use std::error::Error as StdError;
use std::fmt;
use std::result;

use base64;
use serde_json;

/// A crate private constructor for `Error`.
pub(crate) fn new_error(kind: ErrorKind) -> Error {
    Error(Box::new(kind))
}

/// A type alias for `Result<T, jsonwebtoken::Error>`.
pub type Result<T> = result::Result<T, Error>;

/// An error that can occur when encoding/decoding JWTs
#[derive(Debug)]
pub struct Error(Box<ErrorKind>);

impl Error {
    /// Return the specific type of this error.
    pub fn kind(&self) -> &ErrorKind {
        &self.0
    }

    /// Unwrap this error into its underlying type.
    pub fn into_kind(self) -> ErrorKind {
        *self.0
    }
}

/// The specific type of an error.
#[derive(Debug)]
pub enum ErrorKind {
    /// When a token doesn't have a valid JWT shape
    InvalidToken,
    /// When the signature doesn't match
    InvalidSignature,
    /// When the secret given is not a valid RSA key
    InvalidRsaKey,
    /// When the algorithm from string doesn't match the one passed to `from_str`
    InvalidAlgorithmName,

    // validation error
    /// When a token’s `exp` claim indicates that it has expired
    ExpiredSignature,
    /// When a token’s `iss` claim does not match the expected issuer
    InvalidIssuer,
    /// When a token’s `aud` claim does not match one of the expected audience values
    InvalidAudience,
    /// When a token’s `aud` claim does not match one of the expected audience values
    InvalidSubject,
    /// When a token’s `iat` claim is in the future
    InvalidIssuedAt,
    /// When a token’s nbf claim represents a time in the future
    ImmatureSignature,
    /// When the algorithm in the header doesn't match the one passed to `decode`
    InvalidAlgorithm,

    // 3rd party errors
    /// An error happened when decoding some base64 text
    Base64(base64::DecodeError),
    /// An error happened while serializing/deserializing JSON
    Json(serde_json::Error),
    /// Some of the text was invalid UTF-8
    Utf8(::std::string::FromUtf8Error),

    /// Hints that destructuring should not be exhaustive.
    ///
    /// This enum may grow additional variants, so this makes sure clients
    /// don't count on exhaustive matching. (Otherwise, adding a new variant
    /// could break existing code.)
    #[doc(hidden)]
    __Nonexhaustive,
}

impl StdError for Error {
    fn description(&self) -> &str {
        match *self.0 {
            ErrorKind::InvalidToken => "invalid token",
            ErrorKind::InvalidSignature => "invalid signature",
            ErrorKind::InvalidRsaKey => "invalid RSA key",
            ErrorKind::ExpiredSignature => "expired signature",
            ErrorKind::InvalidIssuer => "invalid issuer",
            ErrorKind::InvalidAudience => "invalid audience",
            ErrorKind::InvalidSubject => "invalid subject",
            ErrorKind::InvalidIssuedAt => "invalid issued at",
            ErrorKind::ImmatureSignature => "immature signature",
            ErrorKind::InvalidAlgorithm => "algorithms don't match",
            ErrorKind::Base64(ref err) => err.description(),
            ErrorKind::Json(ref err) => err.description(),
            ErrorKind::Utf8(ref err) => err.description(),
            _ => unreachable!(),
        }
    }

    fn cause(&self) -> Option<&StdError> {
        match *self.0 {
            ErrorKind::InvalidToken => None,
            ErrorKind::InvalidSignature => None,
            ErrorKind::InvalidRsaKey => None,
            ErrorKind::ExpiredSignature => None,
            ErrorKind::InvalidIssuer => None,
            ErrorKind::InvalidAudience => None,
            ErrorKind::InvalidSubject => None,
            ErrorKind::InvalidIssuedAt => None,
            ErrorKind::ImmatureSignature => None,
            ErrorKind::InvalidAlgorithm => None,
            ErrorKind::Base64(ref err) => Some(err),
            ErrorKind::Json(ref err) => Some(err),
            ErrorKind::Utf8(ref err) => Some(err),
            _ => unreachable!(),
        }
    }
}

impl fmt::Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self.0 {
            ErrorKind::InvalidToken => write!(f, "invalid token"),
            ErrorKind::InvalidSignature => write!(f, "invalid signature"),
            ErrorKind::InvalidRsaKey => write!(f, "invalid RSA key"),
            ErrorKind::ExpiredSignature => write!(f, "expired signature"),
            ErrorKind::InvalidIssuer => write!(f, "invalid issuer"),
            ErrorKind::InvalidAudience => write!(f, "invalid audience"),
            ErrorKind::InvalidSubject => write!(f, "invalid subject"),
            ErrorKind::InvalidIssuedAt => write!(f, "invalid issued at"),
            ErrorKind::ImmatureSignature => write!(f, "immature signature"),
            ErrorKind::InvalidAlgorithm => write!(f, "algorithms don't match"),
            ErrorKind::Base64(ref err) => write!(f, "base64 error: {}", err),
            ErrorKind::Json(ref err) => write!(f, "JSON error: {}", err),
            ErrorKind::Utf8(ref err) => write!(f, "UTF-8 error: {}", err),
            _ => unreachable!(),
        }
    }
}

impl From<base64::DecodeError> for Error {
    fn from(err: base64::DecodeError) -> Error {
        new_error(ErrorKind::Base64(err))
    }
}

impl From<serde_json::Error> for Error {
    fn from(err: serde_json::Error) -> Error {
        new_error(ErrorKind::Json(err))
    }
}

impl From<::std::string::FromUtf8Error> for Error {
    fn from(err: ::std::string::FromUtf8Error) -> Error {
        new_error(ErrorKind::Utf8(err))
    }
}

impl From<ErrorKind> for Error {
    fn from(kind: ErrorKind) -> Error {
        new_error(kind)
    }
}