use std::fmt::Display;
use std::fs;
use std::io::{Error, ErrorKind, Read, Result, Write};
use std::path::{Path, PathBuf};
use std::str::FromStr;

#[macro_export]
macro_rules! method {
    ($file:tt $with:tt $out:tt) => {
        pub fn $file(&self) -> Result<$out> {
            self.$with(stringify!($file))
        }
    };

    ($file:expr, $method:tt $with:tt $out:tt) => {
        pub fn $method(&self) -> Result<$out> {
            self.$with($file)
        }
    };
}

#[macro_export]
macro_rules! trait_method {
    ($file:tt $with:tt $out:tt) => {
        fn $file(&self) -> Result<$out> {
            self.$with(stringify!($file))
        }
    };

    ($file:expr, $method:tt $with:tt $out:tt) => {
        fn $method(&self) -> Result<$out> {
            self.$with($file)
        }
    };
}

#[macro_export]
macro_rules! set_method {
    ($file:expr, $method:tt $with:ty) => {
        pub fn $method(&self, input: $with) -> Result<()> {
            use numtoa::NumToA;
            let mut buf = [0u8; 20];
            self.write_file($file, input.numtoa_str(10, &mut buf))
        }
    };

    ($file:expr, $method:tt) => {
        pub fn $method<B: AsRef<[u8]>>(&self, input: B) -> Result<()> {
            self.write_file($file, input.as_ref())
        }
    };
}

#[macro_export]
macro_rules! set_trait_method {
    ($file:expr, $method:tt $with:ty) => {
        fn $method(&self, input: $with) -> Result<()> {
            use numtoa::NumToA;
            let mut buf = [0u8; 20];
            self.write_file($file, input.numtoa_str(10, &mut buf))
        }
    };

    ($file:expr, $method:tt) => {
        fn $method<B: AsRef<[u8]>>(&self, input: B) -> Result<()> {
            self.write_file($file, input.as_ref())
        }
    };
}

pub trait SysClass: Sized {
    /// Sets the base directory, which defaults to `class`.
    fn base() -> &'static str {
        "class"
    }
    /// Return the class of the sys object, the name of a folder in `/sys/${base}``
    fn class() -> &'static str;

    /// Create a sys object from an absolute path without checking path for validity
    unsafe fn from_path_unchecked(path: PathBuf) -> Self;

    /// Return the path of the sys object
    fn path(&self) -> &Path;

    /// Return the path to the sys objects, the full path of a folder in /sys/class
    fn dir() -> PathBuf {
        Path::new("/sys/").join(Self::base()).join(Self::class())
    }

    /// Create a sys object from a path, checking it for validity
    fn from_path(path: &Path) -> Result<Self> {
        {
            let parent = path.parent().ok_or_else(|| {
                Error::new(
                    ErrorKind::InvalidInput,
                    format!("{}: does not have parent", path.display()),
                )
            })?;

            let dir = Self::dir();
            if parent != dir {
                return Err(Error::new(
                    ErrorKind::InvalidInput,
                    format!("{}: is not a child of {}", path.display(), dir.display()),
                ));
            }
        }

        fs::read_dir(&path)?;

        Ok(unsafe { Self::from_path_unchecked(path.to_owned()) })
    }

    /// Retrieve all of the object instances of a sys class
    fn all() -> Result<Vec<Self>> {
        let mut ret = Vec::new();

        for entry_res in fs::read_dir(Self::dir())? {
            let entry = entry_res?;
            ret.push(Self::from_path(&entry.path())?);
        }

        Ok(ret)
    }

    /// Retrieve all of the object instances of a sys class, with a boxed iterator
    fn iter() -> Box<dyn Iterator<Item = Result<Self>>>
    where
        Self: 'static,
    {
        match fs::read_dir(Self::dir()) {
            Ok(entries) => Box::new(
                entries.map(|entry_res| entry_res.and_then(|entry| Self::from_path(&entry.path()))),
            ),
            Err(why) => Box::new(::std::iter::once(Err(why))),
        }
    }

    /// Create a sys object by id, checking it for validity
    fn new(id: &str) -> Result<Self> {
        Self::from_path(&Self::dir().join(id))
    }

    /// Return the id of the sys object
    fn id(&self) -> &str {
        self.path()
            .file_name()
            .unwrap() // A valid path does not end in .., so safe
            .to_str()
            .unwrap() // A valid path must be valid UTF-8, so safe
    }

    /// Read a file underneath the sys object
    fn read_file<P: AsRef<Path>>(&self, name: P) -> Result<String> {
        let mut data = String::new();

        {
            let path = self.path().join(name.as_ref());
            let mut file = fs::OpenOptions::new().read(true).open(path)?;
            file.read_to_string(&mut data)?;
        }

        Ok(data)
    }

    /// Parse a number from a file underneath the sys object
    fn parse_file<F: FromStr, P: AsRef<Path>>(&self, name: P) -> Result<F>
    where
        F::Err: Display,
    {
        self.read_file(name.as_ref())?
            .trim()
            .parse()
            .map_err(|err| {
                Error::new(
                    ErrorKind::InvalidData,
                    format!("{}: {}", name.as_ref().display(), err),
                )
            })
    }

    /// Read a file underneath the sys object and trim whitespace
    fn trim_file<P: AsRef<Path>>(&self, name: P) -> Result<String> {
        let data = self.read_file(name)?;
        Ok(data.trim().to_string())
    }

    /// Write a file underneath the sys object
    fn write_file<P: AsRef<Path>, S: AsRef<[u8]>>(&self, name: P, data: S) -> Result<()> {
        {
            let path = self.path().join(name.as_ref());
            let mut file = fs::OpenOptions::new().write(true).open(path)?;
            file.write_all(data.as_ref())?
        }

        Ok(())
    }
}