Got distracted while sorting photos and wrote a thing to help me find duplicate files.

dupe-detector.m

//
//  main.m
//  dupe-detector
//
//  Created by Jonathan Fischer on 1/1/14.
//  Copyright (c) 2014 Jonathan Fischer. All rights reserved.
//

#import <Foundation/Foundation.h>
#import <CommonCrypto/CommonDigest.h>
#import "FMDB/FMDatabase.h"

static void printUsage()
{
    printf("Usage: dupe-detector -db <database> -path <path>\n");
}

static void createTables(FMDatabase *db)
{
    [db executeUpdate:@"CREATE TABLE IF NOT EXISTS files (id INTEGER PRIMARY KEY AUTOINCREMENT, path STRING, hash_id INTEGER)"];
    [db executeUpdate:@"CREATE TABLE IF NOT EXISTS hashes (id INTEGER PRIMARY KEY AUTOINCREMENT, hash STRING, count INTEGER)"];
}

static NSUInteger insertHash(FMDatabase *db, NSString *hash)
{
    FMResultSet *results = [db executeQuery:@"SELECT id FROM hashes WHERE hash = ?", hash];
    if ([results next]) {
        return [results longForColumn:@"id"];
    } else {
        // New hash
        [db executeUpdate:@"INSERT INTO hashes VALUES (NULL, ?, 0)", hash];
        return db.lastInsertRowId;
    }
}

static void insertFile(FMDatabase *db, NSString *filePath, NSUInteger hashId)
{
    NSNumber *realHashId = [NSNumber numberWithInteger:hashId];
    FMResultSet *results = [db executeQuery:@"SELECT id, path FROM files WHERE path = ?", filePath];
    if ([results next]) {
        NSNumber *fileId = [NSNumber numberWithInteger:[results longForColumn:@"id"]];
        [db executeUpdate:@"UPDATE files SET hash_id = ? WHERE id = ?", realHashId, fileId];
    } else {
        [db executeUpdate:@"INSERT INTO files VALUES (NULL, ?, ?)", filePath, realHashId];
    }
}

static void updateHashes(FMDatabase *db)
{
    [db executeUpdate:@"UPDATE hashes SET count = (SELECT COUNT(hash_id) FROM files WHERE files.hash_id = hashes.id)"];
}

static NSString *HashStringForFile(NSURL *fileURL)
{
    NSData *data = [NSData dataWithContentsOfURL:fileURL];
    unsigned char outputData[CC_MD5_DIGEST_LENGTH];
    CC_MD5(data.bytes, (CC_LONG)data.length, outputData);

    NSMutableString *hashStr = [NSMutableString string];
    int i = 0;
    for (i = 0;i < CC_MD5_DIGEST_LENGTH; i++) {
        [hashStr appendFormat:@"%02x", outputData[i]];
    }

    return hashStr;
}

int main(int argc, const char * argv[])
{
    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    NSString *basePath = [defaults stringForKey:@"path"];
    if (basePath == nil) {
        printUsage();
        return 0;
    }

    NSString *databasePath = [defaults stringForKey:@"db"];
    if (databasePath == nil) {
        printUsage();
        return 0;
    }

    FMDatabase *database = [FMDatabase databaseWithPath:databasePath];
    if (databasePath == nil) {
        NSLog(@"Couldn't open database at path %@", databasePath);
        return 0;
    }
    [database open];

    createTables(database);

    NSLog(@"Base path is %@", basePath);

    NSFileManager *fileManager = [NSFileManager defaultManager];

    NSURL *baseUrl = [NSURL URLWithString:basePath];

    NSDirectoryEnumerator *enumerator = [fileManager enumeratorAtURL:baseUrl
                                          includingPropertiesForKeys:@[NSURLPathKey, NSURLIsDirectoryKey]
                                                             options:NSDirectoryEnumerationSkipsHiddenFiles
                                                        errorHandler:NULL];
    if (enumerator == nil) {
        NSLog(@"Unable to get a directory enumerator for path %@", basePath);
        return -1;
    }

    for (NSURL *fileURL in enumerator) {
        NSString *filePath;
        [fileURL getResourceValue:&filePath forKey:NSURLPathKey error:nil];
        NSString *hashString = HashStringForFile(fileURL);

        NSUInteger hashId = insertHash(database, hashString);
        insertFile(database, filePath, hashId);
    }

    updateHashes(database);

    return 0;
}