package checker

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

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

// legacyRecordsRule emits one CheckState per distinct legacy record type
// found in the zone (not one per occurrence). This matches how operators
// think about remediation ("fix the SPF record" is one task even when
// the zone has six SPF records) and keeps the report's "fix these first"
// section focused.
type legacyRecordsRule struct{}

func (r *legacyRecordsRule) Name() string { return "legacy_records" }

func (r *legacyRecordsRule) Description() string {
	return "Detects DNS record types deprecated by the IETF (SPF, A6, KEY/SIG/NXT, WKS, MD/MF, NSAP, …) and reports each occurrence with the relevant RFC reference and a migration suggestion."
}

func (r *legacyRecordsRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, opts sdk.CheckerOptions) []sdk.CheckState {
	var data LegacyData
	if err := obs.Get(ctx, ObservationKeyLegacy, &data); err != nil {
		return []sdk.CheckState{{
			Status:   sdk.StatusError,
			Message:  fmt.Sprintf("failed to load legacy-records observation: %v", err),
			RuleName: r.Name(),
			Code:     "legacy_records_error",
		}}
	}

	if len(data.Findings) == 0 {
		// Even with zero findings we acknowledge the scan so the report
		// does not look empty. CollectErrors are surfaced as Info so a
		// silent-skip path doesn't masquerade as a clean pass.
		states := []sdk.CheckState{{
			Status:   sdk.StatusOK,
			Message:  fmt.Sprintf("No legacy record types detected (%d service(s) scanned)", data.ServicesScanned),
			RuleName: r.Name(),
			Code:     "legacy_records_clean",
		}}
		for _, e := range data.CollectErrors {
			states = append(states, sdk.CheckState{
				Status:   sdk.StatusInfo,
				Message:  "Skipped during scan: " + e,
				RuleName: r.Name(),
				Code:     "legacy_records_skip",
			})
		}
		return states
	}

	groups := groupFindings(data.Findings)
	out := make([]sdk.CheckState, 0, len(groups))
	for _, g := range groups {
		info := deprecatedTypes[g.Rrtype]
		out = append(out, sdk.CheckState{
			Status:   severityToStatus(info.Severity),
			Message:  buildMessage(g, info),
			RuleName: r.Name(),
			Code:     "legacy_" + strings.ToLower(g.TypeName),
			Subject:  g.TypeName,
			Meta: map[string]any{
				"rrtype":      g.Rrtype,
				"type":        g.TypeName,
				"reason":      info.Reason,
				"replacement": info.Replacement,
				"how_to_fix":  info.HowToFix,
				"severity":    info.Severity.String(),
				"locations":   g.Locations,
			},
		})
	}
	return out
}

func severityToStatus(s DeprecatedSeverity) sdk.Status {
	switch s {
	case SeverityCrit:
		return sdk.StatusCrit
	case SeverityWarn:
		return sdk.StatusWarn
	default:
		return sdk.StatusInfo
	}
}

func buildMessage(g groupedFinding, info DeprecationInfo) string {
	loc := "1 occurrence"
	if n := len(g.Locations); n > 1 {
		loc = fmt.Sprintf("%d occurrences", n)
	}
	if info.Replacement != "" {
		return fmt.Sprintf("%s record found (%s). %s; use %s instead.",
			g.TypeName, loc, info.Reason, info.Replacement)
	}
	return fmt.Sprintf("%s record found (%s). %s.",
		g.TypeName, loc, info.Reason)
}

// groupedFinding aggregates Finding entries by record type so the rule
// emits one CheckState per type, with Locations carrying the per-instance
// detail for the report.
type groupedFinding struct {
	Rrtype    uint16
	TypeName  string
	Locations []FindingLocation
}

type FindingLocation struct {
	Subdomain   string `json:"subdomain"`
	Name        string `json:"name,omitempty"`
	ServiceType string `json:"service_type,omitempty"`
}

func groupFindings(fs []Finding) []groupedFinding {
	bytype := map[uint16]*groupedFinding{}
	for _, f := range fs {
		g, ok := bytype[f.Rrtype]
		if !ok {
			g = &groupedFinding{Rrtype: f.Rrtype, TypeName: f.TypeName}
			bytype[f.Rrtype] = g
		}
		g.Locations = append(g.Locations, FindingLocation{
			Subdomain:   f.Subdomain,
			Name:        f.Name,
			ServiceType: f.ServiceType,
		})
	}

	out := make([]groupedFinding, 0, len(bytype))
	for _, g := range bytype {
		sort.SliceStable(g.Locations, func(i, j int) bool {
			return g.Locations[i].Subdomain < g.Locations[j].Subdomain
		})
		out = append(out, *g)
	}
	// Sort groups by descending severity then by type name so the most
	// urgent finding bubbles to the top of the rule output (the report
	// preserves this order when ranking the "fix this first" card).
	sort.SliceStable(out, func(i, j int) bool {
		si := deprecatedTypes[out[i].Rrtype].Severity
		sj := deprecatedTypes[out[j].Rrtype].Severity
		if si != sj {
			return si > sj
		}
		return out[i].TypeName < out[j].TypeName
	})
	return out
}