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+// @ts-check
+
+import bigSign from '../util/bigSign'
+import { remapBitfield } from './remap-bitfield.js'
+
+/**
+ * @typedef {'base' | 'defaults' | 'components' | 'utilities' | 'variants' | 'user'} Layer
+ */
+
+/**
+ * @typedef {object} VariantOption
+ * @property {number} id An unique identifier to identify `matchVariant`
+ * @property {function | undefined} sort The sort function
+ * @property {string|null} value The value we want to compare
+ * @property {string|null} modifier The modifier that was used (if any)
+ * @property {bigint} variant The variant bitmask
+ */
+
+/**
+ * @typedef {object} RuleOffset
+ * @property {Layer} layer The layer that this rule belongs to
+ * @property {Layer} parentLayer The layer that this rule originally belonged to. Only different from layer if this is a variant.
+ * @property {bigint} arbitrary 0n if false, 1n if true
+ * @property {bigint} variants Dynamic size. 1 bit per registered variant. 0n means no variants
+ * @property {bigint} parallelIndex Rule index for the parallel variant. 0 if not applicable.
+ * @property {bigint} index Index of the rule / utility in it's given *parent* layer. Monotonically increasing.
+ * @property {VariantOption[]} options Some information on how we can sort arbitrary variants
+ */
+
+export class Offsets {
+ constructor() {
+ /**
+ * Offsets for the next rule in a given layer
+ *
+ * @type {Record<Layer, bigint>}
+ */
+ this.offsets = {
+ defaults: 0n,
+ base: 0n,
+ components: 0n,
+ utilities: 0n,
+ variants: 0n,
+ user: 0n,
+ }
+
+ /**
+ * Positions for a given layer
+ *
+ * @type {Record<Layer, bigint>}
+ */
+ this.layerPositions = {
+ defaults: 0n,
+ base: 1n,
+ components: 2n,
+ utilities: 3n,
+
+ // There isn't technically a "user" layer, but we need to give it a position
+ // Because it's used for ordering user-css from @apply
+ user: 4n,
+
+ variants: 5n,
+ }
+
+ /**
+ * The total number of functions currently registered across all variants (including arbitrary variants)
+ *
+ * @type {bigint}
+ */
+ this.reservedVariantBits = 0n
+
+ /**
+ * Positions for a given variant
+ *
+ * @type {Map<string, bigint>}
+ */
+ this.variantOffsets = new Map()
+ }
+
+ /**
+ * @param {Layer} layer
+ * @returns {RuleOffset}
+ */
+ create(layer) {
+ return {
+ layer,
+ parentLayer: layer,
+ arbitrary: 0n,
+ variants: 0n,
+ parallelIndex: 0n,
+ index: this.offsets[layer]++,
+ options: [],
+ }
+ }
+
+ /**
+ * @returns {RuleOffset}
+ */
+ arbitraryProperty() {
+ return {
+ ...this.create('utilities'),
+ arbitrary: 1n,
+ }
+ }
+
+ /**
+ * Get the offset for a variant
+ *
+ * @param {string} variant
+ * @param {number} index
+ * @returns {RuleOffset}
+ */
+ forVariant(variant, index = 0) {
+ let offset = this.variantOffsets.get(variant)
+ if (offset === undefined) {
+ throw new Error(`Cannot find offset for unknown variant ${variant}`)
+ }
+
+ return {
+ ...this.create('variants'),
+ variants: offset << BigInt(index),
+ }
+ }
+
+ /**
+ * @param {RuleOffset} rule
+ * @param {RuleOffset} variant
+ * @param {VariantOption} options
+ * @returns {RuleOffset}
+ */
+ applyVariantOffset(rule, variant, options) {
+ options.variant = variant.variants
+
+ return {
+ ...rule,
+ layer: 'variants',
+ parentLayer: rule.layer === 'variants' ? rule.parentLayer : rule.layer,
+ variants: rule.variants | variant.variants,
+ options: options.sort ? [].concat(options, rule.options) : rule.options,
+
+ // TODO: Technically this is wrong. We should be handling parallel index on a per variant basis.
+ // We'll take the max of all the parallel indexes for now.
+ // @ts-ignore
+ parallelIndex: max([rule.parallelIndex, variant.parallelIndex]),
+ }
+ }
+
+ /**
+ * @param {RuleOffset} offset
+ * @param {number} parallelIndex
+ * @returns {RuleOffset}
+ */
+ applyParallelOffset(offset, parallelIndex) {
+ return {
+ ...offset,
+ parallelIndex: BigInt(parallelIndex),
+ }
+ }
+
+ /**
+ * Each variant gets 1 bit per function / rule registered.
+ * This is because multiple variants can be applied to a single rule and we need to know which ones are present and which ones are not.
+ * Additionally, every unique group of variants is grouped together in the stylesheet.
+ *
+ * This grouping is order-independent. For instance, we do not differentiate between `hover:focus` and `focus:hover`.
+ *
+ * @param {string[]} variants
+ * @param {(name: string) => number} getLength
+ */
+ recordVariants(variants, getLength) {
+ for (let variant of variants) {
+ this.recordVariant(variant, getLength(variant))
+ }
+ }
+
+ /**
+ * The same as `recordVariants` but for a single arbitrary variant at runtime.
+ * @param {string} variant
+ * @param {number} fnCount
+ *
+ * @returns {RuleOffset} The highest offset for this variant
+ */
+ recordVariant(variant, fnCount = 1) {
+ this.variantOffsets.set(variant, 1n << this.reservedVariantBits)
+
+ // Ensure space is reserved for each "function" in the parallel variant
+ // by offsetting the next variant by the number of parallel variants
+ // in the one we just added.
+
+ // Single functions that return parallel variants are NOT handled separately here
+ // They're offset by 1 (or the number of functions) as usual
+ // And each rule returned is tracked separately since the functions are evaluated lazily.
+ // @see `RuleOffset.parallelIndex`
+ this.reservedVariantBits += BigInt(fnCount)
+
+ return {
+ ...this.create('variants'),
+ variants: this.variantOffsets.get(variant),
+ }
+ }
+
+ /**
+ * @param {RuleOffset} a
+ * @param {RuleOffset} b
+ * @returns {bigint}
+ */
+ compare(a, b) {
+ // Sort layers together
+ if (a.layer !== b.layer) {
+ return this.layerPositions[a.layer] - this.layerPositions[b.layer]
+ }
+
+ // When sorting the `variants` layer, we need to sort based on the parent layer as well within
+ // this variants layer.
+ if (a.parentLayer !== b.parentLayer) {
+ return this.layerPositions[a.parentLayer] - this.layerPositions[b.parentLayer]
+ }
+
+ // Sort based on the sorting function
+ for (let aOptions of a.options) {
+ for (let bOptions of b.options) {
+ if (aOptions.id !== bOptions.id) continue
+ if (!aOptions.sort || !bOptions.sort) continue
+
+ let maxFnVariant = max([aOptions.variant, bOptions.variant]) ?? 0n
+
+ // Create a mask of 0s from bits 1..N where N represents the mask of the Nth bit
+ let mask = ~(maxFnVariant | (maxFnVariant - 1n))
+ let aVariantsAfterFn = a.variants & mask
+ let bVariantsAfterFn = b.variants & mask
+
+ // If the variants the same, we _can_ sort them
+ if (aVariantsAfterFn !== bVariantsAfterFn) {
+ continue
+ }
+
+ let result = aOptions.sort(
+ {
+ value: aOptions.value,
+ modifier: aOptions.modifier,
+ },
+ {
+ value: bOptions.value,
+ modifier: bOptions.modifier,
+ }
+ )
+ if (result !== 0) return result
+ }
+ }
+
+ // Sort variants in the order they were registered
+ if (a.variants !== b.variants) {
+ return a.variants - b.variants
+ }
+
+ // Make sure each rule returned by a parallel variant is sorted in ascending order
+ if (a.parallelIndex !== b.parallelIndex) {
+ return a.parallelIndex - b.parallelIndex
+ }
+
+ // Always sort arbitrary properties after other utilities
+ if (a.arbitrary !== b.arbitrary) {
+ return a.arbitrary - b.arbitrary
+ }
+
+ // Sort utilities, components, etc… in the order they were registered
+ return a.index - b.index
+ }
+
+ /**
+ * Arbitrary variants are recorded in the order they're encountered.
+ * This means that the order is not stable between environments and sets of content files.
+ *
+ * In order to make the order stable, we need to remap the arbitrary variant offsets to
+ * be in alphabetical order starting from the offset of the first arbitrary variant.
+ */
+ recalculateVariantOffsets() {
+ // Sort the variants by their name
+ let variants = Array.from(this.variantOffsets.entries())
+ .filter(([v]) => v.startsWith('['))
+ .sort(([a], [z]) => fastCompare(a, z))
+
+ // Sort the list of offsets
+ // This is not necessarily a discrete range of numbers which is why
+ // we're using sort instead of creating a range from min/max
+ let newOffsets = variants.map(([, offset]) => offset).sort((a, z) => bigSign(a - z))
+
+ // Create a map from the old offsets to the new offsets in the new sort order
+ /** @type {[bigint, bigint][]} */
+ let mapping = variants.map(([, oldOffset], i) => [oldOffset, newOffsets[i]])
+
+ // Remove any variants that will not move letting us skip
+ // remapping if everything happens to be in order
+ return mapping.filter(([a, z]) => a !== z)
+ }
+
+ /**
+ * @template T
+ * @param {[RuleOffset, T][]} list
+ * @returns {[RuleOffset, T][]}
+ */
+ remapArbitraryVariantOffsets(list) {
+ let mapping = this.recalculateVariantOffsets()
+
+ // No arbitrary variants? Nothing to do.
+ // Everyhing already in order? Nothing to do.
+ if (mapping.length === 0) {
+ return list
+ }
+
+ // Remap every variant offset in the list
+ return list.map((item) => {
+ let [offset, rule] = item
+
+ offset = {
+ ...offset,
+ variants: remapBitfield(offset.variants, mapping),
+ }
+
+ return [offset, rule]
+ })
+ }
+
+ /**
+ * @template T
+ * @param {[RuleOffset, T][]} list
+ * @returns {[RuleOffset, T][]}
+ */
+ sort(list) {
+ list = this.remapArbitraryVariantOffsets(list)
+
+ return list.sort(([a], [b]) => bigSign(this.compare(a, b)))
+ }
+}
+
+/**
+ *
+ * @param {bigint[]} nums
+ * @returns {bigint|null}
+ */
+function max(nums) {
+ let max = null
+
+ for (const num of nums) {
+ max = max ?? num
+ max = max > num ? max : num
+ }
+
+ return max
+}
+
+/**
+ * A fast ASCII order string comparison function.
+ *
+ * Using `.sort()` without a custom compare function is faster
+ * But you can only use that if you're sorting an array of
+ * only strings. If you're sorting strings inside objects
+ * or arrays, you need must use a custom compare function.
+ *
+ * @param {string} a
+ * @param {string} b
+ */
+function fastCompare(a, b) {
+ let aLen = a.length
+ let bLen = b.length
+ let minLen = aLen < bLen ? aLen : bLen
+
+ for (let i = 0; i < minLen; i++) {
+ let cmp = a.charCodeAt(i) - b.charCodeAt(i)
+ if (cmp !== 0) return cmp
+ }
+
+ return aLen - bLen
+}