package checker

import (
	"context"
	"fmt"
	"sort"
	"strings"

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

// serialDriftRule flags disagreement between resolvers on the SOA serial.
type serialDriftRule struct{}

func (r *serialDriftRule) Name() string { return "resolver_propagation.serial_drift" }
func (r *serialDriftRule) Description() string {
	return "Flags disagreement on the SOA serial across unfiltered resolvers."
}
func (r *serialDriftRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, _ sdk.CheckerOptions) []sdk.CheckState {
	data, errSt := loadData(ctx, obs)
	if errSt != nil {
		return []sdk.CheckState{*errSt}
	}
	soaKey := rrsetKey(data.Zone, "SOA")
	if data.RRsets[soaKey] == nil {
		return []sdk.CheckState{{Status: sdk.StatusUnknown,
			Code:    "resolver_propagation.serial_drift.skipped",
			Message: "SOA was not probed"}}
	}
	serials := map[uint32][]string{}
	for _, rv := range data.Resolvers {
		if rv.Filtered {
			continue
		}
		p := rv.Probes[soaKey]
		if p == nil || p.Error != "" || p.Rcode != "NOERROR" {
			continue
		}
		if s := extractSerial(p.Records); s != 0 {
			serials[s] = append(serials[s], rv.ID)
		}
	}
	if len(serials) < 2 {
		return []sdk.CheckState{passState("resolver_propagation.serial_drift.ok",
			"SOA serial is consistent across unfiltered resolvers.")}
	}
	var parts []string
	for s, rs := range serials {
		sort.Strings(rs)
		parts = append(parts, fmt.Sprintf("serial %d on %s", s, firstN(rs, 6)))
	}
	sort.Strings(parts)
	return []sdk.CheckState{warnState(CodeSerialDrift, soaKey,
		"SOA serial differs across resolvers, "+strings.Join(parts, "; "))}
}

// staleCacheRule flags resolvers still serving a serial below the declared one.
type staleCacheRule struct{}

func (r *staleCacheRule) Name() string { return "resolver_propagation.stale_cache" }
func (r *staleCacheRule) Description() string {
	return "Flags resolvers still serving an SOA serial below the one saved by happyDomain."
}
func (r *staleCacheRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, _ sdk.CheckerOptions) []sdk.CheckState {
	data, errSt := loadData(ctx, obs)
	if errSt != nil {
		return []sdk.CheckState{*errSt}
	}
	if data.DeclaredSerial == 0 {
		return []sdk.CheckState{{Status: sdk.StatusUnknown,
			Code:    "resolver_propagation.stale_cache.skipped",
			Message: "no declared SOA serial available for comparison"}}
	}
	soaKey := rrsetKey(data.Zone, "SOA")
	if data.RRsets[soaKey] == nil {
		return []sdk.CheckState{{Status: sdk.StatusUnknown,
			Code:    "resolver_propagation.stale_cache.skipped",
			Message: "SOA was not probed"}}
	}
	var below []string
	for _, rv := range data.Resolvers {
		if rv.Filtered {
			continue
		}
		p := rv.Probes[soaKey]
		if p == nil || p.Error != "" || p.Rcode != "NOERROR" {
			continue
		}
		s := extractSerial(p.Records)
		if s != 0 && s < data.DeclaredSerial {
			below = append(below, rv.ID)
		}
	}
	if len(below) == 0 {
		return []sdk.CheckState{passState("resolver_propagation.stale_cache.ok",
			"No resolver is still serving an outdated SOA serial.")}
	}
	sort.Strings(below)
	return []sdk.CheckState{infoState(CodeStaleCache, soaKey,
		fmt.Sprintf("%d resolver(s) still return a serial below the declared one (%d): %s",
			len(below), data.DeclaredSerial, firstN(below, 6)))}
}

// dnssecRule flags DNSSEC failures (SERVFAIL or missing AD) at the zone apex
// on resolvers known to validate.
type dnssecRule struct{}

func (r *dnssecRule) Name() string { return "resolver_propagation.dnssec" }
func (r *dnssecRule) Description() string {
	return "Checks that validating resolvers successfully validate the zone's DNSSEC chain."
}
func (r *dnssecRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, _ sdk.CheckerOptions) []sdk.CheckState {
	data, errSt := loadData(ctx, obs)
	if errSt != nil {
		return []sdk.CheckState{*errSt}
	}
	soaKey := rrsetKey(data.Zone, "SOA")

	var states []sdk.CheckState
	for _, rv := range data.Resolvers {
		if rv.Filtered || !isValidatingResolver(rv.ID) {
			continue
		}
		soa := rv.Probes[soaKey]
		if soa == nil || soa.Error != "" {
			continue
		}
		switch soa.Rcode {
		case "SERVFAIL":
			states = append(states, critState(CodeDNSSECFailure, rv.ID,
				fmt.Sprintf("%s returned SERVFAIL for %s, typically a broken DNSSEC chain", rv.Name, data.Zone)))
		case "NOERROR":
			if !soa.AD {
				states = append(states, infoState(CodeDNSSECUnvalidated, rv.ID,
					fmt.Sprintf("%s did not set AD=1 for %s, zone may not be DNSSEC-signed, or signature is broken", rv.Name, data.Zone)))
			}
		}
	}
	if len(states) == 0 {
		return []sdk.CheckState{passState("resolver_propagation.dnssec.ok",
			"Validating resolvers report no DNSSEC issue.")}
	}
	return states
}