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+# Phase 1: Daily Note Manager (`src/calendar/daily-notes.ts`)
+
+**Status:** Not started
+**Depends on:** Nothing (standalone)
+**Output file:** `src/calendar/daily-notes.ts`
+
+---
+
+## Overview
+
+Core module — no UI, just logic. All daily note path computation, CRUD, indexing, and date detection lives here.
+
+---
+
+## Storage Structure
+
+```
+{rootFolder}/{YYYY}/{MM}/{DD}/{YYYY-MM-DD}.md
+```
+
+- **`rootFolder`** — configurable, defaults to `"Calendar"`
+- **Year** — 4-digit (`2026`)
+- **Month** — 2-digit zero-padded (`01`–`12`)
+- **Day** — 2-digit zero-padded (`01`–`31`)
+- **Filename** — `YYYY-MM-DD.md` (ISO date)
+
+---
+
+## Functions
+
+```
+- getDailyNotePath(date: Moment, rootFolder: string): string
+    Computes: `{rootFolder}/{YYYY}/{MM}/{DD}/{YYYY-MM-DD}.md`
+
+- getDailyNote(app: App, date: Moment, rootFolder: string): TFile | null
+    Looks up vault file at the computed path.
+
+- createDailyNote(app: App, date: Moment, rootFolder: string, template?: string): Promise<TFile>
+    Creates parent folders if needed, creates the file.
+    Uses template content if configured, else empty with frontmatter:
+      ---
+      date: YYYY-MM-DD
+      ---
+
+- openDailyNote(app: App, date: Moment, rootFolder: string, opts: { newLeaf: boolean }): Promise<void>
+    Opens existing note or creates then opens.
+
+- indexDailyNotes(app: App, rootFolder: string): Map<string, TFile>
+    Scans `{rootFolder}/` recursively, parses YYYY/MM/DD structure,
+    returns Map<"YYYY-MM-DD", TFile>.
+
+- getDateFromDailyNote(file: TFile, rootFolder: string): Moment | null
+    Reverse lookup: given a TFile, extract the date if it lives
+    in the daily note folder structure.
+```
+
+---
+
+## Notes
+
+- `moment.js` is available globally in Obsidian as `window.moment()`. No import needed.
+- `indexDailyNotes()` scans only the calendar root folder, not the entire vault.
+- Template support: if `calendarDailyNoteTemplate` is set, new daily notes copy that file's content (with `{{date}}` placeholder replacement).
+- The `day/` folder can hold multiple notes per day for future expansion, but the calendar UI currently shows one note per day.