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// -*- Mode: Go; indent-tabs-mode: t -*-
/*
* Copyright (C) 2024 Canonical Ltd
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 3 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
package patterns
import (
"errors"
"fmt"
)
func parse(tokens []token) (renderNode, error) {
tr := tokenReader{
tokens: tokens,
}
return parseSeq(&tr)
}
func parseSeq(tr *tokenReader) (renderNode, error) {
var s seq
seqLoop:
for {
t := tr.peek()
switch t.tType {
case tokEOF:
break seqLoop
case tokBraceOpen:
inner, err := parseAlt(tr)
if err != nil {
return nil, err
}
s = append(s, inner)
case tokBraceClose:
if tr.depth > 0 {
break seqLoop
}
tr.token()
return nil, errors.New("unmatched '}' character")
case tokText:
tr.token()
s = append(s, literal(t.text))
case tokComma:
if tr.depth > 0 {
break seqLoop
}
tr.token() // discard, we get called in a loop
s = append(s, literal(","))
}
}
return s.optimize()
}
func parseAlt(tr *tokenReader) (renderNode, error) {
var a alt
if t := tr.token(); t.tType != tokBraceOpen {
// Should not occur, caller should call parseAlt on peeking '{'
return nil, fmt.Errorf("internal error: expected '{' at start of alt, but got %v", t)
}
tr.depth++
defer func() {
tr.depth--
}()
if tr.depth >= maxExpandedPatterns {
return nil, fmt.Errorf("nested group depth exceeded maximum number of expanded path patterns (%d)", maxExpandedPatterns)
}
altLoop:
for {
item, err := parseSeq(tr)
if err != nil {
return nil, err
}
a = append(a, item)
switch t := tr.token(); t.tType {
case tokBraceClose:
break altLoop
case tokComma:
continue
case tokEOF:
return nil, errors.New("unmatched '{' character")
default:
return nil, fmt.Errorf("unexpected token %v when parsing alt", t)
}
}
return a.optimize()
}
type tokenReader struct {
tokens []token
depth int
}
func (tr tokenReader) peek() token {
if len(tr.tokens) == 0 {
return token{tType: tokEOF}
}
return tr.tokens[0]
}
func (tr *tokenReader) token() token {
t := tr.peek()
if t.tType != tokEOF {
tr.tokens = tr.tokens[1:]
}
return t
}
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