BSONOIDGenerator.m

//
//  BSONOIDGenerator.m
//  ContentstackPersistence
//
//  Created by Vikram Kalta on 13/02/2024.
//  Copyright © 2024 Contentstack. All rights reserved.
//

#import <Foundation/Foundation.h>
#import <CommonCrypto/CommonDigest.h>
#import "BSONOIDGenerator.h"
#import <UIKit/UIKit.h>

@implementation BSONOIDGenerator
static int _incr = 0;

+ (NSString *) generate:(NSInteger)timestamp {
    int i = _incr++;
    bson_oid_t *oid = malloc(sizeof(bson_oid_t));
    time_t t = time(NULL);

    // Grab the PID
    int pid = [NSProcessInfo processInfo].processIdentifier;

    // Get a device identifier. The specification usually has this as the MAC address
    // or hostname but we already have a unique device identifier.
    //
    NSString *identifier = [[[UIDevice currentDevice] identifierForVendor] UUIDString];

    // MD5 hash the device identifier
    NSString *md5HashOfIdentifier = [self md5HashFromString:identifier];
    const char *cIdentifier = [md5HashOfIdentifier cStringUsingEncoding:NSUTF8StringEncoding];

    // Copy bytes over to our object id. Specification taken from http://www.mongodb.org/display/DOCS/Object+IDs
    bson_swap_endian_len(&oid->bytes[0], &timestamp, 4);
    bson_swap_endian_len(&oid->bytes[4], &cIdentifier, 3);
    bson_swap_endian_len(&oid->bytes[7], &pid, 2);
    bson_swap_endian_len(&oid->bytes[9], &i, 3);
    NSString *str = [self bson_oid_to_string:oid];
    
    free(oid);

    return str;
}

/**
 @discussion Given an NSString, returns the MD5 hash of it. Taken from
 http://stackoverflow.com/questions/1524604/md5-algorithm-in-objective-c
 @param source The source string
 @return MD5 hash as a string
 */
+ (NSString *) md5HashFromString:(NSString *)source {
    const char *cStr = [source UTF8String];
    unsigned char result[16];
    CC_MD5(cStr, strlen(cStr), result);
    return [NSString stringWithFormat:
                @"%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x",
            result[0], result[1], result[2], result[3],
            result[4], result[5], result[6], result[7],
            result[8], result[9], result[10], result[11],
            result[12], result[13], result[14], result[15]
    ];
}

/**
 @discussion Converts a bson_oid_t to an NSString. Mostly taken from https://github.com/mongodb/mongo-c-driver/blob/master/src/bson.c
 @param oid The bson_oid_t to convert
 @return Autoreleased NSString of 24 hex characters
 */
+ (NSString *) bson_oid_to_string:(bson_oid_t *)oid {
    char *str = malloc(sizeof(char) * 25);
    static const char hex[16] = {'0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f'};
    int i;
    for ( i=0; i<12; i++ ) {
        str[2*i]     = hex[( oid->bytes[i] & 0xf0 ) >> 4];
        str[2*i + 1] = hex[ oid->bytes[i] & 0x0f      ];
    }
    str[24] = '\0';
    NSString *string = [NSString stringWithCString:str encoding:NSUTF8StringEncoding];
    free(str);
    return string;
}


/**
 @discussion The ARM architecture is little endian while intel macs are big Endian, so we need to swap endianness if we're compiling on a big Endian architecture.
 @param outp The destination pointer
 @param inp The source pointer
 @param len The length to copy
 */
void bson_swap_endian_len(void *outp, const void *inp, int len) {
    const char *in = (const char *)inp;
    char *out = (char *)outp;
    for (int i = 0; i < len; i ++) {
        #if __DARWIN_BIG_ENDIAN
        out[i] = in[len - 1 - i];
        #elif __DARWIN_LITTLE_ENDIAN
        out[i] = in[i];
        #endif
    }
}

@end