package database

import (
	"context"
	"database/sql"
	"embed"
	"fmt"
	"io/fs"
	"strconv"
	"strings"
	"time"

	"git.yetaga.in/alazyreader/library/book"
	_ "github.com/go-sql-driver/mysql"
)

//go:embed migrations/mysql
var migrationsFS embed.FS

type migration struct {
	id      int
	name    string
	content []byte
}

type MySQL struct {
	connection          *sql.DB
	versionTable        string
	migrationsDirectory string
}

func NewMySQLConnection(user, pass, host, port, db string) (*MySQL, error) {
	dsn := fmt.Sprintf("%s:%s@tcp(%s:%s)/%s", user, pass, host, port, db) // what a strange syntax
	connection, err := sql.Open("mysql", dsn)
	if err != nil {
		return nil, err
	}
	return &MySQL{
		connection:          connection,
		versionTable:        "migrations",
		migrationsDirectory: "/migrations/mysql",
	}, nil
}

func (m *MySQL) PrepareDatabase(ctx context.Context) error {
	if m.connection == nil || m.migrationsDirectory == "" || m.versionTable == "" {
		return fmt.Errorf("uninitialized mysql client")
	}

	tablecheck := `SELECT count(*) AS count
		FROM information_schema.TABLES
		WHERE TABLE_NAME = '` + m.versionTable + `'
		AND TABLE_SCHEMA in (SELECT DATABASE());`
	tableschema := `CREATE TABLE ` + m.versionTable + `(
		id INT NOT NULL,
		name VARCHAR(100) NOT NULL,
		datetime DATE,
		PRIMARY KEY (id))`

	var versionTableExists int
	m.connection.QueryRowContext(ctx, tablecheck).Scan(&versionTableExists)
	if versionTableExists != 0 {
		return nil
	}
	_, err := m.connection.ExecContext(ctx, tableschema)
	return err
}

func (m *MySQL) GetLatestMigration(ctx context.Context) (int, error) {
	if m.connection == nil || m.migrationsDirectory == "" || m.versionTable == "" {
		return 0, fmt.Errorf("uninitialized mysql client")
	}

	var latestMigration int
	err := m.connection.QueryRowContext(ctx, "SELECT MAX(id) FROM "+m.versionTable).Scan(&latestMigration)
	return latestMigration, err
}

func (m *MySQL) RunMigrations(ctx context.Context) (int, error) {
	if m.connection == nil || m.migrationsDirectory == "" || m.versionTable == "" {
		return 0, fmt.Errorf("uninitialized mysql client")
	}

	var migrations map[int]migration
	dir, err := migrationsFS.ReadDir(m.migrationsDirectory)
	if err != nil {
		return 0, nil
	}
	for f := range dir {
		if dir[f].Type().IsRegular() {
			mig := migration{}
			id, name, err := parseMigrationFileName(dir[f].Name())
			if err != nil {
				return 0, err
			}
			mig.id, mig.name = id, name
			mig.content, err = fs.ReadFile(migrationsFS, m.migrationsDirectory+"/"+dir[f].Name())
			migrations[mig.id] = mig
		}
	}

	latestMigrationRan, err := m.GetLatestMigration(ctx)
	if err != nil {
		return 0, err
	}

	// exit if nothing to do (that is, there's no greater migration ID)
	if _, ok := migrations[latestMigrationRan+1]; !ok {
		return latestMigrationRan, nil
	}

	// loop over and apply migrations if required
	tx, err := m.connection.BeginTx(ctx, nil)
	if err != nil {
		return latestMigrationRan, err
	}
	for migrationsToRun := true; migrationsToRun; _, migrationsToRun = migrations[latestMigrationRan+1] {
		mig := migrations[latestMigrationRan+1]
		_, err := tx.ExecContext(ctx, string(mig.content))
		if err != nil {
			nestederr := tx.Rollback()
			if nestederr != nil {
				return latestMigrationRan, nestederr
			}
			return latestMigrationRan, err
		}
		_, err = tx.ExecContext(ctx, "INSERT INTO "+m.versionTable+" (id, name, datetime) VALUES (?, ?, ?)", mig.id, mig.name, time.Now())
		if err != nil {
			nestederr := tx.Rollback()
			if nestederr != nil {
				return latestMigrationRan, nestederr
			}
			return latestMigrationRan, err
		}
		latestMigrationRan = latestMigrationRan + 1
	}
	err = tx.Commit()
	return latestMigrationRan, err
}

func (m *MySQL) GetAllBooks(ctx context.Context) ([]book.Book, error) {
	if m.connection == nil {
		return nil, fmt.Errorf("uninitialized mysql client")
	}

	books := []book.Book{}
	rows, err := m.connection.QueryContext(ctx, "SELECT id, title FROM books")
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	for rows.Next() {
		b := book.Book{}
		err := rows.Scan(&b.ID, &b.Title)
		if err != nil {
			return nil, err
		}
		books = append(books, b)
	}

	return books, nil
}

func (m *MySQL) AddBook(ctx context.Context, b *book.Book) error {
	if m.connection == nil {
		return fmt.Errorf("uninitialized mysql client")
	}

	res, err := m.connection.ExecContext(ctx, "INSERT INTO books (title) VALUES (?)", b.Title)
	if err != nil {
		return err
	}
	i, err := res.RowsAffected()
	if err != nil {
		return err
	}
	if i != 1 {
		return fmt.Errorf("unexpectedly updated more than one row: %d", i)
	}
	return nil
}

func (m *MySQL) UpdateBook(ctx context.Context, old, new *book.Book) error {
	if m.connection == nil {
		return fmt.Errorf("uninitialized mysql client")
	}

	res, err := m.connection.ExecContext(ctx, "UPDATE books SET title=? WHERE id=?", new.Title, old.ID)
	if err != nil {
		return err
	}
	i, err := res.RowsAffected()
	if err != nil {
		return err
	}
	if i != 1 {
		return fmt.Errorf("unexpectedly updated more than one row: %d", i)
	}
	return nil
}

func parseMigrationFileName(filename string) (int, string, error) {
	sp := strings.SplitN(filename, "-", 2)
	i, err := strconv.Atoi(sp[0])
	if err != nil {
		return 0, "", err
	}
	tr := strings.TrimSuffix(sp[1], ".sql")
	return i, tr, nil
}