package services

import (
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"strings"
	"testing"
	"time"
)

// TestPKCEVerification tests PKCE code_challenge and code_verifier validation
func TestPKCEVerification_S256_ValidVerifier(t *testing.T) {
	// Generate a code_verifier
	codeVerifier := "dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk"

	// Calculate expected code_challenge (S256)
	hash := sha256.Sum256([]byte(codeVerifier))
	codeChallenge := base64.RawURLEncoding.EncodeToString(hash[:])

	// Verify the challenge matches
	verifierHash := sha256.Sum256([]byte(codeVerifier))
	calculatedChallenge := base64.RawURLEncoding.EncodeToString(verifierHash[:])

	if calculatedChallenge != codeChallenge {
		t.Errorf("PKCE verification failed: expected %s, got %s", codeChallenge, calculatedChallenge)
	}
}

func TestPKCEVerification_S256_InvalidVerifier(t *testing.T) {
	codeVerifier := "correct-verifier-12345678901234567890"
	wrongVerifier := "wrong-verifier-00000000000000000000"

	// Calculate code_challenge from correct verifier
	hash := sha256.Sum256([]byte(codeVerifier))
	codeChallenge := base64.RawURLEncoding.EncodeToString(hash[:])

	// Calculate challenge from wrong verifier
	wrongHash := sha256.Sum256([]byte(wrongVerifier))
	wrongChallenge := base64.RawURLEncoding.EncodeToString(wrongHash[:])

	if wrongChallenge == codeChallenge {
		t.Error("PKCE verification should fail for wrong verifier")
	}
}

func TestPKCEVerification_Plain_ValidVerifier(t *testing.T) {
	codeVerifier := "plain-text-verifier-12345"
	codeChallenge := codeVerifier // Plain method: challenge = verifier

	if codeVerifier != codeChallenge {
		t.Error("Plain PKCE verification failed")
	}
}

// TestTokenHashing tests that token hashing is consistent
func TestTokenHashing_Consistency(t *testing.T) {
	token := "sample-access-token-12345"

	hash1 := sha256.Sum256([]byte(token))
	hash2 := sha256.Sum256([]byte(token))

	if hash1 != hash2 {
		t.Error("Token hashing should be consistent")
	}
}

func TestTokenHashing_DifferentTokens(t *testing.T) {
	token1 := "token-1-abcdefgh"
	token2 := "token-2-ijklmnop"

	hash1 := sha256.Sum256([]byte(token1))
	hash2 := sha256.Sum256([]byte(token2))

	if hash1 == hash2 {
		t.Error("Different tokens should produce different hashes")
	}
}

// TestScopeValidation tests scope parsing and validation
func TestScopeValidation_ParseScopes(t *testing.T) {
	tests := []struct {
		name           string
		requestedScope string
		allowedScopes  []string
		expectedCount  int
	}{
		{
			name:           "all scopes allowed",
			requestedScope: "openid profile email",
			allowedScopes:  []string{"openid", "profile", "email", "offline_access"},
			expectedCount:  3,
		},
		{
			name:           "some scopes allowed",
			requestedScope: "openid profile admin",
			allowedScopes:  []string{"openid", "profile", "email"},
			expectedCount:  2, // admin not allowed
		},
		{
			name:           "no scopes allowed",
			requestedScope: "admin superuser",
			allowedScopes:  []string{"openid", "profile", "email"},
			expectedCount:  0,
		},
		{
			name:           "empty request defaults",
			requestedScope: "",
			allowedScopes:  []string{"openid", "profile", "email"},
			expectedCount:  0, // Empty request returns 0 from this test logic
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			if tt.requestedScope == "" {
				// Empty scope should use defaults in actual service
				return
			}

			allowedMap := make(map[string]bool)
			for _, scope := range tt.allowedScopes {
				allowedMap[scope] = true
			}

			var validScopes []string
			requestedScopes := splitScopes(tt.requestedScope)
			for _, scope := range requestedScopes {
				if allowedMap[scope] {
					validScopes = append(validScopes, scope)
				}
			}

			if len(validScopes) != tt.expectedCount {
				t.Errorf("Expected %d valid scopes, got %d", tt.expectedCount, len(validScopes))
			}
		})
	}
}

// Helper function for scope splitting
func splitScopes(scopes string) []string {
	if scopes == "" {
		return nil
	}
	var result []string
	start := 0
	for i := 0; i <= len(scopes); i++ {
		if i == len(scopes) || scopes[i] == ' ' {
			if start < i {
				result = append(result, scopes[start:i])
			}
			start = i + 1
		}
	}
	return result
}

// TestRedirectURIValidation tests redirect URI validation
func TestRedirectURIValidation(t *testing.T) {
	tests := []struct {
		name         string
		registeredURIs []string
		requestURI   string
		shouldMatch  bool
	}{
		{
			name:         "exact match",
			registeredURIs: []string{"https://example.com/callback"},
			requestURI:   "https://example.com/callback",
			shouldMatch:  true,
		},
		{
			name:         "no match different domain",
			registeredURIs: []string{"https://example.com/callback"},
			requestURI:   "https://evil.com/callback",
			shouldMatch:  false,
		},
		{
			name:         "no match different path",
			registeredURIs: []string{"https://example.com/callback"},
			requestURI:   "https://example.com/other",
			shouldMatch:  false,
		},
		{
			name:         "multiple URIs - second matches",
			registeredURIs: []string{"https://example.com/callback", "https://example.com/auth"},
			requestURI:   "https://example.com/auth",
			shouldMatch:  true,
		},
		{
			name:         "localhost for development",
			registeredURIs: []string{"http://localhost:3000/callback"},
			requestURI:   "http://localhost:3000/callback",
			shouldMatch:  true,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			matched := false
			for _, uri := range tt.registeredURIs {
				if uri == tt.requestURI {
					matched = true
					break
				}
			}

			if matched != tt.shouldMatch {
				t.Errorf("Expected match=%v, got match=%v", tt.shouldMatch, matched)
			}
		})
	}
}

// TestGrantTypeValidation tests grant type validation
func TestGrantTypeValidation(t *testing.T) {
	tests := []struct {
		name           string
		allowedGrants  []string
		requestedGrant string
		shouldAllow    bool
	}{
		{
			name:           "authorization_code allowed",
			allowedGrants:  []string{"authorization_code", "refresh_token"},
			requestedGrant: "authorization_code",
			shouldAllow:    true,
		},
		{
			name:           "refresh_token allowed",
			allowedGrants:  []string{"authorization_code", "refresh_token"},
			requestedGrant: "refresh_token",
			shouldAllow:    true,
		},
		{
			name:           "password not allowed",
			allowedGrants:  []string{"authorization_code", "refresh_token"},
			requestedGrant: "password",
			shouldAllow:    false,
		},
		{
			name:           "client_credentials not allowed",
			allowedGrants:  []string{"authorization_code", "refresh_token"},
			requestedGrant: "client_credentials",
			shouldAllow:    false,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			allowed := false
			for _, grant := range tt.allowedGrants {
				if grant == tt.requestedGrant {
					allowed = true
					break
				}
			}

			if allowed != tt.shouldAllow {
				t.Errorf("Expected allow=%v, got allow=%v", tt.shouldAllow, allowed)
			}
		})
	}
}

// TestAuthorizationCodeExpiry tests that expired codes should be rejected
func TestAuthorizationCodeExpiry_Logic(t *testing.T) {
	tests := []struct {
		name        string
		expiryMins  int
		usedAfter   int // minutes after creation
		shouldAllow bool
	}{
		{
			name:        "code used within expiry",
			expiryMins:  10,
			usedAfter:   5,
			shouldAllow: true,
		},
		{
			name:        "code used at expiry boundary",
			expiryMins:  10,
			usedAfter:   10,
			shouldAllow: false, // Expired at exactly 10 mins
		},
		{
			name:        "code used after expiry",
			expiryMins:  10,
			usedAfter:   15,
			shouldAllow: false,
		},
		{
			name:        "code used immediately",
			expiryMins:  10,
			usedAfter:   0,
			shouldAllow: true,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			isValid := tt.usedAfter < tt.expiryMins

			if isValid != tt.shouldAllow {
				t.Errorf("Expected allow=%v for code used after %d mins (expiry: %d mins)",
					tt.shouldAllow, tt.usedAfter, tt.expiryMins)
			}
		})
	}
}

// TestClientSecretValidation tests confidential client authentication
func TestClientSecretValidation(t *testing.T) {
	tests := []struct {
		name           string
		isPublic       bool
		storedSecret   string
		providedSecret string
		shouldAllow    bool
	}{
		{
			name:           "public client - no secret needed",
			isPublic:       true,
			storedSecret:   "",
			providedSecret: "",
			shouldAllow:    true,
		},
		{
			name:           "confidential client - correct secret",
			isPublic:       false,
			storedSecret:   "super-secret-123",
			providedSecret: "super-secret-123",
			shouldAllow:    true,
		},
		{
			name:           "confidential client - wrong secret",
			isPublic:       false,
			storedSecret:   "super-secret-123",
			providedSecret: "wrong-secret",
			shouldAllow:    false,
		},
		{
			name:           "confidential client - empty secret",
			isPublic:       false,
			storedSecret:   "super-secret-123",
			providedSecret: "",
			shouldAllow:    false,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			var isValid bool
			if tt.isPublic {
				isValid = true
			} else {
				isValid = tt.storedSecret == tt.providedSecret
			}

			if isValid != tt.shouldAllow {
				t.Errorf("Expected allow=%v, got allow=%v", tt.shouldAllow, isValid)
			}
		})
	}
}

// ========================================
// Extended OAuth 2.0 Tests
// ========================================

// TestCodeVerifierGeneration tests that code verifiers meet RFC 7636 requirements
func TestCodeVerifierGeneration_RFC7636(t *testing.T) {
	tests := []struct {
		name           string
		length         int
		expectedLength int
		description    string
	}{
		{"minimum length (43)", 43, 43, "RFC 7636 minimum"},
		{"standard length (64)", 64, 64, "Recommended length"},
		{"maximum length (128)", 128, 128, "RFC 7636 maximum"},
		{"too short (42) - corrected to minimum", 42, 43, "Should be corrected to minimum"},
		{"too long (129) - corrected to maximum", 129, 128, "Should be corrected to maximum"},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			verifier := generateCodeVerifier(tt.length)

			// Check that length is corrected to valid range
			if len(verifier) != tt.expectedLength {
				t.Errorf("Expected length %d, got %d", tt.expectedLength, len(verifier))
			}

			// Check character set (unreserved characters only: A-Z, a-z, 0-9, -, ., _, ~)
			for _, c := range verifier {
				if !isUnreservedChar(c) {
					t.Errorf("Code verifier contains invalid character: %c", c)
				}
			}
		})
	}
}

// TestCodeVerifierLength_Validation tests length validation logic
func TestCodeVerifierLength_Validation(t *testing.T) {
	tests := []struct {
		name    string
		length  int
		isValid bool
	}{
		{"length 42 - too short", 42, false},
		{"length 43 - minimum valid", 43, true},
		{"length 64 - recommended", 64, true},
		{"length 128 - maximum valid", 128, true},
		{"length 129 - too long", 129, false},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			isValid := tt.length >= 43 && tt.length <= 128
			if isValid != tt.isValid {
				t.Errorf("Expected valid=%v for length %d, got valid=%v",
					tt.isValid, tt.length, isValid)
			}
		})
	}
}

// generateCodeVerifier generates a code verifier of specified length
func generateCodeVerifier(length int) string {
	// Ensure minimum and maximum bounds
	if length < 43 {
		length = 43
	}
	if length > 128 {
		length = 128
	}

	const unreserved = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-._~"

	bytes := make([]byte, length)
	rand.Read(bytes)

	result := make([]byte, length)
	for i, b := range bytes {
		result[i] = unreserved[int(b)%len(unreserved)]
	}

	return string(result)
}

// isUnreservedChar checks if a character is an unreserved character per RFC 3986
func isUnreservedChar(c rune) bool {
	return (c >= 'A' && c <= 'Z') ||
		(c >= 'a' && c <= 'z') ||
		(c >= '0' && c <= '9') ||
		c == '-' || c == '.' || c == '_' || c == '~'
}

// TestCodeChallengeGeneration tests S256 challenge generation
func TestCodeChallengeGeneration_S256(t *testing.T) {
	// Known test vector from RFC 7636 Appendix B
	verifier := "dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk"
	expectedChallenge := "E9Melhoa2OwvFrEMTJguCHaoeK1t8URWbuGJSstw-cM"

	hash := sha256.Sum256([]byte(verifier))
	challenge := base64.RawURLEncoding.EncodeToString(hash[:])

	if challenge != expectedChallenge {
		t.Errorf("S256 challenge mismatch: expected %s, got %s", expectedChallenge, challenge)
	}
}

// TestRefreshTokenRotation tests that refresh tokens are rotated on use
func TestRefreshTokenRotation_Logic(t *testing.T) {
	// Simulate refresh token rotation
	oldToken := "old-refresh-token-123"
	oldTokenHash := hashToken(oldToken)

	// Generate new token
	newToken := generateSecureToken(32)
	newTokenHash := hashToken(newToken)

	// Verify tokens are different
	if oldTokenHash == newTokenHash {
		t.Error("New refresh token should be different from old token")
	}

	// Verify old token would be revoked (simulated by marking revoked_at)
	oldTokenRevoked := true
	if !oldTokenRevoked {
		t.Error("Old refresh token should be revoked after rotation")
	}
}

func hashToken(token string) string {
	hash := sha256.Sum256([]byte(token))
	return hex.EncodeToString(hash[:])
}

func generateSecureToken(length int) string {
	bytes := make([]byte, length)
	rand.Read(bytes)
	return base64.URLEncoding.EncodeToString(bytes)
}

// TestAccessTokenExpiry tests access token expiration handling
func TestAccessTokenExpiry_Scenarios(t *testing.T) {
	tests := []struct {
		name           string
		tokenDuration  time.Duration
		usedAfter      time.Duration
		shouldBeValid  bool
	}{
		{
			name:          "token used immediately",
			tokenDuration: time.Hour,
			usedAfter:     0,
			shouldBeValid: true,
		},
		{
			name:          "token used within validity",
			tokenDuration: time.Hour,
			usedAfter:     30 * time.Minute,
			shouldBeValid: true,
		},
		{
			name:          "token used at expiry",
			tokenDuration: time.Hour,
			usedAfter:     time.Hour,
			shouldBeValid: false,
		},
		{
			name:          "token used after expiry",
			tokenDuration: time.Hour,
			usedAfter:     2 * time.Hour,
			shouldBeValid: false,
		},
		{
			name:          "short-lived token",
			tokenDuration: 5 * time.Minute,
			usedAfter:     6 * time.Minute,
			shouldBeValid: false,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			issuedAt := time.Now()
			expiresAt := issuedAt.Add(tt.tokenDuration)
			usedAt := issuedAt.Add(tt.usedAfter)

			isValid := usedAt.Before(expiresAt)

			if isValid != tt.shouldBeValid {
				t.Errorf("Expected valid=%v for token used after %v (duration: %v)",
					tt.shouldBeValid, tt.usedAfter, tt.tokenDuration)
			}
		})
	}
}

// TestOAuthErrors tests that OAuth error codes are correct
func TestOAuthErrors_RFC6749(t *testing.T) {
	tests := []struct {
		scenario    string
		errorCode   string
		description string
	}{
		{"invalid client_id", "invalid_client", "Client authentication failed"},
		{"invalid grant (code)", "invalid_grant", "Authorization code invalid or expired"},
		{"invalid scope", "invalid_scope", "Requested scope is invalid"},
		{"invalid request", "invalid_request", "Request is missing required parameter"},
		{"unauthorized client", "unauthorized_client", "Client not authorized for this grant type"},
		{"access denied", "access_denied", "Resource owner denied the request"},
	}

	for _, tt := range tests {
		t.Run(tt.scenario, func(t *testing.T) {
			// Verify error codes match RFC 6749 Section 5.2
			validErrors := map[string]bool{
				"invalid_request":          true,
				"invalid_client":           true,
				"invalid_grant":            true,
				"unauthorized_client":      true,
				"unsupported_grant_type":   true,
				"invalid_scope":            true,
				"access_denied":            true,
				"unsupported_response_type": true,
				"server_error":             true,
				"temporarily_unavailable":  true,
			}

			if !validErrors[tt.errorCode] {
				t.Errorf("Error code %s is not a valid OAuth 2.0 error code", tt.errorCode)
			}
		})
	}
}

// TestStateParameter tests state parameter handling for CSRF protection
func TestStateParameter_CSRF(t *testing.T) {
	tests := []struct {
		name          string
		requestState  string
		responseState string
		shouldMatch   bool
	}{
		{
			name:          "matching state",
			requestState:  "abc123xyz",
			responseState: "abc123xyz",
			shouldMatch:   true,
		},
		{
			name:          "non-matching state",
			requestState:  "abc123xyz",
			responseState: "different",
			shouldMatch:   false,
		},
		{
			name:          "empty request state",
			requestState:  "",
			responseState: "abc123xyz",
			shouldMatch:   false,
		},
		{
			name:          "empty response state",
			requestState:  "abc123xyz",
			responseState: "",
			shouldMatch:   false,
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			matches := tt.requestState != "" && tt.requestState == tt.responseState

			if matches != tt.shouldMatch {
				t.Errorf("Expected match=%v, got match=%v", tt.shouldMatch, matches)
			}
		})
	}
}

// TestResponseType tests response_type validation
func TestResponseType_Validation(t *testing.T) {
	tests := []struct {
		name         string
		responseType string
		isValid      bool
	}{
		{"code - valid", "code", true},
		{"token - implicit flow (disabled)", "token", false},
		{"id_token - OIDC", "id_token", false},
		{"code token - hybrid", "code token", false},
		{"empty", "", false},
		{"invalid", "password", false},
	}

	supportedResponseTypes := map[string]bool{
		"code": true, // Only authorization code flow is supported
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			isValid := supportedResponseTypes[tt.responseType]
			if isValid != tt.isValid {
				t.Errorf("Expected valid=%v for response_type=%s, got valid=%v",
					tt.isValid, tt.responseType, isValid)
			}
		})
	}
}

// TestCodeChallengeMethod tests code_challenge_method validation
func TestCodeChallengeMethod_Validation(t *testing.T) {
	tests := []struct {
		name    string
		method  string
		isValid bool
	}{
		{"S256 - recommended", "S256", true},
		{"plain - discouraged but valid", "plain", true},
		{"empty - defaults to plain", "", true},
		{"sha512 - not supported", "sha512", false},
		{"invalid", "md5", false},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			isValid := tt.method == "S256" || tt.method == "plain" || tt.method == ""
			if isValid != tt.isValid {
				t.Errorf("Expected valid=%v for method=%s, got valid=%v",
					tt.isValid, tt.method, isValid)
			}
		})
	}
}

// TestTokenRevocation tests token revocation behavior per RFC 7009
func TestTokenRevocation_RFC7009(t *testing.T) {
	tests := []struct {
		name           string
		tokenExists    bool
		tokenRevoked   bool
		expectSuccess  bool
	}{
		{
			name:          "revoke existing active token",
			tokenExists:   true,
			tokenRevoked:  false,
			expectSuccess: true,
		},
		{
			name:          "revoke already revoked token",
			tokenExists:   true,
			tokenRevoked:  true,
			expectSuccess: true, // RFC 7009: Always return 200
		},
		{
			name:          "revoke non-existent token",
			tokenExists:   false,
			tokenRevoked:  false,
			expectSuccess: true, // RFC 7009: Always return 200
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			// Simulate revocation logic
			// Per RFC 7009, revocation endpoint always returns 200 OK
			success := true

			if success != tt.expectSuccess {
				t.Errorf("Expected success=%v, got success=%v", tt.expectSuccess, success)
			}
		})
	}
}

// TestClientIDGeneration tests client_id format
func TestClientIDGeneration_Format(t *testing.T) {
	// Generate multiple client IDs
	clientIDs := make(map[string]bool)
	for i := 0; i < 100; i++ {
		bytes := make([]byte, 16)
		rand.Read(bytes)
		clientID := hex.EncodeToString(bytes)

		// Check format (32 hex characters)
		if len(clientID) != 32 {
			t.Errorf("Client ID should be 32 characters, got %d", len(clientID))
		}

		// Check uniqueness
		if clientIDs[clientID] {
			t.Error("Client ID should be unique")
		}
		clientIDs[clientID] = true

		// Check only hex characters
		for _, c := range clientID {
			if !((c >= '0' && c <= '9') || (c >= 'a' && c <= 'f')) {
				t.Errorf("Client ID should only contain hex characters, found %c", c)
			}
		}
	}
}

// TestScopeNormalization tests scope string normalization
func TestScopeNormalization(t *testing.T) {
	tests := []struct {
		name     string
		input    string
		expected []string
	}{
		{
			name:     "single scope",
			input:    "openid",
			expected: []string{"openid"},
		},
		{
			name:     "multiple scopes",
			input:    "openid profile email",
			expected: []string{"openid", "profile", "email"},
		},
		{
			name:     "extra spaces",
			input:    "openid  profile   email",
			expected: []string{"openid", "profile", "email"},
		},
		{
			name:     "empty string",
			input:    "",
			expected: []string{},
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			scopes := normalizeScopes(tt.input)

			if len(scopes) != len(tt.expected) {
				t.Errorf("Expected %d scopes, got %d", len(tt.expected), len(scopes))
				return
			}

			for i, scope := range scopes {
				if scope != tt.expected[i] {
					t.Errorf("Expected scope[%d]=%s, got %s", i, tt.expected[i], scope)
				}
			}
		})
	}
}

func normalizeScopes(scope string) []string {
	if scope == "" {
		return []string{}
	}

	parts := strings.Fields(scope) // Handles multiple spaces
	return parts
}

// BenchmarkPKCEVerification benchmarks PKCE S256 verification
func BenchmarkPKCEVerification_S256(b *testing.B) {
	verifier := "dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk"

	for i := 0; i < b.N; i++ {
		hash := sha256.Sum256([]byte(verifier))
		base64.RawURLEncoding.EncodeToString(hash[:])
	}
}

// BenchmarkTokenHashing benchmarks token hashing for storage
func BenchmarkTokenHashing(b *testing.B) {
	token := "sample-access-token-12345678901234567890"

	for i := 0; i < b.N; i++ {
		hash := sha256.Sum256([]byte(token))
		hex.EncodeToString(hash[:])
	}
}

// BenchmarkCodeVerifierGeneration benchmarks code verifier generation
func BenchmarkCodeVerifierGeneration(b *testing.B) {
	for i := 0; i < b.N; i++ {
		generateCodeVerifier(64)
	}
}