/** Small formatting helpers shared by the list views. */

function pad(value: number): string {
  return String(value).padStart(2, '0')
}

/**
 * Render a backend timestamp as `YYYY-MM-DD HH:mm`.
 *
 * The API sends naive local datetimes (`2026-09-18T07:46:40`). Per the ES
 * date-time spec a date-time string without an offset is parsed as *local*
 * time, which is what the server clock already is, so no conversion happens.
 */
export function formatDateTime(value: string | null | undefined): string {
  if (!value) return '—'

  const date = new Date(value)
  if (Number.isNaN(date.getTime())) return value

  return (
    `${date.getFullYear()}-${pad(date.getMonth() + 1)}-${pad(date.getDate())} ` +
    `${pad(date.getHours())}:${pad(date.getMinutes())}`
  )
}

/**
 * Inline style that renders a field the way the paper would.
 *
 * `pt` is a real CSS unit, so 10.5pt shows at the same size it will print at.
 */
export function typographyStyle(field: {
  font_size: number
  font_color: string
}): Record<string, string> {
  return {
    fontSize: `${field.font_size}pt`,
    color: field.font_color,
  }
}

/** Indentation for a heading level: level 1 flush, each deeper level inset. */
export function levelIndent(level: number): string {
  return `${Math.max(0, level - 1) * 18}px`
}

const HEX_PATTERN = /^#?([0-9a-fA-F]{3}|[0-9a-fA-F]{6})$/
const RGB_PATTERN = /^rgba?\(\s*(\d{1,3})\s*,\s*(\d{1,3})\s*,\s*(\d{1,3})\s*(?:,\s*[\d.]+\s*)?\)$/

/**
 * Normalise a colour spelling to `#RRGGBB`, or `null` if unrecognised.
 *
 * Mirrors `normalize_hex_color` on the backend. Doing it here as well means a
 * hand-typed `rgb(255, 0, 0)` is tidied up the moment the field loses focus,
 * instead of travelling to the server to be rejected.
 */
export function normalizeHexColor(value: string): string | null {
  const text = value.trim()

  const rgbMatch = RGB_PATTERN.exec(text)
  if (rgbMatch) {
    const channels = rgbMatch.slice(1, 4).map(Number)
    if (channels.some((channel) => channel > 255)) return null
    return `#${channels.map((channel) => channel.toString(16).padStart(2, '0')).join('')}`.toUpperCase()
  }

  const hexMatch = HEX_PATTERN.exec(text)
  if (hexMatch) {
    const digits = hexMatch[1]!
    const full = digits.length === 3 ? digits.replace(/./g, (char) => char + char) : digits
    return `#${full.toUpperCase()}`
  }

  return null
}