package hammerhead

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

// Hammerhead acts as an OpenID Connect relying party using the authorization
// code flow with PKCE. Identity comes from the provider's userinfo endpoint,
// fetched over TLS with the access token we just received from the token endpoint.

type oidcDoc struct {
	auth, token, userinfo string
	fetched               time.Time
}

type oauthState struct {
	idp, verifier, ret string
	expires            time.Time
}

var oidcClient = &http.Client{Timeout: 10 * time.Second}

func (s *Server) discover(idp *IdP) (*oidcDoc, error) {
	s.mu.Lock()
	d := s.oidc[idp.ID]
	s.mu.Unlock()
	if d != nil && time.Since(d.fetched) < time.Hour {
		return d, nil
	}
	resp, err := oidcClient.Get(strings.TrimRight(idp.Issuer, "/") + "/.well-known/openid-configuration")
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	if resp.StatusCode != 200 {
		return nil, fmt.Errorf("discovery returned %d", resp.StatusCode)
	}
	var doc struct {
		Auth     string `json:"authorization_endpoint"`
		Token    string `json:"token_endpoint"`
		Userinfo string `json:"userinfo_endpoint"`
	}
	if err := json.NewDecoder(io.LimitReader(resp.Body, 1<<20)).Decode(&doc); err != nil {
		return nil, err
	}
	if doc.Auth == "" || doc.Token == "" || doc.Userinfo == "" {
		return nil, errors.New("provider discovery document is missing endpoints")
	}
	d = &oidcDoc{auth: doc.Auth, token: doc.Token, userinfo: doc.Userinfo, fetched: time.Now()}
	s.mu.Lock()
	s.oidc[idp.ID] = d
	s.mu.Unlock()
	return d, nil
}

// baseURL is where browsers reach hammerhead.
func (s *Server) baseURL(r *http.Request) string {
	s.mu.Lock()
	u := s.st.Settings.DashboardURL
	s.mu.Unlock()
	if u != "" {
		return u
	}
	scheme := "http"
	if r.TLS != nil {
		scheme = "https"
	}
	return scheme + "://" + r.Host
}

func safeReturn(p string) string {
	if p == "" || p[0] != '/' || strings.HasPrefix(p, "//") || strings.HasPrefix(p, "/\\") {
		return "/"
	}
	return p
}

func (s *Server) oidcStart(w http.ResponseWriter, r *http.Request) {
	s.mu.Lock()
	var idp *IdP
	for _, p := range s.st.IdPs {
		if p.ID == r.PathValue("id") {
			c := *p
			idp = &c
		}
	}
	s.mu.Unlock()
	if idp == nil {
		http.Error(w, "unknown provider", 404)
		return
	}
	doc, err := s.discover(idp)
	if err != nil {
		http.Error(w, "identity provider unreachable: "+err.Error(), 502)
		return
	}
	state, verifier := randHex(16), randHex(32)
	sum := sha256.Sum256([]byte(verifier))
	s.mu.Lock()
	now := time.Now()
	for k, v := range s.oauth {
		if now.After(v.expires) {
			delete(s.oauth, k)
		}
	}
	s.oauth[state] = oauthState{idp: idp.ID, verifier: verifier, ret: safeReturn(r.URL.Query().Get("return")), expires: now.Add(10 * time.Minute)}
	s.mu.Unlock()
	scopes := idp.Scopes
	if scopes == "" {
		scopes = "openid email profile"
	}
	q := url.Values{
		"response_type":         {"code"},
		"client_id":             {idp.ClientID},
		"redirect_uri":          {s.baseURL(r) + "/auth/oidc/callback"},
		"scope":                 {scopes},
		"state":                 {state},
		"code_challenge":        {base64.RawURLEncoding.EncodeToString(sum[:])},
		"code_challenge_method": {"S256"},
	}
	sep := "?"
	if strings.Contains(doc.auth, "?") {
		sep = "&"
	}
	http.Redirect(w, r, doc.auth+sep+q.Encode(), http.StatusFound)
}

func (s *Server) oidcCallback(w http.ResponseWriter, r *http.Request) {
	q := r.URL.Query()
	s.mu.Lock()
	st, found := s.oauth[q.Get("state")]
	delete(s.oauth, q.Get("state"))
	var idp *IdP
	if found && time.Now().Before(st.expires) {
		for _, p := range s.st.IdPs {
			if p.ID == st.idp {
				c := *p
				idp = &c
			}
		}
	}
	s.mu.Unlock()
	if idp == nil {
		http.Error(w, "sign-in expired, please try again", 400)
		return
	}
	if e := q.Get("error"); e != "" {
		http.Error(w, "identity provider said: "+e, 400)
		return
	}
	email, name, sub, err := s.oidcExchange(r, idp, q.Get("code"), st.verifier)
	if err != nil {
		http.Error(w, "sign-in failed: "+err.Error(), 400)
		return
	}
	uid, err := s.oidcUser(idp, email, name, sub)
	if err != nil {
		http.Error(w, err.Error(), 403)
		return
	}
	s.startSession(w, r, uid)
	s.audit("", email, "login", "oidc:"+idp.Name)
	http.Redirect(w, r, st.ret, http.StatusFound)
}

func (s *Server) oidcExchange(r *http.Request, idp *IdP, code, verifier string) (email, name, sub string, err error) {
	doc, err := s.discover(idp)
	if err != nil {
		return
	}
	resp, err := oidcClient.PostForm(doc.token, url.Values{
		"grant_type": {"authorization_code"}, "code": {code},
		"redirect_uri": {s.baseURL(r) + "/auth/oidc/callback"},
		"client_id":    {idp.ClientID}, "client_secret": {idp.ClientSecret}, "code_verifier": {verifier},
	})
	if err != nil {
		return
	}
	defer resp.Body.Close()
	var tok struct {
		AccessToken string `json:"access_token"`
	}
	if resp.StatusCode != 200 || json.NewDecoder(io.LimitReader(resp.Body, 1<<20)).Decode(&tok) != nil || tok.AccessToken == "" {
		err = fmt.Errorf("token exchange failed (%d)", resp.StatusCode)
		return
	}
	req, _ := http.NewRequest("GET", doc.userinfo, nil)
	req.Header.Set("Authorization", "Bearer "+tok.AccessToken)
	ui, err := oidcClient.Do(req)
	if err != nil {
		return
	}
	defer ui.Body.Close()
	var claims struct {
		Sub               string `json:"sub"`
		Email             string `json:"email"`
		EmailVerified     any    `json:"email_verified"`
		Name              string `json:"name"`
		PreferredUsername string `json:"preferred_username"`
	}
	if ui.StatusCode != 200 || json.NewDecoder(io.LimitReader(ui.Body, 1<<20)).Decode(&claims) != nil {
		err = fmt.Errorf("userinfo failed (%d)", ui.StatusCode)
		return
	}
	// some providers send "true" as a string, some omit it; only an explicit false is refused
	if v, ok := claims.EmailVerified.(bool); ok && !v {
		err = errors.New("your email address is not verified at the identity provider")
		return
	}
	if v, ok := claims.EmailVerified.(string); ok && strings.EqualFold(v, "false") {
		err = errors.New("your email address is not verified at the identity provider")
		return
	}
	if claims.Sub == "" || claims.Email == "" {
		err = errors.New("the identity provider did not return an email address")
		return
	}
	name = claims.Name
	if name == "" {
		name = claims.PreferredUsername
	}
	return strings.ToLower(claims.Email), name, claims.Sub, nil
}

func (s *Server) oidcUser(idp *IdP, email, name, sub string) (string, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	for _, u := range s.st.Users {
		if u.IdP == idp.ID && u.IdPSub == sub {
			return u.ID, nil
		}
	}
	if len(idp.AllowedDomains) > 0 {
		okDomain := false
		for _, d := range idp.AllowedDomains {
			if strings.HasSuffix(email, "@"+strings.ToLower(strings.TrimSpace(d))) {
				okDomain = true
			}
		}
		if !okDomain {
			return "", errors.New("your email domain is not allowed to sign in here")
		}
	}
	if u := s.userByEmail(email); u != nil { // link an existing account by verified email
		if u.IdP == "" {
			u.IdP, u.IdPSub = idp.ID, sub
			s.save()
		}
		return u.ID, nil
	}
	if !idp.AutoProvision {
		return "", errors.New("no account exists for " + email + "; ask an administrator to invite you")
	}
	if name == "" {
		name = email
	}
	u := &User{ID: newID(), Email: email, Name: name, IdP: idp.ID, IdPSub: sub, Created: time.Now()}
	s.st.Users = append(s.st.Users, u)
	if s.findOrg(idp.OrgID) != nil {
		role := s.findRole(idp.RoleID)
		if role == nil || role.OrgID != idp.OrgID {
			for _, r := range s.st.Roles {
				if r.OrgID == idp.OrgID && r.Name == "Member" && r.Builtin {
					role = r
				}
			}
		}
		if role != nil {
			s.st.Members = append(s.st.Members, &Member{UserID: u.ID, OrgID: idp.OrgID, RoleID: role.ID})
		}
	}
	s.save()
	return u.ID, nil
}

// ---------- admin CRUD ----------

func (s *Server) listIdPs(w http.ResponseWriter, r *http.Request, p *principal) {
	s.mu.Lock()
	defer s.mu.Unlock()
	out := []IdP{}
	for _, i := range s.st.IdPs {
		c := *i
		c.ClientSecret = ""
		out = append(out, c)
	}
	writeJSON(w, 200, out)
}

func (s *Server) saveIdP(w http.ResponseWriter, r *http.Request, p *principal) {
	var in IdP
	if !decode(w, r, &in) {
		return
	}
	in.Issuer = strings.TrimRight(strings.TrimSpace(in.Issuer), "/")
	in.Name = strings.TrimSpace(in.Name)
	if in.Name == "" || in.Issuer == "" || in.ClientID == "" {
		fail(w, 400, errors.New("name, issuer URL and client ID are required"))
		return
	}
	if !strings.HasPrefix(in.Issuer, "https://") && !strings.HasPrefix(in.Issuer, "http://") {
		fail(w, 400, errors.New("issuer must be a URL"))
		return
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	if id := r.PathValue("id"); id != "" {
		for _, e := range s.st.IdPs {
			if e.ID == id {
				if in.ClientSecret == "" {
					in.ClientSecret = e.ClientSecret
				}
				in.ID = id
				*e = in
				delete(s.oidc, id)
				s.save()
				ok(w)
				return
			}
		}
		fail(w, 404, errors.New("no such provider"))
		return
	}
	in.ID = newID()
	s.st.IdPs = append(s.st.IdPs, &in)
	s.save()
	ok(w)
}

func (s *Server) deleteIdP(w http.ResponseWriter, r *http.Request, p *principal) {
	id := r.PathValue("id")
	s.mu.Lock()
	defer s.mu.Unlock()
	s.st.IdPs = filter(s.st.IdPs, func(i *IdP) bool { return i.ID != id })
	s.save()
	ok(w)
}