LicenseHandler: Validate license files

Fill in the `check` method to have it validate a license file. If the
file doesn't validate, prints an error message.

A bunch of supporting methods to check if the license file at the
program's prescribed path exists.

Use AquaticPrime's CoreFoundation functions to validate the license
file. Include my public key, generated by the "AquaticPrime Developer"
app, with the CFStringAppend calls copied from the program's generated
"Obfuscated Public Key" text box.

Run the validation check on launch in `main.m`.

Add an `eprintf` macro to print to stderr with a prepended program
identifier.

4 files changed, 87 insertions, 2 deletions

diff --git a/DomeKey/LicenseHandler.h b/DomeKey/LicenseHandler.h
index 6634f28..fb3ab51 100644
--- a/DomeKey/LicenseHandler.h
+++ b/DomeKey/LicenseHandler.h
@@ -8,6 +8,10 @@
 
 #import <Foundation/Foundation.h>
 
+#import "AquaticPrime.h"
+#import "XDG.h"
+#import "errors.h"
+
 @interface LicenseHandler : NSObject
 
 + (void)check;
diff --git a/DomeKey/LicenseHandler.m b/DomeKey/LicenseHandler.m
index b875842..52c5bcf 100644
--- a/DomeKey/LicenseHandler.m
+++ b/DomeKey/LicenseHandler.m
@@ -8,20 +8,93 @@
 
 #import "LicenseHandler.h"
 
+static NSString * const LICENSE_FILE_NAME = @"license.plist";
+
 @implementation LicenseHandler
 
 + (void)check
 {
-    if (/* license file exists */) {
-        // validate license
+    if ([self licenseFileExists]) {
+        if (![self validateLicense]) {
+            eprintf(
+                "The license file '%s' is invalid. "
+                "Try adding your license again using the `--license` flag.\n",
+                [[[self licensePath] path] UTF8String]
+            );
+
+            // TODO: then do trial
+        }
     }
     else {
         // run do_trial();
+        printf("TODO: do trial\n");
     }
 }
 
 + (void)addLicense
 {
+    // Copy license file into path
+    // Validate license
+    // If license doesn't validate, remove copied file
+    // If license does validate, print a success message
+}
+
++ (NSURL *)licensePath
+{
+    return [[XDG domeKeyDataPath]
+        URLByAppendingPathComponent:LICENSE_FILE_NAME
+        isDirectory:NO];
+}
+
++ (BOOL)licenseFileExists
+{
+    NSURL *path = [self licensePath];
+
+    return [[NSFileManager defaultManager]
+        fileExistsAtPath:[path path]];
+}
+
++ (BOOL)validateLicense
+{
+    NSURL *path = [self licensePath];
+    CFURLRef cf_path = CFBridgingRetain(path);
+
+    CFMutableStringRef key = CFStringCreateMutable(NULL, 0);
+    CFStringAppend(key, CFSTR("0xD536F17DA75620927B"));
+    CFStringAppend(key, CFSTR("D"));
+    CFStringAppend(key, CFSTR("D"));
+    CFStringAppend(key, CFSTR("029DDFF1"));
+    CFStringAppend(key, CFSTR("E"));
+    CFStringAppend(key, CFSTR("3"));
+    CFStringAppend(key, CFSTR("3"));
+    CFStringAppend(key, CFSTR("F620B3AFEE024F3A8FC724BF93A"));
+    CFStringAppend(key, CFSTR("906AF20712D39EB5C931BF63068612"));
+    CFStringAppend(key, CFSTR("B0741791485D470745E7C71DC8287A"));
+    CFStringAppend(key, CFSTR(""));
+    CFStringAppend(key, CFSTR("1"));
+    CFStringAppend(key, CFSTR("1"));
+    CFStringAppend(key, CFSTR("9517FC3C60CC3FBF6DA13A0A2F0C"));
+    CFStringAppend(key, CFSTR(""));
+    CFStringAppend(key, CFSTR("D"));
+    CFStringAppend(key, CFSTR("D"));
+    CFStringAppend(key, CFSTR("5F14977DEEB6E32C3B039AADCD3D"));
+    CFStringAppend(key, CFSTR("0C97BD94FC4E0714C2F"));
+    CFStringAppend(key, CFSTR("8"));
+    CFStringAppend(key, CFSTR("8"));
+    CFStringAppend(key, CFSTR("B010622D2"));
+    CFStringAppend(key, CFSTR("36FB7"));
+    CFStringAppend(key, CFSTR("5"));
+    CFStringAppend(key, CFSTR("5"));
+    CFStringAppend(key, CFSTR("9AEF648830DA73C584DE402"));
+    CFStringAppend(key, CFSTR("4AFD071F4F4E90021B"));
+
+    // TODO: returns false on failure
+    APSetKey(key);
+    BOOL validated = APVerifyLicenseFile(cf_path);
+
+    CFRelease(cf_path);
+
+    return validated;
 }
 
 @end
diff --git a/DomeKey/errors.h b/DomeKey/errors.h
new file mode 100644
index 0000000..d1a97ce
--- /dev/null
+++ b/DomeKey/errors.h
@@ -0,0 +1,5 @@
+#define eprintf(...) fprintf( \
+    stderr, \
+    "dome-key: error: " \
+    __VA_ARGS__ \
+)
diff --git a/DomeKey/main.m b/DomeKey/main.m
index 8a9011c..2263bac 100644
--- a/DomeKey/main.m
+++ b/DomeKey/main.m
@@ -9,6 +9,7 @@
 #import <Foundation/Foundation.h>
 #import "DKApplication.h"
 #import "AppDelegate.h"
+#import "LicenseHandler.h"
 #import "Mappings.h"
 #import "dome_key_map.h"
 
@@ -22,6 +23,8 @@ int main(int argc, const char * argv[]) {
 
     config = c_parse_args(argv, argc, config);
 
+    [LicenseHandler check];
+
     if (config->args.reload) {
         return [Mappings dispatchReload];
     } else if (config->args.daemon) {