package handlers

import (
	"crypto/rand"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"
	"time"

	"github.com/breakpilot/ai-compliance-sdk/internal/rbac"
	"github.com/breakpilot/ai-compliance-sdk/internal/sso"
	"github.com/gin-gonic/gin"
	"github.com/golang-jwt/jwt/v5"
	"github.com/google/uuid"
)

// SSOHandlers handles SSO-related HTTP requests.
type SSOHandlers struct {
	store     *sso.Store
	jwtSecret string
}

// NewSSOHandlers creates new SSO handlers.
func NewSSOHandlers(store *sso.Store, jwtSecret string) *SSOHandlers {
	return &SSOHandlers{store: store, jwtSecret: jwtSecret}
}

// ============================================================================
// SSO Configuration CRUD
// ============================================================================

// CreateConfig creates a new SSO configuration for the tenant.
// POST /sdk/v1/sso/configs
func (h *SSOHandlers) CreateConfig(c *gin.Context) {
	var req sso.CreateSSOConfigRequest
	if err := c.ShouldBindJSON(&req); err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
		return
	}

	tenantID := rbac.GetTenantID(c)

	cfg, err := h.store.CreateConfig(c.Request.Context(), tenantID, &req)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
		return
	}

	c.JSON(http.StatusCreated, gin.H{"config": cfg})
}

// ListConfigs lists all SSO configurations for the tenant.
// GET /sdk/v1/sso/configs
func (h *SSOHandlers) ListConfigs(c *gin.Context) {
	tenantID := rbac.GetTenantID(c)

	configs, err := h.store.ListConfigs(c.Request.Context(), tenantID)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
		return
	}

	c.JSON(http.StatusOK, gin.H{
		"configs": configs,
		"total":   len(configs),
	})
}

// GetConfig retrieves an SSO configuration by ID.
// GET /sdk/v1/sso/configs/:id
func (h *SSOHandlers) GetConfig(c *gin.Context) {
	tenantID := rbac.GetTenantID(c)

	configID, err := uuid.Parse(c.Param("id"))
	if err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid config ID"})
		return
	}

	cfg, err := h.store.GetConfig(c.Request.Context(), tenantID, configID)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
		return
	}
	if cfg == nil {
		c.JSON(http.StatusNotFound, gin.H{"error": "sso configuration not found"})
		return
	}

	c.JSON(http.StatusOK, gin.H{"config": cfg})
}

// UpdateConfig updates an SSO configuration.
// PUT /sdk/v1/sso/configs/:id
func (h *SSOHandlers) UpdateConfig(c *gin.Context) {
	tenantID := rbac.GetTenantID(c)

	configID, err := uuid.Parse(c.Param("id"))
	if err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid config ID"})
		return
	}

	var req sso.UpdateSSOConfigRequest
	if err := c.ShouldBindJSON(&req); err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
		return
	}

	cfg, err := h.store.UpdateConfig(c.Request.Context(), tenantID, configID, &req)
	if err != nil {
		if err.Error() == "sso configuration not found" {
			c.JSON(http.StatusNotFound, gin.H{"error": err.Error()})
			return
		}
		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
		return
	}

	c.JSON(http.StatusOK, gin.H{"config": cfg})
}

// DeleteConfig deletes an SSO configuration.
// DELETE /sdk/v1/sso/configs/:id
func (h *SSOHandlers) DeleteConfig(c *gin.Context) {
	tenantID := rbac.GetTenantID(c)

	configID, err := uuid.Parse(c.Param("id"))
	if err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid config ID"})
		return
	}

	if err := h.store.DeleteConfig(c.Request.Context(), tenantID, configID); err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
		return
	}

	c.JSON(http.StatusOK, gin.H{"message": "sso configuration deleted"})
}

// ============================================================================
// SSO Users
// ============================================================================

// ListUsers lists all SSO-provisioned users for the tenant.
// GET /sdk/v1/sso/users
func (h *SSOHandlers) ListUsers(c *gin.Context) {
	tenantID := rbac.GetTenantID(c)

	users, err := h.store.ListUsers(c.Request.Context(), tenantID)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
		return
	}

	c.JSON(http.StatusOK, gin.H{
		"users": users,
		"total": len(users),
	})
}

// ============================================================================
// OIDC Flow
// ============================================================================

// InitiateOIDCLogin initiates the OIDC authorization code flow.
// It looks up the enabled SSO config for the tenant, builds the authorization
// URL, sets a state cookie, and redirects the user to the IdP.
// GET /sdk/v1/sso/oidc/login
func (h *SSOHandlers) InitiateOIDCLogin(c *gin.Context) {
	// Resolve tenant ID from query param
	tenantIDStr := c.Query("tenant_id")
	if tenantIDStr == "" {
		c.JSON(http.StatusBadRequest, gin.H{"error": "tenant_id query parameter is required"})
		return
	}

	tenantID, err := uuid.Parse(tenantIDStr)
	if err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid tenant_id"})
		return
	}

	// Look up the enabled SSO config
	cfg, err := h.store.GetEnabledConfig(c.Request.Context(), tenantID)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
		return
	}
	if cfg == nil {
		c.JSON(http.StatusNotFound, gin.H{"error": "no enabled SSO configuration found for this tenant"})
		return
	}
	if cfg.ProviderType != sso.ProviderTypeOIDC {
		c.JSON(http.StatusBadRequest, gin.H{"error": "SSO configuration is not OIDC"})
		return
	}

	// Discover the authorization endpoint
	discoveryURL := strings.TrimSuffix(cfg.OIDCIssuerURL, "/") + "/.well-known/openid-configuration"
	authEndpoint, _, _, err := discoverOIDCEndpoints(discoveryURL)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": fmt.Sprintf("OIDC discovery failed: %v", err)})
		return
	}

	// Generate state parameter (random bytes + tenant_id for correlation)
	stateBytes := make([]byte, 32)
	if _, err := rand.Read(stateBytes); err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to generate state"})
		return
	}
	state := base64.URLEncoding.EncodeToString(stateBytes) + "." + tenantID.String()

	// Generate nonce
	nonceBytes := make([]byte, 16)
	if _, err := rand.Read(nonceBytes); err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": "failed to generate nonce"})
		return
	}
	nonce := base64.URLEncoding.EncodeToString(nonceBytes)

	// Build authorization URL
	scopes := cfg.OIDCScopes
	if len(scopes) == 0 {
		scopes = []string{"openid", "profile", "email"}
	}

	params := url.Values{
		"client_id":     {cfg.OIDCClientID},
		"redirect_uri":  {cfg.OIDCRedirectURI},
		"response_type": {"code"},
		"scope":         {strings.Join(scopes, " ")},
		"state":         {state},
		"nonce":         {nonce},
	}

	authURL := authEndpoint + "?" + params.Encode()

	// Set state cookie for CSRF protection (HttpOnly, 10 min expiry)
	c.SetCookie("sso_state", state, 600, "/", "", true, true)
	c.SetCookie("sso_nonce", nonce, 600, "/", "", true, true)

	c.Redirect(http.StatusFound, authURL)
}

// HandleOIDCCallback handles the OIDC authorization code callback from the IdP.
// It validates the state, exchanges the code for tokens, extracts user info,
// performs JIT user provisioning, and issues a JWT.
// GET /sdk/v1/sso/oidc/callback
func (h *SSOHandlers) HandleOIDCCallback(c *gin.Context) {
	// Check for errors from the IdP
	if errParam := c.Query("error"); errParam != "" {
		errDesc := c.Query("error_description")
		c.JSON(http.StatusBadRequest, gin.H{
			"error":       errParam,
			"description": errDesc,
		})
		return
	}

	code := c.Query("code")
	stateParam := c.Query("state")
	if code == "" || stateParam == "" {
		c.JSON(http.StatusBadRequest, gin.H{"error": "missing code or state parameter"})
		return
	}

	// Validate state cookie
	stateCookie, err := c.Cookie("sso_state")
	if err != nil || stateCookie != stateParam {
		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid state parameter (CSRF check failed)"})
		return
	}

	// Extract tenant ID from state
	parts := strings.SplitN(stateParam, ".", 2)
	if len(parts) != 2 {
		c.JSON(http.StatusBadRequest, gin.H{"error": "malformed state parameter"})
		return
	}
	tenantID, err := uuid.Parse(parts[1])
	if err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "invalid tenant_id in state"})
		return
	}

	// Look up the enabled SSO config
	cfg, err := h.store.GetEnabledConfig(c.Request.Context(), tenantID)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
		return
	}
	if cfg == nil {
		c.JSON(http.StatusNotFound, gin.H{"error": "no enabled SSO configuration found"})
		return
	}

	// Discover OIDC endpoints
	discoveryURL := strings.TrimSuffix(cfg.OIDCIssuerURL, "/") + "/.well-known/openid-configuration"
	_, tokenEndpoint, userInfoEndpoint, err := discoverOIDCEndpoints(discoveryURL)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": fmt.Sprintf("OIDC discovery failed: %v", err)})
		return
	}

	// Exchange authorization code for tokens
	tokenResp, err := exchangeCodeForTokens(tokenEndpoint, code, cfg.OIDCClientID, cfg.OIDCClientSecret, cfg.OIDCRedirectURI)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": fmt.Sprintf("token exchange failed: %v", err)})
		return
	}

	// Extract user claims from ID token or UserInfo endpoint
	claims, err := extractUserClaims(tokenResp, userInfoEndpoint)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": fmt.Sprintf("failed to extract user claims: %v", err)})
		return
	}

	sub := getStringClaim(claims, "sub")
	email := getStringClaim(claims, "email")
	name := getStringClaim(claims, "name")
	groups := getStringSliceClaim(claims, "groups")

	if sub == "" {
		c.JSON(http.StatusBadRequest, gin.H{"error": "ID token missing 'sub' claim"})
		return
	}
	if email == "" {
		email = sub
	}
	if name == "" {
		name = email
	}

	// JIT provision the user
	user, err := h.store.UpsertUser(c.Request.Context(), tenantID, cfg.ID, sub, email, name, groups)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": fmt.Sprintf("user provisioning failed: %v", err)})
		return
	}

	// Determine roles from role mapping
	roles := resolveRoles(cfg, groups)

	// Generate JWT
	ssoClaims := sso.SSOClaims{
		UserID:      user.ID,
		TenantID:    tenantID,
		Email:       user.Email,
		DisplayName: user.DisplayName,
		Roles:       roles,
		SSOConfigID: cfg.ID,
	}

	jwtToken, err := h.generateJWT(ssoClaims)
	if err != nil {
		c.JSON(http.StatusInternalServerError, gin.H{"error": fmt.Sprintf("JWT generation failed: %v", err)})
		return
	}

	// Clear state cookies
	c.SetCookie("sso_state", "", -1, "/", "", true, true)
	c.SetCookie("sso_nonce", "", -1, "/", "", true, true)

	// Return JWT as JSON (the frontend can also handle redirect)
	c.JSON(http.StatusOK, gin.H{
		"token": jwtToken,
		"user":  user,
		"roles": roles,
	})
}

// ============================================================================
// JWT Generation
// ============================================================================

// generateJWT creates a signed JWT token containing the SSO claims.
func (h *SSOHandlers) generateJWT(claims sso.SSOClaims) (string, error) {
	now := time.Now().UTC()
	expiry := now.Add(24 * time.Hour)

	token := jwt.NewWithClaims(jwt.SigningMethodHS256, jwt.MapClaims{
		"user_id":       claims.UserID.String(),
		"tenant_id":     claims.TenantID.String(),
		"email":         claims.Email,
		"display_name":  claims.DisplayName,
		"roles":         claims.Roles,
		"sso_config_id": claims.SSOConfigID.String(),
		"iss":           "ai-compliance-sdk",
		"iat":           now.Unix(),
		"exp":           expiry.Unix(),
	})

	tokenString, err := token.SignedString([]byte(h.jwtSecret))
	if err != nil {
		return "", fmt.Errorf("failed to sign JWT: %w", err)
	}

	return tokenString, nil
}

// ============================================================================
// OIDC Discovery & Token Exchange (manual HTTP, no external OIDC library)
// ============================================================================

// oidcDiscoveryResponse holds the relevant fields from the OIDC discovery document.
type oidcDiscoveryResponse struct {
	AuthorizationEndpoint string `json:"authorization_endpoint"`
	TokenEndpoint         string `json:"token_endpoint"`
	UserinfoEndpoint      string `json:"userinfo_endpoint"`
	JwksURI               string `json:"jwks_uri"`
	Issuer                string `json:"issuer"`
}

// discoverOIDCEndpoints fetches the OIDC discovery document and returns
// the authorization, token, and userinfo endpoints.
func discoverOIDCEndpoints(discoveryURL string) (authEndpoint, tokenEndpoint, userInfoEndpoint string, err error) {
	client := &http.Client{Timeout: 10 * time.Second}

	resp, err := client.Get(discoveryURL)
	if err != nil {
		return "", "", "", fmt.Errorf("failed to fetch discovery document: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		body, _ := io.ReadAll(resp.Body)
		return "", "", "", fmt.Errorf("discovery endpoint returned %d: %s", resp.StatusCode, string(body))
	}

	var discovery oidcDiscoveryResponse
	if err := json.NewDecoder(resp.Body).Decode(&discovery); err != nil {
		return "", "", "", fmt.Errorf("failed to decode discovery document: %w", err)
	}

	if discovery.AuthorizationEndpoint == "" {
		return "", "", "", fmt.Errorf("discovery document missing authorization_endpoint")
	}
	if discovery.TokenEndpoint == "" {
		return "", "", "", fmt.Errorf("discovery document missing token_endpoint")
	}

	return discovery.AuthorizationEndpoint, discovery.TokenEndpoint, discovery.UserinfoEndpoint, nil
}

// oidcTokenResponse holds the response from the OIDC token endpoint.
type oidcTokenResponse struct {
	AccessToken  string `json:"access_token"`
	IDToken      string `json:"id_token"`
	TokenType    string `json:"token_type"`
	ExpiresIn    int    `json:"expires_in"`
	RefreshToken string `json:"refresh_token,omitempty"`
}

// exchangeCodeForTokens exchanges an authorization code for tokens at the token endpoint.
func exchangeCodeForTokens(tokenEndpoint, code, clientID, clientSecret, redirectURI string) (*oidcTokenResponse, error) {
	client := &http.Client{Timeout: 10 * time.Second}

	data := url.Values{
		"grant_type":   {"authorization_code"},
		"code":         {code},
		"client_id":    {clientID},
		"redirect_uri": {redirectURI},
	}

	req, err := http.NewRequest("POST", tokenEndpoint, strings.NewReader(data.Encode()))
	if err != nil {
		return nil, fmt.Errorf("failed to create token request: %w", err)
	}
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")

	// Use client_secret_basic if provided
	if clientSecret != "" {
		req.SetBasicAuth(clientID, clientSecret)
	}

	resp, err := client.Do(req)
	if err != nil {
		return nil, fmt.Errorf("token request failed: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		body, _ := io.ReadAll(resp.Body)
		return nil, fmt.Errorf("token endpoint returned %d: %s", resp.StatusCode, string(body))
	}

	var tokenResp oidcTokenResponse
	if err := json.NewDecoder(resp.Body).Decode(&tokenResp); err != nil {
		return nil, fmt.Errorf("failed to decode token response: %w", err)
	}

	return &tokenResp, nil
}

// extractUserClaims extracts user claims from the ID token payload.
// If the ID token is unavailable or incomplete, it falls back to the UserInfo endpoint.
func extractUserClaims(tokenResp *oidcTokenResponse, userInfoEndpoint string) (map[string]interface{}, error) {
	claims := make(map[string]interface{})

	// Try to decode ID token payload (without signature verification for claims extraction;
	// in production, you should verify the signature using the JWKS endpoint)
	if tokenResp.IDToken != "" {
		parts := strings.Split(tokenResp.IDToken, ".")
		if len(parts) == 3 {
			payload, err := base64.RawURLEncoding.DecodeString(parts[1])
			if err == nil {
				if err := json.Unmarshal(payload, &claims); err == nil && claims["sub"] != nil {
					return claims, nil
				}
			}
		}
	}

	// Fallback to UserInfo endpoint
	if userInfoEndpoint != "" && tokenResp.AccessToken != "" {
		userClaims, err := fetchUserInfo(userInfoEndpoint, tokenResp.AccessToken)
		if err == nil && userClaims["sub"] != nil {
			return userClaims, nil
		}
	}

	if claims["sub"] != nil {
		return claims, nil
	}

	return nil, fmt.Errorf("could not extract user claims from ID token or UserInfo endpoint")
}

// fetchUserInfo calls the OIDC UserInfo endpoint with the access token.
func fetchUserInfo(userInfoEndpoint, accessToken string) (map[string]interface{}, error) {
	client := &http.Client{Timeout: 10 * time.Second}

	req, err := http.NewRequest("GET", userInfoEndpoint, nil)
	if err != nil {
		return nil, err
	}
	req.Header.Set("Authorization", "Bearer "+accessToken)

	resp, err := client.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("userinfo endpoint returned %d", resp.StatusCode)
	}

	var claims map[string]interface{}
	if err := json.NewDecoder(resp.Body).Decode(&claims); err != nil {
		return nil, err
	}

	return claims, nil
}

// ============================================================================
// Claim Extraction Helpers
// ============================================================================

// getStringClaim extracts a string claim from a claims map.
func getStringClaim(claims map[string]interface{}, key string) string {
	if v, ok := claims[key]; ok {
		if s, ok := v.(string); ok {
			return s
		}
	}
	return ""
}

// getStringSliceClaim extracts a string slice claim from a claims map.
func getStringSliceClaim(claims map[string]interface{}, key string) []string {
	v, ok := claims[key]
	if !ok {
		return nil
	}

	switch val := v.(type) {
	case []interface{}:
		result := make([]string, 0, len(val))
		for _, item := range val {
			if s, ok := item.(string); ok {
				result = append(result, s)
			}
		}
		return result
	case []string:
		return val
	default:
		return nil
	}
}

// resolveRoles maps SSO groups to internal roles using the config's role mapping.
// If no groups match, the default role is returned.
func resolveRoles(cfg *sso.SSOConfig, groups []string) []string {
	if cfg.RoleMapping == nil || len(cfg.RoleMapping) == 0 {
		if cfg.DefaultRoleID != nil {
			return []string{cfg.DefaultRoleID.String()}
		}
		return []string{"compliance_user"}
	}

	roleSet := make(map[string]bool)
	for _, group := range groups {
		if role, ok := cfg.RoleMapping[group]; ok {
			roleSet[role] = true
		}
	}

	if len(roleSet) == 0 {
		if cfg.DefaultRoleID != nil {
			return []string{cfg.DefaultRoleID.String()}
		}
		return []string{"compliance_user"}
	}

	roles := make([]string, 0, len(roleSet))
	for role := range roleSet {
		roles = append(roles, role)
	}
	return roles
}