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const Form = require('./Form')
module.exports = class ListScrollForm extends Form {
// A form that lets the user scroll through a list of items. It
// automatically adjusts to always allow the selected item to be visible.
constructor(layoutType = 'vertical') {
super()
this.layoutType = layoutType
this.scrollItems = 0
}
fixLayout() {
// The scrollItems property represents the item to the very left of where
// we've scrolled, so we know right away that none of those will be
// visible and we won't bother iterating over them.
const itemsPastScroll = this.inputs.slice(this.scrollItems)
// This variable stores how far along the respective axis (as defined by
// posProp) the next element should be.
let nextPos = 0
for (let item of itemsPastScroll) {
item[this.posProp] = nextPos
nextPos += item[this.sizeProp]
// By default, the item should be visible..
item.visible = true
// ..but the item's far edge is past the form's far edge, it isn't
// fully visible and should be hidden.
if (item[this.posProp] + item[this.sizeProp] > this.formEdge) {
item.visible = false
}
// Same deal goes for the close edge. We can check it against 0 since
// the close edge of the form's content is going to be 0, of course!
if (item[this.posProp] < 0) {
item.visible = false
}
}
}
keyPressed(keyBuf) {
super.keyPressed(keyBuf)
const sel = this.inputs[this.curIndex]
// If the item is ahead of our view (either to the right of or below),
// we should move the view so that the item is the farthest right (of all
// the visible items).
if (this.getItemPos(sel) > this.formEdge + this.scrollSize) {
// We can decide how many items to scroll past by moving forward until
// our item's far edge is visible.
let i
let edge = this.formEdge
for (i = 0; i < this.inputs.length; i++) {
if (this.getItemPos(sel) <= edge) break
edge += this.inputs[i][this.sizeProp]
}
// Now that we have the right index to scroll to, apply it!
this.scrollItems = i
}
// Adjusting the number of scroll items is much simpler to deal with if
// the item is behind our view. Since the item's behind, we need to move
// the scroll to be immediately behind it, which is simple since we
// already have its index.
if (this.getItemPos(sel) <= this.scrollSize) {
this.scrollItems = this.curIndex
}
this.fixLayout()
}
getItemPos(item) {
// Gets the position of the item in an unscrolled view.
return this.inputs.slice(0, this.inputs.indexOf(item) + 1)
.reduce((a, b) => a + b[this.sizeProp], 0)
}
get sizeProp() {
// The property used to measure the size of an item. If the layoutType
// isn't valid (that is, 'horizontal' or 'vertical'), it'll return null.
return (
this.layoutType === 'horizontal' ? 'w' :
this.layoutType === 'vertical' ? 'h' :
null
)
}
get posProp() {
// The property used to position an item. Like sizeProp, returns null if
// the layoutType isn't valid.
return (
this.layoutType === 'horizontal' ? 'x' :
this.layoutType === 'vertical' ? 'y' :
null)
}
get edgeProp() {
// The property used to get the far edge of the property. As with
// sizeProp, if the layoutType doesn't have an expected value, it'll
// return null.
return (
this.layoutType === 'horizontal' ? 'right' :
this.layoutType === 'vertical' ? 'bottom' :
null)
}
get formEdge() {
// Returns the value of the far edge of this form. Items farther in the
// list (up to the edge) will be closer to this edge.
return (
this.layoutType === 'horizontal' ? this.contentW :
this.layoutType === 'vertical' ? this.contentH :
null)
}
get scrollSize() {
// Gets the actual length made up by all of the items currently scrolled
// past.
return this.inputs.slice(0, this.scrollItems)
.reduce((a, b) => a + b[this.sizeProp], 0)
}
}
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