package cas

import (
	"crypto/rand"
	"fmt"
	"net/http"
	"net/url"

	"github.com/golang/glog"
)

// Client configuration options
type Options struct {
	URL          *url.URL     // URL to the CAS service
	Store        TicketStore  // Custom TicketStore, if nil a MemoryStore will be used
	Client       *http.Client // Custom http client to allow options for http connections
	SendService  bool         // Custom sendService to determine whether you need to send service param
	URLScheme    URLScheme    // Custom url scheme, can be used to modify the request urls for the client
	Cookie       *http.Cookie // http.Cookie options, uses Path, Domain, MaxAge, HttpOnly, & Secure
	SessionStore SessionStore
}

// Client implements the main protocol
type Client struct {
	tickets   TicketStore
	client    *http.Client
	urlScheme URLScheme
	cookie    *http.Cookie

	sessions    SessionStore
	sendService bool

	stValidator *ServiceTicketValidator
}

// NewClient creates a Client with the provided Options.
func NewClient(options *Options) *Client {
	if glog.V(2) {
		glog.Infof("cas: new client with options %v", options)
	}

	var tickets TicketStore
	if options.Store != nil {
		tickets = options.Store
	} else {
		tickets = &MemoryStore{}
	}

	var sessions SessionStore
	if options.SessionStore != nil {
		sessions = options.SessionStore
	} else {
		sessions = NewMemorySessionStore()
	}

	var urlScheme URLScheme
	if options.URLScheme != nil {
		urlScheme = options.URLScheme
	} else {
		urlScheme = NewDefaultURLScheme(options.URL)
	}

	var client *http.Client
	if options.Client != nil {
		client = options.Client
	} else {
		client = &http.Client{}
	}

	var cookie *http.Cookie
	if options.Cookie != nil {
		cookie = options.Cookie
	} else {
		cookie = &http.Cookie{
			MaxAge:   86400,
			HttpOnly: false,
			Secure:   false,
		}
	}

	return &Client{
		tickets:     tickets,
		client:      client,
		urlScheme:   urlScheme,
		cookie:      cookie,
		sessions:    sessions,
		sendService: options.SendService,
		stValidator: NewServiceTicketValidator(client, options.URL),
	}
}

// Handle wraps a http.Handler to provide CAS authentication for the handler.
func (c *Client) Handle(h http.Handler) http.Handler {
	return &clientHandler{
		c: c,
		h: h,
	}
}

// HandleFunc wraps a function to provide CAS authentication for the handler function.
func (c *Client) HandleFunc(h func(http.ResponseWriter, *http.Request)) http.Handler {
	return c.Handle(http.HandlerFunc(h))
}

// requestURL determines an absolute URL from the http.Request.
func requestURL(r *http.Request) (*url.URL, error) {
	u, err := url.Parse(r.URL.String())
	if err != nil {
		return nil, err
	}

	u.Host = r.Host
	if host := r.Header.Get("X-Forwarded-Host"); host != "" {
		u.Host = host
	}

	u.Scheme = "http"
	if scheme := r.Header.Get("X-Forwarded-Proto"); scheme != "" {
		u.Scheme = scheme
	} else if r.TLS != nil {
		u.Scheme = "https"
	}

	return u, nil
}

// LoginUrlForRequest determines the CAS login URL for the http.Request.
func (c *Client) LoginUrlForRequest(r *http.Request) (string, error) {
	u, err := c.urlScheme.Login()
	if err != nil {
		return "", err
	}

	service, err := requestURL(r)
	if err != nil {
		return "", err
	}

	q := u.Query()
	q.Add("service", sanitisedURLString(service))
	u.RawQuery = q.Encode()

	return u.String(), nil
}

// LogoutUrlForRequest determines the CAS logout URL for the http.Request.
func (c *Client) LogoutUrlForRequest(r *http.Request) (string, error) {
	u, err := c.urlScheme.Logout()
	if err != nil {
		return "", err
	}

	if c.sendService {
		service, err := requestURL(r)
		if err != nil {
			return "", err
		}

		q := u.Query()
		q.Add("service", sanitisedURLString(service))
		u.RawQuery = q.Encode()
	}

	return u.String(), nil
}

// ServiceValidateUrlForRequest determines the CAS serviceValidate URL for the ticket and http.Request.
func (c *Client) ServiceValidateUrlForRequest(ticket string, r *http.Request) (string, error) {
	service, err := requestURL(r)
	if err != nil {
		return "", err
	}
	return c.stValidator.ServiceValidateUrl(service, ticket)
}

// ValidateUrlForRequest determines the CAS validate URL for the ticket and http.Request.
func (c *Client) ValidateUrlForRequest(ticket string, r *http.Request) (string, error) {
	service, err := requestURL(r)
	if err != nil {
		return "", err
	}
	return c.stValidator.ValidateUrl(service, ticket)
}

// RedirectToLogout replies to the request with a redirect URL to log out of CAS.
func (c *Client) RedirectToLogout(w http.ResponseWriter, r *http.Request) {
	u, err := c.LogoutUrlForRequest(r)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	if glog.V(2) {
		glog.Infof("Logging out, redirecting client to %v with status %v",
			u, http.StatusFound)
	}

	c.clearSession(w, r)
	http.Redirect(w, r, u, http.StatusFound)
}

// RedirectToLogout replies to the request with a redirect URL to authenticate with CAS.
func (c *Client) RedirectToLogin(w http.ResponseWriter, r *http.Request) {
	u, err := c.LoginUrlForRequest(r)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	if glog.V(2) {
		glog.Infof("Redirecting client to %v with status %v", u, http.StatusFound)
	}

	http.Redirect(w, r, u, http.StatusFound)
}

// validateTicket performs CAS ticket validation with the given ticket and service.
func (c *Client) validateTicket(ticket string, service *http.Request) error {
	serviceUrl, err := requestURL(service)
	if err != nil {
		return err
	}

	success, err := c.stValidator.ValidateTicket(serviceUrl, ticket)
	if err != nil {
		return err
	}

	if err := c.tickets.Write(ticket, success); err != nil {
		return err
	}

	return nil
}

// getSession finds or creates a session for the request.
//
// A cookie is set on the response if one is not provided with the request.
// Validates the ticket if the URL parameter is provided.
func (c *Client) getSession(w http.ResponseWriter, r *http.Request) {
	cookie := c.getCookie(w, r)

	if s, ok := c.sessions.Get(cookie.Value); ok {
		if t, err := c.tickets.Read(s); err == nil {
			if glog.V(1) {
				glog.Infof("Re-used ticket %s for %s", s, t.User)
			}

			setAuthenticationResponse(r, t)
			return
		} else {
			if glog.V(2) {
				glog.Infof("Ticket %v not in %T: %v", s, c.tickets, err)
			}

			if glog.V(1) {
				glog.Infof("Clearing ticket %s, no longer exists in ticket store", s)
			}

			clearCookie(w, cookie)
		}
	}

	if ticket := r.URL.Query().Get("ticket"); ticket != "" {
		if err := c.validateTicket(ticket, r); err != nil {
			if glog.V(2) {
				glog.Infof("Error validating ticket: %v", err)
			}
			return // allow ServeHTTP()
		}

		c.setSession(cookie.Value, ticket)

		if t, err := c.tickets.Read(ticket); err == nil {
			if glog.V(1) {
				glog.Infof("Validated ticket %s for %s", ticket, t.User)
			}

			setAuthenticationResponse(r, t)
			return
		} else {
			if glog.V(2) {
				glog.Infof("Ticket %v not in %T: %v", ticket, c.tickets, err)
			}

			if glog.V(1) {
				glog.Infof("Clearing ticket %s, no longer exists in ticket store", ticket)
			}

			clearCookie(w, cookie)
		}
	}
}

// getCookie finds or creates the session cookie on the response.
func (c *Client) getCookie(w http.ResponseWriter, r *http.Request) *http.Cookie {
	cookie, err := r.Cookie(sessionCookieName)
	if err != nil {
		// NOTE: Intentionally not enabling HttpOnly so the cookie can
		//       still be used by Ajax requests.
		cookie = &http.Cookie{
			Name:     sessionCookieName,
			Value:    newSessionID(),
			Path:     c.cookie.Path,
			Domain:   c.cookie.Domain,
			MaxAge:   c.cookie.MaxAge,
			HttpOnly: c.cookie.HttpOnly,
			Secure:   c.cookie.Secure,
		}

		if glog.V(2) {
			glog.Infof("Setting %v cookie with value: %v", cookie.Name, cookie.Value)
		}

		r.AddCookie(cookie) // so we can find it later if required
		http.SetCookie(w, cookie)
	}

	return cookie
}

// newSessionId generates a new opaque session identifier for use in the cookie.
func newSessionID() string {
	const alphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"

	// generate 64 character string
	bytes := make([]byte, 64)
	rand.Read(bytes)

	for k, v := range bytes {
		bytes[k] = alphabet[v%byte(len(alphabet))]
	}

	return string(bytes)
}

// clearCookie invalidates and removes the cookie from the client.
func clearCookie(w http.ResponseWriter, c *http.Cookie) {
	c.MaxAge = -1
	http.SetCookie(w, c)
}

// setSession stores the session id to ticket mapping in the Client.
func (c *Client) setSession(id string, ticket string) {
	if glog.V(2) {
		glog.Infof("Recording session, %v -> %v", id, ticket)
	}

	c.sessions.Set(id, ticket)
}

// clearSession removes the session from the client and clears the cookie.
func (c *Client) clearSession(w http.ResponseWriter, r *http.Request) {
	cookie := c.getCookie(w, r)

	if s, ok := c.sessions.Get(cookie.Value); ok {
		if err := c.tickets.Delete(s); err != nil {
			fmt.Printf("Failed to remove %v from %T: %v\n", cookie.Value, c.tickets, err)
			if glog.V(2) {
				glog.Errorf("Failed to remove %v from %T: %v", cookie.Value, c.tickets, err)
			}
		}

		c.deleteSession(s)
	}

	clearCookie(w, cookie)
}

// deleteSession removes the session from the client
func (c *Client) deleteSession(id string) {
	c.sessions.Delete(id)
}