//! VirtIO input device protocol definitions and modern PCI transport.
//!
//! Reference: Linux 7.1 drivers/virtio/virtio_input.c
//!           Linux 7.1 include/uapi/linux/virtio_input.h
//!
//! virtio-input is a paravirt input device used by QEMU. QEMU options:
//!   -device virtio-input-host-pci  (passthrough host input)
//!   -device virtio-input-keyboard
//!   -device virtio-input-mouse
//!   -device virtio-input-tablet
//!
//! The device uses a single event virtqueue (no status queue) and config-space
//! introspection to advertise supported event types and absolute axis ranges.

use log::{debug, info};
use redox_driver_sys::memory::{CacheType, MmioProt, MmioRegion};
use redox_driver_sys::pci::{PciDevice, PciDeviceInfo, PCI_CAP_ID_VNDR};

use crate::DriverError;

// virtio 1.0 §2.1 — device status register bits
pub const DEVICE_STATUS_RESET: u8 = 0x00;
pub const DEVICE_STATUS_ACKNOWLEDGE: u8 = 0x01;
pub const DEVICE_STATUS_DRIVER: u8 = 0x02;
pub const DEVICE_STATUS_DRIVER_OK: u8 = 0x04;
pub const DEVICE_STATUS_FEATURES_OK: u8 = 0x08;
pub const DEVICE_STATUS_NEEDS_RESET: u8 = 0x40;
pub const DEVICE_STATUS_FAILED: u8 = 0x80;
use crate::Result;

const VIRTIO_PCI_CAP_COMMON_CFG: u8 = 1;
const VIRTIO_PCI_CAP_NOTIFY_CFG: u8 = 2;
const VIRTIO_PCI_CAP_ISR_CFG: u8 = 3;
const VIRTIO_PCI_CAP_DEVICE_CFG: u8 = 4;

const COMMON_DEVICE_FEATURE_SELECT: usize = 0x00;
const COMMON_DEVICE_FEATURE: usize = 0x04;
const COMMON_DRIVER_FEATURE_SELECT: usize = 0x08;
const COMMON_DRIVER_FEATURE: usize = 0x0C;
const COMMON_MSIX_CONFIG: usize = 0x10;
const COMMON_NUM_QUEUES: usize = 0x12;
const COMMON_DEVICE_STATUS: usize = 0x14;
const COMMON_QUEUE_SELECT: usize = 0x16;
const COMMON_QUEUE_SIZE: usize = 0x18;
const COMMON_QUEUE_MSIX_VECTOR: usize = 0x1A;
const COMMON_QUEUE_ENABLE: usize = 0x1C;
const COMMON_QUEUE_NOTIFY_OFF: usize = 0x1E;
const COMMON_QUEUE_DESC_LO: usize = 0x20;
const COMMON_QUEUE_DESC_HI: usize = 0x24;
const COMMON_QUEUE_AVAIL_LO: usize = 0x28;
const COMMON_QUEUE_AVAIL_HI: usize = 0x2C;
const COMMON_QUEUE_USED_LO: usize = 0x30;
const COMMON_QUEUE_USED_HI: usize = 0x34;
const COMMON_CFG_REQUIRED_BYTES: usize = COMMON_QUEUE_USED_HI + core::mem::size_of::<u32>();

const ISR_STATUS_OFFSET: usize = 0;
const ISR_CFG_REQUIRED_BYTES: usize = ISR_STATUS_OFFSET + core::mem::size_of::<u8>();
const NOTIFY_CFG_REQUIRED_BYTES: usize = core::mem::size_of::<u16>();

// virtio_input.h enums
pub const VIRTIO_INPUT_CFG_UNSET: u8 = 0x00;
pub const VIRTIO_INPUT_CFG_ID_NAME: u8 = 0x01;
pub const VIRTIO_INPUT_CFG_ID_SERIAL: u8 = 0x02;
pub const VIRTIO_INPUT_CFG_ID_DEVIDS: u8 = 0x03;
pub const VIRTIO_INPUT_CFG_PROP_BITS: u8 = 0x10;
pub const VIRTIO_INPUT_CFG_EV_BITS: u8 = 0x11;
pub const VIRTIO_INPUT_CFG_ABS_INFO: u8 = 0x12;

// virtio_input_event is 8 bytes (type: u16, code: u16, value: u32)
pub const VIRTIO_INPUT_EVENT_SIZE: usize = 8;
pub const VIRTIO_INPUT_CONFIG_SIZE: usize = 40; // select(1) + subsel(1) + size(1) + reserved(5) + payload(32) = 40

/// Required feature bit: VIRTIO_F_VERSION_1 (bit 32).
pub const VIRTIO_F_VERSION_1: u64 = 1u64 << 32;

#[repr(C)]
#[derive(Clone, Copy, Debug, Default)]
struct VirtioPciCap {
    cap_vndr: u8,
    cap_next: u8,
    cap_len: u8,
    cfg_type: u8,
    bar: u8,
    id: u8,
    padding: [u8; 2],
    offset: u32,
    length: u32,
}

#[repr(C)]
#[derive(Clone, Copy, Debug, Default)]
struct VirtioPciNotifyCap {
    cap: VirtioPciCap,
    notify_off_multiplier: u32,
}

fn pci_error(e: redox_driver_sys::DriverError) -> DriverError {
    DriverError::Pci(format!("{e}"))
}

fn read_pci_cap(pci: &mut PciDevice, offset: u8) -> Result<VirtioPciCap> {
    let mut raw = [0u8; 16];
    for (i, byte) in raw.iter_mut().enumerate() {
        *byte = pci.read_config_byte(offset as u64 + i as u64)?;
    }
    Ok(VirtioPciCap {
        cap_vndr: raw[0],
        cap_next: raw[1],
        cap_len: raw[2],
        cfg_type: raw[3],
        bar: raw[4],
        id: raw[5],
        padding: [raw[6], raw[7]],
        offset: u32::from_le_bytes([raw[8], raw[9], raw[10], raw[11]]),
        length: u32::from_le_bytes([raw[12], raw[13], raw[14], raw[15]]),
    })
}

fn read_notify_cap(pci: &mut PciDevice, offset: u8) -> Result<VirtioPciNotifyCap> {
    let mut raw = [0u8; 20];
    for (i, byte) in raw.iter_mut().enumerate() {
        *byte = pci.read_config_byte(offset as u64 + i as u64)?;
    }
    let cap = VirtioPciCap {
        cap_vndr: raw[0],
        cap_next: raw[1],
        cap_len: raw[2],
        cfg_type: raw[3],
        bar: raw[4],
        id: raw[5],
        padding: [raw[6], raw[7]],
        offset: u32::from_le_bytes([raw[8], raw[9], raw[10], raw[11]]),
        length: u32::from_le_bytes([raw[12], raw[13], raw[14], raw[15]]),
    };
    let notify_off_multiplier = u32::from_le_bytes([raw[16], raw[17], raw[18], raw[19]]);
    Ok(VirtioPciNotifyCap { cap, notify_off_multiplier })
}

fn map_cap_region(
    info: &PciDeviceInfo,
    cap: &VirtioPciCap,
    label: &'static str,
    min_bytes: usize,
) -> Result<MmioRegion> {
    if cap.length < min_bytes as u32 {
        return Err(DriverError::Initialization(format!(
            "VirtIO input {label} cap length {min_bytes} required, got {}",
            cap.length
        )));
    }
    let bar = info.bars.get(cap.bar as usize).ok_or_else(|| {
        DriverError::Pci(format!(
            "VirtIO input {label}: BAR index {} out of range",
            cap.bar
        ))
    })?;
    let (phys_addr, bar_size) = bar
        .memory_info()
        .ok_or_else(|| DriverError::Pci(format!("VirtIO input {label}: BAR not memory")))?;
    // Verify the capability range fits within the BAR before mapping.
    // This prevents the MMIO mapping from extending past the BAR's
    // actual physical extent on a real device. (QEMU is permissive
    // and would not catch this; bare-metal hardware would.)
    let cap_end = u64::from(cap.offset)
        .checked_add(u64::from(cap.length))
        .ok_or_else(|| DriverError::Pci(format!("VirtIO input {label} capability range overflow")))?;
    if cap_end > bar_size as u64 {
        return Err(DriverError::Pci(format!(
            "VirtIO input {label} capability range [{:#x}, {:#x}) exceeds BAR{} size {:#x}",
            cap.offset, cap_end, cap.bar, bar_size
        )));
    }
    MmioRegion::map(
        phys_addr + cap.offset as u64,
        cap.length as usize,
        CacheType::Uncacheable,
        MmioProt::READ_WRITE,
    )
    .map_err(|e| DriverError::Mmio(format!("virtio-inputd: failed to map {label}: {e}")))
}

#[derive(Debug)]
pub struct QueueConfig {
    pub index: u16,
    pub size: u16,
    pub notify_off: u16,
}

pub struct VirtioModernPciTransport {
    common_cfg: MmioRegion,
    notify_cfg: MmioRegion,
    isr_cfg: MmioRegion,
    device_cfg: MmioRegion,
    notify_off_multiplier: u32,
}

impl VirtioModernPciTransport {
    pub fn new(info: &PciDeviceInfo, pci: &mut PciDevice) -> Result<Self> {
        let mut common_cap = None;
        let mut notify_cap = None;
        let mut isr_cap = None;
        let mut device_cap = None;

        let cap_ptr = pci.read_config_byte(0x34)?;
        if cap_ptr == 0 {
            return Err(DriverError::Initialization(
                "VirtIO input has no PCI capabilities".into(),
            ));
        }

        let mut offset = cap_ptr;
        let mut visited = 0u8;
        const MAX_CAPS: u8 = 48;
        while offset != 0 && visited < MAX_CAPS {
            visited += 1;
            let cap_id = pci.read_config_byte(offset as u64)?;
            let cap_next = pci.read_config_byte(offset as u64 + 1)?;
            if cap_id == PCI_CAP_ID_VNDR {
                let raw = read_pci_cap(pci, offset)?;
                match raw.cfg_type {
                    VIRTIO_PCI_CAP_COMMON_CFG => common_cap = Some(raw),
                    VIRTIO_PCI_CAP_NOTIFY_CFG => notify_cap = Some(read_notify_cap(pci, offset)?),
                    VIRTIO_PCI_CAP_ISR_CFG => isr_cap = Some(raw),
                    VIRTIO_PCI_CAP_DEVICE_CFG => device_cap = Some(raw),
                    _ => {}
                }
            }
            offset = cap_next;
        }

        info!(
            "virtio-inputd: VirtIO PCI capability scan found {} caps, common={} notify={} isr={} device={}",
            visited,
            common_cap.is_some(),
            notify_cap.is_some(),
            isr_cap.is_some(),
            device_cap.is_some(),
        );

        let common_cap = common_cap
            .ok_or_else(|| DriverError::Initialization("VirtIO input missing common_cfg".into()))?;
        let notify_cap = notify_cap
            .ok_or_else(|| DriverError::Initialization("VirtIO input missing notify_cfg".into()))?;
        let isr_cap = isr_cap
            .ok_or_else(|| DriverError::Initialization("VirtIO input missing isr_cfg".into()))?;
        let device_cap = device_cap
            .ok_or_else(|| DriverError::Initialization("VirtIO input missing device_cfg".into()))?;

        let common_cfg = map_cap_region(info, &common_cap, "common_cfg", COMMON_CFG_REQUIRED_BYTES)?;
        let notify_cfg = map_cap_region(
            info,
            &notify_cap.cap,
            "notify_cfg",
            NOTIFY_CFG_REQUIRED_BYTES,
        )?;
        let isr_cfg = map_cap_region(info, &isr_cap, "isr_cfg", ISR_CFG_REQUIRED_BYTES)?;
        let device_cfg = map_cap_region(info, &device_cap, "device_cfg", VIRTIO_INPUT_CONFIG_SIZE)?;

        info!(
            "virtio-inputd: VirtIO PCI transport mapped for {} (notify multiplier {})",
            info.location, notify_cap.notify_off_multiplier
        );

        Ok(Self {
            common_cfg,
            notify_cfg,
            isr_cfg,
            device_cfg,
            notify_off_multiplier: notify_cap.notify_off_multiplier,
        })
    }

    pub fn initialize_device(&mut self, requested_features: u64) -> Result<u64> {
        debug!("virtio-inputd: VirtIO reset device");
        self.write_device_status(0);
        self.write_device_status(DEVICE_STATUS_ACKNOWLEDGE);
        self.write_device_status(DEVICE_STATUS_ACKNOWLEDGE | DEVICE_STATUS_DRIVER);

        let available = self.read_device_features();
        if (available & requested_features) & VIRTIO_F_VERSION_1 == 0 {
            self.fail(format!(
                "VirtIO input missing VIRTIO_F_VERSION_1 (device features={available:#x})"
            ))?;
        }

        let negotiated = available & requested_features;
        self.write_driver_features(negotiated);

        let mut status = self.device_status();
        status |= DEVICE_STATUS_FEATURES_OK;
        self.write_device_status(status);

        if self.device_status() & DEVICE_STATUS_FEATURES_OK == 0 {
            self.fail("VirtIO input rejected FEATURES_OK during negotiation".into())?;
        }

        info!("virtio-inputd: VirtIO negotiated features device={available:#x} driver={negotiated:#x}");
        Ok(negotiated)
    }

    pub fn finalize_device(&mut self) {
        let status = self.device_status() | DEVICE_STATUS_DRIVER_OK;
        self.write_device_status(status);
    }

    pub fn device_status(&self) -> u8 {
        self.common_cfg.read8(COMMON_DEVICE_STATUS)
    }

    /// Returns true if the device has signalled FAILED or NEEDS_RESET
    /// since the last `finalize_device` call. The drain loop should
    /// check this on each iteration to detect a virtio-input device
    /// that has entered an unrecoverable state and bail out cleanly
    /// (virtio 1.0 §2.1.4 / §2.1.5).
    pub fn device_in_error_state(&self) -> bool {
        let s = self.device_status();
        (s & DEVICE_STATUS_FAILED) != 0 || (s & DEVICE_STATUS_NEEDS_RESET) != 0
    }

    /// Reset the device to a clean state. Called on probe failure paths
    /// after a partial `initialize_device` to avoid leaving the device
    /// in ACKNOWLEDGE | DRIVER with no driver active.
    pub fn reset_device(&mut self) {
        self.write_device_status(DEVICE_STATUS_RESET);
    }

    pub fn read_isr_status(&mut self) -> u8 {
        self.isr_cfg.read8(ISR_STATUS_OFFSET)
    }

    pub fn num_queues(&self) -> u16 {
        self.common_cfg.read16(COMMON_NUM_QUEUES)
    }

    pub fn prepare_queue(&self, index: u16, requested_size: u16) -> Result<QueueConfig> {
        self.select_queue(index);
        let device_size = self.common_cfg.read16(COMMON_QUEUE_SIZE);
        if device_size == 0 {
            return Err(DriverError::Initialization(format!(
                "VirtIO input queue {index} reports size 0"
            )));
        }
        let size = device_size.min(requested_size);
        let notify_off = self.common_cfg.read16(COMMON_QUEUE_NOTIFY_OFF);
        Ok(QueueConfig {
            index,
            size,
            notify_off,
        })
    }

    pub fn activate_queue(
        &self,
        index: u16,
        size: u16,
        desc_addr: u64,
        avail_addr: u64,
        used_addr: u64,
        msix_vector: Option<u16>,
    ) -> Result<()> {
        use std::sync::atomic::{fence, Ordering};
        self.select_queue(index);
        self.common_cfg.write16(COMMON_QUEUE_SIZE, size);
        self.common_cfg
            .write16(COMMON_QUEUE_MSIX_VECTOR, msix_vector.unwrap_or(u16::MAX));
        self.write_u64_pair(COMMON_QUEUE_DESC_LO, COMMON_QUEUE_DESC_HI, desc_addr);
        self.write_u64_pair(COMMON_QUEUE_AVAIL_LO, COMMON_QUEUE_AVAIL_HI, avail_addr);
        self.write_u64_pair(COMMON_QUEUE_USED_LO, COMMON_QUEUE_USED_HI, used_addr);
        // virtio spec §2.8: the queue configuration (addresses, MSIX vector)
        // must be visible to the device before queue_enable transitions
        // to 1. The MMIO region is uncacheable, but a CPU write buffer
        // may still reorder writes to distinct MMIO addresses. An explicit
        // full barrier is the documented hardening — Linux uses
        // `virtio_wmb()` here for the same reason.
        fence(Ordering::SeqCst);
        self.common_cfg.write16(COMMON_QUEUE_ENABLE, 1);
        if self.common_cfg.read16(COMMON_QUEUE_ENABLE) != 1 {
            return Err(DriverError::Initialization(format!(
                "VirtIO input queue {index} refused queue_enable"
            )));
        }
        Ok(())
    }

    pub fn set_config_msix_vector(&self, vector: Option<u16>) {
        self.common_cfg
            .write16(COMMON_MSIX_CONFIG, vector.unwrap_or(u16::MAX));
    }

    pub fn notify_queue(&self, queue_index: u16, notify_off: u16) -> Result<()> {
        let byte_offset = usize::from(notify_off)
            .checked_mul(self.notify_off_multiplier as usize)
            .ok_or_else(|| DriverError::Mmio("VirtIO notify offset overflow".into()))?;
        let end = byte_offset
            .checked_add(core::mem::size_of::<u16>())
            .ok_or_else(|| DriverError::Mmio("VirtIO notify MMIO overflow".into()))?;
        if end > self.notify_cfg.size() {
            return Err(DriverError::Mmio(format!(
                "VirtIO input queue notify outside notify_cfg window: end={end:#x} size={:#x}",
                self.notify_cfg.size()
            )));
        }
        self.notify_cfg.write16(byte_offset, queue_index);
        Ok(())
    }

    // Config-space read helpers (used to enumerate device capabilities)
    pub fn config_write_select(&mut self, select: u8, subsel: u8) {
        self.device_cfg.write8(0, select);
        self.device_cfg.write8(1, subsel);
    }

    pub fn config_read_size(&self) -> u8 {
        self.device_cfg.read8(2)
    }

    pub fn config_read_string(&mut self, max_len: usize, out: &mut [u8]) -> usize {
        let reported = self.config_read_size() as usize;
        let cap = reported.min(out.len()).min(max_len);
        for i in 0..cap {
            out[i] = self.device_cfg.read8(8 + i);
        }
        cap
    }

    pub fn config_read_bitmap(&mut self, max_len: usize, out: &mut [u8]) -> usize {
        let reported = self.config_read_size() as usize;
        let cap = reported.min(out.len()).min(max_len);
        for i in 0..cap {
            out[i] = self.device_cfg.read8(8 + i);
        }
        cap
    }

    pub fn config_read_absinfo(&mut self, abs_code: u8) -> Option<AbsInfo> {
        self.config_write_select(VIRTIO_INPUT_CFG_ABS_INFO, abs_code);
        if self.config_read_size() < 20 {
            return None;
        }
        let min = read_le32(&mut self.device_cfg, 8);
        let max = read_le32(&mut self.device_cfg, 12);
        let fuzz = read_le32(&mut self.device_cfg, 16);
        let flat = read_le32(&mut self.device_cfg, 20);
        let res = read_le32(&mut self.device_cfg, 24);
        Some(AbsInfo { min, max, fuzz, flat, res })
    }

    pub fn config_read_devids(&mut self) -> Option<DevIds> {
        self.config_write_select(VIRTIO_INPUT_CFG_ID_DEVIDS, 0);
        if self.config_read_size() < 8 {
            return None;
        }
        let bustype = read_le16(&mut self.device_cfg, 8);
        let vendor = read_le16(&mut self.device_cfg, 10);
        let product = read_le16(&mut self.device_cfg, 12);
        let version = read_le16(&mut self.device_cfg, 14);
        Some(DevIds { bustype, vendor, product, version })
    }

    fn fail<T>(&mut self, reason: String) -> Result<T> {
        let status = self.device_status() | DEVICE_STATUS_FAILED;
        self.write_device_status(status);
        Err(DriverError::Initialization(reason))
    }

    fn read_device_features(&self) -> u64 {
        self.common_cfg.write32(COMMON_DEVICE_FEATURE_SELECT, 0);
        let low = self.common_cfg.read32(COMMON_DEVICE_FEATURE) as u64;
        self.common_cfg.write32(COMMON_DEVICE_FEATURE_SELECT, 1);
        let high = self.common_cfg.read32(COMMON_DEVICE_FEATURE) as u64;
        low | (high << 32)
    }

    fn write_driver_features(&self, features: u64) {
        self.common_cfg.write32(COMMON_DRIVER_FEATURE_SELECT, 0);
        self.common_cfg
            .write32(COMMON_DRIVER_FEATURE, features as u32);
        self.common_cfg.write32(COMMON_DRIVER_FEATURE_SELECT, 1);
        self.common_cfg
            .write32(COMMON_DRIVER_FEATURE, (features >> 32) as u32);
    }

    fn write_device_status(&mut self, status: u8) {
        self.common_cfg.write8(COMMON_DEVICE_STATUS, status);
    }

    fn select_queue(&self, index: u16) {
        self.common_cfg.write16(COMMON_QUEUE_SELECT, index);
    }

    fn write_u64_pair(&self, lo: usize, hi: usize, value: u64) {
        self.common_cfg.write32(lo, value as u32);
        self.common_cfg.write32(hi, (value >> 32) as u32);
    }
}

/// virtio_input_absinfo (Linux include/uapi/linux/virtio_input.h)
#[derive(Clone, Copy, Debug, Default)]
pub struct AbsInfo {
    pub min: u32,
    pub max: u32,
    pub fuzz: u32,
    pub flat: u32,
    pub res: u32,
}

/// virtio_input_devids
#[derive(Clone, Copy, Debug, Default)]
pub struct DevIds {
    pub bustype: u16,
    pub vendor: u16,
    pub product: u16,
    pub version: u16,
}

/// A decoded virtio_input_event (8 bytes from the wire).
///
/// Wire layout per Linux include/uapi/linux/virtio_input.h:
///   struct virtio_input_event {
///       __le16 type;
///       __le16 code;
///       __le32 value;
///   };
#[derive(Clone, Copy, Debug, Default)]
pub struct VirtioInputEvent {
    pub event_type: u16,
    pub code: u16,
    pub value: i32,
}

impl VirtioInputEvent {
    pub fn read_le(buf: &[u8; VIRTIO_INPUT_EVENT_SIZE]) -> Self {
        Self {
            event_type: u16::from_le_bytes([buf[0], buf[1]]),
            code: u16::from_le_bytes([buf[2], buf[3]]),
            value: i32::from_le_bytes([buf[4], buf[5], buf[6], buf[7]]),
        }
    }
}

fn read_le16(mmio: &mut MmioRegion, offset: usize) -> u16 {
    let b0 = mmio.read8(offset);
    let b1 = mmio.read8(offset + 1);
    u16::from_le_bytes([b0, b1])
}

fn read_le32(mmio: &mut MmioRegion, offset: usize) -> u32 {
    let b0 = mmio.read8(offset);
    let b1 = mmio.read8(offset + 1);
    let b2 = mmio.read8(offset + 2);
    let b3 = mmio.read8(offset + 3);
    u32::from_le_bytes([b0, b1, b2, b3])
}