// Package checker implements the OPENPGPKEY/SMIMEA DANE checker for
// happyDomain. It gathers the facts published by a zone for an
// abstract.OpenPGP or abstract.SMimeCert service (DNS lookup, DNSSEC
// flag, parsed OpenPGP key, parsed X.509 certificate) and lets a
// family of per-test rules judge those facts.
package checker

import (
	"encoding/json"
	"time"
)

// ObservationKey is the key this checker publishes. The payload is an
// *EmailKeyData JSON document.
const ObservationKey = "openpgpkey_smimea"

// Supported service types.
const (
	ServiceOpenPGP    = "abstract.OpenPGP"
	ServiceSMimeCert  = "abstract.SMimeCert"
	KindOpenPGPKey    = "openpgpkey"
	KindSMIMEA        = "smimea"
	OpenPGPKeyPrefix  = "_openpgpkey"
	SMIMEACertPrefix  = "_smimecert"
	DANEOwnerHashSize = 28 // bytes of SHA-256 kept as the owner prefix
)

// EmailKeyData is the observation payload written under ObservationKey.
// It carries only facts; no severities, no judgment, rules decide
// what's OK and what isn't.
type EmailKeyData struct {
	// Kind is "openpgpkey" or "smimea".
	Kind string `json:"kind"`

	// Domain is the FQDN of the zone (origin) that publishes the record.
	Domain string `json:"domain"`

	// Subdomain is the relative name below Domain where the service sits
	// (empty for the zone apex).
	Subdomain string `json:"subdomain,omitempty"`

	// Username is the local part copied from the service. When empty,
	// the username-hash-prefix verification is skipped.
	Username string `json:"username,omitempty"`

	// ExpectedOwner is the FQDN at which the record should be published,
	// per RFC 7929 / RFC 8162.
	ExpectedOwner string `json:"expected_owner,omitempty"`

	// QueriedOwner is the FQDN actually queried (may differ from
	// ExpectedOwner if the service record already carries its own name).
	QueriedOwner string `json:"queried_owner,omitempty"`

	// Resolver is the DNS server that answered the lookup.
	Resolver string `json:"resolver,omitempty"`

	// DNSQueryError is non-empty when the DNS lookup itself failed (no
	// answer received, transport error, etc.).
	DNSQueryError string `json:"dns_query_error,omitempty"`

	// DNSAnswerPresent is nil when the lookup did not complete, false
	// when the authoritative answer was NXDOMAIN / empty, true otherwise.
	DNSAnswerPresent *bool `json:"dns_answer_present,omitempty"`

	// DNSSECSecure is true when the validating resolver set the AD flag
	// on the answer. Nil means the lookup did not complete.
	DNSSECSecure *bool `json:"dnssec_secure,omitempty"`

	// DNSRecordMatchesService is the result of comparing the DNS-returned
	// record bytes against the service-body bytes. Nil when the
	// comparison could not run (DNS failed, or the service body has no
	// record to compare against).
	DNSRecordMatchesService *bool `json:"dns_record_matches_service,omitempty"`

	// ObservedOwnerPrefix is the hash-shaped first label extracted from
	// QueriedOwner (<hex>._openpgpkey.<…> / <hex>._smimecert.<…>), or
	// empty when the owner does not follow that shape.
	ObservedOwnerPrefix string `json:"observed_owner_prefix,omitempty"`

	// ExpectedOwnerPrefix is hex(sha256(Username))[:28]. Empty when
	// Username is empty.
	ExpectedOwnerPrefix string `json:"expected_owner_prefix,omitempty"`

	// RecordCount is the number of records returned at QueriedOwner.
	RecordCount int `json:"record_count"`

	// OpenPGP is populated for kind=openpgpkey.
	OpenPGP *OpenPGPInfo `json:"openpgp,omitempty"`

	// SMIMEA is populated for kind=smimea.
	SMIMEA *SMIMEAInfo `json:"smimea,omitempty"`

	CollectedAt time.Time `json:"collected_at"`
}

// OpenPGPInfo summarises the OpenPGP key observed in the record.
type OpenPGPInfo struct {
	// ParseError is non-empty when the record could not be decoded as a
	// valid OpenPGP key (bad base64, unreadable packet stream, no
	// entity, or no record attached to the service at all). Remaining
	// fields may be zero-valued on this path.
	ParseError string `json:"parse_error,omitempty"`

	// RawSize is the length in bytes of the transport key material.
	RawSize int `json:"raw_size"`

	// PrimaryAlgorithm is the name of the primary key's algorithm,
	// e.g. "RSA", "Ed25519", "ECDSA-NIST-P-256".
	PrimaryAlgorithm string `json:"primary_algorithm,omitempty"`

	// PrimaryBits is the key size in bits for the primary key (0 when
	// the algorithm is of fixed size, e.g. Ed25519).
	PrimaryBits int `json:"primary_bits,omitempty"`

	// Fingerprint is the hex-encoded OpenPGP fingerprint.
	Fingerprint string `json:"fingerprint,omitempty"`

	// KeyID is the short 64-bit key id, hex.
	KeyID string `json:"key_id,omitempty"`

	// UIDs lists the User ID strings carried in the key.
	UIDs []string `json:"uids,omitempty"`

	// CreatedAt is the primary key creation time.
	CreatedAt time.Time `json:"created_at,omitempty"`

	// ExpiresAt is the primary key expiration time (zero for "never").
	ExpiresAt time.Time `json:"expires_at,omitempty"`

	// Revoked is true when the primary key carries a revocation signature.
	Revoked bool `json:"revoked,omitempty"`

	// MatchesUsername is nil when the check was not run (no UIDs or no
	// username), true when at least one UID references <username@…>,
	// false otherwise.
	MatchesUsername *bool `json:"matches_username,omitempty"`

	// Subkeys describes the subordinate keys.
	Subkeys []SubkeyInfo `json:"subkeys,omitempty"`

	// EntityCount is the number of OpenPGP entities parsed from the
	// record. RFC 7929 recommends a single entity per record.
	EntityCount int `json:"entity_count"`

	// HasEncryptionCapability is true when at least one non-revoked,
	// non-expired key in the entity advertises encryption usage flags.
	HasEncryptionCapability bool `json:"has_encryption_capability"`
}

// SubkeyInfo summarises one OpenPGP subkey.
type SubkeyInfo struct {
	Algorithm  string    `json:"algorithm"`
	Bits       int       `json:"bits,omitempty"`
	CanSign    bool      `json:"can_sign,omitempty"`
	CanEncrypt bool      `json:"can_encrypt,omitempty"`
	CanAuth    bool      `json:"can_auth,omitempty"`
	CreatedAt  time.Time `json:"created_at,omitempty"`
	ExpiresAt  time.Time `json:"expires_at,omitempty"`
	Revoked    bool      `json:"revoked,omitempty"`
}

// SMIMEAInfo summarises the S/MIME record.
type SMIMEAInfo struct {
	// ParseError is non-empty when the certificate / SPKI bytes cannot
	// be parsed.
	ParseError string `json:"parse_error,omitempty"`

	Usage        uint8 `json:"usage"`
	Selector     uint8 `json:"selector"`
	MatchingType uint8 `json:"matching_type"`

	// Certificate is populated when the record carries a full X.509
	// certificate (selector 0, matching type 0). For selector 1 + type 0
	// only PublicKey is populated. For matching types 1/2, neither is
	// populated; only the digest is transported.
	Certificate *CertInfo   `json:"certificate,omitempty"`
	PublicKey   *PubKeyInfo `json:"public_key,omitempty"`

	// HashHex, when set, is the hex digest embedded in the record.
	HashHex string `json:"hash_hex,omitempty"`
}

// CertInfo summarises an X.509 certificate.
type CertInfo struct {
	Subject               string    `json:"subject,omitempty"`
	Issuer                string    `json:"issuer,omitempty"`
	SerialHex             string    `json:"serial_hex,omitempty"`
	NotBefore             time.Time `json:"not_before,omitempty"`
	NotAfter              time.Time `json:"not_after,omitempty"`
	SignatureAlgorithm    string    `json:"signature_algorithm,omitempty"`
	PublicKeyAlgorithm    string    `json:"public_key_algorithm,omitempty"`
	PublicKeyBits         int       `json:"public_key_bits,omitempty"`
	EmailAddresses        []string  `json:"email_addresses,omitempty"`
	DNSNames              []string  `json:"dns_names,omitempty"`
	HasEmailProtectionEKU bool      `json:"has_email_protection_eku,omitempty"`
	HasDigitalSignature   bool      `json:"has_digital_signature,omitempty"`
	HasKeyEncipherment    bool      `json:"has_key_encipherment,omitempty"`
	IsSelfSigned          bool      `json:"is_self_signed,omitempty"`
	IsCA                  bool      `json:"is_ca,omitempty"`

	// EmailMatchesUsername is nil when the check was not run (no
	// username or no email SAN on the certificate), true when at least
	// one SAN begins with "<username>@", false otherwise.
	EmailMatchesUsername *bool `json:"email_matches_username,omitempty"`
}

// PubKeyInfo summarises an SPKI-only SMIMEA record.
type PubKeyInfo struct {
	Algorithm string `json:"algorithm,omitempty"`
	Bits      int    `json:"bits,omitempty"`
}

// serviceMessage is a minimal mirror of happyDomain's ServiceMessage JSON
// envelope used to carry the auto-filled service.
type serviceMessage struct {
	Type    string          `json:"_svctype"`
	Domain  string          `json:"_domain"`
	Service json.RawMessage `json:"Service"`
}