feat: rewrite README and expand test coverage

This commit rewrites the project documentation and expands the test suite.

- The README.md is updated to include installation instructions,
  usage examples for basic and lookup modes, an API reference,
  and explanations of BCP 47 and RFC 4647 standards.
- TSDoc comments are added to `src/index.ts` to document functions,
  parameters, and options.
- The test suite in `src/index.spec.ts` is expanded with test cases
  for malformed inputs, edge cases, and real-world browser headers.
- The local `uniq` utility is replaced with the implementation from
  the `es-toolkit` library.

Author: yyxi

README.md

@@ -1,4 +1,82 @@
-# accept-language-parser
+# @escapace/accept-language-parser
 
-Parses the accept-language header from an HTTP request and produces an array of
-language tags.
+Parses HTTP Accept-Language header and returns matched language tags using RFC 4647 algorithms and BCP 47 normalization standards.
+
+## Installation
+
+```bash
+pnpm install @escapace/accept-language-parser
+```
+
+## Usage
+
+```typescript
+import { pick } from '@escapace/accept-language-parser'
+
+// Basic language matching with quality scores
+pick('en-US;q=0.6', ['en', 'pl'])
+// Returns: ['en']
+
+// Lookup algorithm for single best match
+pick('en-US,en;q=0.9,fr;q=0.8', ['en-GB', 'en', 'fr'], { type: 'lookup' })
+// Returns: ['en']
+
+// Empty result when no matches found
+pick('', ['en'])
+// Returns: []
+```
+
+## API
+
+### `pick(acceptLanguage, tags, options?)`
+
+Parses an Accept-Language header and returns matching language tags in preference order.
+
+**Parameters:**
+
+- `acceptLanguage` (string): The Accept-Language header value
+- `tags` (string[]): Array of supported BCP 47 language tags
+- `options` (Options, optional): Configuration options
+
+**Returns:** `string[]` - Array of matched language tags ordered by preference
+
+**Options:**
+
+- `forgiving` (boolean, default: false): Handle malformed language tags gracefully
+- `type` ('basic' | 'lookup', default: 'basic'): Language matching algorithm
+
+**Language Matching Algorithms:**
+
+- `'basic'`: Implements RFC 4647 Section 3.3.1 Basic Filtering. Returns all matching language tags using prefix matching. More specific tags match less specific ranges (e.g., 'en' range matches 'en-GB' tag). Processes all available language tags and returns every tag that matches the Accept-Language preferences.
+
+- `'lookup'`: Implements RFC 4647 Section 3.4 Lookup matching. Returns the single best matching language tag, prioritizing more specific matches. Finds and returns only the most appropriate match from the available options, following language tag hierarchy and preference order.
+
+## Accept-Language Header Format
+
+The Accept-Language header specifies language preferences using quality scores:
+
+```
+Accept-Language: en-US,en;q=0.9,fr;q=0.8,*;q=0.1
+```
+
+- Languages without quality scores default to `q=1.0` (highest priority)
+- Quality scores range from 0.0 to 1.0
+- The `*` wildcard matches any language
+
+## BCP 47 Language Tags
+
+Follows BCP 47 standards for language tag formatting and matching. Language tags use formats like:
+
+- `en` (language)
+- `en-US` (language-region)
+- `zh-Hant-CN` (language-script-region)
+
+Tags are automatically normalized for consistent matching using Unicode CLDR recommendations.
+
+## Credits
+
+Uses functionality from:
+
+- **[bcp-47-normalize](https://github.com/wooorm/bcp-47-normalize)** - BCP 47 language tag normalization and canonicalization
+- **[bcp-47-match](https://github.com/wooorm/bcp-47-match)** - RFC 4647 compliant language tag matching algorithms
+- **[Hono](https://github.com/honojs/hono)** - Accept header parsing utilities ([accept.ts](https://github.com/honojs/hono/blob/main/src/utils/accept.ts))

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@escapace/accept-language-parser",
-  "description": "",
+  "description": "Parse HTTP Accept-Language header and return matched language tags",
   "version": "0.0.0",
   "author": {
     "name": "escapace",
@@ -17,6 +17,7 @@
     "@escapace/pnpm-pack": "0.6.0",
     "@ls-lint/ls-lint": "2.3.1",
     "@vitest/coverage-v8": "3.2.4",
+    "es-toolkit": "1.39.8",
     "eslint": "9.32.0",
     "eslint-config-escapace": "5.8.0",
     "esroll": "0.4.5",