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serialization.js
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serialization.js
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//----------------------------------------------------------------------
//
// This source file is part of the Folktale project.
//
// Licensed under MIT. See LICENCE for full licence information.
// See CONTRIBUTORS for the list of contributors to the project.
//
//----------------------------------------------------------------------
// --[ Dependencies ]---------------------------------------------------
const { tagSymbol, typeSymbol } = require('../data');
const mapValues = require('folktale/core/object/map-values');
const values = require('folktale/core/object/values');
const extend = require('folktale/helpers/extend');
// --[ Constants ]------------------------------------------------------
const typeJsonKey = '@@type';
const tagJsonKey = '@@tag';
const valueJsonKey = '@@value';
// --[ Helpers ]--------------------------------------------------------
/*~
* type: ((Object 'a) => 'b) => ([Object 'a]) => Object 'b
*/
const arrayToObject = (extractKey) => (array) =>
array.reduce((object, element) => {
object[extractKey(element)] = element;
return object;
}, {});
/*~
* type: (String) => (Object 'a) => 'a | None
*/
const property = (propertyName) => (object) => object[propertyName];
/*~
* type: ([Object 'a]) => Object 'a
*/
const indexByType = arrayToObject(property(typeSymbol));
/*~
* type: (String, String) => Bool
*/
const assertType = (given, expected) => {
if (expected !== given) {
throw new TypeError(`
The JSON structure was generated from ${expected}.
You are trying to parse it as ${given}.
`);
}
};
/*~
* type: |
* type JSONSerialisation = {
* "@@type": String,
* "@@tag": String,
* "@@value": Object Any
* }
* type JSONParser = {
* fromJSON: (JSONSerialisation, Array JSONParser) => Variant
* }
*
* (Object JSONParser) => (JSONSerialisation) => Any
*/
const parseValue = (parsers) => (value) => {
if (value !== null && typeof value[typeJsonKey] === 'string') {
const type = value[typeJsonKey];
if (parsers[type]) {
return parsers[type].fromJSON(value, parsers, true);
} else {
return value;
}
} else {
return value;
}
};
/*~
* type: ('a) => JSON
*/
const serializeValue = (value) =>
value !== null && typeof value.toJSON === 'function' ? value.toJSON()
: /* otherwise */ value;
// --[ Implementation ]-------------------------------------------------
/*~
* stability: experimental
* authors:
* - "@boris-marinov"
*
* type: |
* (Variant, ADT) => Void
*/
const serialization = (variant, adt) => {
const typeName = adt[typeSymbol];
const tagName = variant.prototype[tagSymbol];
/*~
* stability: experimental
* module: null
* authors:
* - "@boris-marinov"
*
* type: |
* type JSONSerialisation = {
* "@@type": String,
* "@@tag": String,
* "@@value": Object Any
* }
*
* Variant . () => JSONSerialisation
*/
variant.prototype.toJSON = function() {
return {
[typeJsonKey]: typeName,
[tagJsonKey]: tagName,
[valueJsonKey]: mapValues(this, serializeValue)
};
};
/*~
* stability: experimental
* module: null
* authors:
* - "@boris-marinov"
*
* type: |
* type JSONSerialisation = {
* "@@type": String,
* "@@tag": String,
* "@@value": Object Any
* }
* type JSONParser = {
* fromJSON: (JSONSerialisation, Array JSONParser) => Variant
* }
*
* (JSONSerialisation, Array JSONParser) => Variant
*/
adt.fromJSON = function(value, parsers = { [typeName]: adt }, keysIndicateType = false) {
const valueTypeName = value[typeJsonKey];
const valueTagName = value[tagJsonKey];
const valueContents = value[valueJsonKey];
assertType(typeName, valueTypeName);
const parsersByType = keysIndicateType ? parsers
: /*otherwise*/ indexByType(values(parsers));
const parsedValue = mapValues(valueContents, parseValue(parsersByType));
return extend(Object.create(adt[valueTagName].prototype), parsedValue);
};
};
// --[ Exports ]--------------------------------------------------------
module.exports = serialization;