// Package database provides the database/sql lifecycle used by GoOmni projects.
// It deliberately does not import a database driver; each application chooses one.
package database

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"os"
	"strconv"
	"strings"
	"time"
)

type Config struct {
	Driver          string
	DSN             string
	MaxOpenConns    int
	MaxIdleConns    int
	ConnMaxLifetime time.Duration
	ConnMaxIdleTime time.Duration
	PingTimeout     time.Duration
}

func DefaultConfig() Config {
	return Config{
		MaxOpenConns:    10,
		MaxIdleConns:    5,
		ConnMaxLifetime: 30 * time.Minute,
		ConnMaxIdleTime: 5 * time.Minute,
		PingTimeout:     5 * time.Second,
	}
}

// ConfigFromEnv reads GO_OMNI_DB_* style settings. DSN is required.
func ConfigFromEnv(prefix string) (Config, error) {
	prefix = strings.TrimSpace(prefix)
	if prefix == "" {
		prefix = "GO_OMNI_DB_"
	}
	cfg := DefaultConfig()
	cfg.Driver = strings.TrimSpace(os.Getenv(prefix + "DRIVER"))
	if cfg.Driver == "" {
		cfg.Driver = "mysql"
	}
	cfg.DSN = strings.TrimSpace(os.Getenv(prefix + "DSN"))
	if cfg.DSN == "" {
		return Config{}, fmt.Errorf("%sDSN is required", prefix)
	}
	var err error
	if cfg.MaxOpenConns, err = envInt(prefix+"MAX_OPEN_CONNS", cfg.MaxOpenConns); err != nil {
		return Config{}, err
	}
	if cfg.MaxIdleConns, err = envInt(prefix+"MAX_IDLE_CONNS", cfg.MaxIdleConns); err != nil {
		return Config{}, err
	}
	if cfg.ConnMaxLifetime, err = envDuration(prefix+"CONN_MAX_LIFETIME", cfg.ConnMaxLifetime); err != nil {
		return Config{}, err
	}
	if cfg.ConnMaxIdleTime, err = envDuration(prefix+"CONN_MAX_IDLE_TIME", cfg.ConnMaxIdleTime); err != nil {
		return Config{}, err
	}
	if cfg.PingTimeout, err = envDuration(prefix+"PING_TIMEOUT", cfg.PingTimeout); err != nil {
		return Config{}, err
	}
	return cfg, cfg.Validate()
}

func (c Config) Validate() error {
	if strings.TrimSpace(c.Driver) == "" {
		return errors.New("database driver is required")
	}
	if strings.TrimSpace(c.DSN) == "" {
		return errors.New("database DSN is required")
	}
	if c.MaxOpenConns < 0 || c.MaxIdleConns < 0 {
		return errors.New("database pool limits cannot be negative")
	}
	if c.MaxIdleConns > c.MaxOpenConns && c.MaxOpenConns > 0 {
		return errors.New("max idle connections cannot exceed max open connections")
	}
	if c.ConnMaxLifetime < 0 || c.ConnMaxIdleTime < 0 || c.PingTimeout <= 0 {
		return errors.New("database timeouts are invalid")
	}
	return nil
}

// DB owns a connection pool and exposes the embedded database/sql methods.
type DB struct {
	*sql.DB
	config Config
}

func Open(ctx context.Context, cfg Config) (*DB, error) {
	if ctx == nil {
		ctx = context.Background()
	}
	if err := cfg.Validate(); err != nil {
		return nil, err
	}
	db, err := sql.Open(cfg.Driver, cfg.DSN)
	if err != nil {
		return nil, fmt.Errorf("open database: %w", err)
	}
	if cfg.MaxOpenConns > 0 {
		db.SetMaxOpenConns(cfg.MaxOpenConns)
	}
	// database/sql uses zero to disable idle connections; do not leave its
	// default pool size in place when the caller explicitly chooses zero.
	db.SetMaxIdleConns(cfg.MaxIdleConns)
	db.SetConnMaxLifetime(cfg.ConnMaxLifetime)
	db.SetConnMaxIdleTime(cfg.ConnMaxIdleTime)
	checkCtx, cancel := context.WithTimeout(ctx, cfg.PingTimeout)
	defer cancel()
	if err := db.PingContext(checkCtx); err != nil {
		_ = db.Close()
		return nil, fmt.Errorf("ping database: %w", err)
	}
	return &DB{DB: db, config: cfg}, nil
}

func (db *DB) Config() Config { return db.config }

func (db *DB) Health(ctx context.Context) error {
	if db == nil || db.DB == nil {
		return errors.New("database is not initialized")
	}
	if ctx == nil {
		ctx = context.Background()
	}
	checkCtx, cancel := context.WithTimeout(ctx, db.config.PingTimeout)
	defer cancel()
	return db.PingContext(checkCtx)
}

// InTx commits only when work returns nil. Any work error or panic rolls back.
func (db *DB) InTx(ctx context.Context, options *sql.TxOptions, work func(*sql.Tx) error) (err error) {
	if db == nil || db.DB == nil {
		return errors.New("database is not initialized")
	}
	tx, err := db.BeginTx(ctx, options)
	if err != nil {
		return fmt.Errorf("begin transaction: %w", err)
	}
	defer func() {
		rollbackErr := tx.Rollback()
		if rollbackErr != nil && !errors.Is(rollbackErr, sql.ErrTxDone) {
			err = errors.Join(err, fmt.Errorf("rollback transaction: %w", rollbackErr))
		}
	}()
	if err = work(tx); err != nil {
		return err
	}
	if err = tx.Commit(); err != nil {
		return fmt.Errorf("commit transaction: %w", err)
	}
	return nil
}

func envInt(key string, fallback int) (int, error) {
	value := strings.TrimSpace(os.Getenv(key))
	if value == "" {
		return fallback, nil
	}
	parsed, err := strconv.Atoi(value)
	if err != nil {
		return 0, fmt.Errorf("%s must be an integer: %w", key, err)
	}
	return parsed, nil
}

func envDuration(key string, fallback time.Duration) (time.Duration, error) {
	value := strings.TrimSpace(os.Getenv(key))
	if value == "" {
		return fallback, nil
	}
	parsed, err := time.ParseDuration(value)
	if err != nil {
		return 0, fmt.Errorf("%s must be a duration: %w", key, err)
	}
	return parsed, nil
}