Refactor pkg/dal implementation

* Reworked errors to not brick the system (things keep track of
  issues.
* Reworked internal state management -- keeping invalid things
  present, cleanning up the code, utilizing issues.
* Cleanup/improve error messages

pkg/dal/diff.go

@@ -5,8 +5,10 @@ type (
 
 	// ModelDiff defines one identified missmatch between two models
 	ModelDiff struct {
-		Type     modelDiffType
+		Type modelDiffType
+		// Original will be nil when a new attribute is being added
 		Original *Attribute
+		// Asserted will be nil wen an existing attribute is being removed
 		Asserted *Attribute
 	}
 
@@ -14,8 +16,9 @@ type (
 )
 
 const (
-	AttributeMissing       modelDiffType = "attributeMissing"
-	AttributeTypeMissmatch modelDiffType = "typeMissmatch"
+	AttributeMissing              modelDiffType = "attributeMissing"
+	AttributeTypeMissmatch        modelDiffType = "typeMissmatch"
+	AttributeSensitivityMissmatch modelDiffType = "sensitivityMissmatch"
 )
 
 // Diff calculates the diff between models a and b where a is used as base
@@ -34,6 +37,21 @@ func (a *Model) Diff(b *Model) (out ModelDiffSet) {
 		}
 	}
 
+	aIndex := make(map[string]struct {
+		found bool
+		attr  *Attribute
+	})
+	for _, _attr := range a.Attributes {
+		attr := _attr
+		aIndex[attr.Ident] = struct {
+			found bool
+			attr  *Attribute
+		}{
+			attr: attr,
+		}
+	}
+
+	// Deleted and update ones
 	for _, _attrA := range a.Attributes {
 		attrA := _attrA
 
@@ -55,6 +73,32 @@ func (a *Model) Diff(b *Model) (out ModelDiffSet) {
 				Asserted: attrBAux.attr,
 			})
 		}
+
+		// Other stuff
+		// @todo improve; for now it'll do
+		if attrA.SensitivityLevel != attrBAux.attr.SensitivityLevel {
+			out = append(out, &ModelDiff{
+				Type:     AttributeSensitivityMissmatch,
+				Original: attrA,
+				Asserted: attrBAux.attr,
+			})
+		}
+	}
+
+	// New
+	for _, _attrB := range b.Attributes {
+		attrB := _attrB
+
+		// Missmatches
+		_, ok := aIndex[attrB.Ident]
+		if !ok {
+			out = append(out, &ModelDiff{
+				Type:     AttributeMissing,
+				Original: nil,
+				Asserted: attrB,
+			})
+			continue
+		}
 	}
 
 	return