________________________________________________________________________

This file is part of Logtalk <https://logtalk.org/>  
SPDX-FileCopyrightText: 1998-2026 Paulo Moura <pmoura@logtalk.org>  
SPDX-License-Identifier: Apache-2.0

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
________________________________________________________________________


`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](../../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
