const internalCredentialBearerRegexp = /^Bearer\s+(.+)$/i

// Bearer credential 的标准文本形态是 "Bearer <token>"。
// 这个辅助函数统一去掉多余空白和 Bearer 前缀，使判断、格式化和解析共享同一条规范化规则。
const internalNormalizeBearerToken = (token: string): string => {
  return token.trim().replace(/^Bearer\s+/i, "")
}

/**
 * @description 判断输入值是否为 Bearer 凭据字符串。
 *
 * @example
 *   ```
 *   // Expect: true
 *   const example1 = isBearerCredential("Bearer token-value")
 *   // Expect: false
 *   const example2 = isBearerCredential("Basic token-value")
 *   ```
 */
export const isBearerCredential = (input: string): boolean => {
  return internalCredentialBearerRegexp.test(input.trim())
}

/**
 * @description 把原始 token 格式化为 Bearer 凭据字符串。
 *
 * 当输入值只包含空白字符时，该函数会抛出 RangeError，避免产出一个连 Bearer 校验器都不会接受的无效凭据字符串。
 *
 * @example
 *   ```
 *   // Expect: "Bearer token-value"
 *   const example1 = formatBearerCredential("token-value")
 *   // Expect: "Bearer token-value"
 *   const example2 = formatBearerCredential("  token-value  ")
 *   // Expect: throws RangeError
 *   const example3 = () => formatBearerCredential("   ")
 *   ```
 */
export const formatBearerCredential = (token: string): string => {
  const normalizedToken = internalNormalizeBearerToken(token)

  if (normalizedToken.length === 0) {
    throw new RangeError("Expected token to contain at least one non-whitespace character")
  }

  return `Bearer ${normalizedToken}`
}

/**
 * @description 从 Bearer 凭据字符串中提取原始 token。
 *
 * 当输入值不是 Bearer 格式时，该函数返回 `undefined`。
 *
 * @example
 *   ```
 *   // Expect: "token-value"
 *   const example1 = parseBearerCredential("Bearer token-value")
 *   // Expect: undefined
 *   const example2 = parseBearerCredential("Basic token-value")
 *   ```
 */
export const parseBearerCredential = (input: string | undefined): string | undefined => {
  if (input === undefined) {
    return undefined
  }

  if (isBearerCredential(input) === false) {
    return undefined
  }

  const normalizedToken = internalNormalizeBearerToken(input)
  return normalizedToken.length === 0 ? undefined : normalizedToken
}