Refactor Sudoku field and solver implementation

logic/strategies/strategy.go

@@ -12,8 +12,8 @@ import (
 
 type Strategy interface {
 	Init(f *field.Field)
-	ApplyAll() []field.ExternalChange
-	ApplyNext() field.ExternalChange
+	ApplyAll() ([]field.ExternalChange, error)
+	ApplyNext() (field.ExternalChange, error)
 	Name() string
 	SearchProgressableCells() int
 }
@@ -40,35 +40,40 @@ func (b *Base) Init(f *field.Field) {
 	b.field = f
 }
 
-func (b *Base) ApplyAll() []field.ExternalChange {
+func (b *Base) ApplyAll() ([]field.ExternalChange, error) {
 	changesCopy := make([]field.ExternalChange, len(b.changes))
 	copy(changesCopy, b.changes)
-
-	for _, change := range b.changes {
-		b.field.AddChange(&change)
-	}
-
 	b.changes = b.changes[:0]
-
-	return changesCopy
+	if err := b.field.AddChanges(changesCopy); err != nil {
+		return nil, err
+	}
+	return changesCopy, nil
 }
 
-func (b *Base) ApplyNext() field.ExternalChange {
+func (b *Base) ApplyNext() (field.ExternalChange, error) {
 	if len(b.changes) < 1 {
-		return field.ExternalChange{}
+		return field.ExternalChange{}, nil
 	}
-
 	changeCopy := b.changes[0]
-
-	b.field.AddChange(&b.changes[0])
-
 	b.changes = b.changes[1:]
+	if err := b.field.AddChange(&changeCopy); err != nil {
+		return field.ExternalChange{}, err
+	}
+	return changeCopy, nil
+}
 
-	return changeCopy
+func (b *Base) queue(change field.ExternalChange) {
+	for _, existing := range b.changes {
+		if existing.Cell == change.Cell && existing.Action == change.Action &&
+			existing.Value == change.Value && existing.From == change.From {
+			return
+		}
+	}
+	b.changes = append(b.changes, change)
 }
 
 func (b *Base) getName() string {
-	return "Unkown"
+	return "Unknown"
 }
 
 func (b *Base) Name() string {