// Package classes holds the SEO plugin's logic: the service every writer
// goes through, the entry store and the effective-SEO resolver.
package classes

import (
	"context"
	"errors"
	"sync/atomic"

	"git.golem15.com/golem15/summercms/modules/backpack"
	"git.golem15.com/golem15/summercms/modules/cabana"
	"git.golem15.com/golem15/summercms/modules/compass"
	"git.golem15.com/golem15/summercms/modules/signpost"
	"gorm.io/gorm"
)

// ErrNotBooted is returned when the service has no booted application.
var ErrNotBooted = errors.New("golem15.seo: app is not booted")

// Service is the plugin's single entry point for reads and writes of SEO
// data. The admin extension, the admin controllers, the listeners, the job
// and the API all call it, so every write goes through the same checks and
// history.
type Service struct {
	app *backpack.App
	// robots is the last production robots.txt served, answered when the
	// store fails (D-22: never a 5xx).
	robots atomic.Pointer[string]
}

// NewService returns the service of a booted application. The database
// and the signpost registry are looked up when used, so a binary that runs
// a console command without a database still boots.
func NewService(app *backpack.App) (*Service, error) {
	if app == nil {
		return nil, ErrNotBooted
	}
	return &Service{app: app}, nil
}

// App returns the booted application.
func (s *Service) App() *backpack.App {
	if s == nil {
		return nil
	}
	return s.app
}

type txKey struct{}

// WithTx returns ctx carrying tx, the transaction an API write or a batch
// runs in, so every read of the service (the resolver, the redirect set,
// the settings) sees the uncommitted changes of that transaction.
func WithTx(ctx context.Context, tx *gorm.DB) context.Context {
	if tx == nil {
		return ctx
	}
	return context.WithValue(ctx, txKey{}, tx)
}

// DB returns the transaction carried by ctx (WithTx, else the admin write
// transaction of cabana.TxFromContext), else the application's database
// bound to ctx.
func (s *Service) DB(ctx context.Context) (*gorm.DB, error) {
	if tx, ok := ctx.Value(txKey{}).(*gorm.DB); ok && tx != nil {
		return tx, nil
	}
	if tx, ok := cabana.TxFromContext(ctx); ok && tx != nil {
		return tx, nil
	}
	if s == nil || s.app == nil {
		return nil, ErrNotBooted
	}
	db, ok := s.app.Lookup[*gorm.DB]()
	if !ok || db == nil {
		return nil, errors.New("golem15.seo: database is not configured")
	}
	return db.WithContext(ctx), nil
}

// Registry returns the menu item type registry, nil when none is published.
func (s *Service) Registry() *signpost.Registry {
	if s == nil || s.app == nil {
		return nil
	}
	reg, _ := s.app.Lookup[*signpost.Registry]()
	return reg
}

// GormDB returns the application's database without a transaction, the
// handle lagoon.Transaction opens a write on.
func (s *Service) GormDB() (*gorm.DB, error) {
	if s == nil || s.app == nil {
		return nil, ErrNotBooted
	}
	db, ok := s.app.Lookup[*gorm.DB]()
	if !ok || db == nil {
		return nil, errors.New("golem15.seo: database is not configured")
	}
	return db, nil
}

// Config returns the application config, nil when there is none.
func (s *Service) Config() *compass.Config {
	if s == nil || s.app == nil {
		return nil
	}
	return s.app.Config
}