//! Virtual Node Support
//! VNodes represent lazily-constructed VDom trees that support diffing and event handlers.
//!
//! These VNodes should be *very* cheap and *very* fast to construct - building a full tree should be insanely quick.

use bumpalo::Bump;
pub use vcomponent::VComponent;
pub use velement::VElement;
pub use velement::{Attribute, Listener, NodeKey};
pub use vnode::VNode;
pub use vtext::VText;

/// A domtree represents the result of "Viewing" the context
/// It's a placeholder over vnodes, to make working with lifetimes easier
pub struct DomTree;

/// Tools for the base unit of the virtual dom - the VNode
/// VNodes are intended to be quickly-allocated, lightweight enum values.
///
/// Components will be generating a lot of these very quickly, so we want to
/// limit the amount of heap allocations / overly large enum sizes.
mod vnode {
    use super::*;

    #[derive(Debug)]
    pub enum VNode<'src> {
        /// An element node (node type `ELEMENT_NODE`).
        Element(&'src VElement<'src>),

        /// A text node (node type `TEXT_NODE`).
        ///
        /// Note: This wraps a `VText` instead of a plain `String` in
        /// order to enable custom methods like `create_text_node()` on the
        /// wrapped type.
        Text(VText<'src>),

        /// A "suspended component"
        /// This is a masqeurade over an underlying future that needs to complete
        /// When the future is completed, the VNode will then trigger a render
        Suspended,

        /// A User-defined componen node (node type COMPONENT_NODE)
        Component(VComponent<'src>),
    }

    impl<'a> VNode<'a> {
        /// Low-level constructor for making a new `Node` of type element with given
        /// parts.
        ///
        /// This is primarily intended for JSX and templating proc-macros to compile
        /// down into. If you are building nodes by-hand, prefer using the
        /// `dodrio::builder::*` APIs.
        #[inline]
        pub fn element(
            bump: &'a Bump,
            key: NodeKey,
            tag_name: &'a str,
            listeners: &'a [Listener<'a>],
            attributes: &'a [Attribute<'a>],
            children: &'a [VNode<'a>],
            namespace: Option<&'a str>,
        ) -> VNode<'a> {
            let element = bump.alloc_with(|| VElement {
                key,
                tag_name,
                listeners,
                attributes,
                children,
                namespace,
            });
            VNode::Element(element)
        }

        /// Construct a new text node with the given text.
        #[inline]
        pub fn text(text: &'a str) -> VNode<'a> {
            VNode::Text(VText { text })
        }

        #[inline]
        pub(crate) fn key(&self) -> NodeKey {
            match &self {
                VNode::Text(_) => NodeKey::NONE,
                VNode::Element(e) => e.key,
                VNode::Suspended => {
                    todo!()
                }
                VNode::Component(_) => {
                    todo!()
                }
            }
        }
    }
}

mod velement {

    // use crate::{events::VirtualEvent, innerlude::CbIdx};

    use crate::{events::VirtualEvent, innerlude::ScopeIdx};

    use super::*;
    use std::fmt::Debug;

    #[derive(Debug)]
    pub struct VElement<'a> {
        /// Elements have a tag name, zero or more attributes, and zero or more
        pub key: NodeKey,
        pub tag_name: &'a str,
        pub listeners: &'a [Listener<'a>],
        pub attributes: &'a [Attribute<'a>],
        pub children: &'a [VNode<'a>],
        pub namespace: Option<&'a str>,
        // The HTML tag, such as "div"
        // pub tag: &'a str,

        // pub tag_name: &'a str,
        // pub attributes: &'a [Attribute<'a>],
        // todo: hook up listeners
        // pub listeners: &'a [Listener<'a>],
        // / HTML attributes such as id, class, style, etc
        // pub attrs: HashMap<String, String>,
        // TODO: @JON Get this to not heap allocate, but rather borrow
        // pub attrs: HashMap<&'static str, &'static str>,

        // TODO @Jon, re-enable "events"
        //
        // /// Events that will get added to your real DOM element via `.addEventListener`
        // pub events: Events,
        // pub events: HashMap<String, ()>,

        // /// The children of this `VNode`. So a <div> <em></em> </div> structure would
        // /// have a parent div and one child, em.
        // pub children: Vec<VNode>,
    }

    impl<'a> VElement<'a> {
        // The tag of a component MUST be known at compile time
        pub fn new(_tag: &'a str) -> Self {
            todo!()
            // VElement {
            //     tag,
            //     attrs: HashMap::new(),
            //     events: HashMap::new(),
            //     // events: Events(HashMap::new()),
            //     children: vec![],
            // }
        }
    }

    /// An attribute on a DOM node, such as `id="my-thing"` or
    /// `href="https://example.com"`.
    #[derive(Clone, Debug, serde::Serialize, serde::Deserialize)]
    pub struct Attribute<'a> {
        pub name: &'static str,
        pub value: &'a str,
    }

    impl<'a> Attribute<'a> {
        /// Get this attribute's name, such as `"id"` in `<div id="my-thing" />`.
        #[inline]
        pub fn name(&self) -> &'a str {
            self.name
        }

        /// The attribute value, such as `"my-thing"` in `<div id="my-thing" />`.
        #[inline]
        pub fn value(&self) -> &'a str {
            self.value
        }

        /// Certain attributes are considered "volatile" and can change via user
        /// input that we can't see when diffing against the old virtual DOM. For
        /// these attributes, we want to always re-set the attribute on the physical
        /// DOM node, even if the old and new virtual DOM nodes have the same value.
        #[inline]
        pub(crate) fn is_volatile(&self) -> bool {
            match self.name {
                "value" | "checked" | "selected" => true,
                _ => false,
            }
        }
    }

    pub struct ListenerHandle {
        pub event: &'static str,
        pub scope: ScopeIdx,
        pub id: usize,
    }

    /// An event listener.
    pub struct Listener<'bump> {
        /// The type of event to listen for.
        pub(crate) event: &'static str,

        pub scope: ScopeIdx,
        pub id: usize,

        // pub(crate) _i: &'bump str,
        // #[serde(skip_serializing, skip_deserializing, default="")]
        // /// The callback to invoke when the event happens.
        pub(crate) callback: &'bump (dyn Fn(VirtualEvent)),
    }
    impl Debug for Listener<'_> {
        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            f.debug_struct("Listener")
                .field("event", &self.event)
                .finish()
        }
    }
    pub(crate) type ListenerCallback<'a> = &'a (dyn Fn(VirtualEvent));
    union CallbackFatPtr<'a> {
        callback: ListenerCallback<'a>,
        parts: (u32, u32),
    }
    impl Listener<'_> {
        #[inline]
        pub(crate) fn get_callback_parts(&self) -> (u32, u32) {
            assert_eq!(
                std::mem::size_of::<ListenerCallback>(),
                std::mem::size_of::<CallbackFatPtr>()
            );

            unsafe {
                let fat = CallbackFatPtr {
                    callback: self.callback,
                };
                let (a, b) = fat.parts;
                debug_assert!(a != 0);
                (a, b)
            }
        }
    }

    /// The key for keyed children.
    ///
    /// Keys must be unique among siblings.
    ///
    /// If any sibling is keyed, then they all must be keyed.
    #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
    pub struct NodeKey(pub(crate) u32);

    impl Default for NodeKey {
        fn default() -> NodeKey {
            NodeKey::NONE
        }
    }
    impl NodeKey {
        /// The default, lack of a key.
        pub const NONE: NodeKey = NodeKey(u32::MAX);

        /// Is this key `NodeKey::NONE`?
        #[inline]
        pub fn is_none(&self) -> bool {
            *self == Self::NONE
        }

        /// Is this key not `NodeKey::NONE`?
        #[inline]
        pub fn is_some(&self) -> bool {
            !self.is_none()
        }

        /// Create a new `NodeKey`.
        ///
        /// `key` must not be `u32::MAX`.
        #[inline]
        pub fn new(key: u32) -> Self {
            debug_assert_ne!(key, u32::MAX);
            NodeKey(key)
        }
    }

    // todo
    // use zst enum for element type. Something like ValidElements::div
}

mod vtext {
    #[derive(Debug, PartialEq, serde::Serialize, serde::Deserialize)]
    pub struct VText<'bump> {
        pub text: &'bump str,
    }

    impl<'a> VText<'a> {
        // / Create an new `VText` instance with the specified text.
        pub fn new(text: &'a str) -> Self
// pub fn new<S>(text: S) -> Self
        // where
        //     S: Into<str>,
        {
            VText { text: text.into() }
        }
    }
}

/// Virtual Components for custom user-defined components
/// Only supports the functional syntax
mod vcomponent {
    use crate::innerlude::{Context, FC};
    use std::{any::TypeId, marker::PhantomData};

    use super::DomTree;

    #[derive(Debug)]
    pub struct VComponent<'src> {
        _p: PhantomData<&'src ()>,
        pub(crate) props: Box<dyn std::any::Any>,
        pub(crate) props_type: TypeId,
        pub(crate) comp: *const (),
        pub(crate) caller: Caller,
    }

    pub struct Caller(Box<dyn Fn(Context) -> DomTree>);
    impl std::fmt::Debug for Caller {
        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            todo!()
        }
    }

    impl<'a> VComponent<'a> {
        // use the type parameter on props creation and move it into a portable context
        // this lets us keep scope generic *and* downcast its props when we need to:
        // - perform comparisons when diffing (memoization)
        // -
        pub fn new<P>(comp: FC<P>, props: P) -> Self {
            let caller = move |ctx: Context| {
                let t = comp(ctx, &props);
                t
            };
            // let _caller = comp as *const ();
            // let _props = Box::new(props);

            // cast to static?
            // how do we save the type of props ?
            // do it in the caller function?
            // something like

            // the "true" entrpypoint
            //
            // |caller| caller.call(fn, Props {})
            // fn call<P>(f, new_props) {
            //     let old_props = old.downcast_ref::<P>();
            //     if new_props == old_props {
            //         return;
            //     } else {
            //         // set the new props
            //         // call the fn
            //     }
            // }

            todo!()
            // Self {
            //     _p: PhantomData {},
            //     props,
            //     caller,
            // }
        }
    }
}