// Pure logic of the live tools. No React here, so it stays easy to test.

export type OutputTone = "default" | "muted" | "success" | "error"
export type OutputLine = { text: string; tone?: OutputTone }

/* ── Contrast check (WCAG 2.2) ──────────────────────────────────────── */

export function parseHex(input: string): [number, number, number] | null {
  const hex = input.trim().replace(/^#/, "")
  const full =
    hex.length === 3
      ? hex
          .split("")
          .map((c) => c + c)
          .join("")
      : hex
  if (!/^[0-9a-f]{6}$/i.test(full)) return null
  return [0, 2, 4].map((i) => parseInt(full.slice(i, i + 2), 16)) as [
    number,
    number,
    number,
  ]
}

function relativeLuminance([r, g, b]: [number, number, number]) {
  const channel = (value: number) => {
    const c = value / 255
    return c <= 0.04045 ? c / 12.92 : ((c + 0.055) / 1.055) ** 2.4
  }
  return 0.2126 * channel(r) + 0.7152 * channel(g) + 0.0722 * channel(b)
}

export function contrastRatio(
  a: [number, number, number],
  b: [number, number, number]
) {
  const [light, dark] = [relativeLuminance(a), relativeLuminance(b)].sort(
    (x, y) => y - x
  )
  return (light + 0.05) / (dark + 0.05)
}

export function runContrastCheck(fg: string, bg: string): OutputLine[] {
  const command: OutputLine = {
    text: `$ kontrast --text ${fg} --hintergrund ${bg}`,
    tone: "muted",
  }
  const fgRgb = parseHex(fg)
  const bgRgb = parseHex(bg)

  if (!fgRgb || !bgRgb) {
    return [
      command,
      { text: "fehler: bitte Farben als Hex angeben, z. B. #1a1a1a", tone: "error" },
    ]
  }

  // Floor instead of round, otherwise 4.499 would be reported as passing 4.5
  const ratio = Math.floor(contrastRatio(fgRgb, bgRgb) * 100) / 100
  const check = (label: string, min: number): OutputLine => {
    const pass = ratio >= min
    return {
      text: `${label.padEnd(22)}${pass ? "bestanden" : "nicht bestanden"}  (min. ${min}:1)`,
      tone: pass ? "success" : "error",
    }
  }

  return [
    command,
    { text: `verhältnis             ${ratio.toFixed(2)} : 1` },
    check("AA fließtext", 4.5),
    check("AA große schrift", 3),
    check("AA bedienelemente", 3),
    check("AAA fließtext", 7),
  ]
}

/* ── Search snippet check ───────────────────────────────────────────── */

const TITLE_RANGE = [30, 60] as const
const DESCRIPTION_RANGE = [70, 160] as const

function rangeLine(
  label: string,
  length: number,
  [min, max]: readonly [number, number]
): OutputLine {
  const ok = length >= min && length <= max
  const hint = length < min ? "zu kurz" : length > max ? "wird abgeschnitten" : "passt"
  return {
    text: `${label.padEnd(16)}${String(length).padStart(3)} zeichen  ${hint}  (${min}–${max})`,
    tone: ok ? "success" : "error",
  }
}

export function runSnippetCheck(title: string, description: string): OutputLine[] {
  const lines: OutputLine[] = [
    { text: "$ snippet --pruefen", tone: "muted" },
    rangeLine("titel", title.trim().length, TITLE_RANGE),
    rangeLine("beschreibung", description.trim().length, DESCRIPTION_RANGE),
  ]

  const titleWords = new Set(
    title
      .toLowerCase()
      .split(/[^\p{L}\p{N}]+/u)
      .filter((word) => word.length > 3)
  )
  const shared = description
    .toLowerCase()
    .split(/[^\p{L}\p{N}]+/u)
    .filter((word) => titleWords.has(word))

  lines.push(
    shared.length > 0
      ? { text: `suchbegriff      in beiden: ${[...new Set(shared)].join(", ")}`, tone: "success" }
      : {
          text: "suchbegriff      titel und beschreibung teilen kein wort",
          tone: "error",
        }
  )

  return lines
}

export function truncate(text: string, max: number) {
  const trimmed = text.trim()
  return trimmed.length > max ? `${trimmed.slice(0, max - 1).trimEnd()} …` : trimmed
}