Split migrations folder (#21549)

There are too many files in `models/migrations` folder so that I split
them into sub folders.

models/migrations/v1_6/v71.go

@@ -0,0 +1,81 @@
+// Copyright 2018 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package v1_6 // nolint
+
+import (
+	"fmt"
+
+	"code.gitea.io/gitea/models/migrations/base"
+	"code.gitea.io/gitea/modules/timeutil"
+	"code.gitea.io/gitea/modules/util"
+
+	"xorm.io/xorm"
+)
+
+func AddScratchHash(x *xorm.Engine) error {
+	// TwoFactor see models/twofactor.go
+	type TwoFactor struct {
+		ID               int64 `xorm:"pk autoincr"`
+		UID              int64 `xorm:"UNIQUE"`
+		Secret           string
+		ScratchToken     string
+		ScratchSalt      string
+		ScratchHash      string
+		LastUsedPasscode string             `xorm:"VARCHAR(10)"`
+		CreatedUnix      timeutil.TimeStamp `xorm:"INDEX created"`
+		UpdatedUnix      timeutil.TimeStamp `xorm:"INDEX updated"`
+	}
+
+	if err := x.Sync2(new(TwoFactor)); err != nil {
+		return fmt.Errorf("Sync2: %w", err)
+	}
+
+	sess := x.NewSession()
+	defer sess.Close()
+
+	if err := sess.Begin(); err != nil {
+		return err
+	}
+
+	// transform all tokens to hashes
+	const batchSize = 100
+	for start := 0; ; start += batchSize {
+		tfas := make([]*TwoFactor, 0, batchSize)
+		if err := sess.Limit(batchSize, start).Find(&tfas); err != nil {
+			return err
+		}
+		if len(tfas) == 0 {
+			break
+		}
+
+		for _, tfa := range tfas {
+			// generate salt
+			salt, err := util.CryptoRandomString(10)
+			if err != nil {
+				return err
+			}
+			tfa.ScratchSalt = salt
+			tfa.ScratchHash = base.HashToken(tfa.ScratchToken, salt)
+
+			if _, err := sess.ID(tfa.ID).Cols("scratch_salt, scratch_hash").Update(tfa); err != nil {
+				return fmt.Errorf("couldn't add in scratch_hash and scratch_salt: %w", err)
+			}
+
+		}
+	}
+
+	// Commit and begin new transaction for dropping columns
+	if err := sess.Commit(); err != nil {
+		return err
+	}
+	if err := sess.Begin(); err != nil {
+		return err
+	}
+
+	if err := base.DropTableColumns(sess, "two_factor", "scratch_token"); err != nil {
+		return err
+	}
+	return sess.Commit()
+}