todo.export-csv

export function exportCsv(todos: readonly Todo[]): string

import { exportCsv } from "#fune/todo.export-csv@^1";

import { type Todo } from "./todo_item.ts";  ← from todo.item ^1.0.0 · built alongside by fune

const HEADER = [
  "id", "title", "notes", "done", "priority", "due", "tags",
  "recurrenceFrequency", "recurrenceInterval", "recurrenceAnchor", "createdAt", "completedAt", "order",
];

/** Quote a field only when RFC 4180 needs it: a comma, a double quote, CR or LF. */
function field(text: string): string {
  if (!/[",\r\n]/.test(text)) return text;
  return '"' + text.split('"').join('""') + '"';
}

/**
 * Todos as CSV, one row per todo in the order given, under a fixed header
 * of 13 columns. Nothing is escaped for spreadsheets: a title starting with
 * "=" is written as it is, so the file reads back exactly (see README).
 */
export function exportCsv(todos: readonly Todo[]): string {
  const lines = [HEADER.join(",")];
  for (const todo of todos) {
    const rule = todo.recurrence ?? null;
    const cells = [
      todo.id,
      todo.title,
      todo.notes ?? "",
      todo.done ? "true" : "false",
      todo.priority,
      todo.due ?? "",
      todo.tags.join(" "),
      rule === null ? "" : rule.frequency,
      rule === null ? "" : String(rule.interval),
      rule === null ? "" : rule.anchor,
      todo.createdAt,
      todo.completedAt ?? "",
      String(todo.order),
    ];
    lines.push(cells.map(field).join(","));
  }
  return lines.map((line) => line + "\r\n").join("");
}

Install

fune build

With that line in your source, in a TypeScript project (language typescript in fune.project), fune build resolves it and its 1 dependency, pins them in fune.lock, downloads only the TypeScript package of each, and builds the code above into your project’s .fune/build, one readable file per capability with a header linking back here. Or pin a range in fune.project and build in one step:

fune add todo.export-csv

The manifest, vectors and README with only the TypeScript implementation. Install it without the registry with fune add ./todo.export-csv-1.0.0-typescript.fune, or fetch it from a terminal with fune pull todo.export-csv@1.0.0:typescript.

The whole function, every language, is one file too: todo.export-csv-1.0.0.fune, 17,768 bytes, sha256 f2f17720f311707190e8643af25b46732546ab8cf545f39a5f5f873f7139bc83. It installs into a project of any language.

// fune: before todo.export-csv

// fune: after todo.export-csv

// fune: replace todo.item in todo.export-csv

// fune: step todo.export-csv after <n|label>

More from the author

CSV as in [RFC 4180, Common Format and MIME Type for Comma-Separated Values (CSV) Files](https://www.rfc-editor.org/rfc/rfc4180). The same format is written by todo.export-csv and read by todo.import-csv.

- A header row, then one row per todo. todo.export-csv writes these 13 columns in this order: `id,title,notes,done,priority,due,tags,recurrenceFrequency,recurrenceInterval,recurrenceAnchor,createdAt,completedAt,order` - `done` is `true` or `false`. `tags` are joined with single spaces. The repeat takes three columns, all empty when the todo does not repeat. `order` and `recurrenceInterval` are decimal integers. A null field (`notes`, `due`, `completedAt`) is empty. - A field is quoted with double quotes exactly when it contains a comma, a double quote, CR or LF, and a double quote inside it is doubled. Nothing else is quoted, and spaces are kept as they are. - Every row, the last one included, ends with CRLF.

**Caveat for spreadsheets.** Nothing is escaped against formula injection: a title such as `=1+1` or `=HYPERLINK(...)` is written as it is, because prefixing it with `'` would change the title when the file is read back. If your app offers the file for opening in Excel, LibreOffice or Google Sheets, warn people, or write a separate spreadsheet export that escapes cells starting with `=`, `+`, `-` or `@`.

## Why it is shaped this way

One column per field, with the repeat split into three plain columns rather than packed into one, so the file is readable in a spreadsheet and easy for other tools to produce. Columns are named after the `Todo` fields, so the header documents itself.

CRLF line endings and minimal quoting are what RFC 4180 describes and what spreadsheets expect; quoting only when needed keeps the file diff-friendly.

## Edge cases

- No todos: just the header line, still ending in CRLF. - Notes that are `""` are written as an empty field, the same as null notes, so they read back as null. Every other valid list reads back exactly: `importCsv(exportCsv(todos))` equals `todos`. - Line breaks inside notes (LF, CRLF or a lone CR) are kept inside quotes as they are. - It does not validate and never throws: a todo is written as it is, even an invalid one (a negative order is written `-1`). Validate on the way in, or let todo.import-csv refuse the file. - The text is a string; encode it as UTF-8 when saving. No byte order mark is written (some versions of Excel need one to read UTF-8; add `\uFEFF` in front if yours does, todo.import-csv accepts it).

Files