// SPDX-FileCopyrightText: 2026 Echolot contributors
// SPDX-License-Identifier: GPL-3.0-or-later

package oidc

import (
	"context"
	"crypto"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha256"
	"encoding/base64"
	"encoding/json"
	"errors"
	"math/big"
	"net/http"
	"net/http/httptest"
	"testing"
	"time"
)

// A self-contained IdP: real keys, real signatures, real discovery and JWKS documents. Testing
// token verification against anything less than a genuine signer proves nothing — the failure
// modes that matter here (accepting `none`, accepting another client's token, accepting an
// expired one) all look fine to a mock that just returns success.
type testIdP struct {
	*httptest.Server
	rsaKey *rsa.PrivateKey
	ecKey  *ecdsa.PrivateKey
}

func newIdP(t *testing.T) *testIdP {
	t.Helper()
	rk, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		t.Fatal(err)
	}
	ek, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
	if err != nil {
		t.Fatal(err)
	}
	idp := &testIdP{rsaKey: rk, ecKey: ek}

	mux := http.NewServeMux()
	mux.HandleFunc("/.well-known/openid-configuration", func(w http.ResponseWriter, r *http.Request) {
		_ = json.NewEncoder(w).Encode(Discovery{
			Issuer:                idp.URL,
			AuthorizationEndpoint: idp.URL + "/auth",
			TokenEndpoint:         idp.URL + "/token",
			JWKSURI:               idp.URL + "/jwks",
		})
	})
	mux.HandleFunc("/jwks", func(w http.ResponseWriter, r *http.Request) {
		_ = json.NewEncoder(w).Encode(map[string]any{"keys": []map[string]string{
			{
				"kty": "RSA", "kid": "rsa-1", "alg": "RS256", "use": "sig",
				"n": raw(rk.N.Bytes()),
				"e": raw(big.NewInt(int64(rk.E)).Bytes()),
			},
			{
				"kty": "EC", "kid": "ec-1", "alg": "ES256", "use": "sig", "crv": "P-256",
				"x": raw(ek.X.Bytes()), "y": raw(ek.Y.Bytes()),
			},
		}})
	})
	idp.Server = httptest.NewServer(mux)
	t.Cleanup(idp.Close)
	return idp
}

func raw(b []byte) string { return base64.RawURLEncoding.EncodeToString(b) }

func (i *testIdP) sign(t *testing.T, alg, kid string, claims map[string]any) string {
	t.Helper()
	h, _ := json.Marshal(map[string]string{"alg": alg, "kid": kid, "typ": "JWT"})
	p, _ := json.Marshal(claims)
	signing := raw(h) + "." + raw(p)
	digest := sha256.Sum256([]byte(signing))

	var sig []byte
	switch alg {
	case "RS256":
		s, err := rsa.SignPKCS1v15(rand.Reader, i.rsaKey, crypto.SHA256, digest[:])
		if err != nil {
			t.Fatal(err)
		}
		sig = s
	case "ES256":
		r, s, err := ecdsa.Sign(rand.Reader, i.ecKey, digest[:])
		if err != nil {
			t.Fatal(err)
		}
		// JWS wants fixed-width r||s, not ASN.1.
		sig = make([]byte, 64)
		r.FillBytes(sig[:32])
		s.FillBytes(sig[32:])
	default:
		t.Fatalf("unsupported test alg %q", alg)
	}
	return signing + "." + raw(sig)
}

func (i *testIdP) claims(extra map[string]any) map[string]any {
	c := map[string]any{
		"iss": i.URL, "sub": "user-1", "aud": "echolot",
		"exp": time.Now().Add(time.Hour).Unix(), "iat": time.Now().Unix(),
		"email": "someone@example.net", "groups": []string{"users"},
	}
	for k, v := range extra {
		c[k] = v
	}
	return c
}

func verifier(i *testIdP, adminGroup string) *Verifier {
	return New(Config{
		Issuer: i.URL, ClientID: "echolot", AppClientID: "echolot-app", AdminGroup: adminGroup,
	}, i.Client())
}

func TestAcceptsAGenuineToken(t *testing.T) {
	idp := newIdP(t)
	v := verifier(idp, "")
	for _, tc := range []struct{ alg, kid string }{{"RS256", "rsa-1"}, {"ES256", "ec-1"}} {
		got, err := v.Verify(context.Background(), idp.sign(t, tc.alg, tc.kid, idp.claims(nil)))
		if err != nil {
			t.Fatalf("%s: %v", tc.alg, err)
		}
		if got.Subject != "user-1" || got.Email != "someone@example.net" {
			t.Fatalf("%s: claims not parsed: %+v", tc.alg, got)
		}
		if want := idp.URL + "#user-1"; got.AccountID() != want {
			t.Errorf("AccountID = %q, want %q", got.AccountID(), want)
		}
	}
}

// "alg": "none" is the oldest JWT forgery there is: strip the signature, declare no algorithm,
// and a naive verifier accepts anything. It must not even reach the key lookup.
func TestRejectsAlgNone(t *testing.T) {
	idp := newIdP(t)
	v := verifier(idp, "")
	h, _ := json.Marshal(map[string]string{"alg": "none", "kid": "rsa-1", "typ": "JWT"})
	p, _ := json.Marshal(idp.claims(nil))
	token := raw(h) + "." + raw(p) + "."
	if _, err := v.Verify(context.Background(), token); !errors.Is(err, ErrSignature) {
		t.Fatalf("alg=none was not refused as a signature failure: %v", err)
	}
}

// The other classic: declare HS256 so the verifier treats the RSA *public* key as an HMAC secret,
// which the attacker also has. The allow-list has no symmetric algorithms at all.
func TestRejectsSymmetricAlgorithmConfusion(t *testing.T) {
	idp := newIdP(t)
	v := verifier(idp, "")
	h, _ := json.Marshal(map[string]string{"alg": "HS256", "kid": "rsa-1", "typ": "JWT"})
	p, _ := json.Marshal(idp.claims(nil))
	token := raw(h) + "." + raw(p) + "." + raw([]byte("whatever"))
	if _, err := v.Verify(context.Background(), token); !errors.Is(err, ErrSignature) {
		t.Fatalf("HS256 confusion was not refused: %v", err)
	}
}

func TestRejectsATamperedPayload(t *testing.T) {
	idp := newIdP(t)
	v := verifier(idp, "")
	good := idp.sign(t, "RS256", "rsa-1", idp.claims(nil))
	// Swap the payload for one claiming to be somebody else, keeping the valid signature.
	forged, _ := json.Marshal(idp.claims(map[string]any{"sub": "admin"}))
	parts := []byte(good)
	dot1, dot2 := 0, 0
	for i, c := range parts {
		if c == '.' {
			if dot1 == 0 {
				dot1 = i
			} else {
				dot2 = i
			}
		}
	}
	token := string(parts[:dot1+1]) + raw(forged) + string(parts[dot2:])
	if _, err := v.Verify(context.Background(), token); !errors.Is(err, ErrSignature) {
		t.Fatalf("a swapped payload was not refused: %v", err)
	}
}

// A token from the same IdP but issued to a different client is perfectly valid — just not for
// us. Accepting it would let any other client of the same provider authenticate here.
func TestRejectsAnotherClientsToken(t *testing.T) {
	idp := newIdP(t)
	v := verifier(idp, "")
	tok := idp.sign(t, "RS256", "rsa-1", idp.claims(map[string]any{"aud": "some-other-app"}))
	if _, err := v.Verify(context.Background(), tok); !errors.Is(err, ErrClaims) {
		t.Fatalf("another client's token was accepted: %v", err)
	}
}

func TestAcceptsAudienceArrayContainingUs(t *testing.T) {
	idp := newIdP(t)
	v := verifier(idp, "")
	tok := idp.sign(t, "RS256", "rsa-1", idp.claims(map[string]any{"aud": []string{"other", "echolot"}}))
	if _, err := v.Verify(context.Background(), tok); err != nil {
		t.Fatalf("an audience array including us was refused: %v", err)
	}
}

func TestRejectsExpiredAndFutureTokens(t *testing.T) {
	idp := newIdP(t)
	v := verifier(idp, "")
	expired := idp.sign(t, "RS256", "rsa-1", idp.claims(map[string]any{
		"exp": time.Now().Add(-time.Hour).Unix(),
	}))
	if _, err := v.Verify(context.Background(), expired); !errors.Is(err, ErrClaims) {
		t.Errorf("expired token accepted: %v", err)
	}
	future := idp.sign(t, "RS256", "rsa-1", idp.claims(map[string]any{
		"iat": time.Now().Add(time.Hour).Unix(),
	}))
	if _, err := v.Verify(context.Background(), future); !errors.Is(err, ErrClaims) {
		t.Errorf("token issued in the future accepted: %v", err)
	}
}

// A token signed by a completely different provider, with its own keys and its own kid.
func TestRejectsATokenFromAnotherIssuer(t *testing.T) {
	ours, theirs := newIdP(t), newIdP(t)
	v := verifier(ours, "")
	tok := theirs.sign(t, "RS256", "rsa-1", theirs.claims(nil))
	if _, err := v.Verify(context.Background(), tok); err == nil {
		t.Fatal("a token from another issuer was accepted")
	}
}

func TestRejectsMalformedTokens(t *testing.T) {
	idp := newIdP(t)
	v := verifier(idp, "")
	for _, bad := range []string{"", "not-a-token", "a.b", "a.b.c.d", "...", "!!!.???.***"} {
		if _, err := v.Verify(context.Background(), bad); err == nil {
			t.Errorf("%q was accepted", bad)
		}
	}
}

// With no admin group configured, nobody is an admin. An operator who has not said who may
// administer the server has not thereby said "anyone who can log in".
func TestNobodyIsAdminUntilAGroupIsConfigured(t *testing.T) {
	idp := newIdP(t)
	claims := &Claims{Groups: []string{"users", "echolot-admins"}}

	if verifier(idp, "").IsAdmin(claims) {
		t.Error("someone was an admin with no admin group configured")
	}
	if !verifier(idp, "echolot-admins").IsAdmin(claims) {
		t.Error("a member of the configured group was not an admin")
	}
	if verifier(idp, "other-group").IsAdmin(claims) {
		t.Error("a non-member was an admin")
	}
	if verifier(idp, "echolot-admins").IsAdmin(nil) {
		t.Error("an absent identity was an admin")
	}
}

// A discovery document whose issuer disagrees with the configured one means we were redirected
// somewhere — and would otherwise have fetched that somewhere's signing keys while believing
// they belonged to the configured provider.
func TestRefusesDiscoveryThatRenamesTheIssuer(t *testing.T) {
	mux := http.NewServeMux()
	srv := httptest.NewServer(mux)
	defer srv.Close()
	mux.HandleFunc("/.well-known/openid-configuration", func(w http.ResponseWriter, r *http.Request) {
		_ = json.NewEncoder(w).Encode(Discovery{Issuer: "https://somewhere.else", JWKSURI: srv.URL + "/jwks"})
	})
	v := New(Config{Issuer: srv.URL, ClientID: "echolot"}, srv.Client())
	if _, err := v.Discover(context.Background()); err == nil {
		t.Fatal("discovery accepted a document for a different issuer")
	}
}

func TestDisabledWithoutConfiguration(t *testing.T) {
	v := New(Config{}, nil)
	if v.Config().Enabled() {
		t.Fatal("an unconfigured verifier reports itself enabled")
	}
	if _, err := v.Verify(context.Background(), "x.y.z"); !errors.Is(err, ErrDisabled) {
		t.Fatalf("want ErrDisabled, got %v", err)
	}
}

// Two clients, because the phone and the admin UI have different properties: an APK cannot keep a
// secret (public + PKCE) while the server can (confidential). Both must be accepted — but only
// those two. "Any client of this issuer" would let every other application registered with the
// same IdP authenticate here, which is the whole reason the audience check exists.
func TestBothRegisteredClientsAreAccepted(t *testing.T) {
	idp := newIdP(t)
	v := verifier(idp, "")

	for _, aud := range []any{"echolot", "echolot-app", []string{"echolot-app", "other"}} {
		tok := idp.sign(t, "RS256", "rsa-1", idp.claims(map[string]any{"aud": aud}))
		if _, err := v.Verify(context.Background(), tok); err != nil {
			t.Errorf("aud %v was refused: %v", aud, err)
		}
	}
	// A third application at the same issuer is still not us.
	tok := idp.sign(t, "RS256", "rsa-1", idp.claims(map[string]any{"aud": "someone-elses-app"}))
	if _, err := v.Verify(context.Background(), tok); !errors.Is(err, ErrClaims) {
		t.Fatalf("a third client's token was accepted: %v", err)
	}
}

// Either client id alone is enough to make sign-in usable: an operator may register only the app
// (no admin UI login) or only the server.
func TestEitherClientIDAloneEnablesSignIn(t *testing.T) {
	if !(Config{Issuer: "https://i", ClientID: "a"}).Enabled() {
		t.Error("a server-only configuration was reported disabled")
	}
	if !(Config{Issuer: "https://i", AppClientID: "b"}).Enabled() {
		t.Error("an app-only configuration was reported disabled")
	}
	if (Config{Issuer: "https://i"}).Enabled() {
		t.Error("an issuer with no client at all was reported enabled")
	}
}