3 files changed, 82 insertions, 22 deletions

diff --git a/entity/id.go b/entity/id.go
index 8f3dc25b..49398da8 100644
--- a/entity/id.go
+++ b/entity/id.go
@@ -79,21 +79,3 @@ func (i Id) Validate() error {
 	}
 	return nil
 }
-
-/*
- * Sorting
- */
-
-type Alphabetical []Id
-
-func (a Alphabetical) Len() int {
-	return len(a)
-}
-
-func (a Alphabetical) Less(i, j int) bool {
-	return a[i] < a[j]
-}
-
-func (a Alphabetical) Swap(i, j int) {
-	a[i], a[j] = a[j], a[i]
-}
diff --git a/entity/id_interleaved.go b/entity/id_interleaved.go
index 0ce2ba00..28c59a42 100644
--- a/entity/id_interleaved.go
+++ b/entity/id_interleaved.go
@@ -1,13 +1,91 @@
 package entity
 
 import (
+	"fmt"
+	"io"
 	"strings"
+
+	"github.com/pkg/errors"
 )
 
+const UnsetCombinedId = CombinedId("unset")
+
+// CombinedId is an Id holding information from both a primary Id and a secondary Id.
+// While it looks like a regular Id, do not just cast from one to another.
+// Instead, use CombineIds and SeparateIds to create it and split it.
+type CombinedId string
+
+// String return the identifier as a string
+func (ci CombinedId) String() string {
+	return string(ci)
+}
+
+// Human return the identifier, shortened for human consumption
+func (ci CombinedId) Human() string {
+	format := fmt.Sprintf("%%.%ds", humanIdLength)
+	return fmt.Sprintf(format, ci)
+}
+
+func (ci CombinedId) HasPrefix(prefix string) bool {
+	return strings.HasPrefix(string(ci), prefix)
+}
+
+// UnmarshalGQL implement the Unmarshaler interface for gqlgen
+func (ci *CombinedId) UnmarshalGQL(v interface{}) error {
+	_, ok := v.(string)
+	if !ok {
+		return fmt.Errorf("CombinedIds must be strings")
+	}
+
+	*ci = v.(CombinedId)
+
+	if err := ci.Validate(); err != nil {
+		return errors.Wrap(err, "invalid CombinedId")
+	}
+
+	return nil
+}
+
+// MarshalGQL implement the Marshaler interface for gqlgen
+func (ci CombinedId) MarshalGQL(w io.Writer) {
+	_, _ = w.Write([]byte(`"` + ci.String() + `"`))
+}
+
+// Validate tell if the Id is valid
+func (ci CombinedId) Validate() error {
+	// Special case to detect outdated repo
+	if len(ci) == 40 {
+		return fmt.Errorf("outdated repository format, please use https://github.com/MichaelMure/git-bug-migration to upgrade")
+	}
+	if len(ci) != idLength {
+		return fmt.Errorf("invalid length")
+	}
+	for _, r := range ci {
+		if (r < 'a' || r > 'z') && (r < '0' || r > '9') {
+			return fmt.Errorf("invalid character")
+		}
+	}
+	return nil
+}
+
+// PrimaryPrefix is a helper to extract the primary prefix.
+// If practical, use SeparateIds instead.
+func (ci CombinedId) PrimaryPrefix() string {
+	primaryPrefix, _ := SeparateIds(string(ci))
+	return primaryPrefix
+}
+
+// SecondaryPrefix is a helper to extract the secondary prefix.
+// If practical, use SeparateIds instead.
+func (ci CombinedId) SecondaryPrefix() string {
+	_, secondaryPrefix := SeparateIds(string(ci))
+	return secondaryPrefix
+}
+
 // CombineIds compute a merged Id holding information from both the primary Id
 // and the secondary Id.
 //
-// This allow to later find efficiently a secondary element because we can access
+// This allows to later find efficiently a secondary element because we can access
 // the primary one directly instead of searching for a primary that has a
 // secondary matching the Id.
 //
@@ -32,7 +110,7 @@ import (
 // 7:    4P, 3S
 // 10:   6P, 4S
 // 16:  11P, 5S
-func CombineIds(primary Id, secondary Id) Id {
+func CombineIds(primary Id, secondary Id) CombinedId {
 	var id strings.Builder
 
 	for i := 0; i < idLength; i++ {
@@ -46,7 +124,7 @@ func CombineIds(primary Id, secondary Id) Id {
 		}
 	}
 
-	return Id(id.String())
+	return CombinedId(id.String())
 }
 
 // SeparateIds extract primary and secondary prefix from an arbitrary length prefix
diff --git a/entity/id_interleaved_test.go b/entity/id_interleaved_test.go
index ef9218c9..1dc79145 100644
--- a/entity/id_interleaved_test.go
+++ b/entity/id_interleaved_test.go
@@ -9,7 +9,7 @@ import (
 func TestInterleaved(t *testing.T) {
 	primary := Id("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWX______________")
 	secondary := Id("YZ0123456789+/________________________________________________")
-	expectedId := Id("aYbZc0def1ghij2klmn3opqr4stuv5wxyz6ABCD7EFGH8IJKL9MNOP+QRST/UVWX")
+	expectedId := CombinedId("aYbZc0def1ghij2klmn3opqr4stuv5wxyz6ABCD7EFGH8IJKL9MNOP+QRST/UVWX")
 
 	interleaved := CombineIds(primary, secondary)
 	require.Equal(t, expectedId, interleaved)