//! A `ViewHandle` represents an underlying `NSView`. You're passed a reference to one during your
//! `ViewController::did_load()` method. This method is safe to store and use, however as it's
//! UI-specific it's not thread safe.
//!
//! You can use this struct to configure how a view should look and layout. It implements
//! AutoLayout - for more information, see the AutoLayout tutorial.

use std::rc::Rc;
use std::cell::RefCell;

use objc_id::ShareId;
use objc::runtime::{Class, Object};
use objc::{msg_send, sel, sel_impl};

use crate::foundation::{id, nil, YES, NO, NSArray, NSString};
use crate::color::Color;
use crate::layout::{Layout, LayoutAnchorX, LayoutAnchorY, LayoutAnchorDimension};
use crate::pasteboard::PasteboardType;

mod class;
use class::{register_view_class, register_view_class_with_delegate};

pub mod controller;
pub use controller::ViewController;

pub mod traits;
pub use traits::ViewDelegate;

pub(crate) static VIEW_DELEGATE_PTR: &str = "rstViewDelegatePtr";

/// A helper method for instantiating view classes and applying default settings to them.
fn allocate_view(registration_fn: fn() -> *const Class) -> id { 
    unsafe {
        let view: id = msg_send![registration_fn(), new];
        let _: () = msg_send![view, setTranslatesAutoresizingMaskIntoConstraints:NO];
        let _: () = msg_send![view, setWantsLayer:YES];
        view 
    }
}

/// A clone-able handler to a `ViewController` reference in the Objective C runtime. We use this
/// instead of a stock `View` for easier recordkeeping, since it'll need to hold the `View` on that
/// side anyway.
#[derive(Debug)]
pub struct View<T = ()> {
    /// A pointer to the Objective-C runtime view controller.
    pub objc: ShareId<Object>,

    /// An internal callback pointer that we use in delegate loopbacks. Default implementations
    /// don't require this.
    pub(crate) internal_callback_ptr: Option<*const RefCell<T>>,

    /// A pointer to the delegate for this view.
    pub delegate: Option<Rc<RefCell<T>>>,

    /// A pointer to the Objective-C runtime top layout constraint.
    pub top: LayoutAnchorY,

    /// A pointer to the Objective-C runtime leading layout constraint.
    pub leading: LayoutAnchorX,

    /// A pointer to the Objective-C runtime trailing layout constraint.
    pub trailing: LayoutAnchorX,

    /// A pointer to the Objective-C runtime bottom layout constraint.
    pub bottom: LayoutAnchorY,

    /// A pointer to the Objective-C runtime width layout constraint.
    pub width: LayoutAnchorDimension,

    /// A pointer to the Objective-C runtime height layout constraint.
    pub height: LayoutAnchorDimension,

    /// A pointer to the Objective-C runtime center X layout constraint.
    pub center_x: LayoutAnchorX,

    /// A pointer to the Objective-C runtime center Y layout constraint.
    pub center_y: LayoutAnchorY
}

impl Default for View {
    fn default() -> Self {
        View::new()
    }
}

impl View {
    /// Returns a default `View`, suitable for 
    pub fn new() -> Self {
        let view = allocate_view(register_view_class);

        View {
            internal_callback_ptr: None,
            delegate: None,
            top: LayoutAnchorY::new(unsafe { msg_send![view, topAnchor] }),
            leading: LayoutAnchorX::new(unsafe { msg_send![view, leadingAnchor] }),
            trailing: LayoutAnchorX::new(unsafe { msg_send![view, trailingAnchor] }),
            bottom: LayoutAnchorY::new(unsafe { msg_send![view, bottomAnchor] }),
            width: LayoutAnchorDimension::new(unsafe { msg_send![view, widthAnchor] }),
            height: LayoutAnchorDimension::new(unsafe { msg_send![view, heightAnchor] }),
            center_x: LayoutAnchorX::new(unsafe { msg_send![view, centerXAnchor] }),
            center_y: LayoutAnchorY::new(unsafe { msg_send![view, centerYAnchor] }),
            objc: unsafe { ShareId::from_ptr(view) },
        }
    }
}

impl<T> View<T> where T: ViewDelegate + 'static {
    /// Initializes a new View with a given `ViewDelegate`. This enables you to respond to events
    /// and customize the view as a module, similar to class-based systems.
    pub fn with(delegate: T) -> View<T> {
        let delegate = Rc::new(RefCell::new(delegate));
        
        let internal_callback_ptr = {
            let cloned = Rc::clone(&delegate);
            Rc::into_raw(cloned)
        };

        let view = allocate_view(register_view_class_with_delegate::<T>);
        unsafe {
            //let view: id = msg_send![register_view_class_with_delegate::<T>(), new];
            //let _: () = msg_send![view, setTranslatesAutoresizingMaskIntoConstraints:NO];
            (&mut *view).set_ivar(VIEW_DELEGATE_PTR, internal_callback_ptr as usize);
        };

        let mut view = View {
            internal_callback_ptr: Some(internal_callback_ptr),
            delegate: None,
            top: LayoutAnchorY::new(unsafe { msg_send![view, topAnchor] }),
            leading: LayoutAnchorX::new(unsafe { msg_send![view, leadingAnchor] }),
            trailing: LayoutAnchorX::new(unsafe { msg_send![view, trailingAnchor] }),
            bottom: LayoutAnchorY::new(unsafe { msg_send![view, bottomAnchor] }),
            width: LayoutAnchorDimension::new(unsafe { msg_send![view, widthAnchor] }),
            height: LayoutAnchorDimension::new(unsafe { msg_send![view, heightAnchor] }),
            center_x: LayoutAnchorX::new(unsafe { msg_send![view, centerXAnchor] }),
            center_y: LayoutAnchorY::new(unsafe { msg_send![view, centerYAnchor] }),
            objc: unsafe { ShareId::from_ptr(view) },
        };

        {
            let mut delegate = delegate.borrow_mut();
            (*delegate).did_load(view.clone_as_handle()); 
        }

        view.delegate = Some(delegate);
        view
    }
}

impl<T> View<T> {
    /// An internal method that returns a clone of this object, sans references to the delegate or
    /// callback pointer. We use this in calling `did_load()` - implementing delegates get a way to
    /// reference, customize and use the view but without the trickery of holding pieces of the
    /// delegate - the `View` is the only true holder of those.
    pub(crate) fn clone_as_handle(&self) -> View {
        View {
            internal_callback_ptr: None,
            delegate: None,
            top: self.top.clone(),
            leading: self.leading.clone(),
            trailing: self.trailing.clone(),
            bottom: self.bottom.clone(),
            width: self.width.clone(),
            height: self.height.clone(),
            center_x: self.center_x.clone(),
            center_y: self.center_y.clone(),
            objc: self.objc.clone()
        }
    }

    /// Call this to set the background color for the backing layer.
    pub fn set_background_color(&self, color: Color) {
        let bg = color.into_platform_specific_color();
        
        unsafe {
            let cg: id = msg_send![bg, CGColor];
            let layer: id = msg_send![&*self.objc, layer];
            let _: () = msg_send![layer, setBackgroundColor:cg];
        }
    }

    /// Register this view for drag and drop operations.
    pub fn register_for_dragged_types(&self, types: &[PasteboardType]) {
        unsafe {
            let types: NSArray = types.into_iter().map(|t| {
                // This clone probably doesn't need to be here, but it should also be cheap as
                // this is just an enum... and this is not an oft called method.
                let x: NSString = t.clone().into();
                x.into_inner()
            }).collect::<Vec<id>>().into();

            let _: () = msg_send![&*self.objc, registerForDraggedTypes:types.into_inner()];
        }
    }
}

impl<T> Layout for View<T> {
    fn get_backing_node(&self) -> ShareId<Object> {
        self.objc.clone()
    }

    fn add_subview<V: Layout>(&self, view: &V) {
        let backing_node = view.get_backing_node();

        unsafe {
            let _: () = msg_send![&*self.objc, addSubview:backing_node];
        }
    }
}

impl<T> Drop for View<T> {
    /// A bit of extra cleanup for delegate callback pointers. If the originating `View` is being
    /// dropped, we do some logic to release the loopback ptr. We also go ahead and check to see if
    /// this has a superview (i.e, it's in the heirarchy) on the AppKit side. If it does, we go
    /// ahead and remove it - this is intended to match the semantics of how Rust handles things.
    ///
    /// There are, thankfully, no delegates we need to break here.
    fn drop(&mut self) {
        if let Some(ptr) = &self.internal_callback_ptr {
            unsafe {
                let superview: id = msg_send![&*self.objc, superview];
                if superview != nil {
                    let _: () = msg_send![&*self.objc, removeFromSuperview];
                }

                let _ = Rc::from_raw(ptr);
            }
        }
    }
}