engine refactor

internal/engine/operators.go

@@ -0,0 +1,69 @@
+package engine
+
+import "fmt"
+
+// Operator is a scalar comparison used by generalised constraints like
+// Altitude and Time. A constraint fires when its Operator.Test(value, limit)
+// returns true.
+type Operator int
+
+const (
+	OpLess         Operator = iota // value < limit
+	OpLessEqual                    // value ≤ limit
+	OpGreater                      // value > limit
+	OpGreaterEqual                 // value ≥ limit
+	OpEqual                        // value == limit
+)
+
+// Test evaluates op(value, limit).
+func (o Operator) Test(value, limit float64) bool {
+	switch o {
+	case OpLess:
+		return value < limit
+	case OpLessEqual:
+		return value <= limit
+	case OpGreater:
+		return value > limit
+	case OpGreaterEqual:
+		return value >= limit
+	case OpEqual:
+		return value == limit
+	}
+	return false
+}
+
+// String returns the symbol "<", "<=", ">", ">=", "==".
+func (o Operator) String() string {
+	switch o {
+	case OpLess:
+		return "<"
+	case OpLessEqual:
+		return "<="
+	case OpGreater:
+		return ">"
+	case OpGreaterEqual:
+		return ">="
+	case OpEqual:
+		return "=="
+	}
+	return "?"
+}
+
+// ParseOperator maps a textual operator to its Operator constant.
+// Accepts "<", "<=", "le", ">", ">=", "ge", "==", "eq".
+func ParseOperator(s string) (Operator, error) {
+	switch s {
+	case "<", "lt":
+		return OpLess, nil
+	case "<=", "le":
+		return OpLessEqual, nil
+	case ">", "gt":
+		return OpGreater, nil
+	case ">=", "ge":
+		return OpGreaterEqual, nil
+	case "==", "eq":
+		return OpEqual, nil
+	default:
+		return 0, fmt.Errorf("unknown operator %q", s)
+	}
+}