extern crate libc;

use std::error::Error;
use std::io;
use std::fmt;
use std::ptr;
use std::ops::Drop;
use libc::{c_void, c_int};

#[cfg(windows)]
use std::mem;

fn errno() -> i32 {
    io::Error::last_os_error().raw_os_error().unwrap_or(-1)
}

#[cfg(unix)]
fn page_size() -> usize {
    unsafe { libc::sysconf(libc::_SC_PAGESIZE) as usize }
}

#[cfg(windows)]
fn page_size() -> usize {
    unsafe {
        let mut info = mem::zeroed();
        libc::GetSystemInfo(&mut info);

        info.dwPageSize as usize
    }
}

// Round up `from` to be divisible by `to`
fn round_up(from: usize, to: usize) -> usize {
    let r = if from % to == 0 {
        from
    } else {
        from + to - (from % to)
    };
    if r == 0 {
        to
    } else {
        r
    }
}

/// Type of memory map
#[derive(Copy,Clone)]
pub enum MemoryMapKind {
    /// Virtual memory map. Usually used to change the permissions of a given
    /// chunk of memory.  Corresponds to `VirtualAlloc` on Windows.
    File(*const u8),
    /// Virtual memory map. Usually used to change the permissions of a given
    /// chunk of memory, or for allocation. Corresponds to `VirtualAlloc` on
    /// Windows.
    Virtual,
}

/// Options memory map created with.
#[derive(Copy,Clone)]
pub enum MemoryMapOption {
    /// The memory should be readable.
    Readable,
    /// The memory should be writable.
    Writable,
    /// The memory should be executable.
    Executable,
    /// Create a map for a specific address range. Corresponds to `MAP_FIXED` on
    /// POSIX.
    Addr(*const u8),
    /// Create a memory mapping for a file with a given HANDLE.
    #[cfg(windows)]
    Fd(libc::HANDLE),
    /// Create a memory mapping for a file with a given fd.
    #[cfg(not(windows))]
    Fd(c_int),
    /// When using `MapFd`, the start of the map is `usize` bytes from the start
    /// of the file.
    Offset(usize),
    /// On POSIX, this can be used to specify the default flags passed to
    /// `mmap`. By default it uses `MAP_PRIVATE` and, if not using `MapFd`,
    /// `MAP_ANON`. This will override both of those. This is platform-specific
    /// (the exact values used) and ignored on Windows.
    NonStandardFlags(c_int),
}

/// Possible errors when creating a map.
#[derive(Debug,Clone,Copy)]
pub enum MemoryMapError {
    /// # The following are POSIX-specific
    ///
    /// fd was not open for reading or, if using `MapWritable`, was not open for
    /// writing.
    FdNotAvail,
    /// fd was not valid
    InvalidFd,
    /// Either the address given by `MapAddr` or offset given by `MapOffset` was
    /// not a multiple of `MemoryMap::granularity` (unaligned to page size).
    Unaligned,
    /// With `MapFd`, the fd does not support mapping.
    NoMapSupport,
    /// If using `MapAddr`, the address + `min_len` was outside of the process's
    /// address space. If using `MapFd`, the target of the fd didn't have enough
    /// resources to fulfill the request.
    NoMem,
    /// A zero-length map was requested. This is invalid according to
    /// [POSIX](http://pubs.opengroup.org/onlinepubs/9699919799/functions/mmap.html).
    /// Not all platforms obey this, but this wrapper does.
    ZeroLength,
    /// Unrecognized error. The inner value is the unrecognized errno.
    Unknown(isize),
    /// # The following are Windows-specific
    ///
    /// Unsupported combination of protection flags
    /// (`MapReadable`/`MapWritable`/`MapExecutable`).
    UnsupProt,
    /// When using `MapFd`, `MapOffset` was given (Windows does not support this
    /// at all)
    UnsupOffset,
    /// When using `MapFd`, there was already a mapping to the file.
    AlreadyExists,
    /// Unrecognized error from `VirtualAlloc`. The inner value is the return
    /// value of GetLastError.
    VirtualAlloc(i32),
    /// Unrecognized error from `CreateFileMapping`. The inner value is the
    /// return value of `GetLastError`.
    CreateFileMappingW(i32),
    /// Unrecognized error from `MapViewOfFile`. The inner value is the return
    /// value of `GetLastError`.
    MapViewOfFile(i32),
}

impl fmt::Display for MemoryMapError {
    fn fmt(&self, out: &mut fmt::Formatter) -> fmt::Result {
        let str = match *self {
            MemoryMapError::FdNotAvail => "fd not available for reading or writing",
            MemoryMapError::InvalidFd => "Invalid fd",
            MemoryMapError::Unaligned => {
                "Unaligned address, invalid flags, negative length or unaligned offset"
            }
            MemoryMapError::NoMapSupport => "File doesn't support mapping",
            MemoryMapError::NoMem => "Invalid address, or not enough available memory",
            MemoryMapError::UnsupProt => "Protection mode unsupported",
            MemoryMapError::UnsupOffset => "Offset in virtual memory mode is unsupported",
            MemoryMapError::AlreadyExists => "File mapping for specified file already exists",
            MemoryMapError::ZeroLength => "Zero-length mapping not allowed",
            MemoryMapError::Unknown(code) => return write!(out, "Unknown error = {}", code),
            MemoryMapError::VirtualAlloc(code) => {
                return write!(out, "VirtualAlloc failure = {}", code)
            }
            MemoryMapError::CreateFileMappingW(code) => {
                return write!(out, "CreateFileMappingW failure = {}", code)
            }
            MemoryMapError::MapViewOfFile(code) => {
                return write!(out, "MapViewOfFile failure = {}", code)
            }
        };
        write!(out, "{}", str)
    }
}

impl Error for MemoryMapError {
    fn description(&self) -> &str {
        "memory map error"
    }
}

/// A memory mapped file or chunk of memory. This is a very system-specific
/// interface to the OS's memory mapping facilities (`mmap` on POSIX,
/// `VirtualAlloc`/`CreateFileMapping` on Windows). It makes no attempt at
/// abstracting platform differences, besides in error values returned. Consider
/// yourself warned.
///
/// The memory map is released (unmapped) when the destructor is run, so don't
/// let it leave scope by accident if you want it to stick around.
pub struct MemoryMap {
    data: *mut u8,
    len: usize,
    kind: MemoryMapKind,
}

#[cfg(unix)]
impl MemoryMap {
    /// Create a new mapping with the given `options`, at least `min_len` bytes
    /// long. `min_len` must be greater than zero; see the note on
    /// `ErrZeroLength`.
    pub fn new(min_len: usize, options: &[MemoryMapOption]) -> Result<MemoryMap, MemoryMapError> {
        use libc::off_t;

        if min_len == 0 {
            return Err(MemoryMapError::ZeroLength);
        }

        let mut addr: *const u8 = ptr::null();
        let mut prot = 0;
        let mut flags = libc::MAP_PRIVATE;
        let mut fd = -1;
        let mut offset = 0;
        let mut custom_flags = false;
        let len = round_up(min_len, page_size());

        for &option in options {
            match option {
                MemoryMapOption::Readable => prot |= libc::PROT_READ,
                MemoryMapOption::Writable => prot |= libc::PROT_WRITE,
                MemoryMapOption::Executable => prot |= libc::PROT_EXEC,
                MemoryMapOption::Addr(addr_) => {
                    flags |= libc::MAP_FIXED;
                    addr = addr_;
                }
                MemoryMapOption::Fd(fd_) => {
                    flags |= libc::MAP_FILE;
                    fd = fd_;
                }
                MemoryMapOption::Offset(offset_) => offset = offset_ as off_t,
                MemoryMapOption::NonStandardFlags(f) => {
                    custom_flags = true;
                    flags = f;
                }
            }
        }

        if fd == -1 && !custom_flags {
            flags |= libc::MAP_ANON;
        }

        let r: *mut libc::c_void = unsafe {
            libc::mmap(addr as *mut c_void,
                       len as libc::size_t,
                       prot,
                       flags,
                       fd,
                       offset)
        };

        if r == libc::MAP_FAILED {
            Err(match errno() {
                libc::EACCES => MemoryMapError::FdNotAvail,
                libc::EBADF => MemoryMapError::InvalidFd,
                libc::EINVAL => MemoryMapError::Unaligned,
                libc::ENODEV => MemoryMapError::NoMapSupport,
                libc::ENOMEM => MemoryMapError::NoMem,
                code => MemoryMapError::Unknown(code as isize),
            })
        } else {
            let mut kind = MemoryMapKind::File(ptr::null());
            if fd == -1 {
                kind = MemoryMapKind::Virtual;
            }

            Ok(MemoryMap {
                data: r as *mut u8,
                len: len,
                kind: kind,
            })
        }
    }

    /// Granularity that the offset or address must be for `MapOffset` and
    /// `MapAddr` respectively.
    pub fn granularity() -> usize {
        page_size()
    }

    /// Flushes changes in memory back to the filesystem.
    pub fn flush(&self, offset: usize, len: usize) -> Result<(), MemoryMapError> {
        let flags = libc::MS_SYNC | libc::MS_INVALIDATE;
        let alignment = (self.data as usize + offset) % page_size();
        let aligned_offset = offset as isize - alignment as isize;
        let aligned_len = len + alignment;

        let result = unsafe {
            libc::msync(self.data.offset(aligned_offset) as *mut c_void,
                        aligned_len as libc::size_t,
                        flags)
        };

        match result {
            0 => Ok(()),
            _ => Err(MemoryMapError::Unknown(result as isize)),
        }
    }

    /// Flushes changes in memory back to the filesystem asynchronously.
    pub fn flush_async(&self, offset: usize, len: usize) -> Result<(), MemoryMapError> {
        let flags = libc::MS_ASYNC | libc::MS_INVALIDATE;
        let alignment = (self.data as usize + offset) % page_size();
        let aligned_offset = offset - alignment;
        let aligned_len = len + alignment;

        let result = unsafe {
            libc::msync(self.data.offset(aligned_offset as isize) as *mut c_void,
                        aligned_len as libc::size_t,
                        flags)
        };

        match result {
            0 => Ok(()),
            _ => Err(MemoryMapError::Unknown(result as isize)),
        }

    }
}

#[cfg(unix)]
impl Drop for MemoryMap {
    /// Unmap the mapping. Panics if `munmap` panics.
    fn drop(&mut self) {
        if self.len == 0 {
            return;
        }

        unsafe {
            // `munmap` only panics due to logic errors.
            libc::munmap(self.data as *mut c_void, self.len as libc::size_t);
        }
    }
}

#[cfg(windows)]
impl MemoryMap {
    /// Create a new mapping with given `options`, at least `min_len` bytes long.
    pub fn new(min_len: usize, options: &[MemoryMapOption]) -> Result<MemoryMap, MemoryMapError> {
        use libc::types::os::arch::extra::{LPVOID, DWORD, SIZE_T};

        let mut lp_address: LPVOID = ptr::null_mut();
        let (mut readable, mut writable, mut executable) = (false, false, false);
        let mut handle = None;
        let mut offset: usize = 0;
        let mut len = round_up(min_len, page_size());

        for &option in options {
            match option {
                MemoryMapOption::MapReadable => readable = true,
                MemoryMapOption::MapWritable => writable = true,
                MemoryMapOption::MapExecutable => executable = true,
                MemoryMapOption::MapAddr(addr_) => lp_address = addr_ as LPVOID,
                MemoryMapOption::MapFd(handle_) => handle = Some(handle_),
                MemoryMapOption::MapOffset(offset_) => offset = offset_,
                MemoryMapOption::MapNonStandardFlags(..) => {}
            }
        }

        let fl_protect = match (executable, readable, writable) {
            (false, false, false) if handle.is_none() => libc::PAGE_NOACCESS,
            (false, true, false) => libc::PAGE_READONLY,
            (false, true, true) => libc::PAGE_READWRITE,
            (true, false, false) if handle.is_none() => libc::PAGE_EXECUTE,
            (true, true, false) => libc::PAGE_EXECUTE_READ,
            (true, true, true) => libc::PAGE_EXECUTE_READWRITE,
            _ => return Err(MemoryMapError::ErrUnsupProt),
        };

        if let Some(handle) = handle {
            let dw_desired_access = match (executable, readable, writable) {
                (false, true, false) => libc::FILE_MAP_READ,
                (false, true, true) => libc::FILE_MAP_WRITE,
                (true, true, false) => libc::FILE_MAP_READ | libc::FILE_MAP_EXECUTE,
                (true, true, true) => libc::FILE_MAP_WRITE | libc::FILE_MAP_EXECUTE,
                // In reality, we should never get here, because of the check above.
                _ => return Err(MemoryMapError::ErrUnsupProt),
            };

            unsafe {
                let h_file = handle;
                let mapping = libc::CreateFileMapping(h_file,
                                                      ptr::null_mut(),
                                                      fl_protect,
                                                      0,
                                                      0,
                                                      ptr::null());
                if mapping == ptr::null_mut() {
                    return Err(MemoryMapError::ErrCreateFileMappingW(errno()));
                }

                if errno() as c_int == libc::ERROR_ALREADY_EXISTS {
                    return Err(MemoryMapError::ErrAlreadyExists);
                }

                let r = libc::MapViewOfFile(mapping,
                                            dw_desired_access,
                                            ((len as u64) >> 32) as DWORD,
                                            (offset & 0xffff_ffff) as DWORD,
                                            0);
                match r as usize {
                    0 => return Err(MemoryMapError::ErrMapViewOfFile(errno())),
                    _ => {
                        return Ok(MemoryMap {
                            data: r as *mut u8,
                            len: len,
                            kind: MapFile(mapping as *const u8),
                        })
                    }
                }
            }
        } else {
            if offset != 0 {
                return Err(MemoryMapError::ErrUnsupOffset);
            }

            let r = unsafe {
                libc::VirtualAlloc(lp_address,
                                   len as SIZE_T,
                                   libc::MEM_COMMIT | libc::MEM_RESERVE,
                                   fl_protect)
            };

            match r as usize {
                0 => return Err(MemoryMapError::ErrVirtualAlloc()),
                _ => {
                    return Ok(MemoryMap {
                        data: r as *mut u8,
                        len: len,
                        kind: MemoryMapKind::MapVirtual,
                    })
                }
            }
        }
    }

    /// Granularity of MapAddr() and MapOffset parameter values.
    /// This may be greater than the value returned by page_size().
    pub fn granularity() -> usize {
        use std::mem;
        unsafe {
            let mut info = mem::zeroed();
            libc::GetSystemInfo(&mut info);

            return info.dwAllocationGranularity as usize;
        }
    }
}

#[cfg(windows)]
impl Drop for MemoryMap {
    /// Unmap the mapping. Panics the task if any of `VirtualFree`,
    /// `UnmapViewOfFile` or `CloseHandle` fail.
    fn drop(&mut self) {
        use libc::types::os::arch::extra::{LPCVOID, HANDLE};
        use libc::consts::os::extra::FALSE;

        if self.len == 0 {
            return;
        }

        unsafe {
            match self.kind {
                MemoryMapKind::MapVirtual => {
                    if libc::VirtualFree(self.data as *mut c_void, 0, libc::MEM_RELEASE) == 0 {
                        println!("VirtualFree failed: {}", errno());
                    }
                }
                MemoryMapKind::MapFile => {
                    if libc::UnmapViewOfFile(self.data as LPCVOID) == FALSE {
                        println!("UnmapViewOfFile failed: {}", errno());
                    }
                    if libc::CloseHandle(mapping as HANDLE) == FALSE {
                        println!("CloseHandle failed: {}", errno());
                    }
                }
            }
        }
    }
}


impl MemoryMap {
    ///Returns pointer to the memory created or modified by this map.
    pub fn data(&self) -> *mut u8 {
        self.data
    }

    /// Returns the number of bytes this map applies to.
    pub fn len(&self) -> usize {
        self.len
    }

    // Returns true if this map has length equal to 0.
    pub fn is_empty(&self) -> bool {
        self.len == 0
    }

    /// Returns the type of mapping this represents.
    pub fn kind(&self) -> MemoryMapKind {
        self.kind
    }

    pub fn set_data(&mut self, data: *mut u8) {
        self.data = data;
    }
}