RVPagerSnapHelperListenable.kt

package com.d4vidi.vp2rv.core

import android.support.annotation.Px
import android.support.v7.widget.LinearLayoutManager
import android.support.v7.widget.RecyclerView
import android.view.View

data class VisiblePageState(
        var index: Int,
        var view: View,
        @Px var viewCenterX: Int,
        @Px var distanceToSettledPixels: Int,
        var distanceToSettled: Float)

interface RVPagerStateListener {
    fun onPageScroll(pagesState: List<VisiblePageState>) {}
    fun onScrollStateChanged(state: Int) {}
    fun onPageSelected(index: Int) {}
}

open class RVPagerSnapHelperListenable(private val maxPages: Int = 3) : RecyclerView.OnScrollListener() {
    fun attachToRecyclerView(recyclerView: RecyclerView, listener: RVPagerStateListener) {
        assertRecyclerViewSetup(recyclerView)
        setUpSnapHelper(recyclerView, listener)
        setUpScrollListener(recyclerView, listener)
    }

    protected fun setUpScrollListener(recyclerView: RecyclerView, listener: RVPagerStateListener) =
        PagerSnapScrollListener(recyclerView, listener, maxPages)

    protected fun setUpSnapHelper(recyclerView: RecyclerView, listener: RVPagerStateListener) =
        PagerSnapHelperVerbose(recyclerView, listener).attachToRecyclerView(recyclerView)

    protected fun assertRecyclerViewSetup(recyclerView: RecyclerView) {
        if (recyclerView.layoutManager !is LinearLayoutManager) {
            throw IllegalArgumentException("RVPagerSnapHelperListenable can only work with a linear layout manager")
        }

        if ((recyclerView.layoutManager as LinearLayoutManager).orientation != LinearLayoutManager.HORIZONTAL) {
            throw IllegalArgumentException("RVPagerSnapHelperListenable can only work with a horizontal orientation")
        }
    }
}