1// Copyright 2013 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
5package language
6
7import (
8	"errors"
9	"strconv"
10	"strings"
11
12	"golang.org/x/text/internal/language"
13)
14
15// ValueError is returned by any of the parsing functions when the
16// input is well-formed but the respective subtag is not recognized
17// as a valid value.
18type ValueError interface {
19	error
20
21	// Subtag returns the subtag for which the error occurred.
22	Subtag() string
23}
24
25// Parse parses the given BCP 47 string and returns a valid Tag. If parsing
26// failed it returns an error and any part of the tag that could be parsed.
27// If parsing succeeded but an unknown value was found, it returns
28// ValueError. The Tag returned in this case is just stripped of the unknown
29// value. All other values are preserved. It accepts tags in the BCP 47 format
30// and extensions to this standard defined in
31// https://www.unicode.org/reports/tr35/#Unicode_Language_and_Locale_Identifiers.
32// The resulting tag is canonicalized using the default canonicalization type.
33func Parse(s string) (t Tag, err error) {
34	return Default.Parse(s)
35}
36
37// Parse parses the given BCP 47 string and returns a valid Tag. If parsing
38// failed it returns an error and any part of the tag that could be parsed.
39// If parsing succeeded but an unknown value was found, it returns
40// ValueError. The Tag returned in this case is just stripped of the unknown
41// value. All other values are preserved. It accepts tags in the BCP 47 format
42// and extensions to this standard defined in
43// https://www.unicode.org/reports/tr35/#Unicode_Language_and_Locale_Identifiers.
44// The resulting tag is canonicalized using the canonicalization type c.
45func (c CanonType) Parse(s string) (t Tag, err error) {
46	tt, err := language.Parse(s)
47	if err != nil {
48		return makeTag(tt), err
49	}
50	tt, changed := canonicalize(c, tt)
51	if changed {
52		tt.RemakeString()
53	}
54	return makeTag(tt), err
55}
56
57// Compose creates a Tag from individual parts, which may be of type Tag, Base,
58// Script, Region, Variant, []Variant, Extension, []Extension or error. If a
59// Base, Script or Region or slice of type Variant or Extension is passed more
60// than once, the latter will overwrite the former. Variants and Extensions are
61// accumulated, but if two extensions of the same type are passed, the latter
62// will replace the former. For -u extensions, though, the key-type pairs are
63// added, where later values overwrite older ones. A Tag overwrites all former
64// values and typically only makes sense as the first argument. The resulting
65// tag is returned after canonicalizing using the Default CanonType. If one or
66// more errors are encountered, one of the errors is returned.
67func Compose(part ...interface{}) (t Tag, err error) {
68	return Default.Compose(part...)
69}
70
71// Compose creates a Tag from individual parts, which may be of type Tag, Base,
72// Script, Region, Variant, []Variant, Extension, []Extension or error. If a
73// Base, Script or Region or slice of type Variant or Extension is passed more
74// than once, the latter will overwrite the former. Variants and Extensions are
75// accumulated, but if two extensions of the same type are passed, the latter
76// will replace the former. For -u extensions, though, the key-type pairs are
77// added, where later values overwrite older ones. A Tag overwrites all former
78// values and typically only makes sense as the first argument. The resulting
79// tag is returned after canonicalizing using CanonType c. If one or more errors
80// are encountered, one of the errors is returned.
81func (c CanonType) Compose(part ...interface{}) (t Tag, err error) {
82	var b language.Builder
83	if err = update(&b, part...); err != nil {
84		return und, err
85	}
86	b.Tag, _ = canonicalize(c, b.Tag)
87	return makeTag(b.Make()), err
88}
89
90var errInvalidArgument = errors.New("invalid Extension or Variant")
91
92func update(b *language.Builder, part ...interface{}) (err error) {
93	for _, x := range part {
94		switch v := x.(type) {
95		case Tag:
96			b.SetTag(v.tag())
97		case Base:
98			b.Tag.LangID = v.langID
99		case Script:
100			b.Tag.ScriptID = v.scriptID
101		case Region:
102			b.Tag.RegionID = v.regionID
103		case Variant:
104			if v.variant == "" {
105				err = errInvalidArgument
106				break
107			}
108			b.AddVariant(v.variant)
109		case Extension:
110			if v.s == "" {
111				err = errInvalidArgument
112				break
113			}
114			b.SetExt(v.s)
115		case []Variant:
116			b.ClearVariants()
117			for _, v := range v {
118				b.AddVariant(v.variant)
119			}
120		case []Extension:
121			b.ClearExtensions()
122			for _, e := range v {
123				b.SetExt(e.s)
124			}
125		// TODO: support parsing of raw strings based on morphology or just extensions?
126		case error:
127			if v != nil {
128				err = v
129			}
130		}
131	}
132	return
133}
134
135var errInvalidWeight = errors.New("ParseAcceptLanguage: invalid weight")
136
137// ParseAcceptLanguage parses the contents of an Accept-Language header as
138// defined in http://www.ietf.org/rfc/rfc2616.txt and returns a list of Tags and
139// a list of corresponding quality weights. It is more permissive than RFC 2616
140// and may return non-nil slices even if the input is not valid.
141// The Tags will be sorted by highest weight first and then by first occurrence.
142// Tags with a weight of zero will be dropped. An error will be returned if the
143// input could not be parsed.
144func ParseAcceptLanguage(s string) (tag []Tag, q []float32, err error) {
145	var entry string
146	for s != "" {
147		if entry, s = split(s, ','); entry == "" {
148			continue
149		}
150
151		entry, weight := split(entry, ';')
152
153		// Scan the language.
154		t, err := Parse(entry)
155		if err != nil {
156			id, ok := acceptFallback[entry]
157			if !ok {
158				return nil, nil, err
159			}
160			t = makeTag(language.Tag{LangID: id})
161		}
162
163		// Scan the optional weight.
164		w := 1.0
165		if weight != "" {
166			weight = consume(weight, 'q')
167			weight = consume(weight, '=')
168			// consume returns the empty string when a token could not be
169			// consumed, resulting in an error for ParseFloat.
170			if w, err = strconv.ParseFloat(weight, 32); err != nil {
171				return nil, nil, errInvalidWeight
172			}
173			// Drop tags with a quality weight of 0.
174			if w <= 0 {
175				continue
176			}
177		}
178
179		tag = append(tag, t)
180		q = append(q, float32(w))
181	}
182	sortStable(&tagSort{tag, q})
183	return tag, q, nil
184}
185
186// consume removes a leading token c from s and returns the result or the empty
187// string if there is no such token.
188func consume(s string, c byte) string {
189	if s == "" || s[0] != c {
190		return ""
191	}
192	return strings.TrimSpace(s[1:])
193}
194
195func split(s string, c byte) (head, tail string) {
196	if i := strings.IndexByte(s, c); i >= 0 {
197		return strings.TrimSpace(s[:i]), strings.TrimSpace(s[i+1:])
198	}
199	return strings.TrimSpace(s), ""
200}
201
202// Add hack mapping to deal with a small number of cases that occur
203// in Accept-Language (with reasonable frequency).
204var acceptFallback = map[string]language.Language{
205	"english": _en,
206	"deutsch": _de,
207	"italian": _it,
208	"french":  _fr,
209	"*":       _mul, // defined in the spec to match all languages.
210}
211
212type tagSort struct {
213	tag []Tag
214	q   []float32
215}
216
217func (s *tagSort) Len() int {
218	return len(s.q)
219}
220
221func (s *tagSort) Less(i, j int) bool {
222	return s.q[i] > s.q[j]
223}
224
225func (s *tagSort) Swap(i, j int) {
226	s.tag[i], s.tag[j] = s.tag[j], s.tag[i]
227	s.q[i], s.q[j] = s.q[j], s.q[i]
228}
229