Add query package with first set of conditions and tests

database/query/query.go

@@ -0,0 +1,98 @@
+package query
+
+import (
+	"fmt"
+	"regexp"
+)
+
+// Example:
+// q.New("core:/",
+//   q.Where("a", q.GreaterThan, 0),
+//   q.Where("b", q.Equals, 0),
+//   q.Or(
+//       q.Where("c", q.StartsWith, "x"),
+//       q.Where("d", q.Contains, "y")
+//     )
+//   )
+
+var (
+	prefixExpr = regexp.MustCompile("^[a-z-]+:")
+)
+
+// Query contains a compiled query.
+type Query struct {
+	prefix     string
+	conditions []Condition
+}
+
+// New creates a new query.
+func New(prefix string, conditions ...Condition) (*Query, error) {
+	// check prefix
+	if !prefixExpr.MatchString(prefix) {
+		return nil, fmt.Errorf("invalid prefix: %s", prefix)
+	}
+
+	// check conditions
+	var err error
+	for _, cond := range conditions {
+		err = cond.check()
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	// return query
+	return &Query{
+		prefix:     prefix,
+		conditions: conditions,
+	}, nil
+}
+
+// MustCompile creates a new query and panics on an error.
+func MustCompile(prefix string, conditions ...Condition) *Query {
+	q, err := New(prefix, conditions...)
+	if err != nil {
+		panic(err)
+	}
+	return q
+}
+
+// Prepend prepends (check first) new query conditions to the query.
+func (q *Query) Prepend(conditions ...Condition) error {
+	// check conditions
+	var err error
+	for _, cond := range conditions {
+		err = cond.check()
+		if err != nil {
+			return err
+		}
+	}
+
+	q.conditions = append(conditions, q.conditions...)
+	return nil
+}
+
+// Append appends (check last) new query conditions to the query.
+func (q *Query) Append(conditions ...Condition) error {
+	// check conditions
+	var err error
+	for _, cond := range conditions {
+		err = cond.check()
+		if err != nil {
+			return err
+		}
+	}
+
+	q.conditions = append(q.conditions, conditions...)
+	return nil
+}
+
+// Matches checks whether the query matches the supplied data object.
+func (q *Query) Matches(f Fetcher) bool {
+	for _, cond := range q.conditions {
+		if !cond.complies(f) {
+			return false
+		}
+	}
+	return true
+}