From 687a3bff89f9688361cb28235c732c9a7dca4b24 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ramirez=20Vargas=2C=20Jos=C3=A9=20Pablo?=
 <webJose@gmail.com>
Date: Wed, 19 Feb 2025 13:05:57 -0600
Subject: [PATCH] feat:  Add the LinkContext component

Closes FEATURE:  Option to preserve query parameters #9 .
---
 src/lib/Link/Link.svelte               | 176 ++++++++++++++-----------
 src/lib/Link/README.md                 |   1 +
 src/lib/LinkContext/LinkContext.svelte |  91 +++++++++++++
 src/lib/LinkContext/README.md          |  45 +++++++
 src/lib/index.ts                       |   1 +
 5 files changed, 236 insertions(+), 78 deletions(-)
 create mode 100644 src/lib/LinkContext/LinkContext.svelte
 create mode 100644 src/lib/LinkContext/README.md

diff --git a/src/lib/Link/Link.svelte b/src/lib/Link/Link.svelte
index 5c441ee..97bdb5b 100644
--- a/src/lib/Link/Link.svelte
+++ b/src/lib/Link/Link.svelte
@@ -1,108 +1,128 @@
 <script lang="ts">
 	import { location } from '$lib/core/Location.js';
 	import { joinPaths, resolveHashValue } from '$lib/core/RouterEngine.svelte.js';
+	import { getLinkContext, type ILinkContext } from '$lib/LinkContext/LinkContext.svelte';
 	import { getRouterContext } from '$lib/Router/Router.svelte';
 	import type { ActiveState } from '$lib/types.js';
 	import { type Snippet } from 'svelte';
 	import type { HTMLAnchorAttributes } from 'svelte/elements';
 
-	type Props = HTMLAnchorAttributes & {
-		/**
-		 * Sets the hash mode of the component.
-		 *
-		 * If `true`, the component will search for the immediate parent router configured for single hash routing.
-		 *
-		 * If a string, the component will search for the immediate parent router configured for multi hash routing
-		 * that matches the string.
-		 *
-		 * If `false`, the component will search for the immediate parent router configured for path routing.
-		 *
-		 * If left undefined, it will resolve to one of the previous values based on the `implicitMode` routing option.
-		 *
-		 * **IMPORTANT**:  Because the hash value directly affects the search for the parent router, it cannot be
-		 * reactively set to different values at will.  If you must do this, destroy and recreate the component
-		 * whenever the hash changes:
-		 *
-		 * @example
-		 * ```svelte
-		 * {#key hash}
-		 * 	   <Link {hash} />
-		 * {/key}
-		 * ```
-		 * 
-		 * Unlike other components, the `Link` component does not need a parent router to function.  It can be used 
-		 * anywhere in the application.  The following features, however, will not work:
-		 * 
-		 * - The `activeState` property:  It depends on the parent router to set its active state reactively when a 
-		 * route becomes active.
-		 * - The `prependBasePath` property:  It depends on the parent router to set the base path for the link.
-		 */
-		hash?: boolean | string;
-		/**
-		 * Sets the URL to navigate to.  Never use a full URL; always use relative or absolute paths.
-		 */
-		href: string;
-		/**
-		 * Configures the link so it replaces the current URL as opposed to pushing the URL as a new entry in the 
-		 * browser's History API.
-		 */
-		replace?: boolean;
-		/**
-		 * Sets the state object to pass to the browser's History API when pushing or replacing the URL.
-		 * 
-		 * If a function is provided, it will be called and its return value will be used as the state object.
-		 */
-		state?: any;
-		/**
-		 * Sets the various options that are used to automatically style the anchor tag whenever a particular route 
-		 * becomes active.
-		 * 
-		 * **IMPORTANT**:  This only works if the component is within a `Router` component.
-		 */
-		activeState?: ActiveState;
-		/**
-		 * Configures the component to prepend the parent router's base path to the `href` property.
-		 * 
-		 * This is recommended to achieve path independence in the application.  If, say, a NavBar component contains 
-		 * links to different parts of the application, and this is a reusable component or a micro-frontend, then the 
-		 * Link components inside the NavBar will inherit whatever route the controller shell has assigned to the 
-		 * instance of the NavBar.
-		 * 
-		 * **IMPORTANT**:  This only works if the component is within a `Router` component.
-		 */
-		prependBasePath?: boolean;
-		/**
-		 * Renders the children of the component.
-		 */
-		children?: Snippet;
-	};
+	type Props = HTMLAnchorAttributes &
+		ILinkContext & {
+			/**
+			 * Sets the hash mode of the component.
+			 *
+			 * If `true`, the component will search for the immediate parent router configured for single hash routing.
+			 *
+			 * If a string, the component will search for the immediate parent router configured for multi hash routing
+			 * that matches the string.
+			 *
+			 * If `false`, the component will search for the immediate parent router configured for path routing.
+			 *
+			 * If left undefined, it will resolve to one of the previous values based on the `implicitMode` routing option.
+			 *
+			 * **IMPORTANT**:  Because the hash value directly affects the search for the parent router, it cannot be
+			 * reactively set to different values at will.  If you must do this, destroy and recreate the component
+			 * whenever the hash changes:
+			 *
+			 * @example
+			 * ```svelte
+			 * {#key hash}
+			 * 	   <Link {hash} />
+			 * {/key}
+			 * ```
+			 *
+			 * Unlike other components, the `Link` component does not need a parent router to function.  It can be used
+			 * anywhere in the application.  The following features, however, will not work:
+			 *
+			 * - The `activeState` property:  It depends on the parent router to set its active state reactively when a
+			 * route becomes active.
+			 * - The `prependBasePath` property:  It depends on the parent router to set the base path for the link.
+			 */
+			hash?: boolean | string;
+			/**
+			 * Sets the URL to navigate to.  Never use a full URL; always use relative or absolute paths.
+			 */
+			href: string;
+			/**
+			 * Sets the state object to pass to the browser's History API when pushing or replacing the URL.
+			 *
+			 * If a function is provided, it will be called and its return value will be used as the state object.
+			 */
+			state?: any;
+			/**
+			 * Sets the various options that are used to automatically style the anchor tag whenever a particular route
+			 * becomes active.
+			 *
+			 * **IMPORTANT**:  This only works if the component is within a `Router` component.
+			 */
+			activeState?: ActiveState;
+			/**
+			 * Renders the children of the component.
+			 */
+			children?: Snippet;
+		};
 
 	let {
 		hash,
 		href,
-		replace = false,
+		replace,
 		state,
 		activeState,
 		class: cssClass,
 		style,
-		prependBasePath = false,
+		prependBasePath,
+		preserveQuery,
 		children,
 		...restProps
 	}: Props = $props();
 
 	const router = getRouterContext(resolveHashValue(hash));
+	const linkContext = getLinkContext();
 
-	let isActive = $derived(!!router?.routeStatus[activeState?.key ?? '']?.match);
-	let calcHref = $derived(prependBasePath ? joinPaths(router?.basePath ?? '', href) : href);
+	const calcReplace = $derived(replace ?? linkContext?.replace ?? false);
+	const calcPreserveQuery = $derived(preserveQuery ?? linkContext?.preserveQuery ?? false);
+	const calcPrependBasePath = $derived(prependBasePath ?? linkContext?.prependBasePath ?? false);
+	const isActive = $derived(!!router?.routeStatus[activeState?.key ?? '']?.match);
+	const calcHref = $derived(buildHref());
+
+	function buildHref() {
+		const pathname = calcPrependBasePath ? joinPaths(router?.basePath ?? '', href) : href;
+		if (hash || !calcPreserveQuery || !location.url.searchParams.size) {
+			return pathname;
+		}
+		let searchParams: URLSearchParams;
+		if (calcPreserveQuery === true) {
+			searchParams = location.url.searchParams;
+		} else {
+			searchParams = new URLSearchParams();
+			const transferValue = (key: string) => {
+				const value = location.url.searchParams.getAll(key);
+				if (value) {
+					value.forEach((v) => searchParams.append(key, v));
+				}
+			};
+			if (Array.isArray(calcPreserveQuery)) {
+				for (let key of calcPreserveQuery) {
+					transferValue(key);
+				}
+			} else {
+				transferValue(calcPreserveQuery);
+			}
+		}
+		return `${pathname}?${searchParams}`;
+	}
 
 	function handleClick(event: MouseEvent) {
 		event.preventDefault();
 		const newState = typeof state === 'function' ? state() : state;
 		if (typeof hash === 'string') {
-			location.navigate(calcHref, hash, { replace, state: newState });
-		}
-		else {
-			location.navigate(!!hash ? `#${calcHref}` : calcHref, { replace, state: newState });
+			location.navigate(calcHref, hash, { replace: calcReplace, state: newState });
+		} else {
+			location.navigate(!!hash ? `#${calcHref}` : calcHref, {
+				replace: calcReplace,
+				state: newState
+			});
 		}
 	}
 
diff --git a/src/lib/Link/README.md b/src/lib/Link/README.md
index 0f4d9e7..c270a4f 100644
--- a/src/lib/Link/README.md
+++ b/src/lib/Link/README.md
@@ -13,6 +13,7 @@ SPA-friendly navigation (navigation without reloading).
 | `state` | `any` | `undefined` | | Sets the state object to pass to the browser's History API when pushing or replacing the URL. |
 | `activeState` | `ActiveState` | `undefined` | | Sets the various options that are used to automatically style the anchor tag whenever a particular route becomes active. |
 | `prependBasePath` | `boolean` | `false` | | Configures the component to prepend the parent router's base path to the `href` property. |
+| `preserveQuery` | `boolean \| string \| string[]` | `false` | | Configures the component to preserve the query string whenever it triggers navigation. |
 | `children` | `Snippet` | `undefined` | | Renders the children of the component. |
 
 [Online Documentation](https://wjfe-n-savant.hashnode.space/wjfe-n-savant/components/link)
diff --git a/src/lib/LinkContext/LinkContext.svelte b/src/lib/LinkContext/LinkContext.svelte
new file mode 100644
index 0000000..3629125
--- /dev/null
+++ b/src/lib/LinkContext/LinkContext.svelte
@@ -0,0 +1,91 @@
+<script lang="ts" module>
+	import { getContext, setContext, type Snippet } from 'svelte';
+
+	export type ILinkContext = {
+		/**
+		 * Configures the link so it replaces the current URL as opposed to pushing the URL as a new entry in the
+		 * browser's History API.
+		 */
+		replace?: boolean;
+		/**
+		 * Configures the component to prepend the parent router's base path to the `href` property.
+		 *
+		 * This is recommended to achieve path independence in the application.  If, say, a NavBar component contains
+		 * links to different parts of the application, and this is a reusable component or a micro-frontend, then the
+		 * Link components inside the NavBar will inherit whatever route the controller shell has assigned to the
+		 * instance of the NavBar.
+		 *
+		 * **IMPORTANT**:  This only works if the component is within a `Router` component.
+		 */
+		prependBasePath?: boolean;
+		/**
+		 * Configures the component to preserve the query string whenever it triggers navigation.
+		 *
+		 * This is useful when you have query string values that are controlled by components that are not changing
+		 * with the route.  For example, a search component that is not part of the route but is used to filter the
+		 * data displayed on the page.
+		 *
+		 * Set to `false` to not preserve the query string.
+		 *
+		 * Set to `true` to preserve the entire query string.
+		 *
+		 * Set to a string or an array of strings to preserve only the specified query string values.
+		 */
+		preserveQuery?: boolean | string | string[];
+	};
+
+	class _LinkContext implements ILinkContext {
+		replace = $state(false);
+		prependBasePath = $state(false);
+		preserveQuery = $state<ILinkContext['preserveQuery']>(false);
+
+		constructor(
+			replace: boolean,
+			prependBasePath: boolean,
+			preserveQuery: ILinkContext['preserveQuery']
+		) {
+			this.replace = replace;
+			this.prependBasePath = prependBasePath;
+			this.preserveQuery = preserveQuery;
+		}
+	}
+
+	const linkCtxKey = Symbol();
+
+	export function getLinkContext() {
+		return getContext<ILinkContext | undefined>(linkCtxKey);
+	}
+</script>
+
+<script lang="ts">
+	type Props = ILinkContext & {
+		/**
+		 * Renders the children of the component.
+		 */
+		children?: Snippet;
+	};
+
+	let {
+		replace = false,
+		prependBasePath = false,
+		preserveQuery = false,
+		children,
+	}: Props = $props();
+
+	const parentContext = getLinkContext();
+	const context = new _LinkContext(
+		parentContext?.replace ?? replace,
+		parentContext?.prependBasePath ?? prependBasePath,
+		parentContext?.preserveQuery ?? preserveQuery
+	);
+
+	setContext(linkCtxKey, context);
+
+	$effect.pre(() => {
+		context.prependBasePath = prependBasePath;
+		context.replace = replace;
+		context.preserveQuery = preserveQuery;
+	});
+</script>
+
+{@render children?.()}
diff --git a/src/lib/LinkContext/README.md b/src/lib/LinkContext/README.md
new file mode 100644
index 0000000..f1b1fa2
--- /dev/null
+++ b/src/lib/LinkContext/README.md
@@ -0,0 +1,45 @@
+# LinkContext
+
+The `LinkContext` component is used to create context for `Link` components.  This context can be used to set, in 
+mass, the `replace`, `prependBasePath` and `preserveQuery` properties.
+
+Instead of writing this:
+
+```svelte
+<Link prependBasePath preserveQuery href="...">...</Link>
+<Link prependBasePath preserveQuery href="...">...</Link>
+<Link prependBasePath preserveQuery href="...">...</Link>
+<Link prependBasePath preserveQuery href="...">...</Link>
+```
+
+You can do:
+
+```svelte
+<LinkContext prependBasePath preserveQuery>
+    <Link href="...">...</Link>
+    <Link href="...">...</Link>
+    <Link href="...">...</Link>
+</LinkContext>
+```
+
+Unlike the rest of components in this library, this one does not support the `hash` property.  The context is 
+inherited by all links among its children.
+
+**Note**:  The `preserveQuery` option only has an effect on path routing links since hash routing links should not 
+lose the query string.
+
+## Priorities
+
+The `Link` component will give priority to an explicitly-set value at its property level.  If a property-level value is 
+not found, then the context-provided property value is used.  If there is no context, then the default value takes over.
+
+## Props
+
+| Property | Type | Default Value | Bindable | Description |
+|-|-|-|-|-|
+| `replace` | `boolean` | `false` | | Configures the link so it replaces the current URL as opposed to pushing the URL as a new entry in the browser's History API. |
+| `prependBasePath` | `boolean` | `false` | | Configures the component to prepend the parent router's base path to the `href` property. |
+| `preserveQuery` | `boolean \| string \| string[]` | `false` | | Configures the component to preserve the query string whenever it triggers navigation. |
+| `children` | `Snippet` | `undefined` | | Renders the children of the component. |
+
+[Online Documentation](https://wjfe-n-savant.hashnode.space/wjfe-n-savant/components/linkcontext)
diff --git a/src/lib/index.ts b/src/lib/index.ts
index b808b43..47cfb3c 100644
--- a/src/lib/index.ts
+++ b/src/lib/index.ts
@@ -42,6 +42,7 @@ export function init(options?: InitOptions): () => void {
 
 export * from "$lib/Link/Link.svelte";
 export { default as Link } from "$lib/Link/Link.svelte";
+export { default as LinkContext } from "$lib/LinkContext/LinkContext.svelte";
 export * from "$lib/Route/Route.svelte";
 export { default as Route } from "$lib/Route/Route.svelte";
 export * from "$lib/Router/Router.svelte";