//! Delivery domain logic — enqueue, fetch, peek, ack.
//!
//! Pure business logic operating on `Store` trait and domain types.
//!
//! ## Multi-device delivery
//!
//! When a message is enqueued for a recipient identity, the service resolves
//! all registered device IDs for that identity and enqueues a copy of the
//! payload to each device-scoped queue. The queue key is a composite of
//! `identity_key + device_id`, so each device maintains its own sequence
//! counter and ack state.
//!
//! If the recipient has no registered devices, the message is delivered to
//! the bare `identity_key` queue (backwards compatible with single-device
//! clients).

use std::sync::Arc;

use dashmap::DashMap;
use tokio::sync::Notify;

use crate::storage::Store;

use super::types::*;

/// Build a device-scoped recipient key: `identity_key || device_id`.
/// When `device_id` is empty, returns a clone of `identity_key` (single-device compat).
fn device_recipient_key(identity_key: &[u8], device_id: &[u8]) -> Vec<u8> {
    if device_id.is_empty() {
        return identity_key.to_vec();
    }
    let mut key = Vec::with_capacity(identity_key.len() + device_id.len());
    key.extend_from_slice(identity_key);
    key.extend_from_slice(device_id);
    key
}

/// Shared state needed by delivery operations.
pub struct DeliveryService {
    pub store: Arc<dyn Store>,
    pub waiters: Arc<DashMap<Vec<u8>, Arc<Notify>>>,
}

impl DeliveryService {
    /// Resolve the device-scoped recipient keys for an identity.
    /// Returns a list of composite keys (identity_key + device_id) for each
    /// registered device. If no devices are registered, returns a single-element
    /// list with the bare identity_key for backwards compatibility.
    fn resolve_device_keys(&self, identity_key: &[u8]) -> Vec<Vec<u8>> {
        let devices = self.store.list_devices(identity_key).unwrap_or_default();
        if devices.is_empty() {
            vec![identity_key.to_vec()]
        } else {
            devices
                .into_iter()
                .map(|(device_id, _, _)| device_recipient_key(identity_key, &device_id))
                .collect()
        }
    }

    /// Wake any long-polling waiter for the given recipient key.
    fn wake_waiter(&self, recipient_key: &[u8]) {
        if let Some(notify) = self.waiters.get(recipient_key) {
            notify.notify_one();
        }
    }

    /// Enqueue a payload for delivery to all devices of the recipient.
    ///
    /// Returns the sequence number from the *first* device queue (for backwards
    /// compatibility with single-device callers).
    pub fn enqueue(&self, req: EnqueueReq) -> Result<EnqueueResp, crate::storage::StorageError> {
        let ttl = if req.ttl_secs > 0 {
            Some(req.ttl_secs)
        } else {
            None
        };

        let device_keys = self.resolve_device_keys(&req.recipient_key);
        let mut first_seq = 0;

        for (i, dk) in device_keys.iter().enumerate() {
            let start = std::time::Instant::now();
            let seq = self.store.enqueue(
                dk,
                &req.channel_id,
                req.payload.clone(),
                ttl,
            )?;
            crate::metrics::record_storage_latency("enqueue", start.elapsed());
            if i == 0 {
                first_seq = seq;
            }
            self.wake_waiter(dk);
        }

        // Also wake the bare identity_key waiter (legacy clients).
        self.wake_waiter(&req.recipient_key);

        Ok(EnqueueResp {
            seq: first_seq,
            delivery_proof: Vec::new(), // Proof generated at RPC handler layer (see v2_handlers/delivery.rs)
        })
    }

    /// Fetch and drain queued messages for a specific device.
    ///
    /// The `recipient_key` should be the device-scoped composite key
    /// (`identity_key + device_id`) or bare `identity_key` for single-device.
    pub fn fetch(&self, req: FetchReq) -> Result<FetchResp, crate::storage::StorageError> {
        let start = std::time::Instant::now();
        let messages = if req.limit > 0 {
            self.store
                .fetch_limited(&req.recipient_key, &req.channel_id, req.limit as usize)?
        } else {
            self.store.fetch(&req.recipient_key, &req.channel_id)?
        };
        crate::metrics::record_storage_latency("fetch", start.elapsed());

        Ok(FetchResp {
            payloads: messages
                .into_iter()
                .map(|(seq, data)| Envelope { seq, data })
                .collect(),
        })
    }

    /// Peek at messages without removing them.
    pub fn peek(&self, req: PeekReq) -> Result<PeekResp, crate::storage::StorageError> {
        let messages = self.store.peek(
            &req.recipient_key,
            &req.channel_id,
            if req.limit > 0 { req.limit as usize } else { 0 },
        )?;

        Ok(PeekResp {
            payloads: messages
                .into_iter()
                .map(|(seq, data)| Envelope { seq, data })
                .collect(),
        })
    }

    /// Acknowledge messages up to a sequence number.
    pub fn ack(&self, req: AckReq) -> Result<(), crate::storage::StorageError> {
        self.store
            .ack(&req.recipient_key, &req.channel_id, req.seq_up_to)?;
        Ok(())
    }

    /// Batch enqueue to multiple recipients (with multi-device fan-out for each).
    ///
    /// Returns one sequence number per recipient identity (from the first device queue).
    pub fn batch_enqueue(
        &self,
        req: BatchEnqueueReq,
    ) -> Result<BatchEnqueueResp, crate::storage::StorageError> {
        let ttl = if req.ttl_secs > 0 {
            Some(req.ttl_secs)
        } else {
            None
        };

        let mut seqs = Vec::with_capacity(req.recipient_keys.len());
        for rk in &req.recipient_keys {
            let device_keys = self.resolve_device_keys(rk);
            let mut first_seq = 0;

            for (i, dk) in device_keys.iter().enumerate() {
                let seq = self.store.enqueue(dk, &req.channel_id, req.payload.clone(), ttl)?;
                if i == 0 {
                    first_seq = seq;
                }
                self.wake_waiter(dk);
            }

            self.wake_waiter(rk);
            seqs.push(first_seq);
        }

        Ok(BatchEnqueueResp { seqs })
    }

    /// Build a device-scoped recipient key from identity_key and device_id.
    /// Public helper for RPC handlers to build the correct fetch/ack key.
    pub fn device_recipient_key(identity_key: &[u8], device_id: &[u8]) -> Vec<u8> {
        device_recipient_key(identity_key, device_id)
    }
}

#[cfg(test)]
#[allow(clippy::unwrap_used)]
mod tests {
    use super::*;
    use crate::storage::FileBackedStore;

    fn test_service() -> (tempfile::TempDir, DeliveryService) {
        let dir = tempfile::tempdir().unwrap();
        let store = Arc::new(FileBackedStore::open(dir.path()).unwrap());
        let svc = DeliveryService {
            store,
            waiters: Arc::new(DashMap::new()),
        };
        (dir, svc)
    }

    #[test]
    fn enqueue_single_device_backwards_compat() {
        let (_dir, svc) = test_service();
        let ik = vec![1u8; 32];
        let ch = vec![0u8; 16];

        // No devices registered — should enqueue to bare identity_key.
        let resp = svc
            .enqueue(EnqueueReq {
                recipient_key: ik.clone(),
                payload: b"hello".to_vec(),
                channel_id: ch.clone(),
                ttl_secs: 0,
            })
            .unwrap();
        assert_eq!(resp.seq, 0);

        // Fetch from bare identity_key.
        let fetched = svc
            .fetch(FetchReq {
                recipient_key: ik,
                channel_id: ch,
                limit: 10,
            })
            .unwrap();
        assert_eq!(fetched.payloads.len(), 1);
        assert_eq!(fetched.payloads[0].data, b"hello");
    }

    #[test]
    fn enqueue_multi_device_fanout() {
        let (_dir, svc) = test_service();
        let ik = vec![2u8; 32];
        let ch = vec![0u8; 16];
        let dev_a = b"device-a".to_vec();
        let dev_b = b"device-b".to_vec();

        // Register two devices.
        svc.store
            .register_device(&ik, &dev_a, "Phone")
            .unwrap();
        svc.store
            .register_device(&ik, &dev_b, "Laptop")
            .unwrap();

        // Enqueue a message.
        svc.enqueue(EnqueueReq {
            recipient_key: ik.clone(),
            payload: b"fanout-msg".to_vec(),
            channel_id: ch.clone(),
            ttl_secs: 0,
        })
        .unwrap();

        // Each device should receive the message on its own queue.
        let key_a = device_recipient_key(&ik, &dev_a);
        let key_b = device_recipient_key(&ik, &dev_b);

        let msgs_a = svc
            .fetch(FetchReq {
                recipient_key: key_a,
                channel_id: ch.clone(),
                limit: 10,
            })
            .unwrap();
        assert_eq!(msgs_a.payloads.len(), 1);
        assert_eq!(msgs_a.payloads[0].data, b"fanout-msg");

        let msgs_b = svc
            .fetch(FetchReq {
                recipient_key: key_b,
                channel_id: ch.clone(),
                limit: 10,
            })
            .unwrap();
        assert_eq!(msgs_b.payloads.len(), 1);
        assert_eq!(msgs_b.payloads[0].data, b"fanout-msg");

        // Bare identity_key queue should be empty (not used when devices exist).
        let msgs_bare = svc
            .fetch(FetchReq {
                recipient_key: ik,
                channel_id: ch,
                limit: 10,
            })
            .unwrap();
        assert!(msgs_bare.payloads.is_empty());
    }

    #[test]
    fn batch_enqueue_multi_device() {
        let (_dir, svc) = test_service();
        let ik1 = vec![3u8; 32];
        let ik2 = vec![4u8; 32];
        let ch = vec![0u8; 16];
        let dev = b"dev1".to_vec();

        // ik1 has a device, ik2 has none.
        svc.store
            .register_device(&ik1, &dev, "Phone")
            .unwrap();

        let resp = svc
            .batch_enqueue(BatchEnqueueReq {
                recipient_keys: vec![ik1.clone(), ik2.clone()],
                payload: b"batch-msg".to_vec(),
                channel_id: ch.clone(),
                ttl_secs: 0,
            })
            .unwrap();
        assert_eq!(resp.seqs.len(), 2);

        // ik1 device should have the message.
        let key_1 = device_recipient_key(&ik1, &dev);
        let msgs_1 = svc
            .fetch(FetchReq {
                recipient_key: key_1,
                channel_id: ch.clone(),
                limit: 10,
            })
            .unwrap();
        assert_eq!(msgs_1.payloads.len(), 1);

        // ik2 (no devices) should have it on bare key.
        let msgs_2 = svc
            .fetch(FetchReq {
                recipient_key: ik2,
                channel_id: ch,
                limit: 10,
            })
            .unwrap();
        assert_eq!(msgs_2.payloads.len(), 1);
    }

    #[test]
    fn device_recipient_key_construction() {
        let ik = vec![1u8; 32];
        let dev = b"my-device".to_vec();

        // With device_id.
        let key = device_recipient_key(&ik, &dev);
        assert_eq!(key.len(), 32 + dev.len());
        assert_eq!(&key[..32], &ik[..]);
        assert_eq!(&key[32..], dev.as_slice());

        // Empty device_id returns bare identity_key.
        let bare = device_recipient_key(&ik, &[]);
        assert_eq!(bare, ik);
    }
}