package agents

import (
	"context"
	"encoding/json"
	"errors"
	"log/slog"
	"net/http"

	"github.com/sentry/sentry/api/authz"
)

// store is the narrow interface Handler depends on -- *Store (store.go)
// is the production implementation; tests use a fake, same pattern as
// dashboards.store/queryapi's SQLRunner.
type store interface {
	List(ctx context.Context, tenantID string) ([]Agent, error)
	Get(ctx context.Context, tenantID, host string) (*Agent, error)
	SetOverride(ctx context.Context, tenantID, host string, override ConfigOverride, updatedBy string) (*Agent, error)
	ClearOverride(ctx context.Context, tenantID, host string) error
}

type Handler struct {
	logger     *slog.Logger
	store      store
	authorizer authz.Authorizer
}

func NewHandler(logger *slog.Logger, store store, authorizer authz.Authorizer) *Handler {
	return &Handler{logger: logger, store: store, authorizer: authorizer}
}

// RegisterRoutes: viewing inventory is RoleViewer (same bar as viewing
// a dashboard); editing an agent's remote config is RoleEditor -- an
// operational-tuning action, not an admin-only one, matching the RBAC
// matrix's treatment of alert rules/notification targets rather than
// user/role management.
func (h *Handler) RegisterRoutes(mux *http.ServeMux) {
	mux.HandleFunc("GET /agents", authz.RequireRole(h.authorizer, authz.RoleViewer, h.handleList))
	mux.HandleFunc("GET /agents/{host}", authz.RequireRole(h.authorizer, authz.RoleViewer, h.handleGet))
	mux.HandleFunc("PUT /agents/{host}/config", authz.RequireRole(h.authorizer, authz.RoleEditor, h.handleSetConfig))
	mux.HandleFunc("DELETE /agents/{host}/config", authz.RequireRole(h.authorizer, authz.RoleEditor, h.handleClearConfig))
}

// tenantID mirrors dashboards.Handler.tenantID exactly -- resolved from
// the authenticated identity, never from a client-supplied field
// (there isn't one here to begin with; host alone identifies an agent
// within a tenant).
func (h *Handler) tenantID(r *http.Request) string {
	if id, ok := authz.IdentityFromContext(r.Context()); ok && id.TenantID != "" {
		return id.TenantID
	}
	return "default"
}

func (h *Handler) updatedBy(r *http.Request) string {
	if id, ok := authz.IdentityFromContext(r.Context()); ok {
		return id.UserID
	}
	return ""
}

func (h *Handler) handleList(w http.ResponseWriter, r *http.Request) {
	list, err := h.store.List(r.Context(), h.tenantID(r))
	if err != nil {
		h.logger.Error("listing agents", "error", err)
		writeError(w, http.StatusInternalServerError, "listing agents failed")
		return
	}
	writeJSON(w, http.StatusOK, list)
}

func (h *Handler) handleGet(w http.ResponseWriter, r *http.Request) {
	a, err := h.store.Get(r.Context(), h.tenantID(r), r.PathValue("host"))
	if err != nil {
		h.writeStoreErr(w, err, "getting agent")
		return
	}
	writeJSON(w, http.StatusOK, a)
}

// setConfigRequest is deliberately the same shape as ConfigOverride
// (Handler just decodes straight into it) -- every field optional,
// unset means "no override for this field." A caller changing just one
// field (e.g. only heartbeat_interval_ms) must still send the fields
// they want to KEEP as an override alongside it, since SetOverride
// replaces the whole stored override -- the web UI's edit form always
// reads the agent's current DesiredOverride first and PUTs back the
// full merged set, same pattern any other "edit form that PUTs a whole
// resource" in this codebase already uses (e.g. dashboards' PUT).
func (h *Handler) handleSetConfig(w http.ResponseWriter, r *http.Request) {
	var override ConfigOverride
	if !decodeJSON(w, r, &override) {
		return
	}
	if err := validateOverride(override); err != nil {
		writeError(w, http.StatusBadRequest, err.Error())
		return
	}

	a, err := h.store.SetOverride(r.Context(), h.tenantID(r), r.PathValue("host"), override, h.updatedBy(r))
	if err != nil {
		h.writeStoreErr(w, err, "setting agent config")
		return
	}
	writeJSON(w, http.StatusOK, a)
}

func (h *Handler) handleClearConfig(w http.ResponseWriter, r *http.Request) {
	if err := h.store.ClearOverride(r.Context(), h.tenantID(r), r.PathValue("host")); err != nil {
		h.writeStoreErr(w, err, "clearing agent config")
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// validateOverride rejects the two footguns a naive remote-config-edit
// feature could otherwise ship: a batch/heartbeat interval of 0 would
// mean "flush constantly"/"heartbeat constantly," hammering ingest and
// the agent's own CPU for no operator-intended reason -- floors match
// this codebase's other real floors (alerting's own
// eval_interval_seconds >= 30, found live during the heartbeat feature
// this builds on). There is deliberately no validation here for
// tls/ingest fields, because ConfigOverride has no such fields at all
// -- ingest connection details are not a remotely-editable dimension of
// an agent's config, full stop (see /docs/agent-management-design.md's
// security boundary section).
func validateOverride(o ConfigOverride) error {
	if o.BatchMaxSize != nil && *o.BatchMaxSize < 1 {
		return errors.New("batch_max_size must be at least 1")
	}
	if o.BatchFlushIntervalMS != nil && *o.BatchFlushIntervalMS < 100 {
		return errors.New("batch_flush_interval_ms must be at least 100")
	}
	if o.HeartbeatIntervalMS != nil && *o.HeartbeatIntervalMS < 5000 {
		return errors.New("heartbeat_interval_ms must be at least 5000 (5s)")
	}
	return nil
}

func (h *Handler) writeStoreErr(w http.ResponseWriter, err error, action string) {
	if errors.Is(err, ErrNotFound) {
		writeError(w, http.StatusNotFound, "agent not found")
		return
	}
	h.logger.Error(action, "error", err)
	writeError(w, http.StatusInternalServerError, action+" failed")
}

const maxBodyBytes = 1 << 20 // 1 MiB, same cap as queryapi/dashboards

func decodeJSON(w http.ResponseWriter, r *http.Request, v any) bool {
	r.Body = http.MaxBytesReader(w, r.Body, maxBodyBytes)
	if err := json.NewDecoder(r.Body).Decode(v); err != nil {
		writeError(w, http.StatusBadRequest, "invalid JSON body: "+err.Error())
		return false
	}
	return true
}

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

type errorResponse struct {
	Error string `json:"error"`
}

func writeError(w http.ResponseWriter, status int, msg string) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(errorResponse{Error: msg})
}