extern crate openvr_sys;

use std::sync::atomic::{Ordering, AtomicBool, ATOMIC_BOOL_INIT};
use std::{fmt, error, ptr, mem};
use std::ffi::{CStr, CString};
use std::cell::Cell;

use openvr_sys as sys;

mod tracking;

pub mod system;
pub mod compositor;
pub mod render_models;
pub mod property;

pub use tracking::*;

pub use sys::VkPhysicalDevice_T;
pub use sys::VkDevice_T;
pub use sys::VkInstance_T;
pub use sys::VkQueue_T;

static INITIALIZED: AtomicBool = ATOMIC_BOOL_INIT;

/// Initialize OpenVR
///
/// # Panics
///
/// When the library has already been initialized
///
/// # Safety
///
/// The `Context` MUST be dropped or shut down with `Context::shutdown` before shutting down the graphics API.
pub unsafe fn init(ty: ApplicationType) -> Result<Context, InitError> {
    if INITIALIZED.swap(true, Ordering::Acquire) {
        panic!("OpenVR has already been initialized!");
    }

    let mut error = sys::EVRInitError_VRInitError_None;
    sys::VR_InitInternal(&mut error, ty as sys::EVRApplicationType);
    if error != sys::EVRInitError_VRInitError_None {
        return Err(InitError(error));
    }
    if !sys::VR_IsInterfaceVersionValid(sys::IVRSystem_Version.as_ptr() as *const i8) {
        sys::VR_ShutdownInternal();
        return Err(InitError(sys::EVRInitError_VRInitError_Init_InterfaceNotFound));
    }
    Ok(Context { live: Cell::new(true) })
}

pub struct System<'a>(&'a sys::VR_IVRSystem_FnTable);
pub struct Compositor<'a>(&'a sys::VR_IVRCompositor_FnTable);
pub struct RenderModels<'a>(&'a sys::VR_IVRRenderModels_FnTable);

/// Entry points into OpenVR.
///
/// At most one of this object may exist at a time.
pub struct Context { live: Cell<bool> }

fn load<T>(suffix: &[u8]) -> Result<*const T, InitError> {
    let mut magic = Vec::from(b"FnTable:".as_ref());
    magic.extend(suffix);
    let mut error = sys::EVRInitError_VRInitError_None;
    let result = unsafe { sys::VR_GetGenericInterface(magic.as_ptr() as *const i8, &mut error) };
    if error != sys::EVRInitError_VRInitError_None {
        return Err(InitError(sys::EVRInitError_VRInitError_Init_InterfaceNotFound));
    }
    Ok(result as *const T)
}

impl Context {
    pub fn system(&self) -> Result<System, InitError> { load(sys::IVRSystem_Version).map(|x| unsafe { System(&*x) }) }
    pub fn compositor(&self) -> Result<Compositor, InitError> { load(sys::IVRCompositor_Version).map(|x| unsafe { Compositor(&*x) }) }
    pub fn render_models(&self) -> Result<RenderModels, InitError> { load(sys::IVRRenderModels_Version).map(|x| unsafe { RenderModels(&*x) }) }
}

impl Drop for Context {
    fn drop(&mut self) {
        unsafe { self.shutdown() }
    }
}

impl Context {
    /// Shut down OpenVR. Repeated calls are safe.
    ///
    /// Called implicitly by `Context::drop`. This MUST be called before shutting down the graphics API, or OpenVR may
    /// invoke undefined behavior.
    ///
    /// # Safety
    ///
    /// No OpenVR calls may be made after this has been called unless a new `Context` is subsequently constructed.
    pub unsafe fn shutdown(&self) {
        if self.live.replace(false) {
            sys::VR_ShutdownInternal();
            INITIALIZED.store(false, Ordering::Release);
        }
    }
}

#[derive(Debug, Copy, Clone, Eq, PartialEq)]
pub enum ApplicationType {
    /// Some other kind of application that isn't covered by the other entries 
    Other = sys::EVRApplicationType_VRApplication_Other as isize,
    /// Application will submit 3D frames
    Scene = sys::EVRApplicationType_VRApplication_Scene as isize,
    /// Application only interacts with overlays
    Overlay = sys::EVRApplicationType_VRApplication_Overlay as isize,
    /// Application should not start SteamVR if it's not already running, and should not keep it running if everything
    /// else quits.
    Background = sys::EVRApplicationType_VRApplication_Background as isize,
    /// Init should not try to load any drivers. The application needs access to utility interfaces (like IVRSettings
    /// and IVRApplications) but not hardware.
    Utility = sys::EVRApplicationType_VRApplication_Utility as isize,
    /// Reserved for vrmonitor
    VRMonitor = sys::EVRApplicationType_VRApplication_VRMonitor as isize,
    /// Reserved for Steam
    SteamWatchdog = sys::EVRApplicationType_VRApplication_SteamWatchdog as isize,
    /// Start up SteamVR
    Bootstrapper = sys::EVRApplicationType_VRApplication_Bootstrapper as isize,
}

#[derive(Copy, Clone)]
pub struct InitError(sys::EVRInitError);

impl fmt::Debug for InitError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let msg = unsafe {
            CStr::from_ptr(sys::VR_GetVRInitErrorAsSymbol(self.0))
        };
        f.pad(msg.to_str().expect("OpenVR init error symbol was not valid UTF-8"))
    }
}

impl error::Error for InitError {
    fn description(&self) -> &str {
        let msg = unsafe {
            CStr::from_ptr(sys::VR_GetVRInitErrorAsEnglishDescription(self.0))
        };
        msg.to_str().expect("OpenVR init error description was not valid UTF-8")
    }
}

impl fmt::Display for InitError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.pad(error::Error::description(self))
    }
}

#[derive(Debug, Copy, Clone, Eq, PartialEq)]
pub enum Eye {
    Left = sys::EVREye_Eye_Left as isize,
    Right = sys::EVREye_Eye_Right as isize,
}

/// Helper to call OpenVR functions that return strings
unsafe fn get_string<F: FnMut(*mut std::os::raw::c_char, u32) -> u32>(mut f: F) -> Option<CString> {
    let n = f(ptr::null_mut(), 0);
    if n == 0 { return None }
    let mut storage = Vec::new();
    storage.reserve_exact(n as usize);
    storage.resize(n as usize, mem::uninitialized());
    let n_ = f(storage.as_mut_ptr() as *mut _, n);
    assert!(n == n_);
    storage.truncate((n-1) as usize); // Strip trailing null
    Some(CString::from_vec_unchecked(storage))
}

#[repr(C)]
#[derive(Debug, Copy, Clone)]
pub struct ControllerAxis {
    pub x: f32,
    pub y: f32,
}

#[repr(C)]
#[derive(Debug, Copy, Clone)]
pub struct ControllerState {
    pub packet_num: u32,
    pub button_pressed: u64,
    pub button_touched: u64,
    pub axis: [ControllerAxis; 5],
}