// ==UserScript==
// @name         HjklNavigation
// @namespace    com.gmail.fujifruity.greasemonkey
// @version      1.5.1
// @description  Shortcuts for Google Search result. j/k to move focus, l/h to open in new/background tab.
// @author       fujifruity
// @include      https://www.google.com/search*
// @grant        GM.openInTab
// @license      MIT
// @downloadURL none
// ==/UserScript==

{
    const items = [...document.querySelectorAll('#rso .g')].filter(e => e.className == 'g')

    const open = isBackground => {
        const url = findCurrentItem().querySelector('a').href
        GM.openInTab(url, isBackground)
    }
    const getVisibleItems = () => items.filter(e => {
        const r = e.getBoundingClientRect();
        return 0 < r.top && r.top < window.innerHeight || 0 < r.bottom && r.bottom < window.innerHeight
    })
    const tag = "hjklNavigationCurrentItem"
    const findCurrentItem = () => items.find(e => e.hasAttribute(tag))

    const moveCursor = step => {
        const currentItem = findCurrentItem()
        const visibleItems = getVisibleItems()
        if (!visibleItems.includes(currentItem)) {
            const centerVisible = visibleItems[parseInt(visibleItems.length / 2)]
            select(centerVisible)
            return
        }
        const nextIdx = (items.indexOf(currentItem) + step + items.length) % items.length
        select(items[nextIdx])
    }
    const select = item => {
        // deselect current item
        const currentItem = findCurrentItem()
        currentItem?.setAttribute('style', "background-color: null;")
        currentItem?.removeAttribute(tag)
        item.style.backgroundColor = 'lightyellow'
        item.setAttribute(tag, '')
        item.scrollIntoView({ behavior: "smooth", block: "center" })
    }
    items[0].style.backgroundColor = 'lightyellow'
    items[0].setAttribute(tag, '')

    window.addEventListener('keydown', event => {
        if (event.target.tagName == "INPUT" || event.ctrlKey || event.altKey) return
        switch (event.key) {
            case 'j': {
                moveCursor(+1)
                break
            }
            case 'k': {
                moveCursor(-1)
                break
            }
            case 'l': {
                open(false)
                break
            }
            case 'h': {
                open(true)
                break
            }
        }
    })

}