package chain

import (
	"context"
	"crypto/ed25519"
	"crypto/rand"
	"encoding/base64"
	"encoding/hex"
	"strings"
	"testing"
	"time"

	"basicstack.de/proofedmesh/services/verification-service/internal/canonical"
	"basicstack.de/proofedmesh/services/verification-service/internal/dsse"
	"basicstack.de/proofedmesh/services/verification-service/internal/registry"
	"basicstack.de/proofedmesh/services/verification-service/internal/store"
	"basicstack.de/proofedmesh/services/verification-service/internal/tlog"
)

const (
	approvalKeyID  = "trust-api/approval-signer-2026-q4"
	transformKeyID = "trust-api/agent-testagent-transform-2026-q4"
)

// fixedClock returns a deterministic Now function.
func fixedClock(ts time.Time) func() time.Time { return func() time.Time { return ts } }

// fakeFetcher is a map-backed tlog.Fetcher.
type fakeFetcher struct {
	entries map[string]tlog.Entry
}

func (f *fakeFetcher) Fetch(_ context.Context, ref string) (tlog.Entry, error) {
	e, ok := f.entries[ref]
	if !ok {
		return tlog.Entry{}, tlog.ErrNotFound
	}
	return e, nil
}

// fixture bundles everything a happy-path test needs. Negative-path
// tests derive from fixture and mutate exactly one input.
type fixture struct {
	t              *testing.T
	now            time.Time
	payloadHash    string
	decisionID     string
	sinkTarget     string
	approvalEntry  tlog.Entry
	transformEntry tlog.Entry
	tree           *memTree
	keyring        *registry.Static
	storev         store.Store
}

func newFixture(t *testing.T) *fixture {
	t.Helper()

	now := time.Date(2026, 10, 25, 20, 0, 0, 0, time.UTC)

	payloadHash := "sha256:" + hex.EncodeToString(sha(seedBytes("payload-xyz")))

	keyring := registry.NewStatic()
	// Approval signer.
	apPub, apPriv, err := ed25519.GenerateKey(rand.Reader)
	if err != nil {
		t.Fatalf("gen approval key: %v", err)
	}
	keyring.Register(approvalKeyID, apPub)
	// Transform signer.
	trPub, trPriv, err := ed25519.GenerateKey(rand.Reader)
	if err != nil {
		t.Fatalf("gen transform key: %v", err)
	}
	keyring.Register(transformKeyID, trPub)

	// Approval statement. Content_hash is self-asserted — in the real
	// pipeline the orchestrator computes it from the preview's canonical
	// content; here we just mint a stable value and reuse it as the
	// subject digest to satisfy the content-binding check.
	approvalContent := "sha256:" + hex.EncodeToString(sha(seedBytes("approval-xyz")))
	apStmt := map[string]any{
		"_type": "https://in-toto.io/Statement/v1",
		"subject": []any{map[string]any{
			"name":   "approval/pv-xyz",
			"digest": map[string]any{"sha256": stripSha256Prefix(approvalContent)},
		}},
		"predicateType": "https://basicstack.de/attestations/approval/v1",
		"predicate": map[string]any{
			"approval_schema":          "basicstack.de/attestations/approval/v1",
			"preview_id":               "pv-xyz",
			"session_id":               "sess-xyz",
			"content_hash":             approvalContent,
			"allowed_transformations":  []any{"expense.map_to_sink"},
			"allowed_sinks":            []any{"sink:dummy-sink"},
			"expires_at":               now.Add(10 * time.Minute).Format(time.RFC3339),
			"performed_by": map[string]any{
				"iss":        "https://pocket.local",
				"sub":        "user-xyz",
				"session_id": "sess-xyz",
			},
			"performed_at":        now.Format(time.RFC3339),
			"verification_digits": "1234",
		},
	}
	apBytes, err := canonical.Marshal(apStmt)
	if err != nil {
		t.Fatalf("canonical approval: %v", err)
	}
	apEnv := dsse.Sign("application/vnd.in-toto+json", apBytes, approvalKeyID, apPriv)

	// Transform statement. Subject digest == payload_hash (hex only).
	trStmt := map[string]any{
		"_type": "https://in-toto.io/Statement/v1",
		"subject": []any{map[string]any{
			"name":   "transform/wf-xyz/handover",
			"digest": map[string]any{"sha256": stripSha256Prefix(payloadHash)},
		}},
		"predicateType": "https://basicstack.de/attestations/transform/v1",
		"predicate": map[string]any{
			"workflow_id":       "wf-xyz",
			"actor":             "agent-testagent-transform",
			"operation":         "expense.map_to_sink",
			"sink_target":       "sink:dummy-sink",
			"approval_ref":      "(filled below)",
			"transform_version": "v0.1.0",
			"issued_at":         now.Format(time.RFC3339),
		},
	}
	trBytes, err := canonical.Marshal(trStmt)
	if err != nil {
		t.Fatalf("canonical transform: %v", err)
	}
	trEnv := dsse.Sign("application/vnd.in-toto+json", trBytes, transformKeyID, trPriv)

	// Build a two-leaf Merkle tree out of the two envelopes.
	tree := &memTree{}
	apEntry := tree.add(apEnv)
	trEntry := tree.add(trEnv)
	tree.refreshProofs(&apEntry, &trEntry)

	return &fixture{
		t:              t,
		now:            now,
		payloadHash:    payloadHash,
		decisionID:     "dec-xyz-1",
		sinkTarget:     "sink:dummy-sink",
		approvalEntry:  apEntry,
		transformEntry: trEntry,
		tree:           tree,
		keyring:        keyring,
		storev:         store.NewMemory(),
	}
}

func (f *fixture) verifier() *Verifier {
	fetcher := &fakeFetcher{entries: map[string]tlog.Entry{
		f.approvalEntry.ContentHash:  f.approvalEntry,
		f.transformEntry.ContentHash: f.transformEntry,
	}}
	return &Verifier{
		TLog:    fetcher,
		Keyring: f.keyring,
		Store:   f.storev,
		Now:     fixedClock(f.now),
		Approval: ApprovalConfig{
			ExpectedKeyID:  approvalKeyID,
			TransformKeyID: transformKeyID,
		},
	}
}

func (f *fixture) request() Request {
	return Request{
		DecisionID:   f.decisionID,
		ApprovalRef:  f.approvalEntry.ContentHash,
		TransformRef: f.transformEntry.ContentHash,
		PayloadHash:  f.payloadHash,
		SinkTarget:   f.sinkTarget,
	}
}

func TestVerify_HappyPath(t *testing.T) {
	f := newFixture(t)
	v := f.verifier()
	verdict, err := v.Verify(context.Background(), f.request())
	if err != nil {
		t.Fatalf("verify: %v", err)
	}
	if !verdict.Valid {
		t.Fatalf("verdict not valid: %+v", verdict)
	}
	if verdict.Replay {
		t.Fatalf("verdict replay flag unexpectedly set")
	}
	if len(verdict.Actors) != 2 {
		t.Fatalf("actors: want 2, got %v", verdict.Actors)
	}
	if verdict.Actors[0] != approvalKeyID || verdict.Actors[1] != transformKeyID {
		t.Fatalf("actors: %v", verdict.Actors)
	}
}

func TestVerify_Replay(t *testing.T) {
	f := newFixture(t)
	v := f.verifier()
	// First call reserves the decision_id.
	verdict, err := v.Verify(context.Background(), f.request())
	if err != nil || !verdict.Valid {
		t.Fatalf("first call: want valid=true, got valid=%v err=%v reasons=%v", verdict.Valid, err, verdict.Reasons)
	}
	// Second call with the SAME decision_id MUST land as replay=true,
	// valid=false — the store refuses the insert so the chain does not
	// re-authorise the sink write.
	v2 := f.verifier()
	v2.Store = f.storev // keep the same store so the first row is still there
	verdict2, err := v2.Verify(context.Background(), f.request())
	if err != nil {
		t.Fatalf("second call err: %v", err)
	}
	if verdict2.Valid {
		t.Fatalf("second call: want valid=false, got %+v", verdict2)
	}
	if !verdict2.Replay {
		t.Fatalf("second call: want replay=true, got %+v", verdict2)
	}
	if !containsReason(verdict2.Reasons, ReasonReplay) {
		t.Fatalf("replay reason missing: %v", verdict2.Reasons)
	}
}

func TestVerify_BadSignature(t *testing.T) {
	f := newFixture(t)
	// Flip a bit in the transform signature so dsse.Verify rejects it.
	env := f.transformEntry.Envelope
	raw, _ := base64.RawURLEncoding.DecodeString(env.Signatures[0].Sig)
	raw[0] ^= 0xff
	env.Signatures[0].Sig = base64.RawURLEncoding.EncodeToString(raw)
	f.transformEntry.Envelope = env

	v := f.verifier()
	verdict, err := v.Verify(context.Background(), f.request())
	if err != nil {
		t.Fatalf("verify: %v", err)
	}
	if verdict.Valid {
		t.Fatalf("verdict unexpectedly valid")
	}
	if !containsReason(verdict.Reasons, ReasonTransformSignatureInvalid) {
		t.Fatalf("want %s, got %v", ReasonTransformSignatureInvalid, verdict.Reasons)
	}
}

func TestVerify_InclusionProofMissing(t *testing.T) {
	f := newFixture(t)
	// Drop the audit path on the approval entry — the proof should fail
	// to recompute the tree root.
	f.approvalEntry.InclusionProof.Hashes = nil

	v := f.verifier()
	verdict, err := v.Verify(context.Background(), f.request())
	if err != nil {
		t.Fatalf("verify: %v", err)
	}
	if verdict.Valid {
		t.Fatalf("verdict unexpectedly valid")
	}
	if !hasPrefix(verdict.Reasons, ReasonApprovalInclusionInvalid) {
		t.Fatalf("want %s*, got %v", ReasonApprovalInclusionInvalid, verdict.Reasons)
	}
}

func TestVerify_HashDrift(t *testing.T) {
	f := newFixture(t)
	// Flip the payload_hash the caller claims; transform.subject.digest
	// no longer matches.
	driftHash := "sha256:" + hex.EncodeToString(sha(seedBytes("wrong-payload")))
	req := f.request()
	req.PayloadHash = driftHash

	v := f.verifier()
	verdict, err := v.Verify(context.Background(), req)
	if err != nil {
		t.Fatalf("verify: %v", err)
	}
	if verdict.Valid {
		t.Fatalf("verdict unexpectedly valid")
	}
	if !hasPrefix(verdict.Reasons, ReasonTransformHashDrift) {
		t.Fatalf("want %s*, got %v", ReasonTransformHashDrift, verdict.Reasons)
	}
}

func TestVerify_SinkNotAllowed(t *testing.T) {
	f := newFixture(t)
	req := f.request()
	req.SinkTarget = "sink:unknown"
	v := f.verifier()
	verdict, err := v.Verify(context.Background(), req)
	if err != nil {
		t.Fatalf("verify: %v", err)
	}
	if verdict.Valid {
		t.Fatalf("verdict unexpectedly valid")
	}
	if !hasPrefix(verdict.Reasons, ReasonSinkNotAllowed) {
		t.Fatalf("want %s*, got %v", ReasonSinkNotAllowed, verdict.Reasons)
	}
}

func TestVerify_Expired(t *testing.T) {
	f := newFixture(t)
	// Push the clock past the approval's expires_at.
	v := f.verifier()
	v.Now = fixedClock(f.now.Add(30 * time.Minute))
	verdict, err := v.Verify(context.Background(), f.request())
	if err != nil {
		t.Fatalf("verify: %v", err)
	}
	if verdict.Valid {
		t.Fatalf("verdict unexpectedly valid")
	}
	if !hasPrefix(verdict.Reasons, ReasonApprovalExpired) {
		t.Fatalf("want %s*, got %v", ReasonApprovalExpired, verdict.Reasons)
	}
}

func TestVerify_OperationNotAllowed(t *testing.T) {
	// Rebuild the fixture with a transform that uses an operation the
	// approval does not list — this is a stricter negative than SinkNotAllowed
	// since it exercises predicate.allowed_transformations.
	f := newFixtureCustom(t, func(trPredicate map[string]any) {
		trPredicate["operation"] = "expense.unauthorised"
	})
	v := f.verifier()
	verdict, err := v.Verify(context.Background(), f.request())
	if err != nil {
		t.Fatalf("verify: %v", err)
	}
	if verdict.Valid {
		t.Fatalf("verdict unexpectedly valid")
	}
	if !hasPrefix(verdict.Reasons, ReasonTransformationNotAllowed) {
		t.Fatalf("want %s*, got %v", ReasonTransformationNotAllowed, verdict.Reasons)
	}
}

// ----- helpers -----

// newFixtureCustom builds a fixture with a transform-predicate mutation
// applied before signing. Used by tests that need to exercise fields
// outside the default fixture (e.g. operation not in allowed_transformations).
func newFixtureCustom(t *testing.T, mutateTransform func(map[string]any)) *fixture {
	t.Helper()
	f := newFixture(t)
	// Pull the transform payload out, mutate, re-sign, re-tree.
	_, trPriv, _ := ed25519.GenerateKey(rand.Reader)
	// Re-register with the registry so the signing matches.
	trPub := trPriv.Public().(ed25519.PublicKey)
	f.keyring.Register(transformKeyID, trPub)

	trPredicate := map[string]any{
		"workflow_id":       "wf-xyz",
		"actor":             "agent-testagent-transform",
		"operation":         "expense.map_to_sink",
		"sink_target":       "sink:dummy-sink",
		"approval_ref":      "(filled below)",
		"transform_version": "v0.1.0",
		"issued_at":         f.now.Format(time.RFC3339),
	}
	mutateTransform(trPredicate)

	trStmt := map[string]any{
		"_type": "https://in-toto.io/Statement/v1",
		"subject": []any{map[string]any{
			"name":   "transform/wf-xyz/handover",
			"digest": map[string]any{"sha256": stripSha256Prefix(f.payloadHash)},
		}},
		"predicateType": "https://basicstack.de/attestations/transform/v1",
		"predicate":     trPredicate,
	}
	trBytes, err := canonical.Marshal(trStmt)
	if err != nil {
		t.Fatalf("re-canonicalise transform: %v", err)
	}
	trEnv := dsse.Sign("application/vnd.in-toto+json", trBytes, transformKeyID, trPriv)

	// Rebuild the tree so proofs stay consistent.
	tree := &memTree{}
	apEntry := tree.add(f.approvalEntry.Envelope)
	trEntry := tree.add(trEnv)
	tree.refreshProofs(&apEntry, &trEntry)
	f.approvalEntry = apEntry
	f.transformEntry = trEntry
	f.tree = tree
	return f
}

func containsReason(reasons []string, want string) bool {
	for _, r := range reasons {
		if r == want {
			return true
		}
	}
	return false
}

func hasPrefix(reasons []string, prefix string) bool {
	for _, r := range reasons {
		if r == prefix || len(r) > len(prefix) && strings.HasPrefix(r, prefix+":") {
			return true
		}
	}
	return false
}