# `uuid`

This library implements a Universally Unique Identifier (UUID) generator. Currently version 1, version 3, version 4, version 5, and version 7 UUIDs are supported. Version 5 support requires a Prolog backend with support for unbounded integer arithmetic. For reference material, see e.g.

https://en.wikipedia.org/wiki/Universally_unique_identifier

Some backends provide time stamps with low granularity (e.g., seconds but not milliseconds or nanoseconds). To compensate, the generation of version 1 UUIDs uses 14 random bits for the clock sequence.

Some backends only provide access to local time. On those backends, the `uuid_v1/2` and `uuid_v7/1` predicates preserve the backend behavior and use the available local time fields when computing the UUID timestamp. To compute UUID timestamps using UTC instead, use the `uuid_v1/3` and `uuid_v7/2` predicates and pass the current local UTC offset as `Z`, `+HH:MM`, or `-HH:MM`.

The generation of version 4 and version 7 UUIDs uses the `/dev/urandom` random number generator when available. This includes macOS, Linux, *BSD, and other POSIX operating-systems. On Windows, a pseudo-random generator is used, but randomized using the current wall time.

Version 3 and version 5 UUIDs are namespace-name based UUIDs using the MD5 and SHA-1 hash functions, respectively.

Version 7 UUIDs are time-ordered using a Unix Epoch timestamp in milliseconds, as specified in RFC 9562. They are recommended over version 1 UUIDs for new applications due to improved entropy and sortability characteristics.

UUIDs can be generated as atoms, lists of characters, or lists of character codes.

See also the `cuid2`, `ksuid`, `ids`, `nanoid`, `snowflakeid`, and `ulid` libraries.

## API documentation

Open the ../../apis/library_index.html#uuid link in a web browser.

## Loading

To load all entities in this library, load the `loader.lgt` file:

    | ?- logtalk_load(uuid(loader)).

## Testing

To test this library predicates, load the `tester.lgt` file:

    | ?- logtalk_load(uuid(tester)).

## Generating version 1 UUIDs

By default, version 1 UUIDs are generated as atoms. For example:

    | ?- uuid::uuid_v1([0xf2,0xd1,0x90,0x94,0xdc,0x4b], UUID).
    UUID = '00a66fc0-82cf-11eb-bc83-f2d19094dc4b'
    yes

To generate a UUID using a list of characters representation, use instead the `uuid/1` parametric object:

    | ?- uuid(chars)::uuid_v1([0xf2,0xd1,0x90,0x94,0xdc,0x4b], UUID).
    UUID = ['0','0',d,e,'9','0',c,'0',-,'8','2',c,f,-,'1','1',e,b,-,
            a,'9','8','5',-,f,'2',d,'1','9','0','9','4',d,c,'4',b]
    yes

Similarly, to get a UUID using a list of character codes representation:

    | ?- uuid(codes)::uuid_v1([0xf2,0xd1,0x90,0x94,0xdc,0x4b], UUID).
    UUID = [48,48,52,99,99,54,99,48,45,56,50,99,102,45,49,49,101,98,45,
            98,57,102,52,45,102,50,100,49,57,48,57,52,100,99,52,98]
    yes

When the backend only provides access to local time, use `uuid_v1/3` with the current local UTC offset to compute the UUID timestamp using UTC:

    | ?- uuid::uuid_v1([0xf2,0xd1,0x90,0x94,0xdc,0x4b], '+01:00', UUID).
    UUID = '00a66fc0-82cf-11eb-bc83-f2d19094dc4b'
    yes

## Generating version 4 UUIDs

By default, version 4 UUIDs are generated as atoms. For example:

    | ?- uuid::uuid_v4(UUID).
    UUID = '1c652782-69c5-4252-88c8-09e576a44db5'
    yes

To generate a UUID using a list of characters representation, use instead the `uuid/1` parametric object:

    | ?- uuid(chars)::uuid_v4(UUID).
    UUID = [d,'3',d,'3','3','5','1','3',-,'8','1',e,c,-,'4',d,'2','6',-,
            '9',f,'2','2',-,e,d,'9','5',e,'0','0',e,'1','5','7','0']
    yes

Similar to get a UUID using a list of character codes representation:

    | ?- uuid(codes)::uuid_v4(UUID).
    UUID = [102,97,52,54,57,98,100,50,45,51,57,54,51,45,52,97,100,55,45,
            98,50,50,55,45,101,100,52,99,56,55,99,54,53,55,102,98]
    yes

## Generating version 3 UUIDs

Version 3 UUIDs are namespace-name based UUIDs using the MD5 hash function. For example:

    | ?- uuid::uuid_v3('6ba7b810-9dad-11d1-80b4-00c04fd430c8', 'www.widgets.com', UUID).
    UUID = '3d813cbb-47fb-32ba-91df-831e1593ac29'
    yes

To generate a UUID using a list of characters representation, use instead the `uuid/1` parametric object:

    | ?- uuid(chars)::uuid_v3('6ba7b810-9dad-11d1-80b4-00c04fd430c8', 'www.widgets.com', UUID).
    UUID = ['3',d,'8','1','3',c,b,b,-,'4','7',f,b,-,'3','2',b,a,-,
            '9','1',d,f,-,'8','3','1',e,'1','5','9','3',a,c,'2','9']
    yes

Similarly, to get a UUID using a list of character codes representation:

    | ?- uuid(codes)::uuid_v3('6ba7b810-9dad-11d1-80b4-00c04fd430c8', 'www.widgets.com', UUID).
    UUID = [51,100,56,49,51,99,98,98,45,52,55,102,98,45,51,50,98,97,45,
            57,49,100,102,45,56,51,49,101,49,53,57,51,97,99,50,57]
    yes

## Generating version 5 UUIDs

Version 5 UUIDs are namespace-name based UUIDs using the SHA-1 hash function. This predicate is only available on Prolog backends with support for unbounded integer arithmetic. For example:

    | ?- uuid::uuid_v5('6ba7b810-9dad-11d1-80b4-00c04fd430c8', 'www.widgets.com', UUID).
    UUID = '21f7f8de-8051-5b89-8680-0195ef798b6a'
    yes

To generate a UUID using a list of characters representation, use instead the `uuid/1` parametric object:

    | ?- uuid(chars)::uuid_v5('6ba7b810-9dad-11d1-80b4-00c04fd430c8', 'www.widgets.com', UUID).
    UUID = ['2','1',f,'7',f,'8',d,e,-,'8','0','5','1',-,'5',b,'8','9',-,
            '8','6','8','0',-,'0','1','9','5',e,f,'7','9','8',b,'6',a]
    yes

Similarly, to get a UUID using a list of character codes representation:

    | ?- uuid(codes)::uuid_v5('6ba7b810-9dad-11d1-80b4-00c04fd430c8', 'www.widgets.com', UUID).
    UUID = [50,49,102,55,102,56,100,101,45,56,48,53,49,45,53,98,56,57,45,
            56,54,56,48,45,48,49,57,53,101,102,55,57,56,98,54,97]
    yes

## Generating version 7 UUIDs

Version 7 UUIDs are time-ordered using the Unix Epoch timestamp in milliseconds (as specified in RFC 9562). By default, version 7 UUIDs are generated as atoms. For example:

    | ?- uuid::uuid_v7(UUID).
    UUID = '018d5f3c-9b5a-7c4e-8f2a-1b3c4d5e6f70'
    yes

To generate a UUID using a list of characters representation, use instead the `uuid/1` parametric object:

    | ?- uuid(chars)::uuid_v7(UUID).
    UUID = ['0','1','8',d,'5',f,'3',c,-,'9',b,'5',a,-,'7',c,'4',e,-,
            '8',f,'2',a,-,'1',b,'3',c,'4',d,'5',e,'6',f,'7','0']
    yes

Similar to get a UUID using a list of character codes representation:

    | ?- uuid(codes)::uuid_v7(UUID).
    UUID = [48,49,56,100,53,102,51,99,45,57,98,53,97,45,55,99,52,101,45,
            56,102,50,97,45,49,98,51,99,52,100,53,101,54,102,55,48]
    yes

When the backend only provides access to local time, use `uuid_v7/2` with the current local UTC offset to compute the UUID timestamp using UTC:

    | ?- uuid::uuid_v7('+01:00', UUID).
    UUID = '018d5f3c-9b5a-7c4e-8f2a-1b3c4d5e6f70'
    yes

## Generating the Nil and Max UUIDs

Predicates are also provided that return the Nil and Max UUIDs:

    | ?- uuid::uuid_nil(UUID).
    UUID = '00000000-0000-0000-0000-000000000000'
    yes

    | ?- uuid::uuid_max(UUID).
    UUID = 'FFFFFFFF-FFFF-FFFF-FFFF-FFFFFFFFFFFF'
    yes