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/**
* @typedef {Object} MinimalSelectionItem
* @property {number} from
* @property {number} to
*/
/** A selection of pieces to download.
* @typedef {MinimalSelectionItem & {
* offset: number,
* priority: number,
* notify?: function
* isStreamSelection?: boolean
* }} SelectionItem
*/
/**
* @typedef {MinimalSelectionItem & {notify: function}} NotificationItem
*/
export class Selections {
/** @type {Array<SelectionItem>} */
_items = []
/**
* @param {MinimalSelectionItem & {isStreamSelection?: boolean}} item Interval to be removed from the selection
*/
remove (item) {
for (let i = 0; i < this._items.length; i++) {
const existing = this._items[i]
if (existing.isStreamSelection) {
if (item.isStreamSelection) {
// If both are stream selections and they match, then we remove the first matching item, then we break the loop
if (existing.from === item.from && existing.to === item.to) {
this._items.splice(i, 1)
// for stream selections, we only remove one item at a time
// ergo we break the loop after removing the first matching item
break
}
} else {
// we only remove stream selections when the `isStreamSelection` flag is true and they match
continue
}
} else {
if (isLowerIntersecting(item, existing)) {
existing.to = Math.max(item.from - 1, 0)
} else if (isUpperIntersecting(item, existing)) {
existing.from = item.to + 1
} else if (isInsideExisting(item, existing)) {
const replacingItems = []
const existingStart = { ...existing, to: Math.max(item.from - 1, 0) }
if (existingStart.to - existingStart.from >= 0 && item.from !== 0) replacingItems.push(existingStart)
const existingEnd = { ...existing, from: item.to + 1 }
if (existingEnd.to - existingEnd.from >= 0) replacingItems.push(existingEnd)
this._items.splice(i, 1, ...replacingItems)
i = i - 1 + replacingItems.length // decrement i to offset splice
} else if (isCoveringExisting(item, existing)) {
this._items.splice(i, 1)
i--
}
}
}
}
/**
* @param {SelectionItem & NotificationItem} newItem
*/
insert (newItem) {
if (newItem.from > newItem.to) {
throw new Error('Invalid interval')
}
if (!newItem.isStreamSelection) {
const { notify: oldNotify } = newItem
// Merge notifications of intersecting items into the new item's notify function
const intersectingNotifyFunctions = []
for (const existing of this._items) {
if (existing.notify && isIntersecting(newItem, existing)) {
intersectingNotifyFunctions.push(existing.notify)
}
}
if (intersectingNotifyFunctions.length > 0) {
newItem.notify = () => {
intersectingNotifyFunctions.forEach(fn => fn())
oldNotify?.()
}
}
// Remove or truncate intersecting items to make room for the new item
this.remove(newItem)
}
this._items.push(newItem)
}
/** @param {(a: SelectionItem, b: SelectionItem) => number} sortFn */
sort (sortFn = (a, b) => a.from - b.from) {
this._items.sort(sortFn)
}
get length () {
return this._items.length
}
/** @param {number} index */
get (index) {
return this._items[index]
}
swap (i, j) {
const temp = this._items[i]
this._items[i] = this._items[j]
this._items[j] = temp
}
clear () {
this._items.length = 0
}
/** @returns {Generator<SelectionItem & {remove: () => void, replaceWith: (MinimalSelectionItem[]) => void}>} */
* [Symbol.iterator] () {
for (let i = 0; i < this._items.length; i++) {
const item = this._items[i]
item.remove = () => {
this._items.splice(i, 1)
i--
}
yield item
delete item.remove
}
}
}
/**
* Examples:
* existing: 1-10 | 1-10
* new_item: 8-12 | 10-15
* @param {MinimalSelectionItem} newItem
* @param {MinimalSelectionItem} existing
* @returns {boolean} returns true if the new item's lower end is intersecting with the existing item
*/
export function isLowerIntersecting (newItem, existing) {
return (newItem.from <= existing.to) && (newItem.from > existing.from) && (newItem.to > existing.to)
}
/**
* Examples:
* existing: 20-25 | 20-25
* new_item: 15-22 | 15-20
* @param {MinimalSelectionItem} newItem
* @param {MinimalSelectionItem} existing
* @returns {boolean} returns true if the new item's upper end is intersecting with the existing item
*/
export function isUpperIntersecting (newItem, existing) {
return (newItem.to >= existing.from) && (newItem.to < existing.to) && (newItem.from < existing.from)
}
/**
* Examples:
* existing: 10-20 | 10-20 | 10-20
* new_item: 12-15 | 20-20 | 15-20
* @param {MinimalSelectionItem} newItem
* @param {MinimalSelectionItem} existing
* @returns {boolean} returns true if the new item is completely inside the existing item
*/
export function isInsideExisting (newItem, existing) {
const existingIntervalSize = existing.to - existing.from
const newItemIntervalSize = newItem.to - newItem.from
return newItem.from >= existing.from && newItem.to <= existing.to && (newItemIntervalSize < existingIntervalSize)
}
/**
* Examples:
* existing: 10-20 | 10-20 | 10-20
* new_item: 10-21 | 09-20 | 10-20
* @param {MinimalSelectionItem} newItem
* @param {MinimalSelectionItem} existing
* @returns {boolean} returns true if the new item is covering the existing item
*/
export function isCoveringExisting (newItem, existing) {
return newItem.from <= existing.from && newItem.to >= existing.to
}
export const isIntersecting = (newItem, existing) => () =>
isLowerIntersecting(newItem, existing) ||
isUpperIntersecting(newItem, existing) ||
isInsideExisting(newItem, existing) ||
isCoveringExisting(newItem, existing)
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