package auth

import (
	"net/http"
	"net/url"

	"github.com/google/go-querystring/query"
)

type AuthorizeParams struct {
	// A string-encoded JSON object that specifies the claims to include in the ID token.
	// For information about claims, see Requesting claims: https://dev.twitch.tv/docs/authentication/getting-tokens-oidc/#requesting-claims
	//
	// Only used for OIDC auth flows
	Claims *Claims `url:"claims,omitempty"`

	// Set to true to force the user to re-authorize your app’s access to their resources.
	// The default is false.
	ForceVerify *bool `url:"force_verify,omitempty"`

	// Although optional, you are strongly encouraged to pass a nonce string to help
	// prevent Cross-Site Request Forgery (CSRF) attacks. The server returns this string
	// to you in the ID token’s list of claims. If this string doesn’t match the nonce
	// string that you passed, ignore the response. The nonce string should be randomly
	// generated and unique for each OAuth request.
	//
	// Only used for OIDC auth flows
	Nonce *string `url:"nonce,omitempty"`

	// Must be set to code for Authorization code grant flow.
	// Recommended for Server-to-Server flows. (with backend)
	//
	// Must be set to token for Implicit grant flow.
	// Recommended for Client-to-Server flows. (no backend)
	ResponseType string `url:"response_type"`

	// A space-delimited list of scopes. The APIs that you’re calling identify the
	// scopes you must list. The list must include the openid scope. Don’t forget to
	// URL encode the list.
	Scope []Scope `url:"scope,space"`

	// Although optional, you are strongly encouraged to pass a state string to help
	// prevent Cross-Site Request Forgery (CSRF) attacks. The server returns this string
	// to you in your redirect URI (see the state parameter in the fragment portion of
	// the URI). If this string doesn’t match the state string that you passed, ignore
	// the response. The state string should be randomly generated and unique for each
	// OAuth request.
	State *string `url:"state,omitempty"`
}

const AuthorizeUrl = "https://id.twitch.tv/oauth2/authorize"

// AuthorizeUrl returns the URL to redirect the user to for authorization.
func (c *Client) AuthorizeUrl(params *AuthorizeParams) *url.URL {
	v, _ := query.Values(params)
	v.Set("client_id", c.clientId)
	v.Set("redirect_uri", c.redirectUri)
	url, _ := url.Parse(AuthorizeUrl)
	url.RawQuery = v.Encode()
	return url
}

type AuthorizeHandler struct {
	client *Client
	scopes []Scope
}

var _ http.Handler = (*AuthorizeHandler)(nil)

// AuthorizeHandler returns an http.Handler that redirects the user to the
// authorization URL.
func (c *Client) AuthorizeHandler(scopes []Scope) http.Handler {
	return &AuthorizeHandler{
		client: c,
		scopes: scopes,
	}
}

// ServeHTTP implements http.Handler.
func (h *AuthorizeHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	state := GenerateState()

	if err := h.client.stateStorage.Save(w, state); err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	url := h.client.AuthorizeUrl(&AuthorizeParams{
		ResponseType: "code",
		Scope:        h.scopes,
		State:        &state,
	})

	http.Redirect(w, r, url.String(), http.StatusFound)
}