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// Copyright 2022 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT
package vars
import (
"fmt"
"strings"
"unicode"
"unicode/utf8"
)
// ErrWrongSyntax represents a wrong syntax with a template
type ErrWrongSyntax struct {
Template string
}
func (err ErrWrongSyntax) Error() string {
return fmt.Sprintf("wrong syntax found in %s", err.Template)
}
// ErrVarMissing represents an error that no matched variable
type ErrVarMissing struct {
Template string
Var string
}
func (err ErrVarMissing) Error() string {
return fmt.Sprintf("the variable %s is missing for %s", err.Var, err.Template)
}
// Expand replaces all variables like {var} by `vars` map, it always returns the expanded string regardless of errors
// if error occurs, the error part doesn't change and is returned as it is.
func Expand(template string, vars map[string]string) (string, error) {
// in the future, if necessary, we can introduce some escape-char,
// for example: it will use `#' as a reversed char, templates will use `{#{}` to do escape and output char '{'.
var buf strings.Builder
var err error
posBegin := 0
strLen := len(template)
for posBegin < strLen {
// find the next `{`
pos := strings.IndexByte(template[posBegin:], '{')
if pos == -1 {
buf.WriteString(template[posBegin:])
break
}
// copy texts between vars
buf.WriteString(template[posBegin : posBegin+pos])
// find the var between `{` and `}`/end
posBegin += pos
posEnd := posBegin + 1
for posEnd < strLen {
if template[posEnd] == '}' {
posEnd++
break
} // in the future, if we need to support escape chars, we can do: if (isEscapeChar) { posEnd+=2 }
posEnd++
}
// the var part, it can be "{", "{}", "{..." or or "{...}"
part := template[posBegin:posEnd]
posBegin = posEnd
if part == "{}" || part[len(part)-1] != '}' {
// treat "{}" or "{..." as error
err = ErrWrongSyntax{Template: template}
buf.WriteString(part)
} else {
// now we get a valid key "{...}"
key := part[1 : len(part)-1]
keyFirst, _ := utf8.DecodeRuneInString(key)
if unicode.IsSpace(keyFirst) || unicode.IsPunct(keyFirst) || unicode.IsControl(keyFirst) {
// the if key doesn't start with a letter, then we do not treat it as a var now
buf.WriteString(part)
} else {
// look up in the map
if val, ok := vars[key]; ok {
buf.WriteString(val)
} else {
// write the non-existing var as it is
buf.WriteString(part)
err = ErrVarMissing{Template: template, Var: key}
}
}
}
}
return buf.String(), err
}
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