# redux-sac

## Slice redux objects (reducers, middleware, ...)

### `subReducer(key, reducer, additionalKey, ...)`

Creates a wrapper reducer that calls `reducer`
on the sub-state specified by `key`.
Key can go in different formats, see `cowValueModel` below.
Rest of the state is left untouched.

```js
const r = subReducer("persons", personReducer);
  
r({persons: ["John", "Jill"], cars: ["Honda"]}, action);
// => {
//   persons: personReducer(["John", "Jill"], action), 
//   cars: ["Honda"]
// }
```

Respects redux convention that if no change was made,
the identical object should be returned. So in previous case,
if `personReducer` would return the identical array,
`r` would return the state object it was passed in.

If persons were deeper in hierarchy, it could have been created as
`const r = subReducer("files.persons", personReducer);` for example.

You may pass additional keys
as addition arguments. In that case, additional parts of state
will be fetched and passed to a sub-reducer:

```js
const r = subReducer("persons", personReducer, "assets.cars");
  
r({persons: ["John", "Jill"], assets: {cars: ["Honda"]}}, action);
// => {
//   persons: personReducer(["John", "Jill"], action, ["Honda"]), 
//   assets: {cars: ["Honda"]}
// }
```

This technique is mentioned in Redux docs, in "Beyond combineReducers" page.

### `subMiddleware(key | selectorFn, middleware)`

Creates a wrapper middleware
on the sub-state specified by `key`
or the selector function `selectorFn`
by decorating `getState` part of the passed arg.
The `key` can have different format, see `cowValueModel` below.
Rest of the passed arg is left untouched.

```js
const r = subMiddleware("persons", ({getState}) => next => action => {
  console.log(JSON.stringify(getState()));
  return next(action);
});
  
const altR = subMiddleware(state => state.persons, ({getState}) => next => action => {
  console.log(JSON.stringify(getState()));
  return next(action);
});
  
// use r or altR in creation of store
  
store.getState();
// => {persons: ["John", "Jill"], cars: ["Honda"]}
store.dispatch({type: "any"});
// console => ["John","Jill"] 
```

If persons were deeper in hierarchy, it could have been created as
`const r = subMiddleware("files.persons", ...);` for example.

You can use `subMiddleware` to sub-state anything
getting one parameter in which
one of the properties passed is `getState` function;
it is not special-case for middleware.
For example, it is usable for wrapping `redux-effex` effect function.

### `subEffex(key | selectorFn, effects)`

Creates a wrapper around each element
of the effects array
on the sub-state specified by `key`
or by selector function `selectorFn`
by decorating `effect` function with `subMiddleware`
and returns the array of the wrapped effects.

```js
const effects = [{
  action: "foo",
  effect: ({getState}) => {
    console.log(JSON.stringify(getState()));
  }
}];
  
const e = subEffex("persons", effects);
const altE = subEffex(state => state.persons, effects);
  
// use e or altE in creation of store
  
store.getState();
// => {persons: ["John", "Jill"], cars: ["Honda"]}
store.dispatch({type: "foo"});
// console => ["John","Jill"] 
```

## Compose

### `composeReducers(reducer1, reducer2, ...)`

Creates a wrapper reducer that calls passed reducers
one after another, passing intermediate states.
and returning the result of the last one.

Useful to "concatenate" a few `subReducer`s. like:

```js
composeReducers(
  subReducer("files.persons", personReducer, "assets.swag"),
  subReducer("files.clients", clientReducer, "news"),
  subReducer("assets", assetReducer),
  baseReducer
)
```

## Redux helpers

### `cowValueModel(key, ...)`

Creates an overloaded function allowing
to set or get specified key from any object.

It gets when one arg passed, sets when two args passed.
Setting `undefined` ends up as plain get
(ES2015 default arguments semantics),
so props are not created when not present
if setting `undefined`; other values including `null` are ok
and create nonpresent props.

Specify keys by passing a list of keys to `cowValueModel`.
Key can be either:
 - number
 - array of Keys
 - anything else, which is `toString()`ed and dot-split.

Set-usage (two-arg) returns a copy with specified (sub-)property changed;
in case no change actually happens, returns the original object.

```js
const name = cowValueModel("name");
  
name({name: "Tom"});
// => "Tom"
name({name: "Tom"}, "Jerry");
// => {name: "Jerry"}
  
const city = cowValueModel("address.city");
const city2 = cowValueModel("address", "city");
// and other forms, like:
// const city3 = cowValueModel(["address", "city"]);
// const city4 = cowValueModel("address", [[], "city"]);
// const city5 = cowValueModel([[], "address.city"]);
// etc.
const object = {address: {city: "New York"}};
  
city(object);
// => "New York"
city2(object);
// => "New York"
city(object, "London");
// => {address: {city: "London"}}
city2(object, "London");
// => {address: {city: "London"}}
object;
// => {address: {city: "New York"}}
city(object, "New York") === object;
// => true
city2(object, "New York") === object;
// => true
  
city(undefined);
// => undefined
city(null);
// => undefined
city({});
// => undefined
city({address: null});
// => undefined
city({address: {}});
// => undefined
city({address: {city: null}});
// => null
  
city(undefined, "London");
// => {address: {city: "London"}}
city(null, "London");
// => {address: {city: "London"}}
city({}, "London");
// => {address: {city: "London"}}
city({address: null}, "London");
// => {address: {city: "London"}}
city({address: {}}, "London");
// => {address: {city: "London"}}
city({address: {city: null}}, "London");
// => {address: {city: "London"}}
```

If you put a number in a list of keys to use,
an object will be treated as an array (unlike the default string case,
where it is treated as an object), so copy wil be created
using `[...obj]`, not using `{...obj}`.

That way you can create eg. `const c = cowValueObject("person", 34, "name")`
to access `obj.person[34].name` with `c(obj)` / `c(obj, val)`.

### `typedAction(type, [fn])`

This creates an action creator function that amends existing `fn` by:
  - adding a `type` property to the result, as well as
  - adding a `TYPE` property to action creator itself.

So for example:

```js
export const answerQuestion =
  typedAction("answer question", (index, answer) => ({
    payload: {index, answer}
  }));
```

allows you to call `answerQuestion(2, "Albert Einstein")` to create
`{type: "answer question", payload: {index: 2, answer: "Albert Einstein"}}`;
but it also allows you to use `case answerQuestion.TYPE:` in your reducer,
since `answerQuestion.TYPE === "answer question"`.
IOW, this removes the two-space problem of having `const FOO_BAR_TYPE`
as well as `fooBar` action creator.


In case you don't pass the `fn` argument, the action creator only creates `{type}`.

### `cowWorkshop(keys, fn = x => x)(obj, [options])`

This is multipurpose enumerate-and-act function to manipulate objects
using `cowValueModel`. The `options` argument can contain these additional fields:
  - `result` -- where to put elements (`obj` by default),
  - `resultKeys` -- what keys to use to put into `result` (`keys` by default)
  - `diff` -- where to put diffing elements (`undefined` by default)

Function enumerates over keys and performs
"get key from obj, call fn on value, put transformed value into resultKey in result"
operations over them, using `cowValueModel` for getting as well as putting.
Additionally, if putting actually resulted in change,
the result key and value is also put into `diff`.
It then returns `{result, diff}` object.

```js
cowWorkshop(["a", "b.c"])();
// does nothing
// => {result: undefined, diff: undefined}
  
cowWorkshop(["a", "b.c"], () => null)();
// sets a and b.c to null
// => {result: {a: null, b: {c: null}}, diff: {a: null, b: {c: null}}}
  
const data = {a: 'foo', b: {c: null}};
cowWorkshop(["a", "b.c"], JSON.stringify)(data);
// changes a and b.c to string representation; change to a is noop
// => {result: {a: 'foo', b: {c: 'null'}}, diff: {b: {c: 'null'}}}
  
const stored = {ay: 'bar', beecee: 'baz', cee: 'quux'};
const data = {a: 'foo', b: {c: null}};
cowWorkshop(["a", "b.c"])(data, {result: stored, resultKeys: ["ay", "beecee"]});
// "copies" a and b.c into `stored` under different keys
// => {result: {ay: 'foo', beecee: null, cee: 'quux'}, diff: {ay: 'foo', beecee: null}}
  
const data = {a: 'foo', b: {c: 'bar'}, c: 'quux'};
cowWorkshop(["a", "b.c"], () => null)(data);
// "nulls" a few fields
// => {result: {a: null, b: {c: null}, c: 'quux'}, diff: {a: null, b: {c: null}}}
```