PasteboardHelper - Load .eml files from Mail.app (macOS)

PasteboardHelper.h

//
//  PasteboardHelper.h
//  Spaceboard
//
//  Created by mmackh on 28.03.22.
//

#import <Foundation/Foundation.h>

@class PasteboardHelperPromiseResolveRequest;

@interface PasteboardHelper : NSObject

+ (void)submitRequest:(PasteboardHelperPromiseResolveRequest *_Nonnull)request;

+ (NSString *_Nonnull)identifierAppleMailPasteboardTypeAutomator;

@end

@interface PasteboardHelperPromiseResolveRequest : NSObject

+ (instancetype _Nonnull )requestWithTimeout:(NSTimeInterval)timeout identifier:(NSString * _Nullable)identifier estimatedFileCount:(NSInteger)estimatedFileCount completionHandler:(void(^_Nonnull)(NSArray<NSURL*>* _Nonnull fileURLs))completionHandler;

+ (NSInteger)currentlyEstimatedFileCount;

@end

PasteboardHelper.m

//
//  PasteboardHelper.m
//  Spaceboard
//
//  Created by mmackh on 28.03.22.
//

#import "PasteboardHelper.h"

@import AppKit;

@interface PasteboardHelper ()

+ (instancetype)sharedHelper;

@property (nonatomic) NSMutableArray *queue;
@property (nonatomic) dispatch_queue_t dispatchQueue;

@end

@interface PasteboardHelperPromiseResolveRequest ()

@property (nonatomic) NSTimer *timeoutTimer;
@property (nonatomic) NSTimeInterval timeout;
@property (nonatomic) NSString *identifier;
@property (nonatomic) NSInteger fileCount;
@property (nonatomic, copy) void(^completionHandler)(NSArray *fileURLs);

@property (nonatomic) NSURL *directoryURL;

@property (nonatomic) int const fileDescriptor;
@property (nonatomic) dispatch_source_t source;
@property (nonatomic) PasteboardRef pasteboard;

- (NSURL *)directoryURL;

- (void)invalidateDirectoryWatcher;
- (void)startDirectoryWatcher;

@end

@implementation PasteboardHelper

+ (instancetype)sharedHelper {
    static PasteboardHelper *sharedHelper = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedHelper = [[PasteboardHelper alloc] init];
    });
    return sharedHelper;
}

- (instancetype)init {
    self = [super init];
    if (!self) return nil;
    
    self.queue = [NSMutableArray new];
    self.dispatchQueue = dispatch_queue_create("com.pasteboardhelper.queue", DISPATCH_QUEUE_SERIAL);
    
    return self;
}

+ (void)submitRequest:(PasteboardHelperPromiseResolveRequest *)request {
    PasteboardHelper *sharedHelper = [PasteboardHelper sharedHelper];
    [sharedHelper.queue addObject:request];
    
    request.timeoutTimer = [NSTimer scheduledTimerWithTimeInterval:request.timeout target:self selector:@selector(timeoutRequest:) userInfo:request.identifier repeats:NO];
    
    NSString *requestIdentifier = request.identifier;
    dispatch_async(sharedHelper.dispatchQueue, ^{
        NSURL *directoryURL = request.directoryURL;
        
        NSPasteboard *dragPasteboard = [NSPasteboard pasteboardWithName:NSPasteboardNameDrag];
        PasteboardRef pbref = NULL;
        OSStatus state = PasteboardCreate((CFStringRef)dragPasteboard.name, &pbref);
        if (!pbref || state != noErr) {
            [PasteboardHelper processRequestWithIdentifier:requestIdentifier];
            return;
        }
        request.pasteboard = pbref;
        
        [request startDirectoryWatcher];
        
        dispatch_async(dispatch_get_main_queue(), ^{
            PasteboardSynchronize(pbref);
            PasteboardSetPasteLocation(pbref, (CFURLRef)directoryURL);
            
            NSString *targetPath = [dragPasteboard propertyListForType:(NSString *)kPasteboardTypeFileURLPromise];
            
            // macOS 12 workaround, doesn't respect PasteboardSetPasteLocation for one Email being dragged and dropped
            if (targetPath && ![targetPath isEqualToString:directoryURL.path]) {
                request.directoryURL = [NSURL fileURLWithPath:targetPath];
                [request startDirectoryWatcher];
            }
        });
    });
}

+ (void)timeoutRequest:(NSTimer *)timer {
    [self processRequestWithIdentifier:timer.userInfo];
}

+ (void)processRequestWithIdentifier:(NSString *)identifier {
    PasteboardHelper *sharedHelper = [PasteboardHelper sharedHelper];
    PasteboardHelperPromiseResolveRequest *currentRequest = nil;
    for (PasteboardHelperPromiseResolveRequest *request in sharedHelper.queue) {
        if ([identifier isEqualToString:request.identifier]) {
            currentRequest = request;
            break;
        }
    }
    
    NSError *error = nil;
    NSArray *fileURLs = [[NSFileManager defaultManager] contentsOfDirectoryAtURL:currentRequest.directoryURL includingPropertiesForKeys:nil options:0 error:&error];
    dispatch_async(dispatch_get_main_queue(), ^{
        if (error) {
            currentRequest.completionHandler(@[]);
        } else {
            currentRequest.completionHandler(fileURLs);
        }
    });
    
    [currentRequest invalidateDirectoryWatcher];
    
    if (currentRequest.pasteboard) {
        CFRelease(currentRequest.pasteboard);
        currentRequest.pasteboard = NULL;
    }
    
    [currentRequest.timeoutTimer invalidate];
    currentRequest.timeoutTimer = nil;
    
    [sharedHelper.queue removeObject:currentRequest];
}

+ (NSString *)identifierAppleMailPasteboardTypeAutomator {
    return @"com.apple.mail.PasteboardTypeAutomator";
}

@end

@implementation PasteboardHelperPromiseResolveRequest

+ (instancetype _Nonnull )requestWithTimeout:(NSTimeInterval)timeout identifier:(NSString * _Nullable)identifier estimatedFileCount:(NSInteger)estimatedFileCount completionHandler:(void(^_Nonnull)(NSArray<NSURL*>* _Nonnull fileURLs))completionHandler {
    PasteboardHelperPromiseResolveRequest *request = [PasteboardHelperPromiseResolveRequest new];
    request.timeout = timeout;
    request.identifier = identifier ?: @"pasteboard";
    request.fileCount = !estimatedFileCount ? 1 : estimatedFileCount;
    request.completionHandler = completionHandler;
    
    NSString *path = [NSTemporaryDirectory() stringByAppendingPathComponent:request.identifier];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    if ([fileManager fileExistsAtPath:path]) {
        [fileManager removeItemAtPath:path error:nil];
    }
    [fileManager createDirectoryAtPath:path withIntermediateDirectories:YES attributes:nil error:nil];
    request.directoryURL = [NSURL fileURLWithPath:[NSTemporaryDirectory() stringByAppendingPathComponent:request.identifier]];
    
    return request;
}

+ (NSInteger)currentlyEstimatedFileCount {
    NSPasteboard *dragPasteboard = [NSPasteboard pasteboardWithName:NSPasteboardNameDrag];
    if ([dragPasteboard canReadItemWithDataConformingToTypes:@[[PasteboardHelper identifierAppleMailPasteboardTypeAutomator]]]) {
        id plist = [dragPasteboard propertyListForType:[PasteboardHelper identifierAppleMailPasteboardTypeAutomator]];
        if ([plist isKindOfClass:[NSArray class]]) {
            return [plist count];
        }
    }
    return dragPasteboard.pasteboardItems.count;
}

- (void)invalidateDirectoryWatcher {
    if (self.source) {
        dispatch_source_cancel(self.source);
        self.source = NULL;
    }
    if (self.fileDescriptor > 0) {
        close(self.fileDescriptor);
    }
}

- (void)startDirectoryWatcher {
    [self invalidateDirectoryWatcher];
    
    NSString *requestIdentifier = self.identifier;
    __block NSInteger fileCount = self.fileCount;
    
    // check if file location already contains the number of items for request, return success immediatly
    if ([[NSFileManager defaultManager] contentsOfDirectoryAtPath:self.directoryURL.path error:nil].count == fileCount) {
        [PasteboardHelper processRequestWithIdentifier:requestIdentifier];
        return;
    }
    
    int const fileDescriptor = open(self.directoryURL.path.fileSystemRepresentation, O_EVTONLY);
    if (fileDescriptor < 0) {
        [PasteboardHelper processRequestWithIdentifier:requestIdentifier];
        return;
    }
    self.fileDescriptor = fileDescriptor;
    
    dispatch_source_t source = dispatch_source_create(DISPATCH_SOURCE_TYPE_VNODE, fileDescriptor, DISPATCH_VNODE_WRITE | DISPATCH_VNODE_DELETE, PasteboardHelper.sharedHelper.dispatchQueue);
    self.source = source;
    
    dispatch_source_set_event_handler(source, ^() {
        unsigned long const data = dispatch_source_get_data(source);
        if (data & DISPATCH_VNODE_WRITE) {
            fileCount -= 1;
            
            if (fileCount > 0) return;
            
            [PasteboardHelper processRequestWithIdentifier:requestIdentifier];
        }
    });
    dispatch_resume(source);
}

@end