use reqwest::header::{HeaderValue, ACCEPT};
use std::fmt::Debug;

/// Represents an ActivityPub inbox.
///
/// It routes an incoming Activity through the registered handlers.
///
/// # Example
///
/// ```rust
/// # extern crate activitypub;
/// # use activitypub::{actor::Person, activity::{Announce, Create}, object::Note};
/// # use plume_common::activity_pub::inbox::*;
/// # struct User;
/// # impl FromId<()> for User {
/// #     type Error = ();
/// #     type Object = Person;
/// #
/// #     fn from_db(_: &(), _id: &str) -> Result<Self, Self::Error> {
/// #         Ok(User)
/// #     }
/// #
/// #     fn from_activity(_: &(), obj: Person) -> Result<Self, Self::Error> {
/// #         Ok(User)
/// #     }
/// # }
/// # impl AsActor<&()> for User {
/// #    fn get_inbox_url(&self) -> String {
/// #        String::new()
/// #    }
/// #    fn is_local(&self) -> bool { false }
/// # }
/// # struct Message;
/// # impl FromId<()> for Message {
/// #     type Error = ();
/// #     type Object = Note;
/// #
/// #     fn from_db(_: &(), _id: &str) -> Result<Self, Self::Error> {
/// #         Ok(Message)
/// #     }
/// #
/// #     fn from_activity(_: &(), obj: Note) -> Result<Self, Self::Error> {
/// #         Ok(Message)
/// #     }
/// # }
/// # impl AsObject<User, Create, &()> for Message {
/// #     type Error = ();
/// #     type Output = ();
/// #
/// #     fn activity(self, _: &(), _actor: User, _id: &str) -> Result<(), ()> {
/// #         Ok(())
/// #     }
/// # }
/// # impl AsObject<User, Announce, &()> for Message {
/// #     type Error = ();
/// #     type Output = ();
/// #
/// #     fn activity(self, _: &(), _actor: User, _id: &str) -> Result<(), ()> {
/// #         Ok(())
/// #     }
/// # }
/// #
/// # let mut act = Create::default();
/// # act.object_props.set_id_string(String::from("https://test.ap/activity")).unwrap();
/// # let mut person = Person::default();
/// # person.object_props.set_id_string(String::from("https://test.ap/actor")).unwrap();
/// # act.create_props.set_actor_object(person).unwrap();
/// # act.create_props.set_object_object(Note::default()).unwrap();
/// # let activity_json = serde_json::to_value(act).unwrap();
/// #
/// # let conn = ();
/// #
/// let result: Result<(), ()> = Inbox::handle(&conn, activity_json)
///    .with::<User, Announce, Message>()
///    .with::<User, Create,   Message>()
///    .done();
/// ```
pub enum Inbox<'a, C, E, R>
where
    E: From<InboxError<E>> + Debug,
{
    /// The activity has not been handled yet
    ///
    /// # Structure
    ///
    /// - the context to be passed to each handler.
    /// - the activity
    /// - the reason it has not been handled yet
    NotHandled(&'a C, serde_json::Value, InboxError<E>),

    /// A matching handler have been found but failed
    ///
    /// The wrapped value is the error returned by the handler
    Failed(E),

    /// The activity was successfully handled
    ///
    /// The wrapped value is the value returned by the handler
    Handled(R),
}

/// Possible reasons of inbox failure
#[derive(Debug)]
pub enum InboxError<E: Debug> {
    /// None of the registered handlers matched
    NoMatch,

    /// No ID was provided for the incoming activity, or it was not a string
    InvalidID,

    /// The activity type matched for at least one handler, but then the actor was
    /// not of the expected type
    InvalidActor(Option<E>),

    /// Activity and Actor types matched, but not the Object
    InvalidObject(Option<E>),

    /// Error while dereferencing the object
    DerefError,
}

impl<T: Debug> From<InboxError<T>> for () {
    fn from(_: InboxError<T>) {}
}

/*
 Type arguments:
 - C: Context
 - E: Error
 - R: Result
*/
impl<'a, C, E, R> Inbox<'a, C, E, R>
where
    E: From<InboxError<E>> + Debug,
{
    /// Creates a new `Inbox` to handle an incoming activity.
    ///
    /// # Parameters
    ///
    /// - `ctx`: the context to pass to each handler
    /// - `json`: the JSON representation of the incoming activity
    pub fn handle(ctx: &'a C, json: serde_json::Value) -> Inbox<'a, C, E, R> {
        Inbox::NotHandled(ctx, json, InboxError::NoMatch)
    }

    /// Registers an handler on this Inbox.
    pub fn with<A, V, M>(self, proxy: Option<&reqwest::Proxy>) -> Inbox<'a, C, E, R>
    where
        A: AsActor<&'a C> + FromId<C, Error = E>,
        V: activitypub::Activity,
        M: AsObject<A, V, &'a C, Error = E> + FromId<C, Error = E>,
        M::Output: Into<R>,
    {
        if let Inbox::NotHandled(ctx, mut act, e) = self {
            if serde_json::from_value::<V>(act.clone()).is_ok() {
                let act_clone = act.clone();
                let act_id = match act_clone["id"].as_str() {
                    Some(x) => x,
                    None => return Inbox::NotHandled(ctx, act, InboxError::InvalidID),
                };

                // Get the actor ID
                let actor_id = match get_id(act["actor"].clone()) {
                    Some(x) => x,
                    None => return Inbox::NotHandled(ctx, act, InboxError::InvalidActor(None)),
                };

                if Self::is_spoofed_activity(&actor_id, &act) {
                    return Inbox::NotHandled(ctx, act, InboxError::InvalidObject(None));
                }

                // Transform this actor to a model (see FromId for details about the from_id function)
                let actor = match A::from_id(
                    ctx,
                    &actor_id,
                    serde_json::from_value(act["actor"].clone()).ok(),
                    proxy,
                ) {
                    Ok(a) => a,
                    // If the actor was not found, go to the next handler
                    Err((json, e)) => {
                        if let Some(json) = json {
                            act["actor"] = json;
                        }
                        return Inbox::NotHandled(ctx, act, InboxError::InvalidActor(Some(e)));
                    }
                };

                // Same logic for "object"
                let obj_id = match get_id(act["object"].clone()) {
                    Some(x) => x,
                    None => return Inbox::NotHandled(ctx, act, InboxError::InvalidObject(None)),
                };
                let obj = match M::from_id(
                    ctx,
                    &obj_id,
                    serde_json::from_value(act["object"].clone()).ok(),
                    proxy,
                ) {
                    Ok(o) => o,
                    Err((json, e)) => {
                        if let Some(json) = json {
                            act["object"] = json;
                        }
                        return Inbox::NotHandled(ctx, act, InboxError::InvalidObject(Some(e)));
                    }
                };

                // Handle the activity
                match obj.activity(ctx, actor, &act_id) {
                    Ok(res) => Inbox::Handled(res.into()),
                    Err(e) => Inbox::Failed(e),
                }
            } else {
                // If the Activity type is not matching the expected one for
                // this handler, try with the next one.
                Inbox::NotHandled(ctx, act, e)
            }
        } else {
            self
        }
    }

    /// Transforms the inbox in a `Result`
    pub fn done(self) -> Result<R, E> {
        match self {
            Inbox::Handled(res) => Ok(res),
            Inbox::NotHandled(_, _, err) => Err(E::from(err)),
            Inbox::Failed(err) => Err(err),
        }
    }

    fn is_spoofed_activity(actor_id: &str, act: &serde_json::Value) -> bool {
        use serde_json::Value::{Array, Object, String};

        let attributed_to = act["object"].get("attributedTo");
        if attributed_to.is_none() {
            return false;
        }
        let attributed_to = attributed_to.unwrap();
        match attributed_to {
            Array(v) => v.iter().all(|i| match i {
                String(s) => s != actor_id,
                Object(obj) => obj.get("id").map_or(true, |s| s != actor_id),
                _ => false,
            }),
            String(s) => s != actor_id,
            Object(obj) => obj.get("id").map_or(true, |s| s != actor_id),
            _ => false,
        }
    }
}

/// Get the ActivityPub ID of a JSON value.
///
/// If the value is a string, its value is returned.
/// If it is an object, and that its `id` field is a string, we return it.
///
/// Otherwise, `None` is returned.
fn get_id(json: serde_json::Value) -> Option<String> {
    match json {
        serde_json::Value::String(s) => Some(s),
        serde_json::Value::Object(map) => map.get("id")?.as_str().map(ToString::to_string),
        _ => None,
    }
}

/// A trait for ActivityPub objects that can be retrieved or constructed from ID.
///
/// The two functions to implement are `from_activity` to create (and save) a new object
/// of this type from its AP representation, and `from_db` to try to find it in the database
/// using its ID.
///
/// When dealing with the "object" field of incoming activities, `Inbox` will try to see if it is
/// a full object, and if so, save it with `from_activity`. If it is only an ID, it will try to find
/// it in the database with `from_db`, and otherwise dereference (fetch) the full object and parse it
/// with `from_activity`.
pub trait FromId<C>: Sized {
    /// The type representing a failure
    type Error: From<InboxError<Self::Error>> + Debug;

    /// The ActivityPub object type representing Self
    type Object: activitypub::Object;

    /// Tries to get an instance of `Self` from an ActivityPub ID.
    ///
    /// # Parameters
    ///
    /// - `ctx`: a context to get this instance (= a database in which to search)
    /// - `id`: the ActivityPub ID of the object to find
    /// - `object`: optional object that will be used if the object was not found in the database
    ///   If absent, the ID will be dereferenced.
    fn from_id(
        ctx: &C,
        id: &str,
        object: Option<Self::Object>,
        proxy: Option<&reqwest::Proxy>,
    ) -> Result<Self, (Option<serde_json::Value>, Self::Error)> {
        match Self::from_db(ctx, id) {
            Ok(x) => Ok(x),
            _ => match object {
                Some(o) => Self::from_activity(ctx, o).map_err(|e| (None, e)),
                None => Self::from_activity(ctx, Self::deref(id, proxy.cloned())?)
                    .map_err(|e| (None, e)),
            },
        }
    }

    /// Dereferences an ID
    fn deref(
        id: &str,
        proxy: Option<reqwest::Proxy>,
    ) -> Result<Self::Object, (Option<serde_json::Value>, Self::Error)> {
        if let Some(proxy) = proxy {
            reqwest::ClientBuilder::new().proxy(proxy)
        } else {
            reqwest::ClientBuilder::new()
        }
        .connect_timeout(Some(std::time::Duration::from_secs(5)))
        .build()
        .map_err(|_| (None, InboxError::DerefError.into()))?
        .get(id)
        .header(
            ACCEPT,
            HeaderValue::from_str(
                &super::ap_accept_header()
                    .into_iter()
                    .collect::<Vec<_>>()
                    .join(", "),
            )
            .map_err(|_| (None, InboxError::DerefError.into()))?,
        )
        .send()
        .map_err(|_| (None, InboxError::DerefError))
        .and_then(|mut r| {
            let json: serde_json::Value = r
                .json()
                .map_err(|_| (None, InboxError::InvalidObject(None)))?;
            serde_json::from_value(json.clone())
                .map_err(|_| (Some(json), InboxError::InvalidObject(None)))
        })
        .map_err(|(json, e)| (json, e.into()))
    }

    /// Builds a `Self` from its ActivityPub representation
    fn from_activity(ctx: &C, activity: Self::Object) -> Result<Self, Self::Error>;

    /// Tries to find a `Self` with a given ID (`id`), using `ctx` (a database)
    fn from_db(ctx: &C, id: &str) -> Result<Self, Self::Error>;
}

/// Should be implemented by anything representing an ActivityPub actor.
///
/// # Type arguments
///
/// - `C`: the context to be passed to this activity handler from the `Inbox` (usually a database connection)
pub trait AsActor<C> {
    /// Return the URL of this actor's inbox
    fn get_inbox_url(&self) -> String;

    /// If this actor has shared inbox, its URL should be returned by this function
    fn get_shared_inbox_url(&self) -> Option<String> {
        None
    }

    /// `true` if this actor comes from the running ActivityPub server/instance
    fn is_local(&self) -> bool;
}

/// Should be implemented by anything representing an ActivityPub object.
///
/// # Type parameters
///
/// - `A`: the actor type
/// - `V`: the ActivityPub verb/activity
/// - `O`: the ActivityPub type of the Object for this activity (usually the type corresponding to `Self`)
/// - `C`: the context needed to handle the activity (usually a database connection)
///
/// # Example
///
/// An implementation of AsObject that handles Note creation by an Account model,
/// representing the Note by a Message type, without any specific context.
///
/// ```rust
/// # extern crate activitypub;
/// # use activitypub::{activity::Create, actor::Person, object::Note};
/// # use plume_common::activity_pub::inbox::{AsActor, AsObject, FromId};
/// # struct Account;
/// # impl FromId<()> for Account {
/// #     type Error = ();
/// #     type Object = Person;
/// #
/// #     fn from_db(_: &(), _id: &str) -> Result<Self, Self::Error> {
/// #         Ok(Account)
/// #     }
/// #
/// #     fn from_activity(_: &(), obj: Person) -> Result<Self, Self::Error> {
/// #         Ok(Account)
/// #     }
/// # }
/// # impl AsActor<()> for Account {
/// #    fn get_inbox_url(&self) -> String {
/// #        String::new()
/// #    }
/// #    fn is_local(&self) -> bool { false }
/// # }
/// #[derive(Debug)]
/// struct Message {
///     text: String,
/// }
///
/// impl FromId<()> for Message {
///     type Error = ();
///     type Object = Note;
///
///     fn from_db(_: &(), _id: &str) -> Result<Self, Self::Error> {
///         Ok(Message { text: "From DB".into() })
///     }
///
///     fn from_activity(_: &(), obj: Note) -> Result<Self, Self::Error> {
///         Ok(Message { text: obj.object_props.content_string().map_err(|_| ())? })
///     }
/// }
///
/// impl AsObject<Account, Create, ()> for Message {
///     type Error = ();
///     type Output = ();
///
///     fn activity(self, _: (), _actor: Account, _id: &str) -> Result<(), ()> {
///         println!("New Note: {:?}", self);
///         Ok(())
///     }
/// }
/// ```
pub trait AsObject<A, V, C>
where
    V: activitypub::Activity,
{
    /// What kind of error is returned when something fails
    type Error;

    /// What is returned by `AsObject::activity`, if anything is returned
    type Output = ();

    /// Handle a specific type of activity dealing with this type of objects.
    ///
    /// The implementations should check that the actor is actually authorized
    /// to perform this action.
    ///
    /// # Parameters
    ///
    /// - `self`: the object on which the activity acts
    /// - `ctx`: the context passed to `Inbox::handle`
    /// - `actor`: the actor who did this activity
    /// - `id`: the ID of this activity
    fn activity(self, ctx: C, actor: A, id: &str) -> Result<Self::Output, Self::Error>;
}

#[cfg(test)]
mod tests {
    use super::*;
    use activitypub::{activity::*, actor::Person, object::Note};

    struct MyActor;
    impl FromId<()> for MyActor {
        type Error = ();
        type Object = Person;

        fn from_db(_: &(), _id: &str) -> Result<Self, Self::Error> {
            Ok(MyActor)
        }

        fn from_activity(_: &(), _obj: Person) -> Result<Self, Self::Error> {
            Ok(MyActor)
        }
    }

    impl AsActor<&()> for MyActor {
        fn get_inbox_url(&self) -> String {
            String::from("https://test.ap/my-actor/inbox")
        }

        fn is_local(&self) -> bool {
            false
        }
    }

    struct MyObject;
    impl FromId<()> for MyObject {
        type Error = ();
        type Object = Note;

        fn from_db(_: &(), _id: &str) -> Result<Self, Self::Error> {
            Ok(MyObject)
        }

        fn from_activity(_: &(), _obj: Note) -> Result<Self, Self::Error> {
            Ok(MyObject)
        }
    }
    impl AsObject<MyActor, Create, &()> for MyObject {
        type Error = ();
        type Output = ();

        fn activity(self, _: &(), _actor: MyActor, _id: &str) -> Result<Self::Output, Self::Error> {
            println!("MyActor is creating a Note");
            Ok(())
        }
    }

    impl AsObject<MyActor, Like, &()> for MyObject {
        type Error = ();
        type Output = ();

        fn activity(self, _: &(), _actor: MyActor, _id: &str) -> Result<Self::Output, Self::Error> {
            println!("MyActor is liking a Note");
            Ok(())
        }
    }

    impl AsObject<MyActor, Delete, &()> for MyObject {
        type Error = ();
        type Output = ();

        fn activity(self, _: &(), _actor: MyActor, _id: &str) -> Result<Self::Output, Self::Error> {
            println!("MyActor is deleting a Note");
            Ok(())
        }
    }

    impl AsObject<MyActor, Announce, &()> for MyObject {
        type Error = ();
        type Output = ();

        fn activity(self, _: &(), _actor: MyActor, _id: &str) -> Result<Self::Output, Self::Error> {
            println!("MyActor is announcing a Note");
            Ok(())
        }
    }

    fn build_create() -> Create {
        let mut act = Create::default();
        act.object_props
            .set_id_string(String::from("https://test.ap/activity"))
            .unwrap();
        let mut person = Person::default();
        person
            .object_props
            .set_id_string(String::from("https://test.ap/actor"))
            .unwrap();
        act.create_props.set_actor_object(person).unwrap();
        let mut note = Note::default();
        note.object_props
            .set_id_string(String::from("https://test.ap/note"))
            .unwrap();
        act.create_props.set_object_object(note).unwrap();
        act
    }

    #[test]
    fn test_inbox_basic() {
        let act = serde_json::to_value(build_create()).unwrap();
        let res: Result<(), ()> = Inbox::handle(&(), act)
            .with::<MyActor, Create, MyObject>(None)
            .done();
        assert!(res.is_ok());
    }

    #[test]
    fn test_inbox_multi_handlers() {
        let act = serde_json::to_value(build_create()).unwrap();
        let res: Result<(), ()> = Inbox::handle(&(), act)
            .with::<MyActor, Announce, MyObject>(None)
            .with::<MyActor, Delete, MyObject>(None)
            .with::<MyActor, Create, MyObject>(None)
            .with::<MyActor, Like, MyObject>(None)
            .done();
        assert!(res.is_ok());
    }

    #[test]
    fn test_inbox_failure() {
        let act = serde_json::to_value(build_create()).unwrap();
        // Create is not handled by this inbox
        let res: Result<(), ()> = Inbox::handle(&(), act)
            .with::<MyActor, Announce, MyObject>(None)
            .with::<MyActor, Like, MyObject>(None)
            .done();
        assert!(res.is_err());
    }

    struct FailingActor;
    impl FromId<()> for FailingActor {
        type Error = ();
        type Object = Person;

        fn from_db(_: &(), _id: &str) -> Result<Self, Self::Error> {
            Err(())
        }

        fn from_activity(_: &(), _obj: Person) -> Result<Self, Self::Error> {
            Err(())
        }
    }
    impl AsActor<&()> for FailingActor {
        fn get_inbox_url(&self) -> String {
            String::from("https://test.ap/failing-actor/inbox")
        }

        fn is_local(&self) -> bool {
            false
        }
    }

    impl AsObject<FailingActor, Create, &()> for MyObject {
        type Error = ();
        type Output = ();

        fn activity(
            self,
            _: &(),
            _actor: FailingActor,
            _id: &str,
        ) -> Result<Self::Output, Self::Error> {
            println!("FailingActor is creating a Note");
            Ok(())
        }
    }

    #[test]
    fn test_inbox_actor_failure() {
        let act = serde_json::to_value(build_create()).unwrap();

        let res: Result<(), ()> = Inbox::handle(&(), act.clone())
            .with::<FailingActor, Create, MyObject>(None)
            .done();
        assert!(res.is_err());

        let res: Result<(), ()> = Inbox::handle(&(), act.clone())
            .with::<FailingActor, Create, MyObject>(None)
            .with::<MyActor, Create, MyObject>(None)
            .done();
        assert!(res.is_ok());
    }
}