From f754182c476b5a95357c7d69835c5eeaddfb6f42 Mon Sep 17 00:00:00 2001
From: Rick Hohler <rick.hohler@gmail.com>
Date: Fri, 19 Dec 2025 23:31:53 -0600
Subject: [PATCH] feat: Add GitObjectLayout strategy

- Implements GitObjectLayout for generating git-style directory paths from hashes
- Adds unit tests for layout generation
- Fixes redundant public modifier warning in HashAlgorithmProtocol
---
 .../Hashing/HashAlgorithmProtocol.swift       |  2 +-
 .../Algorithms/Storage/GitObjectLayout.swift  | 50 +++++++++++++++++++
 .../Algorithms/GitObjectLayoutTests.swift     | 45 +++++++++++++++++
 3 files changed, 96 insertions(+), 1 deletion(-)
 create mode 100644 Sources/DesignAlgorithmsKit/Algorithms/Storage/GitObjectLayout.swift
 create mode 100644 Tests/DesignAlgorithmsKitTests/Algorithms/GitObjectLayoutTests.swift

diff --git a/Sources/DesignAlgorithmsKit/Algorithms/Hashing/HashAlgorithmProtocol.swift b/Sources/DesignAlgorithmsKit/Algorithms/Hashing/HashAlgorithmProtocol.swift
index e91846e..6b90b63 100644
--- a/Sources/DesignAlgorithmsKit/Algorithms/Hashing/HashAlgorithmProtocol.swift
+++ b/Sources/DesignAlgorithmsKit/Algorithms/Hashing/HashAlgorithmProtocol.swift
@@ -33,7 +33,7 @@ public extension HashAlgorithmProtocol {
     /// - Returns: Hash value as Data, or empty Data if UTF-8 conversion fails
     /// - Note: UTF-8 conversion failure returns empty Data, which will hash to a valid hash value.
     ///   This path is testable by creating strings that fail UTF-8 conversion (rare but possible).
-    public static func hash(string: String) -> Data {
+    static func hash(string: String) -> Data {
         guard let data = string.data(using: .utf8) else {
             // UTF-8 conversion failed - return hash of empty data
             // This is a valid fallback that ensures we always return a hash
diff --git a/Sources/DesignAlgorithmsKit/Algorithms/Storage/GitObjectLayout.swift b/Sources/DesignAlgorithmsKit/Algorithms/Storage/GitObjectLayout.swift
new file mode 100644
index 0000000..9f1f6e5
--- /dev/null
+++ b/Sources/DesignAlgorithmsKit/Algorithms/Storage/GitObjectLayout.swift
@@ -0,0 +1,50 @@
+//
+//  GitObjectLayout.swift
+//  DesignAlgorithmsKit
+//
+//  Created for DesignAlgorithmsKit
+//
+
+import Foundation
+
+/// Git-Style Directory Layout Strategy
+///
+/// Implements the directory layout strategy used by Git for loose objects,
+/// where a content hash is split into a directory (prefix) and filename (remainder).
+///
+/// Example:
+/// Hash: "a1b2c3d4..."
+/// Directory: "a1"
+/// Filename: "b2c3d4..."
+/// Path: "a1/b2c3d4..."
+public struct GitObjectLayout {
+    
+    /// The length of the prefix used for the directory name
+    public static let prefixLength = 2
+    
+    /// Generates the layout components for a given hash.
+    /// - Parameter hash: The hex string representation of the hash.
+    /// - Returns: A tuple containing the directory, filename, and combined relative path.
+    ///            If the hash is too short (<= prefixLength), returns empty directory and the hash as filename.
+    public static func layout(for hash: String) -> (directory: String, filename: String, path: String) {
+        guard hash.count > Self.prefixLength else {
+            return (directory: "", filename: hash, path: hash)
+        }
+        
+        let prefixIndex = hash.index(hash.startIndex, offsetBy: Self.prefixLength)
+        let prefix = String(hash[..<prefixIndex])
+        let suffix = String(hash[prefixIndex...])
+        
+        // Ensure path separator is handled by caller or returned as standard relative path
+        let path = "\(prefix)/\(suffix)"
+        
+        return (directory: prefix, filename: suffix, path: path)
+    }
+    
+    /// Generates the relative path for a given hash.
+    /// - Parameter hash: The hex string representation of the hash.
+    /// - Returns: The relative path string (e.g., "ab/cdef...").
+    public static func path(for hash: String) -> String {
+        return layout(for: hash).path
+    }
+}
diff --git a/Tests/DesignAlgorithmsKitTests/Algorithms/GitObjectLayoutTests.swift b/Tests/DesignAlgorithmsKitTests/Algorithms/GitObjectLayoutTests.swift
new file mode 100644
index 0000000..45499f7
--- /dev/null
+++ b/Tests/DesignAlgorithmsKitTests/Algorithms/GitObjectLayoutTests.swift
@@ -0,0 +1,45 @@
+import XCTest
+@testable import DesignAlgorithmsKit
+
+final class GitObjectLayoutTests: XCTestCase {
+    
+    func testLayoutGeneration() {
+        let hash = "a1b2c3d4e5f6"
+        let layout = GitObjectLayout.layout(for: hash)
+        
+        XCTAssertEqual(layout.directory, "a1")
+        XCTAssertEqual(layout.filename, "b2c3d4e5f6")
+        XCTAssertEqual(layout.path, "a1/b2c3d4e5f6")
+    }
+    
+    func testShortHash() {
+        let hash = "ab"
+        let layout = GitObjectLayout.layout(for: hash)
+        
+        // Expect behavior for short hashes (implementation specific: no split)
+        XCTAssertEqual(layout.path, "ab")
+        XCTAssertEqual(layout.directory, "")
+        XCTAssertEqual(layout.filename, "ab")
+        
+        let hash2 = "a"
+        let layout2 = GitObjectLayout.layout(for: hash2)
+        XCTAssertEqual(layout2.path, "a")
+        XCTAssertEqual(layout2.directory, "")
+        XCTAssertEqual(layout2.filename, "a")
+    }
+    
+    func testPathHelper() {
+        let hash = "1234567890"
+        XCTAssertEqual(GitObjectLayout.path(for: hash), "12/34567890")
+    }
+    
+    func testStandardGitHash() {
+        // Example SHA-1 hash
+        let hash = "5e80dc522e0327ba4944d180bbf261904e545805"
+        let layout = GitObjectLayout.layout(for: hash)
+        
+        XCTAssertEqual(layout.directory, "5e")
+        XCTAssertEqual(layout.filename, "80dc522e0327ba4944d180bbf261904e545805")
+        XCTAssertEqual(layout.path, "5e/80dc522e0327ba4944d180bbf261904e545805")
+    }
+}