MainWidgetAdapter.kt

package co.riiid.vida.main.study.widget

import android.view.ViewGroup
import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentManager
import androidx.fragment.app.FragmentStatePagerAdapter
import androidx.viewpager.widget.ViewPager

class MainWidgetAdapter(fm: FragmentManager) : FragmentStatePagerAdapter(fm) {

    companion object {
        const val FRAGMENT_SIZE = 7

        const val LOOP_COUNT = Int.MAX_VALUE

        /**
         * 첫 페이지를 표시하기 위한 중간 부분의 위치.
         */
        const val INITIAL_POS = LOOP_COUNT / 2 - (LOOP_COUNT / 2 % FRAGMENT_SIZE)
    }

    override fun getItem(position: Int): Fragment {
        return when (compressedPos(position)) {
            0 -> TodayStatusFragment.newInstance()
            1 -> ScoreFragment.newInstance()
            2 -> LcRcFragment.newInstance()
            3 -> GradeFragment.newInstance()
            4 -> ComboFragment.newInstance()
            5 -> DDayFragment.newInstance()
            6 -> CoinFragment.newInstance()
            else -> throw IndexOutOfBoundsException()
        }
    }

    override fun getCount(): Int {
        return LOOP_COUNT
    }

    val compressedCount: Int
        get() = FRAGMENT_SIZE

    fun inCompressedBounds(position: Int): Boolean =
        compressedPos(position) in (0 until FRAGMENT_SIZE)

    override fun instantiateItem(container: ViewGroup, position: Int): Any {
        return super.instantiateItem(container, compressedPos(position))
    }

    override fun destroyItem(container: ViewGroup, position: Int, `object`: Any) {
        super.destroyItem(container, compressedPos(position), `object`)
    }

    fun getFragment(container: ViewGroup, position: Int): WidgetFragment? =
        instantiateItem(container, position) as? WidgetFragment

    private fun compressedPos(position: Int): Int = position % FRAGMENT_SIZE
}

internal val ViewPager.compressedCurrentItem: Int
    get() = currentItem.rem(MainWidgetAdapter.FRAGMENT_SIZE)