package checker

import (
	"context"
	"fmt"

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

// cnameCoexistenceRule flags sibling RRsets at the CNAME's owner (RFC 1034
// §3.6.2, RFC 2181 §10.1). Severity follows the shared allowApexCNAME option
// when the owner is the apex; A/AAAA siblings at apex are excused when the
// zone publishes ALIAS/ANAME flattening and recognizeApexFlattening is on.
type cnameCoexistenceRule struct{}

func (cnameCoexistenceRule) Name() string { return "cname_coexistence" }
func (cnameCoexistenceRule) Description() string {
	return "Flags other RRsets that sit at the same owner as a CNAME (RFC 1034 §3.6.2 / RFC 2181 §10.1). Honours allowApexCNAME and recognizeApexFlattening."
}

func (cnameCoexistenceRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, opts sdk.CheckerOptions) []sdk.CheckState {
	data, errState := loadAlias(ctx, obs)
	if errState != nil {
		return errState
	}
	if !apexKnown(data) {
		return skipped("apex lookup failed")
	}
	if !data.OwnerHasCNAME {
		return skipped("owner has no CNAME")
	}
	if len(data.Coexisting) == 0 {
		return okState(data.Owner, "CNAME is the only RRset at its owner")
	}

	isApex := data.OwnerIsApex
	recognize := recognizeApexFlattening(opts)
	allow := allowApexCNAME(opts)

	var out []sdk.CheckState
	for _, rr := range data.Coexisting {
		// A/AAAA at apex alongside a CNAME is excused when we recognise
		// ALIAS/ANAME flattening: two different owners cannot legally
		// coexist, but a provider-side flattener can still serve that.
		if isApex && recognize && data.ApexFlattening && (rr.Type == "A" || rr.Type == "AAAA") {
			continue
		}
		status := sdk.StatusCrit
		if isApex && allow {
			status = sdk.StatusWarn
		}
		out = append(out, withHint(sdk.CheckState{
			Status:  status,
			Subject: data.Owner,
			Message: fmt.Sprintf("%s and CNAME both exist at %s (RFC 1034 §3.6.2 / RFC 2181 §10.1)", rr.Type, data.Owner),
			Code:    rr.Type,
		}, "Remove the sibling record or move it under a different label; a name cannot simultaneously carry a CNAME and other data."))
	}
	if len(out) == 0 {
		return okState(data.Owner, "CNAME coexistence exempted by ALIAS/ANAME flattening")
	}
	return out
}