package monitor

import "context"
import "crypto/tls"
import "crypto/x509"
import "encoding/json"
import "fmt"
import "io"
import "net"
import "net/http"
import "net/http/httptrace"
import "net/url"
import "strings"
import "sync"
import "time"

import "codit/internal/models"

// urlCheckConfig is the type-specific JSON config for a url monitor. The probe
// runs DNS resolve + TCP connect, and for http/https a request, and for https
// (unless disabled) a TLS-certificate-expiry facet — all as phases of one probe.
type urlCheckConfig struct {
	Protocol       string `json:"protocol"`
	Port           int    `json:"port"`
	Method         string `json:"method"`
	ExpectedStatus int    `json:"expected_status"`
	Keyword        string `json:"keyword"`
	CheckCert      *bool  `json:"check_cert"`
	CertWarnDays   int    `json:"cert_warn_days"`
	ClientCertRef  string `json:"client_cert_ref"`
}

const urlBodyLimit int64 = 64 * 1024
const certDefaultWarnDays int = 14

func parseURLConfig(raw string) urlCheckConfig {
	var cfg urlCheckConfig
	if strings.TrimSpace(raw) != "" {
		_ = json.Unmarshal([]byte(raw), &cfg)
	}
	if cfg.Protocol == "" {
		cfg.Protocol = models.MonitorProtocolHTTPS
	}
	if cfg.CertWarnDays <= 0 {
		cfg.CertWarnDays = certDefaultWarnDays
	}
	return cfg
}

func defaultPortFor(protocol string) string {
	switch protocol {
	case models.MonitorProtocolHTTP:
		return "80"
	case models.MonitorProtocolHTTPS:
		return "443"
	default:
		return ""
	}
}

// urlTrace captures per-phase timing/errors from an httptrace-instrumented
// request. The trace callbacks may fire from a background dial goroutine that
// outlives client.Do when the request is canceled or times out, so all access
// is guarded by mu; readers take a point-in-time snapshot() instead of touching
// fields directly.
type urlTrace struct {
	mu           sync.Mutex
	connectStart time.Time
	connectMs    int64
	connectDone  bool
	connectErr   error
	tlsStart     time.Time
	tlsMs        int64
	tlsDone      bool
	tlsErr       error
	certs        []*x509.Certificate
}

// urlTraceSnapshot is an unsynchronized, point-in-time copy of the fields
// readers need. Once taken it is safe to read without locking.
type urlTraceSnapshot struct {
	connectMs   int64
	connectDone bool
	connectErr  error
	tlsMs       int64
	tlsDone     bool
	tlsErr      error
	certs       []*x509.Certificate
}

func (tr *urlTrace) snapshot() urlTraceSnapshot {
	tr.mu.Lock()
	defer tr.mu.Unlock()
	return urlTraceSnapshot{
		connectMs:   tr.connectMs,
		connectDone: tr.connectDone,
		connectErr:  tr.connectErr,
		tlsMs:       tr.tlsMs,
		tlsDone:     tr.tlsDone,
		tlsErr:      tr.tlsErr,
		certs:       tr.certs,
	}
}

func checkURL(ctx context.Context, policy EgressPolicy, m models.Monitor, productID string, tlsCtx *TLSContext) models.MonitorCheckResult {
	var cfg urlCheckConfig
	var target string
	var protocol string
	var host string
	var port string
	var requestURL string

	cfg = parseURLConfig(m.Config)
	protocol = cfg.Protocol
	target = strings.TrimSpace(m.Target)
	if target == "" {
		return failResult("no target configured")
	}

	if strings.Contains(target, "://") {
		var u *url.URL
		var err error
		u, err = url.Parse(target)
		if err != nil || u.Hostname() == "" {
			return failResult(fmt.Sprintf("invalid URL: %v", err))
		}
		if u.Scheme == models.MonitorProtocolHTTP || u.Scheme == models.MonitorProtocolHTTPS {
			protocol = u.Scheme
		}
		host = u.Hostname()
		port = u.Port()
		if port == "" {
			port = defaultPortFor(protocol)
		}
		requestURL = target
	} else {
		host, port = hostAndPort(target, defaultPortFor(protocol))
		if protocol != models.MonitorProtocolTCP {
			requestURL = protocol + "://" + net.JoinHostPort(host, port)
		}
	}
	if cfg.Port > 0 {
		port = fmt.Sprintf("%d", cfg.Port)
	}
	if port == "" {
		return failResult("target must include a port for this protocol")
	}

	if protocol == models.MonitorProtocolTCP {
		return probeTCP(ctx, policy, m, host, port)
	}
	return probeHTTP(ctx, policy, m, cfg, protocol, host, port, requestURL, productID, tlsCtx)
}

// probeTCP runs the DNS + connect facets only.
func probeTCP(ctx context.Context, policy EgressPolicy, m models.Monitor, host string, port string) models.MonitorCheckResult {
	var facets []models.MonitorFacetResult
	var ips []net.IP
	var chosen net.IP
	var resolved string
	var start time.Time
	var dnsMs int64
	var conn net.Conn
	var dialer net.Dialer
	var connMs int64
	var err error

	start = time.Now()
	ips, chosen, err = policy.ResolveValidated(ctx, host)
	dnsMs = time.Since(start).Milliseconds()
	if err != nil {
		facets = append(facets, facet(models.MonitorFacetDNS, models.MonitorStateDown, dnsMs, classifyDialError(err)))
		return aggregateResult(facets, "", 0)
	}
	resolved = joinIPs(ips)
	facets = append(facets, facet(models.MonitorFacetDNS, models.MonitorStateUp, dnsMs, resolved))

	dialer = net.Dialer{Timeout: checkTimeout(m)}
	start = time.Now()
	conn, err = dialer.DialContext(ctx, "tcp", net.JoinHostPort(chosen.String(), port))
	connMs = time.Since(start).Milliseconds()
	if err != nil {
		facets = append(facets, facet(models.MonitorFacetConnect, models.MonitorStateDown, connMs, classifyDialError(err)))
		return aggregateResult(facets, resolved, 0)
	}
	conn.Close()
	facets = append(facets, facet(models.MonitorFacetConnect, models.MonitorStateUp, connMs, fmt.Sprintf("connected to %s:%s", host, port)))
	return aggregateResult(facets, resolved, 0)
}

// probeHTTP runs DNS + connect + (https) TLS-cert + HTTP facets via one request.
func probeHTTP(ctx context.Context, policy EgressPolicy, m models.Monitor, cfg urlCheckConfig, protocol string, host string, port string, requestURL string, productID string, tlsCtx *TLSContext) models.MonitorCheckResult {
	var facets []models.MonitorFacetResult
	var ips []net.IP
	var chosen net.IP
	var resolved string
	var start time.Time
	var dnsMs int64
	var timeout time.Duration
	var tr *urlTrace
	var snap urlTraceSnapshot
	var tlsClientCfg *tls.Config
	var transport *http.Transport
	var client *http.Client
	var req *http.Request
	var resp *http.Response
	var body []byte
	var method string
	var reqMs int64
	var isHTTPS bool
	var checkCert bool
	var ci certInfo
	var err error

	isHTTPS = protocol == models.MonitorProtocolHTTPS
	checkCert = isHTTPS && (cfg.CheckCert == nil || *cfg.CheckCert)
	timeout = checkTimeout(m)

	start = time.Now()
	ips, chosen, err = policy.ResolveValidated(ctx, host)
	dnsMs = time.Since(start).Milliseconds()
	if err != nil {
		facets = append(facets, facet(models.MonitorFacetDNS, models.MonitorStateDown, dnsMs, classifyDialError(err)))
		return aggregateResult(facets, "", 0)
	}
	resolved = joinIPs(ips)
	facets = append(facets, facet(models.MonitorFacetDNS, models.MonitorStateUp, dnsMs, resolved))

	tr = &urlTrace{}
	// Probe reachability/response independent of chain trust; the cert facet
	// judges expiry separately so an expired cert is "degraded/down cert" rather
	// than an opaque connection failure. A client cert (mTLS) is presented when
	// the deployment resolved one for this monitor.
	tlsClientCfg = &tls.Config{InsecureSkipVerify: true, ServerName: host}
	if tlsCtx != nil && tlsCtx.ClientCert != nil {
		tlsClientCfg.Certificates = []tls.Certificate{*tlsCtx.ClientCert}
	}
	transport = &http.Transport{
		// Pin every dial to the policy-validated IP (anti DNS-rebinding); the
		// request still uses the hostname for SNI/Host.
		DialContext: func(dialCtx context.Context, network string, addr string) (net.Conn, error) {
			var d net.Dialer
			d = net.Dialer{Timeout: timeout}
			return d.DialContext(dialCtx, network, net.JoinHostPort(chosen.String(), port))
		},
		TLSClientConfig:       tlsClientCfg,
		TLSHandshakeTimeout:   timeout,
		ResponseHeaderTimeout: timeout,
		DisableKeepAlives:     true,
	}
	client = &http.Client{Timeout: timeout, Transport: transport}

	method = strings.ToUpper(strings.TrimSpace(cfg.Method))
	if method == "" {
		method = http.MethodGet
	}
	req, err = http.NewRequestWithContext(httptrace.WithClientTrace(ctx, traceHooks(tr)), method, requestURL, nil)
	if err != nil {
		facets = append(facets, facet(models.MonitorFacetConnect, models.MonitorStateDown, 0, fmt.Sprintf("request error: %v", err)))
		return aggregateResult(facets, resolved, 0)
	}
	req.Header.Set("User-Agent", productID+"-monitor/1.0")

	start = time.Now()
	resp, err = client.Do(req)
	reqMs = time.Since(start).Milliseconds()

	// Snapshot the trace once Do returns; a background dial goroutine may still
	// mutate tr after a timeout/cancel, so never read its fields directly.
	snap = tr.snapshot()

	// connect facet
	if snap.connectDone {
		if snap.connectErr != nil {
			facets = append(facets, facet(models.MonitorFacetConnect, models.MonitorStateDown, snap.connectMs, classifyDialError(snap.connectErr)))
			return aggregateResult(facets, resolved, 0)
		}
		facets = append(facets, facet(models.MonitorFacetConnect, models.MonitorStateUp, snap.connectMs, fmt.Sprintf("connected to %s:%s", host, port)))
	} else {
		facets = append(facets, facet(models.MonitorFacetConnect, models.MonitorStateDown, reqMs, classifyDialError(orErr(err, "connection failed"))))
		return aggregateResult(facets, resolved, 0)
	}

	// Flag whether the presented server cert chains to one of our own PKI CAs
	// (informational; computed regardless of the cert facet being enabled).
	if tlsCtx != nil && issuerIsOurs(snap.certs, tlsCtx.OurCAs) {
		ci.issuerKnown = true
	}

	// tls/cert facet (https only, unless disabled)
	if checkCert {
		var f models.MonitorFacetResult
		var cf certInfo
		f, cf = certFacet(snap, cfg.CertWarnDays, host)
		cf.issuerKnown = ci.issuerKnown
		ci = cf
		facets = append(facets, f)
		if f.State == models.MonitorStateDown && resp == nil {
			return finalize(facets, resolved, ci)
		}
	}

	// http facet
	if err != nil {
		facets = append(facets, facet(models.MonitorFacetHTTP, models.MonitorStateDown, reqMs, classifyDialError(err)))
		return finalize(facets, resolved, ci)
	}
	defer resp.Body.Close()
	body, _ = io.ReadAll(io.LimitReader(resp.Body, urlBodyLimit))
	facets = append(facets, httpFacet(cfg, resp.StatusCode, string(body), reqMs))
	return finalize(facets, resolved, ci)
}

func traceHooks(tr *urlTrace) *httptrace.ClientTrace {
	return &httptrace.ClientTrace{
		ConnectStart: func(network string, addr string) {
			tr.mu.Lock()
			tr.connectStart = time.Now()
			tr.mu.Unlock()
		},
		ConnectDone: func(network string, addr string, err error) {
			tr.mu.Lock()
			defer tr.mu.Unlock()
			tr.connectDone = true
			tr.connectErr = err
			if !tr.connectStart.IsZero() {
				tr.connectMs = time.Since(tr.connectStart).Milliseconds()
			}
		},
		TLSHandshakeStart: func() {
			tr.mu.Lock()
			tr.tlsStart = time.Now()
			tr.mu.Unlock()
		},
		TLSHandshakeDone: func(state tls.ConnectionState, err error) {
			tr.mu.Lock()
			defer tr.mu.Unlock()
			tr.tlsDone = true
			tr.tlsErr = err
			tr.certs = state.PeerCertificates
			if !tr.tlsStart.IsZero() {
				tr.tlsMs = time.Since(tr.tlsStart).Milliseconds()
			}
		},
	}
}

// certInfo carries the leaf-certificate detail surfaced on the status row.
// TLSContext carries deployment-resolved TLS material for a check: a client
// certificate to present for mTLS, and this deployment's own CA pool so the
// probe can flag a server cert issued by an internal CA. Resolved by the manager
// (which has DB access) and passed to the checker; nil fields mean "not used".
type TLSContext struct {
	ClientCert *tls.Certificate
	OurCAs     *x509.CertPool
}

type certInfo struct {
	expiresAt   int64
	subject     string
	issuer      string
	sans        string
	mismatch    bool
	issuerKnown bool
}

// issuerIsOurs reports whether the presented leaf chains to a CA in our own PKI
// store, using the presented intermediates. Trust here is informational (the
// probe judges reachability separately), so verification is done as-of the
// leaf's own validity window to avoid failing merely on expiry.
func issuerIsOurs(certs []*x509.Certificate, pool *x509.CertPool) bool {
	var leaf *x509.Certificate
	var inter *x509.CertPool
	var c *x509.Certificate
	var err error

	if pool == nil || len(certs) == 0 {
		return false
	}
	leaf = certs[0]
	inter = x509.NewCertPool()
	for _, c = range certs[1:] {
		inter.AddCert(c)
	}
	_, err = leaf.Verify(x509.VerifyOptions{
		Roots:         pool,
		Intermediates: inter,
		CurrentTime:   leaf.NotBefore,
		KeyUsages:     []x509.ExtKeyUsage{x509.ExtKeyUsageAny},
	})
	return err == nil
}

// certFacet evaluates the leaf certificate: validity window + hostname coverage.
// The probe ignores cert trust for reachability, so an expiry warning or a
// hostname mismatch is surfaced here (degraded) rather than failing the check.
func certFacet(tr urlTraceSnapshot, warnDays int, host string) (models.MonitorFacetResult, certInfo) {
	var ci certInfo
	var leaf *x509.Certificate
	var now time.Time
	var days int64
	var state string
	var notes []string

	if !tr.tlsDone || tr.tlsErr != nil {
		var msg string
		msg = "TLS handshake failed"
		if tr.tlsErr != nil {
			msg = fmt.Sprintf("TLS handshake failed: %v", tr.tlsErr)
		}
		return facet(models.MonitorFacetTLS, models.MonitorStateDown, tr.tlsMs, msg), ci
	}
	if len(tr.certs) == 0 {
		return facet(models.MonitorFacetTLS, models.MonitorStateDown, tr.tlsMs, "server presented no certificate"), ci
	}

	leaf = tr.certs[0]
	ci.expiresAt = leaf.NotAfter.Unix()
	// Modern certs often leave the Subject CN empty (identity lives in the SAN);
	// fall back to the full Subject/Issuer DN so the row is never blank.
	ci.subject = strings.TrimSpace(leaf.Subject.CommonName)
	if ci.subject == "" {
		ci.subject = strings.TrimSpace(leaf.Subject.String())
	}
	ci.issuer = strings.TrimSpace(leaf.Issuer.CommonName)
	if ci.issuer == "" {
		ci.issuer = strings.TrimSpace(leaf.Issuer.String())
	}
	ci.sans = strings.Join(leaf.DNSNames, ", ")
	now = time.Now()
	state = models.MonitorStateUp

	if now.Before(leaf.NotBefore) {
		state = models.MonitorStateDown
		notes = append(notes, fmt.Sprintf("not valid until %s", leaf.NotBefore.UTC().Format("2006-01-02")))
	} else if now.After(leaf.NotAfter) {
		state = models.MonitorStateDown
		notes = append(notes, fmt.Sprintf("expired %s", leaf.NotAfter.UTC().Format("2006-01-02")))
	} else {
		days = int64(leaf.NotAfter.Sub(now).Hours() / 24)
		if days <= int64(warnDays) {
			state = models.MonitorStateDegraded
			notes = append(notes, fmt.Sprintf("expires in %d days (%s)", days, leaf.NotAfter.UTC().Format("2006-01-02")))
		} else {
			notes = append(notes, fmt.Sprintf("valid, expires in %d days", days))
		}
	}

	// Hostname coverage: surfaced (degraded) but never fails the probe.
	if host != "" && net.ParseIP(host) == nil && leaf.VerifyHostname(host) != nil {
		ci.mismatch = true
		state = worseState(state, models.MonitorStateDegraded)
		notes = append(notes, fmt.Sprintf("hostname %q not covered by certificate", host))
	}

	return facet(models.MonitorFacetTLS, state, tr.tlsMs, strings.Join(notes, "; ")), ci
}

// finalize aggregates facets and attaches cert detail to the result.
func finalize(facets []models.MonitorFacetResult, resolved string, ci certInfo) models.MonitorCheckResult {
	var r models.MonitorCheckResult
	r = aggregateResult(facets, resolved, ci.expiresAt)
	r.CertSubject = ci.subject
	r.CertIssuer = ci.issuer
	r.CertSANs = ci.sans
	r.CertHostMismatch = ci.mismatch
	r.CertIssuerKnown = ci.issuerKnown
	return r
}

func httpFacet(cfg urlCheckConfig, status int, body string, latencyMs int64) models.MonitorFacetResult {
	var statusOK bool
	if cfg.ExpectedStatus > 0 {
		statusOK = status == cfg.ExpectedStatus
	} else {
		statusOK = status >= 200 && status < 400
	}
	if !statusOK {
		return facet(models.MonitorFacetHTTP, models.MonitorStateDown, latencyMs, fmt.Sprintf("unexpected status %d %s", status, http.StatusText(status)))
	}
	if strings.TrimSpace(cfg.Keyword) != "" && !strings.Contains(body, cfg.Keyword) {
		return facet(models.MonitorFacetHTTP, models.MonitorStateDown, latencyMs, fmt.Sprintf("keyword %q not found", cfg.Keyword))
	}
	return facet(models.MonitorFacetHTTP, models.MonitorStateUp, latencyMs, fmt.Sprintf("%d %s", status, http.StatusText(status)))
}

func facet(name string, state string, latencyMs int64, message string) models.MonitorFacetResult {
	return models.MonitorFacetResult{Name: name, State: state, LatencyMs: latencyMs, Message: message}
}

// aggregateResult folds facets into a single result: state = worst facet state,
// latency = the http/connect facet latency, message = summary.
func aggregateResult(facets []models.MonitorFacetResult, resolved string, certExpiresAt int64) models.MonitorCheckResult {
	var f models.MonitorFacetResult
	var state string
	var latency int64
	var summary string
	state = models.MonitorStateUp
	for _, f = range facets {
		state = worseState(state, f.State)
		if f.Name == models.MonitorFacetHTTP || f.Name == models.MonitorFacetConnect {
			latency = f.LatencyMs
		}
	}
	// Summary: on failure/degraded, the FIRST facet at the worst state (the phase
	// that failed). When up, the LAST successful facet — the deepest phase reached
	// (http > tls > connect > dns) — which reads more usefully (e.g. "http: 200 OK"
	// rather than the DNS-resolved IP).
	if state == models.MonitorStateUp {
		var i int
		for i = len(facets) - 1; i >= 0; i-- {
			if facets[i].State == state {
				summary = fmt.Sprintf("%s: %s", facets[i].Name, facets[i].Message)
				break
			}
		}
	} else {
		for _, f = range facets {
			if f.State == state {
				summary = fmt.Sprintf("%s: %s", f.Name, f.Message)
				break
			}
		}
	}
	return models.MonitorCheckResult{
		// degraded (e.g. cert nearing expiry) is still reachable, so it does not
		// count as a failure for the down threshold.
		OK:            state != models.MonitorStateDown,
		State:         state,
		LatencyMs:     latency,
		Message:       summary,
		CertExpiresAt: certExpiresAt,
		ResolvedValue: resolved,
		Facets:        facets,
	}
}

func joinIPs(ips []net.IP) string {
	var parts []string
	var ip net.IP
	for _, ip = range ips {
		parts = append(parts, ip.String())
	}
	return strings.Join(parts, ", ")
}

func orErr(err error, fallback string) error {
	if err != nil {
		return err
	}
	return fmt.Errorf("%s", fallback)
}