import { isValidEan13 } from './barcode'

/**
 * Label-scale barcodes: EAN-13 in the GS1 restricted-circulation range
 * (prefix 20–29) with the item PLU and a weight or price embedded — the
 * supermarket produce path where every scan must be zero keystrokes.
 * Layout: [2-digit prefix][PLU][value][check]; PLU + value = 10 digits.
 * The layout is per-store scale configuration, hence a profile row.
 */
export interface ScaleBarcodeProfile {
  /** Which 2-digit prefixes this store's scales emit, e.g. ['21']. */
  prefixes: string[]
  pluLength: 4 | 5 | 6
  valueKind: 'weight' | 'price'
  /** value → quantity (weight: grams with divisor 1000 → kg) or paise. */
  valueDivisor: number
}

export type ScaleParse =
  | { kind: 'scale-weight'; plu: string; qty: number }
  | { kind: 'scale-price'; plu: string; pricePaise: number }
  | { kind: 'not-scale' }
  | { kind: 'invalid'; reason: string }

export function parseScaleBarcode(code: string, profile: ScaleBarcodeProfile): ScaleParse {
  if (!/^\d{13}$/.test(code)) return { kind: 'not-scale' }
  if (!profile.prefixes.includes(code.slice(0, 2))) return { kind: 'not-scale' }
  if (!isValidEan13(code)) return { kind: 'invalid', reason: 'check-digit' }
  const valueLength = 10 - profile.pluLength
  const plu = code.slice(2, 2 + profile.pluLength)
  const value = Number(code.slice(2 + profile.pluLength, 2 + profile.pluLength + valueLength))
  if (profile.valueKind === 'weight') {
    const qty = value / profile.valueDivisor
    if (qty <= 0) return { kind: 'invalid', reason: 'zero-weight' }
    return { kind: 'scale-weight', plu, qty }
  }
  return { kind: 'scale-price', plu, pricePaise: value }
}