// Package cbssl provides browser-based SSL certificate chain validation.
// It validates certificates against actual browser CA root stores (Chrome, Firefox).
package cbssl

import (
	"crypto/tls"
	"crypto/x509"
	"encoding/pem"
	"fmt"
	"log"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"github.com/pkg/errors"

	"rocketgit.ru/rsmon/worker/app/models"
)

const stateOK = "OK"

// BrowserType represents the type of browser to use for CA roots
type BrowserType string

// Browser type constants for CA root selection.
const (
	BrowserChrome  BrowserType = "chrome"
	BrowserFirefox BrowserType = "firefox"
	BrowserAll     BrowserType = "all"
)

var (
	// Certificate pools for different browsers
	chromeRoots  *x509.CertPool
	firefoxRoots *x509.CertPool
	once         sync.Once
)

// BrowserCertPools holds the certificate pools for different browsers
type BrowserCertPools struct {
	Chrome  *x509.CertPool
	Firefox *x509.CertPool
}

func init() {
	// Initialize certificate pools
	once.Do(func() {
		var err error
		chromeRoots, firefoxRoots, err = LoadBrowserCARoots()
		if err != nil {
			log.Printf("Warning: failed to load browser CA roots: %v", err)
			// Fall back to system roots
			chromeRoots = x509.NewCertPool()
			firefoxRoots = x509.NewCertPool()
			systemRoots, err := x509.SystemCertPool()
			if err == nil {
				chromeRoots = systemRoots
				firefoxRoots = systemRoots
			}
		}
	})
}

// Perform executes the browser-based SSL certificate check
func Perform(c *models.Check) *Result {
	result := &Result{}
	result.State = stateOK

	// Get URL to check
	checkURL, err := getCheckURL(c)
	if err != nil {
		result.State = "FAIL"
		result.Error = errors.Wrap(err, "invalid url")
		return result
	}
	log.Println("CBSSL URL:", checkURL)

	// Parse hostname from URL
	parsedURL, err := url.Parse(checkURL)
	if err != nil {
		result.State = "FAIL"
		result.Error = errors.Wrap(err, "failed to parse url")
		return result
	}
	hostname := parsedURL.Hostname()

	// Get browser type - default to checking all browsers
	// TODO: Add Browser field to CheckSettings to allow per-check configuration
	browserType := BrowserAll

	// Create custom TLS client that validates against browser roots
	client := &http.Client{
		Timeout: time.Second * 30,
		CheckRedirect: func(_ *http.Request, _ []*http.Request) error {
			return http.ErrUseLastResponse
		},
		Transport: &http.Transport{
			TLSClientConfig: &tls.Config{
				ServerName: hostname,
				MinVersion: tls.VersionTLS12,
				// We'll set RootCAs per request to test against different browsers
			},
		},
	}

	// Test against Chrome roots
	if browserType == BrowserChrome || browserType == BrowserAll {
		chromeResult := testWithBrowser(client, checkURL, chromeRoots, "Chrome")
		result.ChromeValid = chromeResult.Valid
		result.ChromeError = chromeResult.ErrorMsg
		result.ChromeChain = chromeResult.ChainInfo
		if !chromeResult.Valid {
			result.State = "ERR"
			result.Error = errors.New("certificate validation failed against Chrome roots")
			if chromeResult.ErrorMsg != "" {
				result.Warnings = append(result.Warnings, fmt.Sprintf("Chrome: %s", chromeResult.ErrorMsg))
			}
		}
	}

	// Test against Firefox roots
	if browserType == BrowserFirefox || browserType == BrowserAll {
		firefoxResult := testWithBrowser(client, checkURL, firefoxRoots, "Firefox")
		result.FirefoxValid = firefoxResult.Valid
		result.FirefoxError = firefoxResult.ErrorMsg
		result.FirefoxChain = firefoxResult.ChainInfo
		if !firefoxResult.Valid && result.State == stateOK {
			result.State = "ERR"
			result.Error = errors.New("certificate validation failed against Firefox roots")
		}
		if firefoxResult.ErrorMsg != "" {
			result.Warnings = append(result.Warnings, fmt.Sprintf("Firefox: %s", firefoxResult.ErrorMsg))
		}
	}

	// Get certificate info for expiration check
	certInfo, err := getCertificateInfo(checkURL)
	if err != nil {
		if result.State == stateOK {
			result.State = "WARN"
		}
		result.Warnings = append(result.Warnings, fmt.Sprintf("Failed to get certificate info: %v", err))
	} else {
		result.Expires = &certInfo.NotAfter
		result.Subject = certInfo.Subject.CommonName
		result.Issuer = certInfo.Issuer.CommonName
		result.DNSNames = certInfo.DNSNames

		// Check expiration
		exp := time.Until(certInfo.NotAfter).Hours() / 24
		if exp < 2 {
			if result.State == stateOK {
				result.State = "WARN"
			}
			result.Warnings = append(result.Warnings, fmt.Sprintf("Certificate expires in %.1f days", exp))
		}
	}

	return result
}

// testWithBrowser tests the certificate against a specific browser's CA roots
func testWithBrowser(client *http.Client, checkURL string, roots *x509.CertPool, browserName string) BrowserTestResult {
	result := BrowserTestResult{Valid: false}

	// Clone transport and set custom root CAs
	transport, ok := client.Transport.(*http.Transport)
	if !ok {
		result.ErrorMsg = fmt.Sprintf("failed to get transport for %s", browserName)
		return result
	}

	customTransport := transport.Clone()
	customTransport.TLSClientConfig.RootCAs = roots

	// Create new client with custom transport
	customClient := &http.Client{
		Timeout:       client.Timeout,
		CheckRedirect: client.CheckRedirect,
		Transport:     customTransport,
	}

	req, err := http.NewRequest("GET", checkURL, http.NoBody)
	if err != nil {
		result.ErrorMsg = fmt.Sprintf("failed to create request for %s: %v", browserName, err)
		return result
	}

	req.Header.Set("Cache-Control", "max-age=0")
	req.Header.Set("Connection", "close")
	req.Header.Set("User-Agent", getUserAgent(browserName))

	resp, err := customClient.Do(req)
	if err != nil {
		// Check if it's a certificate verification error
		if strings.Contains(err.Error(), "certificate") || strings.Contains(err.Error(), "x509") {
			result.ErrorMsg = fmt.Sprintf("certificate verification failed: %v", err)
		} else {
			result.ErrorMsg = fmt.Sprintf("connection failed: %v", err)
		}
		return result
	}
	defer resp.Body.Close() //nolint:errcheck // accepted lint exception

	result.Valid = true

	// Get chain info
	if resp.TLS != nil && len(resp.TLS.VerifiedChains) > 0 {
		chain := resp.TLS.VerifiedChains[0]
		result.ChainInfo = buildChainInfo(chain)
	}

	return result
}

// BrowserTestResult represents the result of testing against a specific browser
type BrowserTestResult struct {
	Valid     bool
	ErrorMsg  string
	ChainInfo []CertInfo
}

func buildChainInfo(chain []*x509.Certificate) []CertInfo {
	info := make([]CertInfo, 0, len(chain))
	for _, cert := range chain {
		info = append(info, CertInfo{
			Subject:   cert.Subject.CommonName,
			Issuer:    cert.Issuer.CommonName,
			NotBefore: cert.NotBefore,
			NotAfter:  cert.NotAfter,
			IsCA:      cert.IsCA,
			PublicKey: cert.PublicKeyAlgorithm.String(),
			Signature: cert.SignatureAlgorithm.String(),
		})
	}
	return info
}

func getUserAgent(browserName string) string {
	switch browserName {
	case "Chrome":
		return "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36"
	case "Firefox":
		return "Mozilla/5.0 (X11; Linux x86_64; rv:134.0) Gecko/20100101 Firefox/134.0"
	default:
		return "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36"
	}
}

// getCertificateInfo retrieves certificate information without validation
func getCertificateInfo(checkURL string) (*x509.Certificate, error) {
	parsedURL, err := url.Parse(checkURL)
	if err != nil {
		return nil, err
	}
	hostname := parsedURL.Hostname()

	client := &http.Client{
		Timeout: time.Second * 30,
		Transport: &http.Transport{
			TLSClientConfig: &tls.Config{
				ServerName:         hostname,
				InsecureSkipVerify: true,
			},
		},
	}

	resp, err := client.Get(checkURL)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close() //nolint:errcheck // accepted lint exception

	if resp.TLS == nil || len(resp.TLS.PeerCertificates) == 0 {
		return nil, fmt.Errorf("no TLS certificates found")
	}

	return resp.TLS.PeerCertificates[0], nil
}

// getCheckURL constructs the URL to check from the check configuration
func getCheckURL(c *models.Check) (string, error) {
	if c.URL != nil && *c.URL != "" {
		ur := *c.URL
		u, err := url.Parse(ur)
		if err != nil {
			return "", errors.Wrap(err, "bad url")
		}
		if u.Scheme == "" {
			u.Scheme = "https"
		}
		return u.String(), nil
	}
	return "https://" + c.Monitor.Host, nil
}

// LoadBrowserCARoots loads CA root certificates from browser installations
func LoadBrowserCARoots() (chrome, firefox *x509.CertPool, err error) {
	chrome = x509.NewCertPool()
	firefox = x509.NewCertPool()

	// Load Chrome/Chromium CA roots (uses system certs on Linux)
	// On Alpine Linux, this is typically /etc/ssl/certs/ca-certificates.crt
	chromeLoaded := false

	// Try common certificate bundle locations
	certPaths := []string{
		"/etc/ssl/certs/ca-certificates.crt",      // Alpine/Debian
		"/etc/ssl/cert.pem",                       // macOS
		"/etc/pki/tls/certs/ca-bundle.crt",        // RHEL/CentOS
		"/usr/local/share/ca-certificates/",       // Custom certs
		"/data/rsmon/docker/cert-bundles/output/", // Our custom bundled certs
	}

	for _, certPath := range certPaths {
		if loadCertsFromPath(chrome, certPath) {
			chromeLoaded = true
			break
		}
	}

	// Load Firefox CA roots (NSS database)
	// Firefox uses its own NSS database at ~/.pki/nssdb/ or uses system roots
	firefoxLoaded := loadFirefoxCARoots(firefox)

	// If Firefox failed to load, use Chrome/system roots as fallback
	if !firefoxLoaded && chromeLoaded {
		firefox = chrome
	}

	// If both failed, return error
	if !chromeLoaded {
		return nil, nil, fmt.Errorf("failed to load any CA certificates")
	}

	return chrome, firefox, nil
}

// loadCertsFromPath loads certificates from a file or directory
func loadCertsFromPath(pool *x509.CertPool, path string) bool {
	info, err := os.Stat(path)
	if err != nil {
		return false
	}

	if info.IsDir() {
		// Load all .crt and .pem files from directory
		files, err := os.ReadDir(path)
		if err != nil {
			return false
		}
		loaded := false
		for _, file := range files {
			if file.IsDir() {
				continue
			}
			ext := filepath.Ext(file.Name())
			if ext == ".crt" || ext == ".pem" {
				fullPath := filepath.Join(path, file.Name())
				if pool.AppendCertsFromPEM(readFile(fullPath)) {
					loaded = true
				}
			}
		}
		return loaded
	}

	// Load single file
	return pool.AppendCertsFromPEM(readFile(path))
}

func readFile(path string) []byte {
	data, err := os.ReadFile(path)
	if err != nil {
		return nil
	}
	return data
}

// loadFirefoxCARoots loads Firefox CA roots from NSS database
// On Linux, Firefox typically uses the system's CA certificates via libnssckbi.so
func loadFirefoxCARoots(pool *x509.CertPool) bool {
	// Firefox on Linux usually uses the system certificate database
	// Try to load from Mozilla's built-in certificate bundle if available
	paths := []string{
		"/usr/lib/x86_64-linux-gnu/libnssckbi.so",         // Debian/Ubuntu NSS module
		"/usr/lib/libnssckbi.so",                          // Generic path
		"/data/rsmon/docker/cert-bundles/output/mozilla/", // Our bundled Mozilla certs
	}

	for _, path := range paths {
		if loadCertsFromPath(pool, path) {
			return true
		}
	}

	return false
}

// ParsePEMCerts parses PEM-encoded certificates from data
func ParsePEMCerts(data []byte) ([]*x509.Certificate, error) {
	var certs []*x509.Certificate
	var block *pem.Block

	rest := data
	for {
		block, rest = pem.Decode(rest)
		if block == nil {
			break
		}
		if block.Type == "CERTIFICATE" {
			cert, err := x509.ParseCertificate(block.Bytes)
			if err != nil {
				return nil, err
			}
			certs = append(certs, cert)
		}
	}

	if len(certs) == 0 {
		return nil, fmt.Errorf("no certificates found")
	}

	return certs, nil
}