Add optional time ranges and a calendar day view

Tasks can now have a start/end time on their deadline date. The new
Calendar view shows a day as a timeline (with a week strip and projected
repeats of recurring tasks), and the task form lists what is already
planned that day and flags overlaps. Existing databases are migrated to
schema v2 automatically, with a backup copy taken first.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/main.py

@@ -8,13 +8,14 @@ import time
 from collections import defaultdict, deque
 from contextlib import asynccontextmanager
 from datetime import date, datetime, timedelta, timezone
+from datetime import time as Time
 from pathlib import Path
 from typing import Literal, Optional
 
 from fastapi import Depends, FastAPI, HTTPException, Request, Response
 from fastapi.responses import JSONResponse
 from fastapi.staticfiles import StaticFiles
-from pydantic import BaseModel, Field, field_validator
+from pydantic import BaseModel, Field, field_validator, model_validator
 
 from . import db
 
@@ -30,7 +31,7 @@ if not APP_PASSWORD or not SECRET_KEY or "change-me" in (APP_PASSWORD, SECRET_KE
 
 COOKIE_NAME = "whattodo_session"
 CSRF_HEADER = "x-whattodo"
-EXPORT_VERSION = 1
+EXPORT_VERSION = 2
 STATIC_DIR = Path(__file__).parent / "static"
 
 # Changing the password (or secret) invalidates all existing sessions.
@@ -186,6 +187,21 @@ def norm_tags(tags: list[str]) -> list[str]:
     return out[:20]
 
 
+def fmt_time(t) -> Optional[str]:
+    return t.strftime("%H:%M") if isinstance(t, Time) else t
+
+
+def check_times(due, start: Optional[str], end: Optional[str]) -> Optional[str]:
+    """Return an error message if the time fields don't make sense together."""
+    if (start or end) and not due:
+        return "A time needs a deadline date"
+    if end and not start:
+        return "An end time needs a start time"
+    if start and end and end <= start:
+        return "End time must be after start time"
+    return None
+
+
 def clean_title(v: Optional[str]) -> Optional[str]:
     if v is None:
         return v
@@ -212,6 +228,8 @@ class TaskIn(BaseModel):
     category_id: Optional[int] = None
     priority: int = Field(0, ge=0, le=3)
     due_date: Optional[date] = None
+    start_time: Optional[Time] = None
+    end_time: Optional[Time] = None
     tags: list[str] = []
     recurrence: Recurrence = "none"
     recur_interval: int = Field(1, ge=1, le=365)
@@ -219,6 +237,13 @@ class TaskIn(BaseModel):
 
     _title = field_validator("title")(clean_title)
 
+    @model_validator(mode="after")
+    def _times(self):
+        error = check_times(self.due_date, fmt_time(self.start_time), fmt_time(self.end_time))
+        if error:
+            raise ValueError(error)
+        return self
+
 
 class TaskPatch(BaseModel):
     title: Optional[str] = Field(None, max_length=500)
@@ -226,6 +251,8 @@ class TaskPatch(BaseModel):
     category_id: Optional[int] = None
     priority: Optional[int] = Field(None, ge=0, le=3)
     due_date: Optional[date] = None
+    start_time: Optional[Time] = None
+    end_time: Optional[Time] = None
     tags: Optional[list[str]] = None
     recurrence: Optional[Recurrence] = None
     recur_interval: Optional[int] = Field(None, ge=1, le=365)
@@ -281,6 +308,8 @@ def row_to_task(r: sqlite3.Row, subtasks: list[dict]) -> dict:
         "category_id": r["category_id"],
         "priority": r["priority"],
         "due_date": r["due_date"],
+        "start_time": r["start_time"],
+        "end_time": r["end_time"],
         "tags": json.loads(r["tags"]),
         "recurrence": r["recurrence"],
         "recur_interval": r["recur_interval"],
@@ -330,12 +359,13 @@ def insert_task(conn: sqlite3.Connection, t: dict, done: bool = False, done_at:
     now = now_iso()
     due = t.get("due_date")
     cur = conn.execute(
-        """INSERT INTO tasks (title, notes, category_id, priority, due_date, tags, recurrence,
-                              recur_interval, done, done_at, created_at, updated_at)
-           VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)""",
+        """INSERT INTO tasks (title, notes, category_id, priority, due_date, start_time, end_time,
+                              tags, recurrence, recur_interval, done, done_at, created_at, updated_at)
+           VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)""",
         (
             t["title"], t.get("notes", ""), t.get("category_id"), t.get("priority", 0),
             due.isoformat() if isinstance(due, date) else due,
+            fmt_time(t.get("start_time")), fmt_time(t.get("end_time")),
             json.dumps(norm_tags(t.get("tags", []))), t.get("recurrence", "none"),
             t.get("recur_interval", 1), int(done), done_at, created_at or now, updated_at or now,
         ),
@@ -413,7 +443,7 @@ def create_task(body: TaskIn, conn=Depends(get_conn)):
 
 @app.patch("/api/tasks/{task_id}")
 def update_task(task_id: int, body: TaskPatch, conn=Depends(get_conn)):
-    get_task(conn, task_id)
+    current = get_task(conn, task_id)
     fields = body.model_dump(exclude_unset=True)
     subtasks = fields.pop("subtasks", None)
     for key in ("title", "notes", "priority", "tags", "recurrence", "recur_interval"):
@@ -425,6 +455,13 @@ def update_task(task_id: int, body: TaskPatch, conn=Depends(get_conn)):
         fields["tags"] = json.dumps(norm_tags(fields["tags"]))
     if fields.get("due_date") is not None:
         fields["due_date"] = fields["due_date"].isoformat()
+    for key in ("start_time", "end_time"):
+        if key in fields:
+            fields[key] = fmt_time(fields[key])
+    merged = {k: fields.get(k, current[k]) for k in ("due_date", "start_time", "end_time")}
+    error = check_times(merged["due_date"], merged["start_time"], merged["end_time"])
+    if error:
+        raise HTTPException(422, error)
     fields["updated_at"] = now_iso()
     with conn:
         conn.execute(