# Phase 5: Search - Research

**Researched:** 2026-01-31
**Domain:** Search/filtering for SvelteKit + SQLite application
**Confidence:** HIGH

## Summary

This phase implements text search and filtering for the TaskPlaner entries list. The research covers six key areas: SQLite search strategy, client vs server filtering, search state management, debouncing in Svelte 5, text highlighting, and recent searches storage.

The recommended approach is **client-side filtering** since all entries are already loaded on the page (small dataset). This provides instant feedback without network latency and keeps filters session-only as specified. The existing `svelte-persisted-store` package handles recent searches storage, and native Svelte 5 `$effect` with cleanup handles debouncing elegantly.

**Primary recommendation:** Filter entries client-side using `$derived` with a search/filter state object, debounce the search input with `$effect`, and use the HTML `<mark>` element for text highlighting.

## Standard Stack

The established libraries/tools for this domain:

### Core (Already Installed - No New Dependencies)
| Library | Version | Purpose | Why Standard |
|---------|---------|---------|--------------|
| Svelte 5 | ^5.48.2 | $state, $effect, $derived for reactive filtering | Native reactivity, already in project |
| svelte-persisted-store | ^0.12.0 | Recent searches in localStorage | Already used for preferences |

### Supporting (No Installation Needed)
| Library | Version | Purpose | When to Use |
|---------|---------|---------|-------------|
| Native HTML `<mark>` | N/A | Text highlighting | Semantic, no JS needed |
| Native `$effect` cleanup | N/A | Debouncing | Built into Svelte 5 |

### Alternatives Considered
| Instead of | Could Use | Tradeoff |
|------------|-----------|----------|
| Client filtering | Server-side with URL params | Server adds latency; client is instant for small datasets |
| Native `<mark>` | mark.js library | Library adds weight; `<mark>` sufficient for simple highlighting |
| svelte-persisted-store | Custom localStorage | Already have the dependency, consistent with existing code |
| Native `$effect` debounce | lodash.debounce | Extra dependency; native pattern is clean in Svelte 5 |
| svelte-focus-key | Manual keydown listener | Known Svelte 5 bug with `svelte:window` keydown and `preventDefault()` |

**Installation:**
```bash
# No new dependencies required
npm install svelte-focus-key  # OPTIONAL: Only if manual approach proves buggy
```

## Architecture Patterns

### Recommended Component Structure
```
src/lib/components/
├── SearchBar.svelte          # Search input with debounce + "/" shortcut
├── FilterBar.svelte          # Tags, type, date range filters
├── EntryList.svelte          # Modified to accept filtered entries
└── SearchableEntryList.svelte # Wrapper combining search + filters + list
```

### Pattern 1: Client-Side Filtering with $derived

**What:** All filtering logic in a single `$derived` expression that reacts to search/filter state changes.

**When to use:** Small to medium datasets already loaded on the client (< 1000 entries).

**Example:**
```typescript
// Source: Svelte 5 reactivity docs
let searchQuery = $state('');
let selectedTags: string[] = $state([]);
let typeFilter: 'task' | 'thought' | 'all' = $state('all');
let dateRange = $state<{ start: string | null; end: string | null }>({ start: null, end: null });

let filteredEntries = $derived(() => {
  let result = entries;

  // Text search (title + content)
  if (searchQuery.length >= 2) {
    const query = searchQuery.toLowerCase();
    result = result.filter(e =>
      e.title?.toLowerCase().includes(query) ||
      e.content.toLowerCase().includes(query)
    );
  }

  // Tag filter (AND logic - must have ALL selected tags)
  if (selectedTags.length > 0) {
    result = result.filter(e =>
      selectedTags.every(tagName =>
        e.tags.some(t => t.name === tagName)
      )
    );
  }

  // Type filter
  if (typeFilter !== 'all') {
    result = result.filter(e => e.type === typeFilter);
  }

  // Date range filter
  if (dateRange.start) {
    result = result.filter(e => e.createdAt >= dateRange.start);
  }
  if (dateRange.end) {
    result = result.filter(e => e.createdAt <= dateRange.end);
  }

  return result;
});
```

### Pattern 2: Debounced Search with $effect Cleanup

**What:** Delay search execution until user stops typing, using `$effect` return function for cleanup.

**When to use:** Any text input that triggers computation or API calls.

**Example:**
```svelte
<!-- Source: Svelte 5 $effect docs + minimalistdjango.com -->
<script lang="ts">
  let inputValue = $state('');
  let debouncedValue = $state('');

  $effect(() => {
    const timeout = setTimeout(() => {
      debouncedValue = inputValue;
    }, 300); // 300ms debounce

    return () => clearTimeout(timeout);
  });
</script>

<input bind:value={inputValue} placeholder="Search..." />
```

### Pattern 3: "/" Key Focus with Manual Event Listener

**What:** Focus search input when "/" is pressed, avoiding known Svelte 5 bug.

**When to use:** GitHub-style keyboard shortcuts for search.

**Example:**
```svelte
<!-- Source: Svelte GitHub issue #15474 workaround -->
<script lang="ts">
  import { onMount } from 'svelte';

  let searchInput: HTMLInputElement;

  onMount(() => {
    function handleKeydown(e: KeyboardEvent) {
      // Skip if already in an input/textarea
      if (e.target instanceof HTMLInputElement || e.target instanceof HTMLTextAreaElement) {
        return;
      }

      if (e.key === '/') {
        e.preventDefault();
        searchInput?.focus();
      }
    }

    document.addEventListener('keydown', handleKeydown);
    return () => document.removeEventListener('keydown', handleKeydown);
  });
</script>

<input bind:this={searchInput} type="text" placeholder='Press "/" to search' />
```

**Note:** There is a known bug (Svelte issue #15474, March 2025) where `svelte:window onkeydown` with `e.preventDefault()` does not prevent the "/" character from being typed into the focused input. The workaround is to use native `document.addEventListener`.

### Pattern 4: Text Highlighting with `<mark>`

**What:** Wrap matching text in semantic `<mark>` element for highlighting.

**When to use:** Displaying search results with highlighted matches.

**Example:**
```typescript
// Source: bitsofco.de, MDN <mark> docs
function highlightMatch(text: string, query: string): string {
  if (!query || query.length < 2) return text;

  // Escape regex special characters in query
  const escaped = query.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
  const regex = new RegExp(`(${escaped})`, 'gi');

  return text.replace(regex, '<mark class="font-bold bg-transparent">$1</mark>');
}
```

```svelte
<!-- Usage in component -->
<p>{@html highlightMatch(entry.content, searchQuery)}</p>
```

**Security note:** Use `{@html}` carefully. The `highlightMatch` function only wraps matched text, but ensure the original content is already sanitized if it comes from user input.

### Anti-Patterns to Avoid

- **Re-fetching from server on every keystroke:** Use debouncing and client-side filtering for session-only filters
- **Storing filter state in URL:** Context specifies "session-only, not persisted in URL, reset on reload"
- **Using `$derived` for debounce:** `$derived` cannot be debounced directly; use `$effect` to update a debounced `$state`
- **Using `svelte:window onkeydown` for "/" focus:** Known bug prevents `preventDefault()` from working correctly

## Don't Hand-Roll

Problems that look simple but have existing solutions:

| Problem | Don't Build | Use Instead | Why |
|---------|-------------|-------------|-----|
| Recent searches persistence | Custom localStorage wrapper | svelte-persisted-store | Already in project, handles sync/serialization |
| Debounce function | Custom debounce util | Native $effect cleanup | Svelte 5 pattern, cleaner than external utility |
| Text highlighting | Custom DOM manipulation | HTML `<mark>` + regex replace | Semantic, accessible, simple |
| Tag filtering UI | Custom multi-select | Existing svelecte component | Already used in TagInput.svelte |

**Key insight:** The project already has all necessary dependencies. New search features can be built entirely with existing tools.

## Common Pitfalls

### Pitfall 1: Forgetting Minimum Character Check
**What goes wrong:** Search triggers on every character, including single letters that match almost everything.
**Why it happens:** Not implementing the "minimum 2 characters" requirement.
**How to avoid:** Guard search filter with `if (query.length >= 2)`.
**Warning signs:** Poor performance, too many results on first keystroke.

### Pitfall 2: Pinned Entries Staying at Top During Search
**What goes wrong:** Pinned entries remain separated when searching/filtering.
**Why it happens:** Not flattening the list during active search.
**How to avoid:** Check `isFiltering` state and skip pinned separation when true.
**Warning signs:** Pinned items don't match search but still appear at top.

### Pitfall 3: "/" Key Typing Into Input
**What goes wrong:** When pressing "/" to focus search, the "/" character appears in the input.
**Why it happens:** Known Svelte 5 bug with `svelte:window onkeydown` and `preventDefault()`.
**How to avoid:** Use native `document.addEventListener` instead of `svelte:window`.
**Warning signs:** "/" appears in search box after pressing hotkey.

### Pitfall 4: Tag Filter AND vs OR Confusion
**What goes wrong:** Selecting multiple tags shows entries with ANY tag instead of ALL tags.
**Why it happens:** Using `some()` instead of `every()` in filter logic.
**How to avoid:** Context specifies AND logic: `selectedTags.every(tag => entry.tags.includes(tag))`.
**Warning signs:** Results include entries missing some selected tags.

### Pitfall 5: Date Comparison with ISO Strings
**What goes wrong:** Date range filter doesn't work correctly.
**Why it happens:** ISO string comparison works for dates but needs consistent formatting.
**How to avoid:** Ensure all dates are in ISO format (YYYY-MM-DD) for string comparison. The schema already uses ISO strings.
**Warning signs:** Entries from edge dates (start/end of range) incorrectly included/excluded.

### Pitfall 6: Memory Leak from Event Listeners
**What goes wrong:** Keyboard shortcut handler accumulates on navigation.
**Why it happens:** Not cleaning up `document.addEventListener` on component unmount.
**How to avoid:** Return cleanup function from `onMount`.
**Warning signs:** Multiple key handlers fire on single keypress.

## Code Examples

Verified patterns from research:

### Complete Search Bar Component
```svelte
<!-- SearchBar.svelte -->
<script lang="ts">
  import { onMount } from 'svelte';

  interface Props {
    value: string;
    onSearch: (query: string) => void;
    recentSearches: string[];
    onSelectRecent: (query: string) => void;
  }

  let { value = $bindable(), onSearch, recentSearches, onSelectRecent }: Props = $props();

  let inputValue = $state(value);
  let searchInput: HTMLInputElement;
  let showRecent = $state(false);

  // Debounce input -> search
  $effect(() => {
    const timeout = setTimeout(() => {
      if (inputValue.length >= 2 || inputValue.length === 0) {
        value = inputValue;
        onSearch(inputValue);
      }
    }, 300);
    return () => clearTimeout(timeout);
  });

  // "/" keyboard shortcut (native listener to avoid Svelte bug)
  onMount(() => {
    function handleKeydown(e: KeyboardEvent) {
      if (e.target instanceof HTMLInputElement || e.target instanceof HTMLTextAreaElement) return;
      if (e.key === '/') {
        e.preventDefault();
        searchInput?.focus();
        showRecent = true;
      }
    }
    document.addEventListener('keydown', handleKeydown);
    return () => document.removeEventListener('keydown', handleKeydown);
  });
</script>

<div class="relative">
  <input
    bind:this={searchInput}
    bind:value={inputValue}
    type="text"
    placeholder='Search entries... (press "/")'
    class="w-full px-4 py-2 border rounded-lg"
    onfocus={() => showRecent = true}
    onblur={() => setTimeout(() => showRecent = false, 200)}
  />

  {#if showRecent && recentSearches.length > 0 && inputValue.length === 0}
    <div class="absolute top-full left-0 right-0 bg-white border rounded-lg shadow-lg mt-1 z-10">
      <div class="px-3 py-2 text-sm text-gray-500">Recent searches</div>
      {#each recentSearches as search}
        <button
          type="button"
          class="w-full px-3 py-2 text-left hover:bg-gray-100"
          onmousedown={() => onSelectRecent(search)}
        >
          {search}
        </button>
      {/each}
    </div>
  {/if}
</div>
```

### Recent Searches Store
```typescript
// src/lib/stores/recentSearches.ts
import { persisted } from 'svelte-persisted-store';

const MAX_RECENT = 5;

export const recentSearches = persisted<string[]>('taskplaner-recent-searches', []);

export function addRecentSearch(query: string): void {
  if (!query || query.length < 2) return;

  recentSearches.update(searches => {
    // Remove if already exists (will re-add at front)
    const filtered = searches.filter(s => s.toLowerCase() !== query.toLowerCase());
    // Add to front, limit to MAX_RECENT
    return [query, ...filtered].slice(0, MAX_RECENT);
  });
}
```

### Date Range Presets
```typescript
// Date range preset helper
function getDatePreset(preset: 'today' | 'week' | 'month'): { start: string; end: string } {
  const now = new Date();
  const end = now.toISOString().split('T')[0]; // Today

  let start: Date;
  switch (preset) {
    case 'today':
      start = now;
      break;
    case 'week':
      start = new Date(now);
      start.setDate(start.getDate() - 7);
      break;
    case 'month':
      start = new Date(now);
      start.setMonth(start.getMonth() - 1);
      break;
  }

  return {
    start: start.toISOString().split('T')[0],
    end
  };
}
```

### Filter State Type
```typescript
// src/lib/types/search.ts
export interface SearchFilters {
  query: string;
  tags: string[];
  type: 'task' | 'thought' | 'all';
  dateRange: {
    start: string | null;
    end: string | null;
  };
}

export const defaultFilters: SearchFilters = {
  query: '',
  tags: [],
  type: 'all',
  dateRange: { start: null, end: null }
};

export function hasActiveFilters(filters: SearchFilters): boolean {
  return (
    filters.query.length >= 2 ||
    filters.tags.length > 0 ||
    filters.type !== 'all' ||
    filters.dateRange.start !== null ||
    filters.dateRange.end !== null
  );
}
```

## State of the Art

| Old Approach | Current Approach | When Changed | Impact |
|--------------|------------------|--------------|--------|
| URL query params for filters | Reactive $state for session-only | Svelte 5 (2024) | Simpler, no URL pollution |
| External debounce libraries | Native $effect cleanup | Svelte 5 (2024) | No dependency needed |
| `on:keydown` directive | `onkeydown` attribute | Svelte 5 (2024) | New syntax, same behavior |
| mark.js for highlighting | Native `<mark>` + regex | Always available | Lighter, semantic |

**Deprecated/outdated:**
- `svelte:window on:keydown` for "/" focus: Has known bug, use native listener instead
- Svelte 4 reactive statements (`$:`) for derived values: Use `$derived` in Svelte 5

## Open Questions

Things that couldn't be fully resolved:

1. **Custom date range picker UI**
   - What we know: Need quick presets (Today, This week, This month) + custom range
   - What's unclear: Best UX pattern for custom date input on mobile
   - Recommendation: Use native `<input type="date">` for start/end; works well on mobile

2. **svelte-focus-key compatibility with Svelte 5**
   - What we know: Package exists specifically for "/" focus use case
   - What's unclear: Whether it's updated for Svelte 5 runes syntax
   - Recommendation: Start with native listener approach; add package if issues arise

## Sources

### Primary (HIGH confidence)
- [Svelte 5 $effect Documentation](https://svelte.dev/docs/svelte/$effect) - cleanup patterns
- [Drizzle ORM Operators](https://orm.drizzle.team/docs/operators) - like/ilike usage
- [Drizzle ORM Select](https://orm.drizzle.team/docs/select) - WHERE clause patterns
- [MDN `<mark>` element](https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/mark) - semantic highlighting

### Secondary (MEDIUM confidence)
- [Minimalist Django - Svelte 5 Debounced Input](https://minimalistdjango.com/snippets/2025-04-04-debounced-input-svelte/) - debounce pattern
- [bitsofco.de - Highlighting search matches](https://bitsofco.de/a-one-line-solution-to-highlighting-search-matches/) - regex replace pattern
- [SvelteKit State Management Docs](https://svelte.dev/docs/kit/state-management) - URL params guidance
- [svelte-focus-key](https://metonym.github.io/svelte-focus-key/) - "/" key focus solution

### Tertiary (LOW confidence - verified against official sources)
- [Svelte Issue #15474](https://github.com/sveltejs/svelte/issues/15474) - svelte:window keydown bug
- [SvelteKit Discussion #9700](https://github.com/sveltejs/kit/discussions/9700) - client vs server filtering

## Metadata

**Confidence breakdown:**
- Standard stack: HIGH - all tools already in project, verified with official docs
- Architecture: HIGH - patterns verified with Svelte 5 docs and working examples
- Pitfalls: MEDIUM - based on GitHub issues and community reports

**Research date:** 2026-01-31
**Valid until:** 2026-03-01 (30 days - Svelte 5 stable, patterns unlikely to change)