package sqlite

import (
	"context"
	"database/sql"
	"errors"
	"io/fs"
	"os"
	"path/filepath"
	"strconv"
	"time"

	logging "github.com/ipfs/go-log/v2"
	_ "github.com/mattn/go-sqlite3"
	"golang.org/x/xerrors"
)

var log = logging.Logger("sqlite")

type MigrationFunc func(ctx context.Context, tx *sql.Tx) error

var pragmas = []string{
	"PRAGMA synchronous = normal",
	"PRAGMA temp_store = memory",
	"PRAGMA mmap_size = 30000000000",
	"PRAGMA auto_vacuum = NONE",
	"PRAGMA automatic_index = OFF",
	"PRAGMA journal_mode = WAL",
	"PRAGMA journal_size_limit = 0", // always reset journal and wal files
	"PRAGMA foreign_keys = ON",
}

const metaTableDdl = `CREATE TABLE IF NOT EXISTS _meta (
	version UINT64 NOT NULL UNIQUE
)`

// metaDdl returns the DDL statements required to create the _meta table and add the required
// up to the given version.
func metaDdl(version uint64) []string {
	var ddls []string
	for i := 1; i <= int(version); i++ {
		ddls = append(ddls, `INSERT OR IGNORE INTO _meta (version) VALUES (`+strconv.Itoa(i)+`)`)
	}
	return append([]string{metaTableDdl}, ddls...)
}

// Open opens a database at the given path. If the database does not exist, it will be created.
func Open(path string) (*sql.DB, error) {
	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
		return nil, xerrors.Errorf("error creating database base directory [@ %s]: %w", path, err)
	}

	_, err := os.Stat(path)
	if err != nil && !errors.Is(err, fs.ErrNotExist) {
		return nil, xerrors.Errorf("error checking file status for database [@ %s]: %w", path, err)
	}

	db, err := sql.Open("sqlite3", path+"?mode=rwc")
	if err != nil {
		return nil, xerrors.Errorf("error opening database [@ %s]: %w", path, err)
	}

	for _, pragma := range pragmas {
		if _, err := db.Exec(pragma); err != nil {
			_ = db.Close()
			return nil, xerrors.Errorf("error setting database pragma %q: %w", pragma, err)
		}
	}

	var foreignKeysEnabled int
	if err := db.QueryRow("PRAGMA foreign_keys;").Scan(&foreignKeysEnabled); err != nil {
		return nil, xerrors.Errorf("failed to check foreign keys setting: %w", err)
	}
	if foreignKeysEnabled == 0 {
		return nil, xerrors.Errorf("foreign keys are not enabled for database [@ %s]", path)
	}

	return db, nil
}

// InitDb initializes the database by checking whether it needs to be created or upgraded.
// The ddls are the DDL statements to create the tables in the database and their initial required
// content. The schemaVersion will be set inside the databse if it is newly created. Otherwise, the
// version is read from the databse and returned. This value should be checked against the expected
// version to determine if the database needs to be upgraded.
// It is up to the caller to close the database if an error is returned by this function.
func InitDb(
	ctx context.Context,
	name string,
	db *sql.DB,
	ddls []string,
	versionMigrations []MigrationFunc,
) error {

	schemaVersion := len(versionMigrations) + 1

	q, err := db.QueryContext(ctx, "SELECT name FROM sqlite_master WHERE type='table' AND name='_meta';")
	if q != nil {
		defer func() { _ = q.Close() }()
	}

	if errors.Is(err, sql.ErrNoRows) || !q.Next() {
		// empty database, create the schema including the _meta table and its versions
		ddls := append(metaDdl(uint64(schemaVersion)), ddls...)
		for _, ddl := range ddls {
			if _, err := db.Exec(ddl); err != nil {
				return xerrors.Errorf("failed to %s database execute ddl %q: %w", name, ddl, err)
			}
		}
		return nil
	}

	if err != nil {
		return xerrors.Errorf("error looking for %s database _meta table: %w", name, err)
	}

	if err := q.Close(); err != nil {
		return xerrors.Errorf("error closing %s database _meta table query: %w", name, err)
	}

	// check the schema version to see if we need to upgrade the database schema
	var foundVersion int
	if err = db.QueryRow("SELECT max(version) FROM _meta").Scan(&foundVersion); err != nil {
		return xerrors.Errorf("invalid %s database version: no version found", name)
	}

	if foundVersion > schemaVersion {
		return xerrors.Errorf("invalid %s database version: version %d is greater than the number of migrations %d", name, foundVersion, len(versionMigrations))
	}

	runVacuum := foundVersion != schemaVersion

	// run a migration for each version that we have not yet applied, where foundVersion is what is
	// currently in the database and schemaVersion is the target version. If they are the same,
	// nothing is run.
	for i := foundVersion + 1; i <= schemaVersion; i++ {
		now := time.Now()

		log.Infof("Migrating %s database to version %d...", name, i)

		tx, err := db.BeginTx(ctx, nil)
		if err != nil {
			return xerrors.Errorf("failed to start %s database transaction: %w", name, err)
		}
		defer func() { _ = tx.Rollback() }()
		// versions start at 1, but the migrations are 0-indexed where the first migration would take us to version 2
		if err := versionMigrations[i-2](ctx, tx); err != nil {
			return xerrors.Errorf("failed to migrate %s database to version %d: %w", name, i, err)
		}
		if _, err := tx.ExecContext(ctx, `INSERT OR IGNORE INTO _meta (version) VALUES (?)`, i); err != nil {
			return xerrors.Errorf("failed to update %s database _meta table: %w", name, err)
		}
		if err := tx.Commit(); err != nil {
			return xerrors.Errorf("failed to commit %s database v%d migration transaction: %w", name, i, err)
		}

		log.Infof("Successfully migrated %s database from version %d to %d in %s", name, i-1, i, time.Since(now))
	}

	if runVacuum {
		// During the large migrations, we have likely increased the WAL size a lot, so lets do some
		// simple DB administration to free up space (VACUUM followed by truncating the WAL file)
		// as this would be a good time to do it when no other writes are happening.
		log.Infof("Performing %s database vacuum and wal checkpointing to free up space after the migration", name)
		_, err := db.ExecContext(ctx, "VACUUM")
		if err != nil {
			log.Warnf("error vacuuming %s database: %s", name, err)
		}
		_, err = db.ExecContext(ctx, "PRAGMA wal_checkpoint(TRUNCATE)")
		if err != nil {
			log.Warnf("error checkpointing %s database wal: %s", name, err)
		}
	}

	return nil
}