/// This package is in charge of connecting to the DB and migrations

package db

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	_ "github.com/mattn/go-sqlite3"
)

var migrations = []func(*sql.Tx) error{migration0, migration1}
var __version = len(migrations)

type DbCtx struct {
	Db      *sql.DB
	Version int
}

func initVersion(tx *sql.Tx) (int, int, error) {
	var version int
	// Check the version
	if err := tx.QueryRow("PRAGMA user_version").Scan(&version); err != nil {
		tx.Rollback()
		return 0, 0, fmt.Errorf("Could not select user_version. %w", err)
	}

	if version < __version {
		_, err := tx.Exec(fmt.Sprintf("PRAGMA user_version=%d", __version))
		if err != nil {
			tx.Rollback()
			return 0, 0, fmt.Errorf("Could not update pragma version. %w", err)
		}
		// Start from 1 so that all migrations are applied
		return version + 1, __version, nil
	} else if version > __version {
		tx.Rollback()
		return 0, 0, errors.New(fmt.Sprintf("Wrong version. Expected %d got %d", __version, version))
	}
	// User is on the latest version, migrations do not need to be ran.
	return version, version, nil
}

func migration0(tx *sql.Tx) error {
	if _, err := tx.Exec(`
		create table if not exists diary_log (
			id integer not null primary key,
			title text,
			created_at int not null default (strftime('%s','now')),
			version int not null default 0
		)
	`); err != nil {
		tx.Rollback()
		return fmt.Errorf("Could not create diary_log. %w", err)
	}
	return nil
}

func migration1(tx *sql.Tx) error {
	if _, err := tx.Exec(`
		create table diary_log_note (
			id integer not null primary key,
			log_id integer,
			body text,
			created_at int not null default (strftime('%s','now')),
			version int not null default 0,
			foreign key(log_id) references diary_log(id)
		)
	`); err != nil {
		tx.Rollback()
		return fmt.Errorf("Could not create diary_log_note. %w", err)
	}
	return nil
}

func initMigrations(tx *sql.Tx, start_from_version int) error {
	if start_from_version == __version {
		return nil
	}

	for migration_idx, migration := range migrations {
		// Version is 1 indexed, while the migration_idx is 0 indexed
		var migration_num = migration_idx + 1
		if migration_num < start_from_version {
			continue
		}
		err := migration(tx)
		if err != nil {
			tx.Rollback()
			return fmt.Errorf("Failed migration %d. %w", migration_num, err)
		}
	}
	return nil
}

func Init(db_location string) (*DbCtx, error) {
	db, err := sql.Open("sqlite3", db_location)
	if err != nil {
		return nil, fmt.Errorf("Could not connect to DB. %w", err)
	}
	if err := db.Ping(); err != nil {
		return nil, fmt.Errorf("Could not ping DB. %w", err)
	}

	ctx := context.Background()
	tx, err := db.BeginTx(ctx, nil)

	if err != nil {
		return nil, err
	}

	old_version, new_version, err := initVersion(tx)
	if err != nil {
		return nil, err
	}

	err = initMigrations(tx, old_version)
	if err != nil {
		return nil, err
	}

	tx.Commit()

	return &DbCtx{db, new_version}, nil
}