package mysql

import (
	"context"
	"database/sql"
	"fmt"
	"net/url"
	"sync"
	"time"

	_ "github.com/go-sql-driver/mysql" // register driver

	"code.nochebuena.dev/go/health"
	"code.nochebuena.dev/go/launcher"
	"code.nochebuena.dev/go/logz"
)

// Executor defines operations shared by pool and transaction.
type Executor interface {
	ExecContext(ctx context.Context, query string, args ...any) (sql.Result, error)
	QueryContext(ctx context.Context, query string, args ...any) (*sql.Rows, error)
	QueryRowContext(ctx context.Context, query string, args ...any) *sql.Row
}

// Tx extends Executor with commit/rollback (no ctx — sql.Tx limitation).
type Tx interface {
	Executor
	Commit() error
	Rollback() error
}

// Client is the database access interface.
type Client interface {
	GetExecutor(ctx context.Context) Executor
	Begin(ctx context.Context) (Tx, error)
	Ping(ctx context.Context) error
	HandleError(err error) error
}

// Component bundles launcher lifecycle, health check, and database client.
type Component interface {
	launcher.Component
	health.Checkable
	Client
}

// UnitOfWork wraps operations in a single database transaction.
type UnitOfWork interface {
	Do(ctx context.Context, fn func(ctx context.Context) error) error
}

// Config holds MySQL connection settings.
//
// DSN parameters Charset, Loc, and ParseTime default to "utf8mb4", "UTC", and
// "true" respectively when left empty, preserving the behaviour of v0.9.0.
// Set them explicitly when you need non-default values (e.g. Loc="Local").
//
// Note on Collation: go-sql-driver v1.8.x negotiates the connection collation
// via a 1-byte handshake ID (max 255). MariaDB 11.4+ collations such as
// utf8mb4_uca1400_as_cs carry IDs > 255 and cannot be set through the DSN
// collation parameter. Set the desired collation at the database/table level
// in your schema migrations instead.
type Config struct {
	Host            string `env:"MYSQL_HOST,required"`
	Port            int    `env:"MYSQL_PORT"               envDefault:"3306"`
	User            string `env:"MYSQL_USER,required"`
	Password        string `env:"MYSQL_PASSWORD,required"`
	Name            string `env:"MYSQL_NAME,required"`
	MaxConns        int    `env:"MYSQL_MAX_CONNS"          envDefault:"5"`
	MinConns        int    `env:"MYSQL_MIN_CONNS"          envDefault:"2"`
	MaxConnLifetime string `env:"MYSQL_MAX_CONN_LIFETIME"  envDefault:"1h"`
	MaxConnIdleTime string `env:"MYSQL_MAX_CONN_IDLE_TIME" envDefault:"30m"`
	// Charset is the connection character set sent as SET NAMES <charset>.
	// Defaults to "utf8mb4" when empty.
	Charset string `env:"MYSQL_CHARSET" envDefault:"utf8mb4"`
	// Loc is the IANA timezone name used for time.Time ↔ MySQL DATETIME
	// conversion. Defaults to "UTC" when empty.
	Loc string `env:"MYSQL_LOC" envDefault:"UTC"`
	// ParseTime controls whether the driver maps DATE/DATETIME columns to
	// time.Time. Valid values: "true", "false". Defaults to "true" when empty.
	ParseTime string `env:"MYSQL_PARSE_TIME" envDefault:"true"`
}

// DSN constructs a MySQL DSN from the configuration.
// Empty Charset, Loc, and ParseTime fields fall back to their safe defaults
// ("utf8mb4", "UTC", "true"), matching the behaviour of v0.9.0.
func (c Config) DSN() string {
	charset := c.Charset
	if charset == "" {
		charset = "utf8mb4"
	}
	loc := c.Loc
	if loc == "" {
		loc = "UTC"
	}
	parseTime := c.ParseTime
	if parseTime == "" {
		parseTime = "true"
	}

	q := url.Values{}
	q.Set("charset", charset)
	q.Set("loc", loc)
	q.Set("parseTime", parseTime)
	// go-sql-driver uses user:pass@tcp(host:port)/db?params
	return fmt.Sprintf("%s:%s@tcp(%s:%d)/%s?%s",
		c.User, c.Password, c.Host, c.Port, c.Name, q.Encode())
}

// ctxTxKey is the context key for the active transaction.
type ctxTxKey struct{}

// --- mysqlComponent ---

type mysqlComponent struct {
	logger logz.Logger
	cfg    Config
	db     *sql.DB
	mu     sync.RWMutex
}

// New returns a mysql Component. Call lc.Append(db) to manage its lifecycle.
func New(logger logz.Logger, cfg Config) Component {
	return &mysqlComponent{logger: logger, cfg: cfg}
}

func (c *mysqlComponent) OnInit() error {
	db, err := sql.Open("mysql", c.cfg.DSN())
	if err != nil {
		return fmt.Errorf("mysql: open: %w", err)
	}
	db.SetMaxOpenConns(c.cfg.MaxConns)
	db.SetMaxIdleConns(c.cfg.MinConns)
	if c.cfg.MaxConnLifetime != "" {
		d, err := time.ParseDuration(c.cfg.MaxConnLifetime)
		if err != nil {
			return fmt.Errorf("MYSQL_MAX_CONN_LIFETIME: %w", err)
		}
		db.SetConnMaxLifetime(d)
	}
	if c.cfg.MaxConnIdleTime != "" {
		d, err := time.ParseDuration(c.cfg.MaxConnIdleTime)
		if err != nil {
			return fmt.Errorf("MYSQL_MAX_CONN_IDLE_TIME: %w", err)
		}
		db.SetConnMaxIdleTime(d)
	}
	c.mu.Lock()
	c.db = db
	c.mu.Unlock()
	return nil
}

func (c *mysqlComponent) OnStart() error {
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	if err := c.Ping(ctx); err != nil {
		return fmt.Errorf("mysql: ping failed: %w", err)
	}
	c.logger.Info("mysql: connected")
	return nil
}

func (c *mysqlComponent) OnStop() error {
	c.mu.Lock()
	defer c.mu.Unlock()
	if c.db != nil {
		c.logger.Info("mysql: closing pool")
		_ = c.db.Close()
		c.db = nil
	}
	return nil
}

func (c *mysqlComponent) Ping(ctx context.Context) error {
	c.mu.RLock()
	db := c.db
	c.mu.RUnlock()
	if db == nil {
		return fmt.Errorf("mysql: not initialized")
	}
	return db.PingContext(ctx)
}

func (c *mysqlComponent) GetExecutor(ctx context.Context) Executor {
	if tx, ok := ctx.Value(ctxTxKey{}).(Executor); ok {
		return tx
	}
	c.mu.RLock()
	db := c.db
	c.mu.RUnlock()
	return db
}

func (c *mysqlComponent) Begin(ctx context.Context) (Tx, error) {
	c.mu.RLock()
	db := c.db
	c.mu.RUnlock()
	if db == nil {
		return nil, fmt.Errorf("mysql: not initialized")
	}
	tx, err := db.BeginTx(ctx, nil)
	if err != nil {
		return nil, err
	}
	return &mysqlTx{Tx: tx}, nil
}

func (c *mysqlComponent) ExecContext(ctx context.Context, query string, args ...any) (sql.Result, error) {
	c.mu.RLock()
	db := c.db
	c.mu.RUnlock()
	return db.ExecContext(ctx, query, args...)
}

func (c *mysqlComponent) QueryContext(ctx context.Context, query string, args ...any) (*sql.Rows, error) {
	c.mu.RLock()
	db := c.db
	c.mu.RUnlock()
	return db.QueryContext(ctx, query, args...)
}

func (c *mysqlComponent) QueryRowContext(ctx context.Context, query string, args ...any) *sql.Row {
	c.mu.RLock()
	db := c.db
	c.mu.RUnlock()
	return db.QueryRowContext(ctx, query, args...)
}

func (c *mysqlComponent) HandleError(err error) error { return HandleError(err) }

// health.Checkable
func (c *mysqlComponent) HealthCheck(ctx context.Context) error { return c.Ping(ctx) }
func (c *mysqlComponent) Name() string                          { return "mysql" }
func (c *mysqlComponent) Priority() health.Level                { return health.LevelCritical }

// --- mysqlTx ---

type mysqlTx struct{ *sql.Tx }

func (t *mysqlTx) ExecContext(ctx context.Context, query string, args ...any) (sql.Result, error) {
	return t.Tx.ExecContext(ctx, query, args...)
}
func (t *mysqlTx) QueryContext(ctx context.Context, query string, args ...any) (*sql.Rows, error) {
	return t.Tx.QueryContext(ctx, query, args...)
}
func (t *mysqlTx) QueryRowContext(ctx context.Context, query string, args ...any) *sql.Row {
	return t.Tx.QueryRowContext(ctx, query, args...)
}
func (t *mysqlTx) Commit() error   { return t.Tx.Commit() }
func (t *mysqlTx) Rollback() error { return t.Tx.Rollback() }

// --- UnitOfWork ---

type unitOfWork struct {
	logger logz.Logger
	client Client
}

// NewUnitOfWork returns a UnitOfWork backed by the given client.
func NewUnitOfWork(logger logz.Logger, client Client) UnitOfWork {
	return &unitOfWork{logger: logger, client: client}
}

func (u *unitOfWork) Do(ctx context.Context, fn func(ctx context.Context) error) error {
	tx, err := u.client.Begin(ctx)
	if err != nil {
		return fmt.Errorf("mysql: begin transaction: %w", err)
	}
	ctx = context.WithValue(ctx, ctxTxKey{}, tx)
	if err := fn(ctx); err != nil {
		if rbErr := tx.Rollback(); rbErr != nil {
			u.logger.Error("mysql: rollback failed", rbErr)
		}
		return err
	}
	return tx.Commit()
}