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// Copyright 2016 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package android
import (
"fmt"
"strings"
"unicode"
)
// Expand substitutes $() variables in a string
// $(var) is passed to Expander(var)
// $$ is converted to $
func Expand(s string, mapping func(string) (string, error)) (string, error) {
// based on os.Expand
buf := make([]byte, 0, 2*len(s))
i := 0
for j := 0; j < len(s); j++ {
if s[j] == '$' {
if j+1 >= len(s) {
return "", fmt.Errorf("expected character after '$'")
}
buf = append(buf, s[i:j]...)
value, w, err := getMapping(s[j+1:], mapping)
if err != nil {
return "", err
}
buf = append(buf, value...)
j += w
i = j + 1
}
}
return string(buf) + s[i:], nil
}
func getMapping(s string, mapping func(string) (string, error)) (string, int, error) {
switch s[0] {
case '(':
// Scan to closing brace
for i := 1; i < len(s); i++ {
if s[i] == ')' {
ret, err := mapping(strings.TrimSpace(s[1:i]))
return ret, i + 1, err
}
}
return "", len(s), fmt.Errorf("missing )")
case '$':
return "$$", 1, nil
default:
i := strings.IndexFunc(s, unicode.IsSpace)
if i == 0 {
return "", 0, fmt.Errorf("unexpected character '%c' after '$'", s[0])
} else if i == -1 {
i = len(s)
}
return "", 0, fmt.Errorf("expected '(' after '$', did you mean $(%s)?", s[:i])
}
}
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