package checker

import (
	"context"
	"fmt"
	"strings"

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

func Rule() sdk.CheckRule {
	return &smtpRule{}
}

type smtpRule struct{}

func (r *smtpRule) Name() string {
	return "smtp_server"
}

func (r *smtpRule) Description() string {
	return "Checks MX discovery, SMTP connectivity, STARTTLS, PTR/FCrDNS and mail-acceptance posture for an email-receiving domain"
}

func (r *smtpRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, opts sdk.CheckerOptions) sdk.CheckState {
	var data SMTPData
	if err := obs.Get(ctx, ObservationKeySMTP, &data); err != nil {
		return sdk.CheckState{
			Status:  sdk.StatusError,
			Message: fmt.Sprintf("failed to load SMTP observation: %v", err),
			Code:    "smtp.observation_error",
		}
	}

	issues := append([]Issue(nil), data.Issues...)

	// Fold related TLS observations so cert/chain problems show up on the
	// SMTP service page without requiring the user to open a separate
	// report.
	related, _ := obs.GetRelated(ctx, TLSRelatedKey)
	issues = append(issues, tlsIssuesFromRelated(related)...)

	worst := sdk.StatusOK
	critMsgs, warnMsgs := []string{}, []string{}
	var firstCritCode, firstWarnCode string

	for _, is := range issues {
		switch is.Severity {
		case SeverityCrit:
			if worst < sdk.StatusCrit {
				worst = sdk.StatusCrit
			}
			if firstCritCode == "" {
				firstCritCode = is.Code
			}
			critMsgs = append(critMsgs, is.Message)
		case SeverityWarn:
			if worst < sdk.StatusWarn {
				worst = sdk.StatusWarn
			}
			if firstWarnCode == "" {
				firstWarnCode = is.Code
			}
			warnMsgs = append(warnMsgs, is.Message)
		}
	}

	// Null-MX is a *declared* refusal of mail; it's an INFO, not a fail.
	if data.MX.NullMX {
		return sdk.CheckState{
			Status:  sdk.StatusInfo,
			Message: "Domain refuses all email via null MX (RFC 7505).",
			Code:    CodeNullMX,
			Meta: map[string]any{
				"null_mx": true,
			},
		}
	}

	meta := map[string]any{
		"has_ipv4":          data.Coverage.HasIPv4,
		"has_ipv6":          data.Coverage.HasIPv6,
		"any_starttls":      data.Coverage.AnySTARTTLS,
		"all_starttls":      data.Coverage.AllSTARTTLS,
		"all_accept_mail":   data.Coverage.AllAcceptMail,
		"mx_count":          len(data.MX.Records),
		"endpoint_count":    len(data.Endpoints),
		"native_issues":     len(data.Issues),
		"related_tls_count": len(related),
	}

	switch worst {
	case sdk.StatusOK:
		return sdk.CheckState{
			Status:  sdk.StatusOK,
			Message: fmt.Sprintf("SMTP operational (%d MX, %d endpoints, TLS=%v)", len(data.MX.Records), len(data.Endpoints), data.Coverage.AllSTARTTLS),
			Code:    "smtp.ok",
			Meta:    meta,
		}
	case sdk.StatusWarn:
		return sdk.CheckState{
			Status:  sdk.StatusWarn,
			Message: "SMTP works with warnings: " + joinTop(warnMsgs, 2),
			Code:    firstWarnCode,
			Meta:    meta,
		}
	default:
		return sdk.CheckState{
			Status:  sdk.StatusCrit,
			Message: "SMTP broken: " + joinTop(critMsgs, 2),
			Code:    firstCritCode,
			Meta:    meta,
		}
	}
}

func joinTop(msgs []string, n int) string {
	if len(msgs) == 0 {
		return ""
	}
	if len(msgs) <= n {
		return strings.Join(msgs, "; ")
	}
	return strings.Join(msgs[:n], "; ") + fmt.Sprintf(" (+%d more)", len(msgs)-n)
}