//! Trusted, in-process application services for a running Runa image.

use std::num::NonZeroUsize;
use std::sync::Arc;

use runa_actor::{ActorId, ActorSnapshot, Event, Message};
use runa_code::{BehaviorSnapshot, CodeStore};
use runa_core::ImplementationId;
use runa_runtime::{Runtime, RuntimeResult};

pub struct ImageApi {
    code: CodeStore,
    runtime: Runtime,
}

impl Default for ImageApi {
    fn default() -> Self {
        Self::new()
    }
}

impl ImageApi {
    pub fn new() -> Self {
        Self {
            code: CodeStore::default(),
            runtime: Runtime::default(),
        }
    }

    pub fn publish_behavior(
        &mut self,
        name: &str,
        expected_revision: Option<u64>,
        source: &str,
    ) -> RuntimeResult<BehaviorSnapshot> {
        let artifact = self.code.compile(source)?;
        self.runtime.publish(Arc::clone(&artifact))?;
        self.code.publish_behavior(name, expected_revision, source)
    }

    pub fn rollback_behavior(
        &mut self,
        name: &str,
        expected_revision: u64,
        target_revision: u64,
    ) -> RuntimeResult<BehaviorSnapshot> {
        self.code
            .rollback_behavior(name, expected_revision, target_revision)
    }

    pub fn behavior(&self, name: &str) -> Option<BehaviorSnapshot> {
        self.code.behavior(name)
    }

    pub fn behaviors(&self) -> Vec<BehaviorSnapshot> {
        self.code.behaviors()
    }

    pub fn behavior_source(&self, name: &str, revision: u64) -> RuntimeResult<&str> {
        let behavior = self.code.behavior(name).ok_or("unknown behavior")?;
        let version = behavior
            .history
            .iter()
            .find(|version| version.revision == revision)
            .ok_or("unknown behavior revision")?;
        self.code
            .artifact(version.implementation_id)
            .map(|artifact| artifact.original_source())
            .ok_or_else(|| "behavior artifact is unavailable".into())
    }

    pub fn spawn(
        &mut self,
        behavior_name: &str,
        state: i64,
        capacity: NonZeroUsize,
    ) -> RuntimeResult<ActorId> {
        let behavior = self
            .code
            .behavior(behavior_name)
            .ok_or("unknown behavior")?;
        self.runtime.spawn(behavior.current, state, capacity)
    }

    pub fn send(&mut self, actor: ActorId, message: Message) -> RuntimeResult<()> {
        self.runtime.send(actor, message)
    }

    pub fn tick(&mut self, ticks: usize, budget: NonZeroUsize) {
        for _ in 0..ticks {
            self.runtime.tick(budget);
        }
    }

    pub fn inspect(&self, actor: ActorId) -> RuntimeResult<ActorSnapshot> {
        self.runtime.inspect(actor)
    }

    pub fn actors(&self) -> Vec<ActorSnapshot> {
        self.runtime.actors()
    }

    pub fn events(&mut self) -> Vec<Event> {
        self.runtime.drain_events()
    }

    pub fn stop(&mut self, actor: ActorId) -> RuntimeResult<()> {
        self.runtime.stop(actor)
    }

    pub fn restart(&mut self, actor: ActorId) -> RuntimeResult<()> {
        self.runtime.restart(actor)
    }

    pub fn pause(&mut self, actor: ActorId) -> RuntimeResult<()> {
        self.runtime.pause(actor)
    }

    pub fn resume(&mut self, actor: ActorId) -> RuntimeResult<()> {
        self.runtime.resume(actor)
    }

    pub fn cancel(&mut self, actor: ActorId) -> RuntimeResult<()> {
        self.runtime.cancel(actor)
    }

    pub fn install(
        &mut self,
        actor: ActorId,
        behavior_name: &str,
    ) -> RuntimeResult<ImplementationId> {
        self.install_with_migration(actor, behavior_name, Ok)
    }

    pub fn install_with_migration(
        &mut self,
        actor: ActorId,
        behavior_name: &str,
        migrate: impl FnOnce(i64) -> RuntimeResult<i64>,
    ) -> RuntimeResult<ImplementationId> {
        let behavior = self
            .code
            .behavior(behavior_name)
            .ok_or("unknown behavior")?;
        self.runtime
            .install_with_migration(actor, behavior.current, migrate)?;
        Ok(behavior.current)
    }
}

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

    fn capacity(n: usize) -> NonZeroUsize {
        NonZeroUsize::new(n).expect("capacity must be positive")
    }

    #[test]
    fn image_api_publishes_spawns_inspects_and_exposes_events() -> RuntimeResult<()> {
        let mut image = ImageApi::new();
        let behavior = image.publish_behavior(
            "counter",
            None,
            "pub fn handle(state, kind, value) { (state + value, []) }",
        )?;
        assert_eq!(
            image.behavior_source("counter", behavior.revision)?,
            "pub fn handle(state, kind, value) { (state + value, []) }"
        );
        let actor = image.spawn("counter", 5, capacity(2))?;
        image.send(actor, Message { kind: 0, value: 7 })?;
        image.tick(100, capacity(10));

        assert_eq!(image.inspect(actor)?.state, 12);
        assert_eq!(image.inspect(actor)?.implementation, behavior.current);
        assert!(
            image
                .events()
                .iter()
                .any(|event| matches!(event, Event::Committed(id) if *id == actor))
        );
        Ok(())
    }

    #[test]
    fn image_api_rejects_stale_behavior_updates_without_changing_current() -> RuntimeResult<()> {
        let mut image = ImageApi::new();
        let first = image.publish_behavior(
            "counter",
            None,
            "pub fn handle(state, kind, value) { (state + value, []) }",
        )?;
        assert!(
            image
                .publish_behavior(
                    "counter",
                    None,
                    "pub fn handle(state, kind, value) { (state - value, []) }"
                )
                .is_err()
        );
        assert_eq!(image.behavior("counter").unwrap().current, first.current);
        Ok(())
    }

    #[test]
    fn image_api_installs_behavior_with_atomic_state_migration() -> RuntimeResult<()> {
        let mut image = ImageApi::new();
        let first = image.publish_behavior(
            "counter",
            None,
            "pub fn handle(state, kind, value) { (state + value, []) }",
        )?;
        image.publish_behavior(
            "counter",
            Some(first.revision),
            "pub fn handle(state, kind, value) { (state * value, []) }",
        )?;
        let actor = image.spawn("counter", 5, capacity(2))?;
        let implementation = image.install_with_migration(actor, "counter", |state| {
            Ok(state.checked_mul(10).ok_or("migration overflow")?)
        })?;

        assert_eq!(image.inspect(actor)?.state, 50);
        assert_eq!(image.inspect(actor)?.implementation, implementation);
        Ok(())
    }
}