Introduce query language (resembling reprepro syntax).

query/lex.go

@@ -0,0 +1,211 @@
+package query
+
+import (
+	"fmt"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+// itemType identifies the type of lex items.
+type itemType int
+
+const eof = -1
+
+const (
+	itemError itemType = iota // error occurred;
+	// value is text of error
+	itemEOF
+	itemLeftParen  // (
+	itemRightParen // )
+	itemOr         // |
+	itemAnd        // ,
+	itemNot        // !
+	itemLt         // <<
+	itemLtEq       // <=, <
+	itemGt         // >>
+	itemGtEq       // >=, >
+	itemEq         // =
+	itemPatMatch   // %
+	itemRegexp     // ~
+	itemString
+)
+
+// item represents a token returned from the scanner.
+type item struct {
+	typ itemType // Type, such as itemNumber.
+	val string   // Value, such as "23.2".
+}
+
+func (i item) String() string {
+	if i.typ == itemString {
+		return fmt.Sprintf("%#v", i.val)
+	}
+	if i.typ == itemEOF {
+		return "<EOL>"
+	}
+	return i.val
+}
+
+// stateFn represents the state of the scanner
+// as a function that returns the next state.
+type stateFn func(*lexer) stateFn
+
+// lexer holds the state of the scanner.
+type lexer struct {
+	name  string    // used only for error reports.
+	input string    // the string being scanned.
+	start int       // start position of this item.
+	pos   int       // current position in the input.
+	width int       // width of last rune read from input.
+	items chan item // channel of scanned items.
+	last  item
+}
+
+func lex(name, input string) (*lexer, chan item) {
+	l := &lexer{
+		name:  name,
+		input: input,
+		items: make(chan item),
+	}
+	go l.run() // Concurrently run state machine.
+	return l, l.items
+}
+
+// emit passes an item back to the client.
+func (l *lexer) emit(t itemType) {
+	l.items <- item{t, l.input[l.start:l.pos]}
+	l.start = l.pos
+}
+
+// run lexes the input by executing state functions until
+// the state is nil.
+func (l *lexer) run() {
+	for state := lexMain; state != nil; {
+		state = state(l)
+	}
+	close(l.items) // No more tokens will be delivered.
+}
+
+// next returns the next rune in the input.
+func (l *lexer) next() (r rune) {
+	if l.pos >= len(l.input) {
+		l.width = 0
+		return eof
+	}
+	r, l.width =
+		utf8.DecodeRuneInString(l.input[l.pos:])
+	l.pos += l.width
+	return r
+}
+
+// ignore skips over the pending input before this point.
+func (l *lexer) ignore() {
+	l.start = l.pos
+}
+
+// backup steps back one rune.
+// Can be called only once per call of next.
+func (l *lexer) backup() {
+	l.pos -= l.width
+}
+
+// peek returns but does not consume
+// the next rune in the input.
+func (l *lexer) peek() rune {
+	r := l.next()
+	l.backup()
+	return r
+}
+
+func (l *lexer) Current() item {
+	if l.last.typ == 0 {
+		l.last = <-l.items
+	}
+
+	return l.last
+}
+
+func (l *lexer) Consume() {
+	l.last = <-l.items
+}
+
+// error returns an error token and terminates the scan
+// by passing back a nil pointer that will be the next
+// state, terminating l.run.
+func (l *lexer) errorf(format string, args ...interface{}) stateFn {
+	l.items <- item{
+		itemError,
+		fmt.Sprintf(format, args...),
+	}
+	return nil
+}
+
+func lexMain(l *lexer) stateFn {
+	switch r := l.next(); {
+	case r == eof:
+		l.emit(itemEOF)
+		return nil
+	case unicode.IsSpace(r):
+		l.ignore()
+	case r == '(':
+		l.emit(itemLeftParen)
+	case r == ')':
+		l.emit(itemRightParen)
+	case r == '|':
+		l.emit(itemOr)
+	case r == ',':
+		l.emit(itemAnd)
+	case r == '!':
+		l.emit(itemNot)
+	case r == '<':
+		r2 := l.next()
+		if r2 == '<' {
+			l.emit(itemLt)
+		} else if r2 == '=' {
+			l.emit(itemLtEq)
+		} else {
+			l.backup()
+			l.emit(itemLtEq)
+		}
+	case r == '>':
+		r2 := l.next()
+		if r2 == '>' {
+			l.emit(itemGt)
+		} else if r2 == '=' {
+			l.emit(itemGtEq)
+		} else {
+			l.backup()
+			l.emit(itemGtEq)
+		}
+	case r == '=':
+		l.emit(itemEq)
+	case r == '%':
+		l.emit(itemPatMatch)
+	case r == '~':
+		l.emit(itemRegexp)
+	default:
+		l.backup()
+		return lexString
+	}
+
+	return lexMain
+}
+
+func lexString(l *lexer) stateFn {
+	for {
+		r := l.next()
+		if unicode.IsSpace(r) || strings.IndexRune("()|,!<>=%~", r) > 0 {
+			l.backup()
+			l.emit(itemString)
+			return lexMain(l)
+		}
+
+		if r == eof {
+			l.emit(itemString)
+			l.emit(itemEOF)
+			return nil
+		}
+	}
+
+}