// Copyright (C) 2026 Dcntrlized
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published
// by the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

package db

import (
	"context"
	"errors"
	"time"

	"github.com/google/uuid"
	"github.com/jackc/pgx/v5"
)

// Subscription is one alarm.subscriptions row: a device that receives the alarm.
//
// A subscription is the SUBSCRIBER IDENTITY (contract rev 10). Either it hangs
// off an account (`SubscriberUserID` set, the pre-rev-10 shape) or it stands
// alone with a device token the service minted at join (`DeviceTokenHash` set,
// `SubscriberUserID` is uuid.Nil). A subscriber is therefore never a fake user:
// there is no auth.users row behind an anonymous one.
type Subscription struct {
	ID               uuid.UUID
	AlertID          uuid.UUID
	SubscriberUserID uuid.UUID
	DeviceID         string
	DeviceLabel      *string
	Platform         *string
	Enabled          bool
	LastSeenAt       *time.Time
	Created          time.Time
	// DeviceTokenHash is the SHA-256 of the token handed to the device once, at
	// join. Nil for account-backed subscriptions.
	DeviceTokenHash *string
}

const subscriptionColumns = `id, alert_id, subscriber_user_id, device_id, device_label,
	platform, enabled, last_seen_at, created, device_token_hash`

func scanSubscription(row pgx.Row) (*Subscription, error) {
	var s Subscription
	var user *uuid.UUID
	err := row.Scan(&s.ID, &s.AlertID, &user, &s.DeviceID, &s.DeviceLabel,
		&s.Platform, &s.Enabled, &s.LastSeenAt, &s.Created, &s.DeviceTokenHash)
	if user != nil {
		s.SubscriberUserID = *user
	}
	if errors.Is(err, pgx.ErrNoRows) {
		return nil, ErrNotFound
	}
	if err != nil {
		return nil, err
	}
	return &s, nil
}

// CreateSubscription inserts a subscription. A duplicate
// (alert_id, subscriber_user_id, device_id) is reported as ErrConflict, which
// the join action turns into the ERR_ALERT_ALREADY_JOINED race fallback — the
// sequential re-scan path is handled by the caller's lookup and never reaches
// this error.
func CreateSubscription(ctx context.Context, s *Subscription) (*Subscription, error) {
	tx, err := Pool().Begin(ctx)
	if err != nil {
		return nil, err
	}
	defer func() { _ = tx.Rollback(ctx) }()

	var actor *uuid.UUID
	if s.SubscriberUserID != uuid.Nil {
		actor = &s.SubscriberUserID
	}

	const q = `INSERT INTO alarm.subscriptions
		(alert_id, subscriber_user_id, device_id, device_label, platform, device_token_hash)
		VALUES ($1, $2, $3, $4, $5, $6)
		RETURNING ` + subscriptionColumns
	row, err := scanSubscription(tx.QueryRow(ctx, q,
		s.AlertID, actor, s.DeviceID, s.DeviceLabel, s.Platform, s.DeviceTokenHash))
	if isUniqueViolation(err) {
		return nil, ErrConflict
	}
	if err != nil {
		return nil, err
	}
	if err := recordEvent(ctx, tx, s.AlertID, actor, EventJoined, ""); err != nil {
		return nil, err
	}
	if err := tx.Commit(ctx); err != nil {
		return nil, err
	}
	return row, nil
}

// GetSubscriptionByDevice is the idempotency lookup for joinAlert.
func GetSubscriptionByDevice(ctx context.Context, alertID, userID uuid.UUID, deviceID string) (*Subscription, error) {
	const q = `SELECT ` + subscriptionColumns + `
		FROM alarm.subscriptions
		WHERE alert_id = $1 AND subscriber_user_id = $2 AND device_id = $3`
	return scanSubscription(Pool().QueryRow(ctx, q, alertID, userID, deviceID))
}

// FindSubscriptionByDevice looks a subscription up by alert and device digest,
// whichever path created it. It is the idempotency lookup for an anonymous
// join, where there is no user id to key on.
func FindSubscriptionByDevice(ctx context.Context, alertID uuid.UUID, deviceID string) (*Subscription, error) {
	const q = `SELECT ` + subscriptionColumns + `
		FROM alarm.subscriptions
		WHERE alert_id = $1 AND device_id = $2
		ORDER BY created
		LIMIT 1`
	return scanSubscription(Pool().QueryRow(ctx, q, alertID, deviceID))
}

// GetSubscriptionByToken resolves the subscriber behind a device token. The
// token itself is never stored: the caller hashes what it received and this
// lookup runs against the unique index.
func GetSubscriptionByToken(ctx context.Context, tokenHash string) (*Subscription, error) {
	const q = `SELECT ` + subscriptionColumns + `
		FROM alarm.subscriptions
		WHERE device_token_hash = $1`
	return scanSubscription(Pool().QueryRow(ctx, q, tokenHash))
}

// RotateDeviceToken replaces the token hash of a subscription. A re-join from
// the same device rotates rather than inserts, so a lost token is recoverable
// with the subscribe token while the old one stops working immediately.
func RotateDeviceToken(ctx context.Context, subscriptionID uuid.UUID, tokenHash string) error {
	tag, err := Pool().Exec(ctx,
		`UPDATE alarm.subscriptions SET device_token_hash = $2 WHERE id = $1`,
		subscriptionID, tokenHash)
	if err != nil {
		return err
	}
	if tag.RowsAffected() == 0 {
		return ErrNotFound
	}
	return nil
}

// GetSubscription fetches one subscription scoped to its alert.
func GetSubscription(ctx context.Context, alertID, subscriptionID uuid.UUID) (*Subscription, error) {
	const q = `SELECT ` + subscriptionColumns + `
		FROM alarm.subscriptions WHERE alert_id = $1 AND id = $2`
	return scanSubscription(Pool().QueryRow(ctx, q, alertID, subscriptionID))
}

// ListSubscriptions returns every device subscribed to an alert, oldest first.
func ListSubscriptions(ctx context.Context, alertID uuid.UUID) ([]Subscription, error) {
	const q = `SELECT ` + subscriptionColumns + `
		FROM alarm.subscriptions WHERE alert_id = $1 ORDER BY created, id`
	rows, err := Pool().Query(ctx, q, alertID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	out := make([]Subscription, 0, 4)
	for rows.Next() {
		var s Subscription
		if err := rows.Scan(&s.ID, &s.AlertID, &s.SubscriberUserID, &s.DeviceID, &s.DeviceLabel,
			&s.Platform, &s.Enabled, &s.LastSeenAt, &s.Created); err != nil {
			return nil, err
		}
		out = append(out, s)
	}
	return out, rows.Err()
}

// DeleteSubscription removes one subscription. ErrNotFound when it was already
// gone, so a repeated removal is visible to the caller.
func DeleteSubscription(ctx context.Context, alertID, subscriptionID uuid.UUID) error {
	tag, err := Pool().Exec(ctx,
		`DELETE FROM alarm.subscriptions WHERE alert_id = $1 AND id = $2`, alertID, subscriptionID)
	if err != nil {
		return err
	}
	if tag.RowsAffected() == 0 {
		return ErrNotFound
	}
	return nil
}

// IsSubscriber reports whether the user has at least one subscription row on
// the alert. It is the authorisation check behind getAlert/alarmStatus.
func IsSubscriber(ctx context.Context, alertID, userID uuid.UUID) (bool, error) {
	var exists bool
	err := Pool().QueryRow(ctx,
		`SELECT EXISTS (SELECT 1 FROM alarm.subscriptions WHERE alert_id = $1 AND subscriber_user_id = $2)`,
		alertID, userID).Scan(&exists)
	return exists, err
}

// UserSubscriptionIDs lists the user's subscription ids on an alert, so a WS
// connection can be tied to the right device rows.
func UserSubscriptionIDs(ctx context.Context, alertID, userID uuid.UUID) ([]uuid.UUID, error) {
	rows, err := Pool().Query(ctx,
		`SELECT id FROM alarm.subscriptions WHERE alert_id = $1 AND subscriber_user_id = $2 ORDER BY created`,
		alertID, userID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var out []uuid.UUID
	for rows.Next() {
		var id uuid.UUID
		if err := rows.Scan(&id); err != nil {
			return nil, err
		}
		out = append(out, id)
	}
	return out, rows.Err()
}

// TouchSubscription stamps last_seen_at. It is called on WS connect and on
// every heartbeat; a no-op update (the row vanished mid-connection) is not an
// error worth propagating.
func TouchSubscription(ctx context.Context, subscriptionID uuid.UUID) error {
	_, err := Pool().Exec(ctx,
		`UPDATE alarm.subscriptions SET last_seen_at = NOW() WHERE id = $1`, subscriptionID)
	return err
}