//! A read-only text widget.

use std::borrow::Cow;
use std::fmt::{Display, Write};

use figures::units::{Px, UPx};
use figures::{Point, Round, Size};
use kludgine::text::{MeasuredText, Text, TextOrigin};
use kludgine::{CanRenderTo, Color, DrawableExt};

use super::input::CowString;
use crate::context::{GraphicsContext, LayoutContext, Trackable, WidgetContext};
use crate::styles::components::TextColor;
use crate::styles::FontFamilyList;
use crate::value::{Dynamic, Generation, IntoReadOnly, ReadOnly, Value};
use crate::widget::{MakeWidgetWithTag, Widget, WidgetInstance, WidgetTag};
use crate::window::WindowLocal;
use crate::ConstraintLimit;

/// A read-only text widget.
#[derive(Debug)]
pub struct Label<T> {
    /// The contents of the label.
    pub display: ReadOnly<T>,
    displayed: String,
    prepared_text: WindowLocal<LabelCacheKey>,
}

impl<T> Label<T>
where
    T: std::fmt::Debug + DynamicDisplay + Send + 'static,
{
    /// Returns a new label that displays `text`.
    pub fn new(text: impl IntoReadOnly<T>) -> Self {
        Self {
            display: text.into_read_only(),
            displayed: String::new(),
            prepared_text: WindowLocal::default(),
        }
    }

    fn prepared_text(
        &mut self,
        context: &mut GraphicsContext<'_, '_, '_, '_>,
        color: Color,
        width: Px,
    ) -> &MeasuredText<Px> {
        let check_generation = self.display.generation();
        context.apply_current_font_settings();
        let current_families = context.current_family_list();
        match self.prepared_text.get(context) {
            Some(cache)
                if cache.text.can_render_to(&context.gfx)
                    && cache.generation == check_generation
                    && cache.color == color
                    && width <= cache.width
                    && cache.text.size.width <= width
                    && cache.families == current_families => {}
            _ => {
                let measured = self.display.map(|text| {
                    self.displayed.clear();
                    if let Err(err) = write!(&mut self.displayed, "{}", text.as_display(context)) {
                        tracing::error!("Error invoking Display: {err}");
                    }
                    context
                        .gfx
                        .measure_text(Text::new(&self.displayed, color).wrap_at(width))
                });
                self.prepared_text.set(
                    context,
                    LabelCacheKey {
                        text: measured,
                        generation: check_generation,
                        width,
                        color,
                        families: current_families,
                    },
                );
            }
        }

        self.prepared_text
            .get(context)
            .map(|cache| &cache.text)
            .expect("always initialized")
    }
}

impl<T> Widget for Label<T>
where
    T: std::fmt::Debug + DynamicDisplay + Send + 'static,
{
    fn redraw(&mut self, context: &mut GraphicsContext<'_, '_, '_, '_>) {
        self.display.invalidate_when_changed(context);

        let size = context.gfx.region().size;
        let center = Point::from(size) / 2;
        let text_color = context.get(&TextColor);

        let prepared_text = self.prepared_text(context, text_color, size.width);

        context.gfx.draw_measured_text(
            prepared_text.translate_by(center.round()),
            TextOrigin::Center,
        );
    }

    fn layout(
        &mut self,
        available_space: Size<ConstraintLimit>,
        context: &mut LayoutContext<'_, '_, '_, '_>,
    ) -> Size<UPx> {
        let color = context.get(&TextColor);
        let width = available_space.width.max().try_into().unwrap_or(Px::MAX);
        let prepared = self.prepared_text(context, color, width);

        prepared.size.try_cast().unwrap_or_default().ceil()
    }

    fn summarize(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        fmt.debug_tuple("Label").field(&self.display).finish()
    }

    fn unmounted(&mut self, context: &mut crate::context::EventContext<'_>) {
        self.prepared_text.clear_for(context);
    }
}

macro_rules! impl_make_widget {
    ($($type:ty => $kind:ty),*) => {
        $(impl MakeWidgetWithTag for $type {
            fn make_with_tag(self, id: WidgetTag) -> WidgetInstance {
                Label::<$kind>::new(self).make_with_tag(id)
            }
        })*
    };
}

impl_make_widget!(
    &'_ str => String,
    String => String,
    CowString => CowString,
    Dynamic<String> => String,
    Dynamic<&'static str> => &'static str,
    Value<String> => String,
    ReadOnly<String> => String
);

impl MakeWidgetWithTag for Cow<'_, str> {
    fn make_with_tag(self, tag: WidgetTag) -> WidgetInstance {
        Label::new(self.into_owned()).make_with_tag(tag)
    }
}

impl MakeWidgetWithTag for &'_ String {
    fn make_with_tag(self, tag: WidgetTag) -> WidgetInstance {
        Label::new(self.clone()).make_with_tag(tag)
    }
}

#[derive(Debug)]
struct LabelCacheKey {
    text: MeasuredText<Px>,
    generation: Option<Generation>,
    width: Px,
    color: Color,
    families: FontFamilyList,
}

/// A context-aware [`Display`] implementation.
///
/// This trait is automatically implemented for all types that implement
/// [`Display`].
pub trait DynamicDisplay {
    /// Format `self` with any needed information from `context`.
    fn fmt(&self, context: &WidgetContext<'_>, f: &mut std::fmt::Formatter<'_>)
        -> std::fmt::Result;

    /// Returns a type that implements [`Display`].
    fn as_display<'display, 'ctx>(
        &'display self,
        context: &'display WidgetContext<'ctx>,
    ) -> DynamicDisplayer<'display, 'ctx>
    where
        Self: Sized,
    {
        DynamicDisplayer(self, context)
    }
}

impl<T> DynamicDisplay for T
where
    T: Display,
{
    fn fmt(
        &self,
        _context: &WidgetContext<'_>,
        f: &mut std::fmt::Formatter<'_>,
    ) -> std::fmt::Result {
        self.fmt(f)
    }
}

/// A generic [`Display`] implementation for a [`DynamicDisplay`] implementor.
pub struct DynamicDisplayer<'a, 'w>(&'a dyn DynamicDisplay, &'a WidgetContext<'w>);

impl Display for DynamicDisplayer<'_, '_> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        self.0.fmt(self.1, f)
    }
}
