Skip installing certificates when they already exist

Fixes #1

Sources/XcodeSimulatorKit/Commands/InstallCACommand.swift

@@ -47,16 +47,34 @@ class InstallCACommand: Command {
     func run() throws {
         let url = URL(fileURLWithPath: options.path!)
         let certificate = try Certificate.load(from: url)
+        let sha1 = certificate.sha1
+
         let certificateName = certificate.subjectSummary ?? "<unknown certificate>"
 
         for device in try Simctl.flatListDevices().filter(using: filteringOptions) {
+            let trustStore = TrustStore(uuid: device.udid)
+            if !trustStore.exists && options.dryRun {
+                print("Would install '\(certificateName)' into '\(device.name)'.")
+                continue
+            }
+
+            let connection = try trustStore.open()
+            if try connection.hasCertificate(with: sha1) {
+                if options.dryRun {
+                    print("Would skip installing '\(certificateName)' into '\(device.name)' – it's already there.")
+                } else {
+                    print("Not installing '\(certificateName)' into '\(device.name)' – it's already there.")
+                }
+                continue
+            }
+
             if options.dryRun {
-                print("Would install \(certificateName) into \(device.name).")
+                print("Would install '\(certificateName)' into '\(device.name)'.")
             } else {
-                print("Installing \(certificateName) into \(device.name).")
-                let trustStore = TrustStore(uuid: device.udid)
+                print("Installing '\(certificateName)' into '\(device.name)'.")
                 try trustStore.open().addCertificate(certificate)
             }
         }
     }
+
 }

Sources/XcodeSimulatorKit/Trust Store/Certificate.swift

@@ -41,6 +41,10 @@ struct Certificate {
         return SecCertificateCopySubjectSummary(certificate) as String?
     }
 
+    var sha1: Data {
+        return Digest.sha1(data)
+    }
+    
     func normalizedSubjectSequence() throws -> Data {
         var error: Unmanaged<CFError>?
         guard let data = SecCertificateCopyNormalizedSubjectContent(certificate, &error) else {

Sources/XcodeSimulatorKit/Trust Store/TrustStore.swift

@@ -85,5 +85,9 @@ struct TrustStore {
             )
             try connection.run(insert)
         }
+
+        func hasCertificate(with sha1: Data) throws -> Bool {
+            return try connection.pluck(tsettings.where(sha1Column == sha1.datatypeValue)) != nil
+        }
     }
 }