package api

import (
	"errors"
	"net/http"
	"strings"
	"time"
)

// Cameras, onboarded from head office instead of from the shop floor.
//
// The shop PC remains the thing that CONNECTS to a camera - it is on the same
// LAN and nothing else can be - so these routes write desired state that the
// agent pulls and applies. Two audiences, two shapes: a tenant never receives
// a camera password, and an agent receives one only for its own site.

// A snapshot is refreshed every minute or so, so a link outliving that is
// pointless; short enough that one in a screenshot is worthless by the time
// anyone reads it.
const snapshotTTL = 5 * time.Minute

func (s *Server) handleCameras(w http.ResponseWriter, r *http.Request) {
	p := PrincipalFrom(r.Context())
	// siteParam, not Query().Get("site_id"): every other filtered endpoint
	// takes both spellings, and this one took only the longer. `?site=chennai`
	// was therefore not a filter but an unknown parameter, silently ignored -
	// so a caller asking for one shop's cameras was handed the whole tenant's.
	// Measured: it made a script skip creating cameras for three shops because
	// another shop's already existed, and deleted a camera from the wrong shop.
	siteID := siteParam(r)
	if siteID != "" {
		var ok bool
		if siteID, ok = s.resolveSiteFilter(w, r, siteID); !ok {
			return
		}
	}
	cams, err := s.Store.Cameras(r.Context(), p.ClientID, siteID)
	if err != nil {
		s.serverError(w, "cameras", err)
		return
	}
	if cams == nil {
		cams = []Camera{}
	}
	s.attachSnapshots(cams)
	writeJSON(w, http.StatusOK, cams)
}

// attachSnapshots swaps each camera's object key for a signed link.
//
// A snapshot is a frame of a shop floor, so it gets the same treatment as a
// face: a short-lived signed URL, never a stored one. Absence is data - most
// deployments store no images at all, and a camera that is merely new has no
// frame yet.
func (s *Server) attachSnapshots(cams []Camera) {
	for i := range cams {
		key := cams[i].Snapshot.Key
		cams[i].Snapshot.Key = ""
		switch {
		case key == "" && cams[i].SnapshotAt != "":
			// Held by this server, because the deployment has no object
			// storage. Served from an endpoint rather than a signed link:
			// there is no third party to delegate to, the bytes are in our own
			// database, and an unauthenticated URL to somebody's shop floor
			// would be a new way in for no gain.
			cams[i].Snapshot = Image{
				Available: true,
				URL:       "/api/cameras/" + cams[i].ID + "/snapshot.jpg",
				ExpiresIn: int(snapshotTTL.Seconds()),
				// Says out loud that this URL needs the session's bearer.
				// Clients used to infer it from the URL being relative, which
				// is true today and stops being true the first time object
				// storage is served from this same host.
				Auth: true,
			}
		case key == "":
			cams[i].Snapshot.Reason = "No picture from this camera yet."
		case s.Blob == nil:
			// A key from a bucket this server can no longer reach. Distinct
			// from "no picture yet": one is waiting, the other is misconfigured.
			cams[i].Snapshot.Reason = "This system is not storing images."
		default:
			url, err := s.Blob.PresignGet(key, snapshotTTL)
			if err != nil {
				s.logf("ERROR presign snapshot: %v", err)
				cams[i].Snapshot.Reason = "That picture could not be loaded."
				continue
			}
			cams[i].Snapshot = Image{Available: true, URL: url,
				ExpiresIn: int(snapshotTTL.Seconds())}
		}
	}
}

func (s *Server) handleCreateCamera(w http.ResponseWriter, r *http.Request) {
	p := PrincipalFrom(r.Context())
	if !p.CanManageSites() {
		writeErr(w, http.StatusForbidden, "forbidden",
			"Your account cannot change camera settings.")
		return
	}
	siteID, ok := s.resolveSite(w, r, r.PathValue("site"))
	if !ok {
		return
	}
	var in CameraInput
	if err := decode(w, r, &in); err != nil {
		badRequest(w, err.Error())
		return
	}
	id := ""
	if in.CameraID != nil {
		id = cameraSlug(*in.CameraID)
	}
	if id == "" && in.Label != nil {
		id = cameraSlug(*in.Label)
	}
	if id == "" {
		badRequest(w, "give the camera a name, such as Entrance")
		return
	}
	if in.Label == nil || trim(*in.Label) == "" {
		in.Label = &id
	}
	if msg, ok := cameraProblem(in); !ok {
		badRequest(w, msg)
		return
	}
	s.saveCamera(w, r, p.ClientID, siteID, id, in, http.StatusCreated)
}

func (s *Server) handleUpdateCamera(w http.ResponseWriter, r *http.Request) {
	p := PrincipalFrom(r.Context())
	if !p.CanManageSites() {
		writeErr(w, http.StatusForbidden, "forbidden",
			"Your account cannot change camera settings.")
		return
	}
	id, ok := s.resolveCamera(w, r, r.PathValue("id"))
	if !ok {
		return
	}
	existing, err := s.Store.CameraByID(r.Context(), p.ClientID, id)
	if err != nil {
		writeErr(w, http.StatusNotFound, "not_found", "That camera no longer exists.")
		return
	}
	var in CameraInput
	if err := decode(w, r, &in); err != nil {
		badRequest(w, err.Error())
		return
	}
	// The camera id is what visits are recorded against. Renaming it would
	// orphan every visit already attributed to the old name, so the label is
	// the thing an operator may change.
	in.CameraID = nil
	s.saveCamera(w, r, p.ClientID, existing.SiteID, existing.CameraID, in, http.StatusOK)
}

func (s *Server) saveCamera(w http.ResponseWriter, r *http.Request,
	clientID, siteID, cameraID string, in CameraInput, code int) {

	p := PrincipalFrom(r.Context())
	cam, err := s.Store.SaveCamera(r.Context(), clientID, siteID, cameraID, in)
	if err != nil {
		if errors.Is(err, ErrNoSecrets) {
			// A camera saved with its password silently dropped is a camera
			// that will not connect, and the operator could not tell that from
			// a wrong password.
			writeErr(w, http.StatusServiceUnavailable, "no_secret_key", err.Error())
			return
		}
		if strings.Contains(err.Error(), "no rows") {
			writeErr(w, http.StatusNotFound, "not_found", "That shop no longer exists.")
			return
		}
		s.serverError(w, "save camera", err)
		return
	}
	s.Store.Audit(r.Context(), AuditEntry{
		ClientID: clientID, ActorID: p.UserID, ActorKind: "user",
		Action: "camera.save", Entity: "camera", EntityID: cam.ID,
		Detail: map[string]any{"camera_id": cam.CameraID, "site_id": siteID},
	})
	// Through the slice, not around it. `attachSnapshots([]Camera{cam})` would
	// decorate a COPY and then serialise the untouched original, so a created
	// camera came back with an empty snapshot object and no reason - the one
	// field whose whole job is to say why there is no picture.
	cams := []Camera{cam}
	s.attachSnapshots(cams)
	writeJSON(w, code, cams[0])
}

func (s *Server) handleDeleteCamera(w http.ResponseWriter, r *http.Request) {
	p := PrincipalFrom(r.Context())
	if !p.CanManageSites() {
		writeErr(w, http.StatusForbidden, "forbidden",
			"Your account cannot change camera settings.")
		return
	}
	id, ok := s.resolveCamera(w, r, r.PathValue("id"))
	if !ok {
		return
	}
	cam, err := s.Store.DeleteCamera(r.Context(), p.ClientID, id)
	if err != nil {
		writeErr(w, http.StatusNotFound, "not_found", "That camera no longer exists.")
		return
	}
	s.Store.Audit(r.Context(), AuditEntry{
		ClientID: p.ClientID, ActorID: p.UserID, ActorKind: "user",
		Action: "camera.delete", Entity: "camera", EntityID: cam.ID,
		Detail: map[string]any{"camera_id": cam.CameraID},
	})
	w.WriteHeader(http.StatusNoContent)
}

// ------------------------------------------------------------------ agent

// handleAgentCameras is the shop PC asking what it should be running.
//
// Authenticated by the agent's own token, and scoped to that agent's site by
// the credential rather than by anything in the request - a site id a caller
// could set would hand one shop another shop's camera passwords.
func (s *Server) handleAgentCameras(w http.ResponseWriter, r *http.Request, ap AgentPrincipal) {
	cams, err := s.Store.AgentCameras(r.Context(), ap.SiteID)
	if err != nil {
		s.serverError(w, "agent cameras", err)
		return
	}
	if cams == nil {
		cams = []AgentCamera{}
	}
	writeJSON(w, http.StatusOK, map[string]any{"cameras": cams})
}

// handleAgentCameraReport records what the shop PC observes and adopts any
// camera it is running that head office does not know about.
func (s *Server) handleAgentCameraReport(w http.ResponseWriter, r *http.Request, ap AgentPrincipal) {
	var rep AgentCameraReport
	if err := decode(w, r, &rep); err != nil {
		badRequest(w, err.Error())
		return
	}
	for i := range rep.Adopt {
		// Slugged here as well as on the operator path. An agent is trusted to
		// report its own site, not to choose an identifier that could collide
		// with a topic segment or a path.
		rep.Adopt[i].CameraID = cameraSlug(rep.Adopt[i].CameraID)
	}
	// ClientID, not Client. AgentPrincipal carries both the tenant's uuid and
	// its human slug, and the slug is the one that reads correctly in a log
	// line - which is exactly why it gets used by mistake in a query that wants
	// the uuid.
	if err := s.Store.ApplyAgentReport(r.Context(), ap.ClientID, ap.SiteID, rep); err != nil {
		s.serverError(w, "agent camera report", err)
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

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

// cameraSlug normalises the id the engine will know this camera by.
//
// It ends up in an object key, a URL path and a topic segment, so it is
// restricted to characters that cannot change what any of those mean.
func cameraSlug(s string) string {
	var b strings.Builder
	lastDash := true
	for _, r := range strings.ToLower(trim(s)) {
		switch {
		case r >= 'a' && r <= 'z', r >= '0' && r <= '9':
			b.WriteRune(r)
			lastDash = false
		case !lastDash:
			b.WriteByte('-')
			lastDash = true
		}
	}
	return clip(strings.Trim(b.String(), "-"), 64)
}

// cameraProblem rejects a camera that cannot possibly connect, with the
// sentence an operator needs rather than a validation code.
func cameraProblem(in CameraInput) (string, bool) {
	if in.Host == nil || trim(*in.Host) == "" {
		return "the camera needs an address on the shop's network, such as 192.168.0.138", false
	}
	if in.Port != nil && (*in.Port < 1 || *in.Port > 65535) {
		return "the port must be between 1 and 65535 - RTSP cameras are usually 554", false
	}
	if in.MaxWidth != nil && *in.MaxWidth < 320 {
		return "frames narrower than 320 pixels are too small to recognise a face in", false
	}
	return "", true
}