store: Add a lastAmongDup column to the cmd table.

store/cmd_hist.go

@@ -10,7 +10,45 @@ import (
 var ErrNoMatchingCmd = errors.New("no matching command line")
 
 func init() {
-	initTable["cmd"] = `create table if not exists cmd (content text)`
+	initTable["cmd"] = func(db *sql.DB) error {
+		_, err := db.Exec(`create table if not exists cmd (content text, lastAmongDup bool)`)
+		if err != nil {
+			return err
+		}
+		return addLastAmongDup(db)
+	}
+}
+
+func addLastAmongDup(db *sql.DB) error {
+	// Upgrade from early version where lastAmongDup is missing.
+	tx, err := db.Begin()
+	if err != nil {
+		return err
+	}
+	rows, err := db.Query("pragma table_info(cmd)")
+	if err != nil {
+		tx.Rollback()
+		return err
+	}
+	hasLastAmongDup, err := hasColumn(rows, "lastAmongDup")
+	if err != nil {
+		tx.Rollback()
+		return err
+	}
+	if !hasLastAmongDup {
+		_, err := db.Exec("alter table cmd add column lastAmongDup bool")
+		if err != nil {
+			tx.Rollback()
+			return err
+		}
+		_, err = db.Exec("update cmd set lastAmongDup = (rowid in (select max(rowid) from cmd group by content));")
+		if err != nil {
+			tx.Rollback()
+			return err
+		}
+	}
+	tx.Commit()
+	return nil
 }
 
 // NextCmdSeq returns the next sequence number of the command history.
@@ -23,7 +61,11 @@ func (s *Store) NextCmdSeq() (int, error) {
 
 // AddCmd adds a new command to the command history.
 func (s *Store) AddCmd(cmd string) error {
-	_, err := s.db.Exec(`insert into cmd (content) values(?)`, cmd)
+	_, err := s.db.Exec(`update cmd set lastAmongDup = 0 where content = ?`, cmd)
+	if err != nil {
+		return err
+	}
+	_, err = s.db.Exec(`insert into cmd (content, lastAmongDup) values(?, 1)`, cmd)
 	return err
 }
 

store/dir_hist.go

@@ -13,7 +13,10 @@ const (
 )
 
 func init() {
-	initTable["dir"] = `create table if not exists dir (path text unique primary key, score real default 0)`
+	initTable["dir"] = func(db *sql.DB) error {
+		_, err := db.Exec(`create table if not exists dir (path text unique primary key, score real default 0)`)
+		return err
+	}
 }
 
 // AddDir adds a directory to the directory history.

store/sqlutil.go

@@ -0,0 +1,26 @@
+package store
+
+import "database/sql"
+
+func hasColumn(rows *sql.Rows, colname string) (bool, error) {
+	cols, err := rows.Columns()
+	if err != nil {
+		return false, err
+	}
+	dests := make([]interface{}, len(cols))
+	var name string
+	for i, col := range cols {
+		if col == "name" {
+			dests[i] = &name
+		} else {
+			dests[i] = new(interface{})
+		}
+	}
+	for rows.Next() {
+		rows.Scan(dests...)
+		if name == colname {
+			return true, nil
+		}
+	}
+	return false, rows.Err()
+}

store/store.go

@@ -14,7 +14,7 @@ type Store struct {
 	db *sql.DB
 }
 
-var initTable = map[string]string{}
+var initTable = map[string](func(*sql.DB) error){}
 
 // DefaultDB returns the default database for storage.
 func DefaultDB(dataDir string) (*sql.DB, error) {
@@ -37,10 +37,10 @@ func NewStore(dataDir string) (*Store, error) {
 func NewStoreDB(db *sql.DB) (*Store, error) {
 	st := &Store{db}
 
-	for t, q := range initTable {
-		_, err := db.Exec(q)
+	for name, fn := range initTable {
+		err := fn(db)
 		if err != nil {
-			return nil, fmt.Errorf("failed to initialize table %s: %v", t, q)
+			return nil, fmt.Errorf("failed to initialize table %s: %v", name, err)
 		}
 	}