package auth

import (
	"context"
	"fmt"

	"google.golang.org/grpc"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/metadata"
	"google.golang.org/grpc/status"
)

// contextKey is a custom type for context keys to avoid collisions.
type contextKey string

const (
	// pubkeyContextKey is the key for storing the authenticated pubkey in context.
	pubkeyContextKey contextKey = "nostr-pubkey"
)

// InterceptorOptions configures the authentication interceptor behavior.
type InterceptorOptions struct {
	// TimestampWindow is the maximum age of auth events in seconds.
	// Events older than this are rejected to prevent replay attacks.
	// Default: 60 seconds
	TimestampWindow int64

	// Required determines whether authentication is mandatory.
	// If true, requests without valid auth are rejected.
	// If false, unauthenticated requests are allowed (pubkey will be empty).
	// Default: false
	Required bool

	// ValidatePayload checks the payload hash tag if present.
	// Default: false
	ValidatePayload bool

	// AllowedNpubs is an optional whitelist of allowed pubkeys (hex format).
	// Config accepts npub format only, normalized to hex at load time.
	// If nil or empty, all valid signatures are accepted.
	// Default: nil (allow all)
	AllowedNpubs []string

	// SkipMethods is a list of gRPC methods that bypass authentication.
	// Useful for public endpoints like health checks or relay info.
	// Example: []string{"/nostr.v1.NostrRelay/QueryEvents"}
	// Default: nil (authenticate all methods)
	SkipMethods []string
}

// DefaultInterceptorOptions returns the default configuration.
func DefaultInterceptorOptions() *InterceptorOptions {
	return &InterceptorOptions{
		TimestampWindow: 60,
		Required:        false,
		ValidatePayload: false,
		AllowedNpubs:    nil,
		SkipMethods:     nil,
	}
}

// NostrUnaryInterceptor creates a gRPC unary interceptor for NIP-98 authentication.
func NostrUnaryInterceptor(opts *InterceptorOptions) grpc.UnaryServerInterceptor {
	if opts == nil {
		opts = DefaultInterceptorOptions()
	}

	return func(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) {
		// Check if this method should skip auth
		if shouldSkipAuth(info.FullMethod, opts.SkipMethods) {
			return handler(ctx, req)
		}

		// Extract and validate auth
		pubkey, err := validateAuthFromContext(ctx, info.FullMethod, opts)
		if err != nil {
			if opts.Required {
				return nil, status.Error(codes.Unauthenticated, err.Error())
			}
			// Auth not required, continue without pubkey
			return handler(ctx, req)
		}

		// Add pubkey to context for handlers
		ctx = context.WithValue(ctx, pubkeyContextKey, pubkey)

		return handler(ctx, req)
	}
}

// NostrStreamInterceptor creates a gRPC stream interceptor for NIP-98 authentication.
func NostrStreamInterceptor(opts *InterceptorOptions) grpc.StreamServerInterceptor {
	if opts == nil {
		opts = DefaultInterceptorOptions()
	}

	return func(srv interface{}, ss grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error {
		// Check if this method should skip auth
		if shouldSkipAuth(info.FullMethod, opts.SkipMethods) {
			return handler(srv, ss)
		}

		// Extract and validate auth
		ctx := ss.Context()
		pubkey, err := validateAuthFromContext(ctx, info.FullMethod, opts)
		if err != nil {
			if opts.Required {
				return status.Error(codes.Unauthenticated, err.Error())
			}
			// Auth not required, continue without pubkey
			return handler(srv, ss)
		}

		// Wrap stream with authenticated context
		wrappedStream := &authenticatedStream{
			ServerStream: ss,
			ctx:          context.WithValue(ctx, pubkeyContextKey, pubkey),
		}

		return handler(srv, wrappedStream)
	}
}

// authenticatedStream wraps a ServerStream with an authenticated context.
type authenticatedStream struct {
	grpc.ServerStream
	ctx context.Context
}

func (s *authenticatedStream) Context() context.Context {
	return s.ctx
}

// validateAuthFromContext extracts and validates the NIP-98 auth event from the context.
func validateAuthFromContext(ctx context.Context, method string, opts *InterceptorOptions) (string, error) {
	// Extract metadata from context
	md, ok := metadata.FromIncomingContext(ctx)
	if !ok {
		return "", fmt.Errorf("missing metadata")
	}

	// Get authorization header
	authHeaders := md.Get("authorization")
	if len(authHeaders) == 0 {
		return "", fmt.Errorf("missing authorization header")
	}

	authHeader := authHeaders[0]

	// Parse the auth event
	event, err := ParseAuthHeader(authHeader)
	if err != nil {
		return "", fmt.Errorf("invalid auth header: %w", err)
	}

	// Validate the event
	validationOpts := ValidationOptions{
		TimestampWindow: opts.TimestampWindow,
		ValidatePayload: opts.ValidatePayload,
		ExpectedMethod:  "POST", // gRPC always uses POST
		// Note: We don't validate URI here because the full URI isn't easily
		// available in the interceptor context. The method name is validated instead.
	}

	if err := ValidateAuthEvent(event, validationOpts); err != nil {
		return "", fmt.Errorf("invalid auth event: %w", err)
	}

	// Extract pubkey
	pubkey := ExtractPubkey(event)

	// Check whitelist if configured (all values are already normalized to hex)
	if len(opts.AllowedNpubs) > 0 {
		if !contains(opts.AllowedNpubs, pubkey) {
			return "", fmt.Errorf("pubkey not in whitelist")
		}
	}

	return pubkey, nil
}

// shouldSkipAuth checks if a method should bypass authentication.
func shouldSkipAuth(method string, skipMethods []string) bool {
	for _, skip := range skipMethods {
		if skip == method {
			return true
		}
	}
	return false
}

// contains checks if a slice contains a string.
func contains(slice []string, item string) bool {
	for _, s := range slice {
		if s == item {
			return true
		}
	}
	return false
}

// PubkeyFromContext retrieves the authenticated pubkey from the context.
// Returns the pubkey and true if authentication was successful, or empty string and false otherwise.
func PubkeyFromContext(ctx context.Context) (string, bool) {
	pubkey, ok := ctx.Value(pubkeyContextKey).(string)
	return pubkey, ok
}

// RequireAuth is a helper that extracts the pubkey and returns an error if not authenticated.
func RequireAuth(ctx context.Context) (string, error) {
	pubkey, ok := PubkeyFromContext(ctx)
	if !ok || pubkey == "" {
		return "", status.Error(codes.Unauthenticated, "authentication required")
	}
	return pubkey, nil
}