use crate::{
    input::{keyboard, mouse, ButtonState},
    layout, Clipboard, Element, Event, Hasher, Layout, Length, Point,
    Rectangle, Size, Widget,
};

use std::collections::HashMap;

#[allow(missing_debug_implementations)]
pub struct PaneGrid<'a, Message, Renderer> {
    state: &'a mut Internal,
    elements: Vec<(Pane, Element<'a, Message, Renderer>)>,
    width: Length,
    height: Length,
    spacing: u16,
    on_drag: Option<Box<dyn Fn(DragEvent) -> Message>>,
}

impl<'a, Message, Renderer> PaneGrid<'a, Message, Renderer> {
    pub fn new<T>(
        state: &'a mut State<T>,
        view: impl Fn(
            Pane,
            &'a mut T,
            Option<Focus>,
        ) -> Element<'a, Message, Renderer>,
    ) -> Self {
        let elements = {
            let focused_pane = state.internal.focused_pane;

            state
                .panes
                .iter_mut()
                .map(move |(pane, pane_state)| {
                    let focus = match focused_pane {
                        FocusedPane::Some {
                            pane: focused_pane,
                            focus,
                        } if *pane == focused_pane => Some(focus),
                        _ => None,
                    };

                    (*pane, view(*pane, pane_state, focus))
                })
                .collect()
        };

        Self {
            state: &mut state.internal,
            elements,
            width: Length::Fill,
            height: Length::Fill,
            spacing: 0,
            on_drag: None,
        }
    }

    /// Sets the width of the [`PaneGrid`].
    ///
    /// [`PaneGrid`]: struct.Column.html
    pub fn width(mut self, width: Length) -> Self {
        self.width = width;
        self
    }

    /// Sets the height of the [`PaneGrid`].
    ///
    /// [`PaneGrid`]: struct.Column.html
    pub fn height(mut self, height: Length) -> Self {
        self.height = height;
        self
    }

    /// Sets the spacing _between_ the panes of the [`PaneGrid`].
    ///
    /// [`PaneGrid`]: struct.Column.html
    pub fn spacing(mut self, units: u16) -> Self {
        self.spacing = units;
        self
    }

    pub fn on_drag(
        mut self,
        f: impl Fn(DragEvent) -> Message + 'static,
    ) -> Self {
        self.on_drag = Some(Box::new(f));
        self
    }
}

#[derive(Debug, Clone, Copy)]
pub enum DragEvent {
    Picked { pane: Pane },
    Dropped { pane: Pane, target: Pane },
    Canceled { pane: Pane },
}

impl<'a, Message, Renderer> Widget<Message, Renderer>
    for PaneGrid<'a, Message, Renderer>
where
    Renderer: self::Renderer + 'static,
    Message: 'static,
{
    fn width(&self) -> Length {
        self.width
    }

    fn height(&self) -> Length {
        self.height
    }

    fn layout(
        &self,
        renderer: &Renderer,
        limits: &layout::Limits,
    ) -> layout::Node {
        let limits = limits.width(self.width).height(self.height);
        let size = limits.resolve(Size::ZERO);

        let regions = self.state.layout.regions(f32::from(self.spacing), size);

        let children = self
            .elements
            .iter()
            .filter_map(|(pane, element)| {
                let region = regions.get(pane)?;
                let size = Size::new(region.width, region.height);

                let mut node =
                    element.layout(renderer, &layout::Limits::new(size, size));

                node.move_to(Point::new(region.x, region.y));

                Some(node)
            })
            .collect();

        layout::Node::with_children(size, children)
    }

    fn on_event(
        &mut self,
        event: Event,
        layout: Layout<'_>,
        cursor_position: Point,
        messages: &mut Vec<Message>,
        renderer: &Renderer,
        clipboard: Option<&dyn Clipboard>,
    ) {
        match event {
            Event::Mouse(mouse::Event::Input {
                button: mouse::Button::Left,
                state,
            }) => match state {
                ButtonState::Pressed => {
                    let mut clicked_region =
                        self.elements.iter().zip(layout.children()).filter(
                            |(_, layout)| {
                                layout.bounds().contains(cursor_position)
                            },
                        );

                    if let Some(((pane, _), _)) = clicked_region.next() {
                        match &self.on_drag {
                            Some(on_drag) if self.state.modifiers.alt => {
                                self.state.focused_pane = FocusedPane::Some {
                                    pane: *pane,
                                    focus: Focus::Dragging,
                                };

                                messages.push(on_drag(DragEvent::Picked {
                                    pane: *pane,
                                }));
                            }
                            _ => {
                                self.state.focused_pane = FocusedPane::Some {
                                    pane: *pane,
                                    focus: Focus::Idle,
                                };
                            }
                        }
                    } else {
                        self.state.focused_pane = FocusedPane::None;
                    }
                }
                ButtonState::Released => {
                    if let FocusedPane::Some {
                        pane,
                        focus: Focus::Dragging,
                    } = self.state.focused_pane
                    {
                        self.state.focused_pane = FocusedPane::Some {
                            pane,
                            focus: Focus::Idle,
                        };

                        if let Some(on_drag) = &self.on_drag {
                            let mut dropped_region = self
                                .elements
                                .iter()
                                .zip(layout.children())
                                .filter(|(_, layout)| {
                                    layout.bounds().contains(cursor_position)
                                });

                            let event = match dropped_region.next() {
                                Some(((target, _), _)) if pane != *target => {
                                    DragEvent::Dropped {
                                        pane,
                                        target: *target,
                                    }
                                }
                                _ => DragEvent::Canceled { pane },
                            };

                            messages.push(on_drag(event));
                        }
                    }
                }
            },
            Event::Keyboard(keyboard::Event::Input { modifiers, .. }) => {
                self.state.modifiers = modifiers;
            }
            _ => {}
        }

        match self.state.focused_pane {
            FocusedPane::Some {
                focus: Focus::Dragging,
                ..
            } => {}
            _ => {
                self.elements.iter_mut().zip(layout.children()).for_each(
                    |((_, pane), layout)| {
                        pane.widget.on_event(
                            event.clone(),
                            layout,
                            cursor_position,
                            messages,
                            renderer,
                            clipboard,
                        )
                    },
                );
            }
        }
    }

    fn draw(
        &self,
        renderer: &mut Renderer,
        defaults: &Renderer::Defaults,
        layout: Layout<'_>,
        cursor_position: Point,
    ) -> Renderer::Output {
        let dragging = match self.state.focused_pane {
            FocusedPane::Some {
                pane,
                focus: Focus::Dragging,
            } => Some(pane),
            _ => None,
        };

        renderer.draw(
            defaults,
            &self.elements,
            dragging,
            layout,
            cursor_position,
        )
    }

    fn hash_layout(&self, state: &mut Hasher) {
        use std::hash::Hash;

        std::any::TypeId::of::<PaneGrid<'_, Message, Renderer>>().hash(state);
        self.width.hash(state);
        self.height.hash(state);
        self.state.layout.hash(state);

        for (_, element) in &self.elements {
            element.hash_layout(state);
        }
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct Pane(usize);

impl Pane {
    pub fn index(&self) -> usize {
        self.0
    }
}

#[derive(Debug)]
pub struct State<T> {
    panes: HashMap<Pane, T>,
    internal: Internal,
}

#[derive(Debug)]
struct Internal {
    layout: Node,
    last_pane: usize,
    focused_pane: FocusedPane,
    modifiers: keyboard::ModifiersState,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Focus {
    Idle,
    Dragging,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum FocusedPane {
    None,
    Some { pane: Pane, focus: Focus },
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Direction {
    Top,
    Bottom,
    Left,
    Right,
}

impl<T> State<T> {
    pub fn new(first_pane_state: T) -> (Self, Pane) {
        let first_pane = Pane(0);

        let mut panes = HashMap::new();
        let _ = panes.insert(first_pane, first_pane_state);

        (
            State {
                panes,
                internal: Internal {
                    layout: Node::Pane(first_pane),
                    last_pane: 0,
                    focused_pane: FocusedPane::None,
                    modifiers: keyboard::ModifiersState::default(),
                },
            },
            first_pane,
        )
    }

    pub fn len(&self) -> usize {
        self.panes.len()
    }

    pub fn get_mut(&mut self, pane: &Pane) -> Option<&mut T> {
        self.panes.get_mut(pane)
    }

    pub fn iter(&self) -> impl Iterator<Item = (Pane, &T)> {
        self.panes.iter().map(|(pane, state)| (*pane, state))
    }

    pub fn iter_mut(&mut self) -> impl Iterator<Item = (Pane, &mut T)> {
        self.panes.iter_mut().map(|(pane, state)| (*pane, state))
    }

    pub fn focused_pane(&self) -> Option<Pane> {
        match self.internal.focused_pane {
            FocusedPane::Some {
                pane,
                focus: Focus::Idle,
            } => Some(pane),
            FocusedPane::Some {
                focus: Focus::Dragging,
                ..
            } => None,
            FocusedPane::None => None,
        }
    }

    pub fn focus(&mut self, pane: &Pane) {
        self.internal.focused_pane = FocusedPane::Some {
            pane: *pane,
            focus: Focus::Idle,
        };
    }

    pub fn focus_adjacent(&mut self, pane: &Pane, direction: Direction) {
        if let Some(pane) = self.internal.layout.find_adjacent(pane, direction)
        {
            self.focus(&pane);
        }
    }

    pub fn split_vertically(&mut self, pane: &Pane, state: T) -> Option<Pane> {
        self.split(Split::Vertical, pane, state)
    }

    pub fn split_horizontally(
        &mut self,
        pane: &Pane,
        state: T,
    ) -> Option<Pane> {
        self.split(Split::Horizontal, pane, state)
    }

    pub fn split(
        &mut self,
        kind: Split,
        pane: &Pane,
        state: T,
    ) -> Option<Pane> {
        let node = self.internal.layout.find(pane)?;

        let new_pane = {
            self.internal.last_pane = self.internal.last_pane.checked_add(1)?;

            Pane(self.internal.last_pane)
        };

        node.split(kind, new_pane);

        let _ = self.panes.insert(new_pane, state);
        self.internal.focused_pane = FocusedPane::Some {
            pane: new_pane,
            focus: Focus::Idle,
        };

        Some(new_pane)
    }

    pub fn swap(&mut self, a: &Pane, b: &Pane) {
        self.internal.layout.update(&|node| match node {
            Node::Split { .. } => {}
            Node::Pane(pane) => {
                if pane == a {
                    *node = Node::Pane(*b);
                } else if pane == b {
                    *node = Node::Pane(*a);
                }
            }
        });
    }

    pub fn close(&mut self, pane: &Pane) -> Option<T> {
        if let Some(sibling) = self.internal.layout.remove(pane) {
            self.internal.focused_pane = FocusedPane::Some {
                pane: sibling,
                focus: Focus::Idle,
            };

            self.panes.remove(pane)
        } else {
            None
        }
    }
}

#[derive(Debug, Clone, Hash)]
enum Node {
    Split {
        kind: Split,
        ratio: u32,
        a: Box<Node>,
        b: Box<Node>,
    },
    Pane(Pane),
}

#[derive(Debug)]
enum Branch {
    First,
    Second,
}

impl Node {
    fn find(&mut self, pane: &Pane) -> Option<&mut Node> {
        match self {
            Node::Split { a, b, .. } => {
                a.find(pane).or_else(move || b.find(pane))
            }
            Node::Pane(p) => {
                if p == pane {
                    Some(self)
                } else {
                    None
                }
            }
        }
    }

    fn find_adjacent(
        &mut self,
        pane: &Pane,
        direction: Direction,
    ) -> Option<Pane> {
        let (pane, _) = self.find_split(pane, &|kind, branch, a, b| match (
            direction, kind, branch,
        ) {
            (Direction::Top, Split::Vertical, Branch::Second)
            | (Direction::Left, Split::Horizontal, Branch::Second) => {
                Some(a.first_pane())
            }
            (Direction::Bottom, Split::Vertical, Branch::First)
            | (Direction::Right, Split::Horizontal, Branch::First) => {
                Some(b.first_pane())
            }
            _ => None,
        });

        pane
    }

    fn find_split<T>(
        &mut self,
        pane: &Pane,
        callback: &impl Fn(Split, Branch, &Node, &Node) -> Option<T>,
    ) -> (Option<T>, bool) {
        match self {
            Node::Split { a, b, kind, .. } => {
                let kind = *kind;
                let (result, found) = a.find_split(pane, callback);

                if result.is_some() {
                    (result, found)
                } else if found {
                    (callback(kind, Branch::First, a, b), true)
                } else {
                    let (result, found) = b.find_split(pane, callback);

                    if result.is_some() {
                        (result, found)
                    } else if found {
                        (callback(kind, Branch::Second, a, b), true)
                    } else {
                        (None, false)
                    }
                }
            }
            Node::Pane(p) => {
                if p == pane {
                    (None, true)
                } else {
                    (None, false)
                }
            }
        }
    }

    fn split(&mut self, kind: Split, new_pane: Pane) {
        *self = Node::Split {
            kind,
            ratio: 500_000,
            a: Box::new(self.clone()),
            b: Box::new(Node::Pane(new_pane)),
        };
    }

    fn update(&mut self, f: &impl Fn(&mut Node)) {
        match self {
            Node::Split { a, b, .. } => {
                a.update(f);
                b.update(f);
            }
            _ => {}
        }

        f(self);
    }

    fn remove(&mut self, pane: &Pane) -> Option<Pane> {
        match self {
            Node::Split { a, b, .. } => {
                if a.pane() == Some(*pane) {
                    *self = *b.clone();
                    Some(self.first_pane())
                } else if b.pane() == Some(*pane) {
                    *self = *a.clone();
                    Some(self.first_pane())
                } else {
                    a.remove(pane).or_else(|| b.remove(pane))
                }
            }
            Node::Pane(_) => None,
        }
    }

    pub fn regions(
        &self,
        spacing: f32,
        size: Size,
    ) -> HashMap<Pane, Rectangle> {
        let mut regions = HashMap::new();

        self.compute_regions(
            spacing / 2.0,
            &Rectangle {
                x: 0.0,
                y: 0.0,
                width: size.width,
                height: size.height,
            },
            &mut regions,
        );

        regions
    }

    fn pane(&self) -> Option<Pane> {
        match self {
            Node::Split { .. } => None,
            Node::Pane(pane) => Some(*pane),
        }
    }

    fn first_pane(&self) -> Pane {
        match self {
            Node::Split { a, .. } => a.first_pane(),
            Node::Pane(pane) => *pane,
        }
    }

    fn compute_regions(
        &self,
        halved_spacing: f32,
        current: &Rectangle,
        regions: &mut HashMap<Pane, Rectangle>,
    ) {
        match self {
            Node::Split { kind, ratio, a, b } => {
                let ratio = *ratio as f32 / 1_000_000.0;
                let (region_a, region_b) =
                    kind.apply(current, ratio, halved_spacing);

                a.compute_regions(halved_spacing, &region_a, regions);
                b.compute_regions(halved_spacing, &region_b, regions);
            }
            Node::Pane(pane) => {
                let _ = regions.insert(*pane, *current);
            }
        }
    }
}

#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq)]
pub enum Split {
    Horizontal,
    Vertical,
}

impl Split {
    fn apply(
        &self,
        rectangle: &Rectangle,
        ratio: f32,
        halved_spacing: f32,
    ) -> (Rectangle, Rectangle) {
        match self {
            Split::Horizontal => {
                let width_left =
                    (rectangle.width * ratio).round() - halved_spacing;
                let width_right = rectangle.width - width_left - halved_spacing;

                (
                    Rectangle {
                        width: width_left,
                        ..*rectangle
                    },
                    Rectangle {
                        x: rectangle.x + width_left + halved_spacing,
                        width: width_right,
                        ..*rectangle
                    },
                )
            }
            Split::Vertical => {
                let height_top =
                    (rectangle.height * ratio).round() - halved_spacing;
                let height_bottom =
                    rectangle.height - height_top - halved_spacing;

                (
                    Rectangle {
                        height: height_top,
                        ..*rectangle
                    },
                    Rectangle {
                        y: rectangle.y + height_top + halved_spacing,
                        height: height_bottom,
                        ..*rectangle
                    },
                )
            }
        }
    }
}

/// The renderer of a [`PaneGrid`].
///
/// Your [renderer] will need to implement this trait before being
/// able to use a [`PaneGrid`] in your user interface.
///
/// [`PaneGrid`]: struct.PaneGrid.html
/// [renderer]: ../../renderer/index.html
pub trait Renderer: crate::Renderer + Sized {
    /// Draws a [`PaneGrid`].
    ///
    /// It receives:
    /// - the elements of the [`PaneGrid`]
    /// - the [`Pane`] that is currently being dragged
    /// - the [`Layout`] of the [`PaneGrid`] and its elements
    /// - the cursor position
    ///
    /// [`Column`]: struct.Row.html
    /// [`Layout`]: ../layout/struct.Layout.html
    fn draw<Message>(
        &mut self,
        defaults: &Self::Defaults,
        content: &[(Pane, Element<'_, Message, Self>)],
        dragging: Option<Pane>,
        layout: Layout<'_>,
        cursor_position: Point,
    ) -> Self::Output;
}

impl<'a, Message, Renderer> From<PaneGrid<'a, Message, Renderer>>
    for Element<'a, Message, Renderer>
where
    Renderer: self::Renderer + 'static,
    Message: 'static,
{
    fn from(
        pane_grid: PaneGrid<'a, Message, Renderer>,
    ) -> Element<'a, Message, Renderer> {
        Element::new(pane_grid)
    }
}