Slider Use Case

slider-use-case.js

let baseState 
    = ({
        page = 1,
        totalPages = 1,
        canGoNext = false,
        canGoPrev = false,
        position = 0,
        direction = null
    } = {}) => ({
        page,
        totalPages,
        canGoNext,
        canGoPrev,
        position,
        direction
    })

const getPosition
    = (totalPages, page) => totalPages === 1 ? 0 : ((1 / totalPages) * (page - 1))

const isLastPage
    = (totalPages, page) => page === totalPages

const isFirstPage
    = (page) => page === 1

const decreasePage
    = (page) => page - 1

const increasePage
    = (page) => page + 1

const getNewPage
    = (totalPages, currentPage, direction) => direction === 'next'
        ? isLastPage(totalPages, currentPage) ? currentPage : increasePage(currentPage)
        : isFirstPage(currentPage) ? currentPage : decreasePage(currentPage)

const Compute
    = (state = baseState()) => {
        let newPage = state.direction === 'next' || state.direction === 'prev'
                ? getNewPage(state.totalPages, state.page, state.direction)
                : state.page

        return {
            ...state,
            page: newPage,
            position: getPosition(state.totalPages, newPage),
            canGoNext: !isLastPage(state.totalPages, state.page),
            canGoPrev: !isFirstPage(state.page)
        }
    }

const Actions
    = (state = baseState()) => ({
        init: (newState = baseState()) => Actions(Compute({
            ...state,
            ...newState
        })),
        next: () => Actions(Compute({
            ...state,
            direction: 'next'
        })),
        prev: () => Actions(Compute({
            ...state,
            direction: 'prev'
        })),
        get: () => ({
            ...state
        })
    })