// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

use std::ffi::{OsStr, OsString};
use std::io;
use std::ops::RangeFrom;
use std::os::raw;
use std::os::windows::prelude::*;

pub struct RegistryKey(Repr);

type HKEY = *mut u8;
type DWORD = u32;
type LPDWORD = *mut DWORD;
type LPCWSTR = *const u16;
type LPWSTR = *mut u16;
type LONG = raw::c_long;
type PHKEY = *mut HKEY;
type PFILETIME = *mut u8;
type LPBYTE = *mut u8;
type REGSAM = u32;

const ERROR_SUCCESS: DWORD = 0;
const ERROR_NO_MORE_ITEMS: DWORD = 259;
const HKEY_LOCAL_MACHINE: HKEY = 0x80000002 as HKEY;
const REG_SZ: DWORD = 1;
const KEY_READ: DWORD = 0x20019;
const KEY_WOW64_32KEY: DWORD = 0x200;

#[link(name = "advapi32")]
extern "system" {
    fn RegOpenKeyExW(
        key: HKEY,
        lpSubKey: LPCWSTR,
        ulOptions: DWORD,
        samDesired: REGSAM,
        phkResult: PHKEY,
    ) -> LONG;
    fn RegEnumKeyExW(
        key: HKEY,
        dwIndex: DWORD,
        lpName: LPWSTR,
        lpcName: LPDWORD,
        lpReserved: LPDWORD,
        lpClass: LPWSTR,
        lpcClass: LPDWORD,
        lpftLastWriteTime: PFILETIME,
    ) -> LONG;
    fn RegQueryValueExW(
        hKey: HKEY,
        lpValueName: LPCWSTR,
        lpReserved: LPDWORD,
        lpType: LPDWORD,
        lpData: LPBYTE,
        lpcbData: LPDWORD,
    ) -> LONG;
    fn RegCloseKey(hKey: HKEY) -> LONG;
}

struct OwnedKey(HKEY);

enum Repr {
    Const(HKEY),
    Owned(OwnedKey),
}

pub struct Iter<'a> {
    idx: RangeFrom<DWORD>,
    key: &'a RegistryKey,
}

unsafe impl Sync for Repr {}
unsafe impl Send for Repr {}

pub static LOCAL_MACHINE: RegistryKey = RegistryKey(Repr::Const(HKEY_LOCAL_MACHINE));

impl RegistryKey {
    fn raw(&self) -> HKEY {
        match self.0 {
            Repr::Const(val) => val,
            Repr::Owned(ref val) => val.0,
        }
    }

    pub fn open(&self, key: &OsStr) -> io::Result<RegistryKey> {
        let key = key.encode_wide().chain(Some(0)).collect::<Vec<_>>();
        let mut ret = 0 as *mut _;
        let err = unsafe {
            RegOpenKeyExW(
                self.raw(),
                key.as_ptr(),
                0,
                KEY_READ | KEY_WOW64_32KEY,
                &mut ret,
            )
        };
        if err == ERROR_SUCCESS as LONG {
            Ok(RegistryKey(Repr::Owned(OwnedKey(ret))))
        } else {
            Err(io::Error::from_raw_os_error(err as i32))
        }
    }

    pub fn iter(&self) -> Iter {
        Iter {
            idx: 0..,
            key: self,
        }
    }

    pub fn query_str(&self, name: &str) -> io::Result<OsString> {
        let name: &OsStr = name.as_ref();
        let name = name.encode_wide().chain(Some(0)).collect::<Vec<_>>();
        let mut len = 0;
        let mut kind = 0;
        unsafe {
            let err = RegQueryValueExW(
                self.raw(),
                name.as_ptr(),
                0 as *mut _,
                &mut kind,
                0 as *mut _,
                &mut len,
            );
            if err != ERROR_SUCCESS as LONG {
                return Err(io::Error::from_raw_os_error(err as i32));
            }
            if kind != REG_SZ {
                return Err(io::Error::new(
                    io::ErrorKind::Other,
                    "registry key wasn't a string",
                ));
            }

            // The length here is the length in bytes, but we're using wide
            // characters so we need to be sure to halve it for the capacity
            // passed in.
            let mut v = Vec::with_capacity(len as usize / 2);
            let err = RegQueryValueExW(
                self.raw(),
                name.as_ptr(),
                0 as *mut _,
                0 as *mut _,
                v.as_mut_ptr() as *mut _,
                &mut len,
            );
            if err != ERROR_SUCCESS as LONG {
                return Err(io::Error::from_raw_os_error(err as i32));
            }
            v.set_len(len as usize / 2);

            // Some registry keys may have a terminating nul character, but
            // we're not interested in that, so chop it off if it's there.
            if v[v.len() - 1] == 0 {
                v.pop();
            }
            Ok(OsString::from_wide(&v))
        }
    }
}

impl Drop for OwnedKey {
    fn drop(&mut self) {
        unsafe {
            RegCloseKey(self.0);
        }
    }
}

impl<'a> Iterator for Iter<'a> {
    type Item = io::Result<OsString>;

    fn next(&mut self) -> Option<io::Result<OsString>> {
        self.idx.next().and_then(|i| unsafe {
            let mut v = Vec::with_capacity(256);
            let mut len = v.capacity() as DWORD;
            let ret = RegEnumKeyExW(
                self.key.raw(),
                i,
                v.as_mut_ptr(),
                &mut len,
                0 as *mut _,
                0 as *mut _,
                0 as *mut _,
                0 as *mut _,
            );
            if ret == ERROR_NO_MORE_ITEMS as LONG {
                None
            } else if ret != ERROR_SUCCESS as LONG {
                Some(Err(io::Error::from_raw_os_error(ret as i32)))
            } else {
                v.set_len(len as usize);
                Some(Ok(OsString::from_wide(&v)))
            }
        })
    }
}