1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
#![deny(
    future_incompatible,
    nonstandard_style,
    rust_2018_idioms,
    missing_docs,
    trivial_casts,
    trivial_numeric_casts,
    unused_qualifications
)]
#![cfg_attr(test, deny(warnings))]

//! Language tags can be used identify human languages, scripts e.g. Latin script, countries and
//! other regions.
//!
//! Language tags are defined in [BCP47](http://tools.ietf.org/html/bcp47), an introduction is
//! ["Language tags in HTML and XML"](http://www.w3.org/International/articles/language-tags/) by
//! the W3C. They are commonly used in HTML and HTTP `Content-Language` and `Accept-Language`
//! header fields.
//!
//! This package currently supports parsing (fully conformant parser), validation, canonicalization,
//! formatting and comparing language tags.
//!
//! # Examples
//! Create a simple language tag representing the French language as spoken
//! in Belgium and print it:
//!
//! ```rust
//! use language_tags::LanguageTag;
//!
//! let langtag = LanguageTag::parse("fr-BE").unwrap();
//! assert_eq!(langtag.to_string(), "fr-BE");
//! ```
//!
//! Parse a tag representing a special type of English specified by private agreement:
//!
//! ```rust
//! use language_tags::LanguageTag;
//! use std::iter::FromIterator;
//!
//! let langtag: LanguageTag = "en-x-twain".parse().unwrap();
//! assert_eq!(langtag.primary_language(), "en");
//! assert_eq!(Vec::from_iter(langtag.private_use_subtags()), vec!["twain"]);
//! ```
//!
//! You can check for equality, but more often you should test if two tags match.
//! In this example we check if the resource in German language is suitable for
//! a user from Austria. While people speaking Austrian German normally understand
//! standard German the opposite is not always true. So the resource can be presented
//! to the user but if the resource was in `de-AT` and a user asked for a representation
//! in `de` the request should be rejected.
//!
//!
//! ```rust
//! use language_tags::LanguageTag;
//!
//! let mut langtag_server = LanguageTag::parse("de-AT").unwrap();
//! let mut langtag_user = LanguageTag::parse("de").unwrap();
//! assert!(langtag_user.matches(&langtag_server));
//! ```

mod iana_registry;
#[cfg(feature = "serde")]
mod serde;

use crate::iana_registry::*;
use std::error::Error;
use std::fmt;
use std::iter::once;
use std::ops::Deref;
use std::str::FromStr;
use std::str::Split;

/// A language tag as described in [RFC 5646](https://tools.ietf.org/html/rfc5646).
///
/// Language tags are used to help identify languages, whether spoken,
/// written, signed, or otherwise signaled, for the purpose of
/// communication.  This includes constructed and artificial languages
/// but excludes languages not intended primarily for human
/// communication, such as programming languages.
#[derive(Eq, PartialEq, Debug, Clone, Hash)]
pub struct LanguageTag {
    /// Syntax described in [RFC 5646 2.1](https://tools.ietf.org/html/rfc5646#section-2.1)
    serialization: String,
    language_end: usize,
    extlang_end: usize,
    script_end: usize,
    region_end: usize,
    variant_end: usize,
    extension_end: usize,
}

impl LanguageTag {
    /// Return the serialization of this language tag.
    ///
    /// This is fast since that serialization is already stored in the `LanguageTag` struct.
    #[inline]
    pub fn as_str(&self) -> &str {
        &self.serialization
    }

    /// Return the serialization of this language tag.
    ///
    /// This consumes the `LanguageTag` and takes ownership of the `String` stored in it.
    #[inline]
    pub fn into_string(self) -> String {
        self.serialization
    }

    /// Return the [primary language subtag](https://tools.ietf.org/html/rfc5646#section-2.2.1).
    ///
    /// ```
    /// use language_tags::LanguageTag;
    ///
    /// let language_tag = LanguageTag::parse("zh-cmn-Hans-CN").unwrap();
    /// assert_eq!(language_tag.primary_language(), "zh");
    /// ```
    #[inline]
    pub fn primary_language(&self) -> &str {
        &self.serialization[..self.language_end]
    }

    /// Return the [extended language subtags](https://tools.ietf.org/html/rfc5646#section-2.2.2).
    ///
    /// Valid language tags have at most one extended language.
    ///
    /// ```
    /// use language_tags::LanguageTag;
    ///
    /// let language_tag = LanguageTag::parse("zh-cmn-Hans-CN").unwrap();
    /// assert_eq!(language_tag.extended_language(), Some("cmn"));
    /// ```
    #[inline]
    pub fn extended_language(&self) -> Option<&str> {
        if self.language_end == self.extlang_end {
            None
        } else {
            Some(&self.serialization[self.language_end + 1..self.extlang_end])
        }
    }

    /// Iterate on the [extended language subtags](https://tools.ietf.org/html/rfc5646#section-2.2.2).
    ///
    /// Valid language tags have at most one extended language.
    ///
    /// ```
    /// use language_tags::LanguageTag;
    ///
    /// let language_tag = LanguageTag::parse("zh-cmn-Hans-CN").unwrap();
    /// assert_eq!(language_tag.extended_language_subtags().collect::<Vec<_>>(), vec!["cmn"]);
    /// ```
    #[inline]
    pub fn extended_language_subtags(&self) -> impl Iterator<Item = &str> {
        self.extended_language().unwrap_or("").split_terminator('-')
    }

    /// Return the [primary language subtag](https://tools.ietf.org/html/rfc5646#section-2.2.1)
    /// and its [extended language subtags](https://tools.ietf.org/html/rfc5646#section-2.2.2).
    ///
    /// ```
    /// use language_tags::LanguageTag;
    ///
    /// let language_tag = LanguageTag::parse("zh-cmn-Hans-CN").unwrap();
    /// assert_eq!(language_tag.full_language(), "zh-cmn");
    /// ```
    #[inline]
    pub fn full_language(&self) -> &str {
        &self.serialization[..self.extlang_end]
    }

    /// Return the [script subtag](https://tools.ietf.org/html/rfc5646#section-2.2.3).
    ///
    /// ```
    /// use language_tags::LanguageTag;
    ///
    /// let language_tag = LanguageTag::parse("zh-cmn-Hans-CN").unwrap();
    /// assert_eq!(language_tag.script(), Some("Hans"));
    /// ```
    #[inline]
    pub fn script(&self) -> Option<&str> {
        if self.extlang_end == self.script_end {
            None
        } else {
            Some(&self.serialization[self.extlang_end + 1..self.script_end])
        }
    }

    /// Return the [region subtag](https://tools.ietf.org/html/rfc5646#section-2.2.4).
    ///
    ///
    /// ```
    /// use language_tags::LanguageTag;
    ///
    /// let language_tag = LanguageTag::parse("zh-cmn-Hans-CN").unwrap();
    /// assert_eq!(language_tag.region(), Some("CN"));
    /// ```
    #[inline]
    pub fn region(&self) -> Option<&str> {
        if self.script_end == self.region_end {
            None
        } else {
            Some(&self.serialization[self.script_end + 1..self.region_end])
        }
    }

    /// Return the [variant subtags](https://tools.ietf.org/html/rfc5646#section-2.2.5).
    ///
    /// ```
    /// use language_tags::LanguageTag;
    ///
    /// let language_tag = LanguageTag::parse("zh-Latn-TW-pinyin").unwrap();
    /// assert_eq!(language_tag.variant(), Some("pinyin"));
    /// ```
    #[inline]
    pub fn variant(&self) -> Option<&str> {
        if self.region_end == self.variant_end {
            None
        } else {
            Some(&self.serialization[self.region_end + 1..self.variant_end])
        }
    }

    /// Iterate on the [variant subtags](https://tools.ietf.org/html/rfc5646#section-2.2.5).
    ///
    /// ```
    /// use language_tags::LanguageTag;
    ///
    /// let language_tag = LanguageTag::parse("zh-Latn-TW-pinyin").unwrap();
    /// assert_eq!(language_tag.variant_subtags().collect::<Vec<_>>(), vec!["pinyin"]);
    /// ```
    #[inline]
    pub fn variant_subtags(&self) -> impl Iterator<Item = &str> {
        self.variant().unwrap_or("").split_terminator('-')
    }

    /// Return the [extension subtags](https://tools.ietf.org/html/rfc5646#section-2.2.6).
    ///
    /// ```
    /// use language_tags::LanguageTag;
    ///
    /// let language_tag = LanguageTag::parse("de-DE-u-co-phonebk").unwrap();
    /// assert_eq!(language_tag.extension(), Some("u-co-phonebk"));
    /// ```
    #[inline]
    pub fn extension(&self) -> Option<&str> {
        if self.variant_end == self.extension_end {
            None
        } else {
            Some(&self.serialization[self.variant_end + 1..self.extension_end])
        }
    }

    /// Iterate on the [extension subtags](https://tools.ietf.org/html/rfc5646#section-2.2.6).
    ///
    /// ```
    /// use language_tags::LanguageTag;
    ///
    /// let language_tag = LanguageTag::parse("de-DE-u-co-phonebk").unwrap();
    /// assert_eq!(language_tag.extension_subtags().collect::<Vec<_>>(), vec![('u', "co-phonebk")]);
    /// ```
    #[inline]
    pub fn extension_subtags(&self) -> impl Iterator<Item = (char, &str)> {
        match self.extension() {
            Some(parts) => ExtensionsIterator::new(parts),
            None => ExtensionsIterator::new(""),
        }
    }

    /// Return the [private use subtags](https://tools.ietf.org/html/rfc5646#section-2.2.7).
    ///
    ///
    /// ```
    /// use language_tags::LanguageTag;
    ///
    /// let language_tag = LanguageTag::parse("de-x-foo-bar").unwrap();
    /// assert_eq!(language_tag.private_use(), Some("x-foo-bar"));
    /// ```
    #[inline]
    pub fn private_use(&self) -> Option<&str> {
        if self.serialization.starts_with("x-") {
            Some(&self.serialization)
        } else if self.extension_end == self.serialization.len() {
            None
        } else {
            Some(&self.serialization[self.extension_end + 1..])
        }
    }

    /// Iterate on the [private use subtags](https://tools.ietf.org/html/rfc5646#section-2.2.7).
    ///
    /// ```
    /// use language_tags::LanguageTag;
    ///
    /// let language_tag = LanguageTag::parse("de-x-foo-bar").unwrap();
    /// assert_eq!(language_tag.private_use_subtags().collect::<Vec<_>>(), vec!["foo", "bar"]);
    /// ```
    #[inline]
    pub fn private_use_subtags(&self) -> impl Iterator<Item = &str> {
        self.private_use()
            .map(|part| &part[2..])
            .unwrap_or("")
            .split_terminator('-')
    }

    /// Create a `LanguageTag` from its serialization.
    ///
    /// This parser accepts the language tags that are "well-formed" according to
    /// [RFC 5646](https://tools.ietf.org/html/rfc5646#section-2.2.9).
    /// Full validation could be done with the `validate` method.
    ///
    /// ```rust
    /// use language_tags::LanguageTag;
    ///
    /// let language_tag = LanguageTag::parse("en-us").unwrap();
    /// assert_eq!(language_tag.into_string(), "en-US")
    /// ```
    ///
    /// # Errors
    ///
    /// If the language tag is not "well-formed" a `ParseError` variant will be returned.
    pub fn parse(input: &str) -> Result<Self, ParseError> {
        //grandfathered tags
        if let Some(tag) = GRANDFATHEREDS
            .iter()
            .find(|record| record.eq_ignore_ascii_case(input))
        {
            // grandfathered tag
            Ok(tag_from_primary_language(*tag))
        } else if input.starts_with("x-") || input.starts_with("X-") {
            // private use
            if !is_alphanumeric_or_dash(input) {
                Err(ParseError::ForbiddenChar)
            } else if input.len() == 2 {
                Err(ParseError::EmptyPrivateUse)
            } else {
                Ok(tag_from_primary_language(input.to_ascii_lowercase()))
            }
        } else {
            parse_language_tag(input)
        }
    }

    /// Check if the language tag is "valid" according to
    /// [RFC 5646](https://tools.ietf.org/html/rfc5646#section-2.2.9).
    ///
    /// It applies the following steps:
    ///
    /// * grandfathereds and private use tags are valid
    /// * There should be no more than one extended language subtag
    ///   (c.f. [errata 5457](https://www.rfc-editor.org/errata/eid5457)).
    /// * Primary language, extended language, script, region and variants should appear
    ///   in the IANA Language Subtag Registry.
    /// * Extended language and variants should have a correct prefix as set
    ///   in the IANA Language Subtag Registry.
    /// * There should be no duplicate variant and singleton (extension) subtags.
    ///
    ///
    /// # Errors
    ///
    /// If the language tag is not "valid" a `ValidationError` variant will be returned.
    pub fn validate(&self) -> Result<(), ValidationError> {
        // The tag is well-formed.
        // always ok

        // Private tag
        if self.serialization.starts_with("x-") {
            return Ok(());
        }

        // The tag is in the list of grandfathered tags
        if is_in_str_slice_set(&GRANDFATHEREDS, &self.serialization) {
            return Ok(());
        }

        // There is no more than one extended language subtag.
        // From [errata 5457](https://www.rfc-editor.org/errata/eid5457).
        if let Some(extended_language) = self.extended_language() {
            if extended_language.contains('-') {
                return Err(ValidationError::MultipleExtendedLanguageSubtags);
            }
        }

        // all of its primary language, extended language, script, region, and variant
        // subtags appear in the IANA Language Subtag Registry as of the
        // particular registry date.
        let primary_language = self.primary_language();
        if !between(primary_language, "qaa", "qtz")
            && !is_in_from_str_slice_set(&LANGUAGES, primary_language)
        {
            return Err(ValidationError::PrimaryLanguageNotInRegistry);
        }
        if let Some(extended_language) = self.extended_language() {
            if let Some(extended_language_prefix) =
                find_in_from_str_slice_map(&EXTLANGS, extended_language)
            {
                if !self.serialization.starts_with(extended_language_prefix) {
                    return Err(ValidationError::WrongExtendedLanguagePrefix);
                }
            } else {
                return Err(ValidationError::ExtendedLanguageNotInRegistry);
            }
        }
        if let Some(script) = self.script() {
            if !between(script, "Qaaa", "Qabx") && !is_in_from_str_slice_set(&SCRIPTS, script) {
                return Err(ValidationError::ScriptNotInRegistry);
            }
        }
        if let Some(region) = self.region() {
            if !between(region, "QM", "QZ")
                && !between(region, "XA", "XZ")
                && !is_in_from_str_slice_set(&REGIONS, region)
            {
                return Err(ValidationError::RegionNotInRegistry);
            }
        }
        for variant in self.variant_subtags() {
            if let Some(variant_prefixes) = find_in_str_slice_map(&VARIANTS, variant) {
                if !variant_prefixes
                    .split(' ')
                    .any(|prefix| self.serialization.starts_with(prefix))
                {
                    return Err(ValidationError::WrongVariantPrefix);
                }
            } else {
                return Err(ValidationError::VariantNotInRegistry);
            }
        }

        // There are no duplicate variant subtags.
        let with_duplicate_variant = self.variant_subtags().enumerate().any(|(id1, variant1)| {
            self.variant_subtags()
                .enumerate()
                .any(|(id2, variant2)| id1 != id2 && variant1 == variant2)
        });
        if with_duplicate_variant {
            return Err(ValidationError::DuplicateVariant);
        }

        // There are no duplicate singleton (extension) subtags.
        if let Some(extension) = self.extension() {
            let mut seen_extensions = AlphanumericLowerCharSet::new();
            let with_duplicate_extension = extension.split('-').any(|subtag| {
                if subtag.len() == 1 {
                    let extension = subtag.chars().next().unwrap();
                    if seen_extensions.contains(extension) {
                        true
                    } else {
                        seen_extensions.insert(extension);
                        false
                    }
                } else {
                    false
                }
            });
            if with_duplicate_extension {
                return Err(ValidationError::DuplicateExtension);
            }
        }

        Ok(())
    }

    /// Check if the language tag is valid according to
    /// [RFC 5646](https://tools.ietf.org/html/rfc5646#section-2.2.9).
    pub fn is_valid(&self) -> bool {
        self.validate().is_ok()
    }

    /// Returns the canonical version of the language tag following
    /// [RFC 5646 4.5](https://tools.ietf.org/html/rfc5646#section-4.5).
    ///
    /// It currently applies the following steps:
    ///
    /// * Grandfathered tags are replaced with the canonical version if possible.
    /// * Redundant tags are replaced with the canonical version if possible.
    /// * Extension languages are promoted to primary language.
    /// * Deprecated languages, scripts, regions and variants are replaced with modern equivalents.
    /// * Suppress-Script is applied to remove default script for a language (e.g. "en-Latn" is canonicalized as "en").
    /// * Variants are deduplicated
    ///
    ///
    /// # Errors
    ///
    /// If there is not a unique way to canonicalize the language tag
    /// a `ValidationError` variant will be returned.
    pub fn canonicalize(&self) -> Result<LanguageTag, ValidationError> {
        //We could not do anything for private use
        if self.serialization.starts_with("x-") {
            return Ok(self.clone());
        }

        // 2 Redundant or grandfathered tags are replaced by their 'Preferred-Value', if there is one.
        if is_in_str_slice_set(&GRANDFATHEREDS, &self.serialization) {
            return Ok(
                if let Some(preferred_value) =
                    find_in_str_slice_map(&GRANDFATHEREDS_PREFERRED_VALUE, &self.serialization)
                {
                    Self::parse(preferred_value).unwrap()
                } else {
                    self.clone()
                },
            );
        }
        if let Some(preferred_value) =
            find_in_str_slice_map(&REDUNDANTS_PREFERRED_VALUE, &self.serialization)
        {
            return Ok(Self::parse(preferred_value).unwrap());
        }
        //TODO: what if a redundant has a some extensions/private use?

        // 3.  Subtags are replaced by their 'Preferred-Value', if there is one.
        // Primary language
        let mut primary_language = self.primary_language();
        if let Some(preferred_value) =
            find_in_from_str_slice_map(&LANGUAGES_PREFERRED_VALUE, primary_language)
        {
            primary_language = preferred_value;
        }

        // Extended language
        // For extlangs, the original primary language subtag is also replaced if there is a primary language subtag in the 'Preferred-Value'.
        let mut extended_language = None;
        if let Some(extlang) = self.extended_language() {
            // We fail if there is more than one (no single possible canonicalization)
            if extlang.contains('-') {
                return Err(ValidationError::MultipleExtendedLanguageSubtags);
            }
            if let Some(preferred_value) =
                find_in_from_str_slice_map(&EXTLANGS_PREFERRED_VALUE, extlang)
            {
                primary_language = preferred_value;
            } else {
                extended_language = Some(extlang);
            }
        }

        let mut serialization = String::with_capacity(self.serialization.len());
        serialization.push_str(primary_language);
        let language_end = serialization.len();
        if let Some(extended_language) = extended_language {
            serialization.push('-');
            serialization.push_str(extended_language);
        }
        let extlang_end = serialization.len();

        // Script
        if let Some(script) = self.script() {
            let script =
                find_in_from_str_slice_map(&SCRIPTS_PREFERRED_VALUE, script).unwrap_or(script);

            // Suppress-Script
            let match_suppress_script =
                find_in_from_str_slice_map(&LANGUAGES_SUPPRESS_SCRIPT, primary_language)
                    .filter(|suppress_script| *suppress_script == script)
                    .is_some();
            if !match_suppress_script {
                serialization.push('-');
                serialization.push_str(script);
            }
        }
        let script_end = serialization.len();

        // Region
        if let Some(region) = self.region() {
            serialization.push('-');
            serialization.push_str(
                find_in_from_str_slice_map(&REGIONS_PREFERRED_VALUE, region).unwrap_or(region),
            );
        }
        let region_end = serialization.len();

        // Variant
        for variant in self.variant_subtags() {
            let variant =
                *find_in_str_slice_map(&VARIANTS_PREFERRED_VALUE, variant).unwrap_or(&variant);
            let variant_already_exists = serialization.split('-').any(|subtag| subtag == variant);
            if !variant_already_exists {
                serialization.push('-');
                serialization.push_str(variant);
            }
        }
        let variant_end = serialization.len();

        //Extension
        // 1.  Extension sequences are ordered into case-insensitive ASCII order by singleton subtags
        if self.extension().is_some() {
            let mut extensions: Vec<_> = self.extension_subtags().collect();
            extensions.sort_unstable();
            for (k, v) in extensions {
                serialization.push('-');
                serialization.push(k);
                serialization.push('-');
                serialization.push_str(v);
            }
        }
        let extension_end = serialization.len();

        //Private use
        if let Some(private_use) = self.private_use() {
            serialization.push('-');
            serialization.push_str(private_use);
        }

        Ok(LanguageTag {
            serialization,
            language_end,
            extlang_end,
            script_end,
            region_end,
            variant_end,
            extension_end,
        })
    }

    /// Matches language tags. The first language acts as a language range, the second one is used
    /// as a normal language tag. None fields in the language range are ignored. If the language
    /// tag has more extlangs than the range these extlangs are ignored. Matches are
    /// case-insensitive.
    ///
    /// For example the range `en-GB` matches only `en-GB` and `en-Arab-GB` but not `en`.
    /// The range `en` matches all language tags starting with `en` including `en`, `en-GB`,
    /// `en-Arab` and `en-Arab-GB`.
    ///
    /// # Panics
    /// If the language range has extensions or private use tags.
    ///
    /// # Examples
    /// ```rust
    /// use language_tags::LanguageTag;
    ///
    /// let range_italian = LanguageTag::parse("it").unwrap();
    /// let tag_german = LanguageTag::parse("de").unwrap();
    /// let tag_italian_switzerland = LanguageTag::parse("it-CH").unwrap();
    /// assert!(!range_italian.matches(&tag_german));
    /// assert!(range_italian.matches(&tag_italian_switzerland));
    ///
    /// let range_spanish_brazil = LanguageTag::parse("es-BR").unwrap();
    /// let tag_spanish = LanguageTag::parse("es").unwrap();
    /// assert!(!range_spanish_brazil.matches(&tag_spanish));
    /// ```
    pub fn matches(&self, other: &LanguageTag) -> bool {
        fn matches_option(a: Option<&str>, b: Option<&str>) -> bool {
            match (a, b) {
                (Some(a), Some(b)) => a == b,
                (None, _) => true,
                (_, None) => false,
            }
        }
        fn matches_iter<'a>(
            a: impl Iterator<Item = &'a str>,
            b: impl Iterator<Item = &'a str>,
        ) -> bool {
            a.zip(b).all(|(x, y)| x == y)
        }
        assert!(self.is_language_range());
        self.full_language() == other.full_language()
            && matches_option(self.script(), other.script())
            && matches_option(self.region(), other.region())
            && matches_iter(self.variant_subtags(), other.variant_subtags())
    }

    /// Checks if it is a language range, meaning that there are no extension and privateuse tags.
    pub fn is_language_range(&self) -> bool {
        self.extension().is_none() && self.private_use().is_none()
    }
}

impl FromStr for LanguageTag {
    type Err = ParseError;

    #[inline]
    fn from_str(input: &str) -> Result<Self, ParseError> {
        Self::parse(input)
    }
}

impl fmt::Display for LanguageTag {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(self.as_str())
    }
}

/// Builds a tag from its primary language
fn tag_from_primary_language(tag: impl Into<String>) -> LanguageTag {
    let serialization = tag.into();
    let end = serialization.len();
    LanguageTag {
        serialization,
        language_end: end,
        extlang_end: end,
        script_end: end,
        region_end: end,
        variant_end: end,
        extension_end: end,
    }
}

/// Handles normal tags.
fn parse_language_tag(input: &str) -> Result<LanguageTag, ParseError> {
    #[derive(PartialEq, Eq)]
    enum State {
        Start,
        AfterLanguage,
        AfterExtLang,
        AfterScript,
        AfterRegion,
        InExtension { expected: bool },
        InPrivateUse { expected: bool },
    }

    let mut serialization = String::with_capacity(input.len());

    let mut state = State::Start;
    let mut language_end = 0;
    let mut extlang_end = 0;
    let mut script_end = 0;
    let mut region_end = 0;
    let mut variant_end = 0;
    let mut extension_end = 0;
    let mut extlangs_count = 0;
    for (subtag, end) in SubTagIterator::new(input) {
        if subtag.is_empty() {
            // All subtags have a maximum length of eight characters.
            return Err(ParseError::EmptySubtag);
        }
        if subtag.len() > 8 {
            // All subtags have a maximum length of eight characters.
            return Err(ParseError::SubtagTooLong);
        }
        if state == State::Start {
            // Primary language
            if subtag.len() < 2 || !is_alphabetic(subtag) {
                return Err(ParseError::InvalidLanguage);
            }
            language_end = end;
            serialization.extend(to_lowercase(subtag));
            if subtag.len() < 4 {
                // extlangs are only allowed for short language tags
                state = State::AfterLanguage;
            } else {
                state = State::AfterExtLang;
            }
        } else if let State::InPrivateUse { .. } = state {
            if !is_alphanumeric(subtag) {
                return Err(ParseError::InvalidSubtag);
            }
            serialization.push('-');
            serialization.extend(to_lowercase(subtag));
            state = State::InPrivateUse { expected: false };
        } else if subtag == "x" || subtag == "X" {
            // We make sure extension is found
            if let State::InExtension { expected: true } = state {
                return Err(ParseError::EmptyExtension);
            }
            serialization.push('-');
            serialization.push('x');
            state = State::InPrivateUse { expected: true };
        } else if subtag.len() == 1 && is_alphanumeric(subtag) {
            // We make sure extension is found
            if let State::InExtension { expected: true } = state {
                return Err(ParseError::EmptyExtension);
            }
            let extension_tag = subtag.chars().next().unwrap().to_ascii_lowercase();
            serialization.push('-');
            serialization.push(extension_tag);
            state = State::InExtension { expected: true };
        } else if let State::InExtension { .. } = state {
            if !is_alphanumeric(subtag) {
                return Err(ParseError::InvalidSubtag);
            }
            extension_end = end;
            serialization.push('-');
            serialization.extend(to_lowercase(subtag));
            state = State::InExtension { expected: false };
        } else if state == State::AfterLanguage && subtag.len() == 3 && is_alphabetic(subtag) {
            extlangs_count += 1;
            if extlangs_count > 3 {
                return Err(ParseError::TooManyExtlangs);
            }
            // valid extlangs
            extlang_end = end;
            serialization.push('-');
            serialization.extend(to_lowercase(subtag));
        } else if (state == State::AfterLanguage || state == State::AfterExtLang)
            && subtag.len() == 4
            && is_alphabetic(subtag)
        {
            // Script
            script_end = end;
            serialization.push('-');
            serialization.extend(to_uppercase_first(subtag));
            state = State::AfterScript;
        } else if (state == State::AfterLanguage
            || state == State::AfterExtLang
            || state == State::AfterScript)
            && (subtag.len() == 2 && is_alphabetic(subtag)
                || subtag.len() == 3 && is_numeric(subtag))
        {
            // Region
            region_end = end;
            serialization.push('-');
            serialization.extend(to_uppercase(subtag));
            state = State::AfterRegion;
        } else if (state == State::AfterLanguage
            || state == State::AfterExtLang
            || state == State::AfterScript
            || state == State::AfterRegion)
            && is_alphanumeric(subtag)
            && (subtag.len() >= 5 && is_alphabetic(&subtag[0..1])
                || subtag.len() >= 4 && is_numeric(&subtag[0..1]))
        {
            // Variant
            variant_end = end;
            serialization.push('-');
            serialization.extend(to_lowercase(subtag));
            state = State::AfterRegion;
        } else {
            return Err(ParseError::InvalidSubtag);
        }
    }

    //We make sure we are in a correct final state
    if let State::InExtension { expected: true } = state {
        return Err(ParseError::EmptyExtension);
    }
    if let State::InPrivateUse { expected: true } = state {
        return Err(ParseError::EmptyPrivateUse);
    }

    //We make sure we have not skipped anyone
    if extlang_end < language_end {
        extlang_end = language_end;
    }
    if script_end < extlang_end {
        script_end = extlang_end;
    }
    if region_end < script_end {
        region_end = script_end;
    }
    if variant_end < region_end {
        variant_end = region_end;
    }
    if extension_end < variant_end {
        extension_end = variant_end;
    }

    Ok(LanguageTag {
        serialization,
        language_end,
        extlang_end,
        script_end,
        region_end,
        variant_end,
        extension_end,
    })
}

struct ExtensionsIterator<'a> {
    input: &'a str,
}

impl<'a> ExtensionsIterator<'a> {
    fn new(input: &'a str) -> Self {
        Self { input }
    }
}

impl<'a> Iterator for ExtensionsIterator<'a> {
    type Item = (char, &'a str);

    fn next(&mut self) -> Option<(char, &'a str)> {
        let mut parts_iterator = self.input.split_terminator('-');
        let singleton = parts_iterator.next()?.chars().next().unwrap();
        let mut content_size: usize = 2;
        for part in parts_iterator {
            if part.len() == 1 {
                let content = &self.input[2..content_size - 1];
                self.input = &self.input[content_size..];
                return Some((singleton, content));
            } else {
                content_size += part.len() + 1;
            }
        }
        let result = self.input.get(2..).map(|content| (singleton, content));
        self.input = "";
        result
    }
}

struct SubTagIterator<'a> {
    split: Split<'a, char>,
    position: usize,
}

impl<'a> SubTagIterator<'a> {
    fn new(input: &'a str) -> Self {
        Self {
            split: input.split('-'),
            position: 0,
        }
    }
}

impl<'a> Iterator for SubTagIterator<'a> {
    type Item = (&'a str, usize);

    fn next(&mut self) -> Option<(&'a str, usize)> {
        let tag = self.split.next()?;
        let tag_end = self.position + tag.len();
        self.position = tag_end + 1;
        Some((tag, tag_end))
    }
}

struct AlphanumericLowerCharSet {
    alphabetic_set: [bool; 26],
    numeric_set: [bool; 10],
}

impl AlphanumericLowerCharSet {
    fn new() -> Self {
        Self {
            alphabetic_set: [false; 26],
            numeric_set: [false; 10],
        }
    }

    fn contains(&mut self, c: char) -> bool {
        if c.is_ascii_digit() {
            self.numeric_set[char_sub(c, '0')]
        } else if c.is_ascii_lowercase() {
            self.alphabetic_set[char_sub(c, 'a')]
        } else if c.is_ascii_uppercase() {
            self.alphabetic_set[char_sub(c, 'A')]
        } else {
            false
        }
    }

    fn insert(&mut self, c: char) {
        if c.is_ascii_digit() {
            self.numeric_set[char_sub(c, '0')] = true
        } else if c.is_ascii_lowercase() {
            self.alphabetic_set[char_sub(c, 'a')] = true
        } else if c.is_ascii_uppercase() {
            self.alphabetic_set[char_sub(c, 'A')] = true
        }
    }
}

fn char_sub(c1: char, c2: char) -> usize {
    (c1 as usize) - (c2 as usize)
}

fn is_alphabetic(s: &str) -> bool {
    s.chars().all(|x| x.is_ascii_alphabetic())
}

fn is_numeric(s: &str) -> bool {
    s.chars().all(|x| x.is_ascii_digit())
}

fn is_alphanumeric(s: &str) -> bool {
    s.chars().all(|x| x.is_ascii_alphanumeric())
}

fn is_alphanumeric_or_dash(s: &str) -> bool {
    s.chars().all(|x| x.is_ascii_alphanumeric() || x == '-')
}

fn to_uppercase(s: &'_ str) -> impl Iterator<Item = char> + '_ {
    s.chars().map(|c| c.to_ascii_uppercase())
}

// Beware: panics if s.len() == 0 (should never happen in our code)
fn to_uppercase_first(s: &'_ str) -> impl Iterator<Item = char> + '_ {
    let mut chars = s.chars();
    once(chars.next().unwrap().to_ascii_uppercase()).chain(chars.map(|c| c.to_ascii_lowercase()))
}

fn to_lowercase(s: &'_ str) -> impl Iterator<Item = char> + '_ {
    s.chars().map(|c| c.to_ascii_lowercase())
}

/// Errors returned by `LanguageTag` parsing
#[derive(Clone, Debug, Eq, PartialEq)]
pub enum ParseError {
    /// If an extension subtag is present, it must not be empty.
    EmptyExtension,
    /// If the `x` subtag is present, it must not be empty.
    EmptyPrivateUse,
    /// The langtag contains a char that is not A-Z, a-z, 0-9 or the dash.
    ForbiddenChar,
    /// A subtag fails to parse, it does not match any other subtags.
    InvalidSubtag,
    /// The given language subtag is invalid.
    InvalidLanguage,
    /// A subtag may be eight characters in length at maximum.
    SubtagTooLong,
    /// A subtag should not be empty.
    EmptySubtag,
    /// At maximum three extlangs are allowed, but zero to one extlangs are preferred.
    TooManyExtlangs,
}

impl Error for ParseError {}

impl fmt::Display for ParseError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(match self {
            Self::EmptyExtension => "if an extension subtag is present, it must not be empty",
            Self::EmptyPrivateUse => "if the `x` subtag is present, it must not be empty",
            Self::ForbiddenChar => "the langtag contains a char not allowed",
            Self::InvalidSubtag => "a subtag fails to parse, it does not match any other subtags",
            Self::InvalidLanguage => "the given language subtag is invalid",
            Self::SubtagTooLong => "a subtag may be eight characters in length at maximum",
            Self::EmptySubtag => "a subtag should not be empty",
            Self::TooManyExtlangs => "at maximum three extlangs are allowed",
        })
    }
}

/// Errors returned by the `LanguageTag` validation
#[derive(Clone, Debug, Eq, PartialEq)]
pub enum ValidationError {
    /// The same variant subtag is only allowed once in a tag.
    DuplicateVariant,
    /// The same extension subtag is only allowed once in a tag before the private use part.
    DuplicateExtension,
    /// only one extended language subtag is allowed
    MultipleExtendedLanguageSubtags,
    /// The primary language is not in the IANA Language Subtag Registry
    PrimaryLanguageNotInRegistry,
    /// The extended language is not in the IANA Language Subtag Registry
    ExtendedLanguageNotInRegistry,
    /// The script is not in the IANA Language Subtag Registry
    ScriptNotInRegistry,
    /// The region is not in the IANA Language Subtag Registry
    RegionNotInRegistry,
    /// A variant is not in the IANA Language Subtag Registry
    VariantNotInRegistry,
    /// The primary language is not the expected extended language prefix from the IANA Language Subtag Registry
    WrongExtendedLanguagePrefix,
    /// The language tag has not one of the expected variant prefix from the IANA Language Subtag Registry
    WrongVariantPrefix,
}

impl Error for ValidationError {}

impl fmt::Display for ValidationError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(match self {
            Self::DuplicateVariant => {
                "the same variant subtag is only allowed once in a tag"
            }
            Self::DuplicateExtension => {
                "the same extension subtag is only allowed once in a tag"
            }
            Self::MultipleExtendedLanguageSubtags => {
                "only one extended language subtag is allowed"
            }
            Self::PrimaryLanguageNotInRegistry => {
                "the primary language is not in the IANA Language Subtag Registry"
            }
            Self::ExtendedLanguageNotInRegistry => {
                "the extended language is not in the IANA Language Subtag Registry"
            }
            Self::ScriptNotInRegistry => {
                "the script is not in the IANA Language Subtag Registry"
            }
            Self::RegionNotInRegistry => {
                "the region is not in the IANA Language Subtag Registry"
            }
            Self::VariantNotInRegistry => {
                "a variant is not in the IANA Language Subtag Registry"
            }
            Self::WrongExtendedLanguagePrefix => {
                "the primary language is not the expected extended language prefix from the IANA Language Subtag Registry"
            }
            Self::WrongVariantPrefix => {
                "the language tag has not one of the expected variant prefix from the IANA Language Subtag Registry"
            }
        })
    }
}

fn between<T: Ord>(value: T, start: T, end: T) -> bool {
    start <= value && value <= end
}

fn is_in_str_slice_set(slice: &[&'static str], value: &str) -> bool {
    slice.binary_search(&value).is_ok()
}

fn is_in_from_str_slice_set<T: Copy + Ord + FromStr>(slice: &[T], value: &str) -> bool {
    match T::from_str(value) {
        Ok(key) => slice.binary_search(&key).is_ok(),
        Err(_) => false,
    }
}

fn find_in_str_slice_map<'a, V>(slice: &'a [(&'static str, V)], value: &str) -> Option<&'a V> {
    if let Ok(position) = slice.binary_search_by_key(&value, |t| t.0) {
        Some(&slice[position].1)
    } else {
        None
    }
}

fn find_in_from_str_slice_map<'a, K: Copy + Ord + FromStr, V: Deref<Target = str>>(
    slice: &'a [(K, V)],
    value: &str,
) -> Option<&'a str> {
    if let Ok(position) = slice.binary_search_by_key(&K::from_str(value).ok()?, |t| t.0) {
        Some(&*slice[position].1)
    } else {
        None
    }
}