package checker

import (
	"encoding/json"
	"fmt"

	"github.com/miekg/dns"
)

// maxNSResultErrors caps the per-NS error list so a flaky server with many
// addresses cannot bloat the JSON observation payload. Once the cap is
// reached, further errors are dropped and a single sentinel entry records the
// number of suppressed messages.
const maxNSResultErrors = 16

// ObservationKey is the observation key for observation data.
const ObservationKey = "authoritative-consistency"

// Severity classifies a finding emitted by the authoritative-consistency checker.
type Severity string

const (
	SeverityInfo Severity = "info"
	SeverityWarn Severity = "warn"
	SeverityCrit Severity = "crit"
)

// Finding codes: stable machine-readable identifiers used by the UI to
// localize and link to remediation docs.
const (
	CodeSerialDrift           = "authoritative_consistency_serial_drift"
	CodeSerialStaleVsSaved    = "authoritative_consistency_serial_stale_vs_saved"
	CodeSerialAheadOfSaved    = "authoritative_consistency_serial_ahead_of_saved"
	CodeNSUnreachable         = "authoritative_consistency_ns_unreachable"
	CodeNSUDPFailed           = "authoritative_consistency_ns_udp_failed"
	CodeNSTCPFailed           = "authoritative_consistency_ns_tcp_failed"
	CodeNSUnresolvable        = "authoritative_consistency_ns_unresolvable"
	CodeLame                  = "authoritative_consistency_lame"
	CodeNoSOA                 = "authoritative_consistency_no_soa"
	CodeNSRRsetDrift          = "authoritative_consistency_ns_rrset_drift"
	CodeNSRRsetMismatchConfig = "authoritative_consistency_ns_rrset_mismatch_config"
	CodeParentDrift           = "authoritative_consistency_parent_drift"
	CodeParentQueryFailed     = "authoritative_consistency_parent_query_failed"
	CodeSOAFieldsDrift        = "authoritative_consistency_soa_fields_drift"
	CodeSlowNS                = "authoritative_consistency_slow_ns"
	CodeEDNSUnsupported       = "authoritative_consistency_edns_unsupported"
	CodeTooFewNS              = "authoritative_consistency_too_few_ns"
	CodeNoNS                  = "authoritative_consistency_no_ns"
)

// Finding describes a single observation produced while running the
// checker testsuite.
type Finding struct {
	// Code is a stable machine-readable identifier (e.g.
	// "authoritative_consistency_serial_drift").
	Code string `json:"code"`

	// Severity grades the finding.
	Severity Severity `json:"severity"`

	// Message is a human-readable explanation.
	Message string `json:"message"`

	// Server is the name server the finding applies to, when the issue is
	// scoped to a specific NS. Empty for zone-wide findings.
	Server string `json:"server,omitempty"`

	// Addr is the IP:port actually queried when the issue was raised. Useful
	// to distinguish IPv4/IPv6 problems on the same NS name.
	Addr string `json:"addr,omitempty"`
}

// NSResult is the per-name-server view of the zone, populated during Collect.
// It carries every signal the evaluator needs to decide whether the zone is
// propagated correctly, plus what the UI needs to render an actionable
// report.
type NSResult struct {
	// Name is the NS hostname (FQDN, lowercase).
	Name string `json:"name"`

	// Addresses is the list of A/AAAA addresses tried for this NS.
	Addresses []string `json:"addresses,omitempty"`

	// ResolveError is set when no address could be resolved for this NS.
	ResolveError string `json:"resolve_error,omitempty"`

	// UDPReachable is true when the NS answered at least once over UDP/53.
	UDPReachable bool `json:"udp_reachable"`

	// TCPReachable is true when the NS answered at least once over TCP/53.
	TCPReachable bool `json:"tcp_reachable"`

	// Authoritative is true when at least one authoritative (AA=1) answer
	// was received for the zone.
	Authoritative bool `json:"authoritative"`

	// Serial is the SOA serial returned by this NS (0 when not reachable or
	// the answer does not carry a SOA).
	Serial uint32 `json:"serial,omitempty"`

	// SOA is the full SOA RR returned by this NS, useful for per-field
	// comparison in the report.
	SOA *dns.SOA `json:"soa,omitempty"`

	// NSRRset is the NS RRset this server returns for the zone (lowercase
	// FQDNs).
	NSRRset []string `json:"ns_rrset,omitempty"`

	// EDNSSupported is true when the NS answered correctly to an EDNS0
	// query.
	EDNSSupported bool `json:"edns_supported"`

	// LatencyMs is the duration (milliseconds) of the SOA query used for
	// the reachability test. 0 when not reachable.
	LatencyMs int64 `json:"latency_ms,omitempty"`

	// Errors collects low-level query errors encountered while probing this
	// NS. Exposed to help operators debug network/firewall issues. Capped
	// at maxNSResultErrors entries; appendError is the only intended writer.
	Errors []string `json:"errors,omitempty"`

	// suppressedErrors counts the messages that were dropped after the cap
	// was reached. Reflected back into Errors as a sentinel line so the
	// operator knows the list is truncated.
	suppressedErrors int
}

// appendError records a probe error on the NS result, deduplicating identical
// messages and capping the total to maxNSResultErrors. Suppressed entries are
// summarised in a trailing sentinel.
func (n *NSResult) appendError(format string, args ...any) {
	msg := fmt.Sprintf(format, args...)
	for _, e := range n.Errors {
		if e == msg {
			return
		}
	}
	if len(n.Errors) >= maxNSResultErrors {
		n.suppressedErrors++
		sentinel := fmt.Sprintf("(%d more error(s) suppressed)", n.suppressedErrors)
		// Replace the previous sentinel in place when present.
		if last := len(n.Errors) - 1; last >= 0 && len(n.Errors[last]) > 0 && n.Errors[last][0] == '(' {
			n.Errors[last] = sentinel
			return
		}
		n.Errors = append(n.Errors, sentinel)
		return
	}
	n.Errors = append(n.Errors, msg)
}

// ObservationData is the observation payload stored by the checker. It
// carries every finding emitted by the testsuite plus the raw observed state
// from each authoritative server.
type ObservationData struct {
	// Zone is the FQDN of the zone under test.
	Zone string `json:"zone"`

	// HasSOA indicates whether the service declares a SOA record (Origin
	// versus NSOnlyOrigin). Drives which tests run.
	HasSOA bool `json:"has_soa"`

	// DeclaredSerial is the SOA serial saved in happyDomain for this zone.
	// Zero when the service is an NSOnlyOrigin.
	DeclaredSerial uint32 `json:"declared_serial,omitempty"`

	// DeclaredNS is the list of NS hostnames declared by the service,
	// lowercased and FQDN-normalized.
	DeclaredNS []string `json:"declared_ns,omitempty"`

	// ParentNS is the list of NS hostnames returned by the parent zone's
	// referral, when parent discovery is enabled. Empty when the parent
	// query is disabled or failed (see ParentQueryError).
	ParentNS []string `json:"parent_ns,omitempty"`

	// ParentQueryError is set when the parent referral query failed.
	ParentQueryError string `json:"parent_query_error,omitempty"`

	// Probed is the final list of NS names that were actually probed
	// (union of DeclaredNS and ParentNS, de-duplicated).
	Probed []string `json:"probed,omitempty"`

	// Results holds the per-NS probe results, keyed by NS hostname.
	Results map[string]*NSResult `json:"results,omitempty"`

	// Findings is the list of issues / observations produced by the run,
	// ordered by (severity desc, code asc, server asc).
	Findings []Finding `json:"findings"`
}

// originService is the minimal local mirror of happyDomain's
// `services/abstract.Origin` type. It is duplicated on purpose so that this
// checker does not have to import the (heavy) happyDomain server module
// just to decode the service payload. github.com/miekg/dns marshals
// dns.SOA / dns.NS to JSON in the same shape happyDomain uses.
type originService struct {
	SOA         *dns.SOA  `json:"soa,omitempty"`
	NameServers []*dns.NS `json:"ns"`
}

// serviceMessage is the minimal local mirror of happyDomain's ServiceMessage
// envelope. We only need the embedded service JSON and the type tag; the
// rest of the meta fields are ignored.
type serviceMessage struct {
	Type    string          `json:"_svctype"`
	Domain  string          `json:"_domain"`
	Service json.RawMessage `json:"Service"`
}