package storage

import (
	"context"
	"database/sql"
	"fmt"
)

func (s *Store) ConfigCommit(ctx context.Context) (Checkpoint, error) {
	return s.checkpoint(ctx, "read config commit", "config_commit")
}

func (s *Store) UserbaseCommit(ctx context.Context) (Checkpoint, error) {
	return s.checkpoint(ctx, "read userbase commit", "userbase_commit")
}

func (s *Store) CompareAndSwapConfigCommit(ctx context.Context, expected Checkpoint, next string) error {
	return s.compareAndSwapCheckpoint(ctx, "compare and swap config commit", "config_commit", expected, next)
}

func (s *Store) CompareAndSwapUserbaseCommit(ctx context.Context, expected Checkpoint, next string) error {
	return s.compareAndSwapCheckpoint(ctx, "compare and swap userbase commit", "userbase_commit", expected, next)
}

func (s *Store) checkpoint(ctx context.Context, operation, column string) (Checkpoint, error) {
	if err := s.checkOpen(operation); err != nil {
		return Checkpoint{}, err
	}
	var value sql.NullString
	query := `SELECT ` + column + ` FROM settings WHERE id = 1`
	if err := s.sql.QueryRowContext(ctx, query).Scan(&value); err != nil {
		return Checkpoint{}, classify(operation, err)
	}
	if !value.Valid {
		return Checkpoint{}, nil
	}
	return Checkpoint{Value: value.String, Set: true}, nil
}

func (s *Store) compareAndSwapCheckpoint(ctx context.Context, operation, column string, expected Checkpoint, next string) error {
	if err := s.checkOpen(operation); err != nil {
		return err
	}
	if next == "" {
		return invalid(operation, fmt.Errorf("next checkpoint is empty"))
	}
	if !expected.Set && expected.Value != "" {
		return invalid(operation, fmt.Errorf("unset expected checkpoint has a value"))
	}
	var result sql.Result
	var err error
	if expected.Set {
		result, err = s.sql.ExecContext(ctx, `UPDATE settings SET `+column+` = ? WHERE id = 1 AND `+column+` = ?`, next, expected.Value)
	} else {
		result, err = s.sql.ExecContext(ctx, `UPDATE settings SET `+column+` = ? WHERE id = 1 AND `+column+` IS NULL`, next)
	}
	if err != nil {
		return classify(operation, err)
	}
	count, err := result.RowsAffected()
	if err != nil {
		return classify(operation+" rows affected", err)
	}
	if count == 0 {
		return fmt.Errorf("%s: %w", operation, ErrConflict)
	}
	return nil
}

func (s *Store) ResetConfigCommit(ctx context.Context, expected Checkpoint, next string) error {
	const operation = "reset config checkpoint"
	if err := s.checkOpen(operation); err != nil {
		return err
	}
	if !expected.Set || expected.Value == "" || next == "" {
		return invalid(operation, fmt.Errorf("both checkpoints must be set"))
	}
	tx, err := s.sql.BeginTx(ctx, nil)
	if err != nil {
		return classify(operation, err)
	}
	defer tx.Rollback()
	count, err := execCount(ctx, tx, operation, `UPDATE settings SET config_commit = ? WHERE id = 1 AND config_commit = ?`, next, expected.Value)
	if err != nil {
		return err
	}
	if count != 1 {
		return fmt.Errorf("%s: %w", operation, ErrConflict)
	}
	if err := writeAudit(ctx, tx, operation, "system", "config.checkpoint_reset", "config", canonicalTime(s.now()), map[string]any{"previous": expected.Value, "commit": next}); err != nil {
		return err
	}
	return classify(operation, tx.Commit())
}