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// SPDX-FileCopyrightText: 2025 Shota FUJI <pockawoooh@gmail.com>
// SPDX-License-Identifier: AGPL-3.0-only

package snapshot

import (
	"database/sql"

	"google.golang.org/protobuf/proto"
)

// Zig に戻りたい...。
// https://konradreiche.com/blog/a-generic-protobuf-reader-with-go-type-parameters/
type ProtoMessage[T any] interface {
	proto.Message
	*T
}

func GetLatest[T any, P ProtoMessage[T]](tx *sql.Tx) (P, uint64, error) {
	var ret P = new(T)

	stmt, err := tx.Prepare(`
		SELECT event_seq, payload FROM snapshots
			LEFT JOIN projections ON snapshots.projection_id = projections.id
			WHERE projection_name = ?
			ORDER BY event_seq DESC
			LIMIT 1
	`)
	if err != nil {
		return nil, 0, err
	}

	row := stmt.QueryRow(ret.ProtoReflect().Descriptor().FullName())

	var seq uint64
	var payload []byte
	err = row.Scan(&seq, &payload)
	if err == sql.ErrNoRows {
		return nil, 0, nil
	}
	if err != nil {
		return nil, 0, err
	}

	if err := proto.Unmarshal(payload, ret); err != nil {
		return nil, 0, err
	}

	return ret, seq, nil
}

func Save(tx *sql.Tx, msg proto.Message, seq uint64) error {
	name := msg.ProtoReflect().Descriptor().FullName()
	payload, err := proto.Marshal(msg)
	if err != nil {
		return err
	}

	_, err = tx.Exec(`
		INSERT INTO projections (projection_name)
			SELECT ?1 WHERE NOT EXISTS (SELECT id FROM projections WHERE projection_name = ?1)
	`, name)
	if err != nil {
		return err
	}

	_, err = tx.Exec(`
		INSERT INTO snapshots (event_seq, projection_id, payload)
			SELECT ?, id, ? FROM projections WHERE projection_name = ? LIMIT 1
	`, seq, payload, name)

	return err
}