
  const ratio = calculateContrastRatio(foreground, background);
  
  const requiredRatio = level === 'AAA'
    ? (textSize === 'large' ? 4.5 : 7)
    : (textSize === 'large' ? 3 : 4.5);
  
  return {
    passes: ratio >= requiredRatio,
    ratio,
    requiredRatio,
  };
}