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/*
This source file is part of the Swift.org open source project
Copyright (c) 2021-2023 Apple Inc. and the Swift project authors
Licensed under Apache License v2.0 with Runtime Library Exception
See https://swift.org/LICENSE.txt for license information
See https://swift.org/CONTRIBUTORS.txt for Swift project authors
*/
import Foundation
/// A list of JSON patches generated as differences between two documents.
public typealias JSONPatchDifferences = [JSONPatchOperation]
typealias CodablePath = [CodingKey]
/// A protocol that defines Diffable conformance for properties and structs in RenderNode JSON.
protocol RenderJSONDiffable {
/// Returns the list of JSON patches (differences) to transform _other_ to _self_.
func difference(from other: Self, at path: CodablePath) -> JSONPatchDifferences
/// Returns if differences between _self_ and _other_ should be reported property-by-property or as a complete replacement.
func isSimilar(to other: Self) -> Bool
}
// If not otherwise defined, difference(from:at:) methods will assume Diffable objects are not similar,
// and should therefore be replaced.
extension RenderJSONDiffable where Self: Equatable {
func isSimilar(to other: Self) -> Bool {
return self == other
}
}
extension Array: RenderJSONDiffable where Element: Equatable & Encodable {
/// Returns the differences between this array and the given one.
func difference(from other: [Element], at path: CodablePath) -> JSONPatchDifferences {
let arrayDiffs = self.difference(from: other)
var differences = arrayDiffs.removals
differences.append(contentsOf: arrayDiffs.insertions)
let patchOperations = differences.map { diff -> JSONPatchOperation in
switch diff {
case .remove(let offset, _, _):
let pointer = JSONPointer(from: path + [JSON.IntegerKey(offset)])
return .remove(pointer: pointer)
case .insert(let offset, let element, _):
let pointer = JSONPointer(from: path + [JSON.IntegerKey(offset)])
return .add(pointer: pointer, encodableValue: element)
}
}
return patchOperations
}
/// Returns the differences between two arrays with diffable values.
func difference(
from other: [Element],
at path: CodablePath
) -> JSONPatchDifferences where Element: RenderJSONDiffable {
// This implementation computes both the insertions and deletions of significantly different elements
// and the per-property differences between elements that are similar to one another.
// First, compute the insertions and deletions based on elements that are _similar_.
let differences = self.difference(from: other) { element1, element2 in
return element1.isSimilar(to: element2)
}
var patchOperations = differences.map { diff -> JSONPatchOperation in
switch diff {
case .remove(let offset, _, _):
let pointer = JSONPointer(from: path + [JSON.IntegerKey(offset)])
return .remove(pointer: pointer)
case .insert(let offset, let element, _):
let pointer = JSONPointer(from: path + [JSON.IntegerKey(offset)])
return .add(pointer: pointer, encodableValue: element)
}
}
// Second, apply the insertions and deletions of significantly different elements so that the
// elements that are _similar_ are aligned (have the same index in both arrays).
let similarOther = other.applying(differences)!
// Finally, iterate over the similar — but not equal — elements to compute their per-property differences.
for (index, value) in enumerated() where similarOther[index] != value {
patchOperations.append(contentsOf: value.difference(from: similarOther[index],
at: path + [JSON.IntegerKey(index)]))
}
return patchOperations
}
// For now, whole arrays should not be replaced.
func isSimilar(to other: [Element]) -> Bool {
return true
}
}
extension Dictionary: RenderJSONDiffable where Key == String, Value: Encodable & Equatable {
/// Returns the differences between this dictionary and the given one.
func difference(from other: [Key: Value], at path: CodablePath) -> JSONPatchDifferences {
var differences = JSONPatchDifferences()
let uniqueKeysSet = Set(self.keys).union(Set(other.keys))
for key in uniqueKeysSet {
if self[key] == nil {
differences.append(.remove(
pointer: JSONPointer(from: path + [JSON.IntegerKey(key)])))
}
else if self[key] != other[key] {
differences.append(.replace(
pointer: JSONPointer(from: path + [JSON.IntegerKey(key)]),
encodableValue: self[key]))
}
}
return differences
}
/// Returns the differences between two dictionaries with diffable values.
func difference(
from other: [Key: Value],
at path: CodablePath
) -> JSONPatchDifferences where Value: RenderJSONDiffable {
var differences = JSONPatchDifferences()
let uniqueKeysSet = Set(self.keys).union(Set(other.keys))
for key in uniqueKeysSet {
differences.append(contentsOf: self[key].difference(from: other[key], at: path + [JSON.IntegerKey(key)]))
}
return differences
}
/// Returns the differences between two dictionaries of arrays with diffable values.
func arrayValueDifference<Element>(
from other: [Key: [Element]],
at path: CodablePath
) -> JSONPatchDifferences where Element: RenderJSONDiffable & Equatable & Encodable {
var differences = JSONPatchDifferences()
let uniqueKeysSet = Set(self.keys).union(Set(other.keys))
for key in uniqueKeysSet {
differences.append(contentsOf: (self[key] as! [Element]?).difference(from: other[key],
at: path + [JSON.IntegerKey(key)]))
}
return differences
}
// For now, we are not replacing whole dictionaries.
func isSimilar(to other: [String: Value]) -> Bool {
return true
}
}
extension Optional: RenderJSONDiffable where Wrapped: RenderJSONDiffable & Equatable & Encodable {
/// Returns the differences between this optional and the given one.
@_disfavoredOverload func difference(from other: Wrapped?, at path: CodablePath) -> JSONPatchDifferences {
var difference = JSONPatchDifferences()
if let current = self, let other {
difference.append(contentsOf: current.difference(from: other, at: path))
} else if other != nil {
difference.append(JSONPatchOperation.remove(
pointer: JSONPointer(from: path)))
} else if let current = self {
difference.append(JSONPatchOperation.add(
pointer: JSONPointer(from: path), encodableValue: current))
}
return difference
}
/// Returns the differences between this array of optional elements and the given one.
func difference<Element>(
from other: [Element]?,
at path: CodablePath
) -> JSONPatchDifferences where Element : RenderJSONDiffable & Equatable & Encodable {
var difference = JSONPatchDifferences()
if let current = self, let other {
difference.append(contentsOf: (current as! [Element]).difference(from: other, at: path))
} else if other != nil {
difference.append(JSONPatchOperation.remove(
pointer: JSONPointer(from: path)))
} else if let current = self {
difference.append(JSONPatchOperation.add(
pointer: JSONPointer(from: path), encodableValue: current))
}
return difference
}
// Optionals should deal with replacements on their own.
func isSimilar(to other: Wrapped?) -> Bool {
return true
}
}
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