package sqlite

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

	_ "modernc.org/sqlite" // register sqlite driver

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

// Executor defines operations shared by the connection 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.
// Honest contract: database/sql Tx does not accept ctx on Commit/Rollback.
type Tx interface {
	Executor
	Commit() error
	Rollback() error
}

// Client is the primary interface for consumers.
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 lifecycle + health + client.
type Component interface {
	launcher.Component
	health.Checkable
	Client
}

// UnitOfWork manages the transaction lifecycle via context injection.
type UnitOfWork interface {
	Do(ctx context.Context, fn func(ctx context.Context) error) error
}

// Config holds connection parameters.
type Config struct {
	// Path is the SQLite file path. Use ":memory:" for in-memory databases.
	Path string `env:"SQLITE_PATH,required"`
	// MaxOpenConns limits concurrent connections. Default: 1.
	MaxOpenConns int `env:"SQLITE_MAX_OPEN_CONNS" envDefault:"1"`
	// MaxIdleConns is the number of idle connections kept in the pool.
	MaxIdleConns int `env:"SQLITE_MAX_IDLE_CONNS" envDefault:"1"`
	// Pragmas are appended to the DSN. Default: WAL + 5s busy timeout + FK enforcement.
	Pragmas string `env:"SQLITE_PRAGMAS" envDefault:"?_journal=WAL&_timeout=5000&_fk=true"`
}

func (c Config) dsn() string {
	return c.Path + c.Pragmas
}

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

// --- sqliteComponent ---

type sqliteComponent struct {
	logger   logz.Logger
	cfg      Config
	db       *sql.DB
	mu       sync.RWMutex
	writeMu  sync.Mutex // serialises writes to prevent SQLITE_BUSY
}

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

func (c *sqliteComponent) OnInit() error {
	db, err := sql.Open("sqlite", c.cfg.dsn())
	if err != nil {
		return fmt.Errorf("sqlite: open: %w", err)
	}
	maxOpen := c.cfg.MaxOpenConns
	if maxOpen == 0 {
		maxOpen = 1
	}
	db.SetMaxOpenConns(maxOpen)
	db.SetMaxIdleConns(c.cfg.MaxIdleConns)
	// Enforce foreign keys per-connection (SQLite disables them by default).
	if _, err := db.Exec("PRAGMA foreign_keys = ON"); err != nil {
		_ = db.Close()
		return fmt.Errorf("sqlite: enable foreign keys: %w", err)
	}
	c.mu.Lock()
	c.db = db
	c.mu.Unlock()
	return nil
}

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

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

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

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

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

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

// --- sqliteTx ---

type sqliteTx struct{ *sql.Tx }

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

// --- UnitOfWork ---

type unitOfWork struct {
	logger  logz.Logger
	client  Client
	writeMu *sync.Mutex
}

// NewUnitOfWork returns a UnitOfWork backed by the given client.
// If client is a *sqliteComponent, the write mutex is used to serialise transactions.
func NewUnitOfWork(logger logz.Logger, client Client) UnitOfWork {
	var mu *sync.Mutex
	if sc, ok := client.(*sqliteComponent); ok {
		mu = &sc.writeMu
	}
	return &unitOfWork{logger: logger, client: client, writeMu: mu}
}

func (u *unitOfWork) Do(ctx context.Context, fn func(ctx context.Context) error) error {
	if u.writeMu != nil {
		u.writeMu.Lock()
		defer u.writeMu.Unlock()
	}
	tx, err := u.client.Begin(ctx)
	if err != nil {
		return fmt.Errorf("sqlite: 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("sqlite: rollback failed", rbErr)
		}
		return err
	}
	return tx.Commit()
}