feat: add Visitor pattern and Graph data structures for compiler optimization (#14)

Author: rickhohler

Sources/DesignAlgorithmsKit/Algorithms/DataStructures/Graph.swift

@@ -0,0 +1,102 @@
+//
+//  Graph.swift
+//  DesignAlgorithmsKit
+//
+//  Graph Data Structures and Algorithms
+//
+
+import Foundation
+
+/// A basic node in a graph.
+public struct GraphNode<T: Hashable>: Hashable, Identifiable {
+    public let id: T
+    public let data: T
+    
+    public init(_ data: T) {
+        self.data = data
+        self.id = data
+    }
+}
+
+/// A generic Graph implemented using an Adjacency List.
+public class Graph<T: Hashable> {
+    
+    private var adjList: [T: [T]] = [:]
+    private var nodes: [T: GraphNode<T>] = [:]
+    
+    public init() {}
+    
+    /// Adds a node to the graph.
+    /// - Parameter data: The data associated with the node.
+    @discardableResult
+    public func addNode(_ data: T) -> GraphNode<T> {
+        if let existing = nodes[data] {
+            return existing
+        }
+        let node = GraphNode(data)
+        nodes[data] = node
+        adjList[data] = []
+        return node
+    }
+    
+    /// Adds a directed edge from source to destination.
+    public func addEdge(from source: T, to destination: T) {
+        addNode(source)
+        addNode(destination)
+        adjList[source]?.append(destination)
+    }
+    
+    /// Returns the neighbors of a node.
+    public func neighbors(of node: T) -> [T] {
+        return adjList[node] ?? []
+    }
+    
+    /// Returns all nodes in the graph.
+    public var allNodes: [T] {
+        return Array(nodes.keys)
+    }
+}
+
+// MARK: - Algorithms
+
+extension Graph {
+    
+    /// Performs Breadth-First Search (BFS) to find all reachable nodes from a set of roots.
+    /// - Parameter roots: The starting nodes.
+    /// - Returns: A Set of reachable node IDs.
+    public func reachability(from roots: [T]) -> Set<T> {
+        var visited = Set<T>()
+        var queue = roots
+        
+        // Mark initial roots as visited if they exist in graph
+        for root in roots {
+            if nodes[root] != nil {
+                visited.insert(root)
+            }
+        }
+        
+        while !queue.isEmpty {
+            let current = queue.removeFirst()
+            
+            guard let neighbors = adjList[current] else { continue }
+            
+            for neighbor in neighbors {
+                if !visited.contains(neighbor) {
+                    visited.insert(neighbor)
+                    queue.append(neighbor)
+                }
+            }
+        }
+        
+        return visited
+    }
+    
+    /// Performs "Tree Shaking" - finding all unreachable nodes.
+    /// - Parameter roots: The root nodes (entry points).
+    /// - Returns: A Set of unreachable node IDs (candidates for removal).
+    public func findUnreachable(from roots: [T]) -> Set<T> {
+        let reachable = reachability(from: roots)
+        let all = Set(allNodes)
+        return all.subtracting(reachable)
+    }
+}

Sources/DesignAlgorithmsKit/Behavioral/Visitor.swift

@@ -0,0 +1,32 @@
+//
+//  Visitor.swift
+//  DesignAlgorithmsKit
+//
+//  Visitor Pattern - Separate algorithms from object structure
+//
+
+import Foundation
+
+/// A generic visitor interface.
+/// Allows for separation of algorithms from the object structure they operate on.
+///
+/// - Result: The type of result produced by the visit.
+public protocol Visitor {
+    associatedtype Result
+    
+    /// Visits a visitable element.
+    /// In a concrete implementation, this would likely dispatch to specific methods based on type.
+    /// However, since Swift doesn't support double dispatch natively without manual casting or overloading
+    /// in the `accept` method of the element, strict type safety often requires the Element to call a specific method on the Visitor.
+    ///
+    /// For a generic protocol, we define the entry point.
+    func visit(_ element: Visitable) -> Result
+}
+
+/// An interface for elements that can be visited.
+public protocol Visitable {
+    /// Accepts a visitor.
+    /// - Parameter visitor: The visitor instance.
+    /// - Returns: The result of the visit.
+    func accept<V: Visitor>(_ visitor: V) -> V.Result
+}

Tests/DesignAlgorithmsKitTests/Algorithms/GraphTests.swift

@@ -0,0 +1,74 @@
+//
+//  GraphTests.swift
+//  DesignAlgorithmsKitTests
+//
+//  Tests for Graph Data Structures and Algorithms
+//
+
+import XCTest
+@testable import DesignAlgorithmsKit
+
+final class GraphTests: XCTestCase {
+    
+    func testGraphConstruction() {
+        let graph = Graph<String>()
+        graph.addNode("A")
+        graph.addEdge(from: "A", to: "B")
+        
+        XCTAssertEqual(graph.allNodes.count, 2)
+        XCTAssertTrue(graph.neighbors(of: "A").contains("B"))
+        XCTAssertTrue(graph.neighbors(of: "B").isEmpty)
+    }
+    
+    func testReachabilitySimple() {
+        let graph = Graph<String>()
+        graph.addEdge(from: "A", to: "B")
+        graph.addEdge(from: "B", to: "C")
+        
+        let reachable = graph.reachability(from: ["A"])
+        
+        XCTAssertTrue(reachable.contains("A"))
+        XCTAssertTrue(reachable.contains("B"))
+        XCTAssertTrue(reachable.contains("C"))
+        XCTAssertEqual(reachable.count, 3)
+    }
+    
+    func testReachabilityCycle() {
+        let graph = Graph<String>()
+        graph.addEdge(from: "A", to: "B")
+        graph.addEdge(from: "B", to: "A") // Cycle
+        
+        let reachable = graph.reachability(from: ["A"])
+        
+        XCTAssertTrue(reachable.contains("A"))
+        XCTAssertTrue(reachable.contains("B"))
+        XCTAssertEqual(reachable.count, 2)
+    }
+    
+    func testTreeShaking() {
+        let graph = Graph<String>()
+        // Reachable Component
+        graph.addEdge(from: "Root", to: "A")
+        graph.addEdge(from: "A", to: "B")
+        
+        // Unreachable Component (Dead Code)
+        graph.addEdge(from: "Dead", to: "MoreDead")
+        
+        let unreachable = graph.findUnreachable(from: ["Root"])
+        
+        XCTAssertTrue(unreachable.contains("Dead"))
+        XCTAssertTrue(unreachable.contains("MoreDead"))
+        XCTAssertFalse(unreachable.contains("Root"))
+        XCTAssertFalse(unreachable.contains("A"))
+    }
+    
+    func testDisconnectedNodes() {
+        let graph = Graph<Int>()
+        graph.addNode(1)
+        graph.addNode(2)
+        
+        let reachable = graph.reachability(from: [1])
+        XCTAssertTrue(reachable.contains(1))
+        XCTAssertFalse(reachable.contains(2))
+    }
+}

Tests/DesignAlgorithmsKitTests/Behavioral/VisitorTests.swift

@@ -0,0 +1,52 @@
+//
+//  VisitorTests.swift
+//  DesignAlgorithmsKitTests
+//
+//  Tests for Visitor Pattern
+//
+
+import XCTest
+@testable import DesignAlgorithmsKit
+
+final class VisitorTests: XCTestCase {
+    
+    // Mocks
+    struct ConcreteElement: Visitable {
+        let name: String
+        func accept<V: Visitor>(_ visitor: V) -> V.Result {
+            return visitor.visit(self)
+        }
+    }
+    
+    struct NameVisitor: Visitor {
+        typealias Result = String
+        
+        func visit(_ element: Visitable) -> String {
+            if let ce = element as? ConcreteElement {
+                return "Visited: \(ce.name)"
+            }
+            return "Unknown"
+        }
+    }
+    
+    func testVisitorTraverse() {
+        let element = ConcreteElement(name: "TestNode")
+        let visitor = NameVisitor()
+        
+        let result = element.accept(visitor)
+        XCTAssertEqual(result, "Visited: TestNode")
+    }
+    
+    func testVisitorUnknownType() {
+        struct UnknownElement: Visitable {
+            func accept<V: Visitor>(_ visitor: V) -> V.Result {
+                return visitor.visit(self)
+            }
+        }
+        
+        let element = UnknownElement()
+        let visitor = NameVisitor()
+        let result = element.accept(visitor)
+        XCTAssertEqual(result, "Unknown")
+    }
+}