// From https://github.com/emilk/egui/blob/e037489ac20a9e419715ae75d205a8baa117c3cf/crates/egui_demo_app/src/frame_history.rs
// Copyright (c) 2018-2021 Emil Ernerfeldt <emil.ernerfeldt@gmail.com>
//
// Permission is hereby granted, free of charge, to any
// person obtaining a copy of this software and associated
// documentation files (the "Software"), to deal in the
// Software without restriction, including without
// limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of
// the Software, and to permit persons to whom the Software
// is furnished to do so, subject to the following
// conditions:
//
// The above copyright notice and this permission notice
// shall be included in all copies or substantial portions
// of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
// ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
// TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
// PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
// SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
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use egui::util::History;

pub struct FrameHistory {
    frame_times: History<f32>,
}

impl Default for FrameHistory {
    fn default() -> Self {
        let max_age: f32 = 1.0;
        let max_len = (max_age * 300.0).round() as usize;
        Self { frame_times: History::new(0..max_len, max_age) }
    }
}

impl FrameHistory {
    // Called first
    pub fn on_new_frame(&mut self, now: f64, previous_frame_time: Option<f32>) {
        let previous_frame_time = previous_frame_time.unwrap_or_default();
        if let Some(latest) = self.frame_times.latest_mut() {
            *latest = previous_frame_time; // rewrite history now that we know
        }
        self.frame_times.add(now, previous_frame_time); // projected
    }

    pub fn mean_frame_time(&self) -> f32 { self.frame_times.average().unwrap_or_default() }

    pub fn fps(&self) -> f32 { 1.0 / self.frame_times.mean_time_interval().unwrap_or_default() }

    pub fn ui(&mut self, ui: &mut egui::Ui) {
        ui.label(format!("Mean CPU usage: {:.2} ms / frame", 1e3 * self.mean_frame_time()))
            .on_hover_text(
                "Includes egui layout and tessellation time.\n\
            Does not include GPU usage, nor overhead for sending data to GPU.",
            );
        egui::warn_if_debug_build(ui);

        egui::CollapsingHeader::new("📊 CPU usage history").default_open(false).show(ui, |ui| {
            self.graph(ui);
        });
    }

    fn graph(&mut self, ui: &mut egui::Ui) -> egui::Response {
        use egui::*;

        ui.label("egui CPU usage history");

        let history = &self.frame_times;

        // TODO(emilk): we should not use `slider_width` as default graph width.
        let height = ui.spacing().slider_width;
        let size = vec2(ui.available_size_before_wrap().x, height);
        let (rect, response) = ui.allocate_at_least(size, Sense::hover());
        let style = ui.style().noninteractive();

        let graph_top_cpu_usage = 0.010;
        let graph_rect = Rect::from_x_y_ranges(history.max_age()..=0.0, graph_top_cpu_usage..=0.0);
        let to_screen = emath::RectTransform::from_to(graph_rect, rect);

        let mut shapes = Vec::with_capacity(3 + 2 * history.len());
        shapes.push(Shape::Rect(epaint::RectShape::new(
            rect,
            style.corner_radius,
            ui.visuals().extreme_bg_color,
            ui.style().noninteractive().bg_stroke,
            StrokeKind::Inside,
        )));

        let rect = rect.shrink(4.0);
        let color = ui.visuals().text_color();
        let line_stroke = Stroke::new(1.0, color);

        if let Some(pointer_pos) = response.hover_pos() {
            let y = pointer_pos.y;
            shapes.push(Shape::line_segment(
                [pos2(rect.left(), y), pos2(rect.right(), y)],
                line_stroke,
            ));
            let cpu_usage = to_screen.inverse().transform_pos(pointer_pos).y;
            let text = format!("{:.1} ms", 1e3 * cpu_usage);
            shapes.push(ui.fonts(|f| {
                Shape::text(
                    f,
                    pos2(rect.left(), y),
                    egui::Align2::LEFT_BOTTOM,
                    text,
                    TextStyle::Monospace.resolve(ui.style()),
                    color,
                )
            }));
        }

        let circle_color = color;
        let radius = 2.0;
        let right_side_time = ui.input(|i| i.time); // Time at right side of screen

        for (time, cpu_usage) in history.iter() {
            let age = (right_side_time - time) as f32;
            let pos = to_screen.transform_pos_clamped(Pos2::new(age, cpu_usage));

            shapes.push(Shape::line_segment([pos2(pos.x, rect.bottom()), pos], line_stroke));

            if cpu_usage < graph_top_cpu_usage {
                shapes.push(Shape::circle_filled(pos, radius, circle_color));
            }
        }

        ui.painter().extend(shapes);

        response
    }
}