/**
 * Contraste des pastilles libellé (liste mails) : luminance WCAG + choix texte blanc / foncé.
 * Les classes `bg-*` sont résolues en hex (palette Tailwind v3 alignée sur les swatches UI).
 */

/** Luminance relative WCAG 2.1 (sRGB, composantes linéaires 0–1). */
export function relativeLuminanceFromSrgbLinear(r: number, g: number, b: number): number {
  return 0.2126 * r + 0.7152 * g + 0.0722 * b
}

function srgbChannelToLinear(c255: number): number {
  const c = c255 / 255
  return c <= 0.03928 ? c / 12.92 : Math.pow((c + 0.055) / 1.055, 2.4)
}

export function hexToRgb(hex: string): [number, number, number] | null {
  const h = hex.trim().replace(/^#/, "")
  if (h.length === 3) {
    const r = parseInt(h[0]! + h[0]!, 16)
    const g = parseInt(h[1]! + h[1]!, 16)
    const b = parseInt(h[2]! + h[2]!, 16)
    if ([r, g, b].some((x) => Number.isNaN(x))) return null
    return [r, g, b]
  }
  if (h.length === 6 || h.length === 8) {
    const r = parseInt(h.slice(0, 2), 16)
    const g = parseInt(h.slice(2, 4), 16)
    const b = parseInt(h.slice(4, 6), 16)
    if ([r, g, b].some((x) => Number.isNaN(x))) return null
    return [r, g, b]
  }
  return null
}

export function relativeLuminanceFromHex(hex: string): number {
  const rgb = hexToRgb(hex)
  if (!rgb) return 0.5
  const [r, g, b] = rgb.map(srgbChannelToLinear) as [number, number, number]
  return relativeLuminanceFromSrgbLinear(r, g, b)
}

/** Ratio de contraste WCAG entre deux luminances (symétrique). */
function contrastRatio(L1: number, L2: number): number {
  const hi = Math.max(L1, L2) + 0.05
  const lo = Math.min(L1, L2) + 0.05
  return hi / lo
}

/** « Chroma » simple sur sRGB 8 bits (0 = gris, plus la valeur monte, plus la couleur est vive). */
function rgb255Chroma(rgb: [number, number, number]): number {
  const [r, g, b] = rgb
  return (Math.max(r, g, b) - Math.min(r, g, b)) / 255
}

/**
 * Choisit blanc ou quasi-noir sur le fond : biais vers le blanc, prise en compte de la saturation
 * (les pastelles saturées type Gmail restent en blanc au lieu de basculer en noir par la seule luminance).
 */
export function labelPillPreferredTextHexOnBackground(bgHex: string): "#ffffff" | "#202124" {
  const rgb = hexToRgb(bgHex)
  if (!rgb) return "#202124"
  const Lbg = relativeLuminanceFromHex(bgHex)
  const chroma = rgb255Chroma(rgb)
  const [r255, g255, b255] = rgb

  // Presque blanc / gris très clair : texte foncé
  if (Lbg >= 0.88 && chroma < 0.12) return "#202124"

  // Fond très sombre : blanc
  if (Lbg <= 0.2) return "#ffffff"

  // Jaune / ambre très clair (peu de bleu, forte composante R+G) : noir plus lisible
  if (
    Lbg >= 0.62 &&
    b255 < 110 &&
    r255 > 185 &&
    g255 > 165 &&
    chroma >= 0.18
  ) {
    return "#202124"
  }

  // Couleurs assez vives et pas trop claires : privilégier le blanc (pastilles type Gmail)
  if (chroma >= 0.12 && Lbg < 0.78) return "#ffffff"

  // Gris / couleurs très désaturées au milieu du spectre de luminance : biais blanc sur le score WCAG
  const rWhite = contrastRatio(Lbg, 1)
  const rBlack = contrastRatio(Lbg, 0)
  const WHITE_BIAS = 1.28
  return rWhite * WHITE_BIAS >= rBlack ? "#ffffff" : "#202124"
}

export function labelPillTextClassForBgHex(bgHex: string): string {
  return labelPillPreferredTextHexOnBackground(bgHex) === "#ffffff"
    ? "text-white/90"
    : "text-[#202124]"
}

/** Palette Tailwind v3 (sRGB) — familles × nuances utilisées par la sidebar / données. */
const TW_BG_HEX = new Map<string, string>([
  // gray
  ["bg-gray-300", "#d1d5db"],
  ["bg-gray-400", "#9ca3af"],
  ["bg-gray-500", "#6b7280"],
  ["bg-gray-600", "#4b5563"],
  ["bg-gray-700", "#374151"],
  // slate
  ["bg-slate-300", "#cbd5e1"],
  ["bg-slate-400", "#94a3b8"],
  ["bg-slate-500", "#64748b"],
  ["bg-slate-600", "#475569"],
  ["bg-slate-700", "#334155"],
  // red
  ["bg-red-300", "#fca5a5"],
  ["bg-red-400", "#f87171"],
  ["bg-red-500", "#ef4444"],
  ["bg-red-600", "#dc2626"],
  ["bg-red-700", "#b91c1c"],
  // orange
  ["bg-orange-300", "#fdba74"],
  ["bg-orange-400", "#fb923c"],
  ["bg-orange-500", "#f97316"],
  ["bg-orange-600", "#ea580c"],
  ["bg-orange-700", "#c2410c"],
  // amber
  ["bg-amber-300", "#fcd34d"],
  ["bg-amber-400", "#fbbf24"],
  ["bg-amber-500", "#f59e0b"],
  ["bg-amber-600", "#d97706"],
  ["bg-amber-700", "#b45309"],
  // yellow
  ["bg-yellow-300", "#fde047"],
  ["bg-yellow-400", "#facc15"],
  ["bg-yellow-500", "#eab308"],
  ["bg-yellow-600", "#ca8a04"],
  ["bg-yellow-700", "#a16207"],
  // lime
  ["bg-lime-300", "#bef264"],
  ["bg-lime-400", "#a3e635"],
  ["bg-lime-500", "#84cc16"],
  ["bg-lime-600", "#65a30d"],
  ["bg-lime-700", "#4d7c0f"],
  // emerald
  ["bg-emerald-300", "#6ee7b7"],
  ["bg-emerald-400", "#34d399"],
  ["bg-emerald-500", "#10b981"],
  ["bg-emerald-600", "#059669"],
  ["bg-emerald-700", "#047857"],
  // teal
  ["bg-teal-300", "#5eead4"],
  ["bg-teal-400", "#2dd4bf"],
  ["bg-teal-500", "#14b8a6"],
  ["bg-teal-600", "#0d9488"],
  ["bg-teal-700", "#0f766e"],
  // cyan
  ["bg-cyan-400", "#22d3ee"],
  ["bg-cyan-500", "#06b6d4"],
  // sky
  ["bg-sky-300", "#7dd3fc"],
  ["bg-sky-400", "#38bdf8"],
  ["bg-sky-500", "#0ea5e9"],
  ["bg-sky-600", "#0284c7"],
  ["bg-sky-700", "#0369a1"],
  // blue
  ["bg-blue-300", "#93c5fd"],
  ["bg-blue-400", "#60a5fa"],
  ["bg-blue-500", "#3b82f6"],
  ["bg-blue-600", "#2563eb"],
  ["bg-blue-700", "#1d4ed8"],
  // indigo
  ["bg-indigo-300", "#a5b4fc"],
  ["bg-indigo-400", "#818cf8"],
  ["bg-indigo-500", "#6366f1"],
  ["bg-indigo-600", "#4f46e5"],
  ["bg-indigo-700", "#4338ca"],
  // violet
  ["bg-violet-400", "#a78bfa"],
  ["bg-violet-500", "#8b5cf6"],
  // purple
  ["bg-purple-300", "#d8b4fe"],
  ["bg-purple-400", "#c084fc"],
  ["bg-purple-500", "#a855f7"],
  ["bg-purple-600", "#9333ea"],
  ["bg-purple-700", "#7e22ce"],
  // fuchsia
  ["bg-fuchsia-500", "#d946ef"],
  // pink
  ["bg-pink-300", "#f9a8d4"],
  ["bg-pink-400", "#f472b6"],
  ["bg-pink-500", "#ec4899"],
  ["bg-pink-600", "#db2777"],
  ["bg-pink-700", "#be185d"],
  // green
  ["bg-green-400", "#4ade80"],
  ["bg-green-500", "#22c55e"],
  // rose
  ["bg-rose-400", "#fb7185"],
  ["bg-rose-500", "#f43f5e"],
])

export function tailwindBgUtilityToHex(bgClass: string): string | null {
  return TW_BG_HEX.get(bgClass.trim()) ?? null
}

/** Classes Tailwind `text-[...]` pour pastille sur fond `bg-*`. */
export function labelPillTextClassForTailwindBgUtility(bgClass: string): string {
  const hex = tailwindBgUtilityToHex(bgClass)
  if (!hex) {
    const c = bgClass.toLowerCase()
    if (/(^|-)(gray|slate|zinc|stone|neutral)(-|$)/.test(c)) return "text-[#202124]"
    return "text-white/90"
  }
  return labelPillTextClassForBgHex(hex)
}