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//! This module defines several types and provides some low-level functions.

use chrono::datetime::{DateTime};
use chrono::naive::datetime::{NaiveDateTime};
use chrono::offset::utc::{UTC};
use rustc_serialize::{Decodable, Decoder, Encodable, Encoder, json};
use rustc_serialize::json::{Json};
use std::ops::Deref;

/// Abstraction for a type wrapper around a generic type.
///
/// It is helpful to put application-specific type wrappers around generic
/// types.  For example, `UserId` and `SessinoId` are really `String` values.
/// But wrapping them in specific types allows to compiler to catch errors, such
/// as arguments that are given in the wrong order.
pub trait Newtype<T: Deref> {
    fn unwrap(self) -> T;
    fn as_slice(&self) -> &<T as Deref>::Target;
}

macro_rules! typed_string {
    ($t:ident) => (
        #[derive(PartialEq, Eq, Clone, Debug)]
        pub struct $t(String);

        impl $t {
            pub fn new(s: String) -> $t {
                $t(s)
            }

            pub fn from_slice(s: &str) -> $t {
                $t(s.to_string())
            }
        }

        impl Newtype<String> for $t {
            fn unwrap(self) -> String {
                let $t(v) = self;
                v
            }
            fn as_slice(&self) -> &str {
                let &$t(ref v) = self;
                v.as_slice()
            }
        }

        impl Decodable for $t {
            fn decode<D: Decoder>(d: &mut D) -> Result<$t, D::Error> {
                d.read_str().map($t::new)
            }
        }

        impl Encodable for $t {
            fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
                s.emit_str(self.as_slice())
            }
        }

        impl json::ToJson for $t {
            fn to_json(&self) -> Json {
                Json::String(self.as_slice().to_string())
            }
        }
    )
}

/// Value that will be an input in signature made by the Tozny app
typed_string!(Challenge);

/// Type for realm key ids
///
/// A realm key id identifies a realm; and when paired with its corresponding
/// secret acts as a credential to make realm-level API calls.
typed_string!(KeyId);

/// When making an API call, specifies which API method will be invoked.
typed_string!(Method);

/// Token that matches up with a specific mobile device.
///
/// A `Presence` value is used to send a push notification to a device, so that
/// the user does not have to scan a QR code.  The response from the
/// `login_challenge` method on `UserApi` includes a `Presence` value.  Store
/// the value to keep track of which device was last used to log into an
/// account.
typed_string!(Presence);

/// Shared secret that proves ownership of a realm key.
typed_string!(Secret);

/// Generated by Tozny; matches a successful authentication event with an
/// application session.
///
/// The response from the `login_challenge` method on `UserApi` includes
/// a `SessionId`.  Use that value when calling `check_session_status` to
/// determine whether the user has authenticated.
typed_string!(SessionId);

/// Specifies which cryptographic algorithm was used to sign a message.
typed_string!(SignatureType);

/// Identifies a Tozny user.
typed_string!(UserId);

/// Wraps a `DateTime<UTC>` value; implements serialization into the format
/// expected by the Tozny API.
#[derive(PartialEq, Eq, Clone, Debug)]
pub struct Timestamp(DateTime<UTC>);

impl Timestamp {
    pub fn new(t: DateTime<UTC>) -> Timestamp {
        Timestamp(t)
    }

    pub fn unwrap(self) -> DateTime<UTC> {
        let Timestamp(t) = self;
        t
    }

    pub fn as_slice(&self) -> &DateTime<UTC> {
        let &Timestamp(ref t) = self;
        t
    }
}

fn int_to_timestamp(seconds: i64) -> Timestamp {
    let naive = NaiveDateTime::from_num_seconds_from_unix_epoch(seconds, 0);
    Timestamp(DateTime::from_utc(naive, UTC))
}

impl Decodable for Timestamp {
    fn decode<D: Decoder>(d: &mut D) -> Result<Timestamp, D::Error> {
        d.read_i64().map(int_to_timestamp)
    }
}

/// Given a time, produces a string representing that time as the number of
/// seconds since January 1, 1970.
impl Encodable for Timestamp {
    fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
        let &Timestamp(ref t) = self;
        let seconds = t.num_seconds_from_unix_epoch();
        s.emit_i64(seconds)
    }
}

impl json::ToJson for Timestamp {
    fn to_json(&self) -> Json {
        Json::I64(self.as_slice().num_seconds_from_unix_epoch())
    }
}

/// Extracts error messages from a Tozny API response.
pub fn error_response(json: &Json) -> Option<&Json> {
    json.find("return")
    .and_then(|val| { val.as_string() })
    .and_then(|ret| {
        if ret == "error" {
            json.find("errors")
        }
        else {
            None
        }
    })
}