// Copyright 2019 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 {
    core::ops::{Deref, DerefMut},
    derivative::Derivative,
    fuchsia_inspect::{Node, Property, StringProperty},
    std::borrow::Borrow,
};

/// Generic wrapper for exporting variables via Inspect. Mutations to
/// the wrapped `value` occur through an `InspectableGuard`, which
/// notifies the `watcher` when `Drop`ped, transparently keeping the Inspect
/// state up-to-date.
///
/// How the `value` is exported is determined by the `Watch` implementation,
/// see e.g. `InspectableDebugString`.
///
/// Not correct for `V`s with interior mutability, because `Inspectable`
/// `Deref`s to `V`, mutations to which will bypass the `watcher`.
#[derive(Derivative)]
#[derivative(Debug, Eq, PartialEq, Hash)]
pub struct Inspectable<V, W>
where
    W: Watch<V>,
{
    value: V,
    #[derivative(Debug = "ignore", PartialEq = "ignore", Hash = "ignore")]
    watcher: W,
}

impl<V, W> Inspectable<V, W>
where
    W: Watch<V>,
{
    /// Creates an `Inspectable` wrapping `value`. Exports `value` via Inspect.
    pub fn new(value: V, node: &Node, name: impl AsRef<str>) -> Self {
        let watcher = W::new(&value, node, name);
        Self { value, watcher }
    }

    /// Returns a guard that `DerefMut`s to the wrapped `value`. The `watcher`
    /// will receive the updated `value` when the guard is `Drop`ped.
    pub fn get_mut(&mut self) -> InspectableGuard<V, W> {
        InspectableGuard { value: &mut self.value, watcher: &mut self.watcher }
    }
}

impl<V, W> Deref for Inspectable<V, W>
where
    W: Watch<V>,
{
    type Target = V;

    fn deref(&self) -> &Self::Target {
        &self.value
    }
}

impl<V, W> Borrow<V> for Inspectable<V, W>
where
    W: Watch<V>,
{
    fn borrow(&self) -> &V {
        &self.value
    }
}

pub trait Watch<V> {
    /// Used by `Inspectable::new()` to create a `Watch`er that exports via
    /// Inspect the `Inspectable`'s wrapped `value`.
    fn new(value: &V, node: &Node, name: impl AsRef<str>) -> Self;

    /// Called by `InspectableGuard` when the guard is dropped, letting the
    /// `Watch`er update its state with the updated `value`.
    fn watch(&mut self, value: &V);
}

#[must_use]
/// Calls self.watcher.watch(self.value) when dropped.
pub struct InspectableGuard<'a, V, W>
where
    W: Watch<V>,
{
    value: &'a mut V,
    watcher: &'a mut W,
}

impl<'a, V, W> Deref for InspectableGuard<'a, V, W>
where
    W: Watch<V>,
{
    type Target = V;

    fn deref(&self) -> &Self::Target {
        self.value
    }
}

impl<'a, V, W> DerefMut for InspectableGuard<'a, V, W>
where
    W: Watch<V>,
{
    fn deref_mut(&mut self) -> &mut Self::Target {
        self.value
    }
}

impl<'a, V, W> Drop for InspectableGuard<'a, V, W>
where
    W: Watch<V>,
{
    fn drop(&mut self) {
        self.watcher.watch(self.value);
    }
}

/// Exports via an Inspect `UintProperty` the `len` of the wrapped `Vec`.
#[derive(Debug)]
pub struct InspectableVectorSizeWatcher {
    len: fuchsia_inspect::UintProperty,
}

impl<V> Watch<Vec<V>> for InspectableVectorSizeWatcher {
    fn new(value: &Vec<V>, node: &Node, name: impl AsRef<str>) -> Self {
        Self { len: node.create_uint(name, value.len() as u64) }
    }

    fn watch(&mut self, vec: &Vec<V>) {
        self.len.set(vec.len() as u64);
    }
}

pub type InspectableVectorSize<V> = Inspectable<Vec<V>, InspectableVectorSizeWatcher>;

/// Exports via an Inspect `StringProperty` the `Debug` representation of
/// the wrapped `value`.
#[derive(Debug)]
pub struct InspectableDebugStringWatcher {
    debug_string: StringProperty,
}

impl<V> Watch<V> for InspectableDebugStringWatcher
where
    V: std::fmt::Debug,
{
    fn new(value: &V, node: &Node, name: impl AsRef<str>) -> Self {
        Self { debug_string: node.create_string(name, format!("{:?}", value)) }
    }

    fn watch(&mut self, value: &V) {
        self.debug_string.set(&format!("{:?}", value))
    }
}

pub type InspectableDebugString<V> = Inspectable<V, InspectableDebugStringWatcher>;

#[cfg(test)]
mod test {
    use {
        super::*,
        fuchsia_inspect::{assert_inspect_tree, Inspector, IntProperty},
        std::collections::HashSet,
    };

    struct InspectableIntWatcher {
        i: IntProperty,
    }
    impl Watch<i64> for InspectableIntWatcher {
        fn new(value: &i64, node: &Node, name: impl AsRef<str>) -> Self {
            Self { i: node.create_int(name, *value) }
        }
        fn watch(&mut self, value: &i64) {
            self.i.set(*value)
        }
    }

    type InspectableInt = Inspectable<i64, InspectableIntWatcher>;
    fn make_inspectable(i: i64) -> (InspectableInt, Inspector) {
        let inspector = Inspector::new();
        let inspectable = InspectableInt::new(i, inspector.root(), "inspectable-int");
        (inspectable, inspector)
    }

    #[test]
    fn test_inspectable_deref() {
        let inspectable = make_inspectable(1).0;

        assert_eq!(*inspectable, 1);
    }

    #[test]
    fn test_guard_deref() {
        let mut inspectable = make_inspectable(1).0;

        assert_eq!(*inspectable.get_mut(), 1);
    }

    #[test]
    fn test_guard_deref_mut() {
        let mut inspectable = make_inspectable(1).0;

        *inspectable.get_mut() = 2;

        assert_eq!(*inspectable, 2);
    }

    #[test]
    fn test_guard_drop_calls_callback() {
        let (mut inspectable, inspector) = make_inspectable(1);

        let mut guard = inspectable.get_mut();
        *guard = 2;
        drop(guard);

        assert_inspect_tree!(
            inspector,
            root: {
                "inspectable-int": 2i64
            }
        );
    }

    #[test]
    fn test_partial_eq() {
        let inspectable0 = make_inspectable(1).0;
        let inspectable1 = make_inspectable(1).0;

        assert_eq!(inspectable0, inspectable1);
    }

    #[test]
    fn test_partial_eq_not() {
        let inspectable0 = make_inspectable(1).0;
        let inspectable1 = make_inspectable(2).0;

        assert_ne!(inspectable0, inspectable1);
    }

    #[test]
    fn test_borrow() {
        let inspectable = make_inspectable(1).0;

        assert_eq!(Borrow::<i64>::borrow(&inspectable), &1);
    }

    #[test]
    fn test_inspectable_in_hash_set() {
        let inspectable = make_inspectable(1).0;
        let mut set = HashSet::new();

        set.insert(inspectable);
        assert!(set.contains(&1));

        set.remove(&1);
        assert!(set.is_empty());
    }
}

#[cfg(test)]
mod test_inspectable_vector_size {
    use super::*;
    use fuchsia_inspect::assert_inspect_tree;

    #[test]
    fn test_initialization() {
        let inspector = fuchsia_inspect::Inspector::new();
        let _inspectable = InspectableVectorSize::new(vec![0], inspector.root(), "test-property");

        assert_inspect_tree!(
            inspector,
            root: {
                "test-property": 1u64
            }
        );
    }

    #[test]
    fn test_watcher() {
        let inspector = fuchsia_inspect::Inspector::new();
        let mut inspectable =
            InspectableVectorSize::new(vec![0], inspector.root(), "test-property");

        inspectable.get_mut().push(1);

        assert_inspect_tree!(
            inspector,
            root: {
                "test-property": 2u64
            }
        );
    }
}

#[cfg(test)]
mod test_inspectable_debug_string {
    use super::*;
    use fuchsia_inspect::assert_inspect_tree;

    #[test]
    fn test_initialization() {
        let inspector = fuchsia_inspect::Inspector::new();
        let _inspectable = InspectableDebugString::new(vec![0], inspector.root(), "test-property");

        assert_inspect_tree!(
            inspector,
            root: {
                "test-property": "[0]"
            }
        );
    }

    #[test]
    fn test_watcher() {
        let inspector = fuchsia_inspect::Inspector::new();
        let mut inspectable =
            InspectableDebugString::new(vec![0], inspector.root(), "test-property");

        inspectable.get_mut().push(1);

        assert_inspect_tree!(
            inspector,
            root: {
                "test-property": "[0, 1]"
            }
        );
    }
}