// Package checker implements the STUN/TURN checker for happyDomain.
//
// The checker drives a target server through the STUN binding and TURN
// allocation/relay protocols (RFC 5389, RFC 5766) using the Pion libraries,
// then exposes a structured observation and a rich HTML report including
// remediation guidance for the most common deployment mistakes.
package checker

import (
	"time"

	sdk "git.happydns.org/checker-sdk-go/checker"
)

// ObservationKeyStunTurn is the observation key for STUN/TURN test data.
const ObservationKeyStunTurn sdk.ObservationKey = "stun_turn"

// Transport identifies the L4/L4-secure transport used to reach an endpoint.
type Transport string

const (
	TransportUDP  Transport = "udp"
	TransportTCP  Transport = "tcp"
	TransportTLS  Transport = "tls"
	TransportDTLS Transport = "dtls"
)

// Endpoint is a single resolved server target to probe.
type Endpoint struct {
	URI       string    `json:"uri"`
	Host      string    `json:"host"`
	Port      uint16    `json:"port"`
	Transport Transport `json:"transport"`
	Secure    bool      `json:"secure"`
	IsTURN    bool      `json:"is_turn"` // false: STUN-only scheme, true: TURN scheme
	Source    string    `json:"source"`  // "uri" or "srv:_turn._udp.example.com"
}

// SubTestStatus mirrors sdk.Status as a string for JSON friendliness.
type SubTestStatus string

const (
	SubTestOK      SubTestStatus = "ok"
	SubTestInfo    SubTestStatus = "info"
	SubTestWarn    SubTestStatus = "warn"
	SubTestCrit    SubTestStatus = "crit"
	SubTestSkipped SubTestStatus = "skipped"
	SubTestError   SubTestStatus = "error"
)

// SubTest is one fine-grained test executed against an endpoint.
type SubTest struct {
	Name       string        `json:"name"`
	Status     SubTestStatus `json:"status"`
	DurationMs int64         `json:"duration_ms"`
	Detail     string        `json:"detail,omitempty"`
	Error      string        `json:"error,omitempty"`
	Fix        string        `json:"fix,omitempty"`
}

// EndpointReport gathers all sub-tests run against a single endpoint.
type EndpointReport struct {
	Endpoint Endpoint  `json:"endpoint"`
	SubTests []SubTest `json:"sub_tests"`
}

// Worst returns the worst sub-test status of the endpoint.
func (e EndpointReport) Worst() SubTestStatus {
	worst := SubTestOK
	for _, t := range e.SubTests {
		if statusRank(t.Status) > statusRank(worst) {
			worst = t.Status
		}
	}
	return worst
}

// FirstFailure returns the first non-OK/Info/Skipped sub-test.
func (e EndpointReport) FirstFailure() *SubTest {
	for i := range e.SubTests {
		s := e.SubTests[i].Status
		if s != SubTestOK && s != SubTestInfo && s != SubTestSkipped {
			return &e.SubTests[i]
		}
	}
	return nil
}

// StunTurnData is the JSON-serializable observation payload.
type StunTurnData struct {
	Zone        string           `json:"zone,omitempty"`
	Mode        string           `json:"mode,omitempty"`
	CollectedAt time.Time        `json:"collected_at"`
	Endpoints   []EndpointReport `json:"endpoints"`
	GlobalError string           `json:"global_error,omitempty"`
}

// statusRank converts a SubTestStatus to an orderable severity.
func statusRank(s SubTestStatus) int {
	switch s {
	case SubTestOK:
		return 0
	case SubTestSkipped:
		return 1
	case SubTestInfo:
		return 2
	case SubTestWarn:
		return 3
	case SubTestCrit:
		return 4
	case SubTestError:
		return 5
	}
	return -1
}

// toSDKStatus converts the worst SubTestStatus seen to an sdk.Status.
func toSDKStatus(s SubTestStatus) sdk.Status {
	switch s {
	case SubTestOK:
		return sdk.StatusOK
	case SubTestInfo, SubTestSkipped:
		return sdk.StatusInfo
	case SubTestWarn:
		return sdk.StatusWarn
	case SubTestCrit:
		return sdk.StatusCrit
	case SubTestError:
		return sdk.StatusError
	}
	return sdk.StatusUnknown
}