Docs improvements + codec

elm.json

@@ -1,16 +1,19 @@
 {
-  "type": "package",
-  "name": "gigobyte/iso8601-duration",
-  "summary": "Parser for ISO 8601 durations",
-  "license": "BSD-3-Clause",
-  "version": "1.0.0",
-  "exposed-modules": ["Iso8601.Duration"],
-  "elm-version": "0.19.0 <= v < 0.20.0",
-  "dependencies": {
-    "elm/core": "1.0.0 <= v < 2.0.0",
-    "elm/parser": "1.1.0 <= v < 2.0.0"
-  },
-  "test-dependencies": {
-    "elm-explorations/test": "1.2.2 <= v < 2.0.0"
-  }
+    "type": "package",
+    "name": "gigobyte/iso8601-duration",
+    "summary": "Parser for ISO 8601 durations",
+    "license": "BSD-3-Clause",
+    "version": "1.0.0",
+    "exposed-modules": [
+        "Iso8601.Duration"
+    ],
+    "elm-version": "0.19.0 <= v < 0.20.0",
+    "dependencies": {
+        "elm/core": "1.0.0 <= v < 2.0.0",
+        "elm/json": "1.1.3 <= v < 2.0.0",
+        "elm/parser": "1.1.0 <= v < 2.0.0"
+    },
+    "test-dependencies": {
+        "elm-explorations/test": "1.2.2 <= v < 2.0.0"
+    }
 }

src/Iso8601/Duration.elm

@@ -1,11 +1,13 @@
-module Iso8601.Duration exposing (Duration, fromString, toString)
+module Iso8601.Duration exposing (Duration, fromString, toString, decoder, encode)
 
-{-| Convert ISO-8601 duration strings to a Duration value and vice versa.
+{-| Convert between ISO-8601 durations strings and `Duration` values.
 
-@docs Duration, fromString, toString
+@docs Duration, fromString, toString, decoder, encode
 
 -}
 
+import Json.Decode as Decode exposing (Decoder)
+import Json.Encode as Encode
 import Parser exposing ((|.), (|=), Parser, Step(..), end, float, loop, oneOf, problem, succeed, symbol)
 
 
@@ -40,7 +42,7 @@ type Element
     | Seconds Float
 
 
-{-| Convert ISO-8601 duration strings to a Duration value.
+{-| Convert from an ISO-8601 duration string to a `Duration` value.
 
 In case a week duration is given only the `days` property will be populated with the number of weeks \* 7.
 
@@ -89,9 +91,9 @@ fromString duration =
                 Nothing
 
 
-{-| Convert a Duration value to a ISO-8601 duration string.
+{-| Convert a `Duration` value to an ISO-8601 duration string.
 
-Week durations are not supported, even values with only days will still be serialized as `PnD`.
+Week durations are not supported, even values with `days` only will still be serialized as `PnD`.
 
 -}
 toString : Duration -> String
@@ -123,6 +125,29 @@ toString duration =
            )
 
 
+{-| Decode an ISO-8601 duration string to a `Duration` value using [`fromString`](#fromString).
+-}
+decoder : Decoder Duration
+decoder =
+    Decode.string
+        |> Decode.andThen
+            (\str ->
+                case fromString str of
+                    Just duration ->
+                        Decode.succeed duration
+
+                    Nothing ->
+                        Decode.fail "Invalid duration string"
+            )
+
+
+{-| Encode a `Duration` value as an ISO-8601 duration string using [`toString`](#toString).
+-}
+encode : Duration -> Encode.Value
+encode =
+    toString >> Encode.string
+
+
 parseElements : Parser (List Element) -> String -> Maybe (List Element)
 parseElements elementParser date =
     Result.toMaybe (Parser.run elementParser date)