package publichttp

import (
	"context"
	"errors"
	"fmt"
	"net"
	"net/http"
	"sync"
	"time"

	"galaxy/authsession/internal/service/confirmemailcode"
	"galaxy/authsession/internal/service/sendemailcode"
	"galaxy/authsession/internal/telemetry"

	"go.uber.org/zap"
)

const (
	defaultAddr              = ":8080"
	defaultReadHeaderTimeout = 2 * time.Second
	defaultReadTimeout       = 10 * time.Second
	defaultIdleTimeout       = time.Minute
	defaultRequestTimeout    = 3 * time.Second
)

// SendEmailCodeUseCase describes the public send-email-code application
// service consumed by the HTTP transport layer.
type SendEmailCodeUseCase interface {
	// Execute validates input and creates a new login challenge.
	Execute(ctx context.Context, input sendemailcode.Input) (sendemailcode.Result, error)
}

// ConfirmEmailCodeUseCase describes the public confirm-email-code application
// service consumed by the HTTP transport layer.
type ConfirmEmailCodeUseCase interface {
	// Execute validates input and completes an existing login challenge.
	Execute(ctx context.Context, input confirmemailcode.Input) (confirmemailcode.Result, error)
}

// Config describes the public HTTP listener owned by authsession.
type Config struct {
	// Addr is the TCP listen address used by the public HTTP server.
	Addr string

	// ReadHeaderTimeout bounds how long the listener may spend reading request
	// headers before the server rejects the connection.
	ReadHeaderTimeout time.Duration

	// ReadTimeout bounds how long the listener may spend reading one public
	// request.
	ReadTimeout time.Duration

	// IdleTimeout bounds how long the listener keeps an idle keep-alive
	// connection open.
	IdleTimeout time.Duration

	// RequestTimeout bounds one application-layer public-auth use-case call.
	RequestTimeout time.Duration
}

// Validate reports whether cfg contains a usable public HTTP listener
// configuration.
func (cfg Config) Validate() error {
	switch {
	case cfg.Addr == "":
		return errors.New("public HTTP addr must not be empty")
	case cfg.ReadHeaderTimeout <= 0:
		return errors.New("public HTTP read header timeout must be positive")
	case cfg.ReadTimeout <= 0:
		return errors.New("public HTTP read timeout must be positive")
	case cfg.IdleTimeout <= 0:
		return errors.New("public HTTP idle timeout must be positive")
	case cfg.RequestTimeout <= 0:
		return errors.New("public HTTP request timeout must be positive")
	default:
		return nil
	}
}

// DefaultConfig returns the default public HTTP listener settings aligned with
// the gateway public-auth transport timeouts.
func DefaultConfig() Config {
	return Config{
		Addr:              defaultAddr,
		ReadHeaderTimeout: defaultReadHeaderTimeout,
		ReadTimeout:       defaultReadTimeout,
		IdleTimeout:       defaultIdleTimeout,
		RequestTimeout:    defaultRequestTimeout,
	}
}

// Dependencies describes the collaborators used by the public HTTP transport
// layer.
type Dependencies struct {
	// SendEmailCode executes the public send-email-code use case.
	SendEmailCode SendEmailCodeUseCase

	// ConfirmEmailCode executes the public confirm-email-code use case.
	ConfirmEmailCode ConfirmEmailCodeUseCase

	// Logger writes structured transport logs. When nil, a no-op logger is
	// used.
	Logger *zap.Logger

	// Telemetry records OpenTelemetry spans and low-cardinality HTTP metrics.
	// When nil, the transport still serves requests with no-op providers.
	Telemetry *telemetry.Runtime
}

// Server owns the public auth HTTP listener exposed by authsession.
type Server struct {
	cfg Config

	handler http.Handler
	logger  *zap.Logger

	stateMu  sync.RWMutex
	server   *http.Server
	listener net.Listener
}

// NewServer constructs one public auth HTTP server for cfg and deps.
func NewServer(cfg Config, deps Dependencies) (*Server, error) {
	if err := cfg.Validate(); err != nil {
		return nil, fmt.Errorf("new public HTTP server: %w", err)
	}

	handler, err := newHandlerWithConfig(cfg, deps)
	if err != nil {
		return nil, fmt.Errorf("new public HTTP server: %w", err)
	}

	logger := deps.Logger
	if logger == nil {
		logger = zap.NewNop()
	}
	logger = logger.Named("public_http")

	return &Server{
		cfg:     cfg,
		handler: handler,
		logger:  logger,
	}, nil
}

// Run binds the configured listener and serves the public auth HTTP surface
// until Shutdown closes the server.
func (s *Server) Run(ctx context.Context) error {
	if ctx == nil {
		return errors.New("run public HTTP server: nil context")
	}
	if err := ctx.Err(); err != nil {
		return err
	}

	listener, err := net.Listen("tcp", s.cfg.Addr)
	if err != nil {
		return fmt.Errorf("run public HTTP server: listen on %q: %w", s.cfg.Addr, err)
	}

	server := &http.Server{
		Handler:           s.handler,
		ReadHeaderTimeout: s.cfg.ReadHeaderTimeout,
		ReadTimeout:       s.cfg.ReadTimeout,
		IdleTimeout:       s.cfg.IdleTimeout,
	}

	s.stateMu.Lock()
	s.server = server
	s.listener = listener
	s.stateMu.Unlock()

	s.logger.Info("public HTTP server started", zap.String("addr", listener.Addr().String()))

	defer func() {
		s.stateMu.Lock()
		s.server = nil
		s.listener = nil
		s.stateMu.Unlock()
	}()

	err = server.Serve(listener)
	switch {
	case err == nil:
		return nil
	case errors.Is(err, http.ErrServerClosed):
		s.logger.Info("public HTTP server stopped")
		return nil
	default:
		return fmt.Errorf("run public HTTP server: serve on %q: %w", s.cfg.Addr, err)
	}
}

// Shutdown gracefully stops the public HTTP server within ctx.
func (s *Server) Shutdown(ctx context.Context) error {
	if ctx == nil {
		return errors.New("shutdown public HTTP server: nil context")
	}

	s.stateMu.RLock()
	server := s.server
	s.stateMu.RUnlock()

	if server == nil {
		return nil
	}

	if err := server.Shutdown(ctx); err != nil && !errors.Is(err, http.ErrServerClosed) {
		return fmt.Errorf("shutdown public HTTP server: %w", err)
	}

	return nil
}

func normalizeDependencies(deps Dependencies) (Dependencies, error) {
	switch {
	case deps.SendEmailCode == nil:
		return Dependencies{}, errors.New("send email code use case must not be nil")
	case deps.ConfirmEmailCode == nil:
		return Dependencies{}, errors.New("confirm email code use case must not be nil")
	case deps.Logger == nil:
		deps.Logger = zap.NewNop()
	}

	deps.Logger = deps.Logger.Named("public_http")
	return deps, nil
}