//! /dev: device files. (Unix's big idea: devices look like files, so `cat`,
//! `>` and every program that reads or writes files can use them.)
//!
//!   /dev/null      reads as empty, swallows writes
//!   /dev/zero      reads as endless zero bytes, swallows writes
//!   /dev/random    random bytes (virtio-rng; /dev/urandom is the same --
//!   /dev/urandom   on modern Linux they only differ before boot-time seeding)
//!   /dev/console   the console terminal (keyboard + screen)
//!   /dev/hvc0      the virtio console: a second terminal
//!   /dev/tty       your controlling terminal, whichever it is (tty.rs)
//!   /dev/ptmx      opening it creates a pseudo-terminal: you get the
//!   /dev/pts/N     master end, and its slave end appears as /dev/pts/N
//!   /dev/fb0       the virtio-gpu framebuffer: pixels at byte offsets,
//!                  plus ioctls (see syscall.rs) for its size, flushing,
//!                  filling rectangles and moving the text console
//!
//! A tiny file system (`DevFs`) mounted at /dev lists them; opening one
//! gives a device-specific `File` (via `Inode::open_device`) instead of the
//! usual read-the-inode file. Linux does the same with "character device"
//! inodes whose `open` is routed to a driver.
//!
//! Stage 19: every node has a fixed identity, like on Linux. Its inode
//! number is the hash of its path (the same every time you look), and its
//! *device number* (`st_rdev`, "major:minor") says which driver it is:
//! 1:3 is null, 5:1 the console, 136:N the pty /dev/pts/N (`DEVICES`).
//! An open device file fstat()s as its node (syscall.rs `fd_stat`), which
//! is how `ttyname()` and the `tty` command find a terminal's name.

use crate::errno::Errno;
use crate::fs::file::{File, KIND_DEVICE, SEEK_CUR, SEEK_END, SEEK_SET, Stat};
use crate::fs::{DirEntry, FileSystem, Inode, InodeKind};
use crate::tty;
use crate::virtio::{console, gpu, rng};
use alloc::{string::String, sync::Arc, vec::Vec};
use spin::Mutex;

pub struct DevFs;

impl FileSystem for DevFs {
    fn name(&self) -> &'static str {
        "devfs"
    }
    fn root(&self) -> Arc<dyn Inode> {
        Arc::new(DevDir)
    }
}

/// Every device node: (name, major, minor, permissions) -- the numbers and
/// modes Linux gives the same devices.
const DEVICES: &[(&str, u64, u64, u32)] = &[
    ("null", 1, 3, 0o666),
    ("zero", 1, 5, 0o666),
    ("random", 1, 8, 0o666),
    ("urandom", 1, 9, 0o666),
    ("tty", 5, 0, 0o666),
    ("console", 5, 1, 0o600),
    ("ptmx", 5, 2, 0o666),
    ("hvc0", 229, 0, 0o600),
    ("fb0", 29, 0, 0o660),
];

/// The major number of /dev/pts/N (whose minor is N).
const PTS_MAJOR: u64 = 136;

/// The devices that exist on this machine.
fn names() -> Vec<&'static str> {
    let mut names = alloc::vec!["console", "null", "ptmx", "pts", "random", "tty", "urandom", "zero"];
    if console::present() {
        names.push("hvc0");
    }
    if gpu::framebuffer().is_some() {
        names.push("fb0");
    }
    names.sort();
    names
}

struct DevDir;

impl Inode for DevDir {
    fn kind(&self) -> InodeKind {
        InodeKind::Directory
    }
    fn size(&self) -> usize {
        names().len()
    }
    fn lookup(&self, name: &str) -> Result<Arc<dyn Inode>, Errno> {
        let name = names().into_iter().find(|n| *n == name).ok_or(Errno::ENOENT)?;
        if name == "pts" {
            return Ok(Arc::new(PtsDir));
        }
        Ok(Arc::new(DevNode(name)))
    }
    fn list(&self) -> Result<Vec<DirEntry>, Errno> {
        let kind = |n| if n == "pts" { InodeKind::Directory } else { InodeKind::Device };
        Ok(names().into_iter().map(|n| DirEntry { name: String::from(n), kind: kind(n), ino: 0 }).collect())
    }
}

/// /dev/pts: one entry per pseudo-terminal (named by number).
struct PtsDir;

impl Inode for PtsDir {
    fn kind(&self) -> InodeKind {
        InodeKind::Directory
    }
    fn size(&self) -> usize {
        tty::pty_count()
    }
    fn lookup(&self, name: &str) -> Result<Arc<dyn Inode>, Errno> {
        let n: usize = name.parse().map_err(|_| Errno::ENOENT)?;
        if !tty::pty_numbers().contains(&n) {
            return Err(Errno::ENOENT);
        }
        Ok(Arc::new(PtsNode(n)))
    }
    fn list(&self) -> Result<Vec<DirEntry>, Errno> {
        Ok(tty::pty_numbers().into_iter().map(|n| DirEntry { name: alloc::format!("{}", n), kind: InodeKind::Device, ino: 0 }).collect())
    }
}

struct PtsNode(usize);

impl Inode for PtsNode {
    fn kind(&self) -> InodeKind {
        InodeKind::Device
    }
    fn size(&self) -> usize {
        0
    }
    fn mode(&self) -> u32 {
        0o620
    }
    fn rdev(&self) -> u64 {
        crate::fs::file::makedev(PTS_MAJOR, self.0 as u64)
    }
    fn open_device(&self) -> Result<Option<Arc<dyn File>>, Errno> {
        tty::open_pts(self.0).map(Some)
    }
}

/// One device's directory entry.
struct DevNode(&'static str);

impl Inode for DevNode {
    fn kind(&self) -> InodeKind {
        InodeKind::Device
    }
    fn size(&self) -> usize {
        match self.0 {
            "fb0" => gpu::framebuffer().map_or(0, |f| f.size_bytes()),
            _ => 0,
        }
    }
    fn mode(&self) -> u32 {
        DEVICES.iter().find(|d| d.0 == self.0).map_or(0o666, |d| d.3)
    }
    fn rdev(&self) -> u64 {
        DEVICES.iter().find(|d| d.0 == self.0).map_or(0, |d| crate::fs::file::makedev(d.1, d.2))
    }
    fn open_device(&self) -> Result<Option<Arc<dyn File>>, Errno> {
        Ok(Some(match self.0 {
            "null" => Arc::new(Null),
            "zero" => Arc::new(Zero),
            "random" | "urandom" => Arc::new(Random(self.0)),
            "console" => tty::console_file(),
            "hvc0" => tty::open_hvc(),
            "tty" => tty::open_ctty()?,
            "ptmx" => tty::open_ptmx()?,
            "fb0" => Arc::new(Framebuffer::new(gpu::framebuffer().ok_or(Errno::ENODEV)?)),
            _ => return Ok(None),
        }))
    }
}

fn device_stat(size: usize) -> Result<Stat, Errno> {
    Ok(Stat { kind: KIND_DEVICE, size: size as u64, mode: 0o666 })
}

struct Null;

impl File for Null {
    fn read(&self, _buf: &mut [u8]) -> Result<usize, Errno> {
        Ok(0)
    }
    fn write(&self, buf: &[u8]) -> Result<usize, Errno> {
        Ok(buf.len())
    }
    fn stat(&self) -> Result<Stat, Errno> {
        device_stat(0)
    }
    fn proc_link(&self) -> Option<String> {
        Some(String::from("/dev/null"))
    }
}

/// /dev/zero: as many zero bytes as you ask for.
struct Zero;

impl File for Zero {
    fn read(&self, buf: &mut [u8]) -> Result<usize, Errno> {
        buf.fill(0);
        Ok(buf.len())
    }
    fn write(&self, buf: &[u8]) -> Result<usize, Errno> {
        Ok(buf.len())
    }
    fn stat(&self) -> Result<Stat, Errno> {
        device_stat(0)
    }
    fn proc_link(&self) -> Option<String> {
        Some(String::from("/dev/zero"))
    }
}

/// /dev/random or /dev/urandom (the name: which one was opened).
struct Random(&'static str);

impl File for Random {
    fn read(&self, buf: &mut [u8]) -> Result<usize, Errno> {
        let n = buf.len().min(65536);
        rng::fill(&mut buf[..n]);
        Ok(n)
    }
    /// Linux mixes written bytes into its pool; we have no pool, so we
    /// just accept them.
    fn write(&self, buf: &[u8]) -> Result<usize, Errno> {
        Ok(buf.len())
    }
    fn stat(&self) -> Result<Stat, Errno> {
        device_stat(0)
    }
    fn proc_link(&self) -> Option<String> {
        Some(alloc::format!("/dev/{}", self.0))
    }
}

/// /dev/fb0: the framebuffer as a file of `stride * height * 4` bytes.
/// Writing changes pixels in memory; they reach the screen on the FLUSH
/// ioctl or when the file is closed (we remember which rows changed).
pub struct Framebuffer {
    pub info: gpu::FbInfo,
    offset: Mutex<usize>,
    dirty: Mutex<Option<(u32, u32)>>, // pixel rows [first, last)
}

impl Framebuffer {
    fn new(info: gpu::FbInfo) -> Framebuffer {
        Framebuffer { info, offset: Mutex::new(0), dirty: Mutex::new(None) }
    }

    fn bytes(&self) -> &'static mut [u8] {
        unsafe { core::slice::from_raw_parts_mut(self.info.base as *mut u8, self.info.size_bytes()) }
    }

    /// Remember that pixel rows [y0, y1) changed.
    pub fn mark_dirty(&self, y0: u32, y1: u32) {
        let mut dirty = self.dirty.lock();
        *dirty = Some(match *dirty {
            Some((a, b)) => (a.min(y0), b.max(y1)),
            None => (y0, y1),
        });
    }

    /// Send the changed rows to the screen.
    pub fn flush(&self) -> bool {
        match self.dirty.lock().take() {
            Some((y0, y1)) => gpu::flush(0, y0, self.info.width, y1 - y0),
            None => true,
        }
    }

    /// Fill a rectangle with one colour (clipped to the screen).
    pub fn fill(&self, x: u32, y: u32, w: u32, h: u32, color: u32) {
        let (x0, y0) = (x.min(self.info.width), y.min(self.info.height));
        let (x1, y1) = (x.saturating_add(w).min(self.info.width), y.saturating_add(h).min(self.info.height));
        for row in y0..y1 {
            let start = (row * self.info.stride) as usize;
            let line = unsafe { core::slice::from_raw_parts_mut(self.info.pixels().add(start), self.info.width as usize) };
            line[x0 as usize..x1 as usize].fill(color);
        }
        if y1 > y0 {
            self.mark_dirty(y0, y1);
        }
    }
}

impl File for Framebuffer {
    fn read(&self, buf: &mut [u8]) -> Result<usize, Errno> {
        let mut offset = self.offset.lock();
        let src = self.bytes();
        let n = buf.len().min(src.len().saturating_sub(*offset));
        buf[..n].copy_from_slice(&src[*offset..*offset + n]);
        *offset += n;
        Ok(n)
    }
    fn write(&self, buf: &[u8]) -> Result<usize, Errno> {
        let mut offset = self.offset.lock();
        let dst = self.bytes();
        if *offset >= dst.len() && !buf.is_empty() {
            return Err(Errno::ENOSPC); // past the end of the screen
        }
        let n = buf.len().min(dst.len() - *offset);
        dst[*offset..*offset + n].copy_from_slice(&buf[..n]);
        let row_bytes = self.info.stride as usize * 4;
        if n > 0 {
            self.mark_dirty((*offset / row_bytes) as u32, ((*offset + n - 1) / row_bytes + 1) as u32);
        }
        *offset += n;
        Ok(n)
    }
    fn seek(&self, offset: i64, whence: u64) -> Result<u64, Errno> {
        let mut pos = self.offset.lock();
        let base = match whence {
            SEEK_SET => 0,
            SEEK_CUR => *pos as i64,
            SEEK_END => self.info.size_bytes() as i64,
            _ => return Err(Errno::EINVAL),
        };
        let new = base.checked_add(offset).filter(|&p| p >= 0).ok_or(Errno::EINVAL)?;
        *pos = new as usize;
        Ok(new as u64)
    }
    fn stat(&self) -> Result<Stat, Errno> {
        device_stat(self.info.size_bytes())
    }
    fn proc_link(&self) -> Option<String> {
        Some(String::from("/dev/fb0"))
    }
    fn as_framebuffer(&self) -> Option<&Framebuffer> {
        Some(self)
    }
}

impl Drop for Framebuffer {
    fn drop(&mut self) {
        self.flush(); // like close() on Linux's deferred-io framebuffers
    }
}