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diff.js
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diff.js
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var isArray = require("x-is-array")
var VPatch = require("../vnode/vpatch")
var isVNode = require("../vnode/is-vnode")
var isVText = require("../vnode/is-vtext")
var isWidget = require("../vnode/is-widget")
var isThunk = require("../vnode/is-thunk")
var handleThunk = require("../vnode/handle-thunk")
var diffProps = require("./diff-props")
module.exports = diff
function diff(a, b) {
var patch = { a: a }
walk(a, b, patch, 0)
return patch
}
function walk(a, b, patch, index) {
if (a === b) {
return
}
var apply = patch[index]
var applyClear = false
if (isThunk(a) || isThunk(b)) {
thunks(a, b, patch, index)
} else if (b == null) {
// If a is a widget we will add a remove patch for it
// Otherwise any child widgets/hooks must be destroyed.
// This prevents adding two remove patches for a widget.
if (!isWidget(a)) {
clearState(a, patch, index)
apply = patch[index]
}
apply = appendPatch(apply, new VPatch(VPatch.REMOVE, a, b))
} else if (isVNode(b)) {
if (isVNode(a)) {
if (a.tagName === b.tagName &&
a.namespace === b.namespace &&
a.key === b.key) {
var propsPatch = diffProps(a.properties, b.properties)
if (propsPatch) {
apply = appendPatch(apply,
new VPatch(VPatch.PROPS, a, propsPatch))
}
apply = diffChildren(a, b, patch, apply, index)
} else {
apply = appendPatch(apply, new VPatch(VPatch.VNODE, a, b))
applyClear = true
}
} else {
apply = appendPatch(apply, new VPatch(VPatch.VNODE, a, b))
applyClear = true
}
} else if (isVText(b)) {
if (!isVText(a)) {
apply = appendPatch(apply, new VPatch(VPatch.VTEXT, a, b))
applyClear = true
} else if (a.text !== b.text) {
apply = appendPatch(apply, new VPatch(VPatch.VTEXT, a, b))
}
} else if (isWidget(b)) {
if (!isWidget(a)) {
applyClear = true
}
apply = appendPatch(apply, new VPatch(VPatch.WIDGET, a, b))
}
if (apply) {
patch[index] = apply
}
if (applyClear) {
clearState(a, patch, index)
}
}
function diffChildren(a, b, patch, apply, index) {
var aChildren = a.children
var orderedSet = reorder(aChildren, b.children)
var bChildren = orderedSet.children
var aLen = aChildren.length
var bLen = bChildren.length
var len = aLen > bLen ? aLen : bLen
for (var i = 0; i < len; i++) {
var leftNode = aChildren[i]
var rightNode = bChildren[i]
index += 1
if (!leftNode) {
if (rightNode) {
// Excess nodes in b need to be added
apply = appendPatch(apply,
new VPatch(VPatch.INSERT, null, rightNode))
}
} else {
walk(leftNode, rightNode, patch, index)
}
if (isVNode(leftNode) && leftNode.count) {
index += leftNode.count
}
}
if (orderedSet.moves) {
// Reorder nodes last
apply = appendPatch(apply, new VPatch(
VPatch.ORDER,
a,
orderedSet.moves
))
}
return apply
}
function clearState(vNode, patch, index) {
// TODO: Make this a single walk, not two
unhook(vNode, patch, index)
destroyWidgets(vNode, patch, index)
}
// Patch records for all destroyed widgets must be added because we need
// a DOM node reference for the destroy function
function destroyWidgets(vNode, patch, index) {
if (isWidget(vNode)) {
if (typeof vNode.destroy === "function") {
patch[index] = appendPatch(
patch[index],
new VPatch(VPatch.REMOVE, vNode, null)
)
}
} else if (isVNode(vNode) && (vNode.hasWidgets || vNode.hasThunks)) {
var children = vNode.children
var len = children.length
for (var i = 0; i < len; i++) {
var child = children[i]
index += 1
destroyWidgets(child, patch, index)
if (isVNode(child) && child.count) {
index += child.count
}
}
} else if (isThunk(vNode)) {
thunks(vNode, null, patch, index)
}
}
// Create a sub-patch for thunks
function thunks(a, b, patch, index) {
var nodes = handleThunk(a, b)
var thunkPatch = diff(nodes.a, nodes.b)
if (hasPatches(thunkPatch)) {
patch[index] = new VPatch(VPatch.THUNK, null, thunkPatch)
}
}
function hasPatches(patch) {
for (var index in patch) {
if (index !== "a") {
return true
}
}
return false
}
// Execute hooks when two nodes are identical
function unhook(vNode, patch, index) {
if (isVNode(vNode)) {
if (vNode.hooks) {
patch[index] = appendPatch(
patch[index],
new VPatch(
VPatch.PROPS,
vNode,
undefinedKeys(vNode.hooks)
)
)
}
if (vNode.descendantHooks || vNode.hasThunks) {
var children = vNode.children
var len = children.length
for (var i = 0; i < len; i++) {
var child = children[i]
index += 1
unhook(child, patch, index)
if (isVNode(child) && child.count) {
index += child.count
}
}
}
} else if (isThunk(vNode)) {
thunks(vNode, null, patch, index)
}
}
function undefinedKeys(obj) {
var result = {}
for (var key in obj) {
result[key] = undefined
}
return result
}
// List diff, naive left to right reordering
function reorder(aChildren, bChildren) {
// O(M) time, O(M) memory
var bChildIndex = keyIndex(bChildren)
var bKeys = bChildIndex.keys
var bFree = bChildIndex.free
if (bFree.length === bChildren.length) {
return {
children: bChildren,
moves: null
}
}
// O(N) time, O(N) memory
var aChildIndex = keyIndex(aChildren)
var aKeys = aChildIndex.keys
var aFree = aChildIndex.free
if (aFree.length === aChildren.length) {
return {
children: bChildren,
moves: null
}
}
// O(MAX(N, M)) memory
var newChildren = []
var freeIndex = 0
var freeCount = bFree.length
var deletedItems = 0
// Iterate through a and match a node in b
// O(N) time,
for (var i = 0 ; i < aChildren.length; i++) {
var aItem = aChildren[i]
var itemIndex
if (aItem.key) {
if (bKeys.hasOwnProperty(aItem.key)) {
// Match up the old keys
itemIndex = bKeys[aItem.key]
newChildren.push(bChildren[itemIndex])
} else {
// Remove old keyed items
itemIndex = i - deletedItems++
newChildren.push(null)
}
} else {
// Match the item in a with the next free item in b
if (freeIndex < freeCount) {
itemIndex = bFree[freeIndex++]
newChildren.push(bChildren[itemIndex])
} else {
// There are no free items in b to match with
// the free items in a, so the extra free nodes
// are deleted.
itemIndex = i - deletedItems++
newChildren.push(null)
}
}
}
var lastFreeIndex = freeIndex >= bFree.length ?
bChildren.length :
bFree[freeIndex]
// Iterate through b and append any new keys
// O(M) time
for (var j = 0; j < bChildren.length; j++) {
var newItem = bChildren[j]
if (newItem.key) {
if (!aKeys.hasOwnProperty(newItem.key)) {
// Add any new keyed items
// We are adding new items to the end and then sorting them
// in place. In future we should insert new items in place.
newChildren.push(newItem)
}
} else if (j >= lastFreeIndex) {
// Add any leftover non-keyed items
newChildren.push(newItem)
}
}
var simulate = newChildren.slice()
var simulateIndex = 0
var removes = []
var inserts = []
var simulateItem
for (var k = 0; k < bChildren.length;) {
var wantedItem = bChildren[k]
simulateItem = simulate[simulateIndex]
// remove items
while (simulateItem === null && simulate.length) {
removes.push(remove(simulate, simulateIndex, null))
simulateItem = simulate[simulateIndex]
}
if (!simulateItem || simulateItem.key !== wantedItem.key) {
// if we need a key in this position...
if (wantedItem.key) {
if (simulateItem && simulateItem.key) {
// if an insert doesn't put this key in place, it needs to move
if (bKeys[simulateItem.key] !== k + 1) {
removes.push(remove(simulate, simulateIndex, simulateItem.key))
simulateItem = simulate[simulateIndex]
// if the remove didn't put the wanted item in place, we need to insert it
if (!simulateItem || simulateItem.key !== wantedItem.key) {
inserts.push({key: wantedItem.key, to: k})
}
// items are matching, so skip ahead
else {
simulateIndex++
}
}
else {
inserts.push({key: wantedItem.key, to: k})
}
}
else {
inserts.push({key: wantedItem.key, to: k})
}
k++
}
// a key in simulate has no matching wanted key, remove it
else if (simulateItem && simulateItem.key) {
removes.push(remove(simulate, simulateIndex, simulateItem.key))
}
}
else {
simulateIndex++
k++
}
}
// remove all the remaining nodes from simulate
while(simulateIndex < simulate.length) {
simulateItem = simulate[simulateIndex]
removes.push(remove(simulate, simulateIndex, simulateItem && simulateItem.key))
}
// If the only moves we have are deletes then we can just
// let the delete patch remove these items.
if (removes.length === deletedItems && !inserts.length) {
return {
children: newChildren,
moves: null
}
}
return {
children: newChildren,
moves: {
removes: removes,
inserts: inserts
}
}
}
function remove(arr, index, key) {
arr.splice(index, 1)
return {
from: index,
key: key
}
}
function keyIndex(children) {
var keys = {}
var free = []
var length = children.length
for (var i = 0; i < length; i++) {
var child = children[i]
if (child.key) {
keys[child.key] = i
} else {
free.push(i)
}
}
return {
keys: keys, // A hash of key name to index
free: free // An array of unkeyed item indices
}
}
function appendPatch(apply, patch) {
if (apply) {
if (isArray(apply)) {
apply.push(patch)
} else {
apply = [apply, patch]
}
return apply
} else {
return patch
}
}