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//! Crate for fetching and modifying the intel_pstate kernel parameters.
//!
//! # Example
//!
//! ```rust,no_run
//! use std::io;
//! use intel_pstate::PState;
//!
//! fn main() -> io::Result<()> {
//!     if let Ok(pstate) = PState::new() {
//!         pstate.set_min_perf_pct(50)?;
//!         pstate.set_max_perf_pct(100)?;
//!         pstate.set_no_turbo(false)?;
//!     }
//!
//!     Ok(())
//! }
//! ```

use std::io::{self, Read, Write};
use std::fmt::Display;
use std::fs::{File, OpenOptions};
use std::path::{Path, PathBuf};
use std::str::FromStr;

/// Handle for fetching and modifying Intel PState kernel parameters.
/// 
/// # Note
/// 
/// - Currently, ony Linux is supported.
/// - Setting parameters will require root permissions.
pub struct PState {
    path: PathBuf,
}

impl PState {
    /// Attempt to fetch a handle to the Intel PState sysfs kernel instance.
    pub fn new() -> io::Result<PState> {
        let path = PathBuf::from("/sys/devices/system/cpu/intel_pstate");
        if path.is_dir() {
            Ok(PState { path })
        } else {
            Err(io::Error::new(io::ErrorKind::NotFound, "intel_pstate directory not found"))
        }
    }

    /// Get the minimum performance percent.
    pub fn min_perf_pct(&self) -> io::Result<u64> {
        parse_file(self.path.join("min_perf_pct"))
    }

    /// Set the minimum performance percent.
    pub fn set_min_perf_pct(&self, value: u64) -> io::Result<()> {
        write_file(self.path.join("min_perf_pct"), format!("{}", value))
    }

    /// Get the maximum performance percent.
    pub fn max_perf_pct(&self) -> io::Result<u64> {
        parse_file(self.path.join("max_perf_pct"))
    }

    /// Set the maximum performance percent.
    pub fn set_max_perf_pct(&self, value: u64) -> io::Result<()> {
        write_file(self.path.join("max_perf_pct"), format!("{}", value))
    }

    /// If true, this signifies that turbo is disabled.
    pub fn no_turbo(&self) -> io::Result<bool> {
        let value: u64 = parse_file(self.path.join("no_turbo"))?;
        Ok(value > 0)
    }

    /// Set the no_turbo value; `true` will disable turbo.
    pub fn set_no_turbo(&self, value: bool) -> io::Result<()> {
        write_file(self.path.join("no_turbo"), if value { "1" } else { "0" })
    }
}

fn read_file<P: AsRef<Path>>(path: P) -> io::Result<String> {
    let mut data = String::new();

    {
        let mut file = File::open(path.as_ref())?;
        file.read_to_string(&mut data)?;
    }

    Ok(data)
}

fn write_file<P: AsRef<Path>, S: AsRef<[u8]>>(path: P, data: S) -> io::Result<()> {
    {
        let mut file = OpenOptions::new().write(true).open(path)?;
        file.write_all(data.as_ref())?
    }

    Ok(())
}

fn parse_file<F: FromStr, P: AsRef<Path>>(path: P) -> io::Result<F> where F::Err: Display {
    read_file(path)?.trim().parse().map_err(|err| {
        io::Error::new(
            io::ErrorKind::InvalidData,
            format!("{}", err)
        )
    })
}