Swift Package Manager support

Sources/Migrating/MigrationChain.swift

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+//
+//  MigrationChain.swift
+//  CoreStore
+//
+//  Copyright © 2015 John Rommel Estropia
+//
+//  Permission is hereby granted, free of charge, to any person obtaining a copy
+//  of this software and associated documentation files (the "Software"), to deal
+//  in the Software without restriction, including without limitation the rights
+//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+//  copies of the Software, and to permit persons to whom the Software is
+//  furnished to do so, subject to the following conditions:
+//
+//  The above copyright notice and this permission notice shall be included in all
+//  copies or substantial portions of the Software.
+//
+//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+//  SOFTWARE.
+//
+
+import Foundation
+import CoreData
+
+
+// MARK: - MigrationChain
+
+/**
+ A `MigrationChain` indicates the sequence of model versions to be used as the order for progressive migrations. This is typically passed to the `DataStack` initializer and will be applied to all stores added to the `DataStack` with `addSQLiteStore(...)` and its variants.
+ 
+ Initializing with empty values (either `nil`, `[]`, or `[:]`) instructs the `DataStack` to use the .xcdatamodel's current version as the final version, and to disable progressive migrations:
+ ```
+ let dataStack = DataStack(migrationChain: nil)
+ ```
+ This means that the mapping model will be computed from the store's version straight to the `DataStack`'s model version.
+ To support progressive migrations, specify the linear order of versions:
+ ```
+ let dataStack = DataStack(migrationChain:
+    ["MyAppModel", "MyAppModelV2", "MyAppModelV3", "MyAppModelV4"])
+ ```
+ or for more complex migration paths, a version tree that maps the key-values to the source-destination versions:
+ ```
+ let dataStack = DataStack(migrationChain: [
+     "MyAppModel": "MyAppModelV3",
+     "MyAppModelV2": "MyAppModelV4",
+     "MyAppModelV3": "MyAppModelV4"
+ ])
+ ```
+ This allows for different migration paths depending on the starting version. The example above resolves to the following paths:
+ - MyAppModel-MyAppModelV3-MyAppModelV4
+ - MyAppModelV2-MyAppModelV4
+ - MyAppModelV3-MyAppModelV4
+ 
+ The `MigrationChain` is validated when passed to the `DataStack` and unless it is empty, will raise an assertion if any of the following conditions are met:
+ - a version appears twice in an array
+ - a version appears twice as a key in a dictionary literal
+ - a loop is found in any of the paths
+ */
+public struct MigrationChain: NilLiteralConvertible, StringLiteralConvertible, DictionaryLiteralConvertible, ArrayLiteralConvertible {
+    
+    // MARK: NilLiteralConvertible
+    
+    public init(nilLiteral: ()) {
+        
+        self.versionTree = [:]
+        self.rootVersions = []
+        self.leafVersions = []
+        self.valid = true
+    }
+    
+    
+    // MARK: StringLiteralConvertible
+    
+    public init(stringLiteral value: String) {
+        
+        self.versionTree = [:]
+        self.rootVersions = [value]
+        self.leafVersions = [value]
+        self.valid = true
+    }
+    
+    
+    // MARK: ExtendedGraphemeClusterLiteralConvertible
+    
+    public init(extendedGraphemeClusterLiteral value: String) {
+        
+        self.versionTree = [:]
+        self.rootVersions = [value]
+        self.leafVersions = [value]
+        self.valid = true
+    }
+    
+    
+    // MARK: UnicodeScalarLiteralConvertible
+    
+    public init(unicodeScalarLiteral value: String) {
+        
+        self.versionTree = [:]
+        self.rootVersions = [value]
+        self.leafVersions = [value]
+        self.valid = true
+    }
+    
+    
+    // MARK: DictionaryLiteralConvertible
+    
+    public init(dictionaryLiteral elements: (String, String)...) {
+        
+        var valid = true
+        var versionTree = [String: String]()
+        elements.forEach { (sourceVersion, destinationVersion) in
+            
+            guard let _ = versionTree.updateValue(destinationVersion, forKey: sourceVersion) else {
+                
+                return
+            }
+            
+            CoreStore.assert(false, "\(typeName(MigrationChain))'s migration chain could not be created due to ambiguous version paths.")
+            
+            valid = false
+        }
+        let leafVersions = Set(
+            elements.filter { (tuple: (String, String)) -> Bool in
+                
+                return versionTree[tuple.1] == nil
+                
+            }.map { $1 }
+        )
+        
+        let isVersionAmbiguous = { (start: String) -> Bool in
+            
+            var checklist: Set<String> = [start]
+            var version = start
+            while let nextVersion = versionTree[version] where nextVersion != version {
+                
+                if checklist.contains(nextVersion) {
+                    
+                    CoreStore.assert(false, "\(typeName(MigrationChain))'s migration chain could not be created due to looping version paths.")
+                    
+                    return true
+                }
+                checklist.insert(nextVersion)
+                version = nextVersion
+            }
+            
+            return false
+        }
+        
+        self.versionTree = versionTree
+        self.rootVersions = Set(versionTree.keys).subtract(versionTree.values)
+        self.leafVersions = leafVersions
+        self.valid = valid && Set(versionTree.keys).union(versionTree.values).filter { isVersionAmbiguous($0) }.count <= 0
+    }
+    
+    
+    // MARK: ArrayLiteralConvertible
+    
+    public init(arrayLiteral elements: String...) {
+        
+        CoreStore.assert(Set(elements).count == elements.count, "\(typeName(MigrationChain))'s migration chain could not be created due to duplicate version strings.")
+        
+        var lastVersion: String?
+        var versionTree = [String: String]()
+        var valid = true
+        for version in elements {
+            
+            if let lastVersion = lastVersion,
+                let _ = versionTree.updateValue(version, forKey: lastVersion) {
+                    
+                    valid = false
+            }
+            lastVersion = version
+        }
+        
+        self.versionTree = versionTree
+        self.rootVersions = Set([elements.first].flatMap { $0 == nil ? [] : [$0!] })
+        self.leafVersions = Set([elements.last].flatMap { $0 == nil ? [] : [$0!] })
+        self.valid = valid
+    }
+    
+    
+    // MARK: Internal
+    
+    internal let rootVersions: Set<String>
+    internal let leafVersions: Set<String>
+    internal let valid: Bool
+    
+    internal var empty: Bool {
+        
+        return self.versionTree.count <= 0
+    }
+    
+    internal func contains(version: String) -> Bool {
+        
+        return self.rootVersions.contains(version)
+            || self.leafVersions.contains(version)
+            || self.versionTree[version] != nil
+    }
+    
+    internal func nextVersionFrom(version: String) -> String? {
+        
+        guard let nextVersion = self.versionTree[version] where nextVersion != version else {
+            
+            return nil
+        }
+        return nextVersion
+    }
+    
+    
+    // MARK: Private
+    
+    private let versionTree: [String: String]
+}
+
+
+// MARK: - MigrationChain: CustomDebugStringConvertible
+
+extension MigrationChain: CustomDebugStringConvertible {
+    
+    public var debugDescription: String {
+        
+        guard self.valid else {
+            
+            return "<invalid migration chain>"
+        }
+        
+        var paths = [String]()
+        for var version in self.rootVersions {
+            
+            var steps = [version]
+            while let nextVersion = self.nextVersionFrom(version) {
+                
+                steps.append(nextVersion)
+                version = nextVersion
+            }
+            paths.append(steps.joinWithSeparator(" → "))
+        }
+        
+        return "[" + paths.joinWithSeparator("], [") + "]"
+    }
+}