use Printer;
use With;
use direction::Direction;
use event::{Event, EventResult};
use std::any::Any;
use std::ops::Deref;
use theme::ColorStyle;
use vec::Vec2;
use view::{Offset, Position, Selector, View};
use views::{Layer, ShadowView};

/// Simple stack of views.
/// Only the top-most view is active and can receive input.
pub struct StackView {
    layers: Vec<Child>,
    last_size: Vec2,
}

enum Placement {
    Floating(Position),
    Fullscreen,
}

impl Placement {
    pub fn compute_offset<S, A, P>(
        &self, size: S, available: A, parent: P
    ) -> Vec2
    where
        S: Into<Vec2>,
        A: Into<Vec2>,
        P: Into<Vec2>,
    {
        match *self {
            Placement::Floating(ref position) => {
                position.compute_offset(size, available, parent)
            }
            Placement::Fullscreen => Vec2::zero(),
        }
    }
}

struct Child {
    view: Box<View>,
    size: Vec2,
    placement: Placement,

    // We cannot call `take_focus` until we've called `layout()`
    // (for instance, a textView must know it will scroll to be focusable).
    // So we want to call `take_focus` right after the first call to `layout`.
    // This flag remembers when we've done that.
    virgin: bool,
}

new_default!(StackView);

impl StackView {
    /// Creates a new empty StackView
    pub fn new() -> Self {
        StackView {
            layers: Vec::new(),
            last_size: Vec2::zero(),
        }
    }

    /// Adds a new full-screen layer on top of the stack.
    ///
    /// Fullscreen layers have no shadow.
    pub fn add_fullscreen_layer<T>(&mut self, view: T)
    where
        T: 'static + View,
    {
        self.layers.push(Child {
            view: Box::new(Layer::new(view)),
            size: Vec2::zero(),
            placement: Placement::Fullscreen,
            virgin: true,
        });
    }

    /// Adds new view on top of the stack in the center of the screen.
    pub fn add_layer<T>(&mut self, view: T)
    where
        T: 'static + View,
    {
        self.add_layer_at(Position::center(), view);
    }

    /// Adds new view on top of the stack in the center of the screen.
    ///
    /// Chainable variant.
    pub fn layer<T>(self, view: T) -> Self
    where
        T: 'static + View,
    {
        self.with(|s| s.add_layer(view))
    }

    /// Adds a new full-screen layer on top of the stack.
    ///
    /// Chainable variant.
    pub fn fullscreen_layer<T>(self, view: T) -> Self
    where
        T: 'static + View,
    {
        self.with(|s| s.add_fullscreen_layer(view))
    }

    /// Adds a view on top of the stack.
    pub fn add_layer_at<T>(&mut self, position: Position, view: T)
    where
        T: 'static + View,
    {
        self.layers.push(Child {
            // Skip padding for absolute/parent-placed views
            view: Box::new(
                ShadowView::new(Layer::new(view))
                    .top_padding(position.y == Offset::Center)
                    .left_padding(position.x == Offset::Center),
            ),
            size: Vec2::new(0, 0),
            placement: Placement::Floating(position),
            virgin: true,
        });
    }

    /// Adds a view on top of the stack.
    ///
    /// Chainable variant.
    pub fn layer_at<T>(self, position: Position, view: T) -> Self
    where
        T: 'static + View,
    {
        self.with(|s| s.add_layer_at(position, view))
    }

    /// Remove the top-most layer.
    pub fn pop_layer(&mut self) {
        self.layers.pop();
    }

    /// Computes the offset of the current top view.
    pub fn offset(&self) -> Vec2 {
        let mut previous = Vec2::zero();
        for layer in &self.layers {
            let offset = layer.placement.compute_offset(
                layer.size,
                self.last_size,
                previous,
            );
            previous = offset;
        }
        previous
    }

    /// Returns the size for each layer in this view.
    pub fn layer_sizes(&self) -> Vec<Vec2> {
        self.layers.iter().map(|layer| layer.size).collect()
    }
}

struct StackPositionIterator<R: Deref<Target = Child>, I: Iterator<Item = R>> {
    inner: I,
    previous: Vec2,
    total_size: Vec2,
}

impl<R: Deref<Target = Child>, I: Iterator<Item = R>>
    StackPositionIterator<R, I> {
    /// Returns a new StackPositionIterator
    pub fn new(inner: I, total_size: Vec2) -> Self {
        let previous = Vec2::zero();
        StackPositionIterator {
            inner,
            previous,
            total_size,
        }
    }
}

impl<R: Deref<Target = Child>, I: Iterator<Item = R>> Iterator
    for StackPositionIterator<R, I> {
    type Item = (R, Vec2);

    fn next(&mut self) -> Option<(R, Vec2)> {
        self.inner.next().map(|v| {
            let offset = v.placement.compute_offset(
                v.size,
                self.total_size,
                self.previous,
            );

            self.previous = offset;

            // eprintln!("{:?}", offset);
            (v, offset)
        })
    }
}

impl View for StackView {
    fn draw(&self, printer: &Printer) {
        let last = self.layers.len();
        printer.with_color(ColorStyle::Primary, |printer| {
            for (i, (v, offset)) in
                StackPositionIterator::new(self.layers.iter(), printer.size)
                    .enumerate()
            {
                v.view
                    .draw(&printer.sub_printer(offset, v.size, i + 1 == last));
            }
        });
    }

    fn on_event(&mut self, event: Event) -> EventResult {
        // Use the stack position iterator to get the offset of the top layer.
        // TODO: save it instead when drawing?
        match StackPositionIterator::new(
            self.layers.iter_mut(),
            self.last_size,
        ).last()
        {
            None => EventResult::Ignored,
            Some((v, offset)) => v.view.on_event(event.relativized(offset)),
        }
    }

    fn layout(&mut self, size: Vec2) {
        self.last_size = size;

        // The call has been made, we can't ask for more space anymore.
        // Let's make do with what we have.

        for layer in &mut self.layers {
            // Give each guy what he asks for, within the budget constraints.
            let size = Vec2::min(size, layer.view.required_size(size));
            layer.size = size;
            layer.view.layout(layer.size);

            // We need to call `layout()` on the view before giving it focus
            // for the first time. Otherwise it will not be properly set up.
            // Ex: examples/lorem.rs: the text view takes focus because it's
            // scrolling, but it only knows that after a call to `layout()`.
            if layer.virgin {
                layer.view.take_focus(Direction::none());
                layer.virgin = false;
            }
        }
    }

    fn required_size(&mut self, size: Vec2) -> Vec2 {
        // The min size is the max of all children's

        self.layers
            .iter_mut()
            .map(|layer| layer.view.required_size(size))
            .fold(Vec2::new(1, 1), Vec2::max)
    }

    fn take_focus(&mut self, source: Direction) -> bool {
        match self.layers.last_mut() {
            None => false,
            Some(v) => v.view.take_focus(source),
        }
    }

    fn call_on_any<'a>(
        &mut self, selector: &Selector,
        mut callback: Box<FnMut(&mut Any) + 'a>,
    ) {
        for layer in &mut self.layers {
            layer
                .view
                .call_on_any(selector, Box::new(|any| callback(any)));
        }
    }

    fn focus_view(&mut self, selector: &Selector) -> Result<(), ()> {
        for layer in &mut self.layers {
            if layer.view.focus_view(selector).is_ok() {
                return Ok(());
            }
        }

        Err(())
    }
}