repo/repo.go

package repo

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"time"
)

var (
	ErrInitRepo  = errors.New("error creating table")
	ErrMarshal   = errors.New("error marshal")
	ErrExecQuery = errors.New("error executing DB query")
	ErrNotFound  = errors.New("not found")
)

type Repo[T any] interface {
	// Create saves object to the repository. If id already exists
	// in the database it is an error.
	Create(ctx context.Context, id string, v *T) error
	// Read returns object with specified id or ErrNotFound
	Read(ctx context.Context, id string) (*T, error)
	// Update updates object with id.
	Update(ctx context.Context, id string, v *T) error
	// Delete deletes object from the database.
	Delete(ctx context.Context, id string) error
}

// OpenOrCreate accepts *sql.DB and tablename and tries to create the named table
// in the database if it does not exist. The DB instance will also be used by the repository.
func OpenOrCreate[T any](ctx context.Context, db *sql.DB, tablename string) (Repo[T], error) {
	if err := initDB(ctx, db, tablename); err != nil {
		return nil, err
	}

	return &repo[T]{
		db:    db,
		table: tablename,
	}, nil
}

type repo[T any] struct {
	db    *sql.DB
	table string
}

func (r *repo[T]) Create(ctx context.Context, id string, v *T) error {
	now := time.Now()

	b, err := marshal(v)
	if err != nil {
		return err
	}

	query := "INSERT INTO " + r.table + " (id, created_at, updated_at, payload) VALUES ($1, $2, $3, $4)"

	if err := r.execContext(ctx, query, id, now, now, string(b)); err != nil {
		return err
	}

	return nil
}

func (r *repo[T]) Read(ctx context.Context, id string) (*T, error) {
	query := "SELECT payload FROM " + r.table + " WHERE id = $1"

	row := r.db.QueryRowContext(ctx, query, id)

	var s string

	err := row.Scan(&s)
	if err != nil && errors.Is(err, sql.ErrNoRows) {
		return nil, errors.Join(ErrNotFound, err)
	} else if err != nil {
		return nil, err
	}

	v, err := unmarshal[T]([]byte(s))
	if err != nil {
		return nil, err
	}

	return v, nil
}

func (r *repo[T]) Update(ctx context.Context, id string, v *T) error {
	now := time.Now()

	b, err := marshal(v)
	if err != nil {
		return err
	}

	query := "UPDATE " + r.table + " SET updated_at = $1, payload = $2 WHERE id = $3"

	if err := r.execContext(ctx, query, now, string(b), id); err != nil {
		return err
	}

	return nil
}

// Delete deletes record with cpecified id.
func (r *repo[T]) Delete(ctx context.Context, id string) error {
	query := "DELETE FROM " + r.table + " WHERE id = $1"

	if err := r.execContext(ctx, query, id); err != nil {
		return err
	}

	return nil
}

func (r *repo[T]) execContext(ctx context.Context, query string, args ...any) error {
	res, err := r.db.ExecContext(ctx, query, args...)
	if err != nil {
		return errors.Join(ErrExecQuery, err)
	}

	affected, err := res.RowsAffected()
	if err != nil {
		return errors.Join(ErrExecQuery, err)
	}

	if affected == 0 {
		return ErrNotFound
	}

	return nil
}

func marshal(v any) ([]byte, error) {
	b, err := json.Marshal(v)
	if err != nil {
		return nil, errors.Join(ErrMarshal, err)
	}

	return b, nil
}

func unmarshal[T any](b []byte) (*T, error) {
	v := new(T)
	if err := json.Unmarshal(b, v); err != nil {
		return nil, errors.Join(ErrMarshal, err)
	}

	return v, nil
}