todo.merge

pub fn merge_todos(current: &[Todo], incoming: &[Todo]) -> Vec<Todo>

fune!(todo.merge@^1);  // then call merge_todos(…)

use std::collections::HashSet;

use super::funejson::Value;  ← the fune runtime: the JSON value the test vectors use; fune build keeps it only where a signature takes one
use super::todo_item::Todo;  ← from todo.item ^1.0.0 · built alongside by fune
use super::todo_item_validate_todo::{todos_from_value, todos_to_value};

/// Manual order: order ascending, ties by position (sort_by_key is stable).
fn in_manual_order(todos: &[Todo], which: &str) -> Vec<Todo> {
    let mut seen: HashSet<&str> = HashSet::new();
    for todo in todos {
        if !seen.insert(todo.id.as_str()) {
            panic!("duplicate id \"{}\" in the {} list", todo.id, which);
        }
    }
    let mut sorted = todos.to_vec();
    sorted.sort_by_key(|todo| todo.order);
    sorted
}

/// Merge by id: a todo in both lists is taken from `incoming`, in the place
/// the current one had; todos only in `incoming` follow in their own manual
/// order. The result is in manual order, renumbered 0 to n-1.
///
/// # Panics
/// On an id that appears twice in either list.
pub fn merge_todos(current: &[Todo], incoming: &[Todo]) -> Vec<Todo> {
    let mine = in_manual_order(current, "current");
    let theirs = in_manual_order(incoming, "incoming");
    let kept: HashSet<&str> = mine.iter().map(|todo| todo.id.as_str()).collect();
    let mut merged: Vec<Todo> = mine
        .iter()
        .map(|todo| theirs.iter().find(|t| t.id == todo.id).unwrap_or(todo).clone())
        .collect();
    merged.extend(theirs.iter().filter(|todo| !kept.contains(todo.id.as_str())).cloned());
    for (order, todo) in merged.iter_mut().enumerate() {
        todo.order = order as i64;
    }
    merged
}

pub fn fune_vector(args: &[Value]) -> Value {
    todos_to_value(&merge_todos(&todos_from_value(&args[0]), &todos_from_value(&args[1])))
}

Install

fune build

With that line in your source, in a Rust project (language rust in fune.project), fune build resolves it and its 1 dependency, pins them in fune.lock, downloads only the Rust 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. A crate’s build.rs runs it before every compile. Or pin a range in fune.project and build in one step:

fune add todo.merge

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

The whole function, every language, is one file too: todo.merge-1.0.0.fune, 19,135 bytes, sha256 70fd49a1e279c942df6f45cf86dbc03153376c38c62cd1836180141e1f1f11db. It installs into a project of any language.

// fune: before todo.merge

// fune: after todo.merge

// fune: replace todo.item in todo.merge

// fune: step todo.merge after <n|label>

More from the author

## Which copy wins

The incoming one. A todo (todo.item) records when it was created and completed but not when it was last edited, so there is no honest way to tell which of two copies is newer. Importing a file is the person saying "these are the versions I want", so the file's row is treated as the newer copy: every field comes from it, done state and timestamps included.

## Order

The result is in manual order (todo.sort's `manual`: `order` ascending, ties by array position), renumbered 0 to n-1, as todo.list's `moveTodo` leaves a list:

1. The current todos in their manual order, each replaced by its incoming copy where there is one. A replaced todo keeps its **current** position: the person arranged this list, and the file's `order` is a position in a different list. 2. Then the todos only in `incoming`, in the incoming list's own manual order, so a file's order among its new rows is kept.

So a new todo whose file `order` is 0 still goes after the existing ones, and gaps in the current orders close up.

## Errors

An id that appears twice in either list is an error (`duplicate id "a" in the incoming list`), because it is ambiguous which copy to keep. The todos are not otherwise checked: todo.import-csv has already checked a file's rows with todo.item's `validateTodo`.

Files