New rule syntax

Co-authored-by: jbdoumenjou <jb.doumenjou@gmail.com>

rules/parser.go

@@ -0,0 +1,97 @@
+package rules
+
+import (
+	"strings"
+
+	"github.com/pkg/errors"
+	"github.com/vulcand/predicate"
+)
+
+type treeBuilder func() *tree
+
+// ParseDomains extract domains from rule
+func ParseDomains(rule string) ([]string, error) {
+	parser, err := newParser()
+	if err != nil {
+		return nil, err
+	}
+
+	parse, err := parser.Parse(rule)
+	if err != nil {
+		return nil, err
+	}
+
+	buildTree, ok := parse.(treeBuilder)
+	if !ok {
+		return nil, errors.New("cannot parse")
+	}
+
+	return lower(parseDomain(buildTree())), nil
+}
+
+func lower(slice []string) []string {
+	var lowerStrings []string
+	for _, value := range slice {
+		lowerStrings = append(lowerStrings, strings.ToLower(value))
+	}
+	return lowerStrings
+}
+
+func parseDomain(tree *tree) []string {
+	switch tree.matcher {
+	case "and", "or":
+		return append(parseDomain(tree.ruleLeft), parseDomain(tree.ruleRight)...)
+	case "Host":
+		return tree.value
+	default:
+		return nil
+	}
+}
+
+func andFunc(left, right treeBuilder) treeBuilder {
+	return func() *tree {
+		return &tree{
+			matcher:   "and",
+			ruleLeft:  left(),
+			ruleRight: right(),
+		}
+	}
+}
+
+func orFunc(left, right treeBuilder) treeBuilder {
+	return func() *tree {
+		return &tree{
+			matcher:   "or",
+			ruleLeft:  left(),
+			ruleRight: right(),
+		}
+	}
+}
+
+func newParser() (predicate.Parser, error) {
+	parserFuncs := make(map[string]interface{})
+
+	for matcherName := range funcs {
+		matcherName := matcherName
+		fn := func(value ...string) treeBuilder {
+			return func() *tree {
+				return &tree{
+					matcher: matcherName,
+					value:   value,
+				}
+			}
+		}
+		parserFuncs[matcherName] = fn
+		parserFuncs[strings.ToLower(matcherName)] = fn
+		parserFuncs[strings.ToUpper(matcherName)] = fn
+		parserFuncs[strings.Title(strings.ToLower(matcherName))] = fn
+	}
+
+	return predicate.NewParser(predicate.Def{
+		Operators: predicate.Operators{
+			AND: andFunc,
+			OR:  orFunc,
+		},
+		Functions: parserFuncs,
+	})
+}