Initial commit

.gitignore

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+node_modules/
+dist/

package.json

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+{
+  "name": "concise-redux",
+  "version": "0.1.0",
+  "description": "A minimal, type-safe abstraction on top of Redux for better developer productivity",
+  "main": "dist/index.js",
+  "types": "dist",
+  "scripts": {
+    "build": "tsc -p ."
+  },
+  "keywords": [
+    "typescript",
+    "redux"
+  ],
+  "author": "João Dias",
+  "license": "ISC",
+  "devDependencies": {
+    "typescript": "^4.2.3"
+  }
+}

src/action-creator.ts

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+import { Action } from "./types/action";
+import { ActionMapConstraints } from "./types/action-constraints";
+import { StringKeysOf } from "./types/utils";
+
+export function ActionCreator<ActionMap extends ActionMapConstraints<ActionMap>>() {
+  return function actionFactory<
+    ActionType extends StringKeysOf<ActionMap>,
+    Payload extends ActionMap[ActionType]
+  >(
+    type: ActionType,
+    /**
+     * We use the tuple syntax to check the Payload type because, by default, conditional types distribute over unions.
+     * With this syntax the union type becomes atomic in the sense that the condition is
+     * checked against the whole type instead of its parts.
+     * This is necessary for the cases where Payload can be a union type, e.g., if it is a nullable type.
+     * More info: https://stackoverflow.com/questions/51365467/issue-with-union-types-and-conditional-types
+     */
+    ...payload: [Payload] extends [void] ? [] : [Payload]
+  ): Action<ActionType, Payload> {
+    /**
+     * The return type of actionFactory is a conditional type.
+     * This works great for consuming code.
+     * However, the compiler is not able to match the return type from the function body. This is a design limitation.
+     * Because of this limitation, we need a type assertion / cast.
+     * More info: https://github.com/microsoft/TypeScript/issues/24929
+     */
+    return (payload.length === 0
+      ? { type }
+      : { type, payload: payload[0] }) as Action<ActionType, Payload>;
+  }
+}

src/index.ts

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+export { storeComponent } from "./store-component";
+export { ActionCreator } from "./action-creator";
+export type { ActionUnion } from "./types/action-union";

src/store-component.ts

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+import { ActionCreator } from "./action-creator";
+import { UnknownAction } from "./types/action";
+import { ActionMapConstraints } from "./types/action-constraints";
+import { ActionUnion } from "./types/action-union";
+import { UnknownCaseReducer, CaseReducers } from "./types/case-reducers";
+
+export function storeComponent<
+  ActionMap extends ActionMapConstraints<ActionMap>,
+  State
+>({
+  initialState,
+  caseReducers,
+}: StoreComponentParams<ActionMap, State>) {
+  return {
+    initialState: Object.freeze(initialState),
+    ActionCreator: ActionCreator<ActionMap>(),
+    reducer: (state = initialState, action: ActionUnion<ActionMap>) => {
+      const caseReducer = caseReducers[action.type];
+      return caseReducer
+        ? apply(caseReducer, state, action)
+        : state;
+    }
+  };
+}
+
+function apply<State>(
+  caseReducer: UnknownCaseReducer<State>,
+  state: State,
+  action: UnknownAction
+): State {
+  return {
+    ...state,
+    ...(typeof caseReducer === 'function'
+      ? action.payload === undefined
+        ? caseReducer(state)
+        : caseReducer(action.payload, state)
+      : caseReducer)
+  }
+}
+
+interface StoreComponentParams<ActionMap extends ActionMapConstraints<ActionMap>, State> {
+  initialState: State,
+  caseReducers: CaseReducers<ActionMap, State>
+}

src/types/action-constraints.ts

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+import { IndexableObject } from "./utils";
+
+export type ActionMapConstraints<ActionMap> = IndexableObject & Required<ActionMap>;

src/types/action-union.ts

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+import { Action } from "./action";
+import { ActionMapConstraints } from "./action-constraints";
+import { StringKeysOf } from "./utils";
+
+export type ActionUnion<ActionMap extends ActionMapConstraints<ActionMap>> = {
+  [ActionType in StringKeysOf<ActionMap>]: Action<ActionType, ActionMap[ActionType]>;
+}[StringKeysOf<ActionMap>];

src/types/action.ts

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+/**
+ * We use the tuple syntax to check the Payload type because, by default, conditional types distribute over unions.
+ * With this syntax the union type becomes atomic in the sense that the condition is
+ * checked against the whole type instead of its parts.
+ * This is necessary for the cases where Payload can be a union type, e.g., if it is a nullable type.
+ * More info: https://stackoverflow.com/questions/51365467/issue-with-union-types-and-conditional-types
+ */
+export type Action<Type extends string, Payload> = Readonly<[Payload] extends [void]
+  ? { type: Type }
+  : { type: Type, payload: Payload }>;
+
+export interface UnknownAction {
+  type: string
+  payload?: unknown
+}

src/types/case-reducers.ts

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+import { ActionMapConstraints } from "./action-constraints";
+import { Immutable, StringKeysOf } from "./utils";
+
+export type CaseReducers<ActionMap extends ActionMapConstraints<ActionMap>, State> = {
+  [ActionType in StringKeysOf<ActionMap>]: [ActionMap[ActionType]] extends [void]
+    ? Partial<State> | UnaryCaseReducer<State>
+    : BinaryCaseReducer<ActionMap[ActionType], State>;
+};
+
+interface UnaryCaseReducer<State> {
+  (state: Immutable<State>): Partial<State>
+}
+
+interface BinaryCaseReducer<Payload, State> {
+  (payload: Immutable<Payload>, state: Immutable<State>): Partial<State>
+}
+
+export type UnknownCaseReducer<State> = Partial<State> | ((...args: any[]) => Partial<State>);

src/types/utils.ts

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+export type IndexableObject = Record<keyof never, any>;
+
+export type StringKeysOf<T> = string & keyof T;
+
+export type Primitive =
+	| null
+	| undefined
+	| string
+	| number
+	| boolean
+	| symbol
+	| bigint;
+
+export type Immutable<T extends IndexableObject> = {
+  readonly [K in keyof T]: T[K] extends Primitive
+    ? T[K]
+    : Immutable<T[K]>
+}

tsconfig.json

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+{
+  "compilerOptions": {
+    /* Visit https://aka.ms/tsconfig.json to read more about this file */
+    /* Basic Options */
+    // "incremental": true,                         /* Enable incremental compilation */
+    "target": "es5", /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', or 'ESNEXT'. */
+    "module": "commonjs", /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', 'es2020', or 'ESNext'. */
+    // "lib": [],                                   /* Specify library files to be included in the compilation. */
+    // "allowJs": true,                             /* Allow javascript files to be compiled. */
+    // "checkJs": true,                             /* Report errors in .js files. */
+    // "jsx": "preserve",                           /* Specify JSX code generation: 'preserve', 'react-native', 'react', 'react-jsx' or 'react-jsxdev'. */
+    "declaration": true, /* Generates corresponding '.d.ts' file. */
+    "declarationMap": true, /* Generates a sourcemap for each corresponding '.d.ts' file. */
+    "sourceMap": true, /* Generates corresponding '.map' file. */
+    // "outFile": "./",                             /* Concatenate and emit output to single file. */
+    "outDir": "dist", /* Redirect output structure to the directory. */
+    // "rootDir": "./",                             /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
+    // "composite": true,                           /* Enable project compilation */
+    // "tsBuildInfoFile": "./",                     /* Specify file to store incremental compilation information */
+    // "removeComments": true,                      /* Do not emit comments to output. */
+    // "noEmit": true,                              /* Do not emit outputs. */
+    // "importHelpers": true,                       /* Import emit helpers from 'tslib'. */
+    // "downlevelIteration": true,                  /* Provide full support for iterables in 'for-of', spread, and destructuring when targeting 'ES5' or 'ES3'. */
+    // "isolatedModules": true,                     /* Transpile each file as a separate module (similar to 'ts.transpileModule'). */
+    /* Strict Type-Checking Options */
+    "strict": true, /* Enable all strict type-checking options. */
+    // "noImplicitAny": true,                       /* Raise error on expressions and declarations with an implied 'any' type. */
+    // "strictNullChecks": true,                    /* Enable strict null checks. */
+    // "strictFunctionTypes": true,                 /* Enable strict checking of function types. */
+    // "strictBindCallApply": true,                 /* Enable strict 'bind', 'call', and 'apply' methods on functions. */
+    // "strictPropertyInitialization": true,        /* Enable strict checking of property initialization in classes. */
+    // "noImplicitThis": true,                      /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "alwaysStrict": true,                        /* Parse in strict mode and emit "use strict" for each source file. */
+    /* Additional Checks */
+    // "noUnusedLocals": true,                      /* Report errors on unused locals. */
+    // "noUnusedParameters": true,                  /* Report errors on unused parameters. */
+    // "noImplicitReturns": true,                   /* Report error when not all code paths in function return a value. */
+    // "noFallthroughCasesInSwitch": true,          /* Report errors for fallthrough cases in switch statement. */
+    // "noUncheckedIndexedAccess": true,            /* Include 'undefined' in index signature results */
+    // "noPropertyAccessFromIndexSignature": true,  /* Require undeclared properties from index signatures to use element accesses. */
+    /* Module Resolution Options */
+    // "moduleResolution": "node",                  /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
+    // "baseUrl": "./",                             /* Base directory to resolve non-absolute module names. */
+    // "paths": {},                                 /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
+    // "rootDirs": [],                              /* List of root folders whose combined content represents the structure of the project at runtime. */
+    // "typeRoots": [],                             /* List of folders to include type definitions from. */
+    // "types": [],                                 /* Type declaration files to be included in compilation. */
+    // "allowSyntheticDefaultImports": true,        /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
+    "esModuleInterop": true, /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
+    // "preserveSymlinks": true,                    /* Do not resolve the real path of symlinks. */
+    // "allowUmdGlobalAccess": true,                /* Allow accessing UMD globals from modules. */
+    /* Source Map Options */
+    // "sourceRoot": "",                            /* Specify the location where debugger should locate TypeScript files instead of source locations. */
+    // "mapRoot": "",                               /* Specify the location where debugger should locate map files instead of generated locations. */
+    // "inlineSourceMap": true,                     /* Emit a single file with source maps instead of having a separate file. */
+    // "inlineSources": true,                       /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */
+    /* Experimental Options */
+    // "experimentalDecorators": true,              /* Enables experimental support for ES7 decorators. */
+    // "emitDecoratorMetadata": true,               /* Enables experimental support for emitting type metadata for decorators. */
+    /* Advanced Options */
+    "skipLibCheck": true, /* Skip type checking of declaration files. */
+    "forceConsistentCasingInFileNames": true /* Disallow inconsistently-cased references to the same file. */
+  },
+  "include": [
+    "src"
+  ]
+}