package traefikoidc

import (
	"context"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/http/cookiejar"
	"net/url"
	"strings"
	"time"
)

// newUUIDv4 returns an RFC 4122 v4 UUID string (e.g.
// "f47ac10b-58cc-4372-a567-0e02b2c3d479") backed by crypto/rand. Used for CSRF
// tokens and other opaque random identifiers — replaces github.com/google/uuid
// to keep the plugin stdlib-only on the production path.
func newUUIDv4() (string, error) {
	var b [16]byte
	if _, err := rand.Read(b[:]); err != nil {
		return "", fmt.Errorf("could not generate UUID: %w", err)
	}
	b[6] = (b[6] & 0x0f) | 0x40 // version 4
	b[8] = (b[8] & 0x3f) | 0x80 // RFC 4122 variant
	return fmt.Sprintf("%08x-%04x-%04x-%04x-%012x",
		b[0:4], b[4:6], b[6:8], b[8:10], b[10:16]), nil
}

// generateNonce creates a cryptographically secure random nonce for OIDC flows.
// The nonce is used to prevent replay attacks and associate client sessions with ID tokens.
// Returns:
//   - A base64 URL-encoded nonce string (43 characters)
//   - An error if the random byte generation fails
func generateNonce() (string, error) {
	nonceBytes := make([]byte, 32)
	_, err := rand.Read(nonceBytes)
	if err != nil {
		return "", fmt.Errorf("could not generate nonce: %w", err)
	}
	return base64.URLEncoding.EncodeToString(nonceBytes), nil
}

// generateCodeVerifier creates a PKCE code verifier according to RFC 7636.
// The code verifier is a cryptographically random string used for the PKCE flow
// to prevent authorization code interception attacks.
// Returns:
//   - A base64 raw URL-encoded code verifier string (43 characters)
//   - An error if the random byte generation fails
func generateCodeVerifier() (string, error) {
	verifierBytes := make([]byte, 32)
	_, err := rand.Read(verifierBytes)
	if err != nil {
		return "", fmt.Errorf("could not generate code verifier: %w", err)
	}
	return base64.RawURLEncoding.EncodeToString(verifierBytes), nil
}

// deriveCodeChallenge creates a PKCE code challenge from the code verifier.
// It computes the SHA-256 hash of the code verifier and base64 URL-encodes it
// according to RFC 7636 specification.
// Parameters:
//   - codeVerifier: The code verifier string
//
// Returns:
//   - The base64 URL encoded SHA-256 hash of the code verifier (code challenge)
func deriveCodeChallenge(codeVerifier string) string {
	hasher := sha256.New()
	hasher.Write([]byte(codeVerifier))
	hash := hasher.Sum(nil)

	return base64.RawURLEncoding.EncodeToString(hash)
}

// TokenResponse represents the standard OAuth 2.0/OIDC token response.
// It contains the tokens and metadata returned by the authorization server during
// code exchange or token refresh operations.
type TokenResponse struct {
	// IDToken contains the OpenID Connect identity token (JWT)
	IDToken string `json:"id_token"`
	// AccessToken is the OAuth 2.0 access token for API access
	AccessToken string `json:"access_token"`
	// RefreshToken allows obtaining new tokens when the access token expires
	RefreshToken string `json:"refresh_token"`
	// TokenType specifies the token type (typically "Bearer")
	TokenType string `json:"token_type"`
	// ExpiresIn indicates token lifetime in seconds
	ExpiresIn int `json:"expires_in"`
}

// exchangeTokens performs OAuth 2.0 token exchange with the authorization server.
// It supports both authorization code and refresh token grant types with PKCE support.
// Parameters:
//   - ctx: Context for request timeout and cancellation
//   - grantType: OAuth grant type ("authorization_code" or "refresh_token")
//   - codeOrToken: Authorization code or refresh token depending on grant type
//   - redirectURL: Redirect URI used in authorization (required for code exchange)
//   - codeVerifier: PKCE code verifier (optional, used with PKCE flow)
//
// Returns:
//   - *TokenResponse: Parsed token response from the authorization server
//   - An error if the token exchange fails (e.g., network error, provider error, invalid grant)
func (t *TraefikOidc) exchangeTokens(ctx context.Context, grantType string, codeOrToken string, redirectURL string, codeVerifier string) (*TokenResponse, error) {
	data := url.Values{
		"grant_type": {grantType},
	}
	// Snapshot client credentials under metadataMu: DCR rewrites clientID/
	// clientSecret/audience at runtime (R137).
	clientID, clientSecret, clientAuthMethod, _, clientAssertion := t.clientCredentials()
	// client_id is sent in the body for every method except client_secret_basic,
	// where it is carried in the Authorization header per RFC 6749 §2.3.1.
	if clientAuthMethod != "client_secret_basic" || clientAssertion != nil {
		data.Set("client_id", clientID)
	}

	if grantType == "authorization_code" {
		data.Set("code", codeOrToken)
		data.Set("redirect_uri", redirectURL)

		if codeVerifier != "" {
			data.Set("code_verifier", codeVerifier)
		}
	} else if grantType == "refresh_token" {
		data.Set("refresh_token", codeOrToken)
	}

	// RFC 8707 §2.2: repeat the same resource indicator sent on the
	// authorization request so refreshed tokens keep the same audience
	// binding as the original grant.
	if t.resource != "" {
		data.Set("resource", t.resource)
	}

	client := t.tokenHTTPClient
	if client == nil {
		// Use shared transport pool to prevent memory leaks
		jar, _ := cookiejar.New(nil) // Safe to ignore: cookiejar creation with nil options rarely fails
		pooledClient := CreateTokenHTTPClient()
		client = &http.Client{
			Transport: pooledClient.Transport,
			Timeout:   pooledClient.Timeout,
			CheckRedirect: func(req *http.Request, via []*http.Request) error {
				if len(via) >= 50 {
					return fmt.Errorf("stopped after 50 redirects")
				}
				return nil
			},
			Jar: jar,
		}
	}

	// Read tokenURL with RLock — needed as audience for private_key_jwt (RFC 7523 §3).
	t.metadataMu.RLock()
	tokenURL := t.tokenURL
	t.metadataMu.RUnlock()

	useBasicAuth := false
	if clientAssertion != nil {
		assertion, err := clientAssertion.Sign(tokenURL, clientID)
		if err != nil {
			return nil, fmt.Errorf("failed to sign client assertion: %w", err)
		}
		data.Set("client_assertion_type", "urn:ietf:params:oauth:client-assertion-type:jwt-bearer")
		data.Set("client_assertion", assertion)
	} else if clientAuthMethod == "client_secret_basic" {
		useBasicAuth = true
	} else {
		data.Set("client_secret", clientSecret)
	}

	req, err := http.NewRequestWithContext(ctx, "POST", tokenURL, strings.NewReader(data.Encode())) //nolint:gosec // tokenURL is the operator-trusted discovery endpoint (metadataMu)
	if err != nil {
		return nil, fmt.Errorf("failed to create token request: %w", err)
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
	if useBasicAuth {
		setOAuthBasicAuth(req, clientID, clientSecret)
	}

	resp, err := client.Do(req) //nolint:gosec // req above targets the trusted tokenURL
	if err != nil {
		return nil, fmt.Errorf("failed to exchange tokens: %w", err)
	}
	defer func() {
		_, _ = io.Copy(io.Discard, resp.Body) // Safe to ignore: draining response body on defer
		_ = resp.Body.Close()                 // Safe to ignore: closing body on defer
	}()

	if resp.StatusCode != http.StatusOK {
		limitReader := io.LimitReader(resp.Body, 1024*10)
		bodyBytes, _ := io.ReadAll(limitReader) // Safe to ignore: reading error body for diagnostics
		// Return a *HTTPError so the retry executor's isRetryableError can
		// classify transient 5xx/429 responses and actually retry (R118).
		// A plain error here made the 5xx/429 retry branch dead in
		// production — every token-endpoint status was treated as permanent.
		return nil, &HTTPError{
			StatusCode: resp.StatusCode,
			Message:    fmt.Sprintf("token endpoint returned status %d: %s", resp.StatusCode, string(bodyBytes)),
		}
	}

	var tokenResponse TokenResponse
	// Cap the decoded body so a corrupted or malicious oversized 200-body cannot
	// drive an unbounded read/allocation. Token responses are small (a few KB).
	if err := json.NewDecoder(io.LimitReader(resp.Body, 1<<20)).Decode(&tokenResponse); err != nil {
		return nil, fmt.Errorf("failed to decode token response: %w", err)
	}

	// RFC 6749 §5.1: a token response MUST include an access_token. A 200
	// that omitted it is a protocol violation, not a success — treat it as an
	// error here so no caller authenticates with a blank token (R158).
	// Previously this seam returned success with an empty access_token and
	// each caller had to re-check "AccessToken == \"\"", which several
	// paths missed.
	if tokenResponse.AccessToken == "" {
		return nil, fmt.Errorf("token endpoint returned 200 without an access_token (RFC 6749 §5.1)")
	}

	return &tokenResponse, nil
}

// getNewTokenWithRefreshToken refreshes access and ID tokens using a refresh token.
// This is used when the current tokens are expired but the refresh token is still valid.
// It now uses the TokenResilienceManager for circuit breaker and retry logic.
// Parameters:
//   - refreshToken: The refresh token to exchange for new tokens
//
// Returns:
//   - *TokenResponse: New token set from the authorization server
//   - An error if the refresh operation fails
//
// redactToken returns a short, stable hash of a token credential suitable for
// debug logging without leaking the credential itself (R138).
func redactToken(token string) string {
	if token == "" {
		return "(empty)"
	}
	sum := sha256.Sum256([]byte(token))
	return fmt.Sprintf("%x", sum[:4])
}

func (t *TraefikOidc) getNewTokenWithRefreshToken(refreshToken string) (*TokenResponse, error) {
	ctx := context.Background()

	// Use token resilience manager if available, otherwise fall back to direct call
	if t.tokenResilienceManager != nil {
		return t.tokenResilienceManager.ExecuteTokenRefresh(ctx, t, refreshToken)
	}

	// Fallback for backward compatibility
	tokenResponse, err := t.exchangeTokens(ctx, "refresh_token", refreshToken, "", "")
	if err != nil {
		return nil, fmt.Errorf("failed to refresh token: %w", err)
	}

	t.logger.Debugf("Refresh token response: token_type=%s expires_in=%d access_token=%s",
		tokenResponse.TokenType, tokenResponse.ExpiresIn, redactToken(tokenResponse.AccessToken))
	return tokenResponse, nil
}

// extractClaims extracts and parses claims from a JWT token without signature verification.
// This is a utility function for quickly accessing token payload data when signature
// verification is not required or has already been performed.
// Parameters:
//   - tokenString: The JWT token string to parse
//
// Returns:
//   - map[string]interface{}: Parsed claims from the token payload
//   - An error if the token format is invalid, decoding fails, or JSON unmarshaling fails
func extractClaims(tokenString string) (map[string]interface{}, error) {
	parts := strings.Split(tokenString, ".")
	if len(parts) != 3 {
		return nil, fmt.Errorf("invalid token format")
	}

	payload, err := base64.RawURLEncoding.DecodeString(parts[1])
	if err != nil {
		return nil, fmt.Errorf("failed to decode token payload: %w", err)
	}

	var claims map[string]interface{}
	if err := json.Unmarshal(payload, &claims); err != nil {
		return nil, fmt.Errorf("failed to unmarshal claims: %w", err)
	}

	return claims, nil
}

// TokenCache provides a specialized cache for JWT tokens and their parsed claims.
// It wraps the UniversalCache with token-specific operations.
type TokenCache struct {
	// cache is the underlying universal cache implementation
	cache *UniversalCache
}

// NewTokenCache creates and initializes a new TokenCache.
// It uses the global cache manager to ensure singleton behavior.
func NewTokenCache() *TokenCache {
	manager := GetUniversalCacheManager(nil)
	return &TokenCache{
		cache: manager.GetTokenCache(),
	}
}

// Set stores parsed token claims in the cache with expiration.
// The token is prefixed to prevent collisions with other cache entries.
// Parameters:
//   - token: The JWT token string (used as cache key)
//   - claims: Parsed claims from the token
//   - expiration: The duration for which the cache entry should be valid
func (tc *TokenCache) Set(token string, claims map[string]interface{}, expiration time.Duration) {
	token = "t-" + token
	_ = tc.cache.Set(token, claims, expiration) // Safe to ignore: cache failures are non-critical
}

// Get retrieves cached claims for a token.
// Parameters:
//   - token: The JWT token string to look up
//
// Returns:
//   - map[string]interface{}: The cached claims if found
//   - A boolean indicating whether the token was found in the cache (true if found, false otherwise)
func (tc *TokenCache) Get(token string) (map[string]interface{}, bool) {
	token = "t-" + token
	value, found := tc.cache.Get(token)
	if !found {
		return nil, false
	}
	claims, ok := value.(map[string]interface{})
	return claims, ok
}

// Delete removes a token from the cache.
// Parameters:
//   - token: The raw token string to remove from the cache
func (tc *TokenCache) Delete(token string) {
	token = "t-" + token
	tc.cache.Delete(token)
}

// Cleanup removes expired entries from the token cache.
// This is a no-op as cleanup is handled internally by UniversalCache.
func (tc *TokenCache) Cleanup() {
	// Cleanup is handled internally by UniversalCache
}

// Close stops the cleanup goroutine and releases resources.
// This is a no-op as the cache is managed globally.
func (tc *TokenCache) Close() {
	// Cache is managed globally by UniversalCacheManager
}

// Clear removes all items from the cache
func (tc *TokenCache) Clear() {
	tc.cache.Clear()
}

// exchangeCodeForToken exchanges an authorization code for tokens.
// This implements the OAuth 2.0 authorization code flow with optional PKCE support.
// It now uses the TokenResilienceManager for circuit breaker and retry logic.
// Parameters:
//   - code: The authorization code received from the authorization server
//   - redirectURL: The redirect URI used in the authorization request
//   - codeVerifier: PKCE code verifier (used if PKCE is enabled)
//
// Returns:
//   - *TokenResponse: The token response containing access, refresh, and ID tokens
//   - An error if the code exchange fails
func (t *TraefikOidc) exchangeCodeForToken(code string, redirectURL string, codeVerifier string) (*TokenResponse, error) {
	ctx := context.Background()

	effectiveCodeVerifier := ""
	if t.enablePKCE && codeVerifier != "" {
		effectiveCodeVerifier = codeVerifier
	}

	// Use token resilience manager if available, otherwise fall back to direct call
	if t.tokenResilienceManager != nil {
		return t.tokenResilienceManager.ExecuteTokenExchange(ctx, t, "authorization_code", code, redirectURL, effectiveCodeVerifier)
	}

	// Fallback for backward compatibility
	tokenResponse, err := t.exchangeTokens(ctx, "authorization_code", code, redirectURL, effectiveCodeVerifier)
	if err != nil {
		return nil, fmt.Errorf("failed to exchange code for token: %w", err)
	}
	return tokenResponse, nil
}

// createStringMap converts a slice of strings to a set-like map for fast lookups.
// This is a utility function for creating efficient membership tests.
// Parameters:
//   - keys: Slice of strings to convert to a map
//
// Returns:
//   - A map where the keys are the strings from the input slice and the values are empty structs
func createStringMap(keys []string) map[string]struct{} {
	result := make(map[string]struct{})
	for _, key := range keys {
		result[key] = struct{}{}
	}
	return result
}

// handleLogout processes user logout requests and performs proper session cleanup.
// It retrieves the ID token for logout URL construction, clears the session,
// and redirects to the provider's logout endpoint or configured post-logout URI.
// It handles potential errors during session retrieval or clearing.
func (t *TraefikOidc) handleLogout(rw http.ResponseWriter, req *http.Request) {
	t.logger.Debug("Processing logout request")
	session, err := t.sessionManager.GetSession(req)
	if err != nil {
		t.logger.Errorf("Error getting session: %v", err)
		http.Error(rw, "Session error", http.StatusInternalServerError)
		return
	}

	idToken := session.GetIDToken()
	accessToken := session.GetAccessToken()
	refreshToken := session.GetRefreshToken()
	// Capture the trusted origin BEFORE Clear wipes the session. redirect_url
	// was persisted at authentication-initiate time (R136) and is therefore
	// the exact scheme+host the IdP already accepted as this deployment's
	// redirect_uri — unlike the current request's Host/X-Forwarded-Host,
	// the browser cannot spoof it on this logout request (FIX-07).
	trustedOrigin := trustedOriginFromRedirectURL(session.GetRedirectURL())

	if err := session.Clear(req, rw); err != nil {
		t.logger.Errorf("Error clearing session: %v", err)
		http.Error(rw, "Session error", http.StatusInternalServerError)
		return
	}

	// Blacklist the session's tokens so a token captured before logout (e.g. a
	// bearer mode access token) cannot be reused until its natural expiry.
	// RevokeToken is a no-op-safe local blacklist (guards nil) and skips
	// empty values.
	for _, tok := range []string{accessToken, idToken, refreshToken} {
		if tok != "" {
			t.RevokeToken(tok)
		}
	}

	// Best-effort provider-side revocation (single logout): the local
	// blacklist only stops reuse in-process, but a token captured before
	// logout (e.g. a bearer-mode access token or the refresh token) stays
	// valid at the IdP and a captured refresh token could keep minting new
	// tokens. Revoke both access and refresh tokens at the provider when a
	// revocation endpoint is available. Each call is bounded by
	// revocationRequestTimeout so a slow or unreachable provider cannot
	// hold the logout redirect open indefinitely (FIX-33). A genuine
	// failure is logged at error level; the expected "no revocation
	// endpoint configured" case (most deployments) stays silent so it
	// doesn't log on every logout.
	if accessToken != "" {
		if err := t.RevokeTokenWithProvider(accessToken, "access_token"); err != nil && !errors.Is(err, ErrRevocationEndpointNotConfigured) {
			t.logger.Errorf("Provider-side revocation failed for access_token: %v", err)
		}
	}
	if refreshToken != "" {
		if err := t.RevokeTokenWithProvider(refreshToken, "refresh_token"); err != nil && !errors.Is(err, ErrRevocationEndpointNotConfigured) {
			t.logger.Errorf("Provider-side revocation failed for refresh_token: %v", err)
		}
	}

	postLogoutRedirectURI := t.postLogoutRedirectURI
	// localRedirect is used when there is no provider end-session endpoint and
	// the plugin redirects the browser itself. It must never be an absolute URL
	// derived from the request host (X-Forwarded-Host is client-controllable and
	// would be an open redirect); use a host-relative path, or the operator's
	// own configured absolute URL, instead.
	//
	// The post_logout_redirect_uri we hand to the IdP has the same constraint:
	// deriving it from baseURL (scheme://client-controlled host) lets an
	// attacker's X-Forwarded-Host steer the browser to an arbitrary origin
	// after logout (open redirect through the IdP). So we build it from
	// trustedOrigin (the redirect_uri origin the IdP already accepted at
	// login, R136) instead; when no trusted origin was recorded (pre-R136
	// session, or logout without a completed login), BuildLogoutURL omits
	// the parameter entirely rather than guessing (FIX-07 corrects R68,
	// which dropped the parameter unconditionally for every non-absolute
	// config value, including the documented default of '/').
	localRedirect := "/"
	switch {
	case strings.HasPrefix(postLogoutRedirectURI, "http"):
		// Operator configured an explicit absolute URL: already a trusted
		// origin on its own, independent of trustedOrigin.
		localRedirect = postLogoutRedirectURI
	case postLogoutRedirectURI == "":
		postLogoutRedirectURI = "" // no trusted origin below leaves it empty
		if trustedOrigin != "" {
			postLogoutRedirectURI = trustedOrigin + "/"
		}
	default:
		// Relative operator-configured path: trusted for the plugin's own
		// redirect, rebuilt against the trusted origin for the IdP.
		localRedirect = normalizeLogoutPath(postLogoutRedirectURI)
		postLogoutRedirectURI = ""
		if trustedOrigin != "" {
			postLogoutRedirectURI = trustedOrigin + localRedirect
		}
	}

	// Read endSessionURL with RLock
	t.metadataMu.RLock()
	endSessionURL := t.endSessionURL
	t.metadataMu.RUnlock()

	if endSessionURL != "" && idToken != "" {
		logoutURL, err := BuildLogoutURL(endSessionURL, idToken, postLogoutRedirectURI)
		if err != nil {
			t.logger.Errorf("Failed to build logout URL: %v", err)
			http.Error(rw, "Logout error", http.StatusInternalServerError)
			return
		}
		// Logout redirects must never be cached: a heuristic-caching proxy
		// replaying the 302 would re-trigger logout for an already
		// logged-out session (R147 cache-directive contract).
		rw.Header().Set("Cache-Control", "no-store")
		http.Redirect(rw, req, logoutURL, http.StatusFound)
		return
	}

	rw.Header().Set("Cache-Control", "no-store")
	http.Redirect(rw, req, localRedirect, http.StatusFound)
}

// trustedOriginFromRedirectURL extracts "scheme://host" from the redirect_uri
// persisted at authentication-initiate time (R136), for reuse as the trusted
// origin when building post_logout_redirect_uri (FIX-07). That redirect_uri
// was already accepted by the IdP as this deployment's own callback, so its
// origin is safe to reuse — unlike the current request's Host/
// X-Forwarded-Host, which the browser controls. Returns "" when redirectURL
// is empty or is not an absolute http(s) URL.
func trustedOriginFromRedirectURL(redirectURL string) string {
	if redirectURL == "" {
		return ""
	}
	u, err := url.Parse(redirectURL)
	if err != nil || u.Host == "" || (u.Scheme != "http" && u.Scheme != "https") {
		return ""
	}
	return u.Scheme + "://" + u.Host
}

// BuildLogoutURL constructs a logout URL for the OIDC provider's end session endpoint.
// It includes the ID token hint and post-logout redirect URI according to OIDC specifications.
// Parameters:
//   - endSessionURL: The provider's logout/end session endpoint
//   - idToken: The ID token to include as a hint
//   - postLogoutRedirectURI: Where to redirect after logout
//
// Returns:
//   - The complete logout URL with query parameters
//   - An error if the provided endSessionURL is invalid
func BuildLogoutURL(endSessionURL, idToken, postLogoutRedirectURI string) (string, error) {
	u, err := url.Parse(endSessionURL)
	if err != nil {
		return "", fmt.Errorf("failed to parse end session URL: %w", err)
	}

	q := u.Query()
	q.Set("id_token_hint", idToken)
	if postLogoutRedirectURI != "" {
		q.Set("post_logout_redirect_uri", postLogoutRedirectURI)
	}
	u.RawQuery = q.Encode()

	return u.String(), nil
}

// setOAuthBasicAuth sets the Authorization header per RFC 6749 §2.3.1: the
// client_id and client_secret are form-urlencoded individually, joined with a
// colon, then base64-encoded. This differs from http.Request.SetBasicAuth,
// which skips the form-urlencode step — that matters for credentials with
// reserved characters (`:`, `@`, `+`, `%`, etc.) where the wire format would
// otherwise diverge from what the spec mandates.
func setOAuthBasicAuth(req *http.Request, clientID, clientSecret string) {
	user := url.QueryEscape(clientID)
	pass := url.QueryEscape(clientSecret)
	auth := base64.StdEncoding.EncodeToString([]byte(user + ":" + pass))
	req.Header.Set("Authorization", "Basic "+auth)
}

// deduplicateScopes removes duplicate scopes from a slice while preserving order.
// This ensures that OAuth scope parameters don't contain duplicates which could
// cause issues with some authorization servers.
// The first occurrence of each scope is kept.
func deduplicateScopes(scopes []string) []string {
	if len(scopes) == 0 {
		return []string{}
	}
	seen := make(map[string]struct{})
	result := []string{}
	for _, scope := range scopes {
		if _, ok := seen[scope]; !ok {
			seen[scope] = struct{}{}
			result = append(result, scope)
		}
	}
	return result
}