// Copyright 2025 The Pigweed Authors
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
//     https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.

#[cfg(feature = "arch_arm_cortex_m")]
mod arm_cortex_m;
#[cfg(feature = "arch_arm_cortex_m")]
pub use arm_cortex_m::Arch;

#[cfg(feature = "arch_host")]
mod host;
#[cfg(feature = "arch_host")]
pub use host::Arch;

use crate::scheduler::{SchedulerState, Stack};
use crate::sync::spinlock::SpinLockGuard;

pub type ArchThreadState = <Arch as ArchInterface>::ThreadState;

pub trait ThreadState {
    #[allow(dead_code)]
    fn new() -> Self;

    // Switch to this thread.
    // sched_state: a locked spinlockguard for the main SCHEDULER_STATE struct.
    //   Will potentially be dropped and reacquired across this function, and
    //   a copy will be returned (either still held, or newly reacquired).
    // old_thread_state: thread we're moving from.
    // new_thread_state: must match current_thread and the container for this ThreadState.
    unsafe fn context_switch(
        sched_state: SpinLockGuard<'_, SchedulerState>,
        old_thread_state: *mut ArchThreadState,
        new_thread_state: *mut ArchThreadState,
    ) -> SpinLockGuard<'_, SchedulerState>;

    // Initialize the default frame of the thread which arranges for it to start at the initial_function
    // with one argument passed in the first argument slot.
    #[allow(dead_code)]
    fn initialize_frame(&mut self, stack: Stack, initial_function: fn(usize), arg0: usize);
}

pub trait BareSpinLock {
    type Guard<'a>
    where
        Self: 'a;

    // Rust does not support const function in traits.  However it should be
    // considered that the BareSpinlockApi includes:
    //
    // `const fn new() -> Self`

    fn try_lock(&self) -> Option<Self::Guard<'_>>;

    #[inline(always)]
    fn lock(&self) -> Self::Guard<'_> {
        loop {
            if let Some(sentinel) = self.try_lock() {
                return sentinel;
            }
        }
    }

    // TODO - konkers: Add optimized path for functions that know they are in
    // atomic context (i.e. interrupt handlers).
}

pub trait ArchInterface {
    type ThreadState: ThreadState;
    type BareSpinLock: BareSpinLock;

    fn early_init() {}
    fn init() {}

    fn panic() -> ! {
        #[allow(clippy::empty_loop)]
        loop {}
    }
    // fill in more arch implementation functions from the kernel here:
    // arch-specific backtracing
    #[allow(dead_code)]
    fn enable_interrupts();
    #[allow(dead_code)]
    fn disable_interrupts();
    #[allow(dead_code)]
    fn interrupts_enabled() -> bool;

    #[allow(dead_code)]
    fn idle() {}
}