feat: add inspect by index command

cobble.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+	"fmt"
 	"github.com/spf13/cobra"
 	"log"
 	"os"
@@ -45,8 +46,24 @@ var up = &cobra.Command{
 	},
 }
 
+var inspect = &cobra.Command{
+	Use:   "inspect",
+	Short: "Prints the nth migration in the history",
+	Run: func(cmd *cobra.Command, args []string) {
+		migrationRoot := args[0]
+		migrationIndex, _ := strconv.Atoi(args[1])
+
+		migrationGraph, _ := NewMigrationGraphFromDirectory(migrationRoot)
+		migrationHistory, _ := migrationGraph.GetLinearHistory()
+		migration := migrationHistory[migrationIndex]
+		sql, _ := migration.Sql()
+		fmt.Printf("%s:\n%s", migration.Name, sql)
+	},
+}
+
 func main() {
 	cli.AddCommand(up)
+	cli.AddCommand(inspect)
 
 	if err := cli.Execute(); err != nil {
 		log.Fatal(err)

migration.go

@@ -21,20 +21,38 @@ func NewMigration(path string, name string, requires string) Migration {
 	}
 }
 
+func (m *Migration) Bytes() ([]byte, error) {
+	migrationPath := m.Path
+	migrationBytes, err := os.ReadFile(migrationPath)
+
+	if err != nil {
+		return []byte{}, err
+	}
+
+	return migrationBytes, nil
+}
+
+func (m *Migration) Text() (string, error) {
+	migrationBytes, err := m.Bytes()
+	return string(migrationBytes), err
+}
+
+func (m *Migration) Sql() (string, error) {
+	migrationBytes, err := m.Bytes()
+
+	return string(StripComments(migrationBytes)), err
+}
+
 // Applies a migration to the given database connection.
 //
 // If an error is returned while trying to read the migration file
 // or execute the SQL it contains, the error is returned.
 func (m *Migration) ApplyMigration(db DB) error {
-	migrationPath := m.Path
-	migrationBytes, err := os.ReadFile(migrationPath)
+	migrationSql, err := m.Sql()
 
 	if err != nil {
 		return err
 	}
-
-	migrationSql := string(migrationBytes)
-
 	log.Printf("SQL: %s", migrationSql)
 
 	err = db.Execute(migrationSql)

parser.go

@@ -1,8 +1,3 @@
-// Migration tooling
-//
-// Runs migrations in-order based on files found in the migration
-// root directory provided as argument.
-
 package main
 
 import (
@@ -24,6 +19,28 @@ func cutPrefixAndTrim(b []byte, prefix []byte) []byte {
 	return bytes.TrimSpace(withoutPrefix)
 }
 
+func StripComments(sql []byte) []byte {
+	scanner := bufio.NewScanner(bytes.NewReader(sql))
+
+	sqlWithoutComments := []byte{}
+
+	for scanner.Scan() {
+		currentBytes := scanner.Bytes()
+
+		if !bytes.HasPrefix(currentBytes, commentPrefix) {
+			sqlWithoutComments = append(sqlWithoutComments, currentBytes...)
+			sqlWithoutComments = append(sqlWithoutComments, []byte("\n")...)
+		}
+	}
+
+	totalLength := len(sqlWithoutComments)
+
+	if totalLength > 0 {
+		return sqlWithoutComments[:totalLength-1]
+	}
+	return sqlWithoutComments
+}
+
 // Extracts any migration headers present in the migration source file.
 // Headers are left in comments of the form:
 // -- <header-name>: ...