use std::mem;
use libc::{c_int, c_uint, c_void, c_ulong, pid_t};
use errno::Errno;
use {Result, Error};

pub type CloneFlags = c_uint;

pub static CLONE_VM:             CloneFlags = 0x00000100;
pub static CLONE_FS:             CloneFlags = 0x00000200;
pub static CLONE_FILES:          CloneFlags = 0x00000400;
pub static CLONE_SIGHAND:        CloneFlags = 0x00000800;
pub static CLONE_PTRACE:         CloneFlags = 0x00002000;
pub static CLONE_VFORK:          CloneFlags = 0x00004000;
pub static CLONE_PARENT:         CloneFlags = 0x00008000;
pub static CLONE_THREAD:         CloneFlags = 0x00010000;
pub static CLONE_NEWNS:          CloneFlags = 0x00020000;
pub static CLONE_SYSVSEM:        CloneFlags = 0x00040000;
pub static CLONE_SETTLS:         CloneFlags = 0x00080000;
pub static CLONE_PARENT_SETTID:  CloneFlags = 0x00100000;
pub static CLONE_CHILD_CLEARTID: CloneFlags = 0x00200000;
pub static CLONE_DETACHED:       CloneFlags = 0x00400000;
pub static CLONE_UNTRACED:       CloneFlags = 0x00800000;
pub static CLONE_CHILD_SETTID:   CloneFlags = 0x01000000;
pub static CLONE_NEWUTS:         CloneFlags = 0x04000000;
pub static CLONE_NEWIPC:         CloneFlags = 0x08000000;
pub static CLONE_NEWUSER:        CloneFlags = 0x10000000;
pub static CLONE_NEWPID:         CloneFlags = 0x20000000;
pub static CLONE_NEWNET:         CloneFlags = 0x40000000;
pub static CLONE_IO:             CloneFlags = 0x80000000;

// Support a maximum CPU set of 1024 nodes
#[cfg(all(target_arch = "x86_64", target_os = "linux"))]
mod cpuset_attribs {
    use super::CpuMask;
    pub const CPU_SETSIZE:           usize = 1024;
    pub const CPU_MASK_BITS:         usize = 64;

    #[inline]
    pub fn set_cpu_mask_flag(cur: CpuMask, bit: usize) -> CpuMask {
        cur | (1u64 << bit)
    }

    #[inline]
    pub fn clear_cpu_mask_flag(cur: CpuMask, bit: usize) -> CpuMask {
        cur & !(1u64 << bit)
    }
}

#[cfg(all(target_arch = "x86", target_os = "linux"))]
mod cpuset_attribs {
    use super::CpuMask;
    pub const CPU_SETSIZE:           usize = 1024;
    pub const CPU_MASK_BITS:         usize = 32;

    #[inline]
    pub fn set_cpu_mask_flag(cur: CpuMask, bit: usize) -> CpuMask {
        cur | (1u32 << bit)
    }

    #[inline]
    pub fn clear_cpu_mask_flag(cur: CpuMask, bit: usize) -> CpuMask {
        cur & !(1u32 << bit)
    }
}

#[cfg(all(target_arch = "arm", any(target_os = "linux", target_os = "android")))]
mod cpuset_attribs {
    use super::CpuMask;
    // bionic only supports up to 32 independent CPUs, instead of 1024.
    pub const CPU_SETSIZE:          usize = 32;
    pub const CPU_MASK_BITS:        usize = 32;

    #[inline]
    pub fn set_cpu_mask_flag(cur: CpuMask, bit: usize) -> CpuMask {
        cur | (1u32 << bit)
    }

    #[inline]
    pub fn clear_cpu_mask_flag(cur: CpuMask, bit: usize) -> CpuMask {
        cur & !(1u32 << bit)
    }
}


pub type CloneCb<'a> = Box<FnMut() -> isize + 'a>;

// A single CPU mask word
pub type CpuMask = c_ulong;

// Structure representing the CPU set to apply
#[repr(C)]
#[derive(Clone, Copy)]
pub struct CpuSet {
    cpu_mask: [CpuMask; cpuset_attribs::CPU_SETSIZE/cpuset_attribs::CPU_MASK_BITS]
}

impl CpuSet {
    pub fn new() -> CpuSet {
        CpuSet {
            cpu_mask: unsafe { mem::zeroed() }
        }
    }

    pub fn set(&mut self, field: usize) {
        let word = field / cpuset_attribs::CPU_MASK_BITS;
        let bit = field % cpuset_attribs::CPU_MASK_BITS;

        self.cpu_mask[word] = cpuset_attribs::set_cpu_mask_flag(self.cpu_mask[word], bit);
    }

    pub fn unset(&mut self, field: usize) {
        let word = field / cpuset_attribs::CPU_MASK_BITS;
        let bit = field % cpuset_attribs::CPU_MASK_BITS;

        self.cpu_mask[word] = cpuset_attribs::clear_cpu_mask_flag(self.cpu_mask[word], bit);
    }
}

mod ffi {
    use libc::{c_void, c_int, pid_t, size_t};
    use super::CpuSet;

    type CloneCb = extern "C" fn (data: *const super::CloneCb) -> c_int;

    // We cannot give a proper #[repr(C)] to super::CloneCb
    #[allow(improper_ctypes)]
    extern {
        // create a child process
        // doc: http://man7.org/linux/man-pages/man2/clone.2.html
        pub fn clone(
            cb: *const CloneCb,
            child_stack: *mut c_void,
            flags: super::CloneFlags,
            arg: *mut super::CloneCb,
            ...) -> c_int;

        // disassociate parts of the process execution context
        // doc: http://man7.org/linux/man-pages/man2/unshare.2.html
        pub fn unshare(flags: super::CloneFlags) -> c_int;

        // Set the current CPU set that a task is allowed to run on
        pub fn sched_setaffinity(__pid: pid_t, __cpusetsize: size_t, __cpuset: *const CpuSet) -> c_int;
    }
}

pub fn sched_setaffinity(pid: isize, cpuset: &CpuSet) -> Result<()> {
    use libc::{pid_t, size_t};

    let res = unsafe {
        ffi::sched_setaffinity(pid as pid_t, mem::size_of::<CpuSet>() as size_t, mem::transmute(cpuset))
    };

    if res != 0 {
        Err(Error::Sys(Errno::last()))
    } else {
        Ok(())
    }
}

pub fn clone(mut cb: CloneCb, stack: &mut [u8], flags: CloneFlags) -> Result<pid_t> {
    extern "C" fn callback(data: *mut CloneCb) -> c_int {
        let cb: &mut CloneCb = unsafe { &mut *data };
        (*cb)() as c_int
    }

    let res = unsafe {
        let ptr = stack.as_mut_ptr().offset(stack.len() as isize);
        ffi::clone(mem::transmute(callback), ptr as *mut c_void, flags, &mut cb)
    };

    if res < 0 {
        return Err(Error::Sys(Errno::last()));
    }

    Ok(res)
}

pub fn unshare(flags: CloneFlags) -> Result<()> {
    let res = unsafe { ffi::unshare(flags) };

    if res != 0 {
        return Err(Error::Sys(Errno::last()));
    }

    Ok(())
}