LogDog: Update to archival V2.

appengine/logdog/coordinator/logStream_migrate.go

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package coordinator
+
+import (
+        "fmt"
+        "time"
+
+        ds "github.com/luci/gae/service/datastore"
+)
+
+func (s *LogStream) migrateSchema() error {
+        switch s.Schema {
+        case "":
+                // Pre-schema versioned schema. Migrate to "1".
+                //
+                // To do this, we:
+                // - See if the ArchiveWhole property is available. If it is, we set the
+                //   ArchiveLogEntryCount to equal TerminalIndex+1. Otherwise, we leave
+                //   ArchiveLogEntryCount at zero, as there is no (easy) way to determine
+                //   its value.
+
+                // Determine archival state.
+                if s.Archived() {
+                        switch props := s.extra["ArchiveWhole"]; len(props) {
+                        case 0:
+                                break
+
+                        case 1:
+                                if v, ok := props[0].Value().(bool); ok && v {
+                                        s.ArchiveLogEntryCount = s.TerminalIndex + 1
+                                }
+
+                        default:
+                                return fmt.Errorf("pre-schema ArchiveWhole has %d values", len(props))
+                        }
+                }
+
+                // Backfill time based on state.
+                switch {
+                case s.Archived():
+                        if dt := dateTimeProp(s.extra["ArchivedTime"]); dt.IsZero() {
+                                s.ArchivedTime = s.Created
+                        }
+                        fallthrough
+
+                case s.Terminated():
+                        if dt := dateTimeProp(s.extra["TerminatedTime"]); dt.IsZero() {
+                                s.TerminatedTime = s.Created
+                        }
+                        fallthrough
+
+                default:
+                        break
+                }
+
+                // Migration complete!
+                s.Schema = currentLogStreamSchema
+                fallthrough
+
+        case currentLogStreamSchema:
+                return nil
+
+        default:
+                return fmt.Errorf("unrecognized log stream schema %q", s.Schema)
+        }
+}
+
+// dateTimeProp returns the time.Time value of a single-property slice, or
+// a zero time.Time if the slice wasn't single-value or didn't contain a
+// time.Time.
+func dateTimeProp(props []ds.Property) time.Time {
+        if len(props) == 1 {
+                if t, ok := props[0].Value().(time.Time); ok {
+                        return t
+                }
+        }
+        return time.Time{}
+}