NSAppleScript category to make calling AppleScript handlers (functions) easier

NSAppleScript+RunHandler.h

//
//  NSAppleScript+RunHandler.h
//  astest
//
//  Created by Rob Wells on 30/01/2014.
//  Copyright (c) 2014 Rob Wells. All rights reserved.
//

#ifndef kASAppleScriptSuite
#define kASAppleScriptSuite 'ascr'
#endif

#ifndef kASSubroutineEvent
#define kASSubroutineEvent 'psbr'
#endif

#ifndef keyASSubroutineName
#define keyASSubroutineName 'snam'
#endif

#import <Foundation/Foundation.h>

@interface NSAppleScript (RunHandler)

- (id)fetchObjectFromDescriptor:(NSAppleEventDescriptor *)descriptor;

- (NSAppleEventDescriptor *)makeParameters:(NSArray *)paramArray;
- (NSAppleEventDescriptor *)callHandler:(NSString *)handlerName
                         withParameters:(NSAppleEventDescriptor *)parameters;
- (id)getResultFromHandler:(NSString *)handlerName
            withParameters:(NSAppleEventDescriptor *)parameters;

@end

NSAppleScript+RunHandler.m

//
//  NSAppleScript+RunHandler.m
//  astest
//
//  Created by Rob Wells on 30/01/2014.
//  Copyright (c) 2014 Rob Wells. All rights reserved.
//

#import "NSAppleScript+RunHandler.h"

@implementation NSAppleScript (RunHandler)

- (NSAppleEventDescriptor *)makeParameters:(NSArray *)paramArray {
    
    // Create list of parameters
    NSAppleEventDescriptor *paramsDescriptor = [NSAppleEventDescriptor listDescriptor];
    
    // Loop through paramArray, turning the objects into descriptors
    int i;
    for (i = 0; i < paramArray.count; i++) {
        id parameter = paramArray[i];
        if ([parameter isKindOfClass:[NSAppleEventDescriptor class]]) {
            // Already a descriptor, add it as is
            [paramsDescriptor insertDescriptor:parameter atIndex:i + 1];
            
        } else if ([parameter isKindOfClass:[NSString class]]) {
            // Create a string descriptor
            [paramsDescriptor
             insertDescriptor:[NSAppleEventDescriptor
                               descriptorWithString:parameter]
             atIndex:i + 1];
            
        } else if ([parameter respondsToSelector:@selector(intValue)]) {
            // Create descriptor with number's int value
            [paramsDescriptor
             insertDescriptor:[NSAppleEventDescriptor
                               descriptorWithInt32:[parameter intValue]]
             atIndex:i + 1];
            
        } else if ([parameter isKindOfClass:[NSArray class]]) {
            // Create a list descriptor from an NSArray
            NSAppleEventDescriptor *arrayParam = [self makeParameters:parameter];
            [paramsDescriptor insertDescriptor:arrayParam
                                       atIndex:i + 1];
        } else {
            return nil;
        }
    }
    return paramsDescriptor;
}

- (NSAppleEventDescriptor *)callHandler:(NSString *)handlerName
                         withParameters:(NSAppleEventDescriptor *)parameters {
    
    // Create the AppleEvent target
    ProcessSerialNumber psn = {0, kCurrentProcess};
    NSAppleEventDescriptor *target = [NSAppleEventDescriptor
                                      descriptorWithDescriptorType:typeProcessSerialNumber
                                      bytes:&psn
                                      length:sizeof(ProcessSerialNumber)];
    
    // Create descriptor with handler to call
    // Routine name must be lowercase
    NSAppleEventDescriptor *handler = [NSAppleEventDescriptor
                                       descriptorWithString:[handlerName lowercaseString]];
    
    // Create the event for an AppleScript subroutine,
    // set the method name and the list of parameters
    NSAppleEventDescriptor *event = [NSAppleEventDescriptor
                                     appleEventWithEventClass:kASAppleScriptSuite
                                     eventID:kASSubroutineEvent
                                     targetDescriptor:target
                                     returnID:kAutoGenerateReturnID
                                     transactionID:kAnyTransactionID];
    
    [event setParamDescriptor:handler forKeyword:keyASSubroutineName];
    if (parameters) {
        [event setParamDescriptor:parameters forKeyword:keyDirectObject];
    }
    
    // Call the event in AppleScript
    NSDictionary *errorDict;
    NSAppleEventDescriptor *returnedDescriptor = [self executeAppleEvent:event
                                                                   error:&errorDict];
    if (!returnedDescriptor) {
        NSLog(@"%@: %@", handlerName, errorDict[NSAppleScriptErrorMessage]);
    }
    
    return returnedDescriptor;
}

- (id)getResultFromHandler:(NSString *)handlerName
            withParameters:(NSAppleEventDescriptor *)parameters {
    NSAppleEventDescriptor *rawResult = [self callHandler:handlerName
                                           withParameters:parameters];
    return [self fetchObjectFromDescriptor:rawResult];
}

- (id)fetchObjectFromDescriptor:(NSAppleEventDescriptor *)descriptor {
    NSString *returnType = NSFileTypeForHFSTypeCode([descriptor descriptorType]);

    if ([returnType isEqualToString:@"'utxt'"]) {
        // Returned data is a string
        return [descriptor stringValue];
    } else if ([returnType isEqualToString:@"'long'"]) {
        // Integer
        return [NSNumber numberWithInt:[descriptor int32Value]];
    } else if ([returnType isEqualToString:@"'doub'"]) {
        // Floating-point number
        CGFloat result;
        [[descriptor data] getBytes:&result length:[descriptor data].length];
        return [NSNumber numberWithFloat:result];
    } else if ([returnType isEqualToString:@"'list'"]) {
        // List (array) - note AppleScript is 1-based
        NSMutableArray *resultArray = [[NSMutableArray alloc] init];
        NSInteger i;
        for (i = 1; i <= [descriptor numberOfItems]; i++) {
            [resultArray addObject:
             [self fetchObjectFromDescriptor:[descriptor descriptorAtIndex:i]]];
        }
        return resultArray;
    } else if ([returnType isEqualToString:@"'reco'"]) {
        // Record (dictionary)
        // Stored as a list in the descriptor's internal array of returned
        // objects, in the form [key, value, key, value…]
        
        NSArray *recordAsArray = [self fetchObjectFromDescriptor:
                                  [descriptor descriptorAtIndex:1]];
        NSMutableDictionary *dict = [[NSMutableDictionary alloc] init];
        NSInteger i;
        for (i = 0; i < recordAsArray.count; i += 2) {
            [dict setObject:recordAsArray[i + 1] forKey:recordAsArray[i]];
        }
        return dict;
    }
    
    return [NSNull null];
}

@end