//! An object mapper for looking up `rpc::Object`s by ID.

//!

//! This mapper stores strong or weak references, and uses a generational index

//! to keep track of names for them.

//!

//! TODO RPC: Add an object diagram here once the implementation settles down.

use std::sync::{Arc, Weak};

use rand::RngExt;

use slotmap_careful::{Key as _, KeyData, SlotMap};

use tor_rpcbase as rpc;

pub(crate) mod methods;

slotmap_careful::new_key_type! {

    pub(crate) struct GenIdx;

}

/// A weak or a strong reference to an RPC object.

//

// Note: This type does not pack very efficiently, due to Rust's current lack

// of alignment-based niche optimization.

// If this ever matters, we can either use two slotmaps, or we can implement

// some kind of kludgey hack on our own.

#[derive(Clone, derive_more::From)]

enum ObjectRef {

    /// A strong reference.

    Strong(Arc<dyn rpc::Object>),

    /// A weak reference reference.

    Weak(Weak<dyn rpc::Object>),

}

impl ObjectRef {

    /// Return this reference as an Arc, if it is present.

        }

}

/// A mechanism to look up RPC `Objects` by their `ObjectId`.

#[derive(Default)]

pub(crate) struct ObjMap {

    /// Generationally indexed arena of strong object references.

    arena: SlotMap<GenIdx, ObjectRef>,

}

/// Encoding functions for GenIdx.

///

/// The encoding is deliberately nondeterministic: we want to avoid situations

/// where applications depend on the details of our ObjectIds, or hardcode the

/// ObjectIds they expect, or rely on the same  weak generational index getting

/// encoded the same way every time they see it.

///

/// The encoding is deliberately non-cryptographic: we do not want to imply

/// that this gives any security. It is just a mild deterrent to misuse.

///

/// If you find yourself wanting to reverse-engineer this code so that you can

/// analyze these object IDs, please contact the Arti developers instead and let

/// us give you a better way to do whatever you want.

impl GenIdx {

    /// The length of a byte-encoded (but not base-64 encoded) GenIdx.

    pub(crate) const BYTE_LEN: usize = 16;

    /// Encode `self` into an rpc::ObjectId that we can give to a client.

    /// As `encode`, but take a Rng as an argument. For testing.

        use base64ct::Encoding;

    /// As `encode_with_rng`, but return an array of bytes.

        use tor_bytes::Writer;

    /// Attempt to decode `id` into a `GenIdx` than an ObjMap can use.

        use base64ct::Encoding;

    /// As `try_decode`, but take a slice of bytes.

        use tor_bytes::Reader;

}

impl ObjMap {

    /// Create a new empty ObjMap.

    /// Unconditionally insert a strong entry for `value` in self, and return its index.

    /// Unconditionally insert a weak entry for `value` in self, and return its index.

    /// Return the entry from this ObjMap for `idx`.

    /// Remove the entry at `idx`.

    ///

    /// Return true if anything was removed.

    /// Testing only: Assert that every invariant for this structure is met.

    #[cfg(test)]

}

/// A failure from ObjMap::lookup.

///

/// (This type is immediately returned into rpc::LookupError before we return it.)

#[derive(Clone, Debug, thiserror::Error)]

pub(crate) enum LookupError {

    /// There was no object with the given ID.

    #[error("Object not found")]

    NoObject,

    /// The object was present, but it was a weak reference that expired.

    #[error("Object expired")]

    Expired,

}

impl LookupError {

    /// Convert this `LookupError` into an [`rpc::LookupError`]

        }

}

#[cfg(test)]

mod test {

    // @@ begin test lint list maintained by maint/add_warning @@

    #![allow(clippy::bool_assert_comparison)]

    #![allow(clippy::clone_on_copy)]

    #![allow(clippy::dbg_macro)]

    #![allow(clippy::mixed_attributes_style)]

    #![allow(clippy::print_stderr)]

    #![allow(clippy::print_stdout)]

    #![allow(clippy::single_char_pattern)]

    #![allow(clippy::unwrap_used)]

    #![allow(clippy::unchecked_time_subtraction)]

    #![allow(clippy::useless_vec)]

    #![allow(clippy::needless_pass_by_value)]

    //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->

    use super::*;

    use derive_deftly::Deftly;

    use tor_rpcbase::templates::*;

    #[derive(Clone, Debug, Deftly)]

    #[derive_deftly(Object)]

    struct ExampleObject(#[allow(unused)] String);

    #[test]

    fn map_basics() {

        // Insert an object, make sure it gets inserted twice, and look it up.

        let obj1 = Arc::new(ExampleObject("abcdef".to_string()));

        let mut map = ObjMap::new();

        map.assert_okay();

        let id1 = map.insert_strong(obj1.clone());

        let id2 = map.insert_strong(obj1.clone());

        assert_ne!(id1, id2);

        let obj1: Arc<dyn rpc::Object> = obj1;

        let obj_out1 = map.lookup(id1).unwrap();

        let obj_out2 = map.lookup(id2).unwrap();

        assert!(Arc::ptr_eq(&obj1, &obj_out1));

        assert!(Arc::ptr_eq(&obj1, &obj_out2));

        map.assert_okay();

        map.remove(id1);

        assert!(map.lookup(id1).is_err());

        let obj_out2b = map.lookup(id2).unwrap();

        assert!(Arc::ptr_eq(&obj_out2, &obj_out2b));

        map.assert_okay();

    }

    #[test]

    fn strong_and_weak() {

        // Make sure that a strong object behaves like one, and so does a weak

        // object.

        let obj1: Arc<dyn rpc::Object> = Arc::new(ExampleObject("hello".to_string()));

        let obj2: Arc<dyn rpc::Object> = Arc::new(ExampleObject("world".to_string()));

        let mut map = ObjMap::new();

        let id1 = map.insert_strong(obj1.clone());

        let id2 = map.insert_weak(&obj2);

        {

            let out1 = map.lookup(id1).unwrap();

            let out2 = map.lookup(id2).unwrap();

            assert!(Arc::ptr_eq(&obj1, &out1));

            assert!(Arc::ptr_eq(&obj2, &out2));

        }

        map.assert_okay();

        // Now drop every object we've got, and see what we can still find.

        drop(obj1);

        drop(obj2);

        {

            let out1 = map.lookup(id1);

            let out2 = map.lookup(id2);

            // This one was strong, so it is still there.

            assert!(out1.is_ok());

            // This one is weak so it went away.

            assert!(out2.is_err());

        }

        map.assert_okay();

    }

    #[test]

    fn remove() {

        // Make sure that removing an object makes it go away.

        let obj1: Arc<dyn rpc::Object> = Arc::new(ExampleObject("hello".to_string()));

        let obj2: Arc<dyn rpc::Object> = Arc::new(ExampleObject("world".to_string()));

        let mut map = ObjMap::new();

        let id1 = map.insert_strong(obj1.clone());

        let id2 = map.insert_weak(&obj2);

        map.assert_okay();

        map.remove(id1);

        map.assert_okay();

        assert!(map.lookup(id1).is_err());

        assert!(map.lookup(id2).is_ok());

        map.remove(id2);

        map.assert_okay();

        assert!(map.lookup(id1).is_err());

        assert!(map.lookup(id2).is_err());

    }

    #[test]

    fn duplicates() {

        let obj1: Arc<dyn rpc::Object> = Arc::new(ExampleObject("hello".to_string()));

        let obj2: Arc<dyn rpc::Object> = Arc::new(ExampleObject("world".to_string()));

        let mut map = ObjMap::new();

        let id1 = map.insert_strong(obj1.clone());

        let id2 = map.insert_weak(&obj2);

        {

            assert_ne!(id2, map.insert_weak(&obj1));

            assert_ne!(id2, map.insert_weak(&obj2));

        }

        {

            assert_ne!(id1, map.insert_strong(obj1.clone()));

            assert_ne!(id2, map.insert_strong(obj2.clone()));

        }

    }

    #[test]

    fn objid_encoding() {

        fn test_roundtrip(a: u32, b: u32, rng: &mut tor_basic_utils::test_rng::TestingRng) {

            let a: u64 = a.into();

            let b: u64 = b.into();

            let data = KeyData::from_ffi((a << 33) | (1_u64 << 32) | b);

            let idx = GenIdx::from(data);

            let s1 = idx.encode_with_rng(rng);

            let s2 = idx.encode_with_rng(rng);

            assert_ne!(s1, s2);

            assert_eq!(idx, GenIdx::try_decode(&s1).unwrap());

            assert_eq!(idx, GenIdx::try_decode(&s2).unwrap());

        }

        let mut rng = tor_basic_utils::test_rng::testing_rng();

        test_roundtrip(0, 1, &mut rng);

        test_roundtrip(0, 2, &mut rng);

        test_roundtrip(1, 1, &mut rng);

        test_roundtrip(0xffffffff, 0xffffffff, &mut rng);

        for _ in 0..256 {

            test_roundtrip(rng.random(), rng.random(), &mut rng);

        }

    }

}