Add framework composition runner

internal/framework/validators/validators.go

@@ -0,0 +1,64 @@
+package validators
+
+import (
+	"fmt"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/notarius/internal/core/artifacts"
+	"gitea.maximumdirect.net/eric/notarius/internal/framework/contracts"
+)
+
+const (
+	ReasonApproved = "approved"
+)
+
+func Approved(candidateIndex int) contracts.ValidationDecision {
+	return contracts.ValidationDecision{
+		CandidateIndex: candidateIndex,
+		Approved:       true,
+		ReasonCode:     ReasonApproved,
+		Message:        ReasonApproved,
+	}
+}
+
+func Rejected(candidateIndex int, reasonCode string, message string) contracts.ValidationDecision {
+	return contracts.ValidationDecision{
+		CandidateIndex: candidateIndex,
+		Approved:       false,
+		ReasonCode:     strings.TrimSpace(reasonCode),
+		Message:        strings.TrimSpace(message),
+	}
+}
+
+func EnforceDecisionCardinality(candidates []artifacts.Candidate, decisions []contracts.ValidationDecision) error {
+	if len(candidates) != len(decisions) {
+		return fmt.Errorf("validator returned %d decisions for %d candidates", len(decisions), len(candidates))
+	}
+
+	expected := make(map[int]struct{}, len(candidates))
+	for _, candidate := range candidates {
+		if _, ok := expected[candidate.Index]; ok {
+			return fmt.Errorf("candidate index %d is duplicated", candidate.Index)
+		}
+		expected[candidate.Index] = struct{}{}
+	}
+
+	seen := make(map[int]struct{}, len(decisions))
+	for _, decision := range decisions {
+		if _, ok := expected[decision.CandidateIndex]; !ok {
+			return fmt.Errorf("validator returned decision for unknown candidate index %d", decision.CandidateIndex)
+		}
+		if _, ok := seen[decision.CandidateIndex]; ok {
+			return fmt.Errorf("validator returned duplicate decision for candidate index %d", decision.CandidateIndex)
+		}
+		seen[decision.CandidateIndex] = struct{}{}
+	}
+
+	for candidateIndex := range expected {
+		if _, ok := seen[candidateIndex]; !ok {
+			return fmt.Errorf("validator did not return decision for candidate index %d", candidateIndex)
+		}
+	}
+
+	return nil
+}