use bevy_utils::tracing::warn;

use crate::{
    archetype::{Archetype, ArchetypeComponentId},
    component::ComponentId,
    query::Access,
    world::World,
};
use std::borrow::Cow;

/// A [`System`] identifier.
#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
pub struct SystemId(pub usize);

impl SystemId {
    /// Creates a new random `SystemId`.
    #[allow(clippy::new_without_default)]
    pub fn new() -> Self {
        SystemId(rand::random::<usize>())
    }
}

/// An ECS system that can be added to a [Schedule](crate::schedule::Schedule)
///
/// Systems are functions with all arguments implementing [SystemParam](crate::system::SystemParam).
///
/// Systems are added to an application using `AppBuilder::add_system(my_system.system())`
/// or similar methods, and will generally run once per pass of the main loop.
///
/// Systems are executed in parallel, in opportunistic order; data access is managed automatically.
/// It's possible to specify explicit execution order between specific systems,
/// see [SystemDescriptor](crate::schedule::SystemDescriptor).
pub trait System: Send + Sync + 'static {
    /// The system's input. See [`In`](crate::system::In) for [`FunctionSystem`](crate::system::FunctionSystem)s.
    type In;
    /// The system's output.
    type Out;
    /// Returns the system's name.
    fn name(&self) -> Cow<'static, str>;
    /// Returns the system's [`SystemId`].
    fn id(&self) -> SystemId;
    /// Register a new archetype for this system.
    fn new_archetype(&mut self, archetype: &Archetype);
    /// Returns the system's component [`Access`].
    fn component_access(&self) -> &Access<ComponentId>;
    /// Returns the system's archetype component [`Access`].
    fn archetype_component_access(&self) -> &Access<ArchetypeComponentId>;
    /// Returns true if the system is [`Send`].
    fn is_send(&self) -> bool;
    /// Runs the system with the given input in the world. Unlike [`System::run`], this function
    /// takes a shared reference to [`World`] and may therefore break Rust's aliasing rules, making
    /// it unsafe to call.
    ///
    /// # Safety
    ///
    /// This might access world and resources in an unsafe manner. This should only be called in one
    /// of the following contexts:
    ///     1. This system is the only system running on the given world across all threads.
    ///     2. This system only runs in parallel with other systems that do not conflict with the
    ///        [`System::archetype_component_access()`].
    unsafe fn run_unsafe(&mut self, input: Self::In, world: &World) -> Self::Out;
    /// Runs the system with the given input in the world.
    fn run(&mut self, input: Self::In, world: &mut World) -> Self::Out {
        // SAFE: world and resources are exclusively borrowed
        unsafe { self.run_unsafe(input, world) }
    }
    fn apply_buffers(&mut self, world: &mut World);
    /// Initialize the system.
    fn initialize(&mut self, _world: &mut World);
    fn check_change_tick(&mut self, change_tick: u32);
}

/// A convenience type alias for a boxed [`System`] trait object.
pub type BoxedSystem<In = (), Out = ()> = Box<dyn System<In = In, Out = Out>>;

pub(crate) fn check_system_change_tick(
    last_change_tick: &mut u32,
    change_tick: u32,
    system_name: &str,
) {
    let tick_delta = change_tick.wrapping_sub(*last_change_tick);
    const MAX_DELTA: u32 = (u32::MAX / 4) * 3;
    // Clamp to max delta
    if tick_delta > MAX_DELTA {
        warn!(
            "Too many intervening systems have run since the last time System '{}' was last run; it may fail to detect changes.",
            system_name
        );
        *last_change_tick = change_tick.wrapping_sub(MAX_DELTA);
    }
}