nomad-shell/shell/qml/NavigationManager.qml

import QtQuick
import NomadInput 1.0

QtObject {
    id: manager

    property Item rootItem: null
    property list<QtObject> items
    property var currentItem: null

    function focusItem(item) {
        if (!item) {
            return
        }

        currentItem = item 

        if (typeof item.navFocus === "function") {
            item.navFocus()
        }
    }

    function registerItem(item) {
        if (!item) {
            return
        }

        for (let i = 0; i < items.length; i++) {
            if (items[i] === item) {
                return
            }
        }

        items.push(item)
    }

    function unregisterItem(item) {
        if (!item) {
            return
        }

        for (let i = 0; i < items.length; i++) {
            if (items[i] === item) {
                items.splice(i, 1)

                if (currentItem === item) {
                    currentItem = null
                }

                return;
            }
        }
    }

    function move(action) {
        if (!currentItem || !rootItem) {
            return
        }

        let dx = 0
        let dy = 0

        switch(action) {
        case InputManager.Left:
            dx = -1
            break

        case InputManager.Right:
            dx = 1
            break

        case InputManager.Up:
            dy = -1
            break

        case InputManager.Down:
            dy = 1
            break

        default:
            return
        }

        let currentCenter = currentItem.mapToItem(rootItem, currentItem.width / 2, currentItem.height / 2)

        let bestItem = null 
        let bestScore = Infinity

        for (let i = 0; i < items.length; i++) {
            let candidate = items[i]

            if (!candidate) {
                continue
            }

            if (candidate === currentItem) {
                continue
            }

            if (!candidate.visible || !candidate.enabled) {
                continue
            }

            let candidateCenter = candidate.mapToItem(rootItem, candidate.width / 2, candidate.height / 2)

            let differenceX = candidateCenter.x - currentCenter.x 
            let differenceY = candidateCenter.y - currentCenter.y 

            let forwardDistance
            let sidewaysDistance

            if (dx !== 0) {
                forwardDistance = differenceX * dx 
                sidewaysDistance = Math.abs(differenceY)
            } else {
                forwardDistance = differenceY * dy
                sidewaysDistance = Math.abs(differenceX)
            }

            if (forwardDistance <= 0) {
                continue
            }

            let score = forwardDistance + sidewaysDistance * 2

            if (score < bestScore) {
                bestScore = score
                bestItem = candidate
            }
            console.log("candidate:", candidate, "center:", candidateCenter.x, candidateCenter.y, "difference:", differenceX, differenceY)
        }

        if (bestItem) {
            focusItem(bestItem)
        }

        console.log("MOVE", inputManager.actionName(action), "current:", currentItem, "center:", currentCenter.x, currentCenter.y)
    }
}