#![allow(clippy::arc_with_non_send_sync)]

use std::sync::{Arc, Condvar, Mutex};
use std::time::Duration;

use crate::vm::Vm;
use crate::{vm_debug, vm_trace, vm_warn};
use oxide_kernel::kernel::KernelCore;

struct VmPoolInner {
    available: Vec<Vm>,
    total_count: usize,
}

pub struct VmPool {
    kernel_core: Arc<KernelCore>,
    inner: Mutex<VmPoolInner>,
    condvar: Condvar,
    max_size: Option<usize>,
}

pub struct VmGuard {
    vm: Option<Vm>,
    pool: Arc<VmPool>,
    dirty: bool,
}

impl VmPool {
    pub fn new(kernel_core: Arc<KernelCore>, _min_size: usize, max_size: Option<usize>) -> Arc<Self> {
        Arc::new(Self {
            kernel_core,
            inner: Mutex::new(VmPoolInner {
                available: Vec::new(),
                total_count: 0,
            }),
            condvar: Condvar::new(),
            max_size,
        })
    }

    fn new_vm(core: &Arc<KernelCore>) -> Vm {
        Vm::with_kernel_core(Arc::clone(core))
    }

    fn replace_vm(&self) -> Vm {
        Self::new_vm(&self.kernel_core)
    }

    pub fn spawn(self: &Arc<Self>) -> VmGuard {
        loop {
            let mut inner = self.inner.lock().unwrap();

            if let Some(vm) = inner.available.pop() {
                vm_trace!("pool: reused vm, {} available", inner.available.len());
                return VmGuard {
                    vm: Some(vm),
                    pool: Arc::clone(self),
                    dirty: false,
                };
            }

            let can_grow = match self.max_size {
                Some(max) => inner.total_count < max,
                None => true,
            };

            if can_grow {
                inner.total_count += 1;
                vm_debug!("pool: growing to {} vms", inner.total_count);
                drop(inner);
                let vm = Self::new_vm(&self.kernel_core);
                return VmGuard {
                    vm: Some(vm),
                    pool: Arc::clone(self),
                    dirty: false,
                };
            }

            let (guard, wait) = self.condvar.wait_timeout(inner, Duration::from_secs(5)).unwrap();
            inner = guard;
            if wait.timed_out() {
                vm_warn!("pool: wait timeout, force-growing to {} vms", inner.total_count + 1);
                inner.total_count += 1;
                drop(inner);
                let vm = Self::new_vm(&self.kernel_core);
                return VmGuard {
                    vm: Some(vm),
                    pool: Arc::clone(self),
                    dirty: false,
                };
            }
        }
    }
}

impl VmGuard {
    pub fn vm(&self) -> &Vm {
        self.vm.as_ref().expect("VmGuard has no VM")
    }

    pub fn vm_mut(&mut self) -> &mut Vm {
        self.vm.as_mut().expect("VmGuard has no VM")
    }
}

impl Drop for VmGuard {
    fn drop(&mut self) {
        let Some(mut vm) = self.vm.take() else {
            return;
        };

        let mut inner = self.pool.inner.lock().unwrap();

        if self.dirty {
            vm_debug!("pool: discarding dirty vm");
            let new_vm = self.pool.replace_vm();
            inner.available.push(new_vm);
        } else {
            vm.full_reset();
            inner.available.push(vm);
            vm_trace!("pool: recycled clean vm, {} available", inner.available.len());
        }

        self.pool.condvar.notify_one();
    }
}

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

    fn test_kernel() -> Arc<KernelCore> {
        KernelCore::new(KernelConfig::minimal())
    }

    #[test]
    fn test_pool_spawn_returns_guard() {
        let kernel = test_kernel();
        let pool = VmPool::new(kernel, 1, None);
        let guard = pool.spawn();
        drop(guard);
    }

    #[test]
    fn test_pool_recycle_on_drop() {
        let kernel = test_kernel();
        let pool = VmPool::new(kernel, 1, None);
        let guard = pool.spawn();
        drop(guard);
        let guard2 = pool.spawn();
        drop(guard2);
    }

    #[test]
    fn test_pool_grows_if_empty() {
        let kernel = test_kernel();
        let pool = VmPool::new(Arc::clone(&kernel), 1, Some(3));
        let g1 = pool.spawn();
        let g2 = pool.spawn();
        drop(g1);
        drop(g2);
    }
}