commit e3c31484aee7e7e35ede8d3ebc1c77061d2e800f
Author: Matthias Puchstein <matthias@puchstein.bayern>
Date:   Fri Nov 14 16:02:27 2025 +0100

    added AGENTS.md

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+# StudIP Sync Agent
+
+## Goal
+
+Implement a command-line tool in Rust that performs a **one-way sync** of files from Stud.IP (JSON:API at Uni Trier) to the local filesystem. [web:68]  
+The local directory structure must be: `<semester>/<course>/<studip-folders>/<files>`. [web:88]
+
+## Environment
+
+- Target OS: Linux (Arch, follow XDG base directory conventions). [web:135]
+- Language: Rust (2021 edition).
+- Use `reqwest` + `tokio` for HTTP and async, `serde` for JSON and TOML, and standard Rust CLI patterns. [web:111][web:131]
+- Build as a single binary named `studip-sync`.
+
+## Code Quality: Formatting and Linting
+
+- Use `rustfmt` as the standard formatter for all Rust code; code must be kept `cargo fmt` clean. [web:144][web:148]
+- Use `clippy` as the linter; the project must pass `cargo clippy --all-targets --all-features -- -D warnings` with no warnings. [web:144][web:149][web:159]
+- Add a `rustfmt.toml` and (optionally) a `clippy.toml` where needed, but prefer default settings to stay idiomatic. [web:144][web:151]
+- If CI is present, include steps that run `cargo fmt --all -- --check`, `cargo clippy --all-targets --all-features -- -D warnings`, and `cargo test`. [web:147][web:150][web:159]
+
+## API
+
+- Base URL: configurable, default `https://studip.uni-trier.de`. [web:68]
+- JSON:API root: `<base_url>/jsonapi.php/v1`. [web:68]
+- Authentication: HTTP Basic (username/password), encoded once as base64 and stored in TOML config. [web:1][web:118]
+- Use JSON:API routes such as:
+  - `GET /users/me` to resolve the current user and related links (courses, folders, file-refs). [web:68][web:106]
+  - `GET /users/{user_id}/courses` to list enrolled courses. [web:85]
+  - Course-specific routes for folders and documents/file-refs, using the documented JSON:API routes for Stud.IP (e.g. `/courses/{course_id}/documents`). [web:88][web:93]
+
+## Configuration (TOML, including paths)
+
+All configuration and state in this project must use **TOML**. [web:131]
+
+- Primary config file: XDG-compliant, e.g. `~/.config/studip-sync/config.toml`. [web:131][web:135]
+- Example `config.toml` keys:
+
+```
+
+base_url = "https://studip.uni-trier.de"
+jsonapi_path = "/jsonapi.php/v1"
+
+# Authorization header value without the "Basic " prefix, base64("username:password").
+
+basic_auth_b64 = "..."
+
+# Local base directory for synced files.
+
+download_root = "/home/<user>/StudIP"
+
+# Maximum concurrent HTTP downloads.
+
+max_concurrent_downloads = 3
+
+```
+
+- The `download_root` directory determines where the tool creates `semester/course/folders/files`. [web:68]
+- The config file must be created with mode `0600` and never contain anything except necessary settings and the base64-encoded credential. [web:118][web:122]
+
+### Credentials and auth
+
+- On first run (or when running `studip-sync auth`), prompt interactively for username and password. [web:118]
+- Construct `username:password`, base64-encode it, and store the result as `basic_auth_b64` in `config.toml`. [web:1][web:118]
+- At runtime, send `Authorization: Basic <basic_auth_b64>` on all JSON:API requests. [web:1][web:68]
+- Never log or print the password, `basic_auth_b64`, or full `Authorization` header. [web:118][web:128]
+- On HTTP `401` or `403` from a known-good endpoint like `/users/me`, treat this as auth failure:
+- Non-interactive runs: exit with a non-zero code and a clear message asking the user to run `studip-sync auth`. [web:118]
+- Interactive runs: optionally prompt again and update `basic_auth_b64`.
+
+## State (TOML as well)
+
+- State file must also be TOML, stored under XDG data dir, e.g. `~/.local/share/studip-sync/state.toml`. [web:131][web:135]
+- State is non-secret cached data:
+
+```
+
+user_id = "cbcee42edfea9232fecc3e414ef79d06"
+
+[semesters."ws2526"]
+id = "830eb86ad41d8f695d016647d557218a"
+title = "Wintersemester 2025/26"
+
+[semesters."ss25"]
+id = "..."
+title = "Sommersemester 2025"
+
+[courses."830eb86a-...-course-id"]
+name = "Rechnerstrukturen - Übung"
+semester_key = "ws2526"
+last_sync = "2025-11-14T12:34:56Z"
+
+```
+
+- The tool should:
+- Cache `user_id` after the first successful `/users/me` call. [web:68][web:106]
+- Cache semester IDs and human-readable keys (`ws2526`, `ss25`) after discovering them via JSON:API. [web:68]
+- Optionally store course and last-sync metadata to reduce API calls (e.g. using `filter[since]` if supported). [web:88][web:93]
+
+## Directory structure
+
+- All downloads must go under `download_root`, respecting:
+  `download_root/<semester_key>/<course_name>/<studip_folder_path>/<file>`.
+- `semester_key` is resolved from the state file (`ws2526`, `ss25`, etc.). [web:68]
+- `course_name` and Stud.IP folder/file names should be normalized to safe filesystem paths (handle spaces, umlauts, and special characters) while staying human-readable. [web:68][web:104]
+
+## Sync semantics
+
+- One-way sync: Stud.IP → local filesystem only; never upload or modify data on Stud.IP. [web:68]
+- Default behavior:
+- Create directories and download new or changed files under `download_root`.
+- Never delete local files by default.
+- Provide optional flags:
+- `--prune`: delete local files that no longer exist on Stud.IP.
+- `--dry-run`: print planned actions (creates/downloads/deletes) without modifying the filesystem.
+
+## Minimizing API usage and load
+
+- Use cached `user_id` and semester mappings from `state.toml` to avoid repeated discovery calls. [web:68]
+- When listing course documents, use JSON:API pagination and any available filters (e.g. `filter[since]`) supported by Stud.IP’s document routes. [web:88][web:93]
+- Avoid re-downloading unchanged files by checking JSON:API attributes such as ID, size, and modification time against the stored state. [web:93][web:106]
+
+## CLI interface
+
+- Binary name: `studip-sync`.
+- Subcommands:
+- `studip-sync auth`: set or update credentials; writes `config.toml`.
+- `studip-sync sync`: perform sync from Stud.IP to `download_root`.
+- `studip-sync list-courses`: list known courses with semester keys and IDs from state (refreshing if needed).
+- Use standard exit codes:
+- `0` on success.
+- Non-zero on errors (auth failure, network error, JSON parse error, filesystem failure). [web:118]
+
+## Performance & safety
+
+- Limit concurrent HTTP requests (configurable via `max_concurrent_downloads`, default 3). [web:68]
+- Stream file downloads directly to disk; do not load entire files into memory. [web:88]
+- Handle HTTP and I/O errors gracefully with clear messages and without panicking.
+- Keep dependencies minimal and use idiomatic Rust project structuring for maintainability. [web:136][web:137]
+
+## Extensibility
+
+- Internally, separate concerns into modules:
+- `config` (TOML load/save for config and state).
+- `studip_client` (JSON:API HTTP client).
+- `sync` (sync logic and directory mapping).
+- `cli` (argument parsing, subcommands). [web:136][web:137]
+- Represent core entities as Rust types: `Semester`, `Course`, `Folder`, `FileRef`. [web:68][web:93]
+- Design so that a future `MoodleProvider` can implement the same internal traits (e.g. `LmsProvider`) without changing the CLI surface.