package abono

import (
	"context"
	"errors"
	"fmt"
	"time"

	"gorm.io/gorm"
)

// Comp statuses, as the schema's CHECK allows them.
const (
	compActive   = "active"
	compCanceled = "canceled"
)

type compRow struct {
	ID        int64
	Subject   string
	Plan      string
	Status    string
	EndsAt    *time.Time
	Note      string
	CreatedAt time.Time
	UpdatedAt time.Time
}

func (compRow) TableName() string { return "abono_comps" }

// Comp gives subject the plan without payment, until endsAt or for good
// when endsAt is nil, and returns the comp's id. It is a comp, not a
// grant, so it is never confused with "grants access". OnChange runs in the
// same transaction, and its error undoes the comp.
func (s *Service) Comp(ctx context.Context, subject, plan string, endsAt *time.Time, note string) (int64, error) {
	if subject == "" || plan == "" {
		return 0, errors.New("abono: Comp needs a subject and a plan")
	}
	now := s.now()
	row := compRow{Subject: subject, Plan: plan, Status: compActive, Note: note, CreatedAt: now, UpdatedAt: now}
	if endsAt != nil {
		e := endsAt.UTC()
		row.EndsAt = &e
	}
	err := s.tx(ctx, func(tx *gorm.DB) error {
		if err := tx.Create(&row).Error; err != nil {
			return err
		}
		return s.changed(ctx, tx, subject)
	})
	if err != nil {
		return 0, err
	}
	return row.ID, nil
}

// EndComp ends a comp now. Ending one already ended changes nothing and
// tells nobody. OnChange runs in the same transaction, and its error leaves
// the comp as it was.
func (s *Service) EndComp(ctx context.Context, id int64) error {
	return s.tx(ctx, func(tx *gorm.DB) error {
		var row compRow
		switch err := tx.Where("id = ?", id).Take(&row).Error; {
		case errors.Is(err, gorm.ErrRecordNotFound):
			return fmt.Errorf("abono: comp %d: %w", id, ErrNotFound)
		case err != nil:
			return err
		}
		if row.Status == compCanceled {
			return nil
		}
		if err := tx.Exec(`UPDATE abono_comps SET status = ?, updated_at = ? WHERE id = ?`,
			compCanceled, s.now(), id).Error; err != nil {
			return err
		}
		return s.changed(ctx, tx, row.Subject)
	})
}