settings.clj

(ns spec.settings
  "Organizes and validates your settings with clojure.spec and spec-tools."
  (:require [clojure.string :as str]
            [clojure.spec.alpha :as s]
            [spec-tools.spec :as spec]
            [spec-tools.core :as st]
            [spec-tools.data-spec :as ds]))

(defmacro for-map
  "Like for, but returns a map. Expects the result to be a pair or map."
  {:style/indent 1
   :private true}
  [& body]
  `(->> (for ~@body)
        (into {})))

(defn env
  "SampleAPI settings from the environment"
  [& [filter-prefix]]
  (for-map [[s v] (System/getenv)
            :when (and filter-prefix (str/starts-with? s filter-prefix))]
    {(-> (str/lower-case s)
         (str/replace "sampleapi_" "")
         (str/replace "_" "-")
         keyword)
     v}))

(defn props
  "SampleAPI settings from properties"
  [& [filter-prefix]]
  (for-map [[s v] (System/getProperties)
            :when (and filter-prefix (str/starts-with? s filter-prefix))]
    {(-> (str/lower-case s)
         (str/replace-first "sampleapi." "")
         (str/replace "." "-")
         keyword)
     v}))

(defn defaults
  "SampleAPI settings defaults"
  []
  (for-map [[setting {:keys [default] :as config}] settings-config
            :when (not= (config :default ::not-set) ::not-set)]
    {setting default}))

(defn all-settings
  "SampleAPI settings. If given a filter prefix"
  [& [filter-prefix]]
  (merge (env (when filter-prefix (str/upper-case filter-prefix)))
         (props (when filter-prefix (str/lower-case filter-prefix)))
         (defaults)))

(defn validate-settings-fn
  "Validates all-settings meet the settings-spec. Exits the process with explanation on failure."
  [settings-spec all-settings]
  (st/decode settings-spec all-settings st/string-transformer))

(defn validate-settings!
  ([settings-spec]
   (validate-settings! settings-spec (all-settings)))
  ([settings-spec all-settings]
   (let [settings (validate-settings-fn settings-spec all-settings)]
     (if (= ::s/invalid settings)
       (do
         (println "Invalid settings configuration. See spec output:")
         (println
          (with-out-str
            (st/explain settings-spec all-settings st/string-transformer)))
         (System/exit 1))
       settings))))

(defn settings-spec
  [spec-name settings-config]
  (->> {:spec ~(for-map [[setting {:keys [spec]}] settings-config]
                        {setting spec})
        :name ::settings}
       ds/spec))

(comment

  (require '[clojure.spec.alpha :as s])
  (require '[spec-tools.spec :as spec])
  (require '[spec.settings :as ss])

  ;; declare your configuration
  (def settings-config
    {:debug {:spec spec/boolean?
             :default false}
     :num-processes {:spec spec/integer?
                     :default 4}})

  ;; specify your config
  (s/def ::settings (ss/settings-spec ::settings settings-config))

  ;; validate your settings
  (ss/validate-settings! ::settings (all-settings "sampleapp"))

  )