Add DDI mount support and document usage requirements (#2)

Sources/DeveloperDiskImageService.swift

@@ -0,0 +1,90 @@
+import Foundation
+
+public struct DDIPaths: Sendable {
+
+    public var imagePath: String
+
+    public var trustcachePath: String
+
+    public var manifestPath: String
+
+    public init(imagePath: String, trustcachePath: String, manifestPath: String) {
+        self.imagePath = imagePath
+        self.trustcachePath = trustcachePath
+        self.manifestPath = manifestPath
+    }
+
+    public static func `default`(in directory: URL) -> DDIPaths {
+        DDIPaths(
+            imagePath: directory.appendingPathComponent("DDI/Image.dmg").path,
+            trustcachePath: directory.appendingPathComponent("DDI/Image.dmg.trustcache").path,
+            manifestPath: directory.appendingPathComponent("DDI/BuildManifest.plist").path)
+    }
+
+    var allFilesExist: Bool {
+        let fileManager = FileManager.default
+        return fileManager.fileExists(atPath: imagePath)
+            && fileManager.fileExists(atPath: trustcachePath)
+            && fileManager.fileExists(atPath: manifestPath)
+    }
+}
+
+public actor DeveloperDiskImageService {
+
+    public static let shared = DeveloperDiskImageService()
+
+    private let session: URLSession
+
+    public init(session: URLSession = .shared) {
+        self.session = session
+    }
+
+    private struct DownloadItem {
+        let name: String
+        let destinationPath: String
+        let urlString: String
+    }
+
+    private static let baseURL = "https://github.com/doronz88/DeveloperDiskImage/raw/refs/heads/main/PersonalizedImages/Xcode_iOS_DDI_Personalized"
+
+    public func downloadIfNeeded(to paths: DDIPaths, progress: @escaping (Double, String) -> Void = { _, _ in }) async throws {
+        guard !paths.allFilesExist else { return }
+        try await download(to: paths, progress: progress)
+    }
+
+    public func download(to paths: DDIPaths, progress: @escaping (Double, String) -> Void = { _, _ in }) async throws {
+        let items = [
+            DownloadItem(name: "BuildManifest.plist", destinationPath: paths.manifestPath, urlString: "\(Self.baseURL)/BuildManifest.plist"),
+            DownloadItem(name: "Image.dmg", destinationPath: paths.imagePath, urlString: "\(Self.baseURL)/Image.dmg"),
+            DownloadItem(name: "Image.dmg.trustcache", destinationPath: paths.trustcachePath, urlString: "\(Self.baseURL)/Image.dmg.trustcache"),
+        ]
+
+        let total = Double(items.count)
+        for (index, item) in items.enumerated() {
+            progress(Double(index) / total, "Downloading \(item.name)...")
+            try await downloadFile(from: item.urlString, to: URL(fileURLWithPath: item.destinationPath))
+            progress(Double(index + 1) / total, "\(item.name) ready")
+        }
+    }
+
+    private func downloadFile(from urlString: String, to destinationURL: URL) async throws {
+        guard let url = URL(string: urlString), url.scheme?.lowercased() == "https" else {
+            throw StikJITError.ddiDownload("invalid URL \(urlString)")
+        }
+
+        let (temporaryURL, response) = try await session.download(from: url)
+        guard let httpResponse = response as? HTTPURLResponse else {
+            throw StikJITError.ddiDownload("invalid response for \(urlString)")
+        }
+        guard (200..<300).contains(httpResponse.statusCode) else {
+            throw StikJITError.ddiDownload("HTTP \(httpResponse.statusCode) for \(urlString)")
+        }
+
+        let fileManager = FileManager.default
+        try fileManager.createDirectory(at: destinationURL.deletingLastPathComponent(), withIntermediateDirectories: true)
+        if fileManager.fileExists(atPath: destinationURL.path) {
+            try fileManager.removeItem(at: destinationURL)
+        }
+        try fileManager.moveItem(at: temporaryURL, to: destinationURL)
+    }
+}