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▓▓   ░▒▓ D̷O̷C̷H̷A̷Z̷K̷O̷T̷R̷O̷N̷-̷5̷0̷0̷0̷ ▓▒░                              ▓▓
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▓▓   [ K I N D E R G A R T E N   A T T E N D A N C E   S Y S T E M ] ▓▓
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Simple web application for tracking kindergarten attendance with a parent excuse feature (must be submitted before 08:00).

Built as a modern Go 1.26 reference — structured logging, method-aware routing, graceful shutdown, slices generics, middleware, and table-driven tests.

Features

• Two classes (16 children each)
• Absence excuses accepted until 08:00 on the given day
• Attendance list per class
• Parent authorization — only the assigned parent can excuse their child
• Health endpoint for load-balancer / k8s probes
• Graceful shutdown on SIGINT / SIGTERM
• Persistent JSON file storage

Requirements

• Go 1.26

Installation & Running

git clone <your-repo-url>
cd dochazkotron-5000
go mod tidy
go run main.go

Open http://localhost:8080 (or set PORT env variable).

Environment Variables

Variable	Default	Description
PORT	8080	HTTP server port
DATA_FILE	attendance.json	Path to the JSON data file

API Endpoints

Health Check (GET)

curl http://localhost:8080/health

Response:

{"status":"ok"}

Excuse a Child (POST)

curl -X POST http://localhost:8080/excuse \
  -H "Content-Type: application/json" \
  -d '{"child_id":"child_0_0","parent_id":"parent1"}'

Parameters:

• child_id — Child ID (e.g. child_0_0)
• parent_id — Parent ID (must match the child's assigned parent)

Constraints:

• Excuses are accepted only until 08:00 on the given day.
• A parent can only excuse their own children.

Success Response:

{"status":"excused"}

Error Responses:

• 400 Bad Request — Invalid JSON, missing fields, or excuse time expired
• 403 Forbidden — Parent does not match child or unknown parent
• 404 Not Found — Child not found

Get Class Attendance (GET)

curl "http://localhost:8080/attendance/class1"

Path Variable:

• class_id — Class ID (class1 or class2)

Response:

{
  "Dítě 1-1": true,
  "Dítě 1-2": false
}

• true — Child is absent and not excused (needs attention)
• false — Child is excused

Modern Go Patterns Used

This project is intentionally kept small to serve as a learning reference. Key modern patterns:

Feature	Where	Why
slog	main()	Structured, leveled logging instead of log
http.ServeMux method + path matching	main()	Go 1.22+: POST /excuse, GET /attendance/{class_id}
r.PathValue("class_id")	handleAttendance	Extract route variables without third-party routers
signal.NotifyContext	main()	Graceful shutdown with context cancellation
http.Server timeouts	main()	Production-hardened server config
http.MaxBytesHandler	main()	Request body size limits
os.Root	store	Go 1.24+: sandboxed file I/O prevents path traversal
slices.All / maps.All	store	Go 1.23+: range-over-func iterators
slices.IndexFunc	store	Generic slice search
range over integers	newStore	for j := range 16
cmp.Or	main()	Default-value fallback
time.DateOnly	store	"2006-01-02" constant
errors.Is sentinel errors	handlers + tests	Clean error classification
sync.RWMutex	store	Many concurrent readers, one writer
Middleware chaining	app.chain	Composable recoverPanic + logRequest
t.Parallel() + table-driven tests	main_test.go	Fast, scalable test suite
httptest through ServeMux	main_test.go	Tests routing + path values together
Injected clock function	app struct	Deterministic time in tests

Data Storage

All data is stored in attendance.json (override with DATA_FILE).

Example structure:

{
  "classes": [
    {
      "id": "class1",
      "name": "Třída 1",
      "children": [
        {
          "id": "child_0_0",
          "name": "Dítě 1-1",
          "class_id": "class1",
          "parent_id": "parent1"
        }
      ]
    }
  ],
  "attendances": [],
  "parents": ["parent1", "parent2"]
}

Data Model

Children

• Each class contains 16 children.
• Every child has:
  • id — Unique identifier (e.g. child_0_0)
  • name — Display name
  • class_id — Class identifier
  • parent_id — Parent ID used for excuse authorization

Testing

go test -v -race ./...

Tests cover:

• Store logic (excuse, attendance, validation, persistence)
• HTTP handlers (routing, status codes, JSON responses)
• Middleware (panic recovery, request logging)
• Time constraint logic

Production Notes

• The server runs with read/write timeouts and graceful shutdown.
• For HTTPS, place a reverse proxy (Nginx, Caddy, Traefik) or a cloud load balancer in front.
• The JSON file uses 0600 permissions. For production workloads, migrate to a real database.
• Authentication is parent-ID-based in this demo. Add OAuth2 / JWT for real deployments.

License

MIT