package httpclient

import (
	"errors"
	"fmt"
	"net"
	"net/http"
	"strconv"
	"time"

	retry "github.com/avast/retry-go/v4"
	"github.com/sony/gobreaker"

	"code.nochebuena.dev/einherjar/contracts/logging"
	corelogz "code.nochebuena.dev/einherjar/core/logz"
	"code.nochebuena.dev/einherjar/core/xerrors"
)

// Compile-time interface verification (I-8 / CT-5).
var _ Provider = (*httpClientImpl)(nil)

// New returns a Provider with the given configuration.
func New(logger logging.Logger, cfg Config) Provider {
	name := cfg.Name
	if name == "" {
		name = "http"
	}
	cb := gobreaker.NewCircuitBreaker(gobreaker.Settings{
		Name:    name,
		Timeout: cfg.CBTimeout,
		ReadyToTrip: func(counts gobreaker.Counts) bool {
			return counts.ConsecutiveFailures >= cfg.CBThreshold
		},
		OnStateChange: func(n string, from, to gobreaker.State) {
			logger.Warn("httpclient: circuit breaker state change",
				"name", n, "from", from.String(), "to", to.String())
		},
	})
	return &httpClientImpl{
		client: &http.Client{
			Timeout: cfg.Timeout,
			Transport: &http.Transport{
				DialContext: (&net.Dialer{Timeout: cfg.DialTimeout}).DialContext,
			},
		},
		logger: logger,
		cfg:    cfg,
		cb:     cb,
	}
}

// NewWithDefaults returns a Provider with sensible defaults.
func NewWithDefaults(logger logging.Logger) Provider {
	return New(logger, DefaultConfig())
}

type httpClientImpl struct {
	client *http.Client
	logger logging.Logger
	cfg    Config
	cb     *gobreaker.CircuitBreaker
}

func (c *httpClientImpl) Do(req *http.Request) (*http.Response, error) {
	var resp *http.Response

	result, err := c.cb.Execute(func() (any, error) {
		var innerErr error
		var retryAfterDelay time.Duration
		retryErr := retry.Do(
			func() error {
				if id := corelogz.GetRequestID(req.Context()); id != "" {
					req.Header.Set("X-Request-ID", id)
				}
				start := time.Now()
				resp, innerErr = c.client.Do(req)
				latency := time.Since(start)
				if innerErr != nil {
					c.logger.Debug("httpclient: request error",
						"err", innerErr, "url", req.URL.String())
					return innerErr
				}
				c.logger.Info("httpclient: request completed",
					"method", req.Method,
					"url", req.URL.String(),
					"status", resp.StatusCode,
					"latency", latency.String(),
				)
				if resp.StatusCode == http.StatusTooManyRequests {
					if ra := resp.Header.Get("Retry-After"); ra != "" {
						if secs, err := strconv.Atoi(ra); err == nil {
							retryAfterDelay = time.Duration(secs) * time.Second
						}
					}
					return fmt.Errorf("rate limited: %d", resp.StatusCode)
				}
				if resp.StatusCode >= 500 {
					return fmt.Errorf("server error: %d", resp.StatusCode)
				}
				return nil
			},
			retry.Attempts(c.cfg.MaxRetries),
			retry.Delay(c.cfg.RetryDelay),
			retry.DelayType(func(n uint, err error, config *retry.Config) time.Duration {
				if retryAfterDelay > 0 {
					d := retryAfterDelay
					retryAfterDelay = 0
					return d
				}
				return retry.BackOffDelay(n, err, config)
			}),
			retry.LastErrorOnly(true),
		)
		return resp, retryErr
	})

	if err != nil {
		if errors.Is(err, gobreaker.ErrOpenState) {
			return nil, xerrors.New(xerrors.ErrUnavailable,
				"external service unavailable (circuit open)").WithError(err)
		}
		if resp != nil {
			return nil, MapStatusToError(resp.StatusCode, "external API error")
		}
		return nil, xerrors.New(xerrors.ErrInternal, "network or timeout error").WithError(err)
	}

	if r, ok := result.(*http.Response); ok {
		return r, nil
	}
	return resp, nil
}