use std::path::{Path,PathBuf};
use std::process::{Command,ExitStatus,Stdio};
use std::mem;
use libc::{self, c_char};
use std::ffi::CStr;
use std::str::from_utf8_unchecked;
use std::env;
use std::fs::File;
use std::io::{self,Seek,Read,BufReader,SeekFrom};

use failure::ResultExt;

use crate::Result;

fn search_path(filename: &str) -> Result<PathBuf> {
    let path_var = env::var("PATH")?;
    for mut path in env::split_paths(&path_var) {
        path.push(filename);
        if path.exists() {
            return Ok(path);
        }
    }
    Err(format_err!("Could not find {} in $PATH", filename))
}

pub fn ensure_command_exists(cmd: &str) -> Result<()> {
    let path = Path::new(cmd);
    if !path.is_absolute() {
        search_path(cmd)?;
        return Ok(())
    } else if path.exists() {
        return Ok(())
    }
    Err(format_err!("Cannot execute '{}': command does not exist", cmd))
}

pub fn exec_cmdline<S: AsRef<str>>(cmd_path: &str, args: S) -> Result<()> {
    ensure_command_exists(cmd_path)?;
    let args: Vec<&str> = args.as_ref().split_whitespace().collect::<Vec<_>>();
    let status = Command::new(cmd_path)
        .args(args)
        .stderr(Stdio::inherit())
        .status()?;

    check_cmd_status(cmd_path, &status)
}

pub fn exec_cmdline_quiet<S: AsRef<str>>(cmd_path: &str, args: S) -> Result<()> {
    ensure_command_exists(cmd_path)?;
    let args: Vec<&str> = args.as_ref().split_whitespace().collect::<Vec<_>>();
    let status = Command::new(cmd_path)
        .args(args)
        .stderr(Stdio::null())
        .stdout(Stdio::null())
        .status()?;

    check_cmd_status(cmd_path, &status)
}

pub fn exec_cmdline_with_output<S: AsRef<str>>(cmd_path: &str, args: S) -> Result<String> {
    ensure_command_exists(cmd_path)?;
    let args: Vec<&str> = args.as_ref().split_whitespace().collect::<Vec<_>>();
    let res = Command::new(cmd_path)
        .args(args)
        .stderr(Stdio::inherit())
        .output()
        .context(format!("unable to execute {}", cmd_path))?;

    check_cmd_status(cmd_path, &res.status)?;
    Ok(String::from_utf8(res.stdout).unwrap().trim().to_owned())
}

fn check_cmd_status(cmd_path: &str, status: &ExitStatus) -> Result<()> {
    if !status.success() {
        match status.code() {
            Some(code) => bail!("command {} failed with exit code: {}", cmd_path, code),
            None => bail!("command {} failed with no exit code", cmd_path),
        }
    }
    Ok(())
}

pub fn sha256<P: AsRef<Path>>(path: P) -> Result<String> {
    let output = exec_cmdline_with_output("/usr/bin/sha256sum", format!("{}", path.as_ref().display()))
        .context(format!("failed to calculate sha256 on {}", path.as_ref().display()))?;

    let v: Vec<&str> = output.split_whitespace().collect();
    Ok(v[0].trim().to_owned())
}

pub enum FileRange {
    All,
    Offset(usize),
    Range{offset: usize, len: usize},
}

fn ranged_reader<P: AsRef<Path>>(path: P, range: FileRange) -> Result<Box<dyn Read>> {
    let mut f = File::open(path.as_ref())?;
    let offset = match range {
        FileRange::All => 0,
        FileRange::Offset(n) => n,
        FileRange::Range {offset, len: _} => offset,
    };
    if offset > 0 {
        f.seek(SeekFrom::Start(offset as u64))?;
    }
    let r = BufReader::new(f);
    if let FileRange::Range {offset: _, len} = range {
        Ok(Box::new(r.take(len as u64)))
    } else {
        Ok(Box::new(r))
    }
}

///
/// Execute a command, pipe the contents of a file to stdin, return the output as a `String`
///
pub fn exec_cmdline_pipe_input<S,P>(cmd_path: &str, args: S, input: P, range: FileRange) -> Result<String>
    where S: AsRef<str>, P: AsRef<Path>
{
    let mut r = ranged_reader(input.as_ref(), range)?;
    ensure_command_exists(cmd_path)?;
    let args: Vec<&str> = args.as_ref().split_whitespace().collect::<Vec<_>>();
    let mut child = Command::new(cmd_path)
        .args(args)
        .stdin(Stdio::piped())
        .stdout(Stdio::piped())
        .stderr(Stdio::inherit())
        .spawn()
        .context(format!("unable to execute {}", cmd_path))?;

    let stdin = child.stdin.as_mut().unwrap();
    io::copy(&mut r, stdin)?;
    let output = child.wait_with_output()?;
    Ok(String::from_utf8(output.stdout).unwrap().trim().to_owned())
}

pub fn xz_compress<P: AsRef<Path>>(path: P) -> Result<()> {
    exec_cmdline("/usr/bin/xz", format!("-T0 {}", path.as_ref().display()))
        .context(format!("failed to compress {}", path.as_ref().display()))?;
    Ok(())
}

pub fn xz_decompress<P: AsRef<Path>>(path: P) -> Result<()> {
    exec_cmdline("/usr/bin/xz", format!("-d {}", path.as_ref().display()))
        .context(format!("failed to decompress {}", path.as_ref().display()))?;
    Ok(())
}

pub fn mount<P: AsRef<Path>>(source: &str, target: P, options: Option<&str>) -> Result<()> {
    let paths = format!("{} {}", source, target.as_ref().display());
    let args = match options {
        Some(s) => format!("{} {}", s, paths),
        None => paths,
    };
    exec_cmdline("/usr/bin/mount", args)
}

pub fn umount<P: AsRef<Path>>(path: P) -> Result<()> {
    let args = format!("{}", path.as_ref().display());
    exec_cmdline("/usr/bin/umount", args)
}


#[repr(C)]
#[derive(Clone, Copy)]
pub struct UtsName(libc::utsname);

#[allow(dead_code)]
impl UtsName {
    pub fn sysname(&self) -> &str {
        to_str(&(&self.0.sysname as *const c_char ) as *const *const c_char)
    }

    pub fn nodename(&self) -> &str {
        to_str(&(&self.0.nodename as *const c_char ) as *const *const c_char)
    }

    pub fn release(&self) -> &str {
        to_str(&(&self.0.release as *const c_char ) as *const *const c_char)
    }

    pub fn version(&self) -> &str {
        to_str(&(&self.0.version as *const c_char ) as *const *const c_char)
    }

    pub fn machine(&self) -> &str {
        to_str(&(&self.0.machine as *const c_char ) as *const *const c_char)
    }
}

pub fn uname() -> UtsName {
    unsafe {
        let mut ret: UtsName = mem::uninitialized();
        libc::uname(&mut ret.0);
        ret
    }
}

#[inline]
fn to_str<'a>(s: *const *const c_char) -> &'a str {
    unsafe {
        let res = CStr::from_ptr(*s).to_bytes();
        from_utf8_unchecked(res)
    }
}