import { parseBigInt } from './parseBigInt.ts'

export interface NumberToBigIntOptions {
  /**
   * The number of digits starting from the right of the returned bigint to consider as decimal
   * places.
   *
   * @default 18n
   */
  precision?: bigint | undefined
}

/**
 * Converts a number to a bigint. Decimals to the right of `precision` are truncated.
 *
 * @param value - The number to convert to a bigint.
 * @param options - Conversion options.
 * @returns The bigint representation of `value`
 */
export function numberToBigInt(value: number, options?: NumberToBigIntOptions): bigint {
  const { precision = 18n } = options ?? {}
  if (precision < 0n) {
    throw new Error(`[numberToBigInt] \`precision\` must be positive, got ${precision}`)
  }
  // If `value` has decimals and `precision` is at least 1, parse it as a string
  if (value % 1 !== 0 && precision >= 1n) {
    const parsedValue = parseBigInt(String(value), { precision })
    if (parsedValue === null) {
      throw new Error(
        `[numberToBigInt] Failed to parse ${value} as a bigint with precision ${precision}`,
      )
    }
    return parsedValue
  } else {
    const precisionFactor = 10n ** precision
    return BigInt(Math.trunc(value)) * precisionFactor
  }
}