use crate::prelude::*;

pub struct Pad {
    pub padding: Padding,
    pub inner: StrongWidget,
}

impl Widget for Pad {
    fn draw(&mut self, painter: &mut Painter) -> Size {
        // The inner's own alignment, not the near edge. This reports the
        // inner's size plus the padding, so where the box is that answer the
        // inset box is exactly the inner and alignment has no room to move
        // it; where the box is bigger -- a share of a row, a rule over this
        // widget -- the slack is the inner's to sit in, and forcing the near
        // edge pinned it to a corner it had not asked for.
        //
        // Padding is an inset of both: it comes off the frame, so `rel(1)`
        // under it fills this widget rather than overflowing it by the
        // padding, and it comes off the box, so what is drawn sits inside.
        // The two stay distinct -- the box can be narrower still, where a row
        // asked this widget in the room left, and a text wraps at that.
        let inset = |lead: Px, trail: Px| {
            Place::Within(Part::Inset {
                lead: Len::from_parts(Rel::ZERO, lead),
                trail: Len::from_parts(Rel::ZERO, trail),
            })
        };
        let place = [
            inset(self.padding.left, self.padding.right),
            inset(self.padding.top, self.padding.bottom),
        ];
        // Read from this widget's own frame rather than written as a
        // fraction of it: a frame is a length of the window like everything
        // else here, and taking the padding off is the whole of what this
        // widget does to it.
        let narrow = [
            (Axis::X, self.padding.left + self.padding.right),
            (Axis::Y, self.padding.top + self.padding.bottom),
        ]
        .map(|(axis, pixels)| Some(painter.frame_len(axis) - Len::from_parts(Rel::ZERO, pixels)));
        let inner = painter.widget_at(&self.inner, narrow, place).size();
        Size {
            x: LayoutLen {
                px: inner.x.px + self.padding.left + self.padding.right,
                ..inner.x
            },
            y: LayoutLen {
                px: inner.y.px + self.padding.top + self.padding.bottom,
                ..inner.y
            },
        }
    }
}

pub struct Padding {
    pub left: Px,
    pub right: Px,
    pub top: Px,
    pub bottom: Px,
}

impl Padding {
    pub const ZERO: Self = Self {
        left: Px::ZERO,
        right: Px::ZERO,
        top: Px::ZERO,
        bottom: Px::ZERO,
    };

    pub fn uniform(amt: impl UiNum) -> Self {
        let amt = Px::from_num(amt);
        Self {
            left: amt,
            right: amt,
            top: amt,
            bottom: amt,
        }
    }
    /// `region` less this padding on each side.
    pub fn region_of(&self, mut region: UiRegion) -> UiRegion {
        region.x.start.px += self.left;
        region.y.start.px += self.top;
        region.x.end.px -= self.right;
        region.y.end.px -= self.bottom;
        region
    }

    pub fn region(&self) -> UiRegion {
        self.region_of(UiRegion::FULL)
    }
    pub fn x(amt: impl UiNum) -> Self {
        let amt = Px::from_num(amt);
        Self {
            left: amt,
            right: amt,
            ..Self::ZERO
        }
    }
    pub fn y(amt: impl UiNum) -> Self {
        let amt = Px::from_num(amt);
        Self {
            top: amt,
            bottom: amt,
            ..Self::ZERO
        }
    }

    pub fn top(amt: impl UiNum) -> Self {
        let mut s = Self::ZERO;
        s.top = Px::from_num(amt);
        s
    }

    pub fn bottom(amt: impl UiNum) -> Self {
        let mut s = Self::ZERO;
        s.bottom = Px::from_num(amt);
        s
    }

    pub fn left(amt: impl UiNum) -> Self {
        let mut s = Self::ZERO;
        s.left = Px::from_num(amt);
        s
    }

    pub fn right(amt: impl UiNum) -> Self {
        let mut s = Self::ZERO;
        s.right = Px::from_num(amt);
        s
    }

    pub fn with_top(mut self, amt: impl UiNum) -> Self {
        self.top = Px::from_num(amt);
        self
    }

    pub fn with_bottom(mut self, amt: impl UiNum) -> Self {
        self.bottom = Px::from_num(amt);
        self
    }

    pub fn with_left(mut self, amt: impl UiNum) -> Self {
        self.left = Px::from_num(amt);
        self
    }

    pub fn with_right(mut self, amt: impl UiNum) -> Self {
        self.right = Px::from_num(amt);
        self
    }
}

impl<T: UiNum> From<T> for Padding {
    fn from(amt: T) -> Self {
        Self::uniform(amt)
    }
}