--- /dev/null
+/*
+ Based on the "jsonpath" spec/concept.
+
+ http://goessner.net/articles/JsonPath/
+ https://code.google.com/p/json-path/
+*/
+
+package query
+
+import (
+ "fmt"
+)
+
+const maxInt = int(^uint(0) >> 1)
+
+type queryParser struct {
+ flow chan token
+ tokensBuffer []token
+ query *Query
+ union []pathFn
+ err error
+}
+
+type queryParserStateFn func() queryParserStateFn
+
+// Formats and panics an error message based on a token
+func (p *queryParser) parseError(tok *token, msg string, args ...interface{}) queryParserStateFn {
+ p.err = fmt.Errorf(tok.Position.String()+": "+msg, args...)
+ return nil // trigger parse to end
+}
+
+func (p *queryParser) run() {
+ for state := p.parseStart; state != nil; {
+ state = state()
+ }
+}
+
+func (p *queryParser) backup(tok *token) {
+ p.tokensBuffer = append(p.tokensBuffer, *tok)
+}
+
+func (p *queryParser) peek() *token {
+ if len(p.tokensBuffer) != 0 {
+ return &(p.tokensBuffer[0])
+ }
+
+ tok, ok := <-p.flow
+ if !ok {
+ return nil
+ }
+ p.backup(&tok)
+ return &tok
+}
+
+func (p *queryParser) lookahead(types ...tokenType) bool {
+ result := true
+ buffer := []token{}
+
+ for _, typ := range types {
+ tok := p.getToken()
+ if tok == nil {
+ result = false
+ break
+ }
+ buffer = append(buffer, *tok)
+ if tok.typ != typ {
+ result = false
+ break
+ }
+ }
+ // add the tokens back to the buffer, and return
+ p.tokensBuffer = append(p.tokensBuffer, buffer...)
+ return result
+}
+
+func (p *queryParser) getToken() *token {
+ if len(p.tokensBuffer) != 0 {
+ tok := p.tokensBuffer[0]
+ p.tokensBuffer = p.tokensBuffer[1:]
+ return &tok
+ }
+ tok, ok := <-p.flow
+ if !ok {
+ return nil
+ }
+ return &tok
+}
+
+func (p *queryParser) parseStart() queryParserStateFn {
+ tok := p.getToken()
+
+ if tok == nil || tok.typ == tokenEOF {
+ return nil
+ }
+
+ if tok.typ != tokenDollar {
+ return p.parseError(tok, "Expected '$' at start of expression")
+ }
+
+ return p.parseMatchExpr
+}
+
+// handle '.' prefix, '[]', and '..'
+func (p *queryParser) parseMatchExpr() queryParserStateFn {
+ tok := p.getToken()
+ switch tok.typ {
+ case tokenDotDot:
+ p.query.appendPath(&matchRecursiveFn{})
+ // nested parse for '..'
+ tok := p.getToken()
+ switch tok.typ {
+ case tokenKey:
+ p.query.appendPath(newMatchKeyFn(tok.val))
+ return p.parseMatchExpr
+ case tokenLeftBracket:
+ return p.parseBracketExpr
+ case tokenStar:
+ // do nothing - the recursive predicate is enough
+ return p.parseMatchExpr
+ }
+
+ case tokenDot:
+ // nested parse for '.'
+ tok := p.getToken()
+ switch tok.typ {
+ case tokenKey:
+ p.query.appendPath(newMatchKeyFn(tok.val))
+ return p.parseMatchExpr
+ case tokenStar:
+ p.query.appendPath(&matchAnyFn{})
+ return p.parseMatchExpr
+ }
+
+ case tokenLeftBracket:
+ return p.parseBracketExpr
+
+ case tokenEOF:
+ return nil // allow EOF at this stage
+ }
+ return p.parseError(tok, "expected match expression")
+}
+
+func (p *queryParser) parseBracketExpr() queryParserStateFn {
+ if p.lookahead(tokenInteger, tokenColon) {
+ return p.parseSliceExpr
+ }
+ if p.peek().typ == tokenColon {
+ return p.parseSliceExpr
+ }
+ return p.parseUnionExpr
+}
+
+func (p *queryParser) parseUnionExpr() queryParserStateFn {
+ var tok *token
+
+ // this state can be traversed after some sub-expressions
+ // so be careful when setting up state in the parser
+ if p.union == nil {
+ p.union = []pathFn{}
+ }
+
+loop: // labeled loop for easy breaking
+ for {
+ if len(p.union) > 0 {
+ // parse delimiter or terminator
+ tok = p.getToken()
+ switch tok.typ {
+ case tokenComma:
+ // do nothing
+ case tokenRightBracket:
+ break loop
+ default:
+ return p.parseError(tok, "expected ',' or ']', not '%s'", tok.val)
+ }
+ }
+
+ // parse sub expression
+ tok = p.getToken()
+ switch tok.typ {
+ case tokenInteger:
+ p.union = append(p.union, newMatchIndexFn(tok.Int()))
+ case tokenKey:
+ p.union = append(p.union, newMatchKeyFn(tok.val))
+ case tokenString:
+ p.union = append(p.union, newMatchKeyFn(tok.val))
+ case tokenQuestion:
+ return p.parseFilterExpr
+ default:
+ return p.parseError(tok, "expected union sub expression, not '%s', %d", tok.val, len(p.union))
+ }
+ }
+
+ // if there is only one sub-expression, use that instead
+ if len(p.union) == 1 {
+ p.query.appendPath(p.union[0])
+ } else {
+ p.query.appendPath(&matchUnionFn{p.union})
+ }
+
+ p.union = nil // clear out state
+ return p.parseMatchExpr
+}
+
+func (p *queryParser) parseSliceExpr() queryParserStateFn {
+ // init slice to grab all elements
+ start, end, step := 0, maxInt, 1
+
+ // parse optional start
+ tok := p.getToken()
+ if tok.typ == tokenInteger {
+ start = tok.Int()
+ tok = p.getToken()
+ }
+ if tok.typ != tokenColon {
+ return p.parseError(tok, "expected ':'")
+ }
+
+ // parse optional end
+ tok = p.getToken()
+ if tok.typ == tokenInteger {
+ end = tok.Int()
+ tok = p.getToken()
+ }
+ if tok.typ == tokenRightBracket {
+ p.query.appendPath(newMatchSliceFn(start, end, step))
+ return p.parseMatchExpr
+ }
+ if tok.typ != tokenColon {
+ return p.parseError(tok, "expected ']' or ':'")
+ }
+
+ // parse optional step
+ tok = p.getToken()
+ if tok.typ == tokenInteger {
+ step = tok.Int()
+ if step < 0 {
+ return p.parseError(tok, "step must be a positive value")
+ }
+ tok = p.getToken()
+ }
+ if tok.typ != tokenRightBracket {
+ return p.parseError(tok, "expected ']'")
+ }
+
+ p.query.appendPath(newMatchSliceFn(start, end, step))
+ return p.parseMatchExpr
+}
+
+func (p *queryParser) parseFilterExpr() queryParserStateFn {
+ tok := p.getToken()
+ if tok.typ != tokenLeftParen {
+ return p.parseError(tok, "expected left-parenthesis for filter expression")
+ }
+ tok = p.getToken()
+ if tok.typ != tokenKey && tok.typ != tokenString {
+ return p.parseError(tok, "expected key or string for filter function name")
+ }
+ name := tok.val
+ tok = p.getToken()
+ if tok.typ != tokenRightParen {
+ return p.parseError(tok, "expected right-parenthesis for filter expression")
+ }
+ p.union = append(p.union, newMatchFilterFn(name, tok.Position))
+ return p.parseUnionExpr
+}
+
+func parseQuery(flow chan token) (*Query, error) {
+ parser := &queryParser{
+ flow: flow,
+ tokensBuffer: []token{},
+ query: newQuery(),
+ }
+ parser.run()
+ return parser.query, parser.err
+}
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