json parser

simple-parsers/src/test/scala/JsonParser.scala

@@ -0,0 +1,108 @@
+import cats.data.NonEmptyList
+import cats.parse.{Parser, Rfc5234, StringCodec}
+import org.scalatest.funsuite.AnyFunSuite
+
+import scala.util.Try
+
+class JsonParser extends ParserSuite {
+
+  enum JsonValue {
+    case JsonNull
+    case JsonBoolean(value: Boolean)
+    case JsonNumber(value: BigDecimal)
+    case JsonString(value: String)
+    case JsonArray(values: List[JsonValue])
+    case JsonObject(pairs: List[(String, JsonValue)])
+  }
+  import JsonValue.*
+
+  val comma = Parser.char(',').surroundedBy(Rfc5234.wsp.rep0)
+  val colon = Parser.char(':').surroundedBy(Rfc5234.wsp.rep0)
+
+  val jsonNull: Parser[JsonValue] = Parser.string("null").as(JsonNull).withContext("null")
+  val jsonBoolean: Parser[JsonValue] =
+    (Parser
+      .string("false")
+      .as(JsonBoolean(false)) | Parser.string("true").as(JsonBoolean(true))).withContext("boolean")
+  val jsonNumber: Parser[JsonValue] =
+    cats.parse.Numbers.jsonNumber.mapFilter(s => Try(JsonNumber(BigDecimal(s))).toOption)
+
+  val jsonStringParser: Parser[String] = cats.parse.strings.Json.delimited.parser
+
+  val jsonString: Parser[JsonValue] = jsonStringParser.map(JsonString.apply)
+
+  val jsonScalar: Parser[JsonValue] = jsonNull | jsonBoolean | jsonNumber | jsonString
+
+  val jsonRecur: Parser[JsonValue] = Parser.defer {
+    val jsonValue = jsonRecur | jsonScalar
+    val jsonArray: Parser[JsonValue] = {
+      Parser.string("[]").as(JsonArray(List.empty)).backtrack |
+        jsonValue
+          .repSep(comma)
+          .between(Parser.char('['), Parser.char(']'))
+          .map(nel => JsonArray(nel.toList))
+    }
+
+    val jsonObject: Parser[JsonValue] =
+      Parser.string("{}").as(JsonObject(List.empty)).backtrack |
+        ((jsonStringParser <* colon) ~ jsonValue)
+          .repSep(comma)
+          .between(
+            Parser.char('{'),
+            Parser.char('}')
+          )
+          .map((pairs: NonEmptyList[(String, JsonValue)]) => JsonObject(pairs.toList))
+
+    jsonArray | jsonObject
+  }
+
+  val jsonValue: Parser[JsonValue] = jsonScalar | jsonRecur
+
+  test("null") {
+    assertParses(jsonValue, "null" -> JsonNull)
+  }
+
+  test("true/false") {
+    val validInputs = List(
+      "false" -> JsonBoolean(false),
+      "true"  -> JsonBoolean(true)
+    )
+
+    assertParses(jsonValue, validInputs*)
+  }
+
+  test("jsonNumber") {
+    val validInputs = List(
+      "123"     -> JsonNumber(BigDecimal("123")),
+      "123.123" -> JsonNumber(BigDecimal("123.123"))
+    )
+
+    assertParses(jsonValue, validInputs*)
+  }
+
+  test("jsonString") {
+    val validInputs = List(
+      "\"foo\"" -> JsonString("foo"),
+      "\"æøå\"" -> JsonString("æøå")
+    )
+    assertParses(jsonValue, validInputs*)
+  }
+
+  test("jsonArray") {
+    val validInputs = List(
+      "[]"    -> JsonArray(List.empty),
+      "[1,2]" -> JsonArray(List(JsonNumber(BigDecimal(1)), JsonNumber(BigDecimal(2))))
+    )
+
+    assertParses(jsonValue, validInputs*)
+  }
+
+  test("jsonObject") {
+    val validInputs = List(
+      "{}"             -> JsonObject(List.empty),
+      """{"test":1}""" -> JsonObject(List("test" -> JsonNumber(BigDecimal(1))))
+    )
+
+    assertParses(jsonValue, validInputs*)
+  }
+}