card-to-iban/backend/internal/zarinhub/client.go

package zarinhub

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net"
	"net/http"
	"time"

	"card-to-iban/internal/service"
)

const (
	maxResponseBodySize = 1 << 20

	retryBaseDelay = 200 * time.Millisecond
	retryMaxDelay  = 2 * time.Second
)

type Client struct {
	httpClient    *http.Client
	endpointURL   string
	tokenProvider TokenProvider
	maxRetries    int
	retryWait     func(ctx context.Context, delay time.Duration) bool
}

var _ service.CardToIBANClient = (*Client)(nil)

type TokenProvider interface {
	AccessToken(ctx context.Context) (string, error)
	Invalidate(token string)
}

func NewClient(
	httpClient *http.Client,
	endpointURL string,
	tokenProvider TokenProvider,
	maxRetries int,
) *Client {
	if maxRetries < 0 {
		maxRetries = 0
	}

	return &Client{
		httpClient:    httpClient,
		endpointURL:   endpointURL,
		tokenProvider: tokenProvider,
		maxRetries:    maxRetries,
		retryWait:     waitForRetry,
	}
}

func isRetryable(err error) bool {
	return errors.Is(err, ErrTimeout) ||
		errors.Is(err, ErrUnavailable)
}

func retryDelay(attempt int) time.Duration {
	delay := retryBaseDelay

	for i := 0; i < attempt; i++ {
		delay *= 2

		if delay >= retryMaxDelay {
			return retryMaxDelay
		}
	}

	return delay
}

func waitForRetry(
	ctx context.Context,
	delay time.Duration,
) bool {
	timer := time.NewTimer(delay)
	defer timer.Stop()

	select {
	case <-ctx.Done():
		return false

	case <-timer.C:
		return true
	}
}

func (c *Client) Convert(
	ctx context.Context,
	cardNumber string,
) (service.ConversionResult, error) {
	var (
		result service.ConversionResult
		err    error
	)

	waitFn := c.retryWait
	if waitFn == nil {
		waitFn = waitForRetry
	}

	for attempt := 0; attempt <= c.maxRetries; attempt++ {
		result, err = c.convertOnce(
			ctx,
			cardNumber,
		)

		if err == nil {
			return result, nil
		}

		// Don't retry permanent/non-transient errors.
		if !isRetryable(err) {
			return result, err
		}

		// We already used all configured retries.
		if attempt == c.maxRetries {
			return result, err
		}

		// If the caller canceled the request, stop immediately.
		if ctx.Err() != nil {
			if errors.Is(ctx.Err(), context.Canceled) {
				return result, fmt.Errorf("zarinhub request canceled: %w", ctx.Err())
			}
			return result, err
		}

		delay := retryDelay(attempt)

		if !waitFn(ctx, delay) {
			if errors.Is(ctx.Err(), context.Canceled) {
				return result, fmt.Errorf("zarinhub request canceled: %w", ctx.Err())
			}
			return result, err
		}
	}

	return result, err
}

func (c *Client) convertOnce(
	ctx context.Context,
	cardNumber string,
) (service.ConversionResult, error) {
	accessToken, err := c.tokenProvider.AccessToken(ctx)
	if err != nil {
		return service.ConversionResult{},
			fmt.Errorf("get zarinhub access token: %w", err)
	}

	result, err := c.convert(ctx, cardNumber, accessToken)
	if !errors.Is(err, ErrAuthentication) ||
		result.UpstreamHTTPStatus != http.StatusUnauthorized {
		return result, err
	}

	c.tokenProvider.Invalidate(accessToken)

	accessToken, err = c.tokenProvider.AccessToken(ctx)
	if err != nil {
		return result, fmt.Errorf("refresh zarinhub access token: %w", err)
	}

	return c.convert(ctx, cardNumber, accessToken)
}

func (c *Client) convert(
	ctx context.Context,
	cardNumber string,
	accessToken string,
) (service.ConversionResult, error) {
	payload, err := json.Marshal(convertRequest{
		Card: cardNumber,
	})
	if err != nil {
		return service.ConversionResult{},
			fmt.Errorf("marshal zarinhub request: %w", err)
	}

	req, err := http.NewRequestWithContext(
		ctx,
		http.MethodPost,
		c.endpointURL,
		bytes.NewReader(payload),
	)
	if err != nil {
		return service.ConversionResult{},
			fmt.Errorf("create zarinhub request: %w", err)
	}

	req.Header.Set(
		"Authorization",
		"Bearer "+accessToken,
	)

	req.Header.Set(
		"Content-Type",
		"application/json",
	)

	resp, err := c.httpClient.Do(req)
	if err != nil {
		switch {
		case errors.Is(err, context.DeadlineExceeded):
			return service.ConversionResult{},
				fmt.Errorf("%w: %v", ErrTimeout, err)

		case errors.Is(err, context.Canceled):
			return service.ConversionResult{},
				fmt.Errorf("zarinhub request canceled: %w", err)
		}

		var netErr net.Error

		if errors.As(err, &netErr) && netErr.Timeout() {
			return service.ConversionResult{},
				fmt.Errorf("%w: %v", ErrTimeout, err)
		}

		return service.ConversionResult{},
			fmt.Errorf("%w: %v", ErrUnavailable, err)
	}

	defer resp.Body.Close()

	result := service.ConversionResult{
		UpstreamHTTPStatus: resp.StatusCode,
	}

	body, err := io.ReadAll(
		io.LimitReader(resp.Body, maxResponseBodySize+1),
	)
	if err != nil {
		return result,
			fmt.Errorf(
				"%w: failed to read response body: %v",
				ErrInvalidResponse,
				err,
			)
	}

	if len(body) > maxResponseBodySize {
		return result,
			fmt.Errorf(
				"%w: response body is too large",
				ErrInvalidResponse,
			)
	}

	result.RawResponse = body

	switch {
	case resp.StatusCode == http.StatusUnauthorized ||
		resp.StatusCode == http.StatusForbidden:
		return result, ErrAuthentication

	case resp.StatusCode == http.StatusRequestTimeout:
		return result, ErrTimeout

	case resp.StatusCode == http.StatusTooManyRequests:
		return result, ErrUnavailable

	case resp.StatusCode >= http.StatusInternalServerError:
		return result, ErrUnavailable

	case resp.StatusCode < http.StatusOK ||
		resp.StatusCode >= http.StatusMultipleChoices:
		return result, ErrRejected
	}

	var decoded convertResponse

	if err := json.Unmarshal(body, &decoded); err != nil {
		return result,
			fmt.Errorf("%w: %v", ErrInvalidResponse, err)
	}

	if !decoded.Meta.IsSuccess {
		return result, ErrRejected
	}

	if decoded.Data.IBAN == "" {
		return result,
			fmt.Errorf(
				"%w: successful response did not contain iban",
				ErrInvalidResponse,
			)
	}

	result.IBAN = decoded.Data.IBAN

	return result, nil
}