use core::fmt::Debug;
use core::ptr::NonNull;
use bern_arch::arch::Arch;
use bern_arch::arch::memory_protection::MemoryRegion;
use bern_arch::IMemoryProtection;
use bern_arch::memory_protection::{Access, Config, Permission, Type};
use bern_conf::CONF;
use crate::exec::process::ProcessInternal;
use crate::sched::event::Event;
use crate::stack::Stack;
use crate::time;

#[cfg(feature = "log-defmt")]
use defmt::Formatter;

#[cfg(feature = "_log_fmt")]
use core::fmt::Display;

pub trait RunnableTrait: 'static + FnMut() -> RunnableResult {}
pub type RunnableResult = (); // todo: replace with '!' when possible


/// Transition for next context switch
#[derive(Copy, Clone, PartialEq)]
#[repr(u8)]
pub enum Transition {
    /// No transition
    None,
    /// Task is going into sleep mode
    Sleeping,
    /// Task es beeing blocked and waiting for an event
    Blocked,
    /// Resume suspended task
    Resuming,
    /// Terminate task
    Terminating,
}


/// # Issue with closures and static tasks
///
/// Every closure has its own anonymous type. A closure can only be stored in a
/// generic struct. The task object stored in the task "list" (array) must all
/// have the same size -> not generic. Thus, the closure can only be referenced
/// as trait object. But need to force the closure to be static, so our
/// reference can be as well. A static closure is not possible, as every static
/// needs a specified type.
/// To overcome the issue of storing a closure into a static task we need to
/// **copy** it into a static stack. Access to the closure is provided via a
/// closure trait object, which now references a static object which cannot go
/// out of scope.


/// Task priority.
///
/// 0 is the highest priority.
#[derive(PartialEq, PartialOrd, Debug, Copy, Clone)]
pub struct Priority(u8);
// todo: check priority range at compile time

impl Priority {
    const _HIGHEST: Priority = Priority(0);
    const LOWEST: Priority = Priority(CONF.kernel.priorities - 2);
    const IDLE: Priority = Priority(CONF.kernel.priorities - 1);
    pub(crate) const MAX: Priority = Priority(u8::MAX);

    pub const fn new(prio: u8) -> Self {
        assert!(prio <= Priority::LOWEST.0);
        Priority(prio)
    }

    pub fn is_idle(&self) -> bool {
        self.raw() == Priority::IDLE.raw()
    }

    pub const fn idle() -> Self {
        Priority::IDLE
    }

    pub fn is_interrupt_handler(self) -> bool {
        self.raw() == 0
    }

    pub fn raw(&self) -> u8 {
        self.0
    }
}

impl Default for Priority {
    fn default() -> Self {
        Priority::LOWEST
    }
}

impl From<Priority> for usize {
    fn from(p: Priority) -> Self {
        p.raw() as usize
    }
}

impl From<Priority> for u8 {
    fn from(p: Priority) -> Self {
        p.raw()
    }
}



// todo: manage lifetime of stack & runnable
/// Task control block
pub struct Runnable {
    id: u32,
    process: &'static ProcessInternal,
    transition: Transition,
    runnable_ptr: *mut usize,
    next_wut: u64,
    stack: Stack,
    priority: Priority,
    blocking_event: Option<NonNull<Event>>,
    memory_regions: [MemoryRegion; 3],
    name: &'static str,
}

impl Runnable {
    pub(crate) fn new(process: &'static ProcessInternal, runnable_ptr: *mut usize, stack: Stack, priority: Priority, name: Option<&'static str>) -> Self {
        // prepare memory region configs
        let memory_regions = [
            Arch::prepare_memory_region(
                0,
                Config {
                    addr: process.start_addr() as *const _,
                    memory: Type::SramInternal,
                    size: process.size(),
                    access: Access { user: Permission::ReadWrite, system: Permission::ReadWrite },
                    executable: false
                }),
            Arch::prepare_memory_region(
                1,
                Config {
                    addr: stack.bottom_ptr() as *const _,
                    memory: Type::SramInternal,
                    size: Arch::min_region_size(),
                    access: Access { user: Permission::NoAccess, system: Permission::NoAccess },
                    executable: false
                }),
            Arch::prepare_unused_region(2)
        ];

        Runnable {
            process,
            transition: Transition::None,
            runnable_ptr,
            next_wut: 0,
            stack,
            priority,
            blocking_event: None,
            memory_regions,
            id: 0,
            name: name.unwrap_or("\0"),
        }
    }

    pub(crate) fn runnable_ptr(&self) -> *const usize {
        self.runnable_ptr
    }

    pub(crate) fn stack(&self) -> &Stack {
        &self.stack
    }
    pub(crate) fn stack_mut(&mut self) -> &mut Stack {
        &mut self.stack
    }

    pub(crate) fn next_wut(&self) -> u64 {
        self.next_wut
    }
    pub(crate) fn sleep(&mut self, ms: u32) {
        self.next_wut = time::tick_count() + u64::from(ms);
    }

    pub(crate) fn transition(&self) -> &Transition {
        &self.transition
    }
    pub(crate) fn set_transition(&mut self, transition: Transition) {
        self.transition = transition;
    }

    pub(crate) fn priority(&self) -> Priority {
        self.priority
    }

    pub(crate) fn memory_regions(&self) -> &[MemoryRegion; 3] {
        &self.memory_regions
    }

    pub(crate) fn blocking_event(&self) -> Option<NonNull<Event>> {
        self.blocking_event
    }
    pub(crate) fn set_blocking_event(&mut self, event: NonNull<Event>) {
        self.blocking_event = Some(event);
    }

    pub(crate) fn process(&self) -> &ProcessInternal {
        self.process
    }

    pub(crate) fn id(&self) -> u32 {
        self.id
    }
    pub(crate) fn set_id(&mut self, id: u32) {
        self.id = id;
    }

    pub(crate) fn name(&self) -> &'static str {
        self.name
    }
}

/// Static and non-generic entry point of the task.
///
/// This function simply starts the closure stored on the task stack. It will
/// only be called when the task runs for the first time.
///
/// **Note:** Don't be fooled by the `&mut &mut` the first one is a reference
/// and second one is part of the trait object type
pub(crate) fn entry(entry_fn: &mut &mut (dyn FnMut() -> RunnableResult)) {
    (entry_fn)();
}

#[cfg(feature = "log-defmt")]
impl defmt::Format for Runnable {
    fn format(&self, fmt: Formatter) {
        defmt::write!(fmt, "None    {:02}          {:05}B/{:05}B ({:02}%)",
            self.priority.0,
            self.stack.usage().0,
            self.stack.capacity().0,
            (self.stack.usage().0 as f32 / self.stack.capacity().0 as f32 * 100f32) as u8,
        )
    }
}

#[cfg(feature = "_log_fmt")]
impl Display for Runnable {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        write!(f, "None    {:02}          {:05}B/{:05}B ({:02}%)",
              self.priority.0,
              self.stack.usage().0,
              self.stack.capacity().0,
              (self.stack.usage().0 as f32 / self.stack.capacity().0 as f32 * 100f32) as u8,
        )
    }
}