start adding more complex filter support

operator.go

@@ -0,0 +1,110 @@
+package arango
+
+import (
+	"errors"
+)
+
+// Operator error.
+var (
+	ErrInvalidOperator = errors.New("invalid operator")
+)
+
+var (
+	operators = map[string]string{
+		// Idempotent
+		"==":       "==",
+		"!=":       "!=",
+		">":        ">",
+		">=":       ">=",
+		"<":        "<",
+		"<=":       "<=",
+		"IN":       "IN",
+		"NOT IN":   "NOT IN",
+		"LIKE":     "LIKE",
+		"NOT LIKE": "NOT LIKE",
+
+		// Compatible with Filter.Operator in github.com/recipeer/go/qs
+		"eq":       "==",
+		"neq":      "!=",
+		"gt":       ">",
+		"gte":      ">=",
+		"lt":       "<",
+		"lte":      "<=",
+		"in":       "IN",
+		"not in":   "NOT IN",
+		"like":     "LIKE",
+		"not like": "NOT LIKE",
+	}
+
+	arrayOperators  = []string{"IN", "NOT IN"}
+	boolOperators   = []string{"==", "!="}
+	numberOperators = []string{"==", "!=", ">", ">=", "<", "<="}
+	stringOperators = []string{"==", "!=", ">", ">=", "<", "<=", "LIKE", "NOT LIKE"}
+)
+
+// IsArrayOperator returns true if the given operator can be used with an array value.
+func IsArrayOperator(op string) bool {
+	op, _ = ParseOperator(op)
+	if op == "" {
+		return false
+	}
+	for _, arrOp := range arrayOperators {
+		if arrOp == op {
+			return true
+		}
+	}
+	return false
+}
+
+// IsBoolOperator returns true if the given operator can be used with a Boolean value.
+func IsBoolOperator(op string) bool {
+	op, _ = ParseOperator(op)
+	if op == "" {
+		return false
+	}
+	for _, boolOp := range boolOperators {
+		if boolOp == op {
+			return true
+		}
+	}
+	return false
+}
+
+// IsNumberOperator returns true if the given operator can be used with a numeric value.
+func IsNumberOperator(op string) bool {
+	op, _ = ParseOperator(op)
+	if op == "" {
+		return false
+	}
+	for _, numOp := range numberOperators {
+		if numOp == op {
+			return true
+		}
+	}
+	return false
+}
+
+// IsStringOperator returns true if the given operator can be used with a string value.
+func IsStringOperator(op string) bool {
+	op, _ = ParseOperator(op)
+	if op == "" {
+		return false
+	}
+	for _, strOp := range stringOperators {
+		if strOp == op {
+			return true
+		}
+	}
+	return false
+}
+
+// ParseOperator returns the valid AQL operator for an arbitrary operator string.
+// This supports different inputs, such as Filter.Operator in github.com/recipeer/go/qs
+//
+// If the input operator cannot be mapped to AQL, this function returns ErrInvalidOperator.
+func ParseOperator(op string) (string, error) {
+	if operators[op] == "" {
+		return "", ErrInvalidOperator
+	}
+	return operators[op], nil
+}