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    # ............................................................................................... #
    #
    # Copyright (c) 2012-2018 Institut National des Sciences Appliquées de Lyon (INSA Lyon) and others
    #
    # This program and the accompanying materials are made available under the
    # terms of the Eclipse Public License 2.0 which is available at
    # http://www.eclipse.org/legal/epl-2.0.
    #
    # SPDX-License-Identifier: EPL-2.0
    #
    # ............................................................................................... #

    ----
    A set of useful APIs for dealing with JSON documents from Golo.

    The implementation is backed by [json-simple](https://code.google.com/p/json-simple/). While
    `json-simple` only supports encoding from lists and maps, this API brings support for sets, arrays,
    Golo tuples, dynamic objects and structs.
    ----
    module gololang.JSON

    # ............................................................................................... #

    ----
    Takes any know object, and gives a JSON string representation:

        let data = map[
          ["name", "Somebody"],
          ["age", 69],
          ["friends", list[
            "Mr Bean", "John B", "Larry"
          ]]
        ]
        let asText = JSON.stringify(data)

    `obj` may be a list, an array, a set, a map, a tuple, a dynamic object or a struct. If `obj` is from
    another type then its string representation is given according to `obj: toString()` or `"null"` if
    `obj` is `null`.
    ----
    function stringify = |obj| {
      let res = stringify_walk(obj)
      if (res is null) {
        return "null"
      } else {
        return res: toString()
      }
    }

    local function isSeq = |obj| ->
      (obj oftype java.util.List.class) or
      (obj oftype java.util.Set.class) or
      (obj oftype gololang.Tuple.class) or
      (isArray(obj))

    local function stringify_walk = |obj| {
      if obj oftype java.util.Map.class {
        let json = org.json.simple.JSONObject()
        foreach key in obj: keySet() {
          json: put(key, stringify_walk(obj: get(key)))
        }
        return json
      } else if isSeq(obj) {
        let json = org.json.simple.JSONArray()
        foreach value in obj {
          json: add(stringify_walk(value))
        }
        return json
      } else if obj oftype gololang.DynamicObject.class {
        let json = org.json.simple.JSONObject()
        foreach prop in obj: properties() {
          let value = prop: getValue()
          if not(isClosure(value)) {
            json: put(prop: getKey(), stringify_walk(value))
          }
        }
        return json
      } else if (obj oftype gololang.GoloStruct.class) {
        let json = org.json.simple.JSONObject()
        foreach member in obj: members() {
          json: put(member, stringify_walk(obj: get(member)))
        }
        return json
      }
      return obj
    }

    ----
    Parses a JSON string and gives an object representation as a list or map collection:

        let data = JSON.parse(text)
        println(data: get("name"))
    ----
    function parse = |str| -> org.json.simple.JSONValue.parseWithException(str)

    # ............................................................................................... #

    ----
    Provides a mixin for dynamic objects that includes a `toJSON()` method:

        object: mixin(JSON.dynamicObjectMixin()): toJSON()

    which is equivalent to:

        JSON.stringify(object)
    ----
    function dynamicObjectMixin = ->
      DynamicObject(): define("toJSON", |this| -> stringify(this))

    ----
    Returns a new dynamic object from a JSON string where each first-level entry is mapped into the
    dynamic object:

        let obj = JSON.toDynamicObject(JSON.stringify(map[
          ["a", "1"], ["b", "2"]
        ]))

        println(obj: a())
        println(obj: b())
    ----
    function toDynamicObject = |str| {
      let obj = DynamicObject()
      let map = parse(str)
      foreach key in map: keySet() {
        obj: define(key, map: get(key))
      }
      return obj
    }

    ----
    Returns a new dynamic object from a JSONObject where each level entry is mapped into the
    dynamic object or an array of dynamic objects.
    ----
    local function toDynamicObjectFromJSONObject = |obj| {
      let isJSONObject = |obj| -> obj oftype org.json.simple.JSONObject.class
      let isJSONArray = |obj| -> obj oftype org.json.simple.JSONArray.class

      let parse_object = |level, obj, dyno| {
        let parseMembers = |obj, dyno| {
          obj: each(|key, value| {
            dyno: define(key, value)
            parse_object(key, value, dyno)
          })
        }

        if isJSONObject(obj) {
          if level is null { # root
            parseMembers(obj, dyno)
          } else {
            dyno: define(level, DynamicObject())
            parseMembers(obj, dyno: get(level))
          }
        } else if isJSONArray(obj) {
            dyno: define(level, list[])
            obj: each(|item| {
              if isJSONObject(item) is false and isJSONArray(item) is false {
                dyno: get(level): append(item)
              } else if isJSONObject(item) {
                  let subDyno = DynamicObject()
                  parseMembers(item, subDyno)
                  dyno: get(level): append(subDyno)
              }
            })
        }
        return dyno
      }
      return parse_object(null, obj, DynamicObject())
    }

    ----
    Returns a list of dynamic objects from a JSONArray where each level entry is mapped into the
    dynamic object or an array of dynamic objects.
    ----
    local function toDynamicObjectsListFromJSONArray = |arr| -> arr: map(|obj| -> toDynamicObjectFromJSONObject(obj))

    ----
    Returns a new dynamic object from a JSON string where each level entry is mapped into the
    dynamic object or an array of dynamic objects:

        let obj = JSON.toDynamicObjectFromJSONString("""
          {
            "id":"bob",
            "friends":[
              {"name":"sam"}, {"name":"jane"}, {"name":"john"}
            ],
            "address": {
              "street":"20 Avenue Albert Einstein",
              "city":"Villeurbanne",
              "zip":"69100",
              "country":"France"
            }
          }
        """)

        obj: friends(): get(2): name(): equals("john") # true
        obj: address(): city(): equals("Villeurbanne") # true
    ----
    function toDynamicObjectFromJSONString = |str| -> toDynamicObjectFromJSONObject(parse(str))

    ----
    Returns a list of dynamic objects from a JSON string where each level entry is mapped into the
    dynamic object or an array of dynamic objects:

        let objects = JSON.toDynamicObjectsListFromJSONString("""[
          {"message":"hello"},
          {
            "id":"bob",
            "friends":[
              {"name":"sam"}, {"name":"jane"}, {"name":"john"}
            ],
            "address": {
              "street":"20 Avenue Albert Einstein",
              "city":"Villeurbanne",
              "zip":"69100",
              "country":"France"
            }
          }
        ]""")

        println(objects: get(1): friends(): get(2): name(): equals("john")) # true
        println(objects: get(1): address(): city(): equals("Villeurbanne")) # true
    ----
    function toDynamicObjectsListFromJSONString = |str| -> toDynamicObjectsListFromJSONArray(parse(str))

    ----
    Returns a new dynamic object from a map where each level entry is mapped into the
    dynamic object or an array of dynamic objects:

        let obj = JSON.toDynamicObjectFromMap(map[
          ["id", "bob"],
          ["friends", [
            map[["name", "sam"]],
            map[["name", "jane"]],
            map[["name", "john"]]
          ]],
          ["address", map[
            ["street", "20 Avenue Albert Einstein"],
            ["city", "Villeurbanne"],
            ["zip", "69100"],
            ["country", "France"]
          ]]
        ])

        println(obj: friends(): get(2): name(): equals("john")) # true
        println(obj: address(): city(): equals("Villeurbanne")) # true
    ----
    function toDynamicObjectFromMap = |mapInstance| -> toDynamicObjectFromJSONObject(parse(stringify(mapInstance)))

    ----
    Returns a list of dynamic objects from a collection of maps where each level entry is mapped into the
    dynamic object or an array of dynamic objects:

        let objects = JSON.toDynamicObjectsListFromMapsCollection([
          map[["message", "hello"]],
          map[
            ["id", "bob"],
            ["friends", list[
              map[["name", "sam"]],
              map[["name", "jane"]],
              map[["name", "john"]]
            ]],
            ["address", map[
              ["street", "20 Avenue Albert Einstein"],
              ["city", "Villeurbanne"],
              ["zip", "69100"],
              ["country", "France"]
            ]]
          ]
        ])

        println(objects: get(1): friends(): get(2): name(): equals("john")) # true
        println(objects: get(1): address(): city(): equals("Villeurbanne")) # true
    ----
    function toDynamicObjectsListFromMapsCollection = |mapInstance| -> toDynamicObjectsListFromJSONArray(parse(stringify(mapInstance)))

    # ............................................................................................... #

    ----
    JSON augmentations for structs.
    ----
    augment gololang.GoloStruct {

      ----
      Conveniently adds a `toJSON()` method, which is equivalent to calling `JSON.stringify()`:

          struct Person = { name, age, email }
          # (...)

          Person("Mr Bean", "mrbean@outlook.com", 64): toJSON()
      ----
      function toJSON = |this| -> stringify(this)

      ----
      Populates the elements of a struct based on the values found in a JSON string.

          let str = JSON.stringify(map[
            ["name", "Foo"],
            ["email", "foo@gmail.com"],
            ["age", 99],
            ["gender", "N/A"]
          ])
          let foo = Person(): updateFromJSON(str)

      Note that missing entries from the JSON data yield `null` values in the struct.
      ----
      function updateFromJSON = |this, str| {
        let map = parse(str)
        foreach member in this: members() {
          this: set(member, map: get(member))
        }
        return this
      }
    }

    # ............................................................................................... #