// SPDX-License-Identifier: GPL-2.0
// Copyright (C) 2025 Google LLC.

//! Traits for rendering or updating values exported to DebugFS.

use crate::prelude::*;
use crate::sync::atomic::{Atomic, AtomicBasicOps, AtomicType, Relaxed};
use crate::sync::Mutex;
use crate::uaccess::UserSliceReader;
use core::fmt::{self, Debug, Formatter};
use core::str::FromStr;

/// A trait for types that can be written into a string.
///
/// This works very similarly to `Debug`, and is automatically implemented if `Debug` is
/// implemented for a type. It is also implemented for any writable type inside a `Mutex`.
///
/// The derived implementation of `Debug` [may
/// change](https://doc.rust-lang.org/std/fmt/trait.Debug.html#stability)
/// between Rust versions, so if stability is key for your use case, please implement `Writer`
/// explicitly instead.
pub trait Writer {
    /// Formats the value using the given formatter.
    fn write(&self, f: &mut Formatter<'_>) -> fmt::Result;
}

impl<T: Writer> Writer for Mutex<T> {
    fn write(&self, f: &mut Formatter<'_>) -> fmt::Result {
        self.lock().write(f)
    }
}

impl<T: Debug> Writer for T {
    fn write(&self, f: &mut Formatter<'_>) -> fmt::Result {
        writeln!(f, "{self:?}")
    }
}

/// A trait for types that can be updated from a user slice.
///
/// This works similarly to `FromStr`, but operates on a `UserSliceReader` rather than a &str.
///
/// It is automatically implemented for all atomic integers, or any type that implements `FromStr`
/// wrapped in a `Mutex`.
pub trait Reader {
    /// Updates the value from the given user slice.
    fn read_from_slice(&self, reader: &mut UserSliceReader) -> Result;
}

impl<T: FromStr + Unpin> Reader for Mutex<T> {
    fn read_from_slice(&self, reader: &mut UserSliceReader) -> Result {
        let mut buf = [0u8; 128];
        if reader.len() > buf.len() {
            return Err(EINVAL);
        }
        let n = reader.len();
        reader.read_slice(&mut buf[..n])?;

        let s = core::str::from_utf8(&buf[..n]).map_err(|_| EINVAL)?;
        let val = s.trim().parse::<T>().map_err(|_| EINVAL)?;
        *self.lock() = val;
        Ok(())
    }
}

impl<T: AtomicType + FromStr> Reader for Atomic<T>
where
    T::Repr: AtomicBasicOps,
{
    fn read_from_slice(&self, reader: &mut UserSliceReader) -> Result {
        let mut buf = [0u8; 21]; // Enough for a 64-bit number.
        if reader.len() > buf.len() {
            return Err(EINVAL);
        }
        let n = reader.len();
        reader.read_slice(&mut buf[..n])?;

        let s = core::str::from_utf8(&buf[..n]).map_err(|_| EINVAL)?;
        let val = s.trim().parse::<T>().map_err(|_| EINVAL)?;
        self.store(val, Relaxed);
        Ok(())
    }
}