1 files changed, 118 insertions, 0 deletions
diff --git a/DomainDig/SubdomainDiscoveryService.swift b/DomainDig/SubdomainDiscoveryService.swift
new file mode 100644
index 0000000..57db25d
--- /dev/null
+++ b/DomainDig/SubdomainDiscoveryService.swift
@@ -0,0 +1,118 @@
+import Foundation
+
+enum SubdomainDiscoveryService {
+    static func discover(for domain: String, limit: Int = 25) async -> ServiceResult<[DiscoveredSubdomain]> {
+        let normalizedDomain = normalize(domain)
+        guard !normalizedDomain.isEmpty else {
+            return .empty("No passive subdomains found")
+        }
+
+        return await cache.subdomains(for: normalizedDomain, limit: limit)
+    }
+
+    private static let cache = SubdomainDiscoveryCache()
+
+    private static func normalize(_ domain: String) -> String {
+        domain
+            .trimmingCharacters(in: .whitespacesAndNewlines)
+            .lowercased()
+    }
+}
+
+private actor SubdomainDiscoveryCache {
+    private var cachedResults: [String: ServiceResult<[DiscoveredSubdomain]>] = [:]
+    private var inFlightTasks: [String: Task<ServiceResult<[DiscoveredSubdomain]>, Never>] = [:]
+    private var lastRequestAt: Date?
+
+    func subdomains(for domain: String, limit: Int) async -> ServiceResult<[DiscoveredSubdomain]> {
+        if let cachedResult = cachedResults[domain] {
+            return cachedResult
+        }
+
+        if let inFlightTask = inFlightTasks[domain] {
+            return await inFlightTask.value
+        }
+
+        let task = Task<ServiceResult<[DiscoveredSubdomain]>, Never> {
+            await enforceRateLimit()
+            return await fetchSubdomains(for: domain, limit: limit)
+        }
+        inFlightTasks[domain] = task
+
+        let result = await task.value
+        cachedResults[domain] = result
+        inFlightTasks[domain] = nil
+        return result
+    }
+
+    private func enforceRateLimit() async {
+        if let lastRequestAt {
+            let delay = max(0, 0.75 - Date().timeIntervalSince(lastRequestAt))
+            if delay > 0 {
+                try? await Task.sleep(for: .seconds(delay))
+            }
+        }
+        lastRequestAt = Date()
+    }
+
+    private func fetchSubdomains(for domain: String, limit: Int) async -> ServiceResult<[DiscoveredSubdomain]> {
+        var components = URLComponents(string: "https://crt.sh/")!
+        components.queryItems = [
+            URLQueryItem(name: "q", value: "%.\(domain)"),
+            URLQueryItem(name: "output", value: "json")
+        ]
+
+        guard let url = components.url else {
+            return .error("Subdomain discovery unavailable")
+        }
+
+        do {
+            let request = URLRequest(url: url, timeoutInterval: 10)
+            let (data, response) = try await URLSession.shared.data(for: request)
+            guard let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode == 200 else {
+                return .error("Subdomain discovery unavailable")
+            }
+
+            let entries = try JSONDecoder().decode([CRTShEntry].self, from: data)
+            let subdomains = parseSubdomains(from: entries, domain: domain, limit: limit)
+            return subdomains.isEmpty ? .empty("No passive subdomains found") : .success(subdomains)
+        } catch {
+            return .error(error.localizedDescription)
+        }
+    }
+
+    private func parseSubdomains(from entries: [CRTShEntry], domain: String, limit: Int) -> [DiscoveredSubdomain] {
+        var seen = Set<String>()
+        var results: [DiscoveredSubdomain] = []
+
+        for entry in entries {
+            let names = entry.nameValue
+                .split(separator: "\n")
+                .map { $0.trimmingCharacters(in: .whitespacesAndNewlines).lowercased() }
+
+            for name in names {
+                let sanitized = name.hasPrefix("*.") ? String(name.dropFirst(2)) : name
+                guard sanitized != domain, sanitized.hasSuffix(".\(domain)") else {
+                    continue
+                }
+                guard seen.insert(sanitized).inserted else {
+                    continue
+                }
+                results.append(DiscoveredSubdomain(hostname: sanitized))
+                if results.count == limit {
+                    return results
+                }
+            }
+        }
+
+        return results
+    }
+}
+
+private struct CRTShEntry: Decodable {
+    let nameValue: String
+
+    enum CodingKeys: String, CodingKey {
+        case nameValue = "name_value"
+    }
+}