// Copyright 2026 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package integration

import (
	"encoding/base64"
	"fmt"
	"net/http"
	"net/http/httptest"
	"net/url"
	"testing"
	"time"

	auth_model "code.gitea.io/gitea/models/auth"
	"code.gitea.io/gitea/models/unittest"
	user_model "code.gitea.io/gitea/models/user"
	"code.gitea.io/gitea/modules/json"
	"code.gitea.io/gitea/modules/setting"
	"code.gitea.io/gitea/modules/test"
	"code.gitea.io/gitea/services/auth/source/oauth2"
	"code.gitea.io/gitea/tests"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
)

// TestMigrateAzureADV2ToOIDC simulates a login source migration from the Azure AD V2 OAuth2 provider to the OpenID Connect provider,
// and verifies that setting ExternalIDClaim = "oid" restores account continuity.
//
// Background: Azure AD V2 (goth's azureadv2 provider) fetches the user profile from Microsoft Graph API (/v1.0/me)
// and uses the "id" field - the stable Object ID (OID) - as gothUser.UserID. That OID is stored as ExternalID in external_login_user.
//
// When the admin migrates the same source to OpenID Connect, the goth openidConnect provider defaults to ["sub"] for UserIdClaims.
// Azure AD's "sub" is pairwise (unique per application), so it differs from the OID that was previously stored,
// causing every existing user to appear as a new account.
//
// Setting ExternalIDClaim = "oid" on the OIDC source overrides UserIdClaims to ["oid"],
// so the same OID is extracted and matched against the existing rows, restoring continuity.
func TestMigrateAzureADV2ToOIDC(t *testing.T) {
	defer tests.PrepareTestEnv(t)()
	defer test.MockVariableValue(&setting.OAuth2Client.EnableAutoRegistration, true)()
	// Use UserID (gothUser.UserID) as the Gitea username so that different ExternalID values produce different, non-conflicting usernames.
	defer test.MockVariableValue(&setting.OAuth2Client.Username, setting.OAuth2UsernameUserid)()

	const (
		sourceName = "test-migrate-azure"

		// oidValue is the stable Azure AD Object ID, used as ExternalID by the Azure AD V2 provider.
		oidValue = "oid-object-id-stable"

		// subValue is the pairwise sub issued by Azure AD for OpenID Connect; it differs from oidValue and would produce a separate account if used.
		subValue = "sub-pairwise-value"
	)

	// The fake OIDC server issues tokens containing both sub and oid claims, mirroring what Azure AD v2.0 returns.
	srv := newFakeOIDCServer(t, subValue, oidValue)

	// --- Step 1: Establish the legacy Azure AD V2 state ---
	// Create an azureadv2 auth source. In production this would have been the source used before the migration.
	addOAuth2Source(t, sourceName, oauth2.Source{
		Provider:     "azureadv2",
		ClientID:     "test-client-id",
		ClientSecret: "test-client-secret",
		CustomURLMapping: &oauth2.CustomURLMapping{
			Tenant: "test-tenant-id",
		},
	})
	authSource, err := auth_model.GetActiveOAuth2SourceByAuthName(t.Context(), sourceName)
	require.NoError(t, err)

	// Create a user to represent the "legacy" account that was originally registered through the Azure AD V2 provider.
	legacyUser := &user_model.User{
		Name:  "legacy-azure-user",
		Email: "legacy-azure-user@example.com",
	}
	require.NoError(t, user_model.CreateUser(t.Context(), legacyUser, &user_model.Meta{}))
	require.NoError(t, user_model.LinkExternalToUser(t.Context(), legacyUser, &user_model.ExternalLoginUser{
		ExternalID:    oidValue,
		UserID:        legacyUser.ID,
		LoginSourceID: authSource.ID,
		Provider:      authSource.Name,
	}))

	// --- Step 2: Migrate the source to OIDC without ExternalIDClaim ---
	// The provider type of the OAuth2 source is changed from azureadv2 to openidConnect.
	// Without ExternalIDClaim the goth provider defaults to "sub", which does not match the stored OID, so every sign-in creates a fresh account.
	authSource.Cfg = &oauth2.Source{
		Provider:                      "openidConnect",
		ClientID:                      "test-client-id",
		ClientSecret:                  "test-client-secret",
		OpenIDConnectAutoDiscoveryURL: srv.URL + "/.well-known/openid-configuration",
		// ExternalIDClaim intentionally not set; goth defaults to "sub".
	}
	err = auth_model.UpdateSource(t.Context(), authSource)
	require.NoError(t, err)

	t.Run("without ExternalIDClaim: legacy user is NOT matched", func(t *testing.T) {
		// Confirm the external user with ExternalID=subValue doesn't exist.
		unittest.AssertNotExistsBean(t, &user_model.ExternalLoginUser{ExternalID: subValue, LoginSourceID: authSource.ID}, unittest.OrderBy("external_id ASC"))

		doOIDCSignIn(t, sourceName)

		// "sub" is now the ExternalID - a new user was auto-registered.
		subEntry := unittest.AssertExistsAndLoadBean(t, &user_model.ExternalLoginUser{ExternalID: subValue, LoginSourceID: authSource.ID}, unittest.OrderBy("external_id ASC"))
		// The auto-registered user is NOT the legacy user.
		assert.NotEqual(t, legacyUser.ID, subEntry.UserID)
	})

	// --- Step 3: Set ExternalIDClaim = "oid" to restore account continuity ---
	// Set ExternalIDClaim = "oid" so that the OIDC source extracts the same Object ID that the Azure AD V2 provider previously stored.
	authSource.Cfg.(*oauth2.Source).ExternalIDClaim = "oid"
	err = auth_model.UpdateSource(t.Context(), authSource)
	require.NoError(t, err)

	t.Run("with ExternalIDClaim=oid: legacy user IS matched", func(t *testing.T) {
		// Confirm the legacy oid row has no RawData yet - it was created directly via LinkExternalToUser in setup, without going through an OAuth flow.
		oidEntry := unittest.AssertExistsAndLoadBean(t, &user_model.ExternalLoginUser{ExternalID: oidValue, LoginSourceID: authSource.ID}, unittest.OrderBy("external_id ASC"))
		require.Nil(t, oidEntry.RawData)

		doOIDCSignIn(t, sourceName)

		// After sign-in, RawData should contain both "oid" and "name".
		oidEntry = unittest.AssertExistsAndLoadBean(t, &user_model.ExternalLoginUser{ExternalID: oidValue, LoginSourceID: authSource.ID}, unittest.OrderBy("external_id ASC"))
		assert.Equal(t, oidValue, oidEntry.RawData["oid"])
		assert.Equal(t, "OIDC Test User", oidEntry.RawData["name"])

		// The matched user must still be the original legacy user.
		assert.Equal(t, legacyUser.ID, oidEntry.UserID)
	})
}

// newFakeOIDCServer starts an httptest.Server that implements the minimum OIDC endpoints needed to complete a sign-in flow:
func newFakeOIDCServer(t *testing.T, sub, oid string) *httptest.Server {
	t.Helper()

	var srv *httptest.Server
	srv = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "application/json")
		switch r.URL.Path {
		case "/.well-known/openid-configuration": // discovery document
			_ = json.NewEncoder(w).Encode(map[string]string{
				"issuer":                 srv.URL,
				"authorization_endpoint": srv.URL + "/authorize",
				"token_endpoint":         srv.URL + "/token",
				"userinfo_endpoint":      srv.URL + "/userinfo",
			})
		case "/token": // returns an ID token with both "sub" and "oid" claims so tests can verify which one ends up as ExternalID
			claims := map[string]any{
				"iss": srv.URL,
				"aud": "test-client-id",
				"exp": time.Now().Add(time.Hour).Unix(),
				"sub": sub,
				"oid": oid,
			}
			payload, _ := json.Marshal(claims)
			header := base64.RawURLEncoding.EncodeToString([]byte(`{"alg":"none"}`))

			// build a JWT-shaped string whose payload encodes claims.
			// goth's decodeJWT only base64-decodes the payload without verifying the signature, so no real signing infrastructure is needed.
			idToken := header + "." + base64.RawURLEncoding.EncodeToString(payload) + ".fakesig"

			_ = json.NewEncoder(w).Encode(map[string]any{
				"access_token": "fake-access-token",
				"token_type":   "Bearer",
				"id_token":     idToken,
			})
		case "/userinfo":
			// sub MUST match the id_token sub; goth rejects mismatches.
			_ = json.NewEncoder(w).Encode(map[string]any{
				"sub":   sub,
				"email": sub + "@example.com",
				"name":  "OIDC Test User",
			})
		default:
			http.NotFound(w, r)
		}
	}))
	t.Cleanup(srv.Close)
	return srv
}

// doOIDCSignIn runs a mock OIDC sign-in flow for the given auth source.
func doOIDCSignIn(t *testing.T, sourceName string) {
	t.Helper()
	session := emptyTestSession(t)

	// Step 1: initiate login
	resp := session.MakeRequest(t, NewRequest(t, "GET", "/user/oauth2/"+sourceName), http.StatusTemporaryRedirect)

	// Step 2: extract the UUID state that Gitea embedded in the redirect URL.
	location := resp.Header().Get("Location")
	u, err := url.Parse(location)
	require.NoError(t, err)
	state := u.Query().Get("state")
	require.NotEmpty(t, state, "redirect to OIDC provider must include state")

	// Step 3: simulate the provider redirecting back.
	callbackURL := fmt.Sprintf("/user/oauth2/%s/callback?code=test-code&state=%s", sourceName, url.QueryEscape(state))
	session.MakeRequest(t, NewRequest(t, "GET", callbackURL), http.StatusSeeOther)
}