;; This Source Code Form is subject to the terms of the Mozilla Public
;; License, v. 2.0. If a copy of the MPL was not distributed with this
;; file, You can obtain one at http://mozilla.org/MPL/2.0/.
;;
;; Copyright (c) KALEIDOS INC

(ns app.main.repo
  (:require
   [app.common.data :as d]
   [app.common.exceptions :as ex]
   [app.common.logging :as log]
   [app.common.time :as ct]
   [app.common.transit :as t]
   [app.common.uri :as u]
   [app.config :as cf]
   [app.main.data.event :as-alias ev]
   [app.util.http :as http]
   [app.util.sse :as sse]
   [beicon.v2.core :as rx]
   [cuerdas.core :as str]))

(log/set-level! :info)

;; -- Retry helpers -----------------------------------------------------------

(def ^:private retryable-types
  "Set of error types that are considered transient and safe to retry
  for idempotent (GET) requests."
  #{:network              ; js/fetch network-level failure
    :bad-gateway          ; 502
    :service-unavailable  ; 503
    :offline})            ; status 0 (browser offline)

(defn retryable-error?
  "Return true when `error` represents a transient failure that is safe
  to retry.  Only errors whose `ex-data` `:type` belongs to
  `retryable-types` qualify."
  [error]
  (contains? retryable-types (:type (ex-data error))))

(def default-retry-config
  "Default configuration for the retry mechanism on idempotent requests."
  {:max-retries    3
   :base-delay-ms  1000})

(defn with-retry
  "Wrap `observable-fn` (a zero-arg function returning an Observable) so
  that retryable errors are retried up to `:max-retries` times with
  exponential back-off.  Non-retryable errors propagate immediately.

  Accepts an optional `config` map with:
    :max-retries   – maximum number of retries (default 3)
    :base-delay-ms – base delay in ms; doubles each attempt (default 1000)"
  ([observable-fn]
   (with-retry observable-fn default-retry-config))
  ([observable-fn config]
   (with-retry observable-fn config 0))
  ([observable-fn config attempt]
   (let [{:keys [max-retries base-delay-ms]} (merge default-retry-config config)]
     (->> (observable-fn)
          (rx/catch
           (fn [cause]
             (if (and (retryable-error? cause)
                      (< attempt max-retries))
               ;; bit-shift-left 1 N is equivalent to 2^N: shift the bits of the
               ;; number 1 to the left N positions (e.g. 1 -> 2 -> 4 -> 8 -> 16),
               ;; producing exponential backoff delays of 1x, 2x, 4x, 8x, 16x.
               (let [delay-ms (* base-delay-ms (bit-shift-left 1 attempt))]
                 (log/wrn :hint "retrying request"
                          :attempt (inc attempt)
                          :delay delay-ms
                          :error (ex-message cause))
                 (->> (rx/timer delay-ms)
                      (rx/mapcat (fn [_] (with-retry observable-fn config (inc attempt))))))
               (rx/throw cause))))))))

;; -- Response handling -------------------------------------------------------

(defn handle-response
  [{:keys [status body headers uri] :as response}]
  (cond
    (= 204 status)
    ;; We need to send "something" so the streams listening downstream can act
    (rx/of nil)

    (= 502 status)
    (rx/throw (ex-info "http error" {:type :bad-gateway}))

    (= 503 status)
    (rx/throw (ex-info "http error" {:type :service-unavailable}))

    (= 0 (:status response))
    (rx/throw (ex-info "http error" {:type :offline}))

    (= 200 status)
    (rx/of body)

    (= 413 status)
    (rx/throw (ex-info "http error"
                       {:type :validation
                        :code :request-body-too-large}))

    (and (= status 403)
         (or (= "cloudflare" (get headers "server"))
             (= "challenge" (get headers "cf-mitigated"))))
    (rx/throw (ex-info "http error"
                       {:type :authorization
                        :code :challenge-required}))

    (and (>= status 400) (map? body))
    (rx/throw (ex-info "http error" (assoc body :uri uri :status status)))

    :else
    (rx/throw
     (ex/error :type :internal
               :code :unable-to-process-repository-response
               :hint "unable to process repository response"
               :uri uri
               :status status
               :headers headers
               :data body))))

(def default-options
  {:update-file {:query-params [:id]}
   :get-raw-file {:rename-to :get-file :raw-transit? true}

   :create-file-object-thumbnail
   {:query-params [:file-id :object-id :tag]
    :form-data? true}

   :create-file-thumbnail
   {:query-params [:file-id :revn]
    :form-data? true}

   ::sse/export-binfile
   {:stream? true}

   ::sse/clone-template
   {:stream? true}

   ::sse/import-binfile
   {:stream? true}

   ::sse/permanently-delete-team-files
   {:stream? true}

   ::sse/restore-deleted-team-files
   {:stream? true}

   :export-binfile {:response-type :blob}
   :retrieve-list-of-builtin-templates {:query-params :all}})

(defn- send!
  [id params options]
  (let [{:keys [response-type
                stream?
                form-data?
                raw-transit?
                query-params
                rename-to]}
        (-> (get default-options id)
            (merge options))

        decode-fn
        (if raw-transit?
          http/conditional-error-decode-transit
          http/conditional-decode-transit)

        id     (or rename-to id)
        nid    (name id)
        method (cond
                 (= query-params :all)  :get
                 (str/starts-with? nid "get-") :get
                 :else :post)

        response-type
        (d/nilv response-type :text)

        request
        {:method method
         :uri (u/join cf/public-uri "api/main/methods/" nid)
         :credentials "include"
         :headers {"accept" "application/transit+json,text/event-stream,*/*"
                   "x-external-session-id" (cf/external-session-id)
                   "x-session-id" (str cf/session-id)
                   "x-event-origin" (::ev/origin (meta params))}
         :body (when (= method :post)
                 (if form-data?
                   (http/form-data params)
                   (http/transit-data params)))
         :query (if (= method :get)
                  params
                  (if query-params
                    (select-keys params query-params)
                    nil))
         :response-type
         (if stream? nil response-type)}

        tpoint
        (ct/tpoint-ms)]

    (log/trc :hint "make request" :id id)

    (let [make-request
          (fn []
            (->> (http/fetch request)
                 (rx/map http/response->map)
                 (rx/mapcat (fn [{:keys [headers body] :as response}]
                              (log/trc :hint "response received" :id id :elapsed (tpoint))

                              (let [ctype (get headers "content-type")
                                    response-stream? (str/starts-with? ctype "text/event-stream")
                                    tpoint (ct/tpoint-ms)]

                                (when (and response-stream? (not stream?))
                                  (ex/raise :type :assertion
                                            :code :unexpected-response
                                            :hint "expected normal response, received sse stream"
                                            :uri (:uri response)
                                            :status (:status response)))

                                (if response-stream?
                                  (-> (sse/create-stream body)
                                      (sse/read-stream t/decode-str))

                                  (->> response
                                       (http/process-response-type response-type)
                                       (rx/map decode-fn)
                                       (rx/tap (fn [_]
                                                 (log/trc :hint "response decoded" :id id :elapsed (tpoint))))
                                       (rx/mapcat handle-response))))))))]

      ;; Idempotent (GET) requests are automatically retried on
      ;; transient network / server errors.  Mutations are never
      ;; retried to avoid unintended side-effects.
      (if (= :get method)
        (with-retry make-request)
        (make-request)))))

(defmulti cmd! (fn [id _] id))

(defmethod cmd! :default
  [id params]
  (send! id params nil))

(defmethod cmd! :login-with-oidc
  [_ params]
  (let [uri (u/join cf/public-uri "api/auth/oidc")]
    (->> (http/send! {:method :post
                      :uri uri
                      :credentials "include"
                      :headers {"x-external-session-id" (cf/external-session-id)
                                "x-event-origin" (::ev/origin (meta params))}
                      :query params})
         (rx/map http/conditional-decode-transit)
         (rx/mapcat handle-response))))

(defn- send-export
  [{:keys [blob?] :as params}]
  (->> (http/send! {:method :post
                    :uri (u/join cf/public-uri "api/export")
                    :body (http/transit-data (dissoc params :blob?))
                    :headers {"x-external-session-id" (cf/external-session-id)
                              "x-event-origin" (::ev/origin (meta params))}
                    :credentials "include"
                    :response-type (if blob? :blob :text)})
       (rx/map http/conditional-decode-transit)
       (rx/mapcat handle-response)))

(defmethod cmd! :export
  [_ params]
  (let [default {:wait false :blob? false}]
    (send-export (merge default params))))

(derive :upload-file-media-object ::multipart-upload)
(derive :upload-chunk ::multipart-upload)
(derive :update-profile-photo ::multipart-upload)
(derive :update-team-photo ::multipart-upload)

(defmethod cmd! ::multipart-upload
  [id params]
  (->> (http/send! {:method :post
                    :uri  (u/join cf/public-uri "api/main/methods/" (name id))
                    :credentials "include"
                    :headers {"x-external-session-id" (cf/external-session-id)
                              "x-event-origin" (::ev/origin (meta params))}
                    :body (http/form-data params)})
       (rx/map http/conditional-decode-transit)
       (rx/mapcat handle-response)))