package dav

import (
	"encoding/json"
	"fmt"
	"net"
	"strconv"
	"strings"
	"time"

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

// TLSRelatedKey is the observation key we expect a TLS checker to publish for
// the endpoints we discover. Matches the cross-checker convention documented
// in happydomain3/docs/checker-discovery-endpoint.md.
const TLSRelatedKey sdk.ObservationKey = "tls_probes"

// tlsProbeView is a permissive decode of a TLS probe payload. We intentionally
// only read the fields we need and tolerate missing ones; the TLS checker's
// full schema is owned by that checker.
type tlsProbeView struct {
	Host        string `json:"host,omitempty"`
	Port        uint16 `json:"port,omitempty"`
	Endpoint    string `json:"endpoint,omitempty"`
	TLSVersion  string `json:"tls_version,omitempty"`
	CipherSuite string `json:"cipher_suite,omitempty"`

	HostnameMatch *bool     `json:"hostname_match,omitempty"`
	ChainValid    *bool     `json:"chain_valid,omitempty"`
	NotAfter      time.Time `json:"not_after,omitempty"`

	// Alternative shape used by the reference checker-tls payload sketched
	// in the docs: cert.{notAfter, sanMatch, chainValid, daysRemaining}.
	Cert *struct {
		NotAfter      time.Time `json:"notAfter,omitempty"`
		SANMatch      *bool     `json:"sanMatch,omitempty"`
		ChainValid    *bool     `json:"chainValid,omitempty"`
		DaysRemaining *int      `json:"daysRemaining,omitempty"`
		SubjectCN     string    `json:"subjectCN,omitempty"`
		IssuerCN      string    `json:"issuerCN,omitempty"`
	} `json:"cert,omitempty"`

	Rules []struct {
		Code    string `json:"code,omitempty"`
		Status  string `json:"status,omitempty"`
		Message string `json:"message,omitempty"`
	} `json:"rules,omitempty"`

	Issues []struct {
		Code     string `json:"code,omitempty"`
		Severity string `json:"severity,omitempty"`
		Message  string `json:"message,omitempty"`
		Fix      string `json:"fix,omitempty"`
	} `json:"issues,omitempty"`
}

// address returns the canonical "host:port" string used to match a probe
// against one of our discovered endpoints.
func (v *tlsProbeView) address() string {
	if v.Endpoint != "" {
		return v.Endpoint
	}
	if v.Host != "" && v.Port != 0 {
		return net.JoinHostPort(v.Host, strconv.Itoa(int(v.Port)))
	}
	return ""
}

// certExpiry normalises the two schema shapes into a single (t, ok) pair so
// callers don't have to know which one the TLS checker emits.
func (v *tlsProbeView) certExpiry() (time.Time, bool) {
	if !v.NotAfter.IsZero() {
		return v.NotAfter, true
	}
	if v.Cert != nil && !v.Cert.NotAfter.IsZero() {
		return v.Cert.NotAfter, true
	}
	return time.Time{}, false
}

func (v *tlsProbeView) hostnameOK() (bool, bool) {
	if v.HostnameMatch != nil {
		return *v.HostnameMatch, true
	}
	if v.Cert != nil && v.Cert.SANMatch != nil {
		return *v.Cert.SANMatch, true
	}
	return false, false
}

func (v *tlsProbeView) chainOK() (bool, bool) {
	if v.ChainValid != nil {
		return *v.ChainValid, true
	}
	if v.Cert != nil && v.Cert.ChainValid != nil {
		return *v.Cert.ChainValid, true
	}
	return false, false
}

// parseTLSRelated decodes a RelatedObservation as a TLS probe, returning nil
// when the payload doesn't look like one.
//
// Two payload shapes are accepted:
//
//  1. {"probes": {"<ref>": <probe>, …}}: the current convention used by
//     checker-tls. Each consumer picks its own probe via r.Ref; the value
//     is the DiscoveryEntry.Ref that the producer originally emitted,
//     preserved by the host along the lineage chain.
//  2. <probe>: a single top-level probe object, kept for back-compat with
//     callers that pre-date the keyed map and with unit-test fixtures.
func parseTLSRelated(r sdk.RelatedObservation) *tlsProbeView {
	var keyed struct {
		Probes map[string]tlsProbeView `json:"probes"`
	}
	if err := json.Unmarshal(r.Data, &keyed); err == nil && keyed.Probes != nil {
		if p, ok := keyed.Probes[r.Ref]; ok {
			return &p
		}
		return nil
	}
	var v tlsProbeView
	if err := json.Unmarshal(r.Data, &v); err != nil {
		return nil
	}
	return &v
}

// TLSSummary is what the HTML report renders for each probed endpoint.
type TLSSummary struct {
	Address       string
	TLSVersion    string
	Status        string // "ok", "warn", "fail", "info"
	Detail        string
	NotAfter      time.Time
	DaysRemaining int
}

// tlsCallout captures a cross-checker issue we want to foreground in the
// "Action items" section of the HTML report.
type tlsCallout struct {
	Severity string // "warn" or "crit"
	Title    string
	Body     string
}

// foldTLSRelated walks the TLS probes and returns (1) a per-endpoint summary
// for rendering, (2) callouts for the top of the report when there's anything
// actionable. Callers pass both through the reportData pipeline.
func foldTLSRelated(related []sdk.RelatedObservation) (summaries []TLSSummary, callouts []tlsCallout) {
	for _, r := range related {
		v := parseTLSRelated(r)
		if v == nil {
			continue
		}
		sum := buildTLSSummary(v)
		summaries = append(summaries, sum)
		callouts = append(callouts, buildTLSCallouts(v, sum.Address)...)
	}
	return summaries, callouts
}

func buildTLSSummary(v *tlsProbeView) TLSSummary {
	s := TLSSummary{Address: v.address(), TLSVersion: v.TLSVersion, Status: "ok"}

	if t, ok := v.certExpiry(); ok {
		s.NotAfter = t
		days := int(time.Until(t) / (24 * time.Hour))
		if v.Cert != nil && v.Cert.DaysRemaining != nil {
			days = *v.Cert.DaysRemaining
		}
		s.DaysRemaining = days
		switch {
		case days < 0:
			s.Status = "fail"
			s.Detail = fmt.Sprintf("certificate expired %d day(s) ago", -days)
		case days < 14:
			s.Status = "warn"
			s.Detail = fmt.Sprintf("certificate expires in %d day(s)", days)
		default:
			s.Detail = fmt.Sprintf("certificate valid for %d day(s)", days)
		}
	}

	if ok, has := v.hostnameOK(); has && !ok {
		s.Status = "fail"
		s.Detail = "certificate does not cover the endpoint hostname"
	}
	if ok, has := v.chainOK(); has && !ok {
		s.Status = "fail"
		s.Detail = "certificate chain validation failed"
	}

	// Explicit issues from the TLS checker outrank our inferred status.
	for _, iss := range v.Issues {
		sev := strings.ToLower(iss.Severity)
		switch sev {
		case "crit":
			s.Status = "fail"
		case "warn":
			if s.Status != "fail" {
				s.Status = "warn"
			}
		}
		if iss.Message != "" {
			s.Detail = iss.Message
		}
	}
	return s
}

func buildTLSCallouts(v *tlsProbeView, addr string) []tlsCallout {
	var out []tlsCallout

	// Structured issues from the TLS checker are the preferred source.
	for _, iss := range v.Issues {
		sev := strings.ToLower(iss.Severity)
		if sev != "crit" && sev != "warn" {
			continue
		}
		callout := tlsCallout{
			Severity: sev,
			Title:    fmt.Sprintf("TLS on %s: %s", addr, strings.TrimSpace(iss.Message)),
		}
		if callout.Title == "TLS on "+addr+": " {
			callout.Title = "TLS issue on " + addr
		}
		if iss.Fix != "" {
			callout.Body = iss.Fix
		} else {
			callout.Body = "See the TLS checker report for details."
		}
		out = append(out, callout)
	}
	if len(out) > 0 {
		return out
	}

	// Fallback: synthesize callouts from structured flags.
	if t, ok := v.certExpiry(); ok {
		days := int(time.Until(t) / (24 * time.Hour))
		if v.Cert != nil && v.Cert.DaysRemaining != nil {
			days = *v.Cert.DaysRemaining
		}
		switch {
		case days < 0:
			out = append(out, tlsCallout{
				Severity: "crit",
				Title:    fmt.Sprintf("Certificate on %s has expired", addr),
				Body:     fmt.Sprintf("Renew it. Clients will refuse to connect. Expired %d day(s) ago (valid until %s).", -days, t.Format(time.RFC3339)),
			})
		case days < 14:
			out = append(out, tlsCallout{
				Severity: "warn",
				Title:    fmt.Sprintf("Certificate on %s expires in %d day(s)", addr, days),
				Body:     fmt.Sprintf("Schedule a renewal. Currently valid until %s.", t.Format(time.RFC3339)),
			})
		}
	}
	if ok, has := v.chainOK(); has && !ok {
		out = append(out, tlsCallout{
			Severity: "crit",
			Title:    fmt.Sprintf("Broken certificate chain on %s", addr),
			Body:     "The TLS checker could not validate the chain. Ensure the server sends the full intermediate chain.",
		})
	}
	if ok, has := v.hostnameOK(); has && !ok {
		out = append(out, tlsCallout{
			Severity: "crit",
			Title:    fmt.Sprintf("Certificate does not cover %s", addr),
			Body:     "Add the hostname to the certificate's SANs or point the service at a cert that covers it.",
		})
	}
	return out
}