use crate::mmio::MmioAccess;
use crate::queue::{Descriptor, VirtioQueue};
use libkos::Window;
use types::address::{ByteOffset, PhysicalAddress};
use types::display::Dimension;

/// The command page: commands go out from its start, responses come back
/// at `RESPONSE`.
pub struct GpuDmaAddrs {
    pub cmd_pa: PhysicalAddress,
    pub cmd: Window,
    pub resp_pa: PhysicalAddress,
}

pub const RESPONSE: ByteOffset = ByteOffset::new(512);

/// Command fields (virtio spec 5.7.6.7): a 24-byte header, then the body.
const TYPE: ByteOffset = ByteOffset::new(0);
const BODY: ByteOffset = ByteOffset::new(24);
/// Most bodies start with a rectangle: x, y, width, height.
const RECT_X: ByteOffset = ByteOffset::new(24);
const RECT_Y: ByteOffset = ByteOffset::new(28);
const RECT_W: ByteOffset = ByteOffset::new(32);
const RECT_H: ByteOffset = ByteOffset::new(36);
/// The 24 bytes of header and 16 of rectangle in a display-info response.
const DISPLAY_W: ByteOffset = ByteOffset::new(24 + 8);
const DISPLAY_H: ByteOffset = ByteOffset::new(24 + 12);

pub fn create_2d(mmio: &impl MmioAccess, queue: &VirtioQueue, dma: &GpuDmaAddrs, resource_id: u32, width: Dimension, height: Dimension) -> bool {
    write_cmd_header(&dma.cmd, 0x0101);
    // Resource id, format (134: R8G8B8X8, a window's own byte order, so
    // its rows are copied as they are), width, height.
    dma.cmd.write(BODY, resource_id);
    dma.cmd.write(BODY + 4, 134u32);
    dma.cmd.write(BODY + 8, width.raw() as u32);
    dma.cmd.write(BODY + 12, height.raw() as u32);
    submit_cmd(mmio, queue, dma, 40)
}

pub fn attach_backing(mmio: &impl MmioAccess, queue: &VirtioQueue, dma: &GpuDmaAddrs, resource_id: u32, fb_pa: PhysicalAddress, fb_size: u32) -> bool {
    write_cmd_header(&dma.cmd, 0x0106);
    // Resource id, one memory entry: its address and length.
    dma.cmd.write(BODY, resource_id);
    dma.cmd.write(BODY + 4, 1u32);
    dma.cmd.write(BODY + 8, fb_pa.raw() as u64);
    dma.cmd.write(BODY + 16, fb_size);
    submit_cmd(mmio, queue, dma, 48)
}

pub fn set_scanout(mmio: &impl MmioAccess, queue: &VirtioQueue, dma: &GpuDmaAddrs, scanout_id: u32, resource_id: u32, width: Dimension, height: Dimension) -> bool {
    write_cmd_header(&dma.cmd, 0x0103);
    // The rectangle (from 0, 0), then scanout and resource ids.
    dma.cmd.write(RECT_W, width.raw() as u32);
    dma.cmd.write(RECT_H, height.raw() as u32);
    dma.cmd.write(BODY + 16, scanout_id);
    dma.cmd.write(BODY + 20, resource_id);
    submit_cmd(mmio, queue, dma, 48)
}

/// A rectangle of a resource, in pixels.
#[derive(Clone, Copy, Debug)]
pub struct Rect {
    pub x: u32,
    pub y: u32,
    pub w: u32,
    pub h: u32,
}

/// Copies `rect` of the backing to the host; `offset` is where its top
/// left pixel is in the backing, in bytes.
pub fn transfer_to_host(mmio: &impl MmioAccess, queue: &VirtioQueue, dma: &GpuDmaAddrs, resource_id: u32, rect: Rect, offset: u64) -> bool {
    write_cmd_header(&dma.cmd, 0x0105);
    put_rect(&dma.cmd, rect);
    // Offset into the resource's memory, then the resource id.
    dma.cmd.write(BODY + 16, offset);
    dma.cmd.write(BODY + 24, resource_id);
    submit_cmd(mmio, queue, dma, 56)
}

pub fn resource_flush(mmio: &impl MmioAccess, queue: &VirtioQueue, dma: &GpuDmaAddrs, resource_id: u32, rect: Rect) -> bool {
    write_cmd_header(&dma.cmd, 0x0104);
    put_rect(&dma.cmd, rect);
    dma.cmd.write(BODY + 16, resource_id);
    submit_cmd(mmio, queue, dma, 48)
}

fn write_cmd_header(cmd: &Window, cmd_type: u32) {
    cmd.fill_u32(ByteOffset::ZERO, 128, 0);
    cmd.write(TYPE, cmd_type);
}

fn put_rect(cmd: &Window, r: Rect) {
    cmd.write(RECT_X, r.x);
    cmd.write(RECT_Y, r.y);
    cmd.write(RECT_W, r.w);
    cmd.write(RECT_H, r.h);
}

pub fn get_display_info(mmio: &impl MmioAccess, queue: &VirtioQueue, dma: &GpuDmaAddrs) -> Option<(u32, u32)> {
    write_cmd_header(&dma.cmd, 0x0100);
    let descs = [
        Descriptor { addr: dma.cmd_pa.raw() as u64, len: 24, writable: false },
        Descriptor { addr: dma.resp_pa.raw() as u64, len: 408, writable: true },
    ];
    if !queue.submit(mmio, &descs) { return None; }
    if dma.cmd.read::<u32>(RESPONSE) != 0x1101 { return None; }
    let w: u32 = dma.cmd.read(RESPONSE + DISPLAY_W.raw());
    let h: u32 = dma.cmd.read(RESPONSE + DISPLAY_H.raw());
    if w > 0 && h > 0 { Some((w, h)) } else { None }
}

fn submit_cmd(mmio: &impl MmioAccess, queue: &VirtioQueue, dma: &GpuDmaAddrs, cmd_len: u32) -> bool {
    let descs = [
        Descriptor { addr: dma.cmd_pa.raw() as u64, len: cmd_len, writable: false },
        Descriptor { addr: dma.resp_pa.raw() as u64, len: 24, writable: true },
    ];
    queue.submit(mmio, &descs)
}