Add lexer for reqlog search

pkg/reqlog/lexer.go

@@ -0,0 +1,144 @@
+package reqlog
+
+import (
+	"unicode"
+
+	"github.com/db47h/lex"
+	"github.com/db47h/lex/state"
+)
+
+const (
+	tokEOF = iota
+	tokString
+	tokOpNot
+	tokOpAnd
+	tokOpOr
+	tokOpEq
+	tokOpNeq
+	tokOpGt
+	tokOpGteq
+	tokOpLt
+	tokOpLteq
+	tokOpHas
+	tokOpRe
+	tokOpNre
+	tokParenOpen
+	tokParenClose
+)
+
+type lexItem struct {
+	token lex.Token
+	value string
+}
+
+func lexQuery(s *lex.State) lex.StateFn {
+	str := lexString()
+	quotedString := state.QuotedString(tokString)
+
+	return func(s *lex.State) lex.StateFn {
+		r := s.Next()
+		pos := s.Pos()
+		switch r {
+		case lex.EOF:
+			s.Emit(pos, tokEOF, nil)
+			return nil
+		case '"':
+			return quotedString
+		case '=':
+			if next := s.Next(); next == '~' {
+				s.Emit(pos, tokOpRe, nil)
+			} else {
+				s.Backup()
+				s.Emit(pos, tokOpEq, nil)
+			}
+			return nil
+		case '!':
+			switch next := s.Next(); next {
+			case '=':
+				s.Emit(pos, tokOpNeq, nil)
+				return nil
+			case '~':
+				s.Emit(pos, tokOpNre, nil)
+				return nil
+			default:
+				s.Backup()
+			}
+		case '>':
+			if next := s.Next(); next == '=' {
+				s.Emit(pos, tokOpGteq, nil)
+			} else {
+				s.Backup()
+				s.Emit(pos, tokOpGt, nil)
+			}
+			return nil
+		case '<':
+			if next := s.Next(); next == '=' {
+				s.Emit(pos, tokOpLteq, nil)
+			} else {
+				s.Backup()
+				s.Emit(pos, tokOpLt, nil)
+			}
+			return nil
+		case ':':
+			s.Emit(pos, tokOpHas, nil)
+			return nil
+		case '(':
+			s.Emit(pos, tokParenOpen, nil)
+			return nil
+		case ')':
+			s.Emit(pos, tokParenClose, nil)
+			return nil
+		}
+
+		switch {
+		case unicode.IsSpace(r):
+			// Absorb spaces.
+			for r = s.Next(); unicode.IsSpace(r); r = s.Next() {
+			}
+			s.Backup()
+			return nil
+		default:
+			return str
+		}
+	}
+}
+
+func lexString() lex.StateFn {
+	// Preallocate a buffer to store the value. It will end-up being at
+	// least as large as the largest value scanned.
+	b := make([]rune, 0, 64)
+
+	isStringChar := func(r rune) bool {
+		switch r {
+		case '=', '!', '<', '>', ':', '(', ')':
+			return false
+		}
+		return !(unicode.IsSpace(r) || r == lex.EOF)
+	}
+
+	return func(l *lex.State) lex.StateFn {
+		pos := l.Pos()
+		// Reset buffer and add first char.
+		b = append(b[:0], l.Current())
+		// Read identifier.
+		for r := l.Next(); isStringChar(r); r = l.Next() {
+			b = append(b, r)
+		}
+		// The character returned by the last call to `l.Next` is not part of
+		// the value. Undo it.
+		l.Backup()
+
+		switch {
+		case string(b) == "NOT":
+			l.Emit(pos, tokOpNot, nil)
+		case string(b) == "AND":
+			l.Emit(pos, tokOpAnd, nil)
+		case string(b) == "OR":
+			l.Emit(pos, tokOpOr, nil)
+		default:
+			l.Emit(pos, tokString, string(b))
+		}
+
+		return nil
+	}
+}