// Copyright 2020 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 {
    crate::{
        capability::{CapabilityProvider, OptionalTask},
        channel,
        model::{
            error::ModelError,
            events::{
                error::EventsError,
                registry::{
                    EventRegistry, EventSubscription, ExecutionMode, SubscriptionOptions,
                    SubscriptionType,
                },
                serve::serve_event_source_sync,
                stream::EventStream,
                stream_provider::EventStreamProvider,
            },
            model::Model,
        },
    },
    async_trait::async_trait,
    cm_rust::EventMode,
    fidl::endpoints::ServerEnd,
    fidl_fuchsia_sys2 as fsys, fuchsia_async as fasync, fuchsia_zircon as zx,
    futures::lock::Mutex,
    moniker::ExtendedMoniker,
    std::{
        path::PathBuf,
        sync::{Arc, Weak},
    },
};

/// A system responsible for implementing basic events functionality on a scoped realm.
#[derive(Clone)]
pub struct EventSource {
    /// The component model, needed to route events.
    model: Weak<Model>,

    /// A shared reference to the event registry used to subscribe and dispatch events.
    registry: Weak<EventRegistry>,

    /// The static EventStreamProvider tracks all static event streams. It can be used to take the
    /// server end of the static event streams.
    stream_provider: Weak<EventStreamProvider>,

    /// Used for OpaqueTest:
    /// The implicit static EventStream is dropped when the EventSource goes out of scope.
    /// TODO(fxbug.dev/48245): this shouldn't be done for any EventSource once OpaqueTest goes away.
    resolve_instance_event_stream: Arc<Mutex<Option<fasync::Task<()>>>>,

    /// The options used to subscribe to events.
    options: SubscriptionOptions,
}

impl EventSource {
    /// Creates a new `EventSource` that will be used by the component identified with the given
    /// `target_moniker`.
    pub async fn new(
        model: Weak<Model>,
        options: SubscriptionOptions,
        registry: Weak<EventRegistry>,
        stream_provider: Weak<EventStreamProvider>,
    ) -> Result<Self, ModelError> {
        // TODO(fxbug.dev/48245): this shouldn't be done for any EventSource. Only for tests.
        let resolve_instance_event_stream =
            Arc::new(Mutex::new(match (&options.subscription_type, &options.execution_mode) {
                (SubscriptionType::AboveRoot, ExecutionMode::Debug) => {
                    let stream_provider =
                        stream_provider.upgrade().ok_or(EventsError::StreamProviderNotFound)?;
                    Some(
                        stream_provider
                            .create_static_event_stream(
                                &ExtendedMoniker::ComponentManager,
                                "StartComponentTree".to_string(),
                                vec![EventSubscription::new("resolved".into(), EventMode::Sync)],
                            )
                            .await?,
                    )
                }
                (_, _) => None,
            }));
        Ok(Self { registry, stream_provider, model, resolve_instance_event_stream, options })
    }

    pub async fn new_for_debug(
        model: Weak<Model>,
        registry: Weak<EventRegistry>,
        stream_provider: Weak<EventStreamProvider>,
    ) -> Result<Self, ModelError> {
        Self::new(
            model,
            SubscriptionOptions::new(SubscriptionType::AboveRoot, ExecutionMode::Debug),
            registry,
            stream_provider,
        )
        .await
    }

    /// Drops the `Resolved` event stream, thereby permitting components within the
    /// realm to be started.
    pub async fn start_component_tree(&mut self) {
        let _ = self.take_static_event_stream("StartComponentTree".to_string()).await;
    }

    /// Subscribes to events provided in the `events` vector.
    ///
    /// The client might request to subscribe to events that it's not allowed to see. Events
    /// that are allowed should have been defined in its manifest and either offered to it or
    /// requested from the current realm.
    pub async fn subscribe(
        &mut self,
        requests: Vec<EventSubscription>,
    ) -> Result<EventStream, ModelError> {
        let registry = self.registry.upgrade().ok_or(EventsError::RegistryNotFound)?;
        // Create an event stream for the given events
        registry.subscribe(&self.options, requests).await
    }

    pub async fn take_static_event_stream(
        &self,
        target_path: String,
    ) -> Option<ServerEnd<fsys::EventStreamMarker>> {
        let moniker = match &self.options.subscription_type {
            SubscriptionType::AboveRoot => ExtendedMoniker::ComponentManager,
            SubscriptionType::Component(abs_moniker) => {
                ExtendedMoniker::ComponentInstance(abs_moniker.clone())
            }
        };
        if let Some(stream_provider) = self.stream_provider.upgrade() {
            return stream_provider.take_static_event_stream(&moniker, target_path).await;
        }
        return None;
    }

    /// Serves a `EventSource` FIDL protocol.
    pub fn serve(self, stream: fsys::EventSourceRequestStream) -> fasync::Task<()> {
        fasync::Task::spawn(async move {
            serve_event_source_sync(self, stream).await;
        })
    }
}

#[async_trait]
impl CapabilityProvider for EventSource {
    async fn open(
        self: Box<Self>,
        _flags: u32,
        _open_mode: u32,
        _relative_path: PathBuf,
        server_end: &mut zx::Channel,
    ) -> Result<OptionalTask, ModelError> {
        let server_end = channel::take_channel(server_end);
        let stream = ServerEnd::<fsys::EventSourceMarker>::new(server_end)
            .into_stream()
            .expect("could not convert channel into stream");
        Ok(self.serve(stream).into())
    }
}