//! Dirt classification for widget mutations.
//!
//! Every widget setter knows which pipeline stage its property affects and
//! marks the widget's dirt accordingly; the tree collects it through
//! [`Widget::take_dirt`](crate::widget::Widget::take_dirt) when a mutation
//! borrow ends. Layout dirt implies repainting; paint dirt does not imply
//! relayout.

/// What must be redone because of a mutation.
#[derive(Copy, Clone, Debug, Default, PartialEq, Eq)]
pub struct Dirt {
    /// The widget's size or content geometry may have changed.
    pub layout: bool,
    /// The widget's appearance changed within its current geometry.
    pub paint: bool,
}

impl Dirt {
    pub const CLEAN: Self = Self {
        layout: false,
        paint: false,
    };
    pub const PAINT: Self = Self {
        layout: false,
        paint: true,
    };
    /// Layout-affecting mutations always repaint too.
    pub const LAYOUT: Self = Self {
        layout: true,
        paint: true,
    };

    pub fn is_clean(self) -> bool {
        self == Self::CLEAN
    }

    #[must_use]
    pub fn union(self, other: Self) -> Self {
        Self {
            layout: self.layout || other.layout,
            paint: self.paint || other.paint,
        }
    }

    /// Mark a layout-affecting change.
    pub fn mark_layout(&mut self) {
        *self = self.union(Self::LAYOUT);
    }

    /// Mark a paint-only change.
    pub fn mark_paint(&mut self) {
        *self = self.union(Self::PAINT);
    }
}