// Copyright 2019 The Druid Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! A stepper widget.

use std::f64::EPSILON;
use std::time::Duration;

use crate::kurbo::BezPath;
use crate::piet::{LinearGradient, RenderContext, UnitPoint};
use crate::widget::prelude::*;
use crate::{theme, Point, Rect, TimerToken};

// Delay until stepper starts automatically changing valued when one of the button is held down.
const STEPPER_REPEAT_DELAY: Duration = Duration::from_millis(500);
// Delay between value changes when one of the button is held down.
const STEPPER_REPEAT: Duration = Duration::from_millis(200);

/// A stepper widget for step-wise increasing and decreasing a value.
pub struct Stepper {
    max: f64,
    min: f64,
    step: f64,
    wrap: bool,
    /// Keeps track of which button is currently triggered.
    increase_active: bool,
    decrease_active: bool,
    timer_id: TimerToken,
}

impl Stepper {
    /// Create a new `Stepper`.
    pub fn new() -> Self {
        Stepper {
            max: std::f64::MAX,
            min: std::f64::MIN,
            step: 1.0,
            wrap: false,
            increase_active: false,
            decrease_active: false,
            timer_id: TimerToken::INVALID,
        }
    }

    /// Set the range covered by this slider.
    ///
    /// The default range is `std::f64::MIN..std::f64::MAX`.
    pub fn with_range(mut self, min: f64, max: f64) -> Self {
        self.min = min;
        self.max = max;
        self
    }

    /// Set the steppers amount by which the value increases or decreases.
    ///
    /// The default step is `1.0`.
    pub fn with_step(mut self, step: f64) -> Self {
        self.step = step;
        self
    }

    /// Set whether the stepper should wrap around the minimum/maximum values.
    ///
    /// When wraparound is enabled incrementing above max behaves like this:
    /// - if the previous value is < max it becomes max
    /// - if the previous value is = max it becomes min
    /// Same logic applies for decrementing
    ///
    /// The default is `false`.
    pub fn with_wraparound(mut self, wrap: bool) -> Self {
        self.wrap = wrap;
        self
    }

    fn increment(&mut self, data: &mut f64) {
        let next = *data + self.step;
        let was_greater = *data + EPSILON >= self.max;
        let is_greater = next + EPSILON > self.max;
        *data = match (self.wrap, was_greater, is_greater) {
            (true, true, true) => self.min,
            (true, false, true) => self.max,
            (false, _, true) => self.max,
            _ => next,
        }
    }

    fn decrement(&mut self, data: &mut f64) {
        let next = *data - self.step;
        let was_less = *data - EPSILON <= self.min;
        let is_less = next - EPSILON < self.min;
        *data = match (self.wrap, was_less, is_less) {
            (true, true, true) => self.max,
            (true, false, true) => self.min,
            (false, _, true) => self.min,
            _ => next,
        }
    }
}

impl Default for Stepper {
    fn default() -> Self {
        Self::new()
    }
}

impl Widget<f64> for Stepper {
    fn paint(&mut self, ctx: &mut PaintCtx, _data: &f64, env: &Env) {
        let stroke_width = 2.0;
        let rounded_rect = ctx
            .size()
            .to_rect()
            .inset(-stroke_width / 2.0)
            .to_rounded_rect(4.0);

        let height = ctx.size().height;
        let width = env.get(theme::BASIC_WIDGET_HEIGHT);
        let button_size = Size::new(width, height / 2.);

        ctx.stroke(rounded_rect, &env.get(theme::BORDER_DARK), stroke_width);
        ctx.clip(rounded_rect);

        // draw buttons for increase/decrease
        let increase_button_origin = Point::ORIGIN;
        let decrease_button_origin = Point::new(0., height / 2.0);

        let increase_button_rect = Rect::from_origin_size(increase_button_origin, button_size);
        let decrease_button_rect = Rect::from_origin_size(decrease_button_origin, button_size);

        let active_gradient = LinearGradient::new(
            UnitPoint::TOP,
            UnitPoint::BOTTOM,
            (env.get(theme::PRIMARY_LIGHT), env.get(theme::PRIMARY_DARK)),
        );

        let inactive_gradient = LinearGradient::new(
            UnitPoint::TOP,
            UnitPoint::BOTTOM,
            (env.get(theme::BUTTON_DARK), env.get(theme::BUTTON_LIGHT)),
        );

        // draw buttons that are currently triggered as active
        if self.increase_active {
            ctx.fill(increase_button_rect, &active_gradient);
        } else {
            ctx.fill(increase_button_rect, &inactive_gradient);
        };

        if self.decrease_active {
            ctx.fill(decrease_button_rect, &active_gradient);
        } else {
            ctx.fill(decrease_button_rect, &inactive_gradient);
        };

        // draw up and down triangles
        let mut arrows = BezPath::new();
        arrows.move_to(Point::new(4., height / 2. - 4.));
        arrows.line_to(Point::new(width - 4., height / 2. - 4.));
        arrows.line_to(Point::new(width / 2., 4.));
        arrows.close_path();

        arrows.move_to(Point::new(4., height / 2. + 4.));
        arrows.line_to(Point::new(width - 4., height / 2. + 4.));
        arrows.line_to(Point::new(width / 2., height - 4.));
        arrows.close_path();

        ctx.fill(arrows, &env.get(theme::LABEL_COLOR));
    }

    fn layout(
        &mut self,
        _layout_ctx: &mut LayoutCtx,
        bc: &BoxConstraints,
        _data: &f64,
        env: &Env,
    ) -> Size {
        bc.constrain(Size::new(
            env.get(theme::BASIC_WIDGET_HEIGHT),
            env.get(theme::BORDERED_WIDGET_HEIGHT),
        ))
    }

    fn event(&mut self, ctx: &mut EventCtx, event: &Event, data: &mut f64, env: &Env) {
        let height = env.get(theme::BORDERED_WIDGET_HEIGHT);

        match event {
            Event::MouseDown(mouse) => {
                ctx.set_active(true);

                if mouse.pos.y > height / 2. {
                    self.decrease_active = true;
                    self.decrement(data);
                } else {
                    self.increase_active = true;
                    self.increment(data);
                }

                self.timer_id = ctx.request_timer(STEPPER_REPEAT_DELAY);

                ctx.request_paint();
            }
            Event::MouseUp(_) => {
                ctx.set_active(false);

                self.decrease_active = false;
                self.increase_active = false;
                self.timer_id = TimerToken::INVALID;

                ctx.request_paint();
            }
            Event::Timer(id) if *id == self.timer_id => {
                if self.increase_active {
                    self.increment(data);
                }
                if self.decrease_active {
                    self.decrement(data);
                }
                self.timer_id = ctx.request_timer(STEPPER_REPEAT);
            }
            _ => (),
        }
    }

    fn lifecycle(&mut self, _ctx: &mut LifeCycleCtx, _event: &LifeCycle, _data: &f64, _env: &Env) {}

    fn update(&mut self, ctx: &mut UpdateCtx, old_data: &f64, data: &f64, _env: &Env) {
        if (*data - old_data).abs() > EPSILON {
            ctx.request_paint();
        }
    }
}