// midipak implements compressing and appending MIDI flles
// to a midipak file.
package midipak

import (
	"context"
	"database/sql"
)

// Encoder compresses each of the input files,
// and is expected to be goroutine safe.
type Encoder interface {
	EncodeAll(src, dst []byte) []byte
}

// File stores the name and data of a file.
type File struct {
	Name string
	Data []byte
}

// Create initializes a new midipak.
func Create(ctx context.Context, db *sql.DB) error {
	sqlStmt := "CREATE TABLE files (name TEXT PRIMARY KEY, sz INTEGER NOT NULL, data BLOB);"

	_, err := db.ExecContext(ctx, sqlStmt)
	return err
}

// Pack appends the files to the midipak, after being compressed
// with the provided encoder. Attempting to pack files that already
// exist is an error.
func Pack(ctx context.Context, db *sql.DB, enc Encoder, files []File) error {
	tx, err := db.BeginTx(ctx, nil)
	if err != nil {
		return err
	}

	stmt, err := tx.Prepare("INSERT INTO files(name, sz, data) VALUES (?, ?, ?)")
	if err != nil {
		return err
	}
	defer stmt.Close()

	for _, file := range files {
		sz := len(file.Data)

		_, err = stmt.Exec(file.Name, sz, enc.EncodeAll(file.Data, make([]byte, 0, sz)))
		if err != nil {
			return err
		}
	}

	return tx.Commit()
}