package handlers

import (
	"net/http"
	"sort"
	"time"

	"sneak.berlin/go/dnswatcher/internal/state"
)

// statusDomainInfo holds status information for a monitored domain.
// RecordsByNameserver holds the domain's own records, in the form a
// hostname's Nameservers holds the hostname's.
type statusDomainInfo struct {
	Nameservers         []string                         `json:"nameservers"`
	RecordsByNameserver map[string]*statusHostnameNSInfo `json:"recordsByNameserver"`
	LastChecked         time.Time                        `json:"lastChecked"`
}

// statusHostnameNSInfo holds per-nameserver status for a hostname.
type statusHostnameNSInfo struct {
	Records     map[string][]string `json:"records"`
	Status      string              `json:"status"`
	Error       string              `json:"error,omitempty"`
	LastChecked time.Time           `json:"lastChecked"`
}

// statusHostnameInfo holds status information for a monitored hostname.
type statusHostnameInfo struct {
	Nameservers map[string]*statusHostnameNSInfo `json:"nameservers"`
	LastChecked time.Time                        `json:"lastChecked"`
}

// statusPortInfo holds status information for a monitored port.
// Domains and Hostnames list the apex domains and the hostnames that
// resolve to its address.
type statusPortInfo struct {
	Open        bool      `json:"open"`
	Domains     []string  `json:"domains"`
	Hostnames   []string  `json:"hostnames"`
	LastChecked time.Time `json:"lastChecked"`
}

// statusCertificateInfo holds status information for a TLS certificate.
type statusCertificateInfo struct {
	CommonName              string    `json:"commonName"`
	Issuer                  string    `json:"issuer"`
	NotAfter                time.Time `json:"notAfter"`
	SubjectAlternativeNames []string  `json:"subjectAlternativeNames"`
	Status                  string    `json:"status"`
	Error                   string    `json:"error,omitempty"`
	LastChecked             time.Time `json:"lastChecked"`
}

// statusCounts holds summary counts of monitored resources.
type statusCounts struct {
	Domains      int `json:"domains"`
	Hostnames    int `json:"hostnames"`
	Ports        int `json:"ports"`
	PortsOpen    int `json:"portsOpen"`
	Certificates int `json:"certificates"`
	CertsOK      int `json:"certificatesOk"`
	CertsError   int `json:"certificatesError"`
}

// statusResponse is the full /api/v1/status response.
type statusResponse struct {
	Status       string                            `json:"status"`
	LastUpdated  time.Time                         `json:"lastUpdated"`
	Counts       statusCounts                      `json:"counts"`
	Domains      map[string]*statusDomainInfo      `json:"domains"`
	Hostnames    map[string]*statusHostnameInfo    `json:"hostnames"`
	Ports        map[string]*statusPortInfo        `json:"ports"`
	Certificates map[string]*statusCertificateInfo `json:"certificates"`
}

// HandleStatus returns the monitoring status handler.
func (h *Handlers) HandleStatus() http.HandlerFunc {
	return func(
		writer http.ResponseWriter,
		request *http.Request,
	) {
		snap := h.state.GetSnapshot()

		resp := buildStatusResponse(snap)

		h.respondJSON(
			writer, request,
			resp,
			http.StatusOK,
		)
	}
}

// buildStatusResponse constructs the full status response from
// the current monitoring snapshot.
func buildStatusResponse(
	snap state.Snapshot,
) *statusResponse {
	resp := &statusResponse{
		Status:       "ok",
		LastUpdated:  snap.LastUpdated,
		Domains:      make(map[string]*statusDomainInfo),
		Hostnames:    make(map[string]*statusHostnameInfo),
		Certificates: make(map[string]*statusCertificateInfo),
	}

	hostnames, domainRecords := splitHostnames(snap)

	buildDomains(snap, domainRecords, resp)
	buildHostnames(hostnames, resp)
	resp.Ports = buildPorts(snap)
	buildCertificates(snap, resp)
	buildCounts(resp)

	return resp
}

// splitHostnames returns the records saved in snap.Hostnames in two
// maps: the hostnames' and the apex domains' own. The watcher saves a
// domain's own records there under the domain's name, which has an
// entry in snap.Domains too.
func splitHostnames(
	snap state.Snapshot,
) (map[string]*state.HostnameState, map[string]*state.HostnameState) {
	hostnames := make(map[string]*state.HostnameState)
	domainRecords := make(map[string]*state.HostnameState)

	for name, hs := range snap.Hostnames {
		if _, isDomain := snap.Domains[name]; isDomain {
			domainRecords[name] = hs
		} else {
			hostnames[name] = hs
		}
	}

	return hostnames, domainRecords
}

func buildDomains(
	snap state.Snapshot,
	domainRecords map[string]*state.HostnameState,
	resp *statusResponse,
) {
	for name, ds := range snap.Domains {
		ns := make([]string, len(ds.Nameservers))
		copy(ns, ds.Nameservers)
		sort.Strings(ns)

		records := make(map[string]*statusHostnameNSInfo)
		if hs, ok := domainRecords[name]; ok {
			records = nameserverInfo(hs)
		}

		resp.Domains[name] = &statusDomainInfo{
			Nameservers:         ns,
			RecordsByNameserver: records,
			LastChecked:         ds.LastChecked,
		}
	}
}

func buildHostnames(
	hostnames map[string]*state.HostnameState,
	resp *statusResponse,
) {
	for name, hs := range hostnames {
		resp.Hostnames[name] = &statusHostnameInfo{
			Nameservers: nameserverInfo(hs),
			LastChecked: hs.LastChecked,
		}
	}
}

// nameserverInfo copies each nameserver's answer saved in hs.
func nameserverInfo(
	hs *state.HostnameState,
) map[string]*statusHostnameNSInfo {
	info := make(map[string]*statusHostnameNSInfo)

	for ns, nsState := range hs.RecordsByNameserver {
		recs := make(map[string][]string, len(nsState.Records))
		for rtype, vals := range nsState.Records {
			copied := make([]string, len(vals))
			copy(copied, vals)
			recs[rtype] = copied
		}

		info[ns] = &statusHostnameNSInfo{
			Records:     recs,
			Status:      nsState.Status,
			Error:       nsState.Error,
			LastChecked: nsState.LastChecked,
		}
	}

	return info
}

// buildPorts returns the port entries saved in snap. A port entry
// saves apex domains with its hostnames; they are told apart as in
// splitHostnames, by a domain entry in snap.Domains.
func buildPorts(snap state.Snapshot) map[string]*statusPortInfo {
	ports := make(map[string]*statusPortInfo, len(snap.Ports))

	for key, ps := range snap.Ports {
		domains := []string{}
		hostnames := []string{}

		for _, name := range ps.Hostnames {
			if _, isDomain := snap.Domains[name]; isDomain {
				domains = append(domains, name)
			} else {
				hostnames = append(hostnames, name)
			}
		}

		sort.Strings(domains)
		sort.Strings(hostnames)

		ports[key] = &statusPortInfo{
			Open:        ps.Open,
			Domains:     domains,
			Hostnames:   hostnames,
			LastChecked: ps.LastChecked,
		}
	}

	return ports
}

func buildCertificates(
	snap state.Snapshot,
	resp *statusResponse,
) {
	for key, cs := range snap.Certificates {
		sans := make([]string, len(cs.SubjectAlternativeNames))
		copy(sans, cs.SubjectAlternativeNames)

		resp.Certificates[key] = &statusCertificateInfo{
			CommonName:              cs.CommonName,
			Issuer:                  cs.Issuer,
			NotAfter:                cs.NotAfter,
			SubjectAlternativeNames: sans,
			Status:                  cs.Status,
			Error:                   cs.Error,
			LastChecked:             cs.LastChecked,
		}
	}
}

func buildCounts(resp *statusResponse) {
	var portsOpen, certsOK, certsError int

	for _, ps := range resp.Ports {
		if ps.Open {
			portsOpen++
		}
	}

	for _, cs := range resp.Certificates {
		switch cs.Status {
		case "ok":
			certsOK++
		case "error":
			certsError++
		}
	}

	resp.Counts = statusCounts{
		Domains:      len(resp.Domains),
		Hostnames:    len(resp.Hostnames),
		Ports:        len(resp.Ports),
		PortsOpen:    portsOpen,
		Certificates: len(resp.Certificates),
		CertsOK:      certsOK,
		CertsError:   certsError,
	}
}