// Report allows a migration minion to report if it successfully
// completed its activities for a given migration phase.
func (c *Client) Report(migrationId string, phase migration.Phase, success bool) error {
	args := params.MinionReport{
		MigrationId: migrationId,
		Phase:       phase.String(),
		Success:     success,
	}
	err := c.caller.FacadeCall("Report", args, nil)
	return errors.Trace(err)
}

// SetPhase implements ModelMigration.
func (mig *modelMigration) SetPhase(nextPhase migration.Phase) error {
	now := GetClock().Now().UnixNano()

	phase, err := mig.Phase()
	if err != nil {
		return errors.Trace(err)
	}

	if nextPhase == phase {
		return nil // Already at that phase. Nothing to do.
	}
	if !phase.CanTransitionTo(nextPhase) {
		return errors.Errorf("illegal phase change: %s -> %s", phase, nextPhase)
	}

	nextDoc := mig.statusDoc
	nextDoc.Phase = nextPhase.String()
	nextDoc.PhaseChangedTime = now
	update := bson.M{
		"phase":              nextDoc.Phase,
		"phase-changed-time": now,
	}
	if nextPhase == migration.SUCCESS {
		nextDoc.SuccessTime = now
		update["success-time"] = now
	}
	var ops []txn.Op
	if nextPhase.IsTerminal() {
		nextDoc.EndTime = now
		update["end-time"] = now
		ops = append(ops, txn.Op{
			C:      migrationsActiveC,
			Id:     mig.doc.ModelUUID,
			Assert: txn.DocExists,
			Remove: true,
		})
	}

	ops = append(ops, txn.Op{
		C:      migrationsStatusC,
		Id:     mig.statusDoc.Id,
		Update: bson.M{"$set": update},
		// Ensure phase hasn't changed underneath us
		Assert: bson.M{"phase": mig.statusDoc.Phase},
	})

	if err := mig.st.runTransaction(ops); err == txn.ErrAborted {
		return errors.New("phase already changed")
	} else if err != nil {
		return errors.Annotate(err, "failed to update phase")
	}

	mig.statusDoc = nextDoc
	return nil
}

// SubmitMinionReport implements ModelMigration.
func (mig *modelMigration) SubmitMinionReport(tag names.Tag, phase migration.Phase, success bool) error {
	globalKey, err := agentTagToGlobalKey(tag)
	if err != nil {
		return errors.Trace(err)
	}
	docID := mig.minionReportId(phase, globalKey)
	doc := modelMigMinionSyncDoc{
		Id:          docID,
		MigrationId: mig.Id(),
		Phase:       phase.String(),
		EntityKey:   globalKey,
		Time:        mig.st.clock.Now().UnixNano(),
		Success:     success,
	}
	ops := []txn.Op{{
		C:      migrationsMinionSyncC,
		Id:     docID,
		Insert: doc,
		Assert: txn.DocMissing,
	}}
	err = mig.st.runTransaction(ops)
	if errors.Cause(err) == txn.ErrAborted {
		coll, closer := mig.st.getCollection(migrationsMinionSyncC)
		defer closer()
		var existingDoc modelMigMinionSyncDoc
		err := coll.FindId(docID).Select(bson.M{"success": 1}).One(&existingDoc)
		if err != nil {
			return errors.Annotate(err, "checking existing report")
		}
		if existingDoc.Success != success {
			return errors.Errorf("conflicting reports received for %s/%s/%s",
				mig.Id(), phase.String(), tag)
		}
		return nil
	} else if err != nil {
		return errors.Trace(err)
	}
	return nil
}

func (mig *modelMigration) minionReportId(phase migration.Phase, globalKey string) string {
	return fmt.Sprintf("%s:%s:%s", mig.Id(), phase.String(), globalKey)
}

// SetPhase implements Client.
func (c *client) SetPhase(phase migration.Phase) error {
	args := params.SetMigrationPhaseArgs{
		Phase: phase.String(),
	}
	return c.caller.FacadeCall("SetPhase", args, nil)
}

// IsTerminal returns true when the given phase means a migration has
// finished (successfully or otherwise).
func IsTerminal(phase migration.Phase) bool {
	return phase.IsTerminal()
}