match.go

     1  // Copyright 2015 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package internal
     6  
     7  // This file contains matchers that implement CLDR inheritance.
     8  //
     9  //     See https://unicode.org/reports/tr35/#Locale_Inheritance.
    10  //
    11  // Some of the inheritance described in this document is already handled by
    12  // the cldr package.
    13  
    14  import (
    15  	"golang.org/x/text/language"
    16  )
    17  
    18  // TODO: consider if (some of the) matching algorithm needs to be public after
    19  // getting some feel about what is generic and what is specific.
    20  
    21  // NewInheritanceMatcher returns a matcher that matches based on the inheritance
    22  // chain.
    23  //
    24  // The matcher uses canonicalization and the parent relationship to find a
    25  // match. The resulting match will always be either Und or a language with the
    26  // same language and script as the requested language. It will not match
    27  // languages for which there is understood to be mutual or one-directional
    28  // intelligibility.
    29  //
    30  // A Match will indicate an Exact match if the language matches after
    31  // canonicalization and High if the matched tag is a parent.
    32  func NewInheritanceMatcher(t []language.Tag) *InheritanceMatcher {
    33  	tags := &InheritanceMatcher{make(map[language.Tag]int)}
    34  	for i, tag := range t {
    35  		ct, err := language.All.Canonicalize(tag)
    36  		if err != nil {
    37  			ct = tag
    38  		}
    39  		tags.index[ct] = i
    40  	}
    41  	return tags
    42  }
    43  
    44  type InheritanceMatcher struct {
    45  	index map[language.Tag]int
    46  }
    47  
    48  func (m InheritanceMatcher) Match(want ...language.Tag) (language.Tag, int, language.Confidence) {
    49  	for _, t := range want {
    50  		ct, err := language.All.Canonicalize(t)
    51  		if err != nil {
    52  			ct = t
    53  		}
    54  		conf := language.Exact
    55  		for {
    56  			if index, ok := m.index[ct]; ok {
    57  				return ct, index, conf
    58  			}
    59  			if ct == language.Und {
    60  				break
    61  			}
    62  			ct = ct.Parent()
    63  			conf = language.High
    64  		}
    65  	}
    66  	return language.Und, 0, language.No
    67  }
    68
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