// parent computes the structural parent. This means inheritance may change
// script. So, unlike the CLDR parent, parent(zh-Hant) == zh.
func parent(t language.Tag) language.Tag {
if t.TypeForKey("va") != "" {
t, _ = t.SetTypeForKey("va", "")
return t
}
result := language.Und
if b, s, r := t.Raw(); (r != language.Region{}) {
result, _ = language.Raw.Compose(b, s, t.Extensions())
} else if (s != language.Script{}) {
result, _ = language.Raw.Compose(b, t.Extensions())
} else if (b != language.Base{}) {
result, _ = language.Raw.Compose(t.Extensions())
}
return result
}
// MatchLang finds the index of t in tags, using a matching algorithm used for
// collation and search. tags[0] must be language.Und, the remaining tags should
// be sorted alphabetically.
//
// Language matching for collation and search is different from the matching
// defined by language.Matcher: the (inferred) base language must be an exact
// match for the relevant fields. For example, "gsw" should not match "de".
// Also the parent relation is different, as a parent may have a different
// script. So usually the parent of zh-Hant is und, whereas for MatchLang it is
// zh.
func MatchLang(t language.Tag, tags []language.Tag) int {
// Canonicalize the values, including collapsing macro languages.
t, _ = language.All.Canonicalize(t)
base, conf := t.Base()
// Estimate the base language, but only use high-confidence values.
if conf < language.High {
// The root locale supports "search" and "standard". We assume that any
// implementation will only use one of both.
return 0
}
// Maximize base and script and normalize the tag.
if _, s, r := t.Raw(); (r != language.Region{}) {
p, _ := language.Raw.Compose(base, s, r)
// Taking the parent forces the script to be maximized.
p = p.Parent()
// Add back region and extensions.
t, _ = language.Raw.Compose(p, r, t.Extensions())
} else {
// Set the maximized base language.
t, _ = language.Raw.Compose(base, s, t.Extensions())
}
// Find start index of the language tag.
start := 1 + sort.Search(len(tags)-1, func(i int) bool {
b, _, _ := tags[i+1].Raw()
return base.String() <= b.String()
})
if start < len(tags) {
if b, _, _ := tags[start].Raw(); b != base {
return 0
}
}
// Besides the base language, script and region, only the collation type and
// the custom variant defined in the 'u' extension are used to distinguish a
// locale.
// Strip all variants and extensions and add back the custom variant.
tdef, _ := language.Raw.Compose(t.Raw())
tdef, _ = tdef.SetTypeForKey("va", t.TypeForKey("va"))
// First search for a specialized collation type, if present.
try := []language.Tag{tdef}
if co := t.TypeForKey("co"); co != "" {
tco, _ := tdef.SetTypeForKey("co", co)
try = []language.Tag{tco, tdef}
}
for _, tx := range try {
for ; tx != language.Und; tx = parent(tx) {
for i, t := range tags[start:] {
if b, _, _ := t.Raw(); b != base {
break
}
if tx == t {
return start + i
}
}
}
}
return 0
}