From 088e09dc53a144b19b8e15c225ff29dd5b72ea5a Mon Sep 17 00:00:00 2001
From: slothful-vassal <89943360+slothful-vassal@users.noreply.github.com>
Date: Fri, 20 Feb 2026 10:27:07 +0100
Subject: [PATCH] prevent losing trail filter settings (#814)

* prevent losing trail filter settings

* prevent page from jumping to top on filter update

---------

Co-authored-by: Christian Beutel <>
---
 web/src/lib/util/trail_filter_util.ts | 170 ++++++++++++++++++++++++++
 web/src/routes/trails/+page.svelte    |  75 ++++++++----
 2 files changed, 221 insertions(+), 24 deletions(-)
 create mode 100644 web/src/lib/util/trail_filter_util.ts

diff --git a/web/src/lib/util/trail_filter_util.ts b/web/src/lib/util/trail_filter_util.ts
new file mode 100644
index 00000000..dd8f9a7f
--- /dev/null
+++ b/web/src/lib/util/trail_filter_util.ts
@@ -0,0 +1,170 @@
+import type { TrailFilter } from "$lib/models/trail";
+
+const TRAIL_SORT_OPTIONS = new Set([
+    "name",
+    "distance",
+    "duration",
+    "difficulty",
+    "elevation_gain",
+    "elevation_loss",
+    "like_count",
+    "created",
+    "date",
+]);
+
+function limitToRange(value: number, min: number, max: number): number {
+    return Math.min(Math.max(value, min), max);
+}
+
+function getNumber(value: unknown, fallback: number): number;
+function getNumber(value: unknown, fallback?: number): number | undefined;
+function getNumber(value: unknown, fallback?: number): number | undefined {
+    return typeof value === "number" ? value : fallback;
+}
+
+function getNumberInRange(
+    value: unknown,
+    fallback: number,
+    min: number,
+    max: number,
+): number {
+    return limitToRange(getNumber(value, fallback), min, max);
+}
+
+function asRecord(value: unknown): Record<string, unknown> {
+    return value !== null && typeof value === "object"
+        ? (value as Record<string, unknown>)
+        : {};
+}
+
+function getString(value: unknown, fallback: string): string;
+function getString(value: unknown, fallback?: string): string | undefined;
+function getString(value: unknown, fallback?: string): string | undefined {
+    return typeof value === "string" ? value : fallback;
+}
+
+function getStringArray(value: unknown, fallback: string[]): string[] {
+    return Array.isArray(value)
+        ? value.filter((item): item is string => typeof item === "string")
+        : fallback;
+}
+
+function toDifficulty(value: unknown): 0 | 1 | 2 | undefined {
+    if (value === 0 || value === 1 || value === 2) {
+        return value;
+    }
+    if (value === "easy") {
+        return 0;
+    }
+    if (value === "moderate") {
+        return 1;
+    }
+    if (value === "difficult") {
+        return 2;
+    }
+    return undefined;
+}
+
+function parseDifficulty(
+    value: unknown,
+    fallback: (0 | 1 | 2)[],
+): (0 | 1 | 2)[] {
+    if (!Array.isArray(value)) {
+        return fallback;
+    }
+
+    const parsed = value
+        .map(toDifficulty)
+        .filter((d): d is 0 | 1 | 2 => d !== undefined);
+
+    return parsed.length ? parsed : fallback;
+}
+
+function getBoolean(value: unknown, fallback?: boolean): boolean | undefined {
+    return typeof value === "boolean" ? value : fallback;
+}
+
+export function sanitizeTrailFilter(
+    candidate: unknown,
+    defaultFilter: TrailFilter,
+): TrailFilter {
+    const source = asRecord(candidate);
+    const near = asRecord(source.near);
+
+    const restored: TrailFilter = {
+        ...defaultFilter,
+        q: getString(source.q, defaultFilter.q),
+        category: getStringArray(source.category, defaultFilter.category),
+        tags: getStringArray(source.tags, defaultFilter.tags),
+        difficulty: parseDifficulty(source.difficulty, defaultFilter.difficulty),
+        author: getString(source.author, defaultFilter.author),
+        public: getBoolean(source.public, defaultFilter.public),
+        shared: getBoolean(source.shared, defaultFilter.shared),
+        private: getBoolean(source.private, defaultFilter.private),
+        near: {
+            lat: getNumber(near.lat, defaultFilter.near.lat),
+            lon: getNumber(near.lon, defaultFilter.near.lon),
+            radius: Math.max(1, getNumber(near.radius, defaultFilter.near.radius)),
+        },
+        distanceLimit: defaultFilter.distanceLimit,
+        elevationGainLimit: defaultFilter.elevationGainLimit,
+        elevationLossLimit: defaultFilter.elevationLossLimit,
+        distanceMin: getNumberInRange(
+            source.distanceMin,
+            defaultFilter.distanceMin,
+            0,
+            defaultFilter.distanceLimit,
+        ),
+        distanceMax: getNumberInRange(
+            source.distanceMax,
+            defaultFilter.distanceMax,
+            0,
+            defaultFilter.distanceLimit,
+        ),
+        elevationGainMin: getNumberInRange(
+            source.elevationGainMin,
+            defaultFilter.elevationGainMin,
+            0,
+            defaultFilter.elevationGainLimit,
+        ),
+        elevationGainMax: getNumberInRange(
+            source.elevationGainMax,
+            defaultFilter.elevationGainMax,
+            0,
+            defaultFilter.elevationGainLimit,
+        ),
+        elevationLossMin: getNumberInRange(
+            source.elevationLossMin,
+            defaultFilter.elevationLossMin,
+            0,
+            defaultFilter.elevationLossLimit,
+        ),
+        elevationLossMax: getNumberInRange(
+            source.elevationLossMax,
+            defaultFilter.elevationLossMax,
+            0,
+            defaultFilter.elevationLossLimit,
+        ),
+        startDate: getString(source.startDate, defaultFilter.startDate),
+        endDate: getString(source.endDate, defaultFilter.endDate),
+        completed: getBoolean(source.completed, defaultFilter.completed),
+        liked: getBoolean(source.liked, defaultFilter.liked),
+        sort:
+            typeof source.sort === "string" && TRAIL_SORT_OPTIONS.has(source.sort)
+                ? (source.sort as TrailFilter["sort"])
+                : defaultFilter.sort,
+        sortOrder: source.sortOrder === "-" ? "-" : "+",
+    };
+
+    if (restored.distanceMin > restored.distanceMax) {
+        restored.distanceMin = restored.distanceMax;
+    }
+    if (restored.elevationGainMin > restored.elevationGainMax) {
+        restored.elevationGainMin = restored.elevationGainMax;
+    }
+    if (restored.elevationLossMin > restored.elevationLossMax) {
+        restored.elevationLossMin = restored.elevationLossMax;
+    }
+
+    return restored;
+}
diff --git a/web/src/routes/trails/+page.svelte b/web/src/routes/trails/+page.svelte
index 5be28d49..57ecd789 100644
--- a/web/src/routes/trails/+page.svelte
+++ b/web/src/routes/trails/+page.svelte
@@ -1,20 +1,50 @@
 <script lang="ts">
-    import { goto } from "$app/navigation";
+    import { browser } from "$app/environment";
+    import { beforeNavigate, goto } from "$app/navigation";
     import { page } from "$app/state";
     import TrailFilterPanel from "$lib/components/trail/trail_filter_panel.svelte";
     import TrailList from "$lib/components/trail/trail_list.svelte";
-    import type { Trail, TrailFilter, TrailSearchResult } from "$lib/models/trail";
+    import type { Trail, TrailFilter } from "$lib/models/trail";
     import { trails_search_filter } from "$lib/stores/trail_store";
     import type { Snapshot } from "@sveltejs/kit";
     import { onMount } from "svelte";
     import { _ } from "svelte-i18n";
     import { APIError } from "$lib/util/api_util";
+    import { sanitizeTrailFilter } from "$lib/util/trail_filter_util";
+
+    const TRAIL_LIST_FILTER_STORAGE_KEY = "trailListFilter";
+
+    function restoreStoredFilter(defaultFilter: TrailFilter): TrailFilter {
+        if (!browser) {
+            return defaultFilter;
+        }
+
+        const stored = localStorage.getItem(TRAIL_LIST_FILTER_STORAGE_KEY);
+        if (!stored) {
+            return defaultFilter;
+        }
+
+        try {
+            const parsed = JSON.parse(stored) as Record<string, unknown>;
+            return sanitizeTrailFilter(parsed, defaultFilter);
+        } catch {
+            localStorage.removeItem(TRAIL_LIST_FILTER_STORAGE_KEY);
+            return defaultFilter;
+        }
+    }
+
+    function persistFilter() {
+        if (!browser) {
+            return;
+        }
+        localStorage.setItem(TRAIL_LIST_FILTER_STORAGE_KEY, JSON.stringify(filter));
+    }
 
     let filterExpanded: boolean = $state(true);
 
     let loading: boolean = $state(true);
 
-    let filter: TrailFilter = $state(page.data.filter);
+    let filter: TrailFilter = $state(restoreStoredFilter(page.data.filter));
     const pagination: { page: number; totalPages: number, items: number } = $state({
         page: page.url.searchParams.has("page")
             ? parseInt(page.url.searchParams.get("page")!)
@@ -27,24 +57,7 @@
     export const snapshot: Snapshot<TrailFilter> = {
         capture: () => filter,
         restore: (value) => {
-            const difficultyMap: Record<string, 0 | 1 | 2> = {
-                easy: 0,
-                moderate: 1,
-                difficult: 2,
-            };
-            // defensive copy
-            const migrated = { ...value };
-
-            if (Array.isArray(migrated.difficulty)) {
-                migrated.difficulty = migrated.difficulty.map((d: any) => {
-                    if (typeof d === "string" && d in difficultyMap) {
-                        return difficultyMap[d];
-                    }
-                    return d;
-                });
-            }
-
-            filter = migrated;
+            filter = sanitizeTrailFilter(value, page.data.filter);
             handleFilterUpdate();
         },
     };
@@ -55,15 +68,29 @@
         }
     });
 
+    beforeNavigate(({ to }) => {
+        if (!browser || !to?.url) {
+            return;
+        }
+
+        // Keep filter for in-page navigation (e.g. pagination on /trails).
+        if (to.url.pathname.startsWith("/trails")) {
+            return;
+        }
+
+        localStorage.removeItem(TRAIL_LIST_FILTER_STORAGE_KEY);
+    });
+
     async function handleFilterUpdate() {
         loading = true;
+        persistFilter();
 
-        await paginate(1, pagination.items);
+        await paginate(1, pagination.items, false);
 
         loading = false;
     }
 
-    async function paginate(newPage: number, items: number) {
+    async function paginate(newPage: number, items: number, scrollToTop: boolean = true) {
         pagination.page = newPage;
 
         try {
@@ -101,7 +128,7 @@
         }
         
         page.url.searchParams.set("page", newPage.toString());
-        goto(`?${page.url.searchParams.toString()}`, { keepFocus: true });
+        goto(`?${page.url.searchParams.toString()}`, { keepFocus: true, noScroll: !scrollToTop });
     }
 
     async function doPaginate(newPage: number, items: number) {