1 files changed, 81 insertions, 0 deletions
diff --git a/internal/mapr/parserfieldplan.go b/internal/mapr/parserfieldplan.go
new file mode 100644
index 0000000..fd831a5
--- /dev/null
+++ b/internal/mapr/parserfieldplan.go
@@ -0,0 +1,81 @@
+package mapr
+
+// ParserFieldPlan describes which raw fields a parser needs to materialize.
+type ParserFieldPlan struct {
+	AllFields bool
+	Fields    map[string]struct{}
+}
+
+// Needs reports whether the parser plan requires a field.
+func (p ParserFieldPlan) Needs(field string) bool {
+	if p.AllFields {
+		return true
+	}
+	_, ok := p.Fields[field]
+	return ok
+}
+
+// Capacity returns a reasonable initial capacity for a parsed field map.
+func (p ParserFieldPlan) Capacity() int {
+	if p.AllFields {
+		return 20
+	}
+	if len(p.Fields) == 0 {
+		return 4
+	}
+	return len(p.Fields) + 2
+}
+
+// ParserFieldPlan returns the raw fields required to evaluate the query.
+func (q *Query) ParserFieldPlan() ParserFieldPlan {
+	if q == nil {
+		return ParserFieldPlan{AllFields: true}
+	}
+
+	fields := make(map[string]struct{}, len(q.Select)+len(q.GroupBy)+len(q.Where)*2+len(q.Set))
+	producedBySet := make(map[string]struct{}, len(q.Set))
+
+	add := func(field string) {
+		if field == "" {
+			return
+		}
+		fields[field] = struct{}{}
+	}
+	isProduced := func(field string) bool {
+		_, ok := producedBySet[field]
+		return ok
+	}
+
+	for _, wc := range q.Where {
+		if wc.lType == Field {
+			add(wc.lString)
+		}
+		if wc.rType == Field {
+			add(wc.rString)
+		}
+	}
+
+	for _, sc := range q.Set {
+		switch sc.rType {
+		case Field, FunctionStack:
+			if !isProduced(sc.rString) {
+				add(sc.rString)
+			}
+		}
+		producedBySet[sc.lString] = struct{}{}
+	}
+
+	for _, groupBy := range q.GroupBy {
+		if !isProduced(groupBy) {
+			add(groupBy)
+		}
+	}
+
+	for _, sc := range q.Select {
+		if !isProduced(sc.Field) {
+			add(sc.Field)
+		}
+	}
+
+	return ParserFieldPlan{Fields: fields}
+}