// The versioned admin API (AGENTS.md §4 FR-11, §11 Phase 8).
//
// Another project, the Kotlin admin app (kotlin_phone_app_admin), consumes this
// surface. It is deliberately small and stable: bearer-token auth, JSON in and
// out, and one clear shape for lock, unlock, grant and a state query. Control
// never goes through the Hub (AGENTS.md §8): the app calls this service
// directly.
//
// Every state change is persisted to SQLite, recorded in `overrides` and the
// append-only `audit` log (FR-15), and only then published retained on the
// device's MQTT config topic. The publish is synchronous, so a 200 response
// means the broker has accepted the retained message and every subscriber
// receives it at once (FR-5, FR-11).
package web

import (
	"context"
	"crypto/subtle"
	"encoding/json"
	"errors"
	"net"
	"net/http"
	"strings"
	"time"

	"gitea.lab.audasmedia.com.au/sam/internet_use_control/internal/store"
)

// apiVersion is the version of this surface, carried in the path.
const apiVersion = "v1"

// Actor names written to the audit log and the override history.
const (
	apiActor      = "admin-api"
	keycodeActor  = "device-keycode"
	apiMaxBody    = 8 << 10 // 8 KiB is plenty for these requests
	apiMaxGrant   = 24 * 60 // minutes; a day at a time
	apiMaxLockMin = 7 * 24 * 60
)

// apiDevice is the wire shape of one device. It is versioned by its path, and
// clients must ignore unknown fields so it can grow without a v2.
type apiDevice struct {
	ID         int64      `json:"id"`
	Name       string     `json:"name"`
	Child      string     `json:"child"`
	Platform   string     `json:"platform"`
	Topic      string     `json:"topic"`
	Online     bool       `json:"online"`
	LastSeen   *time.Time `json:"last_seen"`
	Locked     bool       `json:"locked"`
	Until      *time.Time `json:"until"`
	GrantUntil *time.Time `json:"grant_until"`
	Reason     string     `json:"reason"`
	UpdatedAt  time.Time  `json:"updated_at"`
}

// apiResponse is the one response envelope for every endpoint. Exactly one of
// Device or Devices is set on success; Error is set on failure.
type apiResponse struct {
	OK      bool        `json:"ok"`
	Action  string      `json:"action,omitempty"`
	Device  *apiDevice  `json:"device,omitempty"`
	Devices []apiDevice `json:"devices,omitempty"`
	Error   string      `json:"error,omitempty"`
}

// overrideRequest is the body of lock, grant and keycode requests.
type overrideRequest struct {
	// Minutes grants time relative to now. Mutually exclusive with Until.
	Minutes int `json:"minutes"`
	// Until is an absolute RFC3339 instant.
	Until string `json:"until"`
	// DeviceID and Keycode are used only by the device keycode endpoint.
	DeviceID int64  `json:"device_id"`
	Keycode  string `json:"keycode"`
}

// handleAPIListDevices returns every device with its effective state.
func (s *Server) handleAPIListDevices(w http.ResponseWriter, r *http.Request) {
	ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
	defer cancel()

	devs, err := s.store.ListDevices(ctx)
	if err != nil {
		s.log.Error("api list devices", "err", err)
		writeAPIError(w, http.StatusInternalServerError, "could not read devices")
		return
	}
	out := make([]apiDevice, 0, len(devs))
	for _, dev := range devs {
		item, err := s.apiDevice(ctx, dev)
		if err != nil {
			s.log.Error("api effective state", "device", dev.Name, "err", err)
			writeAPIError(w, http.StatusInternalServerError, "could not read device state")
			return
		}
		out = append(out, item)
	}
	writeAPIJSON(w, http.StatusOK, apiResponse{OK: true, Devices: out})
}

// handleAPIState returns one device with its effective state.
func (s *Server) handleAPIState(w http.ResponseWriter, r *http.Request) {
	id, ok := s.deviceID(w, r)
	if !ok {
		writeAPIError(w, http.StatusNotFound, "device not found")
		return
	}
	ctx, cancel := context.WithTimeout(r.Context(), 3*time.Second)
	defer cancel()

	dev, err := s.store.GetDevice(ctx, id)
	if err != nil {
		s.apiDeviceError(w, err)
		return
	}
	item, err := s.apiDevice(ctx, *dev)
	if err != nil {
		s.log.Error("api effective state", "device", dev.Name, "err", err)
		writeAPIError(w, http.StatusInternalServerError, "could not read device state")
		return
	}
	writeAPIJSON(w, http.StatusOK, apiResponse{OK: true, Device: &item})
}

// handleAPILock locks a device now, for a duration or indefinitely.
func (s *Server) handleAPILock(w http.ResponseWriter, r *http.Request) {
	id, ok := s.deviceID(w, r)
	if !ok {
		writeAPIError(w, http.StatusNotFound, "device not found")
		return
	}
	req, ok := decodeOverride(w, r, false)
	if !ok {
		return
	}
	until, err := resolveUntil(req, apiMaxLockMin)
	if err != nil {
		writeAPIError(w, http.StatusBadRequest, err.Error())
		return
	}

	started := time.Now()
	ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
	defer cancel()

	dev, err := s.store.SetDeviceLock(ctx, id, true, until, apiActor, "state.locked")
	if err != nil {
		s.apiDeviceError(w, err)
		return
	}
	s.publishConfig(ctx, *dev)
	s.apiRespond(w, ctx, "lock", dev, started)
}

// handleAPIUnlock clears a manual lock and any grant, returning the device to
// its schedule. It is the opposite of lock.
func (s *Server) handleAPIUnlock(w http.ResponseWriter, r *http.Request) {
	id, ok := s.deviceID(w, r)
	if !ok {
		writeAPIError(w, http.StatusNotFound, "device not found")
		return
	}
	// An empty body is fine; reject a malformed one.
	if !decodeEmpty(w, r) {
		return
	}

	started := time.Now()
	ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
	defer cancel()

	dev, err := s.store.SetDeviceLock(ctx, id, false, nil, apiActor, "state.unlocked")
	if err != nil {
		s.apiDeviceError(w, err)
		return
	}
	s.publishConfig(ctx, *dev)
	s.apiRespond(w, ctx, "unlock", dev, started)
}

// handleAPIGrant gives a device time: it is unlocked until the grant ends, even
// if a weekly window is active, and re-locks automatically when the grant ends
// (the republish loop treats the grant end as a boundary).
func (s *Server) handleAPIGrant(w http.ResponseWriter, r *http.Request) {
	id, ok := s.deviceID(w, r)
	if !ok {
		writeAPIError(w, http.StatusNotFound, "device not found")
		return
	}
	req, ok := decodeOverride(w, r, true)
	if !ok {
		return
	}
	until, err := resolveUntil(req, apiMaxGrant)
	if err != nil {
		writeAPIError(w, http.StatusBadRequest, err.Error())
		return
	}
	if until == nil {
		writeAPIError(w, http.StatusBadRequest, "grant requires minutes or until")
		return
	}

	started := time.Now()
	ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
	defer cancel()

	dev, err := s.store.SetDeviceGrant(ctx, id, *until, apiActor, "override.granted")
	if err != nil {
		s.apiDeviceError(w, err)
		return
	}
	s.publishConfig(ctx, *dev)
	s.apiRespond(w, ctx, "grant", dev, started)
}

// handleDeviceOverride is the on-device keycode path (FR-10). A kid's client
// posts the shared code with its own device id; a correct code grants a short,
// bounded exemption. It intentionally does not use the admin bearer token: the
// device never holds that secret. Failures are throttled per client address and
// audited, because the keycode is the enforcement that the tamper alert
// protects (AGENTS.md §13).
func (s *Server) handleDeviceOverride(w http.ResponseWriter, r *http.Request) {
	if !s.keycodeConfigured(r.Context()) {
		writeAPIError(w, http.StatusServiceUnavailable, "device keycode is not configured")
		return
	}
	req, ok := decodeOverride(w, r, true)
	if !ok {
		return
	}
	if req.DeviceID <= 0 {
		writeAPIError(w, http.StatusBadRequest, "device_id is required")
		return
	}
	req.Keycode = strings.TrimSpace(req.Keycode)
	if req.Keycode == "" {
		writeAPIError(w, http.StatusBadRequest, "keycode is required")
		return
	}

	remote := clientIP(r)
	ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
	defer cancel()

	if s.keycodeThrottled(remote) {
		_ = s.store.Audit(ctx, keycodeActor, "override.keycode_throttled", &req.DeviceID, remote)
		writeAPIError(w, http.StatusTooManyRequests, "too many attempts; try again later")
		return
	}
	if !s.store.VerifyKeycode(ctx, req.Keycode) {
		s.noteKeycodeFailure(remote)
		_ = s.store.Audit(ctx, keycodeActor, "override.keycode_rejected", &req.DeviceID, remote)
		s.log.Warn("device keycode rejected", "device_id", req.DeviceID, "remote", remote)
		writeAPIError(w, http.StatusUnauthorized, "invalid keycode")
		return
	}
	s.noteKeycodeSuccess(remote)

	until, err := resolveUntil(req, apiMaxGrant)
	if err != nil {
		writeAPIError(w, http.StatusBadRequest, err.Error())
		return
	}
	if until == nil {
		// A keycode run without a duration gives a short, fixed exemption.
		t := time.Now().Add(15 * time.Minute).UTC()
		until = &t
	}

	started := time.Now()
	dev, err := s.store.SetDeviceGrant(ctx, req.DeviceID, *until, keycodeActor, "override.keycode")
	if err != nil {
		if errors.Is(err, store.ErrNotFound) {
			writeAPIError(w, http.StatusNotFound, "device not found")
			return
		}
		s.log.Error("device keycode grant", "device_id", req.DeviceID, "err", err)
		writeAPIError(w, http.StatusBadRequest, err.Error())
		return
	}
	s.publishConfig(ctx, *dev)
	s.apiRespond(w, ctx, "keycode", dev, started)
}

// ---------- helpers ----------

// apiDevice combines the stored device with its effective state, so a client
// sees the same `locked`/`until`/`reason` a device is given.
func (s *Server) apiDevice(ctx context.Context, dev store.Device) (apiDevice, error) {
	eff, err := s.store.EffectiveState(ctx, dev, s.now())
	if err != nil {
		return apiDevice{}, err
	}
	return apiDevice{
		ID:         dev.ID,
		Name:       dev.Name,
		Child:      dev.Child,
		Platform:   dev.Platform,
		Topic:      dev.Topic,
		Online:     dev.Online,
		LastSeen:   dev.LastSeen,
		Locked:     eff.Locked,
		Until:      eff.Until,
		GrantUntil: eff.GrantUntil,
		Reason:     eff.Reason,
		UpdatedAt:  dev.StateAt,
	}, nil
}

// apiRespond writes the fresh device after a state change, logging the time
// from request receipt to the retained publish being accepted. That duration is
// the number the Phase 8 definition of done measures.
func (s *Server) apiRespond(w http.ResponseWriter, ctx context.Context, action string, dev *store.Device, started time.Time) {
	item, err := s.apiDevice(ctx, *dev)
	if err != nil {
		s.log.Error("api effective state", "device", dev.Name, "err", err)
		writeAPIError(w, http.StatusInternalServerError, "state saved but could not be read back")
		return
	}
	s.log.Info("admin api "+action, "device", dev.Name, "device_id", dev.ID,
		"locked", item.Locked, "reason", item.Reason,
		"duration_ms", time.Since(started).Milliseconds())
	writeAPIJSON(w, http.StatusOK, apiResponse{OK: true, Action: action, Device: &item})
}

// requireAPIToken guards the admin endpoints. It is deliberately a separate
// credential from the session login (AGENTS.md §11 Phase 8).
func (s *Server) requireAPIToken(next http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if strings.TrimSpace(s.cfg.AdminAPIToken) == "" {
			writeAPIError(w, http.StatusServiceUnavailable, "admin API is not configured")
			return
		}
		token, ok := bearerToken(r)
		if !ok || subtle.ConstantTimeCompare([]byte(token), []byte(s.cfg.AdminAPIToken)) != 1 {
			ctx, cancel := context.WithTimeout(r.Context(), 2*time.Second)
			_ = s.store.Audit(ctx, "anonymous", "admin.token_rejected", nil, r.URL.Path+" from "+clientIP(r))
			cancel()
			s.log.Warn("admin api rejected", "path", r.URL.Path, "remote", r.RemoteAddr)
			w.Header().Set("WWW-Authenticate", `Bearer realm="internet-use-control"`)
			writeAPIError(w, http.StatusUnauthorized, "unauthorized")
			return
		}
		next(w, r)
	}
}

// bearerToken reads "Authorization: Bearer <token>".
func bearerToken(r *http.Request) (string, bool) {
	header := r.Header.Get("Authorization")
	kind, token, found := strings.Cut(header, " ")
	if !found || !strings.EqualFold(kind, "Bearer") {
		return "", false
	}
	token = strings.TrimSpace(token)
	return token, token != ""
}

// decodeOverride reads and bounds the JSON body. When requireBody is false an
// empty body is the same as {}.
func decodeOverride(w http.ResponseWriter, r *http.Request, requireBody bool) (overrideRequest, bool) {
	var req overrideRequest
	if r.Body == nil {
		if requireBody {
			writeAPIError(w, http.StatusBadRequest, "a JSON body is required")
			return req, false
		}
		return req, true
	}
	dec := json.NewDecoder(http.MaxBytesReader(w, r.Body, apiMaxBody))
	err := dec.Decode(&req)
	if err != nil {
		if strings.Contains(err.Error(), "EOF") && !requireBody {
			return req, true
		}
		writeAPIError(w, http.StatusBadRequest, "invalid JSON body")
		return req, false
	}
	// A second JSON value in the body is a mistake.
	if dec.Decode(&struct{}{}) == nil {
		writeAPIError(w, http.StatusBadRequest, "body must contain one JSON object")
		return req, false
	}
	return req, true
}

// decodeEmpty accepts an empty or absent body and rejects anything malformed.
func decodeEmpty(w http.ResponseWriter, r *http.Request) bool {
	if r.Body == nil || r.ContentLength == 0 {
		return true
	}
	_, ok := decodeOverride(w, r, false)
	return ok
}

// resolveUntil turns a request into an absolute end time. Exactly one of
// minutes or until may be set. A nil result with no error means "no end time"
// (only meaningful for a lock).
func resolveUntil(req overrideRequest, maxMinutes int) (*time.Time, error) {
	if req.Minutes < 0 {
		return nil, errors.New("minutes must not be negative")
	}
	if req.Until != "" && req.Minutes > 0 {
		return nil, errors.New("set either minutes or until, not both")
	}
	if req.Until != "" {
		t, err := time.Parse(time.RFC3339, strings.TrimSpace(req.Until))
		if err != nil {
			return nil, errors.New("until must be an RFC3339 instant, for example 2026-10-13T21:00:00+11:00")
		}
		t = t.UTC()
		if !t.After(time.Now()) {
			return nil, errors.New("until must be in the future")
		}
		return &t, nil
	}
	if req.Minutes > maxMinutes {
		return nil, errors.New("minutes is too large")
	}
	if req.Minutes > 0 {
		t := time.Now().Add(time.Duration(req.Minutes) * time.Minute).UTC()
		return &t, nil
	}
	return nil, nil
}

// apiDeviceError maps a store error to an HTTP status.
func (s *Server) apiDeviceError(w http.ResponseWriter, err error) {
	if errors.Is(err, store.ErrNotFound) {
		writeAPIError(w, http.StatusNotFound, "device not found")
		return
	}
	s.log.Error("admin api device", "err", err)
	writeAPIError(w, http.StatusBadRequest, err.Error())
}

func writeAPIJSON(w http.ResponseWriter, code int, body apiResponse) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(code)
	_ = json.NewEncoder(w).Encode(body)
}

func writeAPIError(w http.ResponseWriter, code int, message string) {
	writeAPIJSON(w, code, apiResponse{OK: false, Error: message})
}

// clientIP is the direct peer address. No proxy header is trusted: the service
// is reached through Caddy, but X-Forwarded-For is caller-controlled.
func clientIP(r *http.Request) string {
	host, _, err := net.SplitHostPort(r.RemoteAddr)
	if err != nil {
		return r.RemoteAddr
	}
	return host
}

// ---------- keycode throttle ----------

// keycodeThrottle bounds brute force on the shared code: five failures from one
// address freeze that address for five minutes. It is in memory on purpose —
// the Control Service is a single process, and a restart clearing it is an
// acceptable trade for keeping the store schema small.
const (
	keycodeMaxFailures = 5
	keycodeFreeze      = 5 * time.Minute
)

type keycodeAttempts struct {
	failures int
	blocked  time.Time
}

func (s *Server) keycodeThrottled(remote string) bool {
	s.keycodeMu.Lock()
	defer s.keycodeMu.Unlock()
	a, ok := s.keycode[remote]
	if !ok {
		return false
	}
	if time.Now().Before(a.blocked) {
		return true
	}
	if !a.blocked.IsZero() {
		delete(s.keycode, remote) // freeze over; start fresh
	}
	return false
}

func (s *Server) noteKeycodeFailure(remote string) {
	s.keycodeMu.Lock()
	defer s.keycodeMu.Unlock()
	a := s.keycode[remote]
	a.failures++
	if a.failures >= keycodeMaxFailures {
		a.blocked = time.Now().Add(keycodeFreeze)
		a.failures = 0
	}
	s.keycode[remote] = a
}

func (s *Server) noteKeycodeSuccess(remote string) {
	s.keycodeMu.Lock()
	defer s.keycodeMu.Unlock()
	delete(s.keycode, remote)
}

// keycodeConfigured reports whether any keycode can be verified.
func (s *Server) keycodeConfigured(ctx context.Context) bool {
	_, err := s.store.KeycodeHash(ctx)
	return err == nil
}