use std::sync::Arc;
use chrono::Utc;
use domain::{
    errors::DomainError,
    events::DomainEvent,
    models::notification::{Notification, NotificationType},
    ports::{NotificationRepository, ThoughtRepository},
    value_objects::NotificationId,
};

/// Handles domain events that should create notifications for users.
pub struct NotificationHandler {
    pub thoughts:      Arc<dyn ThoughtRepository>,
    pub notifications: Arc<dyn NotificationRepository>,
}

impl NotificationHandler {
    pub async fn handle(&self, event: &DomainEvent) -> Result<(), DomainError> {
        match event {
            DomainEvent::LikeAdded { like_id: _, user_id, thought_id } => {
                let thought = match self.thoughts.find_by_id(thought_id).await? {
                    Some(t) => t,
                    None => return Ok(()), // thought deleted — skip
                };
                if thought.user_id == *user_id { return Ok(()); } // no self-notifications
                self.notifications.save(&Notification {
                    id: NotificationId::new(),
                    user_id: thought.user_id,
                    notification_type: NotificationType::Like,
                    from_user_id: Some(user_id.clone()),
                    thought_id: Some(thought_id.clone()),
                    read: false,
                    created_at: Utc::now(),
                }).await
            }
            DomainEvent::BoostAdded { boost_id: _, user_id, thought_id } => {
                let thought = match self.thoughts.find_by_id(thought_id).await? {
                    Some(t) => t,
                    None => return Ok(()),
                };
                if thought.user_id == *user_id { return Ok(()); }
                self.notifications.save(&Notification {
                    id: NotificationId::new(),
                    user_id: thought.user_id,
                    notification_type: NotificationType::Boost,
                    from_user_id: Some(user_id.clone()),
                    thought_id: Some(thought_id.clone()),
                    read: false,
                    created_at: Utc::now(),
                }).await
            }
            DomainEvent::FollowAccepted { follower_id, following_id } => {
                // The person being followed (following_id) gets notified
                self.notifications.save(&Notification {
                    id: NotificationId::new(),
                    user_id: following_id.clone(),
                    notification_type: NotificationType::Follow,
                    from_user_id: Some(follower_id.clone()),
                    thought_id: None,
                    read: false,
                    created_at: Utc::now(),
                }).await
            }
            DomainEvent::ThoughtCreated { thought_id, user_id, in_reply_to_id } => {
                let reply_to_id = match in_reply_to_id {
                    Some(id) => id,
                    None => return Ok(()), // not a reply
                };
                let original = match self.thoughts.find_by_id(reply_to_id).await? {
                    Some(t) => t,
                    None => return Ok(()), // original deleted
                };
                if original.user_id == *user_id { return Ok(()); } // no self-notifications
                self.notifications.save(&Notification {
                    id: NotificationId::new(),
                    user_id: original.user_id,
                    notification_type: NotificationType::Reply,
                    from_user_id: Some(user_id.clone()),
                    thought_id: Some(thought_id.clone()),
                    read: false,
                    created_at: Utc::now(),
                }).await
            }
            // All other events: no notification needed in Plan 3
            _ => Ok(()),
        }
    }
}

/// Stub handler for ActivityPub federation — implemented in Plan 4.
pub struct FederationHandler;

impl FederationHandler {
    pub async fn handle(&self, event: &DomainEvent) -> Result<(), DomainError> {
        tracing::debug!(?event, "federation handler (stub — Plan 4)");
        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use domain::{
        models::{thought::{Thought, Visibility}, user::User},
        testing::TestStore,
        value_objects::*,
    };
    use std::sync::Arc;

    fn alice() -> User {
        User::new_local(
            UserId::new(),
            Username::new("alice").unwrap(),
            Email::new("alice@ex.com").unwrap(),
            PasswordHash("h".into()),
        )
    }

    #[tokio::test]
    async fn like_added_creates_notification_for_thought_author() {
        let store = TestStore::default();
        let alice = alice();
        let bob_id = UserId::new();

        let thought = Thought::new_local(
            ThoughtId::new(), alice.id.clone(),
            Content::new_local("hello").unwrap(),
            None, Visibility::Public, None, false,
        );
        store.users.lock().unwrap().push(alice.clone());
        store.thoughts.lock().unwrap().push(thought.clone());

        let handler = NotificationHandler {
            thoughts:      Arc::new(store.clone()),
            notifications: Arc::new(store.clone()),
        };

        handler.handle(&DomainEvent::LikeAdded {
            like_id: LikeId::new(),
            user_id: bob_id.clone(),
            thought_id: thought.id.clone(),
        }).await.unwrap();

        let notifs = store.notifications.lock().unwrap();
        assert_eq!(notifs.len(), 1);
        assert_eq!(notifs[0].user_id, alice.id);
        assert!(matches!(notifs[0].notification_type, NotificationType::Like));
    }

    #[tokio::test]
    async fn self_like_does_not_create_notification() {
        let store = TestStore::default();
        let alice = alice();
        let thought = Thought::new_local(
            ThoughtId::new(), alice.id.clone(),
            Content::new_local("hello").unwrap(),
            None, Visibility::Public, None, false,
        );
        store.users.lock().unwrap().push(alice.clone());
        store.thoughts.lock().unwrap().push(thought.clone());

        let handler = NotificationHandler {
            thoughts:      Arc::new(store.clone()),
            notifications: Arc::new(store.clone()),
        };

        handler.handle(&DomainEvent::LikeAdded {
            like_id: LikeId::new(),
            user_id: alice.id.clone(),
            thought_id: thought.id.clone(),
        }).await.unwrap();

        assert!(store.notifications.lock().unwrap().is_empty());
    }

    #[tokio::test]
    async fn follow_accepted_creates_notification() {
        let store = TestStore::default();
        let alice = alice();
        let bob_id = UserId::new();
        store.users.lock().unwrap().push(alice.clone());

        let handler = NotificationHandler {
            thoughts:      Arc::new(store.clone()),
            notifications: Arc::new(store.clone()),
        };

        handler.handle(&DomainEvent::FollowAccepted {
            follower_id: bob_id.clone(),
            following_id: alice.id.clone(),
        }).await.unwrap();

        let notifs = store.notifications.lock().unwrap();
        assert_eq!(notifs.len(), 1);
        assert_eq!(notifs[0].user_id, alice.id);
        assert!(matches!(notifs[0].notification_type, NotificationType::Follow));
    }

    #[tokio::test]
    async fn reply_creates_notification_for_original_author() {
        let store = TestStore::default();
        let alice = alice();
        let bob_id = UserId::new();

        let original = Thought::new_local(
            ThoughtId::new(), alice.id.clone(),
            Content::new_local("original thought").unwrap(),
            None, Visibility::Public, None, false,
        );
        store.users.lock().unwrap().push(alice.clone());
        store.thoughts.lock().unwrap().push(original.clone());

        let handler = NotificationHandler {
            thoughts:      Arc::new(store.clone()),
            notifications: Arc::new(store.clone()),
        };

        handler.handle(&DomainEvent::ThoughtCreated {
            thought_id: ThoughtId::new(),
            user_id: bob_id.clone(),
            in_reply_to_id: Some(original.id.clone()),
        }).await.unwrap();

        let notifs = store.notifications.lock().unwrap();
        assert_eq!(notifs.len(), 1);
        assert_eq!(notifs[0].user_id, alice.id);
        assert!(matches!(notifs[0].notification_type, NotificationType::Reply));
    }

    #[tokio::test]
    async fn self_reply_does_not_create_notification() {
        let store = TestStore::default();
        let alice = alice();
        let original = Thought::new_local(
            ThoughtId::new(), alice.id.clone(),
            Content::new_local("original").unwrap(),
            None, Visibility::Public, None, false,
        );
        store.users.lock().unwrap().push(alice.clone());
        store.thoughts.lock().unwrap().push(original.clone());

        let handler = NotificationHandler {
            thoughts:      Arc::new(store.clone()),
            notifications: Arc::new(store.clone()),
        };

        handler.handle(&DomainEvent::ThoughtCreated {
            thought_id: ThoughtId::new(),
            user_id: alice.id.clone(),
            in_reply_to_id: Some(original.id.clone()),
        }).await.unwrap();

        assert!(store.notifications.lock().unwrap().is_empty());
    }

    #[tokio::test]
    async fn thought_without_reply_to_creates_no_notification() {
        let store = TestStore::default();
        let alice = alice();
        store.users.lock().unwrap().push(alice.clone());

        let handler = NotificationHandler {
            thoughts:      Arc::new(store.clone()),
            notifications: Arc::new(store.clone()),
        };

        handler.handle(&DomainEvent::ThoughtCreated {
            thought_id: ThoughtId::new(),
            user_id: alice.id.clone(),
            in_reply_to_id: None,
        }).await.unwrap();

        assert!(store.notifications.lock().unwrap().is_empty());
    }
}