package harness

import (
	"bytes"
	"encoding/json"
	"errors"
	"io"
	"net/http"
	"net/http/httptest"
	"sync"
	"testing"
	"time"
)

const mailStubPath = "/api/v1/internal/login-code-deliveries"

// LoginCodeDelivery stores one mail-delivery request received by the external
// mail stub.
type LoginCodeDelivery struct {
	// Email identifies the target e-mail address requested by authsession.
	Email string

	// Code stores the cleartext login code requested by authsession.
	Code string
}

// MailBehavior overrides one external mail-stub response.
type MailBehavior struct {
	// Delay waits before the stub writes its response.
	Delay time.Duration

	// StatusCode overrides the HTTP status returned by the stub. Zero keeps the
	// default `200 OK`.
	StatusCode int

	// RawBody overrides the exact response body returned by the stub. Empty
	// value keeps the default JSON payload for the chosen status.
	RawBody string
}

// MailStub provides one stateful external HTTP mail-service stub.
type MailStub struct {
	server *httptest.Server

	mu         sync.Mutex
	deliveries []LoginCodeDelivery
	behavior   MailBehavior
}

// NewMailStub starts one stateful external HTTP mail-service stub.
func NewMailStub(t testing.TB) *MailStub {
	t.Helper()

	stub := &MailStub{}
	stub.server = httptest.NewServer(http.HandlerFunc(stub.handle))
	t.Cleanup(stub.server.Close)
	return stub
}

// BaseURL returns the stub base URL suitable for service runtime wiring.
func (s *MailStub) BaseURL() string {
	if s == nil || s.server == nil {
		return ""
	}
	return s.server.URL
}

// SetBehavior replaces the current response behavior used by subsequent
// requests.
func (s *MailStub) SetBehavior(behavior MailBehavior) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.behavior = behavior
}

// RecordedDeliveries returns a snapshot of all delivery requests received by
// the stub so far.
func (s *MailStub) RecordedDeliveries() []LoginCodeDelivery {
	s.mu.Lock()
	defer s.mu.Unlock()

	cloned := make([]LoginCodeDelivery, len(s.deliveries))
	copy(cloned, s.deliveries)
	return cloned
}

// Reset clears the recorded deliveries and restores default behavior.
func (s *MailStub) Reset() {
	s.mu.Lock()
	defer s.mu.Unlock()

	s.deliveries = nil
	s.behavior = MailBehavior{}
}

func (s *MailStub) handle(writer http.ResponseWriter, request *http.Request) {
	if request.Method != http.MethodPost || request.URL.Path != mailStubPath {
		http.NotFound(writer, request)
		return
	}

	var payload struct {
		Email string `json:"email"`
		Code  string `json:"code"`
	}
	if err := decodeStrictJSONRequest(request, &payload); err != nil {
		http.Error(writer, err.Error(), http.StatusBadRequest)
		return
	}

	s.mu.Lock()
	s.deliveries = append(s.deliveries, LoginCodeDelivery{
		Email: payload.Email,
		Code:  payload.Code,
	})
	behavior := s.behavior
	s.mu.Unlock()

	if behavior.Delay > 0 {
		timer := time.NewTimer(behavior.Delay)
		defer timer.Stop()

		select {
		case <-request.Context().Done():
			return
		case <-timer.C:
		}
	}

	statusCode := behavior.StatusCode
	if statusCode == 0 {
		statusCode = http.StatusOK
	}

	body := behavior.RawBody
	if body == "" {
		switch statusCode {
		case http.StatusOK:
			body = `{"outcome":"sent"}`
		default:
			body = `{"error":"stubbed mail failure"}`
		}
	}

	writer.Header().Set("Content-Type", "application/json")
	writer.WriteHeader(statusCode)
	_, _ = io.WriteString(writer, body)
}

func decodeStrictJSONRequest(request *http.Request, target any) error {
	decoder := json.NewDecoder(request.Body)
	decoder.DisallowUnknownFields()

	if err := decoder.Decode(target); err != nil {
		return err
	}
	if err := decoder.Decode(&struct{}{}); err != io.EOF {
		if err == nil {
			return errors.New("unexpected trailing JSON input")
		}
		return err
	}

	return nil
}

func decodeStrictJSONPayload(payload []byte, target any) error {
	decoder := json.NewDecoder(bytes.NewReader(payload))
	decoder.DisallowUnknownFields()

	if err := decoder.Decode(target); err != nil {
		return err
	}
	if err := decoder.Decode(&struct{}{}); err != io.EOF {
		if err == nil {
			return errors.New("unexpected trailing JSON input")
		}
		return err
	}

	return nil
}