use core::arch::asm;

use lazy_static::lazy_static;

use crate::log_information;
use crate::sbi::shutdown;
use crate::sync::single_cell::SingleCell;
use crate::trap::context::TrapContext;

const MAX_APP_NUMBER: usize = 32;
const APP_BASE_ADDRESS: usize = 0x80400000;
const APP_SIZE_LIMIT: usize = 0x20000;

struct AppManager {
    app_count: usize,
    current: usize,
    start_addresses: [usize; MAX_APP_NUMBER + 1],
}

lazy_static! {
    static ref APP_MANAGER: SingleCell<AppManager> = unsafe {
        SingleCell::new({
            extern "C" {
                fn _num_app();
            }

            let num_app_ptr = _num_app as usize as *const usize;
            let num_app = num_app_ptr.read_volatile();
            let mut start_addresses: [usize; MAX_APP_NUMBER + 1] = [0; MAX_APP_NUMBER + 1];
            let start_addresses_raw: &[usize] =
                core::slice::from_raw_parts(num_app_ptr.add(1), num_app + 1);
            start_addresses[..=num_app].copy_from_slice(start_addresses_raw);
            AppManager {
                app_count: num_app,
                current: 0,
                start_addresses,
            }
        })
    };
}

impl AppManager {
    pub fn print_app_information(&self) {
        log_information!("[kernel] Application count is {}.", self.app_count);

        for i in 0..self.app_count {
            log_information!(
                "[kernel] Application_{} ({:#x} -> {:#x})",
                i,
                self.start_addresses[i],
                self.start_addresses[i + 1]
            );
        }
    }

    pub fn get_current_app(&self) -> usize {
        self.current
    }

    pub fn move_to_next_app(&mut self) {
        self.current += 1;
    }

    unsafe fn load_app(&self, app_id: usize) {
        if app_id >= self.app_count {
            panic!("Application id is invalid!");
        }

        log_information!("[kernel] Loading application_{}...", app_id);

        core::slice::from_raw_parts_mut(APP_BASE_ADDRESS as *mut u8, APP_SIZE_LIMIT).fill(0);

        let app_source = core::slice::from_raw_parts(
            self.start_addresses[app_id] as *const u8,
            self.start_addresses[app_id + 1] - self.start_addresses[app_id],
        );
        let app_destination =
            core::slice::from_raw_parts_mut(APP_BASE_ADDRESS as *mut u8, app_source.len());
        app_destination.copy_from_slice(app_source);

        // 保证指令缓存的更新
        // 因为上述代码会修改指令数据段
        asm!("fence.i");
    }
}

const USER_STACK_SIZE: usize = 4096 * 2;
const KERNEL_STACK_SIZE: usize = 4096 * 2;

#[repr(align(4096))]
struct UserStack {
    data: [u8; USER_STACK_SIZE],
}

impl UserStack {
    fn get_sp(&self) -> usize {
        self.data.as_ptr() as usize + USER_STACK_SIZE
    }
}

#[repr(align(4096))]
struct KernelStack {
    data: [u8; KERNEL_STACK_SIZE],
}

impl KernelStack {
    fn get_sp(&self) -> usize {
        self.data.as_ptr() as usize + KERNEL_STACK_SIZE
    }

    pub fn push_context(&self, context: TrapContext) -> &'static mut TrapContext {
        let context_pointer = (self.get_sp() - size_of::<TrapContext>()) as *mut TrapContext;
        unsafe {
            *context_pointer = context;
            context_pointer.as_mut().unwrap()
        }
    }
}

static KERNEL_STACK: KernelStack = KernelStack {
    data: [0; KERNEL_STACK_SIZE],
};
static USER_STACK: UserStack = UserStack {
    data: [0; USER_STACK_SIZE],
};

pub fn print_app_information() {
    let app_manager = APP_MANAGER.exclusive_borrow();
    app_manager.print_app_information();
}

pub fn run_next_application() -> ! {
    let mut app_manager = APP_MANAGER.exclusive_borrow();
    let current_app = app_manager.get_current_app();
    if current_app >= app_manager.app_count {
        log_information!("Run out of applications, the os will stop!");
        shutdown(true);
    }

    unsafe {
        app_manager.load_app(current_app);
    }
    app_manager.move_to_next_app();

    // We must drop resource manually
    // As this function will never return!
    drop(app_manager);

    extern "C" {
        fn __restore(context_address: usize);
    }

    unsafe {
        let context_address = KERNEL_STACK.push_context(TrapContext::init_application_context(
            APP_BASE_ADDRESS,
            USER_STACK.get_sp(),
        )) as *const _ as usize;
        __restore(context_address);

        unreachable!()
    }
}