// Copyright 2024 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

use bt_common::packet_encoding::Decodable;
use bt_gatt::client::ServiceCharacteristic;
use bt_gatt::types::Handle;
use bt_gatt::GattTypes;

use crate::error::{Error, ServiceError};
use crate::types::{BatteryLevel, BATTERY_LEVEL_UUID, READ_CHARACTERISTIC_BUFFER_SIZE};

// TODO(aniramakri): Implement this.
pub struct BatteryMonitorEventStream {}

/// Implements the Battery Service client role.
pub struct BatteryMonitorClient<T: GattTypes> {
    /// Represents the underlying GATT LE connection. Kept alive to maintain the
    /// connection to the peer.
    _client: T::Client,
    /// GATT client interface for interacting with the peer's battery service.
    gatt_client: T::PeerService,
    /// GATT Handles associated with the peer's one or more Battery Level
    /// characteristics. The first `Handle` in this list is expected to be
    /// the "primary" one.
    battery_level_handles: Vec<Handle>,
    // TODO(b/335259516): Save Handles for additional characteristics that are discovered.
    /// The current battery level reported by the peer's battery server.
    battery_level: BatteryLevel,
}

impl<T: GattTypes> BatteryMonitorClient<T> {
    pub(crate) async fn create(
        _client: T::Client,
        gatt_client: T::PeerService,
    ) -> Result<Self, Error>
    where
        <T as bt_gatt::GattTypes>::NotificationStream: std::marker::Send,
    {
        // All battery services must contain at least one battery level characteristic.
        let battery_level_characteristics =
            ServiceCharacteristic::<T>::find(&gatt_client, BATTERY_LEVEL_UUID).await?;

        if battery_level_characteristics.is_empty() {
            return Err(Error::Service(ServiceError::MissingCharacteristic));
        }
        // It is valid to have multiple Battery Level Characteristics. If multiple
        // exist, the primary (main) characteristic has a Description field of
        // "main". For now, we assume the first such characteristic is the
        // primary. See BAS 1.1 Section 3.1.2.1. TODO(b/335246946): Check for
        // Characteristic Presentation Format descriptor if
        // multiple characteristics are present. Use this to infer the "primary".
        let battery_level_handles: Vec<Handle> =
            battery_level_characteristics.iter().map(|c| *c.handle()).collect();
        // Get the current battery level of the primary characteristic.
        let (battery_level, _decoded_bytes) = {
            let mut buf = vec![0; READ_CHARACTERISTIC_BUFFER_SIZE];
            let read_bytes =
                battery_level_characteristics.first().unwrap().read(&mut buf[..]).await?;
            BatteryLevel::decode(&buf[0..read_bytes])?
        };

        // TODO(aniramakri): Subscribe to notifications on the battery level
        // characteristic and save as a stream of events.

        Ok(Self { _client, gatt_client, battery_level_handles, battery_level })
    }

    /// Returns a stream of battery events.
    /// The returned Stream _must_ be polled in order to receive the relevant
    /// notification and indications on the battery service.
    /// This method should only be called once.
    /// Returns Some<T> if the battery stream is available, None otherwise.
    pub fn take_event_stream(&mut self) -> Option<BatteryMonitorEventStream> {
        todo!("Implement battery event stream")
    }

    #[cfg(test)]
    fn battery_level(&self) -> BatteryLevel {
        self.battery_level
    }
}

#[cfg(test)]
pub(crate) mod tests {
    use super::*;

    use bt_common::packet_encoding::Error as PacketError;
    use bt_common::Uuid;
    use bt_gatt::test_utils::{FakeClient, FakePeerService, FakeTypes};
    use bt_gatt::types::{
        AttributePermissions, Characteristic, CharacteristicProperties, CharacteristicProperty,
    };
    use futures::{pin_mut, FutureExt};
    use std::task::Poll;

    pub(crate) const BATTERY_LEVEL_HANDLE: Handle = Handle(0x1);
    pub(crate) fn fake_battery_service(battery_level: u8) -> FakePeerService {
        let mut peer_service = FakePeerService::new();
        peer_service.add_characteristic(
            Characteristic {
                handle: BATTERY_LEVEL_HANDLE,
                uuid: BATTERY_LEVEL_UUID,
                properties: CharacteristicProperties(vec![
                    CharacteristicProperty::Read,
                    CharacteristicProperty::Notify,
                ]),
                permissions: AttributePermissions::default(),
                descriptors: vec![],
            },
            vec![battery_level],
        );
        peer_service
    }

    /// Builds a `BatteryMonitorClient` that is connected to a fake GATT service
    /// with a Battery Service.
    fn setup_client(battery_level: u8) -> (BatteryMonitorClient<FakeTypes>, FakePeerService) {
        // Constructs a FakePeerService with a battery level characteristic.
        let fake_peer_service = fake_battery_service(battery_level);
        let mut noop_cx = futures::task::Context::from_waker(futures::task::noop_waker_ref());
        let create_result =
            BatteryMonitorClient::<FakeTypes>::create(FakeClient::new(), fake_peer_service.clone());
        pin_mut!(create_result);
        let polled = create_result.poll_unpin(&mut noop_cx);
        let Poll::Ready(Ok(client)) = polled else {
            panic!("Expected BatteryMonitorClient to be successfully created");
        };

        (client, fake_peer_service)
    }

    #[test]
    fn create_client_and_read_battery_level_success() {
        let battery_level = 20;
        let (monitor, _fake_peer_service) = setup_client(battery_level);
        assert_eq!(monitor.battery_level(), BatteryLevel(battery_level));
    }

    #[test]
    fn empty_battery_service_is_error() {
        let fake_peer_service = FakePeerService::new();
        let mut noop_cx = futures::task::Context::from_waker(futures::task::noop_waker_ref());
        let create_result =
            BatteryMonitorClient::<FakeTypes>::create(FakeClient::new(), fake_peer_service);
        pin_mut!(create_result);
        let polled = create_result.poll_unpin(&mut noop_cx);
        let Poll::Ready(Err(Error::Service(ServiceError::MissingCharacteristic))) = polled else {
            panic!("Expected BatteryMonitorClient failure");
        };
    }

    #[test]
    fn service_missing_battery_level_characteristic_is_error() {
        let mut fake_peer_service = FakePeerService::new();
        // Battery Level characteristic is invalidly formatted.
        fake_peer_service.add_characteristic(
            Characteristic {
                handle: BATTERY_LEVEL_HANDLE,
                uuid: Uuid::from_u16(0x1234), // Random UUID, not Battery Level
                properties: CharacteristicProperties(vec![
                    CharacteristicProperty::Read,
                    CharacteristicProperty::Notify,
                ]),
                permissions: AttributePermissions::default(),
                descriptors: vec![],
            },
            vec![],
        );

        let mut noop_cx = futures::task::Context::from_waker(futures::task::noop_waker_ref());
        let create_result =
            BatteryMonitorClient::<FakeTypes>::create(FakeClient::new(), fake_peer_service);
        pin_mut!(create_result);
        let polled = create_result.poll_unpin(&mut noop_cx);
        let Poll::Ready(Err(Error::Service(ServiceError::MissingCharacteristic))) = polled else {
            panic!("Expected BatteryMonitorClient failure");
        };
    }

    #[test]
    fn invalid_battery_level_value_is_error() {
        // Battery Level characteristic has an empty battery level value.
        let mut fake_peer_service = FakePeerService::new();
        fake_peer_service.add_characteristic(
            Characteristic {
                handle: BATTERY_LEVEL_HANDLE,
                uuid: BATTERY_LEVEL_UUID,
                properties: CharacteristicProperties(vec![
                    CharacteristicProperty::Read,
                    CharacteristicProperty::Notify,
                ]),
                permissions: AttributePermissions::default(),
                descriptors: vec![],
            },
            vec![],
        );
        let mut noop_cx = futures::task::Context::from_waker(futures::task::noop_waker_ref());
        let create_result =
            BatteryMonitorClient::<FakeTypes>::create(FakeClient::new(), fake_peer_service);
        pin_mut!(create_result);
        let polled = create_result.poll_unpin(&mut noop_cx);
        let Poll::Ready(Err(Error::Packet(PacketError::UnexpectedDataLength))) = polled else {
            panic!("Expected BatteryMonitorClient to be successfully created");
        };
    }
}