package event

import (
	"crypto/ed25519"
	"encoding/base64"
	"encoding/json"
	"errors"
	"strings"
	"testing"
	"time"

	"github.com/dariuszjaniak/warp/server/internal/matrix/roomversion"
	"github.com/dariuszjaniak/warp/server/internal/matrix/signing"
)

// The signing key from the spec appendices, section "Cryptographic Test
// Vectors".
const specSeed = "YJDBA9Xnr2sVqXD9Vj7XVUnmFZcZrlw8Md7kMW+3XA1"

func specKey(t *testing.T) *signing.KeyPair {
	t.Helper()
	seed, err := base64.RawStdEncoding.DecodeString(specSeed)
	if err != nil {
		t.Fatalf("decode the spec seed: %v", err)
	}
	priv := ed25519.NewKeyFromSeed(seed)
	pub, ok := priv.Public().(ed25519.PublicKey)
	if !ok {
		t.Fatal("unexpected public key type")
	}
	return &signing.KeyPair{ID: "1", Private: priv, Public: pub}
}

func testKey(t *testing.T) *signing.KeyPair {
	t.Helper()
	key, err := signing.Generate("test")
	if err != nil {
		t.Fatalf("generate a signing key: %v", err)
	}
	return key
}

// TestSpecEventSigningVectors runs the event signing vectors from the spec
// appendices. They were produced for the original event format, so they go
// through a room version whose redaction rules still protect the top-level
// origin and event_id properties — the point of the test is the hashing
// and signing, which has not changed since.
func TestSpecEventSigningVectors(t *testing.T) {
	key := specKey(t)
	rules := roomversion.MustGet(roomversion.V3)

	cases := []struct {
		name string
		in   string
		want string
	}{
		{
			name: "minimal event",
			in: `{
				"room_id": "!x:domain",
				"sender": "@a:domain",
				"origin": "domain",
				"origin_server_ts": 1000000,
				"signatures": {},
				"hashes": {},
				"type": "X",
				"content": {},
				"prev_events": [],
				"auth_events": [],
				"depth": 3,
				"unsigned": {"age_ts": 1000000}
			}`,
			want: `{"auth_events":[],"content":{},"depth":3,` +
				`"hashes":{"sha256":"5jM4wQpv6lnBo7CLIghJuHdW+s2CMBJPUOGOC89ncos"},` +
				`"origin":"domain","origin_server_ts":1000000,"prev_events":[],` +
				`"room_id":"!x:domain","sender":"@a:domain","signatures":{"domain":{"ed25519:1":` +
				`"KxwGjPSDEtvnFgU00fwFz+l6d2pJM6XBIaMEn81SXPTRl16AqLAYqfIReFGZlHi5KLjAWbOoMszkwsQma+lYAg"}},` +
				`"type":"X","unsigned":{"age_ts":1000000}}`,
		},
		{
			name: "event with redactable content",
			in: `{
				"content": {"body": "Here is the message content"},
				"event_id": "$0:domain",
				"origin": "domain",
				"origin_server_ts": 1000000,
				"type": "m.room.message",
				"room_id": "!r:domain",
				"sender": "@u:domain",
				"signatures": {},
				"unsigned": {"age_ts": 1000000}
			}`,
			want: `{"content":{"body":"Here is the message content"},"event_id":"$0:domain",` +
				`"hashes":{"sha256":"onLKD1bGljeBWQhWZ1kaP9SorVmRQNdN5aM2JYU2n/g"},` +
				`"origin":"domain","origin_server_ts":1000000,"room_id":"!r:domain",` +
				`"sender":"@u:domain","signatures":{"domain":{"ed25519:1":` +
				`"Wm+VzmOUOz08Ds+0NTWb1d4CZrVsJSikkeRxh6aCcUwu6pNC78FunoD7KNWzqFn241eYHYMGCA5McEiVPdhzBA"}},` +
				`"type":"m.room.message","unsigned":{"age_ts":1000000}}`,
		},
	}

	for _, tc := range cases {
		t.Run(tc.name, func(t *testing.T) {
			got, err := hashAndSign([]byte(tc.in), rules, "domain", key)
			if err != nil {
				t.Fatalf("hashAndSign: %v", err)
			}
			if string(got) != tc.want {
				t.Errorf("hashAndSign() =\n %s\nwant\n %s", got, tc.want)
			}
		})
	}
}

// buildEvent is the shorthand the tests below use for a signed event in a
// given room version.
func buildEvent(t *testing.T, rules roomversion.Rules, key *signing.KeyPair, b Builder) *Event {
	t.Helper()
	if b.Sender == "" {
		b.Sender = "@alice:warp.test"
	}
	// A version 12 create event has no room ID: the room ID comes from it.
	derivesRoomID := rules.RoomIDIsCreateEventID && b.Type == TypeCreate
	if b.RoomID == "" && !derivesRoomID {
		b.RoomID = "!room:warp.test"
	}
	e, err := b.Build(time.UnixMilli(1700000000000), key, rules)
	if err != nil {
		t.Fatalf("Build %s: %v", b.Type, err)
	}
	return e
}

func TestBuildAndParse(t *testing.T) {
	key := testKey(t)
	rules := roomversion.MustGet(roomversion.V11)

	e := buildEvent(t, rules, key, Builder{
		Type:       "m.room.message",
		Content:    json.RawMessage(`{"body":"hello","msgtype":"m.text"}`),
		PrevEvents: []string{"$abc"},
		AuthEvents: []string{"$create"},
		Depth:      7,
	})

	if !strings.HasPrefix(e.EventID(), "$") {
		t.Errorf("event ID %q does not start with $", e.EventID())
	}
	if e.Type() != "m.room.message" {
		t.Errorf("Type() = %q", e.Type())
	}
	if e.Sender() != "@alice:warp.test" {
		t.Errorf("Sender() = %q", e.Sender())
	}
	if e.RoomID() != "!room:warp.test" {
		t.Errorf("RoomID() = %q", e.RoomID())
	}
	if e.Depth() != 7 {
		t.Errorf("Depth() = %d", e.Depth())
	}
	if e.OriginServerTS() != 1700000000000 {
		t.Errorf("OriginServerTS() = %d", e.OriginServerTS())
	}
	if _, ok := e.StateKey(); ok {
		t.Error("a message event should have no state key")
	}
	if e.IsState() {
		t.Error("IsState() = true for a message event")
	}
	if err := e.VerifyContentHash(); err != nil {
		t.Errorf("VerifyContentHash: %v", err)
	}
	if err := e.VerifySignature("warp.test", key.KeyID(), key.Public); err != nil {
		t.Errorf("VerifySignature: %v", err)
	}

	// Re-parsing the event's own JSON must produce the same ID, which is
	// what makes it safe to store events as JSON and parse them back.
	again, err := Parse(e.JSON(), rules)
	if err != nil {
		t.Fatalf("re-parse: %v", err)
	}
	if again.EventID() != e.EventID() {
		t.Errorf("re-parsed event ID = %q, want %q", again.EventID(), e.EventID())
	}
}

func TestBuildStateEventWithEmptyStateKey(t *testing.T) {
	key := testKey(t)
	rules := roomversion.MustGet(roomversion.V11)
	empty := ""

	e := buildEvent(t, rules, key, Builder{
		Type:     TypePowerLevels,
		StateKey: &empty,
		Content:  json.RawMessage(`{"users":{"@alice:warp.test":100}}`),
	})
	sk, ok := e.StateKey()
	if !ok {
		t.Fatal("StateKey() reports no state key")
	}
	if sk != "" {
		t.Errorf("StateKey() = %q, want the empty string", sk)
	}
	if !e.IsState() {
		t.Error("IsState() = false for a power levels event")
	}
}

// TestEventIDFormatByVersion checks the two encodings of the reference
// hash. Room version 3 uses standard base64 and 4 onwards URL-safe, which
// is why the same event has two different IDs in the two rooms.
func TestEventIDFormatByVersion(t *testing.T) {
	key := specKey(t)
	body := Builder{
		Type:    "m.room.message",
		Sender:  "@a:domain",
		RoomID:  "!r:domain",
		Content: json.RawMessage(`{"body":"ÿþýü"}`),
	}

	ids := map[roomversion.Version]string{}
	for _, v := range []roomversion.Version{roomversion.V3, roomversion.V4} {
		e, err := body.Build(time.UnixMilli(1000000), key, roomversion.MustGet(v))
		if err != nil {
			t.Fatalf("Build for version %s: %v", v, err)
		}
		ids[v] = e.EventID()
	}

	// Both encode the same 32-byte hash, so the IDs are the same length
	// and differ only where the alphabets differ.
	if len(ids[roomversion.V3]) != len(ids[roomversion.V4]) {
		t.Errorf("IDs have different lengths: %q and %q", ids[roomversion.V3], ids[roomversion.V4])
	}
	std := strings.TrimPrefix(ids[roomversion.V3], "$")
	urlSafe := strings.TrimPrefix(ids[roomversion.V4], "$")
	if decoded, err := base64.RawStdEncoding.DecodeString(std); err != nil || len(decoded) != 32 {
		t.Errorf("version 3 ID is not 32 bytes of standard base64: %q (%v)", std, err)
	}
	if decoded, err := base64.RawURLEncoding.DecodeString(urlSafe); err != nil || len(decoded) != 32 {
		t.Errorf("version 4 ID is not 32 bytes of URL-safe base64: %q (%v)", urlSafe, err)
	}
	if strings.ContainsAny(urlSafe, "+/") {
		t.Errorf("version 4 ID contains a character that is not URL-safe: %q", urlSafe)
	}
}

// TestRedactionKeepsEventIDAndSignature is the property the whole hashing
// scheme exists for: a redacted event is still provably the event it claims
// to be.
func TestRedactionKeepsEventIDAndSignature(t *testing.T) {
	key := testKey(t)
	for _, v := range []roomversion.Version{roomversion.V3, roomversion.V10, roomversion.V11, roomversion.V12} {
		t.Run(string(v), func(t *testing.T) {
			rules := roomversion.MustGet(v)
			e := buildEvent(t, rules, key, Builder{
				Type:    "m.room.message",
				Content: json.RawMessage(`{"body":"something private","msgtype":"m.text"}`),
			})

			redacted, err := e.Redact()
			if err != nil {
				t.Fatalf("Redact: %v", err)
			}
			if redacted.EventID() != e.EventID() {
				t.Errorf("redaction changed the event ID: %q became %q", e.EventID(), redacted.EventID())
			}
			if err := redacted.VerifySignature("warp.test", key.KeyID(), key.Public); err != nil {
				t.Errorf("the signature on the redacted event does not verify: %v", err)
			}
			if string(redacted.Content()) != "{}" {
				t.Errorf("redacted content = %s, want {}", redacted.Content())
			}

			// The content hash no longer matches, which is exactly how a
			// receiver tells a redacted copy from a tampered one.
			if err := redacted.VerifyContentHash(); !errors.Is(err, ErrContentHashMismatch) {
				t.Errorf("VerifyContentHash on a redacted event = %v, want ErrContentHashMismatch", err)
			}
		})
	}
}

// TestRedactionProtectedKeys walks the keys each room version protects.
func TestRedactionProtectedKeys(t *testing.T) {
	cases := []struct {
		name        string
		version     roomversion.Version
		event       string
		wantKeys    []string
		wantContent string
	}{
		{
			name:    "version 10 protects the legacy top-level keys",
			version: roomversion.V10,
			event: `{"type":"m.room.message","room_id":"!r:domain","sender":"@u:domain",
				"content":{"body":"x"},"origin":"domain","membership":"join","prev_state":[],
				"origin_server_ts":1,"hashes":{"sha256":"x"},"signatures":{},"age_ts":5}`,
			wantKeys: []string{
				"content", "hashes", "membership", "origin", "origin_server_ts",
				"prev_state", "room_id", "sender", "signatures", "type",
			},
			wantContent: `{}`,
		},
		{
			name:    "version 11 drops the legacy top-level keys",
			version: roomversion.V11,
			event: `{"type":"m.room.message","room_id":"!r:domain","sender":"@u:domain",
				"content":{"body":"x"},"origin":"domain","membership":"join","prev_state":[],
				"origin_server_ts":1,"hashes":{"sha256":"x"},"signatures":{},"age_ts":5}`,
			wantKeys: []string{
				"content", "hashes", "origin_server_ts", "room_id",
				"sender", "signatures", "type",
			},
			wantContent: `{}`,
		},
		{
			name:    "version 10 keeps only the creator of a create event",
			version: roomversion.V10,
			event: `{"type":"m.room.create","room_id":"!r:domain","sender":"@u:domain",
				"content":{"creator":"@u:domain","room_version":"10","m.federate":false},
				"origin_server_ts":1,"hashes":{"sha256":"x"},"signatures":{}}`,
			wantContent: `{"creator":"@u:domain"}`,
		},
		{
			name:    "version 11 keeps all of a create event's content",
			version: roomversion.V11,
			event: `{"type":"m.room.create","room_id":"!r:domain","sender":"@u:domain",
				"content":{"room_version":"11","m.federate":false},
				"origin_server_ts":1,"hashes":{"sha256":"x"},"signatures":{}}`,
			wantContent: `{"m.federate":false,"room_version":"11"}`,
		},
		{
			name:    "version 8 keeps the join rule and allow list",
			version: roomversion.V8,
			event: `{"type":"m.room.join_rules","room_id":"!r:domain","sender":"@u:domain",
				"content":{"join_rule":"restricted","allow":[{"type":"m.room_membership"}],"extra":1},
				"origin_server_ts":1,"hashes":{"sha256":"x"},"signatures":{}}`,
			wantContent: `{"allow":[{"type":"m.room_membership"}],"join_rule":"restricted"}`,
		},
		{
			name:    "version 7 keeps only the join rule",
			version: roomversion.V7,
			event: `{"type":"m.room.join_rules","room_id":"!r:domain","sender":"@u:domain",
				"content":{"join_rule":"restricted","allow":[{"type":"m.room_membership"}]},
				"origin_server_ts":1,"hashes":{"sha256":"x"},"signatures":{}}`,
			wantContent: `{"join_rule":"restricted"}`,
		},
		{
			name:    "version 8 redacts the restricted join authorisation",
			version: roomversion.V8,
			event: `{"type":"m.room.member","room_id":"!r:domain","sender":"@u:domain","state_key":"@u:domain",
				"content":{"membership":"join","join_authorised_via_users_server":"@mod:other"},
				"origin_server_ts":1,"hashes":{"sha256":"x"},"signatures":{}}`,
			wantContent: `{"membership":"join"}`,
		},
		{
			name:    "version 9 keeps the restricted join authorisation",
			version: roomversion.V9,
			event: `{"type":"m.room.member","room_id":"!r:domain","sender":"@u:domain","state_key":"@u:domain",
				"content":{"membership":"join","join_authorised_via_users_server":"@mod:other","displayname":"U"},
				"origin_server_ts":1,"hashes":{"sha256":"x"},"signatures":{}}`,
			wantContent: `{"join_authorised_via_users_server":"@mod:other","membership":"join"}`,
		},
		{
			name:    "version 10 drops a third-party invite entirely",
			version: roomversion.V10,
			event: `{"type":"m.room.member","room_id":"!r:domain","sender":"@u:domain","state_key":"@u:domain",
				"content":{"membership":"invite","third_party_invite":{"display_name":"d","signed":{"token":"t"}}},
				"origin_server_ts":1,"hashes":{"sha256":"x"},"signatures":{}}`,
			wantContent: `{"membership":"invite"}`,
		},
		{
			name:    "version 11 keeps the signed part of a third-party invite",
			version: roomversion.V11,
			event: `{"type":"m.room.member","room_id":"!r:domain","sender":"@u:domain","state_key":"@u:domain",
				"content":{"membership":"invite","third_party_invite":{"display_name":"d","signed":{"token":"t"}}},
				"origin_server_ts":1,"hashes":{"sha256":"x"},"signatures":{}}`,
			wantContent: `{"membership":"invite","third_party_invite":{"signed":{"token":"t"}}}`,
		},
		{
			name:    "version 10 loses the target of a redaction",
			version: roomversion.V10,
			event: `{"type":"m.room.redaction","room_id":"!r:domain","sender":"@u:domain",
				"content":{"reason":"spam"},"redacts":"$target",
				"origin_server_ts":1,"hashes":{"sha256":"x"},"signatures":{}}`,
			wantKeys:    []string{"content", "hashes", "origin_server_ts", "room_id", "sender", "signatures", "type"},
			wantContent: `{}`,
		},
		{
			name:    "version 11 keeps the target of a redaction",
			version: roomversion.V11,
			event: `{"type":"m.room.redaction","room_id":"!r:domain","sender":"@u:domain",
				"content":{"redacts":"$target","reason":"spam"},
				"origin_server_ts":1,"hashes":{"sha256":"x"},"signatures":{}}`,
			wantContent: `{"redacts":"$target"}`,
		},
		{
			name:    "version 11 keeps the invite level of a power levels event",
			version: roomversion.V11,
			event: `{"type":"m.room.power_levels","room_id":"!r:domain","sender":"@u:domain","state_key":"",
				"content":{"invite":50,"ban":50,"notifications":{"room":20}},
				"origin_server_ts":1,"hashes":{"sha256":"x"},"signatures":{}}`,
			wantContent: `{"ban":50,"invite":50}`,
		},
		{
			name:    "version 10 drops the invite level of a power levels event",
			version: roomversion.V10,
			event: `{"type":"m.room.power_levels","room_id":"!r:domain","sender":"@u:domain","state_key":"",
				"content":{"invite":50,"ban":50,"notifications":{"room":20}},
				"origin_server_ts":1,"hashes":{"sha256":"x"},"signatures":{}}`,
			wantContent: `{"ban":50}`,
		},
		{
			name:    "an unknown type keeps no content at all",
			version: roomversion.V11,
			event: `{"type":"com.example.thing","room_id":"!r:domain","sender":"@u:domain",
				"content":{"anything":1},"origin_server_ts":1,"hashes":{"sha256":"x"},"signatures":{}}`,
			wantContent: `{}`,
		},
	}

	for _, tc := range cases {
		t.Run(tc.name, func(t *testing.T) {
			rules := roomversion.MustGet(tc.version)
			got, err := redactJSON([]byte(tc.event), rules)
			if err != nil {
				t.Fatalf("redactJSON: %v", err)
			}

			var obj map[string]json.RawMessage
			if err := json.Unmarshal(got, &obj); err != nil {
				t.Fatalf("the redacted event is not an object: %v", err)
			}
			if tc.wantKeys != nil {
				var keys []string
				for k := range obj {
					keys = append(keys, k)
				}
				if got, want := joinSorted(keys), strings.Join(tc.wantKeys, ","); got != want {
					t.Errorf("top-level keys = %s, want %s", got, want)
				}
			}
			if content := string(obj["content"]); content != tc.wantContent {
				t.Errorf("content = %s, want %s", content, tc.wantContent)
			}
		})
	}
}

func joinSorted(keys []string) string {
	// canonicaljson sorts object keys, so the redacted event already has
	// them in order; this is only for a readable failure message.
	out := make([]string, len(keys))
	copy(out, keys)
	for i := range out {
		for j := i + 1; j < len(out); j++ {
			if out[j] < out[i] {
				out[i], out[j] = out[j], out[i]
			}
		}
	}
	return strings.Join(out, ",")
}

// TestRedactsLocation checks that the builder puts a redaction's target
// where the room version keeps it, and that Redacts reads it back from
// either place.
func TestRedactsLocation(t *testing.T) {
	key := testKey(t)

	t.Run("version 10 uses the top level", func(t *testing.T) {
		rules := roomversion.MustGet(roomversion.V10)
		e := buildEvent(t, rules, key, Builder{
			Type:    TypeRedaction,
			Redacts: "$target",
			Content: json.RawMessage(`{"reason":"spam"}`),
		})
		if e.Redacts() != "$target" {
			t.Errorf("Redacts() = %q, want $target", e.Redacts())
		}
		if !strings.Contains(string(e.JSON()), `"redacts":"$target"`) {
			t.Errorf("redacts is missing from the event: %s", e.JSON())
		}
		if strings.Contains(string(e.Content()), "redacts") {
			t.Errorf("redacts should not be in the content: %s", e.Content())
		}
	})

	t.Run("version 11 uses the content", func(t *testing.T) {
		rules := roomversion.MustGet(roomversion.V11)
		e := buildEvent(t, rules, key, Builder{
			Type:    TypeRedaction,
			Redacts: "$target",
			Content: json.RawMessage(`{"reason":"spam"}`),
		})
		if e.Redacts() != "$target" {
			t.Errorf("Redacts() = %q, want $target", e.Redacts())
		}
		if !strings.Contains(string(e.Content()), `"redacts":"$target"`) {
			t.Errorf("redacts is missing from the content: %s", e.Content())
		}
	})
}

// TestCreateEventRoomIDByVersion covers the room version 12 change that
// makes the room ID the create event's own ID.
func TestCreateEventRoomIDByVersion(t *testing.T) {
	key := testKey(t)

	t.Run("version 11 carries a room ID", func(t *testing.T) {
		rules := roomversion.MustGet(roomversion.V11)
		e := buildEvent(t, rules, key, Builder{
			Type:    TypeCreate,
			Content: json.RawMessage(`{"room_version":"11"}`),
		})
		if e.RoomID() != "!room:warp.test" {
			t.Errorf("RoomID() = %q", e.RoomID())
		}
		roomID, err := RoomIDOfCreateEvent(e)
		if err != nil {
			t.Fatalf("RoomIDOfCreateEvent: %v", err)
		}
		if roomID != "!room:warp.test" {
			t.Errorf("RoomIDOfCreateEvent() = %q", roomID)
		}
	})

	t.Run("version 12 derives the room ID", func(t *testing.T) {
		rules := roomversion.MustGet(roomversion.V12)
		e := buildEvent(t, rules, key, Builder{
			Type:    TypeCreate,
			Content: json.RawMessage(`{"room_version":"12"}`),
		})
		if e.RoomID() != "" {
			t.Errorf("RoomID() = %q, want it to be absent", e.RoomID())
		}
		roomID, err := RoomIDOfCreateEvent(e)
		if err != nil {
			t.Fatalf("RoomIDOfCreateEvent: %v", err)
		}
		if want := "!" + strings.TrimPrefix(e.EventID(), "$"); roomID != want {
			t.Errorf("RoomIDOfCreateEvent() = %q, want %q", roomID, want)
		}
		if strings.Contains(roomID, ":") {
			t.Errorf("a version 12 room ID should carry no domain: %q", roomID)
		}
	})

	t.Run("version 12 rejects a create event with a room ID", func(t *testing.T) {
		rules := roomversion.MustGet(roomversion.V12)
		b := Builder{
			Type:    TypeCreate,
			Sender:  "@alice:warp.test",
			RoomID:  "!room:warp.test",
			Content: json.RawMessage(`{"room_version":"12"}`),
		}
		if _, err := b.Build(time.UnixMilli(1), key, rules); err == nil {
			t.Error("Build accepted a room_id on a version 12 create event")
		}
	})
}

func TestVerifyContentHashDetectsTampering(t *testing.T) {
	key := testKey(t)
	rules := roomversion.MustGet(roomversion.V11)
	e := buildEvent(t, rules, key, Builder{
		Type:    "m.room.message",
		Content: json.RawMessage(`{"body":"the original","msgtype":"m.text"}`),
	})

	tampered := strings.Replace(string(e.JSON()), "the original", "a forgery!!!", 1)
	if tampered == string(e.JSON()) {
		t.Fatal("the test did not change anything")
	}
	parsed, err := Parse([]byte(tampered), rules)
	if err != nil {
		t.Fatalf("Parse: %v", err)
	}
	if err := parsed.VerifyContentHash(); !errors.Is(err, ErrContentHashMismatch) {
		t.Errorf("VerifyContentHash = %v, want ErrContentHashMismatch", err)
	}

	// The signature still verifies, and that is not a hole: it covers the
	// redacted event, whose content is {} either way. Rewriting content is
	// therefore indistinguishable from being sent a redacted copy, and the
	// receiver's answer to a failed hash check is to use the redacted form
	// — so the rewritten content never reaches anybody.
	if err := parsed.VerifySignature("warp.test", key.KeyID(), key.Public); err != nil {
		t.Errorf("the signature should still cover the redacted event: %v", err)
	}

	// Rewriting the hash to match the new content is what the signature
	// does catch, because the signature covers hashes.
	sum, err := contentHash(parsed.JSON())
	if err != nil {
		t.Fatal(err)
	}
	reHashed := strings.Replace(string(parsed.JSON()),
		`"sha256":"`+parsed.ContentHash()+`"`,
		`"sha256":"`+base64.RawStdEncoding.EncodeToString(sum[:])+`"`, 1)
	forged, err := Parse([]byte(reHashed), rules)
	if err != nil {
		t.Fatalf("Parse: %v", err)
	}
	if err := forged.VerifyContentHash(); err != nil {
		t.Fatalf("the test did not recompute the hash correctly: %v", err)
	}
	if err := forged.VerifySignature("warp.test", key.KeyID(), key.Public); err == nil {
		t.Error("the signature verifies on an event whose content and hash were both rewritten")
	}
	if forged.EventID() == e.EventID() {
		t.Error("rewriting the hash should change the event ID")
	}
}

func TestSignAddsASecondSignature(t *testing.T) {
	key := testKey(t)
	rules := roomversion.MustGet(roomversion.V11)
	e := buildEvent(t, rules, key, Builder{
		Type:    "m.room.member",
		Content: json.RawMessage(`{"membership":"invite"}`),
	})

	other, err := signing.Generate("other")
	if err != nil {
		t.Fatal(err)
	}
	countersigned, err := e.Sign("other.example", other)
	if err != nil {
		t.Fatalf("Sign: %v", err)
	}
	if countersigned.EventID() != e.EventID() {
		t.Errorf("countersigning changed the event ID: %q became %q", e.EventID(), countersigned.EventID())
	}
	if err := countersigned.VerifySignature("warp.test", key.KeyID(), key.Public); err != nil {
		t.Errorf("the original signature no longer verifies: %v", err)
	}
	if err := countersigned.VerifySignature("other.example", other.KeyID(), other.Public); err != nil {
		t.Errorf("the second signature does not verify: %v", err)
	}
}

func TestParseRejects(t *testing.T) {
	rules := roomversion.MustGet(roomversion.V11)
	const sigs = `"hashes":{"sha256":"x"},"signatures":{"d":{"ed25519:1":"s"}}`

	cases := []struct {
		name string
		in   string
		want string
	}{
		{"no type", `{"room_id":"!r:d","sender":"@u:d","content":{},` + sigs + `}`, "type is required"},
		{"no sender", `{"type":"m.x","room_id":"!r:d","content":{},` + sigs + `}`, "sender"},
		{"sender is not a user ID", `{"type":"m.x","room_id":"!r:d","sender":"alice","content":{},` + sigs + `}`, "sender"},
		{"no room ID", `{"type":"m.x","sender":"@u:d","content":{},` + sigs + `}`, "room_id"},
		{"room ID with the wrong sigil", `{"type":"m.x","room_id":"@r:d","sender":"@u:d","content":{},` + sigs + `}`, "room_id"},
		{"no content", `{"type":"m.x","room_id":"!r:d","sender":"@u:d",` + sigs + `}`, "content is required"},
		{"content is not an object", `{"type":"m.x","room_id":"!r:d","sender":"@u:d","content":[],` + sigs + `}`, "content must be an object"},
		{"content is null", `{"type":"m.x","room_id":"!r:d","sender":"@u:d","content":null,` + sigs + `}`, "content must be an object"},
		{"no content hash", `{"type":"m.x","room_id":"!r:d","sender":"@u:d","content":{},"signatures":{"d":{"e:1":"s"}}}`, "hashes.sha256 is required"},
		{"no signatures", `{"type":"m.x","room_id":"!r:d","sender":"@u:d","content":{},"hashes":{"sha256":"x"}}`, "signatures is required"},
		{"a float in the content", `{"type":"m.x","room_id":"!r:d","sender":"@u:d","content":{"a":1.5},` + sigs + `}`, "floats"},
		{"a prev event that is not an event ID", `{"type":"m.x","room_id":"!r:d","sender":"@u:d","content":{},"prev_events":["abc"],` + sigs + `}`, "prev_events"},
		{"depth above the limit", `{"type":"m.x","room_id":"!r:d","sender":"@u:d","content":{},"depth":9007199254740992,` + sigs + `}`, "outside the allowed range"},
	}

	for _, tc := range cases {
		t.Run(tc.name, func(t *testing.T) {
			_, err := Parse([]byte(tc.in), rules)
			if err == nil {
				t.Fatal("Parse succeeded, want an error")
			}
			if !strings.Contains(err.Error(), tc.want) {
				t.Errorf("error = %q, want it to mention %q", err, tc.want)
			}
		})
	}
}

func TestParseRejectsOversizedEvent(t *testing.T) {
	key := testKey(t)
	rules := roomversion.MustGet(roomversion.V11)

	b := Builder{
		Type:    "m.room.message",
		Sender:  "@alice:warp.test",
		RoomID:  "!room:warp.test",
		Content: json.RawMessage(`{"body":"` + strings.Repeat("x", MaxEventSize) + `"}`),
	}
	_, err := b.Build(time.UnixMilli(1), key, rules)
	if err == nil {
		t.Fatal("Build accepted an event over the size limit")
	}
	if !strings.Contains(err.Error(), "the limit is") {
		t.Errorf("error = %q, want it to mention the limit", err)
	}
}

func TestParseRejectsTooManyDAGReferences(t *testing.T) {
	rules := roomversion.MustGet(roomversion.V11)
	ids := make([]string, MaxPrevEvents+1)
	for i := range ids {
		ids[i] = "$event" + string(rune('a'+i))
	}
	encoded, err := json.Marshal(ids)
	if err != nil {
		t.Fatal(err)
	}
	raw := `{"type":"m.x","room_id":"!r:d","sender":"@u:d","content":{},"prev_events":` +
		string(encoded) + `,"hashes":{"sha256":"x"},"signatures":{"d":{"ed25519:1":"s"}}}`
	if _, err := Parse([]byte(raw), rules); err == nil {
		t.Error("Parse accepted more than the maximum number of prev_events")
	}
}

func TestMembership(t *testing.T) {
	key := testKey(t)
	rules := roomversion.MustGet(roomversion.V11)
	target := "@bob:warp.test"

	e := buildEvent(t, rules, key, Builder{
		Type:     TypeMember,
		StateKey: &target,
		Content:  json.RawMessage(`{"membership":"invite"}`),
	})
	got, err := e.Membership()
	if err != nil {
		t.Fatalf("Membership: %v", err)
	}
	if got != MembershipInvite {
		t.Errorf("Membership() = %q, want %q", got, MembershipInvite)
	}

	other := buildEvent(t, rules, key, Builder{Type: "m.room.message", Content: json.RawMessage(`{}`)})
	if _, err := other.Membership(); err == nil {
		t.Error("Membership on a message event succeeded, want an error")
	}
}

func TestSenderServer(t *testing.T) {
	key := testKey(t)
	rules := roomversion.MustGet(roomversion.V11)
	e := buildEvent(t, rules, key, Builder{Type: "m.room.message", Content: json.RawMessage(`{}`)})

	got, err := e.SenderServer()
	if err != nil {
		t.Fatalf("SenderServer: %v", err)
	}
	if got != "warp.test" {
		t.Errorf("SenderServer() = %q, want warp.test", got)
	}
}

func TestBuilderRejects(t *testing.T) {
	key := testKey(t)
	rules := roomversion.MustGet(roomversion.V11)

	cases := []struct {
		name string
		b    Builder
	}{
		{"no sender", Builder{Type: "m.x", RoomID: "!r:d"}},
		{"sender is not a user ID", Builder{Type: "m.x", RoomID: "!r:d", Sender: "alice"}},
		{"no type", Builder{RoomID: "!r:d", Sender: "@u:d"}},
		{"no room ID", Builder{Type: "m.x", Sender: "@u:d"}},
		{"negative depth", Builder{Type: "m.x", RoomID: "!r:d", Sender: "@u:d", Depth: -1}},
		{"redacts is not an event ID", Builder{Type: TypeRedaction, RoomID: "!r:d", Sender: "@u:d", Redacts: "nope"}},
		{"content is not an object", Builder{Type: "m.x", RoomID: "!r:d", Sender: "@u:d", Content: json.RawMessage(`[]`)}},
	}

	for _, tc := range cases {
		t.Run(tc.name, func(t *testing.T) {
			if _, err := tc.b.Build(time.UnixMilli(1), key, rules); err == nil {
				t.Error("Build succeeded, want an error")
			}
		})
	}
}

// TestUnsignedIsNotCoveredBySignature mirrors the federation case where a
// server rewrites unsigned.age in transit.
func TestUnsignedIsNotCoveredBySignature(t *testing.T) {
	key := testKey(t)
	rules := roomversion.MustGet(roomversion.V11)
	e := buildEvent(t, rules, key, Builder{
		Type:     "m.room.message",
		Content:  json.RawMessage(`{"body":"hi"}`),
		Unsigned: json.RawMessage(`{"age":10}`),
	})

	rewritten := strings.Replace(string(e.JSON()), `"age":10`, `"age":99`, 1)
	parsed, err := Parse([]byte(rewritten), rules)
	if err != nil {
		t.Fatalf("Parse: %v", err)
	}
	if parsed.EventID() != e.EventID() {
		t.Errorf("rewriting unsigned changed the event ID: %q became %q", e.EventID(), parsed.EventID())
	}
	if err := parsed.VerifySignature("warp.test", key.KeyID(), key.Public); err != nil {
		t.Errorf("rewriting unsigned broke the signature: %v", err)
	}
	if err := parsed.VerifyContentHash(); err != nil {
		t.Errorf("rewriting unsigned broke the content hash: %v", err)
	}
}

// FuzzParse checks that no input makes Parse panic, and that any event it
// accepts round-trips through its own JSON to the same ID.
func FuzzParse(f *testing.F) {
	rules := roomversion.MustGet(roomversion.V11)
	f.Add([]byte(`{"type":"m.x","room_id":"!r:d","sender":"@u:d","content":{},` +
		`"hashes":{"sha256":"x"},"signatures":{"d":{"ed25519:1":"s"}}}`))
	f.Add([]byte(`{}`))
	f.Fuzz(func(t *testing.T, in []byte) {
		e, err := Parse(in, rules)
		if err != nil {
			return
		}
		again, err := Parse(e.JSON(), rules)
		if err != nil {
			t.Fatalf("re-parsing an accepted event failed: %v\nevent: %s", err, e.JSON())
		}
		if again.EventID() != e.EventID() {
			t.Fatalf("event ID is not stable: %q then %q\nevent: %s", e.EventID(), again.EventID(), e.JSON())
		}
		if _, err := e.Redact(); err != nil {
			t.Fatalf("redacting an accepted event failed: %v\nevent: %s", err, e.JSON())
		}
	})
}

// TestAccessors walks the plain field accessors, which the rest of the
// server reads an event through.
func TestAccessors(t *testing.T) {
	key := testKey(t)
	rules := roomversion.MustGet(roomversion.V11)
	e := buildEvent(t, rules, key, Builder{
		Type:       "m.room.message",
		Content:    json.RawMessage(`{"body":"hi"}`),
		PrevEvents: []string{"$prev"},
		AuthEvents: []string{"$auth"},
		Depth:      4,
		Unsigned:   json.RawMessage(`{"age":7}`),
	})

	if got := e.PrevEventIDs(); len(got) != 1 || got[0] != "$prev" {
		t.Errorf("PrevEventIDs() = %v", got)
	}
	if got := e.AuthEventIDs(); len(got) != 1 || got[0] != "$auth" {
		t.Errorf("AuthEventIDs() = %v", got)
	}
	if got := string(e.Unsigned()); got != `{"age":7}` {
		t.Errorf("Unsigned() = %s", got)
	}
	if _, ok := e.Signatures().Get("warp.test", key.KeyID()); !ok {
		t.Errorf("Signatures() has no entry for warp.test: %v", e.Signatures())
	}
	if e.Rules().Version != roomversion.V11 {
		t.Errorf("Rules().Version = %q", e.Rules().Version)
	}
	if e.Version() != roomversion.V11 {
		t.Errorf("Version() = %q", e.Version())
	}
	if e.ContentHash() == "" {
		t.Error("ContentHash() is empty")
	}

	// The reference hash is what the event ID is made of, so it must agree
	// with the ID the event already has.
	hash, err := e.ReferenceHash()
	if err != nil {
		t.Fatalf("ReferenceHash: %v", err)
	}
	if len(hash) != 32 {
		t.Errorf("ReferenceHash() is %d bytes, want 32", len(hash))
	}
	if want := "$" + base64.RawURLEncoding.EncodeToString(hash); want != e.EventID() {
		t.Errorf("the reference hash encodes to %q, but the event ID is %q", want, e.EventID())
	}
}

// TestContentHashAcceptsPaddedBase64 covers the leniency the spec asks for
// when decoding: values get copied between implementations by hand, so a
// padded hash still has to verify.
func TestContentHashAcceptsPaddedBase64(t *testing.T) {
	key := testKey(t)
	rules := roomversion.MustGet(roomversion.V11)
	e := buildEvent(t, rules, key, Builder{Type: "m.room.message", Content: json.RawMessage(`{"body":"hi"}`)})

	sum, err := contentHash(e.JSON())
	if err != nil {
		t.Fatal(err)
	}
	padded := strings.Replace(string(e.JSON()),
		`"sha256":"`+e.ContentHash()+`"`,
		`"sha256":"`+base64.StdEncoding.EncodeToString(sum[:])+`"`, 1)

	parsed, err := Parse([]byte(padded), rules)
	if err != nil {
		t.Fatalf("Parse: %v", err)
	}
	if err := parsed.VerifyContentHash(); err != nil {
		t.Errorf("a padded content hash did not verify: %v", err)
	}
}

// TestRedactARedaction checks that the target of a redaction survives
// being redacted itself, which is why the property moved into the content.
func TestRedactARedaction(t *testing.T) {
	key := testKey(t)

	t.Run("version 11 keeps it", func(t *testing.T) {
		rules := roomversion.MustGet(roomversion.V11)
		e := buildEvent(t, rules, key, Builder{
			Type:    TypeRedaction,
			Redacts: "$target",
			Content: json.RawMessage(`{"reason":"spam"}`),
		})
		redacted, err := e.Redact()
		if err != nil {
			t.Fatalf("Redact: %v", err)
		}
		if redacted.Redacts() != "$target" {
			t.Errorf("Redacts() = %q after redaction, want $target", redacted.Redacts())
		}
	})

	t.Run("version 10 loses it", func(t *testing.T) {
		rules := roomversion.MustGet(roomversion.V10)
		e := buildEvent(t, rules, key, Builder{
			Type:    TypeRedaction,
			Redacts: "$target",
			Content: json.RawMessage(`{"reason":"spam"}`),
		})
		redacted, err := e.Redact()
		if err != nil {
			t.Fatalf("Redact: %v", err)
		}
		if redacted.Redacts() != "" {
			t.Errorf("Redacts() = %q after redaction, want it to be gone", redacted.Redacts())
		}
	})
}