//! 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 crate::{
    events::VirtualEvent,
    innerlude::{Context, Properties, ScopeIdx, FC},
};
use bumpalo::Bump;
use std::{cell::RefCell, fmt::Debug, marker::PhantomData, rc::Rc};

/// A domtree represents the result of "Viewing" the context
/// It's a placeholder over vnodes, to make working with lifetimes easier
pub struct DomTree {
    // this should *never* be publicly accessible to external
    pub root: VNode<'static>,
}

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

    /// A text node (node type `TEXT_NODE`).
    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<'a>,
        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!()
            }
            // Self::PhantomChild { id } => {
            //     todo!()
            // }
            VNode::Component(c) => c.key,
        }
    }
}

// ========================================================
//   VElement (div, h1, etc), attrs, keys, listener handle
// ========================================================
pub struct VElement<'a> {
    /// Elements have a tag name, zero or more attributes, and zero or more
    pub key: NodeKey<'a>,
    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>,
}

/// An attribute on a DOM node, such as `id="my-thing"` or
/// `href="https://example.com"`.
#[derive(Clone, Debug)]
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,

    /// The callback to invoke when the event happens.
    pub(crate) callback: &'bump (dyn Fn(VirtualEvent)),
}

/// 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<'a>(pub(crate) Option<&'a str>);

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

    /// 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: &'a str) -> Self {
        NodeKey(Some(key))
    }
}

#[derive(Debug, PartialEq)]
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 {
        VText { text: text.into() }
    }
}

// ==============================
//   Custom components
// ==============================

/// Virtual Components for custom user-defined components
/// Only supports the functional syntax
pub type StableScopeAddres = RefCell<Option<u32>>;
pub type VCompAssociatedScope = RefCell<Option<ScopeIdx>>;

pub struct VComponent<'src> {
    pub key: NodeKey<'src>,

    pub stable_addr: Rc<StableScopeAddres>,
    pub ass_scope: Rc<VCompAssociatedScope>,

    pub comparator: Rc<dyn Fn(&VComponent) -> bool + 'src>,
    pub caller: Rc<dyn Fn(Context) -> DomTree + 'src>,

    pub children: &'src [VNode<'src>],

    // a pointer into the bump arena (given by the 'src lifetime)
    raw_props: *const (),

    // a pointer to the raw fn typ
    pub user_fc: *const (),
    _p: PhantomData<&'src ()>,
}

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)
    // TODO: lift the requirement that props need to be static
    // we want them to borrow references... maybe force implementing a "to_static_unsafe" trait
    pub fn new<P: Properties + 'a>(component: FC<P>, props: &'a P, key: Option<&'a str>) -> Self {
        let caller_ref = component as *const ();

        let raw_props = props as *const P as *const ();

        let props_comparator = move |other: &VComponent| {
            // Safety:
            // We are guaranteed that the props will be of the same type because
            // there is no way to create a VComponent other than this `new` method.
            //
            // Therefore, if the render functions are identical (by address), then so will be
            // props type paramter (because it is the same render function). Therefore, we can be
            // sure
            if caller_ref == other.user_fc {
                let real_other = unsafe { &*(other.raw_props as *const _ as *const P) };
                real_other == props
            } else {
                false
            }
        };

        let caller = Rc::new(create_closure(component, raw_props));

        let key = match key {
            Some(key) => NodeKey::new(key),
            None => NodeKey(None),
        };

        Self {
            key,
            ass_scope: Rc::new(RefCell::new(None)),
            user_fc: caller_ref,
            raw_props: props as *const P as *const _,
            _p: PhantomData,
            children: &[],
            caller,
            comparator: Rc::new(props_comparator),
            stable_addr: Rc::new(RefCell::new(None)),
        }
    }
}

fn create_closure<'a, P: Properties + 'a>(
    component: FC<P>,
    raw_props: *const (),
) -> impl for<'r> Fn(Context<'r>) -> DomTree + 'a {
    move |ctx: Context| -> DomTree {
        // cast back into the right lifetime
        let safe_props: &'a P = unsafe { &*(raw_props as *const P) };
        component(ctx, safe_props)
    }
}