cumulus/DESIGN.md

# cumulus: design

This is the design approved on 2026-10-01, after six rounds of questions. It's
the reference while cumulus is being built: when a decision changes, this file
changes with it.

## What cumulus is

A keyboard-driven brainstorming app for the terminal, in Rust with ratatui. The
aim is "the idea node graph to end them all": quick idea dumps, mind maps,
whiteboard-style planning and linked notes, in one tool. It runs on Windows and
Linux, with vim keys first and full mouse support.

## Scope

**v1**
- The canvas: nodes, branches, cross-links with every style, folding and focus,
  zoom, the `K` card, the mouse.
- The Outline and Note views, splits and the document bar.
- The key engine: medium vim, which-key, help and status-bar hints.
- Visual, move and connect modes; text editing with vim normal mode.
- The command line, with completion and history.
- Portals, with the jump list, backlinks and breadcrumb.
- Rapid entry and the Inbox.
- RON documents with autosave, reload, backups and undo; file names that follow
  the root's title.
- The startup rules and `cumulus new`.
- TOML config, key and theme files, with named styles and styles set by tags.

**v1.1**: the Board view · the Search picker across documents · `:tidy` and
align · branch out · export (Markdown, plain text) and import (indented lists).

**Later**: peeking into portals and pulling a document back in · branches that
keep themselves tidy · the Links map · backlinks inside a document · picking
single nodes in visual mode · `Alt+hjkl` · opening a body in `$EDITOR` ·
persistent undo · sessions · operator + motion and macros · a tutorial
document · checkbox, link and date fields · Graphviz and Mermaid export · a
Settings view · vim tab pages.

**Not planned unless asked**: `f` hint jumps · a minimap · straight (braille)
lines.

## Decisions

**Documents and structure**
- Each document has one main root, and the document's name is the root's
  title. Loose top-level nodes float around it.
- A tree plus cross-links: each node has at most one parent, and cross-links
  join any two nodes, at most one link per pair.
- A node holds a title (one line, never empty), a body, tags and a color. A new
  node left empty disappears.
- A portal node shows another document's root, live (its title, color and node
  count), and leads there. Portals always land on the root.
- Backlinks are stored in the target document and synced on save, so they
  travel with the files.
- Files live anywhere: there's no workspace folder. Portal paths are relative,
  with `/` on every OS.
- Each file carries a random `uid`, so "where you left off" survives renames and
  a portal can tell when its file was replaced by another document.
- File names follow the root's title, and a rename fixes the portals pointing
  at the file. A folder's default document keeps its name (`ideas.cum`).

**Canvas**
- Free placement: a new node appears next to its parent, and nothing moves
  unless you move it. Moving a node brings its branch along.
- Folding: each branch is Open, Auto (open while the cursor is inside) or
  Closed (a jump inside opens it until you leave). New branches start Open; a
  focus toggle makes Open branches act like Auto.
- Zoom levels: Normal (boxes), Far (one line per node: the same width, half
  the height) and Overview (colored dots: a quarter of the width, a third of
  the height). Far keeps the width because one-line titles collided when
  distances were halved both ways (changed during stage 2). Body text never
  shows on the canvas: `K` pops it up, and the Note view shows all of it.
- Right-angle lines with proper junctions (`├ ┬ ┼`); lines pass under nodes.
- A node's color goes on its border. Each node can pick its border, and the
  theme's named styles and tag rules can set color and border together.
- Connections can set arrowheads (off, end, start, both), a line (solid,
  dashed, dotted, thick, double), a color (a palette color or the node's own)
  and a label, or use a named style. Branches start solid without arrowheads,
  in their parent's color, so a node's color flows down the lines to its
  children (dim when the parent has no color). Cross-links start as dim
  dashed arrows.

**Keys**
- Medium vim: counts, operators with node targets, registers (with `"+` for the
  system clipboard), marks (capital marks across documents), `.` to repeat.
- Tab and `Ctrl-i` jump forward, as in vim, so `a` adds a child.
- `dd` deletes a node with its branch; `x` deletes just the node, and its
  children move up.
- A count on `dd`, `yy`, `>>` or `<<` takes in the next siblings: `3dd`
  deletes this node and the next two, with their branches, as vim's `3dd`
  takes three lines. Which-key says how many as you type (`2d3`: 6 nodes).
- Rapid entry is what happens after `o`, `O` or `a`: Enter starts the next
  sibling, Tab / Shift-Tab indent and outdent it, Enter on an empty line stops.
  Esc switches to vim motions inside the text; a second Esc leaves.
- `C` (connect mode) edits the connection to another node. Aimed at your own
  parent, it styles or cuts the branch line; cutting makes the node loose.
- `M` (move mode) moves the branch; `M` again switches to just the node.
- `gh gj gk gl` move through the tree in every view; plain `hjkl` follow each
  view's layout (on the canvas: the nearest node that way).
- Folds: `za zo zc zR zM`, plus `zf` (Auto) and `zi` (focus).
- `q` stays free for macros; quit with `:q`, `:qa` or `ZZ`.
- Which-key works like skyshift's; the leader menu pops up at once. The status
  bar shows key hints, and `?` opens searchable help.
- Keys can be changed in `keys.toml`, in vim notation.

**Files and saving**
- Documents are RON files ending in `.cum`. Configs are TOML: `config.toml`,
  `keys.toml` and `themes/<name>.toml`.
- Autosave about a second after a change (`autosave = false` for vim-style
  `:w`). A file changed outside cumulus is reloaded; if you also had unsaved
  changes, cumulus asks which to keep. Daily backups go to the data folder.
- Undo per document, while cumulus runs: one step per command, per
  text-editing session, and per node in rapid entry.
- Each document reopens where you left it (cursor, zoom, scroll).

**Screen**
- Vim-style splits; panes on the same document share one cursor.
- Open documents are buffers, listed in a bar at the top; the status bar is at
  the bottom.

**Project**
- A library plus a thin `main.rs`, so build stages can run as examples.
- Rust pinned to 1.90.0; nothing needs nightly.

## Data model (`model/`: pure data, no UI, no files)

```rust
// Ids and units: newtypes, so they can't be mixed up.
NodeId(u32)                      // unique inside a document, never reused while it's open
BufferId(u32)                    // an open document, like vim's buffer numbers (:ls, :b 3)
PaneId(u32)                      // a split
DocUid(u64)                      // stored in the file, survives renames
CanvasPos { x: i32, y: i32 }     // cells at Normal zoom, may be negative
ScreenPos { col: u16, row: u16 } // a terminal cell
Camera { origin: CanvasPos, zoom: Zoom }   // converts between the two
enum Zoom { Normal, Far, Overview }

// Text, checked once when it comes in.
Title    // one line, never empty
Body     // any text
Tag      // lowercase, no spaces, stored without '#'
Label    // a connection label: one short line
ColorName, StyleName   // names looked up in the theme

// A node and its place in the tree.
struct Node  { content: Content, tags: Tags, look: NodeLook, pos: CanvasPos, fold: Fold }
enum Content { Idea(Idea), Portal(Portal) }
enum Fold    { Open, Auto, Closed }
enum Place   { Root, Loose, Child { parent: NodeId, branch: LineLook } }
struct NodeLook { color: Option<ColorName>, border: Option<Border>, style: Option<StyleName> }
enum Border  { Rounded, Square, Double, Thick, Dashed, Hidden }

// Cross-links. Branch lines use the same LineLook.
struct Link     { from: NodeId, to: NodeId, label: Option<Label>, look: LineLook }
struct LineLook { arrows: Option<Arrows>, line: Option<Stroke>, color: Option<LineColor>, style: Option<StyleName> }
enum Arrows     { Off, End, Start, Both }
enum Stroke     { Solid, Dashed, Dotted, Thick, Double }
enum LineColor  { Named(ColorName), FollowNode }

// Between documents.
struct Portal   { path: LinkPath, uid: DocUid, title: Title }  // title: kept in case the file goes missing
struct Backlink { from: LinkPath, uid: DocUid, node: NodeId }

// The document. Its fields are private, so only its methods can change it.
struct Document { uid, root: NodeId, entries: BTreeMap<NodeId, Entry>, loose: Vec<NodeId>,
                  links: BTreeMap<LinkKey, Link>, backlinks: Vec<Backlink>, next_id }
struct Entry    { node: Node, place: Place, children: Vec<NodeId> }
```

The `Option` fields in `NodeLook` and `LineLook` are overrides. A look is built
up in layers: the theme default, then the tag style, then the named style, then
the node's own fields. Each layer only states what it changes.

**Rules the `Document` methods guarantee**
- There is exactly one root, and it can't be deleted or given a parent.
- Each node has at most one parent, and there are no cycles: a move checks
  ancestors first.
- Children keep their order, and the file lists nodes in outline order.
- A link never joins a node to itself, both of its ends always exist, and
  deleting a node removes its links.

**Undo.** Every change runs as a transaction:
`doc.edit(|e| { e.add(…)?; e.update(…)?; Ok(()) })`. The transaction records
the old value of everything it touches. If a step fails, it rolls back; if it
succeeds, that record becomes one undo step. Undo writes the old values back,
redo the new ones. No command needs its own "reverse" code, and the records are
plain data, ready for a persistent undo file later.

**Folding** is one pure function of the document, the cursor and the focus
toggle, so every view folds the same way.

**Portals.** A cache holds each target's root title, color and node count,
refreshed when files change. When a root's title changes, the next save renames
the file, then fixes the portal paths in every document listed in its
backlinks, and the backlink paths in every document it points to.

## Screen and views

```
 cumulus  Garden plans [+] │ Kitchen │ Reading list
┌ Outline ──────────────┐┌ Canvas ───────────────────────────────────────────┐
│ ▾ Garden plans        ││                      ┌──────┐                     │
│   ├ Soil              ││                   ┌──┤ Soil │                     │
│   ├ [Raised beds]     ││                   │  └──────┘                     │
│   │ └ Cedar           ││ ╭──────────────╮  │  ┏━━━━━━━━━━━━━┓    ┌───────┐ │
│   └ Watering          ││ │ Garden plans ├──┼──┨ Raised beds ┠────┤ Cedar │ │
│ ◦ ask about compost   ││ ╰──────────────╯  │  ┗━━━━━━━━━━━━━┛    └───────┘ │
│                       ││                   │  ┌──────────┐                 │
│                       ││                   └──┤ Watering │                 │
│                       ││                      └──────────┘                 │
└───────────────────────┘└───────────────────────────────────────────────────┘
 NORMAL │ Canvas │ Garden plans › Raised beds                               2g
```

| View | What it's for |
|---|---|
| **Canvas** | The 2D map: free placement, 3 zoom levels, right-angle lines and the mouse. |
| **Outline** | Reorganizing and reading: an indented tree with fold markers, `+N` for hidden nodes and `»` for portals, with loose nodes listed at the end. |
| **Note** | Writing: one node's title, tags, color and body (with vim motions inside), plus its links in and out and its children. It follows the cursor. |
| **Board** (v1.1) | Sorting: columns by tag or color. Moving a card to another column changes its tag. |

- **Pickers:** Documents in v1, Search in v1.1.
- **Popups:** which-key (bottom right, as in skyshift), `?` help, the `K` card,
  the right-click menu, confirmations, and the command line with its
  completion list.
- **Top bar:** the open documents. **Bottom bar:** the mode, the view, the
  breadcrumb (or a message), and the keys typed so far (`2g` above).

**Mouse** (on the canvas; other views get click, double-click and scroll):
click selects, double-click edits the title, dragging a node moves it with its
branch, dragging empty space pans, scrolling pans, Ctrl+drag selects a
rectangle, Ctrl+click adds or removes one node, right-click opens a menu built
from the same actions as the keys. Zoom is on the `+` and `-` keys.

## Modes and keys

```rust
enum Mode {
    Normal,
    Insert(TextEdit),     // typing a title or body; rapid entry lives here
    TextNormal(TextEdit), // vim motions inside that text
    Visual(Visual),       // anchor + Rectangle or Branches
    Move(Grab),           // a node or a branch being moved
    Connect(Connect),     // the source node and the link being styled
    Command(CommandLine), // `:` with completion
}
```

Each mode has its own key tables. Which-key, `?` help and `keys.toml` all read
those same tables. The engine handles counts, registers, operator + target
(`d` + `ab`), and keys that take a character after them (`ma`, `fx` inside
text).

| Group | Keys |
|---|---|
| **Move** (every view) | `hjkl` or arrows · `gh gj gk gl` tree moves · `w` `b` next / previous in reading order · `gg` root · `G` last · `/` `n` `N` search · `Ctrl-o` `Ctrl-i` (Tab) jump back / forward · `m{a-z}` `'{a-z}` marks (`A–Z` across documents) · Enter or `gf` through a portal · `gd` follow a cross-link |
| **View** | `zz` center · `Ctrl-e` `Ctrl-y` `zh` `zl` pan · `Ctrl-d` `Ctrl-u` half a screen · `+` `-` zoom · `za zo zc zR zM` folds · `zf` Auto · `zi` focus · `K` body card |
| **Create and edit** | `o` `O` sibling below / above · `a` child · `i` `A` Enter edit the title · `I` edit from its start · `cc` `S` retype |
| **Operators** | `dd` or `dab` delete branch · `dib` delete children · `x` delete just the node · `yy` `yab` `yib` yank · `p` `P` paste after / before · `]p` paste as child · `>>` `<<` indent / outdent · `"a`–`"z` and `"+` registers · `.` repeat · `u` `Ctrl-r` undo / redo |
| **Modes** | `v` `V` visual · `M` move · `C` connect · `:` command · Esc back to normal |
| **Leader** `<Space>` | `c` color · `s` style · `B` border · `t` tags · `p` new portal · `i` inbox · `b` documents · `v` then `c`/`o`/`n` for canvas / outline / note · `w` which-key on/off · `?` help |
| **Panes, documents** | `Ctrl-w v` `Ctrl-w s` split · `Ctrl-w hjkl` focus · `Ctrl-w c` close · `Ctrl-w o` only · `Ctrl-w =` even sizes · `gt` `gT` `]b` `[b` next / previous document · `ZZ` close pane |
| **Typing** | `Ctrl-w` delete word · `Ctrl-u` delete line · arrows, Home, End · Enter (title: done or next sibling; body: new line) · Tab Shift-Tab (new node: child / back out) · Esc to vim motions |
| **Inside text** | `h j k l w b e 0 ^ $ f t x r J o O p P u Ctrl-r .` · `d` `c` `y` with motions and `iw aw i" a" i( a(` · `i a I A` back to typing |
| **Move mode** | `hjkl` 1 cell · `HJKL` 5 cells · `M` branch ↔ node · Enter or Esc done |
| **Connect mode** | move to the target as usual · Enter link · `d` remove · `>` attach as child · `<Space>` style menu (`s` named, `a` arrows, `l` line, `c` color, `t` label) · Esc cancel |
| **Visual** | `d y > < M C` and `<Space>c` `<Space>s` `<Space>t` act on the whole selection · `o` swaps ends |

## Files

**Documents** (`.cum`, RON). A `backlinks: [...]` list appears once another
document has a portal pointing here.

```ron
// cumulus document. Hand edits are fine: cumulus reloads it when it changes.
(
    format: 1,
    uid: "7f3c9a1e52b04d18",
    root: 1,
    nodes: [
        (
            id: 1,
            title: "Garden plans",
            pos: (0, 4),
            color: "green",
        ),
        (
            id: 2,
            parent: 1,
            title: "Raised beds",
            pos: (22, 4),
            tags: "#todo",
            fold: Auto,
            body: "Cedar, three of them.
40 cm high.",
        ),
        (
            id: 3,
            parent: 1,
            portal: (
                path: "kitchen.cum",
                uid: "c01d5e7aa0f3b912",
                title: "Kitchen",
            ),
            pos: (22, 8),
        ),
        (
            id: 4,
            title: "ask about compost",
            pos: (0, 14),
        ),
    ],
    links: [
        (
            from: 2,
            to: 4,
            label: "needs",
            line: Dashed,
            arrows: End,
        ),
    ],
)
```

**Config** (TOML) lives in `%APPDATA%\cumulus` (`~/.config/cumulus` on Linux);
`cumulus --paths` prints the folders. `:config` writes these files with a
comment on every option, and cumulus reloads them when they change.

```toml
# config.toml
theme = "default"            # a file in the themes folder
default_document = "ideas"   # what `cumulus` looks for at startup
autosave = true
mouse = true
which_key = true
which_key_delay = "300ms"
max_node_width = 30
glyphs = "unicode"           # "ascii" for fonts without box-drawing characters
completion_popup = "as-you-type"  # "on-tab": only after Tab, like vim's wildmenu

# keys.toml: sections motions, normal, canvas, outline, note, visual, move,
# connect, list; commands by name (src/input/command.rs); "nothing" unbinds
leader = "<Space>"
[normal]
"<Space>x" = "delete-branch"
"x" = "nothing"
[canvas]
"H" = "previous-document"

# themes/default.toml
accent = "cyan"
[palette]                    # terminal names, 0-255, or "#rrggbb"
red = 167
orange = 208
green = 108                  # … yellow, teal, blue, purple, pink, brown, gray
[modes]
insert = "green"
visual = "magenta"
[styles.node.question]
color = "yellow"
border = "dashed"
[styles.link.blocks]
color = "red"
line = "dashed"
arrows = "end"
label = "blocks"
[tags]
question = "question"        # a #question node gets the "question" style
```

**Data folder:** where you left off in each document (keyed by `uid`), command
history, capital marks, recent documents, daily backups, and lock files. If a
second cumulus opens a document that's already open, it opens it read-only.

**Command line**
- `cumulus` opens `./ideas.cum`, or `~/ideas.cum` if the current folder doesn't
  have one.
- `cumulus garden.cum` opens that file; `cumulus some/folder` opens that
  folder's default document.
- `cumulus new` creates `./ideas.cum`, and `cumulus new "Garden plans"` creates
  `./garden-plans.cum`. If the file already exists, cumulus opens it and says so.
- `cumulus --paths`, `--version` and `--help`.

## Module layout and flow

```
cumulus/
├─ Cargo.toml  rust-toolchain.toml  build.rs  rustfmt.toml  .cargo/config.toml
├─ README.md  DESIGN.md  .gitignore  .gitattributes
├─ examples/       runnable checkpoints during the build (canvas.rs, …)
└─ src/
   ├─ main.rs      command-line arguments, then app::run
   ├─ lib.rs       the module list
   ├─ model/       ids, text, geometry, look, node, portal, link, document, edit, op (edits as
   │               data), history, fold
   ├─ input/       key (vim notation), command (Command enum + names), bindings (default tables),
   │               keymap (+ keys.toml), engine (counts, registers, operators), mouse
   ├─ command/     registry, parse, complete, history
   ├─ view/        mod.rs (the View trait), canvas/ (camera, boxes, lines, route, scene, render,
   │               navigate, placement, view), outline, note, board
   ├─ ui/          text_editor (+ vim normal), which_key, command_line, line_input, status_bar,
   │               document_bar, card, menu, picker, help, theme, glyphs
   ├─ config/      paths, settings, keys_file, theme_file (TOML)
   ├─ storage/     document_file (RON), atomic save, backups, lock, state, watch (change polling)
   └─ app/         action, mode, buffer, commands (keys every view shares), calls (`:` commands);
                   later App, panes (split tree), jumps, registers, portals (cache, backlinks,
                   renames), update, render, terminal (setup, teardown, panic hook)
```

**Flow:** a terminal event comes in → the key engine turns keys into a typed
`Command` (with its count and register) → the focused view answers it with
`Action`s, and `app::commands::shared` answers the commands the view leaves
(undo, marks, adding, deleting, folds, modes…), so a view can give a key its own
meaning → a `:` line is parsed into a `Call` and `app::calls` answers it →
`update` carries out the actions in order, stopping at the first problem:
document actions go to the document's `Buffer` (the only place a document
changes: the edit, its undo step, the cursor and the marks), the rest change
the mode or the app → the screen is drawn from the state.

Edits travel as data (`EditOp`), so views never touch the document. A `Group`
makes several edits one undo step: a whole move-mode session, a mouse drag.

```rust
trait View {   // settled in stage 5
    fn kind(&self) -> ViewKind;
    fn contexts(&self, mode: &Mode) -> &'static [Context];   // its key tables, most specific first
    fn layout(&mut self, area: Rect, ctx: &ViewContext);     // fit to the area, follow the cursor
    fn render(&self, frame: &mut Frame, ctx: &ViewContext);  // draws the layout, changes nothing
    fn command(&mut self, typed: &Typed, ctx: &ViewContext) -> Option<Vec<Action>>; // None: not mine
    fn mouse(&mut self, gesture: Gesture, ctx: &ViewContext) -> Vec<Action>;
}
// ViewContext: the document, the cursor, the mode, the theme and the view settings.
```

What changed from the first sketch: `layout` comes before `render`, because a
view keeps the frame it drew (the canvas matches clicks against it) and moves
its camera to follow the cursor, and drawing should change nothing; `command`
takes the whole `Typed` (counts matter) and returns `None` for commands it
leaves to the shared ones.

## Build order

Hardest parts first, so they shape a simple interface that every view shares
and the core ends up thin. The model comes first because every hard part reads
it.

| # | Stage | What you can run |
|---|---|---|
| 0 | Skeleton: Cargo.toml, toolchain, `build.rs`, rustfmt, aliases, README, DESIGN.md | `cumulus --version` |
| 1 | Model: types, document rules, transactions and undo, folding, RON round trip | `cargo test` |
| 2 | Canvas engine: camera, boxes, a line layer with junctions, right-angle routing, arrows and labels, zoom levels, hit-testing, nearest-node moves, placement | `cargo run --example canvas` |
| 3 | Key engine: notation, tables, counts, registers, operator + target, keys that take a character, which-key, `keys.toml` | the example gets real keys and which-key |
| 4 | Command line: registry, parser, completion (popup + ghost text), history | `:` in the example |
| 5 | The shared `View` interface, `Action` and `Mode`, pulled out of stages 2–4 | the example runs through it |
| 6 | Text editor: typing, plus vim normal mode inside text | editing titles in the example |
| 7 | Outline and Note views; status bar, document bar, help, `K` card, right-click menu, Documents picker | the example with splits |
| 8 | App core: main loop, terminal setup and panic hook, buffers, splits, modes, jumps, marks, registers, files (load, autosave, reload, backups, locks, where you left off), config/theme/keys, portals, backlinks and renames, startup rules | `cumulus`: v1 |
| 9 | v1.1: Board, Search picker, `:tidy` and align, branch out, export/import | |

Each stage ends with `cargo build`, `cargo lint` and `cargo test` passing, and
one commit.

## Crates and tooling

- **Crates:** ratatui 0.30 (with the crossterm 0.29 it ships with) · serde, ron
  0.12 and toml 1 · directories 6 · thiserror 2 and anyhow · arboard 3 (with
  Wayland support) · unicode-width and unicode-segmentation. No testing crates.
  Each crate is added in the stage that first needs it.
- **Toolchain:** `rust-toolchain.toml` pins 1.90.0 with clippy, rustfmt and the
  musl target.
- **`build.rs`:** embeds the git commit for `cumulus --version`.
- **Windows first:** only key Press and Repeat events count; a panic hook
  restores the terminal (raw mode, the screen, the mouse); paths come from
  `directories`.
- **Same as skyshift:** edition 2024, rustfmt at 110 columns, `cargo lint` and
  `cargo linux`, the static C runtime on Windows, LF line endings, `unsafe`
  forbidden.
- **Doc comments** on public types and functions, written where they explain
  something. (The `missing_docs` lint was dropped: it demands a comment on
  every field and enum variant, which is the comment noise we don't want.)

## Tests

- **Keys:** notation, sequences, counts, registers, operator + target,
  overrides, and no binding hiding another.
- **Command line:** parsing, abbreviations, completion ranking, history.
- **Model:** tree rules, undo/redo round trips, folding.
- **Canvas:** camera conversions, routing and junctions (small text snapshots),
  hit-testing, nearest-node moves.
- **Files:** RON round trip, load errors, config parsing, and backlink and
  rename fix-ups, in temporary folders.