use {
    Align,
    Backend,
    CharacterCache,
    Color,
    Colorable,
    Dimensions,
    FontSize,
    Frameable,
    FramedRectangle,
    IndexSlot,
    Labelable,
    Padding,
    Place,
    Position,
    Positionable,
    Range,
    Rect,
    Scalar,
    Sizeable,
    TextWrap,
    Theme,
    TitleBar,
    Ui,
    UiCell,
    Widget,
};
use position;
use position::Direction::{Forwards, Backwards};
use widget::{self, title_bar};


/// **Canvas** is designed to be a "container"-like "parent" widget that simplifies placement of
/// "children" widgets.
///
/// Widgets can be placed on a **Canvas** in a variety of ways using methods from the
/// [**Positionable**](../position/trait.Positionable) trait.
///
/// **Canvas** provides methods for padding the kid widget area which can make using the
/// **Place**-related **Positionable** methods a little easier.
///
/// A **Canvas** can also be divided into a sequence of smaller **Canvas**ses using the `.flow_*`
/// methods. This creates a kind of **Canvas** tree, where each "split" can be sized using the
/// `.length` or `.length_weight` methods.
///
/// See the `canvas.rs` example for a demonstration of the **Canvas** type.
#[derive(Copy, Clone, Debug)]
pub struct Canvas<'a> {
    /// Data necessary and common for all widget builder types.
    pub common: widget::CommonBuilder,
    /// The builder data related to the style of the Canvas.
    pub style: Style,
    /// The label for the **Canvas**' **TitleBar** if there is one.
    pub maybe_title_bar_label: Option<&'a str>, 
    /// A list of child **Canvas**ses as splits of this **Canvas** flowing in the given direction.
    pub maybe_splits: Option<FlowOfSplits<'a>>,
}

/// **Canvas** state to be cached.
#[derive(Clone, Debug, PartialEq)]
pub struct State {
    rectangle_idx: IndexSlot,
    title_bar_idx: IndexSlot,
}

widget_style!{
    KIND;
    /// Unique styling for the Canvas.
    style Style {
        /// The color of the Canvas' rectangle surface.
        - color: Color { theme.background_color }
        /// The width of the frame surrounding the Canvas' rectangle.
        - frame: Scalar { theme.frame_width }
        /// The color of the Canvas' frame.
        - frame_color: Color { theme.frame_color }
        /// If this Canvas is a split of some parent Canvas, this is the length of the split.
        - length: Length { Length::Weight(1.0) }

        /// Padding for the left edge of the Canvas' kid area.
        - pad_left: Scalar { theme.padding.x.start }
        /// Padding for the right edge of the Canvas' kid area.
        - pad_right: Scalar { theme.padding.x.end }
        /// Padding for the bottom edge of the Canvas' kid area.
        - pad_bottom: Scalar { theme.padding.y.start }
        /// Padding for the top edge of the Canvas' kid area.
        - pad_top: Scalar { theme.padding.y.end }

        /// The color of the title bar. Defaults to the color of the Canvas.
        - title_bar_color: Option<Color> { None }
        /// The color of the title bar's text.
        - title_bar_text_color: Color { theme.label_color }
        /// The font size for the title bar's text.
        - title_bar_font_size: FontSize { theme.font_size_medium }
        /// The way in which the title bar's text should wrap.
        - title_bar_maybe_wrap: Option<TextWrap> { Some(TextWrap::Whitespace) }
        /// The distance between lines for multi-line title bar text.
        - title_bar_line_spacing: Scalar { 1.0 }
        /// The horizontal alignment of the title bar text.
        - title_bar_text_align: Align { Align::Middle }
    }
}

/// Unique kind for the widget type.
pub const KIND: widget::Kind = "Canvas";

/// A series of **Canvas** splits along with their unique identifiers.
pub type ListOfSplits<'a> = &'a [(widget::Id, Canvas<'a>)];

/// A series of **Canvas** splits flowing in the specified direction.
pub type FlowOfSplits<'a> = (Direction, ListOfSplits<'a>);

/// The length of a `Split` given as a weight.
///
/// The length is determined by determining what percentage each `Split`'s weight contributes to
/// the total weight of all `Split`s in a flow list.
pub type Weight = Scalar;

/// Used to describe the desired length for a `Split`.
#[derive(Copy, Clone, Debug, PartialEq)]
pub enum Length {
    /// The length as an absolute scalar.
    Absolute(Scalar),
    /// The length as a weight of the non-absolute length of the parent **Canvas**.
    Weight(Weight),
}

/// The direction in which a sequence of canvas splits will be laid out.
#[derive(Copy, Clone, Debug)]
pub enum Direction {
    X(position::Direction),
    Y(position::Direction),
}


impl<'a> Canvas<'a> {

    /// Construct a new Canvas builder.
    pub fn new() -> Self {
        Canvas {
            common: widget::CommonBuilder::new(),
            style: Style::new(),
            maybe_title_bar_label: None,
            maybe_splits: None,
        }
    }

    builder_methods!{
        pub title_bar { maybe_title_bar_label = Some(&'a str) }
        pub pad_left { style.pad_left = Some(Scalar) }
        pub pad_right { style.pad_right = Some(Scalar) }
        pub pad_bottom { style.pad_bottom = Some(Scalar) }
        pub pad_top { style.pad_top = Some(Scalar) }
        pub with_style { style = Style }
    }

    /// Set the length of the Split as an absolute scalar.
    pub fn length(mut self, length: Scalar) -> Self {
        self.style.length = Some(Length::Absolute(length));
        self
    }

    /// Set the length of the Split as a weight.
    ///
    /// The default length weight for each widget is `1.0`.
    pub fn length_weight(mut self, weight: Weight) -> Self {
        self.style.length = Some(Length::Weight(weight));
        self
    }

    /// Set the child Canvas Splits of the current Canvas flowing in a given direction.
    fn flow(mut self, direction: Direction, splits: ListOfSplits<'a>) -> Self {
        self.maybe_splits = Some((direction, splits));
        self
    }

    /// Set the child Canvasses flowing to the right.
    pub fn flow_right(self, splits: ListOfSplits<'a>) -> Self {
        self.flow(Direction::X(Forwards), splits)
    }

    /// Set the child Canvasses flowing to the left.
    pub fn flow_left(self, splits: ListOfSplits<'a>) -> Self {
        self.flow(Direction::X(Backwards), splits)
    }

    /// Set the child Canvasses flowing upwards.
    pub fn flow_up(self, splits: ListOfSplits<'a>) -> Self {
        self.flow(Direction::Y(Forwards), splits)
    }

    /// Set the child Canvasses flowing downwards.
    pub fn flow_down(self, splits: ListOfSplits<'a>) -> Self {
        self.flow(Direction::Y(Backwards), splits)
    }

    /// Set the padding for all edges of the area where child widgets will be placed.
    #[inline]
    pub fn pad(self, pad: Scalar) -> Self {
        self.pad_left(pad).pad_right(pad).pad_bottom(pad).pad_top(pad)
    }

    /// Set the padding of the area where child widgets will be placed.
    #[inline]
    pub fn padding(self, pad: Padding) -> Self {
        self.pad_left(pad.x.start)
            .pad_right(pad.x.end)
            .pad_bottom(pad.y.start)
            .pad_top(pad.y.end)
    }

    /// Set the color of the `Canvas`' `TitleBar` if it is visible.
    pub fn title_bar_color(mut self, color: Color) -> Self {
        self.style.title_bar_color = Some(Some(color));
        self
    }

}


impl<'a> Widget for Canvas<'a> {
    type State = State;
    type Style = Style;

    fn common(&self) -> &widget::CommonBuilder {
        &self.common
    }

    fn common_mut(&mut self) -> &mut widget::CommonBuilder {
        &mut self.common
    }

    fn unique_kind(&self) -> widget::Kind {
        KIND
    }

    fn init_state(&self) -> State {
        State {
            rectangle_idx: IndexSlot::new(),
            title_bar_idx: IndexSlot::new(),
        }
    }

    fn style(&self) -> Style {
        self.style.clone()
    }

    fn default_x_position<B: Backend>(&self, _ui: &Ui<B>) -> Position {
        Position::Place(Place::Middle, None)
    }

    fn default_y_position<B: Backend>(&self, _ui: &Ui<B>) -> Position {
        Position::Place(Place::Middle, None)
    }

    /// The title bar area at which the Canvas can be clicked and dragged.
    ///
    /// Note: the position of the returned **Rect** should be relative to the center of the widget.
    fn drag_area(&self, dim: Dimensions, style: &Style, theme: &Theme) -> Option<Rect> {
        self.maybe_title_bar_label.map(|_| {
            let font_size = style.title_bar_font_size(theme);
            let (h, rel_y) = title_bar_h_rel_y(dim[1], font_size);
            let rel_xy = [0.0, rel_y];
            let dim = [dim[0], h];
            Rect::from_xy_dim(rel_xy, dim)
        })
    }

    /// The area of the widget below the title bar, upon which child widgets will be placed.
    fn kid_area<C: CharacterCache>(&self, args: widget::KidAreaArgs<Self, C>) -> widget::KidArea {
        let widget::KidAreaArgs { rect, style, theme, .. } = args;
        if self.maybe_title_bar_label.is_some() {
            let font_size = style.title_bar_font_size(theme);
            let title_bar = title_bar(rect, font_size);
            widget::KidArea {
                rect: rect.pad_top(title_bar.h()),
                pad: style.padding(theme),
            }
        } else {
            widget::KidArea {
                rect: rect,
                pad: style.padding(theme),
            }
        }
    }

    /// Update the state of the Canvas.
    fn update<B: Backend>(self, args: widget::UpdateArgs<Self, B>) {
        let widget::UpdateArgs { idx, state, rect, mut ui, .. } = args;
        let Canvas { style, maybe_title_bar_label, maybe_splits, .. } = self;

        // FramedRectangle widget as the rectangle backdrop.
        let rectangle_idx = state.rectangle_idx.get(&mut ui);
        let dim = rect.dim();
        let color = style.color(ui.theme());
        let frame = style.frame(ui.theme());
        let frame_color = style.frame_color(ui.theme());
        FramedRectangle::new(dim)
            .color(color)
            .frame(frame)
            .frame_color(frame_color)
            .middle_of(idx)
            .graphics_for(idx)
            .place_on_kid_area(false)
            .set(rectangle_idx, &mut ui);

        // TitleBar widget if we were given some label.
        if let Some(label) = maybe_title_bar_label {
            let title_bar_idx = state.title_bar_idx.get(&mut ui);
            let color = style.title_bar_color(&ui.theme).unwrap_or(color);
            let font_size = style.title_bar_font_size(&ui.theme);
            let label_color = style.title_bar_text_color(&ui.theme);
            let text_align = style.title_bar_text_align(&ui.theme);
            let line_spacing = style.title_bar_line_spacing(&ui.theme);
            let maybe_wrap = style.title_bar_maybe_wrap(&ui.theme);
            TitleBar::new(label, rectangle_idx)
                .and_mut(|title_bar| {
                    title_bar.style.maybe_wrap = Some(maybe_wrap);
                    title_bar.style.text_align = Some(text_align);
                })
                .color(color)
                .frame(frame)
                .frame_color(frame_color)
                .label_font_size(font_size)
                .label_color(label_color)
                .line_spacing(line_spacing)
                .graphics_for(idx)
                .place_on_kid_area(false)
                .set(title_bar_idx, &mut ui);
        }

        // If we were given some child canvas splits, we should instantiate them.
        if let Some((direction, splits)) = maybe_splits {

            let (total_abs, total_weight) =
                splits.iter().fold((0.0, 0.0), |(abs, weight), &(_, split)| {
                    match split.style.length(ui.theme()) {
                        Length::Absolute(a) => (abs + a, weight),
                        Length::Weight(w) => (abs, weight + w),
                    }
                });

            // No need to calculate kid_area again, we'll just get it from the graph.
            let kid_area = ui.kid_area_of(idx).expect("No KidArea found");
            let kid_area_range = match direction {
                Direction::X(_) => kid_area.x,
                Direction::Y(_) => kid_area.y,
            };

            let total_length = kid_area_range.len();
            let non_abs_length = (total_length - total_abs).max(0.0);
            let weight_normaliser = 1.0 / total_weight;

            let length = |split: &Self, ui: &UiCell<B>| -> Scalar {
                match split.style.length(ui.theme()) {
                    Length::Absolute(length) => length,
                    Length::Weight(weight) => weight * weight_normaliser * non_abs_length,
                }
            };

            let set_split = |split_id: widget::Id, split: Canvas<'a>, ui: &mut UiCell<B>| {
                split.parent(idx).set(split_id, ui);
            };

            // Instantiate each of the splits, matching on the direction first for efficiency.
            match direction {

                Direction::X(direction) => match direction {
                    Forwards => for (i, &(split_id, split)) in splits.iter().enumerate() {
                        let w = length(&split, &ui);
                        let split = match i {
                            0 => split.h(kid_area.h()).mid_left_of(idx),
                            _ => split.right(0.0),
                        }.w(w);
                        set_split(split_id, split, &mut ui);
                    },
                    Backwards => for (i, &(split_id, split)) in splits.iter().enumerate() {
                        let w = length(&split, &ui);
                        let split = match i {
                            0 => split.h(kid_area.h()).mid_right_of(idx),
                            _ => split.left(0.0),
                        }.w(w);
                        set_split(split_id, split, &mut ui);
                    },
                },

                Direction::Y(direction) => match direction {
                    Forwards => for (i, &(split_id, split)) in splits.iter().enumerate() {
                        let h = length(&split, &ui);
                        let split = match i {
                            0 => split.w(kid_area.w()).mid_bottom_of(idx),
                            _ => split.up(0.0),
                        }.h(h);
                        set_split(split_id, split, &mut ui);
                    },
                    Backwards => for (i, &(split_id, split)) in splits.iter().enumerate() {
                        let h = length(&split, &ui);
                        let split = match i {
                            0 => split.w(kid_area.w()).mid_top_of(idx),
                            _ => split.down(0.0),
                        }.h(h);
                        set_split(split_id, split, &mut ui);
                    },
                },
            }

        }
    }

}


/// The height and relative y coordinate of a Canvas' title bar given some canvas height and font
/// size for the title bar.
fn title_bar_h_rel_y(canvas_h: Scalar, font_size: FontSize) -> (Scalar, Scalar) {
    let h = title_bar::calc_height(font_size);
    let rel_y = canvas_h / 2.0 - h / 2.0;
    (h, rel_y)
}

/// The Rect for the Canvas' title bar.
fn title_bar(canvas: Rect, font_size: FontSize) -> Rect {
    let (c_w, c_h) = canvas.w_h();
    let (h, rel_y) = title_bar_h_rel_y(c_h, font_size);
    let xy = [0.0, rel_y];
    let dim = [c_w, h];
    Rect::from_xy_dim(xy, dim)
}

impl Style {
    /// Get the Padding for the Canvas' kid area.
    pub fn padding(&self, theme: &Theme) -> position::Padding {
        position::Padding {
            x: Range::new(self.pad_left(theme), self.pad_right(theme)),
            y: Range::new(self.pad_bottom(theme), self.pad_top(theme)),
        }
    }
}

impl<'a> ::color::Colorable for Canvas<'a> {
    builder_method!(color { style.color = Some(Color) });
}

impl<'a> ::frame::Frameable for Canvas<'a> {
    builder_methods!{
        frame { style.frame = Some(Scalar) }
        frame_color { style.frame_color = Some(Color) }
    }
}

impl<'a> ::label::Labelable<'a> for Canvas<'a> {
    fn label(self, text: &'a str) -> Self {
        self.title_bar(text)
    }
    builder_methods!{
        label_color { style.title_bar_text_color = Some(Color) }
        label_font_size { style.title_bar_font_size = Some(FontSize) }
    }
}