package protocol_test

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"os"
	"reflect"
	"testing"

	"git.n1ko.dev/Niko/niko_trust/pkg/identity/signer"
	"git.n1ko.dev/Niko/niko_trust/pkg/protocol"
	"git.n1ko.dev/Niko/niko_trust/pkg/tce"
)

// loadVectorsF is loadVectors for the seed-corpus phase of a fuzz test,
// where the failure controller is a *testing.F.
func loadVectorsF(f *testing.F) *vectorFile {
	b, err := os.ReadFile(vectorsPath)
	if err != nil {
		f.Fatalf("read vectors: %v", err)
	}
	var vf vectorFile
	if err := json.Unmarshal(b, &vf); err != nil {
		f.Fatalf("parse vectors: %v", err)
	}
	return &vf
}

// FuzzDecodeIsTotalAndNonMalleable asserts the two injection properties of
// PROTOCOL.md section 12.4 against arbitrary byte strings:
//
//   - the decoder never panics, hangs or returns a usable object alongside an
//     error (totality);
//   - any input that does decode is exactly the canonical encoding of the
//     decoded object: re-encoding reproduces the input byte for byte
//     (encode(decode(b)) == b). If that failed, two byte strings would denote
//     one object and a signature could be transplanted.
func FuzzDecodeIsTotalAndNonMalleable(f *testing.F) {
	vf := loadVectorsF(f)
	for _, v := range vf.Vectors {
		b, err := hex.DecodeString(v.TCEHex)
		if err != nil {
			f.Fatalf("corpus hex: %v", err)
		}
		f.Add(b)
	}
	f.Add([]byte(nil))
	f.Add([]byte{0x74})

	decode := []struct {
		name  string
		parse func([]byte) (interface{ TCE() []byte }, error)
	}{
		{"identity", func(b []byte) (interface{ TCE() []byte }, error) { return protocol.DecodeIdentity(b) }},
		{"claim", func(b []byte) (interface{ TCE() []byte }, error) { return protocol.DecodeClaim(b) }},
		{"revocation", func(b []byte) (interface{ TCE() []byte }, error) { return protocol.DecodeRevocation(b) }},
		{"request", func(b []byte) (interface{ TCE() []byte }, error) { return protocol.DecodeApprovalRequest(b) }},
		{"response", func(b []byte) (interface{ TCE() []byte }, error) { return protocol.DecodeApprovalResponse(b) }},
		{"assertion", func(b []byte) (interface{ TCE() []byte }, error) { return protocol.DecodeAuthAssertion(b) }},
	}
	encode := map[string]func(interface{ TCE() []byte }) ([]byte, error){
		"identity": func(o interface{ TCE() []byte }) ([]byte, error) {
			return protocol.EncodeIdentity(o.(*protocol.Identity))
		},
		"claim": func(o interface{ TCE() []byte }) ([]byte, error) { return protocol.EncodeClaim(o.(*protocol.Claim)) },
		"revocation": func(o interface{ TCE() []byte }) ([]byte, error) {
			return protocol.EncodeRevocation(o.(*protocol.Revocation))
		},
		"request": func(o interface{ TCE() []byte }) ([]byte, error) {
			return protocol.EncodeApprovalRequest(o.(*protocol.ApprovalRequest))
		},
		"response": func(o interface{ TCE() []byte }) ([]byte, error) {
			return protocol.EncodeApprovalResponse(o.(*protocol.ApprovalResponse))
		},
		"assertion": func(o interface{ TCE() []byte }) ([]byte, error) {
			return protocol.EncodeAuthAssertion(o.(*protocol.AuthAssertion))
		},
	}

	f.Fuzz(func(t *testing.T, b []byte) {
		for _, d := range decode {
			obj, err := d.parse(b)
			if err != nil {
				continue
			}
			if obj == nil {
				t.Fatalf("nil interface from %s", d.name)
			}
			rv := reflect.ValueOf(obj)
			if rv.Kind() == reflect.Ptr && rv.IsNil() {
				t.Fatalf("boxed-nil *%s from %s", rv.Type().Elem(), d.name)
			}
			out, err := encode[d.name](obj)
			if err != nil {
				t.Fatalf("%s: encoder rejected the decoder's own object: %v", d.name, err)
			}
			if !eqBytes(out, b) {
				t.Fatalf("%s: encode(decode(b)) != b:\n got %x\n in  %x", d.name, out, b)
			}
		}
	})
}

// FuzzClaimBuildRoundTrip builds claims of random valid shape and asserts
// decode(encode(x)) == x and object-ID stability. Encoder-determinism is the
// half of section 12.4 that starts from a structured object rather than from
// received bytes.
func FuzzClaimBuildRoundTrip(f *testing.F) {
	f.Add([]byte("seed corpus"))
	f.Add([]byte{})

	f.Fuzz(func(t *testing.T, data []byte) {
		byteAt := func(k int) byte {
			if len(data) == 0 {
				return 0
			}
			return data[k%len(data)]
		}
		issuerSeed := sha256.Sum256(append([]byte("issuer"), data...))
		subjectSeed := sha256.Sum256(append([]byte("subject"), data...))
		issuer, err := signer.FromSeed(issuerSeed[:])
		if err != nil {
			t.Skip("degenerate derived key")
		}
		subject, err := signer.FromSeed(subjectSeed[:])
		if err != nil {
			t.Skip("degenerate derived key")
		}

		claims := map[string]tce.Value{}
		n := 1 + int(byteAt(0))%3
		for i := 0; i < n; i++ {
			key := "k" + string(rune('a'+i))
			switch byteAt(i+1) % 5 {
			case 0:
				claims[key] = tce.Null()
			case 1:
				claims[key] = tce.Bool(true)
			case 2:
				claims[key] = tce.Bool(false)
			case 3:
				claims[key] = tce.String("value-" + key)
			default:
				claims[key] = tce.Int(int64(i) * int64(n))
			}
		}

		c := &protocol.Claim{
			Issuer: issuer.Public(), Subject: subject.Public(),
			Claims: claims, CreatedAt: 1_700_000_000, ExpiresAt: 1_700_086_400,
			Serial: 1, Nonce: nonce(0x5a),
		}
		b, err := protocol.EncodeClaim(c)
		if err != nil {
			t.Fatalf("encode: %v", err)
		}
		dec, err := protocol.DecodeClaim(b)
		if err != nil {
			t.Fatalf("own encoding rejected: %v", err)
		}
		if !eqBytes(dec.TCE(), b) {
			t.Fatal("decoded claim did not retain the encoded bytes")
		}
		re, err := protocol.EncodeClaim(dec)
		if err != nil {
			t.Fatalf("re-encode: %v", err)
		}
		if !eqBytes(re, b) {
			t.Fatalf("decode(encode(x)) != x")
		}
		if !tce.ComputeID(b).Equal(tce.ComputeID(re)) {
			t.Fatal("object ID unstable across a decode/encode cycle")
		}
	})
}