// Warranty period helpers. Periods are always stored in months; custom ones are the active
// rows of the Warranty Periods master and are only offered while
// ProductConfig.customWarrantyPeriodsEnabled is on.
import { ProductConfig, WARRANTY_PERIOD_MONTHS_OPTIONS } from "@/types/master-data"

/** Server limit (WarrantyPeriodService) — mirrored so forms fail fast. */
export const MAX_CUSTOM_WARRANTY_MONTHS = 600

/** "6 months", "1 month", or "24 months (2 years)" when it's a whole number of years. */
export function formatWarrantyPeriod(months: number): string {
  const base = `${months} month${months === 1 ? "" : "s"}`
  if (months >= 12 && months % 12 === 0) {
    const years = months / 12
    return `${base} (${years} year${years === 1 ? "" : "s"})`
  }
  return base
}

export type WarrantyInputUnit = "months" | "years"

/**
 * Validates a typed length ("2" + years) against the existing active custom periods and
 * converts it to months. Returns the months, or an error message fit to show under the input.
 */
export function parseWarrantyInput(
  amount: string,
  unit: WarrantyInputUnit,
  existingCustom: number[],
): { months: number; error?: undefined } | { months?: undefined; error: string } {
  const n = Number(amount)
  if (!amount.trim() || !Number.isInteger(n) || n < 1) return { error: "Enter a whole number of 1 or more." }
  const months = unit === "years" ? n * 12 : n
  if (months > MAX_CUSTOM_WARRANTY_MONTHS)
    return { error: `A warranty period can be at most ${MAX_CUSTOM_WARRANTY_MONTHS} months (50 years).` }
  if ((WARRANTY_PERIOD_MONTHS_OPTIONS as readonly number[]).includes(months))
    return { error: `${formatWarrantyPeriod(months)} is already a default period.` }
  if (existingCustom.includes(months)) return { error: `${formatWarrantyPeriod(months)} already exists.` }
  return { months }
}

/** The period choices for an item: the defaults, plus the active custom ones when enabled. */
export function warrantyPeriodGroups(
  config: ProductConfig | null,
  customMonths: number[],
): { defaults: number[]; custom: number[] } {
  const defaults: number[] = [...WARRANTY_PERIOD_MONTHS_OPTIONS]
  const custom = config?.customWarrantyPeriodsEnabled
    ? [...new Set(customMonths)].filter((m) => !defaults.includes(m)).sort((a, b) => a - b)
    : []
  return { defaults, custom }
}