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'use strict'
const { flattenGrouplike, isGroup } = require('./playlist-utils')
function shuffleGroups(grouplike) {
if (isGroup(grouplike) && grouplike.items.every(isGroup)) {
const items = shuffleArray(grouplike.items.map(shuffleGroups))
return Object.assign({}, grouplike, {items})
} else {
return grouplike
}
}
function makePicker(grouplike, sort, loop) {
// Options to take into consideration:
// - How should the top-level be sorted?
// (e.g. "order", "shuffle", "shuffle-groups")
// - How should looping be handled?
// (e.g. "loop", "no-loop")
// - Also keep in mind aliases for all of the above.
// (e.g. "ordered", "shuffled", "noloop")
//
// What about a shuffle-mode that should simply pick a random track every
// time?
//
// What about a shuffle-mode that re-shuffles the list every time a loop
// happens?
//
// Both of those options could probably be handled via the 'loop' option.
if (![
'order', 'ordered', 'shuffle', 'shuffled', 'shuffle-groups',
'shuffled-groups'
].includes(sort)) {
throw new Error(`Invalid sort mode: ${sort}`)
}
if (![
'loop', 'no-loop', 'no', 'loop-same-order', 'loop-regenerate',
'pick-random'
].includes(loop)) {
throw new Error(`Invalid loop mode: ${loop}`)
}
const topLevel = {items: []}
let generateTopLevel = () => {
if (sort === 'order' || sort === 'ordered') {
topLevel.items = flattenGrouplike(grouplike).items
}
if (sort === 'shuffle' || sort === 'shuffled') {
topLevel.items = shuffleArray(flattenGrouplike(grouplike).items)
}
if (sort === 'shuffle-groups' || sort === 'shuffled-groups') {
topLevel.items = flattenGrouplike(shuffleGroups(grouplike)).items
}
}
generateTopLevel()
let index = 0
return function() {
if (index === topLevel.items.length) {
if (loop === 'loop-same-order' || loop === 'loop') {
index = 0
}
if (loop === 'loop-regenerate') {
generateTopLevel()
index = 0
}
if (loop === 'no-loop' || loop === 'no') {
// Returning null means the picker is done picking.
// (In theory, we could use an ES2015 generator intead, but this works
// well enough.)
return null
}
}
if (index > topLevel.items.length) {
throw new Error(
"Picker index is greater than total item count?" +
`(${index} > ${topLevel.items.length}`
)
}
if (index < topLevel.items.length) {
// Pick-random is a special exception - in this case we don't actually
// care about the value of the index variable; instead we just pick a
// random track from the generated top level.
//
// Loop=pick-random is different from sort=shuffle. Sort=shuffle always
// ensures the same song doesn't play twice in a single shuffle. It's
// like how when you shuffle a deck of cards, you'll still never pick
// the same card twice, until you go all the way through the deck and
// re-shuffle the deck!
//
// Loop=pick-random instead picks a random track every time the picker
// is called. It's more like you reshuffle the complete deck every time
// you pick something.
//
// Now, how should pick-random work when dealing with groups, such as
// when using sort=shuffle-groups? (If I can't find a solution, I'd say
// that's alright.)
if (loop === 'pick-random') {
const pickedIndex = Math.floor(Math.random() * topLevel.items.length)
return topLevel.items[pickedIndex]
}
// If we're using any other mode, we just want to get the current item
// in the playlist, and increment the index variable by one (note i++
// and not ++i; i++ increments AFTER getting i so it gets us the range
// 0..length-1, whereas ++i increments BEFORE, which gets us the range
// 1..length.
return topLevel.items[index++]
}
}
}
function shuffleArray(array) {
// Shuffles the items in an array. Super-interesting post on how it works:
// https://bost.ocks.org/mike/shuffle/
const workingArray = array.slice(0)
let m = array.length
while (m) {
let i = Math.floor(Math.random() * m)
m--
// Stupid lol; avoids the need of a temporary variable!
Object.assign(workingArray, {
[m]: workingArray[i],
[i]: workingArray[m]
})
}
return workingArray
}
module.exports = makePicker
|
