package retry

import (
	"context"
	"fmt"
	"log/slog"
	"time"
)

type Retrier struct {
	maxRetries int
	backoff    []time.Duration
}

func NewRetrier(maxRetries int, backoff []time.Duration) *Retrier {
	return &Retrier{maxRetries: maxRetries, backoff: backoff}
}

// DefaultRetrier returns a retrier with 3 attempts, exponential backoff: 1s, 5s, 30s.
func DefaultRetrier() *Retrier {
	return NewRetrier(3, []time.Duration{1 * time.Second, 5 * time.Second, 30 * time.Second})
}

func (r *Retrier) Do(ctx context.Context, fn func() error) error {
	var lastErr error
	for attempt := 0; attempt <= r.maxRetries; attempt++ {
		if attempt > 0 {
			delay := r.backoff[attempt-1]
			slog.Info("retrying", "attempt", attempt, "delay", delay)
			select {
			case <-ctx.Done():
				return ctx.Err()
			case <-time.After(delay):
			}
		}

		err := fn()
		if err == nil {
			return nil
		}
		lastErr = err
		slog.Warn("attempt failed", "attempt", attempt, "error", err)
	}
	return fmt.Errorf("all %d attempts failed, last error: %w", r.maxRetries+1, lastErr)
}