package authn

import (
	"bytes"
	"crypto/ed25519"
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"encoding/pem"
	"testing"

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

func TestBuildResponseSigningInputChangesWhenSignedFieldChanges(t *testing.T) {
	t.Parallel()

	base := ResponseSigningFields{
		ProtocolVersion: "v1",
		RequestID:       "request-123",
		TimestampMS:     123456789,
		ResultCode:      "ok",
		PayloadHash:     mustSHA256([]byte("payload")),
	}

	baseInput := BuildResponseSigningInput(base)

	tests := []struct {
		name   string
		mutate func(ResponseSigningFields) ResponseSigningFields
	}{
		{
			name: "protocol version",
			mutate: func(fields ResponseSigningFields) ResponseSigningFields {
				fields.ProtocolVersion = "v2"
				return fields
			},
		},
		{
			name: "request id",
			mutate: func(fields ResponseSigningFields) ResponseSigningFields {
				fields.RequestID = "request-456"
				return fields
			},
		},
		{
			name: "timestamp",
			mutate: func(fields ResponseSigningFields) ResponseSigningFields {
				fields.TimestampMS++
				return fields
			},
		},
		{
			name: "result code",
			mutate: func(fields ResponseSigningFields) ResponseSigningFields {
				fields.ResultCode = "denied"
				return fields
			},
		},
		{
			name: "payload hash",
			mutate: func(fields ResponseSigningFields) ResponseSigningFields {
				fields.PayloadHash = mustSHA256([]byte("other"))
				return fields
			},
		},
	}

	for _, tt := range tests {
		tt := tt

		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			mutated := BuildResponseSigningInput(tt.mutate(base))
			assert.False(t, bytes.Equal(baseInput, mutated))
		})
	}
}

func TestParseEd25519ResponseSignerPEMRejectsMalformedPEM(t *testing.T) {
	t.Parallel()

	_, err := ParseEd25519ResponseSignerPEM([]byte("not-pem"))
	require.ErrorIs(t, err, ErrInvalidResponsePrivateKeyPEM)
}

func TestParseEd25519ResponseSignerPEMRejectsNonPKCS8PEM(t *testing.T) {
	t.Parallel()

	_, privateKey, err := ed25519.GenerateKey(rand.Reader)
	require.NoError(t, err)

	pemBytes, err := x509.MarshalPKCS8PrivateKey(privateKey)
	require.NoError(t, err)

	block := pem.Block{
		Type:  "ED25519 PRIVATE KEY",
		Bytes: pemBytes,
	}

	_, err = ParseEd25519ResponseSignerPEM(pem.EncodeToMemory(&block))
	require.ErrorIs(t, err, ErrInvalidResponsePrivateKeyPEM)
}

func TestParseEd25519ResponseSignerPEMRejectsNonEd25519Key(t *testing.T) {
	t.Parallel()

	privateKey, err := rsa.GenerateKey(rand.Reader, 1024)
	require.NoError(t, err)

	pemBytes, err := x509.MarshalPKCS8PrivateKey(privateKey)
	require.NoError(t, err)

	_, err = ParseEd25519ResponseSignerPEM(pem.EncodeToMemory(&pem.Block{
		Type:  "PRIVATE KEY",
		Bytes: pemBytes,
	}))
	require.ErrorIs(t, err, ErrInvalidResponsePrivateKey)
}

func TestSignAndVerifyResponseSignature(t *testing.T) {
	t.Parallel()

	_, privateKey, err := ed25519.GenerateKey(rand.Reader)
	require.NoError(t, err)

	signer, err := NewEd25519ResponseSigner(privateKey)
	require.NoError(t, err)

	fields := ResponseSigningFields{
		ProtocolVersion: "v1",
		RequestID:       "request-123",
		TimestampMS:     123456789,
		ResultCode:      "ok",
		PayloadHash:     mustSHA256([]byte("payload")),
	}

	signature, err := signer.SignResponse(fields)
	require.NoError(t, err)
	require.NoError(t, VerifyResponseSignature(signer.PublicKey(), signature, fields))

	fields.ResultCode = "changed"
	require.ErrorIs(t, VerifyResponseSignature(signer.PublicKey(), signature, fields), ErrInvalidResponseSignature)
}