package checker

import (
	"context"
	"fmt"
	"strings"
	"time"

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

// peerCertificateRule flags successful handshakes in which the server sent
// no certificate. This is distinct from chain validity: if no cert was sent,
// hostname/chain/expiry cannot be evaluated.
type peerCertificateRule struct{}

func (r *peerCertificateRule) Name() string { return "tls.peer_certificate_present" }
func (r *peerCertificateRule) Description() string {
	return "Verifies the server presented a certificate during the TLS handshake."
}

func (r *peerCertificateRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, _ sdk.CheckerOptions) []sdk.CheckState {
	data, errSt := loadData(ctx, obs)
	if errSt != nil {
		return []sdk.CheckState{*errSt}
	}
	if len(data.Probes) == 0 {
		return []sdk.CheckState{emptyCaseState("tls.peer_certificate_present.no_endpoints")}
	}

	var out []sdk.CheckState
	anyHandshake := false
	for _, ref := range sortedRefs(data) {
		p := data.Probes[ref]
		if !p.TLSHandshakeOK {
			continue
		}
		anyHandshake = true
		if !p.NoPeerCert {
			continue
		}
		out = append(out, sdk.CheckState{
			Status:  sdk.StatusCrit,
			Code:    "tls.peer_certificate_present.missing",
			Subject: subjectOf(p),
			Message: fmt.Sprintf("Server on %s completed the handshake but presented no certificate.", p.Endpoint),
			Meta:    metaOf(p),
		})
	}
	if !anyHandshake {
		return []sdk.CheckState{unknownState(
			"tls.peer_certificate_present.skipped",
			"No endpoint completed a TLS handshake.",
		)}
	}
	if len(out) == 0 {
		return []sdk.CheckState{passState(
			"tls.peer_certificate_present.ok",
			"Every endpoint presented a certificate.",
		)}
	}
	return out
}

// chainValidityRule flags invalid certificate chains.
type chainValidityRule struct{}

func (r *chainValidityRule) Name() string { return "tls.chain_validity" }
func (r *chainValidityRule) Description() string {
	return "Verifies the presented certificate chain validates against the system trust store."
}

func (r *chainValidityRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, _ sdk.CheckerOptions) []sdk.CheckState {
	data, errSt := loadData(ctx, obs)
	if errSt != nil {
		return []sdk.CheckState{*errSt}
	}
	if len(data.Probes) == 0 {
		return []sdk.CheckState{emptyCaseState("tls.chain_validity.no_endpoints")}
	}

	var out []sdk.CheckState
	any := false
	for _, ref := range sortedRefs(data) {
		p := data.Probes[ref]
		if p.ChainValid == nil {
			continue
		}
		any = true
		if *p.ChainValid {
			continue
		}
		msg := "Invalid certificate chain"
		if p.ChainVerifyErr != "" {
			msg = "Invalid certificate chain: " + p.ChainVerifyErr
		}
		out = append(out, sdk.CheckState{
			Status:  sdk.StatusCrit,
			Code:    "tls.chain_validity.invalid",
			Subject: subjectOf(p),
			Message: msg,
			Meta:    metaOf(p),
		})
	}
	if !any {
		return []sdk.CheckState{unknownState(
			"tls.chain_validity.skipped",
			"No endpoint yielded a certificate chain to verify.",
		)}
	}
	if len(out) == 0 {
		return []sdk.CheckState{passState(
			"tls.chain_validity.ok",
			"Every presented chain validates against the system trust store.",
		)}
	}
	return out
}

// hostnameMatchRule flags endpoints whose leaf cert does not cover the SNI
// the probe used.
type hostnameMatchRule struct{}

func (r *hostnameMatchRule) Name() string { return "tls.hostname_match" }
func (r *hostnameMatchRule) Description() string {
	return "Verifies the leaf certificate covers the probed hostname (SNI)."
}

func (r *hostnameMatchRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, _ sdk.CheckerOptions) []sdk.CheckState {
	data, errSt := loadData(ctx, obs)
	if errSt != nil {
		return []sdk.CheckState{*errSt}
	}
	if len(data.Probes) == 0 {
		return []sdk.CheckState{emptyCaseState("tls.hostname_match.no_endpoints")}
	}

	var out []sdk.CheckState
	any := false
	for _, ref := range sortedRefs(data) {
		p := data.Probes[ref]
		if p.HostnameMatch == nil {
			continue
		}
		any = true
		if *p.HostnameMatch {
			continue
		}
		out = append(out, sdk.CheckState{
			Status:  sdk.StatusCrit,
			Code:    "tls.hostname_match.mismatch",
			Subject: subjectOf(p),
			Message: fmt.Sprintf("Certificate does not cover %q (SANs: %s)", p.SNI, strings.Join(p.DNSNames, ", ")),
			Meta:    metaOf(p),
		})
	}
	if !any {
		return []sdk.CheckState{unknownState(
			"tls.hostname_match.skipped",
			"No endpoint yielded a certificate to hostname-match.",
		)}
	}
	if len(out) == 0 {
		return []sdk.CheckState{passState(
			"tls.hostname_match.ok",
			"Every certificate covers its probed SNI.",
		)}
	}
	return out
}

// expiryRule flags expired or near-expiry certificates.
type expiryRule struct{}

func (r *expiryRule) Name() string { return "tls.expiry" }
func (r *expiryRule) Description() string {
	return "Flags expired or soon-to-expire leaf certificates."
}

func (r *expiryRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, _ sdk.CheckerOptions) []sdk.CheckState {
	data, errSt := loadData(ctx, obs)
	if errSt != nil {
		return []sdk.CheckState{*errSt}
	}
	if len(data.Probes) == 0 {
		return []sdk.CheckState{emptyCaseState("tls.expiry.no_endpoints")}
	}

	now := time.Now()
	var out []sdk.CheckState
	any := false
	for _, ref := range sortedRefs(data) {
		p := data.Probes[ref]
		if p.NotAfter.IsZero() {
			continue
		}
		any = true
		meta := metaOf(p)
		meta["not_after"] = p.NotAfter
		if p.NotAfter.Before(now) {
			out = append(out, sdk.CheckState{
				Status:  sdk.StatusCrit,
				Code:    "tls.expiry.expired",
				Subject: subjectOf(p),
				Message: "Certificate expired on " + p.NotAfter.Format(time.RFC3339),
				Meta:    meta,
			})
			continue
		}
		if p.NotAfter.Sub(now) < ExpiringSoonThreshold {
			out = append(out, sdk.CheckState{
				Status:  sdk.StatusWarn,
				Code:    "tls.expiry.expiring_soon",
				Subject: subjectOf(p),
				Message: "Certificate expires in less than 14 days (" + p.NotAfter.Format(time.RFC3339) + ")",
				Meta:    meta,
			})
		}
	}
	if !any {
		return []sdk.CheckState{unknownState(
			"tls.expiry.skipped",
			"No endpoint yielded a certificate with an expiry to check.",
		)}
	}
	if len(out) == 0 {
		return []sdk.CheckState{passState(
			"tls.expiry.ok",
			"Every leaf certificate is valid for more than 14 days.",
		)}
	}
	return out
}