from kivy.app import App
from kivy.lang import Builder
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.label import Label
from kivy.animation import Animation
from kivy.core.window import Window
from kivy.metrics import dp
from kivy.clock import mainthread
from kivy.properties import BooleanProperty

Window.size = 400, 600

kv = r'''
PullDown:
    orientation:"vertical"
    Button:
        id:btn
        size_hint:1,None
        height:0
        opacity:0
    ScrollView:
        id:sv
        BoxLayout:
            id:bl
            orientation:"vertical"
            size_hint:1,None
            height: dp(600) if  dp(500) < self.minimum_height < dp(560) else self.minimum_height
'''


class PullDown(BoxLayout):
    sv_open = BooleanProperty(False)  # used to create an event
    animation_ongoing = False

    def on_kv_post(self, base_widget):
        for i in range(5):  # <<<<<<<--------------- buggy for 5 or 6, all others work
            l = Label(size_hint=(1, None), height=dp(110), text="test")
            self.ids.bl.add_widget(l)
        # return super().on_kv_post(base_widget)  #this is an event, not overloading

    def on_touch_down(self, touch):
        if self.collide_point(*touch.pos):
            touch.grab(self)
        if self.sv_open:
            self.collapse(touch)
        return super().on_touch_down(touch)

    def on_touch_move(self, touch):
        if (touch.grab_current is self) and (not self.animation_ongoing):
            if touch.dy < 0 and self.ids.sv.effect_y.overscroll < -dp(150):
                self.expand(touch)
                return False
        return super().on_touch_move(touch)

    def on_touch_up(self, touch):
        if touch.grab_current is self:
            touch.ungrab(self)
        return super().on_touch_up(touch)

    def on_sv_open(self, instance, button_open):
        print(f'{self.sv_open=}')
        # if button_open:
        #     scroll_anim = Animation(scroll_y=1, d=.9)  # this is a hack, might be platform dependent
        #     scroll_anim.start(self.ids.sv)

    @mainthread
    def expand(self, touch):
        self.animation_ongoing = True
        super().on_touch_up(touch)
        anim = Animation(
            height=dp(100),
            opacity=1,
            d=0.3, t="out_cubic"
        )

        def on_animation_complete(*args):
            self.animation_ongoing = False
            self.sv_open = True

        anim.bind(on_complete=on_animation_complete)
        anim.start(self.ids.btn)

    @mainthread
    def collapse(self, touch):
        self.animation_ongoing = True
        super().on_touch_up(touch)
        anim = Animation(
            height=0,
            opacity=0,
            d=0.3, t="out_cubic"
        )

        def on_animation_complete(*args):
            self.animation_ongoing = False
            self.sv_open = False
            self.ids.sv.scroll_y = 1

        anim.bind(on_complete=on_animation_complete)
        anim.start(self.ids.btn)


class Test(App):
    def build(self):
        return Builder.load_string(kv)


Test().run()