use crate::egui::style::WidgetVisuals;
use eframe::egui::{Color32, InnerResponse, Style, Ui};

/// Reduces the alpha of a color (how opaque it is) by a factor.
pub fn set_alpha(color: Color32, factor: f32) -> Color32 {
    if factor == 1.0 {
        // Fast/common path.
        color
    } else {
        color.linear_multiply(factor)
    }
}

/// Same as [`multiply_alpha`], but operates in place.
pub fn set_alpha_in_place(color: &mut Color32, factor: f32) {
    assert!(factor >= 0.0 && factor <= 1.0);
    *color = set_alpha(*color, factor);
}

/// Changes alpha of entire widget style.
fn set_widget_alpha_in_place(widget: &mut WidgetVisuals, factor: f32) {
    set_alpha_in_place(&mut widget.bg_fill, factor);
    set_alpha_in_place(&mut widget.bg_stroke.color, factor);
    set_alpha_in_place(&mut widget.fg_stroke.color, factor);
}

/// Changes alpha of entire style.
pub fn set_style_alpha(style: &Style, factor: f32) -> Style {
    let mut clone = style.clone();
    set_style_alpha_in_place(&mut clone, factor);
    clone
}

/// Changes alpha of entire style, in place.
pub fn set_style_alpha_in_place(style: &mut Style, factor: f32) {
    if factor == 1.0 {
        // Common/fast path.
        return;
    }
    let widgets = &mut style.visuals.widgets;
    for widget in [
        &mut widgets.noninteractive,
        &mut widgets.inactive,
        &mut widgets.hovered,
        &mut widgets.active,
        &mut widgets.open,
    ] {
        set_widget_alpha_in_place(widget, factor);
    }
    set_alpha_in_place(&mut style.visuals.hyperlink_color, factor);
    set_alpha_in_place(&mut style.visuals.faint_bg_color, factor);
    set_alpha_in_place(&mut style.visuals.extreme_bg_color, factor);
    set_alpha_in_place(&mut style.visuals.code_bg_color, factor);
    set_alpha_in_place(&mut style.visuals.window_shadow.color, factor);
}

/// Render some children with the specified alpha from 0 to 1.
pub fn with_alpha<R>(
    ui: &mut Ui,
    alpha: f32,
    add_contents: impl FnOnce(&mut Ui) -> R,
) -> InnerResponse<R> {
    ui.scope(|ui| {
        set_style_alpha_in_place(ui.style_mut(), alpha);
        add_contents(ui)
    })
}