//! Abstraction of the I/O APIC that is used for management of external interrupts.

use core::mem::size_of;
use core::sync::atomic::{AtomicPtr, AtomicU8, Ordering};

use bitfield_struct::bitfield;

use crate::arch::io::VolatileUpdate;

/// The different devices that can send interrupts
#[allow(unused)]
pub enum Device {
    /// Programmable Interrupt Timer
    Timer = 0,
    /// Keyboard
    Keyboard = 1,
    /// First serial interface
    Com1 = 4,
    /// Second serial interface
    Com2 = 3,
    /// Floppy device
    Floppy = 6,
    /// Printer
    LPT1 = 7,
    /// Real time clock
    RealTimeClock = 8,
    /// Mouse
    PS2Mouse = 12,
    /// First hard disk
    IDE1 = 14,
    /// Second hard disk
    IDE2 = 15,
}

/// The I/O APIC's Core component is the IO-redirection table.
/// This table is used to configure a flexible mapping between
/// the interrupt number and the external interruption.
/// Entries within this table have a width of 64 bit.
pub struct IoApic {
    /// Base address of the IOAPIC registers.
    ///
    /// It contains two memory-mapped registers: `IOREGSEL` at `base` and
    /// `IOWIN` at `base + 0x10`.
    pub base: AtomicPtr<u32>,
    overrides: [AtomicU8; 16],
}

/// The shared IOAPIC instance.
pub static IOAPIC: IoApic = IoApic::new();

impl IoApic {
    pub const DEFAULT_BASE: usize = 0xfec0_0000;
    pub const SLOT_MAX: u8 = 24;

    /// Create a new instance that has to be initialize with [Self::init].
    pub const fn new() -> IoApic {
        // Identity mapping (no redirections)
        let mut i = 0;
        let mut overrides = [const { AtomicU8::new(0) }; 16];
        while i < 16 {
            overrides[i] = AtomicU8::new(i as _);
            i += 1;
        }
        IoApic {
            base: AtomicPtr::new(Self::DEFAULT_BASE as _),
            overrides,
        }
    }

    /// Override a slot id, redirecting it
    pub fn set_override(&self, source: usize, global: u8) {
        if source < self.overrides.len() {
            self.overrides[source].store(global, Ordering::Relaxed);
        }
    }

    /// Initializes the I/O APIC.
    ///
    /// This function will initialize the I/O APIC by initializing the
    /// IO-redirection table with sane default values.
    /// The default interrupt-vector number is chosen such that,
    /// in case the interrupt is issued, the panic handler is executed.
    /// In the beginning, all external interrupts are disabled within the I/O APIC.
    /// Apart from the redirection table, the `id`
    /// (read from the system description tables during boot) needs to be passed in.
    pub fn init(&self, id: u8, panic_vector: u8) {
        // Set io apic id
        self.update(Identification::ADDR, |v: Identification| v.with_id(id));

        let reg = self.read::<Version>(Version::ADDR);
        serial!(
            "ioapic version: {:#x}, mre: {}",
            reg.version(),
            reg.max_redirection_entry()
        );

        for i in 0..Self::SLOT_MAX {
            self.config_raw(i, panic_vector, false);
        }
    }

    /// Creates a mapping between an interrupt vector and an external interrupt.
    pub fn config(&self, device: Device, vector: u8, trigger_level: bool) {
        let slot = self.slot(device);
        self.config_raw(slot, vector, trigger_level);
    }
    fn config_raw(&self, slot: u8, vector: u8, trigger_level: bool) {
        let reg_l = self
            .read::<SlotL>(red_l(slot))
            .with_vector(vector)
            .with_delivery_mode(1) // lowest pri
            .with_destination_mode(true) // logical
            .with_polarity(false) // high
            .with_trigger_mode(trigger_level) // edge or level triggered
            .with_mask(true);
        let reg_h = self.read::<SlotH>(red_h(slot)).with_destination(0b1);

        self.write(red_l(slot), reg_l);
        self.write(red_h(slot), reg_h);
    }

    /// Enables or disables interrupts for the given `device`.
    pub fn enable(&self, device: Device, enabled: bool) {
        let slot = self.slot(device);
        self.update(red_l(slot), |v: SlotL| v.with_mask(!enabled));
    }

    /// Returns whether interrupts for the `device` are active.
    pub fn enabled(&self, device: Device) -> bool {
        let slot = self.slot(device);
        !self.read::<SlotL>(red_l(slot)).mask()
    }

    /// Get the slot for the device (respecting redirections from the ACPI Tables).
    fn slot(&self, device: Device) -> u8 {
        let device = device as usize;
        if device < self.overrides.len() {
            self.overrides[device].load(Ordering::Relaxed)
        } else {
            device as _
        }
    }

    /// Write a value to a register.
    ///
    /// Access to the actual IOAPIC registers can be obtained by performing
    /// the following steps:
    ///
    /// 1. Write the number of the IOAPIC register to the address stored in `IOREGSEL`
    /// 2. Read the value from / write the value to the address referred to by `IOWIN`.
    fn write<T>(&self, addr: u32, reg: T) {
        debug_assert!(size_of::<T>() == 4);
        let base = self.base.load(Ordering::Acquire);
        unsafe {
            base.write_volatile(addr);
            base.add(0x10 / size_of::<u32>())
                .cast::<T>()
                .write_volatile(reg);
        }
    }

    /// Read a value from a register.
    fn read<T>(&self, addr: u32) -> T {
        debug_assert!(size_of::<T>() == 4);
        let base = self.base.load(Ordering::Acquire);
        unsafe {
            base.write_volatile(addr);
            base.add(0x10 / size_of::<u32>())
                .cast::<T>()
                .read_volatile()
        }
    }

    /// Read-modify-update the value of a register.
    fn update<T>(&self, addr: u32, f: impl FnOnce(T) -> T) {
        debug_assert!(size_of::<T>() == 4);
        let base = self.base.load(Ordering::Acquire);
        unsafe {
            base.write_volatile(addr);
            base.add(0x10 / size_of::<u32>())
                .cast::<T>()
                .update_volatile(f);
        }
    }
}

/// Returns the redirection table entry address for the `slot` (lower half).
fn red_l(slot: u8) -> u32 {
    2 * (slot as u32) + 0x10
}

/// Returns the redirection table entry address for the `slot` (upper half).
fn red_h(slot: u8) -> u32 {
    2 * (slot as u32) + 0x11
}

/// I/O APIC identification
#[bitfield(u32)]
struct Identification {
    #[bits(24)]
    _p: (),
    #[bits(4)]
    id: u8,
    #[bits(4)]
    _p: (),
}
impl Identification {
    const ADDR: u32 = 0;
}

/// I/O APIC hardware version information
#[bitfield(u32)]
struct Version {
    version: u8,
    _p: u8,
    max_redirection_entry: u8,
    _p: u8,
}
impl Version {
    const ADDR: u32 = 1;
}

/// Entry in the redirection table. Lower Half.
#[bitfield(u32)]
struct SlotL {
    /// Interrupt vector in the "Interrupt Descriptor Table (IDT)" will be
    /// activated when the corresponding external interrupt triggers.
    vector: u8,
    /// The delivery mode denotes the way the interrupts will be delivered
    /// to the local CPU cores, respectively to their local APICs.
    /// - 0: Fixed (send to all cores from the destination mask)
    /// - 1: Lowest priority (send to the lowest priority core from destination mask)
    /// - 2-7: System management / initialization / external interrupts...
    #[bits(3)]
    delivery_mode: u8,
    /// The destination mode defines how the value stored in destination will be interpreted.
    /// Local (true) or physical destination.
    destination_mode: bool,
    /// Delivery status holds whether the interrupt delivery is pending (true) or idle.
    delivery_pending: bool,
    /// The polarity denotes when an interrupt should be issued. This can be low (true) or high.
    polarity: bool,
    /// The remote IRR bit indicates whether the local APIC(s) accept the level interrupt.
    /// The LAPIC EOI sets this read-only flag to zero.
    remote_irr: bool,
    /// The trigger mode states whether the interrupt signaling is level (true) or edge triggered.
    trigger_mode: bool,
    /// Mask (disables) or unmask interrupts for a particular, external source.
    mask: bool,
    #[bits(15)]
    _p: (),
}

/// Entry in the redirection table. Higher Half.
#[bitfield(u32)]
struct SlotH {
    #[bits(24)]
    _p: (),
    /// Interrupt destination.
    ///
    /// The meaning of destination depends on the destination mode:
    /// For the logical destination mode, destination holds a bit mask made up
    /// of the cores that are candidates for receiving the interrupt.
    /// In the single-core case, this value is `1`, in the multi-core case,
    /// the `n` low-order bits needs to be set (with `n` being the number of
    /// CPU cores).
    /// Setting the `n` low-order bits marks all available cores as candidates
    /// for receiving interrupts and thereby balancing the number of interrupts
    /// between the cores.
    destination: u8,
}