use std::sync::Arc;
use std::{any::Any, iter::FusedIterator};

use crate::{Direction, Frame, Id, Rect};

/// What kind is this [`crate::Ui`]?
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum UiKind {
    /// A [`crate::Window`].
    Window,

    /// A [`crate::CentralPanel`].
    CentralPanel,

    /// A left [`crate::SidePanel`].
    LeftPanel,

    /// A right [`crate::SidePanel`].
    RightPanel,

    /// A top [`crate::TopBottomPanel`].
    TopPanel,

    /// A bottom [`crate::TopBottomPanel`].
    BottomPanel,

    /// A [`crate::Frame`].
    Frame,

    /// A [`crate::ScrollArea`].
    ScrollArea,

    /// A [`crate::Resize`].
    Resize,

    /// The content of a regular menu.
    Menu,

    /// The content of a popup menu.
    Popup,

    /// A tooltip, as shown by e.g. [`crate::Response::on_hover_ui`].
    Tooltip,

    /// A picker, such as color picker.
    Picker,

    /// A table cell (from the `egui_extras` crate).
    TableCell,

    /// An [`crate::Area`] that is not of any other kind.
    GenericArea,
}

impl UiKind {
    /// Is this any kind of panel?
    #[inline]
    pub fn is_panel(&self) -> bool {
        matches!(
            self,
            Self::CentralPanel
                | Self::LeftPanel
                | Self::RightPanel
                | Self::TopPanel
                | Self::BottomPanel
        )
    }

    /// Is this any kind of [`crate::Area`]?
    #[inline]
    pub fn is_area(&self) -> bool {
        match self {
            Self::CentralPanel
            | Self::LeftPanel
            | Self::RightPanel
            | Self::TopPanel
            | Self::BottomPanel
            | Self::Frame
            | Self::ScrollArea
            | Self::Resize
            | Self::TableCell => false,

            Self::Window
            | Self::Menu
            | Self::Popup
            | Self::Tooltip
            | Self::Picker
            | Self::GenericArea => true,
        }
    }
}

// ----------------------------------------------------------------------------

/// Information about a [`crate::Ui`] to be included in the corresponding [`UiStack`].
#[derive(Clone, Default, Debug)]
pub struct UiStackInfo {
    pub kind: Option<UiKind>,
    pub frame: Frame,
    pub tags: UiTags,
}

impl UiStackInfo {
    /// Create a new [`UiStackInfo`] with the given kind and an empty frame.
    #[inline]
    pub fn new(kind: UiKind) -> Self {
        Self {
            kind: Some(kind),
            ..Default::default()
        }
    }

    #[inline]
    pub fn with_frame(mut self, frame: Frame) -> Self {
        self.frame = frame;
        self
    }

    /// Insert a tag with no value.
    #[inline]
    pub fn with_tag(mut self, key: impl Into<String>) -> Self {
        self.tags.insert(key, None);
        self
    }

    /// Insert a tag with some value.
    #[inline]
    pub fn with_tag_value(
        mut self,
        key: impl Into<String>,
        value: impl Any + Send + Sync + 'static,
    ) -> Self {
        self.tags.insert(key, Some(Arc::new(value)));
        self
    }
}

// ----------------------------------------------------------------------------

/// User-chosen tags.
///
/// You can use this in any way you want,
/// i.e. to set some tag on a [`crate::Ui`] and then in your own widget check
/// for the existence of this tag up the [`UiStack`].
///
/// Note that egui never sets any tags itself, so this is purely for user code.
///
/// All tagging is transient, and will only live as long as the parent [`crate::Ui`], i.e. within a single render frame.
#[derive(Clone, Default, Debug)]
pub struct UiTags(pub ahash::HashMap<String, Option<Arc<dyn Any + Send + Sync + 'static>>>);

impl UiTags {
    #[inline]
    pub fn insert(
        &mut self,
        key: impl Into<String>,
        value: Option<Arc<dyn Any + Send + Sync + 'static>>,
    ) {
        self.0.insert(key.into(), value);
    }

    #[inline]
    pub fn contains(&self, key: &str) -> bool {
        self.0.contains_key(key)
    }

    /// Get the value of a tag.
    ///
    /// Note that `None` is returned both if the key is set to the value `None`,
    /// and if the key is not set at all.
    #[inline]
    pub fn get_any(&self, key: &str) -> Option<&Arc<dyn Any + Send + Sync + 'static>> {
        self.0.get(key)?.as_ref()
    }

    /// Get the value of a tag.
    ///
    /// Note that `None` is returned both if the key is set to the value `None`,
    /// and if the key is not set at all.
    pub fn get_downcast<T: Any + Send + Sync + 'static>(&self, key: &str) -> Option<&T> {
        self.0.get(key)?.as_ref().and_then(|any| any.downcast_ref())
    }
}

// ----------------------------------------------------------------------------

/// Information about a [`crate::Ui`] and its parents.
///
/// [`UiStack`] serves to keep track of the current hierarchy of [`crate::Ui`]s, such
/// that nested widgets or user code may adapt to the surrounding context or obtain layout information
/// from a [`crate::Ui`] that might be several steps higher in the hierarchy.
///
/// Note: since [`UiStack`] contains a reference to its parent, it is both a stack, and a node within
/// that stack. Most of its methods are about the specific node, but some methods walk up the
/// hierarchy to provide information about the entire stack.
#[derive(Debug)]
pub struct UiStack {
    // stuff that `Ui::child_ui` can deal with directly
    pub id: Id,
    pub info: UiStackInfo,
    pub layout_direction: Direction,
    pub min_rect: Rect,
    pub max_rect: Rect,
    pub parent: Option<Arc<UiStack>>,
}

// these methods act on this specific node
impl UiStack {
    #[inline]
    pub fn kind(&self) -> Option<UiKind> {
        self.info.kind
    }

    #[inline]
    pub fn frame(&self) -> &Frame {
        &self.info.frame
    }

    /// User tags.
    #[inline]
    pub fn tags(&self) -> &UiTags {
        &self.info.tags
    }

    /// Is this [`crate::Ui`] a panel?
    #[inline]
    pub fn is_panel_ui(&self) -> bool {
        self.kind().map_or(false, |kind| kind.is_panel())
    }

    /// Is this a root [`crate::Ui`], i.e. created with [`crate::Ui::new()`]?
    #[inline]
    pub fn is_root_ui(&self) -> bool {
        self.parent.is_none()
    }

    /// This this [`crate::Ui`] a [`crate::Frame`] with a visible stroke?
    #[inline]
    pub fn has_visible_frame(&self) -> bool {
        !self.info.frame.stroke.is_empty()
    }
}

// these methods act on the entire stack
impl UiStack {
    /// Return an iterator that walks the stack from this node to the root.
    #[allow(clippy::iter_without_into_iter)]
    pub fn iter(&self) -> UiStackIterator<'_> {
        UiStackIterator { next: Some(self) }
    }

    /// Check if this node is or is contained in a [`crate::Ui`] of a specific kind.
    pub fn contained_in(&self, kind: UiKind) -> bool {
        self.iter().any(|frame| frame.kind() == Some(kind))
    }
}

// ----------------------------------------------------------------------------

/// Iterator that walks up a stack of `StackFrame`s.
///
/// See [`UiStack::iter`].
pub struct UiStackIterator<'a> {
    next: Option<&'a UiStack>,
}

impl<'a> Iterator for UiStackIterator<'a> {
    type Item = &'a UiStack;

    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        let current = self.next;
        self.next = current.and_then(|frame| frame.parent.as_deref());
        current
    }
}

impl<'a> FusedIterator for UiStackIterator<'a> {}