package api

import (
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"html/template"
	"net/http"
	"net/url"
	"os"
	"strings"
	"time"

	"github.com/mish/dealspace/lib"
)

// OAuthHandlers holds dependencies for OAuth endpoints.
type OAuthHandlers struct {
	DB  *lib.DB
	Cfg *lib.Config
}

// NewOAuthHandlers creates OAuth handlers.
func NewOAuthHandlers(db *lib.DB, cfg *lib.Config) *OAuthHandlers {
	return &OAuthHandlers{DB: db, Cfg: cfg}
}

func baseURL(r *http.Request) string {
	scheme := "https"
	if r.TLS == nil && !strings.HasPrefix(r.Header.Get("X-Forwarded-Proto"), "https") {
		scheme = "http"
	}
	return scheme + "://" + r.Host
}

// Metadata serves GET /.well-known/oauth-authorization-server (RFC 8414).
func (o *OAuthHandlers) Metadata(w http.ResponseWriter, r *http.Request) {
	base := baseURL(r)
	JSONResponse(w, http.StatusOK, map[string]any{
		"issuer":                             base,
		"authorization_endpoint":             base + "/oauth/authorize",
		"token_endpoint":                     base + "/oauth/token",
		"revocation_endpoint":                base + "/oauth/revoke",
		"response_types_supported":           []string{"code"},
		"grant_types_supported":              []string{"authorization_code"},
		"code_challenge_methods_supported":   []string{"S256"},
		"token_endpoint_auth_methods_supported": []string{"none"},
	})
}

// ResourceMetadata serves GET /.well-known/oauth-protected-resource (RFC 9728).
func (o *OAuthHandlers) ResourceMetadata(w http.ResponseWriter, r *http.Request) {
	base := baseURL(r)
	JSONResponse(w, http.StatusOK, map[string]any{
		"resource":              base,
		"authorization_servers": []string{base},
	})
}

// Authorize handles GET /oauth/authorize — shows consent page or redirects to login.
func (o *OAuthHandlers) Authorize(w http.ResponseWriter, r *http.Request) {
	q := r.URL.Query()
	clientID := q.Get("client_id")
	redirectURI := q.Get("redirect_uri")
	responseType := q.Get("response_type")
	codeChallenge := q.Get("code_challenge")
	codeChallengeMethod := q.Get("code_challenge_method")
	state := q.Get("state")
	_ = q.Get("scope") // scope passed through via query string to POST handler

	// Validate required params
	if responseType != "code" {
		oauthError(w, redirectURI, state, "unsupported_response_type", "Only response_type=code is supported")
		return
	}
	if codeChallenge == "" || codeChallengeMethod != "S256" {
		oauthError(w, redirectURI, state, "invalid_request", "PKCE with S256 is required")
		return
	}

	// Validate client
	client, err := lib.OAuthClientByID(o.DB, clientID)
	if err != nil || client == nil {
		oauthError(w, redirectURI, state, "invalid_client", "Unknown client_id")
		return
	}

	// Validate redirect_uri
	if !validRedirectURI(client.RedirectURIs, redirectURI) {
		ErrorResponse(w, http.StatusBadRequest, "invalid_request", "Invalid redirect_uri")
		return
	}

	// Check if user is authenticated via JWT in cookie or Authorization header
	userID := o.extractUserID(r)
	if userID == "" {
		// Redirect to login with return URL
		loginURL := "/app/login?next=" + url.QueryEscape(r.URL.RequestURI())
		http.Redirect(w, r, loginURL, http.StatusFound)
		return
	}

	// Show consent page
	o.serveConsentPage(w, client.ClientName, r.URL.RequestURI())
}

// AuthorizeApprove handles POST /oauth/authorize — processes consent approval.
func (o *OAuthHandlers) AuthorizeApprove(w http.ResponseWriter, r *http.Request) {
	// Parse the original authorize params from the form
	if err := r.ParseForm(); err != nil {
		ErrorResponse(w, http.StatusBadRequest, "invalid_request", "Invalid form data")
		return
	}

	// The form includes the original query string in a hidden field
	originalQuery := r.FormValue("original_query")
	parsedQuery, err := url.ParseQuery(originalQuery)
	if err != nil {
		ErrorResponse(w, http.StatusBadRequest, "invalid_request", "Invalid query parameters")
		return
	}

	clientID := parsedQuery.Get("client_id")
	redirectURI := parsedQuery.Get("redirect_uri")
	codeChallenge := parsedQuery.Get("code_challenge")
	state := parsedQuery.Get("state")
	scope := parsedQuery.Get("scope")

	// Check denial
	if r.FormValue("action") == "deny" {
		oauthRedirect(w, r, redirectURI, state, "", "access_denied")
		return
	}

	// Validate client again
	client, err := lib.OAuthClientByID(o.DB, clientID)
	if err != nil || client == nil {
		ErrorResponse(w, http.StatusBadRequest, "invalid_client", "Unknown client_id")
		return
	}
	if !validRedirectURI(client.RedirectURIs, redirectURI) {
		ErrorResponse(w, http.StatusBadRequest, "invalid_request", "Invalid redirect_uri")
		return
	}

	// User must be authenticated
	userID := o.extractUserID(r)
	if userID == "" {
		ErrorResponse(w, http.StatusUnauthorized, "login_required", "Authentication required")
		return
	}

	// Generate authorization code
	codeBytes := make([]byte, 32)
	if _, err := rand.Read(codeBytes); err != nil {
		ErrorResponse(w, http.StatusInternalServerError, "internal", "Failed to generate code")
		return
	}
	codeStr := hex.EncodeToString(codeBytes)

	oauthCode := &lib.OAuthCode{
		Code:          codeStr,
		ClientID:      clientID,
		UserID:        userID,
		RedirectURI:   redirectURI,
		CodeChallenge: codeChallenge,
		Scope:         scope,
		ExpiresAt:     time.Now().Add(10 * time.Minute).UnixMilli(),
		Used:          false,
	}
	if err := lib.OAuthCodeCreate(o.DB, oauthCode); err != nil {
		ErrorResponse(w, http.StatusInternalServerError, "internal", "Failed to store authorization code")
		return
	}

	oauthRedirect(w, r, redirectURI, state, codeStr, "")
}

// Token handles POST /oauth/token — exchanges authorization code for access token.
func (o *OAuthHandlers) Token(w http.ResponseWriter, r *http.Request) {
	if err := r.ParseForm(); err != nil {
		tokenError(w, "invalid_request", "Invalid form data")
		return
	}

	grantType := r.FormValue("grant_type")
	if grantType != "authorization_code" {
		tokenError(w, "unsupported_grant_type", "Only authorization_code is supported")
		return
	}

	codeStr := r.FormValue("code")
	redirectURI := r.FormValue("redirect_uri")
	clientID := r.FormValue("client_id")
	codeVerifier := r.FormValue("code_verifier")

	if codeStr == "" || clientID == "" || codeVerifier == "" {
		tokenError(w, "invalid_request", "Missing required parameters")
		return
	}

	// Consume the code (marks used, checks expiry)
	code, err := lib.OAuthCodeConsume(o.DB, codeStr)
	if err != nil {
		tokenError(w, "invalid_grant", "Invalid or expired authorization code")
		return
	}

	// Verify client_id matches
	if code.ClientID != clientID {
		tokenError(w, "invalid_grant", "Client mismatch")
		return
	}

	// Verify redirect_uri matches
	if code.RedirectURI != redirectURI {
		tokenError(w, "invalid_grant", "Redirect URI mismatch")
		return
	}

	// Verify PKCE: SHA256(code_verifier) must match code_challenge
	verifierHash := sha256.Sum256([]byte(codeVerifier))
	computedChallenge := base64.RawURLEncoding.EncodeToString(verifierHash[:])
	if computedChallenge != code.CodeChallenge {
		tokenError(w, "invalid_grant", "PKCE verification failed")
		return
	}

	// Generate access token
	tokenBytes := make([]byte, 64)
	if _, err := rand.Read(tokenBytes); err != nil {
		tokenError(w, "server_error", "Failed to generate token")
		return
	}
	tokenStr := hex.EncodeToString(tokenBytes)
	now := time.Now()
	expiresIn := int64(24 * 60 * 60) // 24 hours in seconds

	oauthToken := &lib.OAuthToken{
		Token:     tokenStr,
		ClientID:  clientID,
		UserID:    code.UserID,
		Scope:     code.Scope,
		ExpiresAt: now.Add(24 * time.Hour).UnixMilli(),
		Revoked:   false,
		CreatedAt: now.UnixMilli(),
	}
	if err := lib.OAuthTokenCreate(o.DB, oauthToken); err != nil {
		tokenError(w, "server_error", "Failed to store token")
		return
	}

	w.Header().Set("Content-Type", "application/json")
	w.Header().Set("Cache-Control", "no-store")
	json.NewEncoder(w).Encode(map[string]any{
		"access_token": tokenStr,
		"token_type":   "Bearer",
		"expires_in":   expiresIn,
	})
}

// Revoke handles POST /oauth/revoke — revokes an access token (RFC 7009).
func (o *OAuthHandlers) Revoke(w http.ResponseWriter, r *http.Request) {
	if err := r.ParseForm(); err != nil {
		w.WriteHeader(http.StatusOK)
		return
	}
	tokenStr := r.FormValue("token")
	if tokenStr != "" {
		_ = lib.OAuthTokenRevoke(o.DB, tokenStr)
	}
	// Always return 200 per RFC 7009
	w.WriteHeader(http.StatusOK)
}

// extractUserID checks JWT from Authorization header or ds_token cookie.
func (o *OAuthHandlers) extractUserID(r *http.Request) string {
	// Try Authorization header first
	auth := r.Header.Get("Authorization")
	if strings.HasPrefix(auth, "Bearer ") {
		token := strings.TrimPrefix(auth, "Bearer ")
		claims, err := validateJWT(token, o.Cfg.JWTSecret)
		if err == nil {
			session, err := lib.SessionByID(o.DB, claims.SessionID)
			if err == nil && session != nil && !session.Revoked && session.ExpiresAt >= time.Now().UnixMilli() {
				return claims.UserID
			}
		}
	}

	// Try cookie
	cookie, err := r.Cookie("ds_token")
	if err == nil && cookie.Value != "" {
		claims, err := validateJWT(cookie.Value, o.Cfg.JWTSecret)
		if err == nil {
			session, err := lib.SessionByID(o.DB, claims.SessionID)
			if err == nil && session != nil && !session.Revoked && session.ExpiresAt >= time.Now().UnixMilli() {
				return claims.UserID
			}
		}
	}

	return ""
}

func (o *OAuthHandlers) serveConsentPage(w http.ResponseWriter, appName, authorizeURI string) {
	// Extract query string from the authorize URI
	parsed, _ := url.Parse(authorizeURI)
	queryString := parsed.RawQuery

	layoutCandidates := []string{
		"portal/templates/layouts/auth.html",
		"/opt/dealspace/portal/templates/layouts/auth.html",
	}
	pageCandidates := []string{
		"portal/templates/auth/consent.html",
		"/opt/dealspace/portal/templates/auth/consent.html",
	}

	var layoutPath, pagePath string
	for _, p := range layoutCandidates {
		if _, err := os.Stat(p); err == nil {
			layoutPath = p
			break
		}
	}
	for _, p := range pageCandidates {
		if _, err := os.Stat(p); err == nil {
			pagePath = p
			break
		}
	}

	if layoutPath == "" || pagePath == "" {
		http.Error(w, "Consent template not found", http.StatusInternalServerError)
		return
	}

	tmpl, err := template.ParseFiles(layoutPath, pagePath)
	if err != nil {
		http.Error(w, "Template parse error: "+err.Error(), http.StatusInternalServerError)
		return
	}

	data := struct {
		Title         string
		AppName       string
		OriginalQuery string
	}{
		Title:         "Authorize Application — Dealspace",
		AppName:       appName,
		OriginalQuery: queryString,
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	tmpl.ExecuteTemplate(w, "layout", data)
}

func validRedirectURI(registered []string, uri string) bool {
	parsed, err := url.Parse(uri)
	if err != nil {
		return false
	}
	for _, r := range registered {
		rParsed, err := url.Parse(r)
		if err != nil {
			continue
		}
		// Match scheme + host (port-agnostic for localhost)
		if parsed.Scheme == rParsed.Scheme && parsed.Hostname() == rParsed.Hostname() {
			return true
		}
	}
	return false
}

func oauthError(w http.ResponseWriter, redirectURI, state, errCode, errDesc string) {
	if redirectURI == "" {
		ErrorResponse(w, http.StatusBadRequest, errCode, errDesc)
		return
	}
	oauthRedirect(w, nil, redirectURI, state, "", errCode)
}

func oauthRedirect(w http.ResponseWriter, r *http.Request, redirectURI, state, code, errCode string) {
	u, err := url.Parse(redirectURI)
	if err != nil {
		ErrorResponse(w, http.StatusBadRequest, "invalid_request", "Invalid redirect_uri")
		return
	}
	q := u.Query()
	if code != "" {
		q.Set("code", code)
	}
	if errCode != "" {
		q.Set("error", errCode)
	}
	if state != "" {
		q.Set("state", state)
	}
	u.RawQuery = q.Encode()
	if r != nil {
		http.Redirect(w, r, u.String(), http.StatusFound)
	} else {
		w.Header().Set("Location", u.String())
		w.WriteHeader(http.StatusFound)
	}
}

func tokenError(w http.ResponseWriter, errCode, errDesc string) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(http.StatusBadRequest)
	json.NewEncoder(w).Encode(map[string]string{
		"error":             errCode,
		"error_description": errDesc,
	})
}

// SeedOAuthClient creates the default Claude OAuth client if it doesn't exist.
func SeedOAuthClient(db *lib.DB) {
	client := &lib.OAuthClient{
		ClientID:   "claude",
		ClientName: "Claude",
		RedirectURIs: []string{
			"http://localhost",
			"http://127.0.0.1",
			"http://localhost:0",
			"http://127.0.0.1:0",
		},
		CreatedAt: time.Now().UnixMilli(),
	}
	_ = lib.OAuthClientCreate(db, client)
}