package database

import (
	"fmt"

	"gorm.io/gorm"
)

// Totals is the single row of running totals in a webhook's event
// database. It is what keeps the webhook page's lifetime figures right
// after retention has removed the rows they count, and what lets the
// page show them without counting every row.
//
// Storing an event, creating a delivery and failing a delivery each
// add one, and retention adds what it deletes to the Removed columns.
// Every addition goes through AddTotals, in the transaction that
// writes or deletes the rows it counts.
type Totals struct {
	ID int64 `gorm:"primaryKey"`

	Events     int64 `gorm:"not null"`
	Deliveries int64 `gorm:"not null"`
	Failures   int64 `gorm:"not null"`

	EventsRemoved     int64 `gorm:"not null"`
	DeliveriesRemoved int64 `gorm:"not null"`
	FailuresRemoved   int64 `gorm:"not null"`
}

// TableName names the table AddTotals updates.
func (Totals) TableName() string {
	return "totals"
}

// EventsWithinRetention is how many of the webhook's events are still
// stored.
func (t Totals) EventsWithinRetention() int64 {
	return t.Events - t.EventsRemoved
}

// DeliveriesWithinRetention is how many of the webhook's deliveries
// are still stored.
func (t Totals) DeliveriesWithinRetention() int64 {
	return t.Deliveries - t.DeliveriesRemoved
}

// FailuresWithinRetention is how many of the webhook's failed
// deliveries are still stored.
func (t Totals) FailuresWithinRetention() int64 {
	return t.Failures - t.FailuresRemoved
}

// AddTotals adds each count in add to the webhook's running totals.
// Call it on the transaction that writes or deletes the rows it
// counts, so the totals change exactly when those rows do.
func AddTotals(tx *gorm.DB, add Totals) error {
	err := tx.Exec(
		`UPDATE totals SET
			events = events + ?,
			deliveries = deliveries + ?,
			failures = failures + ?,
			events_removed = events_removed + ?,
			deliveries_removed = deliveries_removed + ?,
			failures_removed = failures_removed + ?`,
		add.Events, add.Deliveries, add.Failures,
		add.EventsRemoved, add.DeliveriesRemoved, add.FailuresRemoved,
	).Error
	if err != nil {
		return fmt.Errorf("adding to running totals: %w", err)
	}

	return nil
}