package validators

import (
	"encoding/json"
	"fmt"
	"net/url"
	"regexp"
	"slices"
	"strings"

	apiv0 "github.com/modelcontextprotocol/registry/pkg/api/v0"
	"github.com/modelcontextprotocol/registry/pkg/model"
)

func ValidateServerJSON(serverJSON *apiv0.ServerJSON) error {
	// Validate server name exists and format
	if _, err := parseServerName(*serverJSON); err != nil {
		return err
	}

	// Validate repository
	if err := validateRepository(&serverJSON.Repository); err != nil {
		return err
	}

	// Validate all packages (basic field validation)
	for _, pkg := range serverJSON.Packages {
		if err := validatePackageField(&pkg); err != nil {
			return err
		}
	}

	// Validate all packages (URL and registry type validation)
	for _, pkg := range serverJSON.Packages {
		if err := validatePackage(&pkg); err != nil {
			return fmt.Errorf("validation failed: %w", err)
		}
	}

	// Validate all remotes
	for _, remote := range serverJSON.Remotes {
		if err := validateRemote(&remote); err != nil {
			return err
		}
	}

	// Validate reverse-DNS namespace matching for remote URLs
	if err := validateRemoteNamespaceMatch(*serverJSON); err != nil {
		return err
	}

	return nil
}

func validateRepository(obj *model.Repository) error {
	// Skip validation for empty repository (optional field)
	if obj.URL == "" && obj.Source == "" {
		return nil
	}

	// validate the repository source
	repoSource := RepositorySource(obj.Source)
	if !IsValidRepositoryURL(repoSource, obj.URL) {
		return fmt.Errorf("%w: %s", ErrInvalidRepositoryURL, obj.URL)
	}

	return nil
}

func validatePackageField(obj *model.Package) error {
	if !HasNoSpaces(obj.Identifier) {
		return ErrPackageNameHasSpaces
	}

	// Validate runtime arguments
	for _, arg := range obj.RuntimeArguments {
		if err := validateArgument(&arg); err != nil {
			return fmt.Errorf("invalid runtime argument: %w", err)
		}
	}

	// Validate package arguments
	for _, arg := range obj.PackageArguments {
		if err := validateArgument(&arg); err != nil {
			return fmt.Errorf("invalid package argument: %w", err)
		}
	}

	return nil
}

// validateArgument validates argument details
func validateArgument(obj *model.Argument) error {
	if obj.Type == model.ArgumentTypeNamed {
		// Validate named argument name format
		if err := validateNamedArgumentName(obj.Name); err != nil {
			return err
		}

		// Validate value and default don't start with the name
		if err := validateArgumentValueFields(obj.Name, obj.Value, obj.Default); err != nil {
			return err
		}
	}
	return nil
}

func validateNamedArgumentName(name string) error {
	// Check if name is required for named arguments
	if name == "" {
		return ErrNamedArgumentNameRequired
	}

	// Check for invalid characters that suggest embedded values or descriptions
	// Valid: "--directory", "--port", "-v", "config", "verbose"
	// Invalid: "--directory <absolute_path_to_adfin_mcp_folder>", "--port 8080"
	if strings.Contains(name, "<") || strings.Contains(name, ">") ||
		strings.Contains(name, " ") || strings.Contains(name, "$") {
		return fmt.Errorf("%w: %s", ErrInvalidNamedArgumentName, name)
	}

	return nil
}

func validateArgumentValueFields(name, value, defaultValue string) error {
	// Check if value starts with the argument name (using startsWith, not contains)
	if value != "" && strings.HasPrefix(value, name) {
		return fmt.Errorf("%w: value starts with argument name '%s': %s", ErrArgumentValueStartsWithName, name, value)
	}

	if defaultValue != "" && strings.HasPrefix(defaultValue, name) {
		return fmt.Errorf("%w: default starts with argument name '%s': %s", ErrArgumentDefaultStartsWithName, name, defaultValue)
	}

	return nil
}

func validateRemote(obj *model.Remote) error {
	if !IsValidURL(obj.URL) {
		return fmt.Errorf("%w: %s", ErrInvalidRemoteURL, obj.URL)
	}
	return nil
}

func validateMCPBPackage(fullURL string) error {
	parsedURL, err := url.Parse(fullURL)
	if err != nil {
		return fmt.Errorf("invalid MCPB package URL: %w", err)
	}

	host := strings.ToLower(parsedURL.Host)
	allowedHosts := []string{
		"github.com",
		"www.github.com",
		"gitlab.com",
		"www.gitlab.com",
	}

	isAllowed := false
	for _, allowed := range allowedHosts {
		if host == allowed {
			isAllowed = true
			break
		}
	}

	if !isAllowed {
		return fmt.Errorf("MCPB packages must be hosted on allowlisted providers (GitHub or GitLab). Host '%s' is not allowed", host)
	}

	// Validate URL path is a proper release URL with strict structure validation
	path := parsedURL.Path
	switch host {
	case "github.com", "www.github.com":
		// GitHub release URLs must match: /owner/repo/releases/download/tag/filename
		if !isValidGitHubReleaseURL(path) {
			return fmt.Errorf("GitHub MCPB packages must be release assets following the pattern '/owner/repo/releases/download/tag/filename'")
		}
	case "gitlab.com", "www.gitlab.com":
		// GitLab release URLs must match specific patterns
		if !isValidGitLabReleaseURL(path) {
			return fmt.Errorf("GitLab MCPB packages must be release assets following patterns '/owner/repo/-/releases/tag/downloads/filename' or '/owner/repo/-/package_files/id/download'")
		}
	}

	return nil
}

// getDefaultRegistryBaseURL returns the default registry base URL for a given registry type
func getDefaultRegistryBaseURL(registryType string) string {
	defaultURLs := map[string]string{
		model.RegistryTypeNPM:   model.RegistryURLNPM,
		model.RegistryTypePyPI:  model.RegistryURLPyPI,
		model.RegistryTypeOCI:   model.RegistryURLDocker,
		model.RegistryTypeNuGet: model.RegistryURLNuGet,
	}

	return defaultURLs[registryType]
}

// isValidGitHubReleaseURL validates that a path follows the GitHub release asset pattern
// Pattern: /owner/repo/releases/download/tag/filename
func isValidGitHubReleaseURL(path string) bool {
	// GitHub release URL pattern: /owner/repo/releases/download/tag/filename
	// - owner: username or organization (1-39 chars, alphanumeric + hyphens, no consecutive hyphens)
	// - repo: repository name (similar rules to owner)
	// - tag: release tag (can contain various characters but not empty)
	// - filename: asset filename (not empty)
	pattern := `^/([a-zA-Z0-9]([a-zA-Z0-9\-]{0,37}[a-zA-Z0-9])?)/([a-zA-Z0-9._\-]+)/releases/download/([^/]+)/([^/]+)$`
	matched, _ := regexp.MatchString(pattern, path)
	return matched
}

// isValidGitLabReleaseURL validates that a path follows GitLab release asset patterns
func isValidGitLabReleaseURL(path string) bool {
	// GitLab release URL patterns:
	// 1. /owner/repo/-/releases/tag/downloads/filename
	// 2. /owner/repo/-/package_files/id/download
	// 3. /group/subgroup/repo/-/releases/tag/downloads/filename (nested groups)
	
	// The key insight is that GitLab URLs have "/-/" as a delimiter that separates the 
	// project path from the GitLab-specific routes. Everything before "/-/" is the project path.
	
	// Pattern 1: Release downloads with /-/releases/tag/downloads/filename
	releasePattern := `^/([a-zA-Z0-9._\-]+(?:/[a-zA-Z0-9._\-]+)*)/-/releases/([^/]+)/downloads/([^/]+)$`
	if matched, _ := regexp.MatchString(releasePattern, path); matched {
		return true
	}
	
	// Pattern 2: Package files with /-/package_files/id/download
	packagePattern := `^/([a-zA-Z0-9._\-]+(?:/[a-zA-Z0-9._\-]+)*)/-/package_files/([0-9]+)/download$`
	if matched, _ := regexp.MatchString(packagePattern, path); matched {
		return true
	}
	
	return false
}

// inferMCPBRegistryBaseURL infers the registry base URL from an MCPB identifier
func inferMCPBRegistryBaseURL(identifier string) string {
	parsedURL, err := url.Parse(identifier)
	if err != nil {
		return ""
	}

	host := strings.ToLower(parsedURL.Host)
	switch host {
	case "github.com", "www.github.com":
		return model.RegistryURLGitHub
	case "gitlab.com", "www.gitlab.com":
		return model.RegistryURLGitLab
	default:
		return ""
	}
}

// validateRegistryType checks if the registry type is supported
func validateRegistryType(registryType string) error {
	// Registry type is required
	if registryType == "" {
		return fmt.Errorf("%w: registry type is required", ErrUnsupportedRegistryType)
	}

	supportedTypes := []string{
		model.RegistryTypeNPM,
		model.RegistryTypePyPI,
		model.RegistryTypeOCI,
		model.RegistryTypeNuGet,
		model.RegistryTypeMCPB,
	}

	for _, supported := range supportedTypes {
		if registryType == supported {
			return nil
		}
	}

	return fmt.Errorf("%w: '%s'. Supported types: %v", ErrUnsupportedRegistryType, registryType, supportedTypes)
}

// validateRegistryBaseURL checks if the registry base URL is valid for the given registry type
func validateRegistryBaseURL(registryType, baseURL string) error {
	// Base URL is required for all registry types except MCPB (which uses direct URLs)
	if baseURL == "" {
		if registryType == model.RegistryTypeMCPB {
			return nil // MCPB packages use direct URLs in the identifier
		}
		return fmt.Errorf("%w: registry base URL is required for registry type '%s'", ErrUnsupportedRegistryBaseURL, registryType)
	}

	// Define expected base URLs for each registry type
	expectedURLs := map[string][]string{
		model.RegistryTypeNPM:   {model.RegistryURLNPM},
		model.RegistryTypePyPI:  {model.RegistryURLPyPI},
		model.RegistryTypeOCI:   {model.RegistryURLDocker},
		model.RegistryTypeNuGet: {model.RegistryURLNuGet},
		model.RegistryTypeMCPB:  {model.RegistryURLGitHub, model.RegistryURLGitLab},
	}

	// Check if the base URL is valid for the registry type
	if expectedURLsForType, exists := expectedURLs[registryType]; exists {
		for _, expected := range expectedURLsForType {
			if baseURL == expected {
				return nil
			}
		}
		return fmt.Errorf("%w: '%s' is not valid for registry type '%s'. Expected: %v",
			ErrMismatchedRegistryTypeAndURL, baseURL, registryType, expectedURLsForType)
	}

	// If registry type is not in our expected URLs map but base URL is provided,
	// it's likely an unsupported base URL
	return fmt.Errorf("%w: '%s'", ErrUnsupportedRegistryBaseURL, baseURL)
}

func validatePackage(pkg *model.Package) error {
	registryType := strings.ToLower(pkg.RegistryType)

	// Only validate if package has an identifier (i.e., it's a real package reference)
	if pkg.Identifier != "" {
		// Validate registry type is supported
		if err := validateRegistryType(registryType); err != nil {
			return err
		}

		// Apply defaults for registry base URL if empty
		if pkg.RegistryBaseURL == "" {
			if registryType == model.RegistryTypeMCPB {
				// For MCPB, infer from identifier
				pkg.RegistryBaseURL = inferMCPBRegistryBaseURL(pkg.Identifier)
			} else {
				// For other types, use default
				pkg.RegistryBaseURL = getDefaultRegistryBaseURL(registryType)
			}
		}

		// Validate registry base URL matches the registry type
		if err := validateRegistryBaseURL(registryType, pkg.RegistryBaseURL); err != nil {
			return err
		}
	}

	// For direct download packages (mcpb or direct URLs)
	if registryType == model.RegistryTypeMCPB ||
		strings.HasPrefix(pkg.Identifier, "http://") || strings.HasPrefix(pkg.Identifier, "https://") {
		parsedURL, err := url.Parse(pkg.Identifier)
		if err != nil {
			return fmt.Errorf("invalid package URL: %w", err)
		}

		// For MCPB packages, validate they're from allowed hosts and are release URLs
		if registryType == model.RegistryTypeMCPB {
			return validateMCPBPackage(pkg.Identifier)
		}

		// For other URL-based packages, just ensure it's valid
		if parsedURL.Scheme == "" || parsedURL.Host == "" {
			return fmt.Errorf("package URL must be a valid absolute URL")
		}
		return nil
	}

	// For other registry-based packages, no special validation needed
	return nil
}

// ValidatePublishRequest validates a complete publish request including extensions
func ValidatePublishRequest(req apiv0.ServerJSON) error {
	// Validate publisher extensions in _meta
	if err := validatePublisherExtensions(req); err != nil {
		return err
	}

	// Validate the server detail (includes all nested validation)
	if err := ValidateServerJSON(&req); err != nil {
		return err
	}

	return nil
}

func validatePublisherExtensions(req apiv0.ServerJSON) error {
	const maxExtensionSize = 4 * 1024 // 4KB limit

	// Check size limit for _meta.publisher extension
	if req.Meta != nil && req.Meta.Publisher != nil {
		extensionsJSON, err := json.Marshal(req.Meta.Publisher)
		if err != nil {
			return fmt.Errorf("failed to marshal _meta.publisher extension: %w", err)
		}
		if len(extensionsJSON) > maxExtensionSize {
			return fmt.Errorf("_meta.publisher extension exceeds 4KB limit (%d bytes)", len(extensionsJSON))
		}
	}

	if req.Meta != nil {
		// Validate that only "publisher" is allowed in _meta during publish (no registry metadata should be present)
		if req.Meta.IOModelContextProtocolRegistry != nil {
			return fmt.Errorf("registry metadata '_meta.io.modelcontextprotocol.registry' is not allowed during publish")
		}
	}

	return nil
}

func parseServerName(serverJSON apiv0.ServerJSON) (string, error) {
	name := serverJSON.Name
	if name == "" {
		return "", fmt.Errorf("server name is required and must be a string")
	}

	// Validate format: dns-namespace/name
	if !strings.Contains(name, "/") {
		return "", fmt.Errorf("server name must be in format 'dns-namespace/name' (e.g., 'com.example.api/server')")
	}

	parts := strings.SplitN(name, "/", 2)
	if len(parts) != 2 || parts[0] == "" || parts[1] == "" {
		return "", fmt.Errorf("server name must be in format 'dns-namespace/name' with non-empty namespace and name parts")
	}

	return name, nil
}

// validateRemoteNamespaceMatch validates that remote URLs match the reverse-DNS namespace
func validateRemoteNamespaceMatch(serverJSON apiv0.ServerJSON) error {
	namespace := serverJSON.Name

	for _, remote := range serverJSON.Remotes {
		if err := validateRemoteURLMatchesNamespace(remote.URL, namespace); err != nil {
			return fmt.Errorf("remote URL %s does not match namespace %s: %w", remote.URL, namespace, err)
		}
	}

	return nil
}

// validateRemoteURLMatchesNamespace checks if a remote URL's hostname matches the publisher domain from the namespace
func validateRemoteURLMatchesNamespace(remoteURL, namespace string) error {
	// Parse the URL to extract the hostname
	parsedURL, err := url.Parse(remoteURL)
	if err != nil {
		return fmt.Errorf("invalid URL format: %w", err)
	}

	hostname := parsedURL.Hostname()
	if hostname == "" {
		return fmt.Errorf("URL must have a valid hostname")
	}

	// Skip validation for localhost and local development URLs
	if hostname == "localhost" || strings.HasSuffix(hostname, ".localhost") || hostname == "127.0.0.1" {
		return nil
	}

	// Extract publisher domain from reverse-DNS namespace
	publisherDomain := extractPublisherDomainFromNamespace(namespace)
	if publisherDomain == "" {
		return fmt.Errorf("invalid namespace format: cannot extract domain from %s", namespace)
	}

	// Check if the remote URL hostname matches the publisher domain or is a subdomain
	if !isValidHostForDomain(hostname, publisherDomain) {
		return fmt.Errorf("remote URL host %s does not match publisher domain %s", hostname, publisherDomain)
	}

	return nil
}

// extractPublisherDomainFromNamespace converts reverse-DNS namespace to normal domain format
// e.g., "com.example" -> "example.com"
func extractPublisherDomainFromNamespace(namespace string) string {
	// Extract the namespace part before the first slash
	namespacePart := namespace
	if slashIdx := strings.Index(namespace, "/"); slashIdx != -1 {
		namespacePart = namespace[:slashIdx]
	}

	// Split into parts and reverse them to get normal domain format
	parts := strings.Split(namespacePart, ".")
	if len(parts) < 2 {
		return ""
	}

	// Reverse the parts to convert from reverse-DNS to normal domain
	slices.Reverse(parts)

	return strings.Join(parts, ".")
}

// isValidHostForDomain checks if a hostname is the domain or a subdomain of the publisher domain
func isValidHostForDomain(hostname, publisherDomain string) bool {
	// Exact match
	if hostname == publisherDomain {
		return true
	}

	// Subdomain match - hostname should end with "." + publisherDomain
	if strings.HasSuffix(hostname, "."+publisherDomain) {
		return true
	}

	return false
}