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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package template

import (
        "bytes"
        "fmt"
        "strings"
        "unicode/utf8"
)

// htmlNospaceEscaper escapes for inclusion in unquoted attribute values.
func htmlNospaceEscaper(args ...interface{}) string {
        s, t := stringify(args...)
        if t == contentTypeHTML {
                return htmlReplacer(stripTags(s), htmlNospaceNormReplacementTable, false)
        }
        return htmlReplacer(s, htmlNospaceReplacementTable, false)
}

// attrEscaper escapes for inclusion in quoted attribute values.
func attrEscaper(args ...interface{}) string {
        s, t := stringify(args...)
        if t == contentTypeHTML {
                return htmlReplacer(stripTags(s), htmlNormReplacementTable, true)
        }
        return htmlReplacer(s, htmlReplacementTable, true)
}

// rcdataEscaper escapes for inclusion in an RCDATA element body.
func rcdataEscaper(args ...interface{}) string {
        s, t := stringify(args...)
        if t == contentTypeHTML {
                return htmlReplacer(s, htmlNormReplacementTable, true)
        }
        return htmlReplacer(s, htmlReplacementTable, true)
}

// htmlEscaper escapes for inclusion in HTML text.
func htmlEscaper(args ...interface{}) string {
        s, t := stringify(args...)
        if t == contentTypeHTML {
                return s
        }
        return htmlReplacer(s, htmlReplacementTable, true)
}

// htmlReplacementTable contains the runes that need to be escaped
// inside a quoted attribute value or in a text node.
var htmlReplacementTable = []string{
        // http://www.w3.org/TR/html5/tokenization.html#attribute-value-unquoted-state: "
        // U+0000 NULL Parse error. Append a U+FFFD REPLACEMENT
        // CHARACTER character to the current attribute's value.
        // "
        // and similarly
        // http://www.w3.org/TR/html5/tokenization.html#before-attribute-value-state
        0:    "\uFFFD",
        '"':  """,
        '&':  "&",
        '\'': "'",
        '+':  "+",
        '<':  "&lt;",
        '>':  "&gt;",
}

// htmlNormReplacementTable is like htmlReplacementTable but without '&' to
// avoid over-encoding existing entities.
var htmlNormReplacementTable = []string{
        0:    "\uFFFD",
        '"':  "&#34;",
        '\'': "&#39;",
        '+':  "&#43;",
        '<':  "&lt;",
        '>':  "&gt;",
}

// htmlNospaceReplacementTable contains the runes that need to be escaped
// inside an unquoted attribute value.
// The set of runes escaped is the union of the HTML specials and
// those determined by running the JS below in browsers:
// <div id=d></div>
// <script>(function () {
// var a = [], d = document.getElementById("d"), i, c, s;
// for (i = 0; i < 0x10000; ++i) {
//   c = String.fromCharCode(i);
//   d.innerHTML = "<span title=" + c + "lt" + c + "></span>"
//   s = d.getElementsByTagName("SPAN")[0];
//   if (!s || s.title !== c + "lt" + c) { a.push(i.toString(16)); }
// }
// document.write(a.join(", "));
// })()</script>
var htmlNospaceReplacementTable = []string{
        0:    "&#xfffd;",
        '\t': "&#9;",
        '\n': "&#10;",
        '\v': "&#11;",
        '\f': "&#12;",
        '\r': "&#13;",
        ' ':  "&#32;",
        '"':  "&#34;",
        '&':  "&amp;",
        '\'': "&#39;",
        '+':  "&#43;",
        '<':  "&lt;",
        '=':  "&#61;",
        '>':  "&gt;",
        // A parse error in the attribute value (unquoted) and 
        // before attribute value states.
        // Treated as a quoting character by IE.
        '`': "&#96;",
}

// htmlNospaceNormReplacementTable is like htmlNospaceReplacementTable but
// without '&' to avoid over-encoding existing entities.
var htmlNospaceNormReplacementTable = []string{
        0:    "&#xfffd;",
        '\t': "&#9;",
        '\n': "&#10;",
        '\v': "&#11;",
        '\f': "&#12;",
        '\r': "&#13;",
        ' ':  "&#32;",
        '"':  "&#34;",
        '\'': "&#39;",
        '+':  "&#43;",
        '<':  "&lt;",
        '=':  "&#61;",
        '>':  "&gt;",
        // A parse error in the attribute value (unquoted) and 
        // before attribute value states.
        // Treated as a quoting character by IE.
        '`': "&#96;",
}

// htmlReplacer returns s with runes replaced acccording to replacementTable
// and when badRunes is true, certain bad runes are allowed through unescaped.
func htmlReplacer(s string, replacementTable []string, badRunes bool) string {
        written, b := 0, new(bytes.Buffer)
        for i, r := range s {
                if int(r) < len(replacementTable) {
                        if repl := replacementTable[r]; len(repl) != 0 {
                                b.WriteString(s[written:i])
                                b.WriteString(repl)
                                // Valid as long as replacementTable doesn't 
                                // include anything above 0x7f.
                                written = i + utf8.RuneLen(r)
                        }
                } else if badRunes {
                        // No-op.
                        // IE does not allow these ranges in unquoted attrs.
                } else if 0xfdd0 <= r && r <= 0xfdef || 0xfff0 <= r && r <= 0xffff {
                        fmt.Fprintf(b, "%s&#x%x;", s[written:i], r)
                        written = i + utf8.RuneLen(r)
                }
        }
        if written == 0 {
                return s
        }
        b.WriteString(s[written:])
        return b.String()
}

// stripTags takes a snippet of HTML and returns only the text content.
// For example, `<b>&iexcl;Hi!</b> <script>...</script>` -> `&iexcl;Hi! `.
func stripTags(html string) string {
        var b bytes.Buffer
        s, c, i, allText := []byte(html), context{}, 0, true
        // Using the transition funcs helps us avoid mangling
        // `<div title="1>2">` or `I <3 Ponies!`.
        for i != len(s) {
                if c.delim == delimNone {
                        st := c.state
                        // Use RCDATA instead of parsing into JS or CSS styles.
                        if c.element != elementNone && !isInTag(st) {
                                st = stateRCDATA
                        }
                        d, nread := transitionFunc[st](c, s[i:])
                        i1 := i + nread
                        if c.state == stateText || c.state == stateRCDATA {
                                // Emit text up to the start of the tag or comment.
                                j := i1
                                if d.state != c.state {
                                        for j1 := j - 1; j1 >= i; j1-- {
                                                if s[j1] == '<' {
                                                        j = j1
                                                        break
                                                }
                                        }
                                }
                                b.Write(s[i:j])
                        } else {
                                allText = false
                        }
                        c, i = d, i1
                        continue
                }
                i1 := i + bytes.IndexAny(s[i:], delimEnds[c.delim])
                if i1 < i {
                        break
                }
                if c.delim != delimSpaceOrTagEnd {
                        // Consume any quote.
                        i1++
                }
                c, i = context{state: stateTag, element: c.element}, i1
        }
        if allText {
                return html
        } else if c.state == stateText || c.state == stateRCDATA {
                b.Write(s[i:])
        }
        return b.String()
}

// htmlNameFilter accepts valid parts of an HTML attribute or tag name or
// a known-safe HTML attribute.
func htmlNameFilter(args ...interface{}) string {
        s, t := stringify(args...)
        if t == contentTypeHTMLAttr {
                return s
        }
        if len(s) == 0 {
                // Avoid violation of structure preservation.
                // <input checked {{.K}}={{.V}}>.
                // Without this, if .K is empty then .V is the value of
                // checked, but otherwise .V is the value of the attribute
                // named .K.
                return filterFailsafe
        }
        s = strings.ToLower(s)
        if t := attrType(s); t != contentTypePlain {
                // TODO: Split attr and element name part filters so we can whitelist
                // attributes.
                return filterFailsafe
        }
        for _, r := range s {
                switch {
                case '0' <= r && r <= '9':
                case 'a' <= r && r <= 'z':
                default:
                        return filterFailsafe
                }
        }
        return s
}

// commentEscaper returns the empty string regardless of input.
// Comment content does not correspond to any parsed structure or
// human-readable content, so the simplest and most secure policy is to drop
// content interpolated into comments.
// This approach is equally valid whether or not static comment content is
// removed from the template.
func commentEscaper(args ...interface{}) string {
        return ""
}