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76 lines
3.0 KiB
Markdown
76 lines
3.0 KiB
Markdown
+++
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title = "Add graph computation module (src/graph.rs)"
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priority = 5
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status = "done"
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ticket_type = "feature"
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dependencies = []
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+++
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Implement `src/graph.rs` — a module that builds a directed dependency graph from a flat list of tickets and provides the data structures needed by the ASCII renderer and JSON output.
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## Motivation
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The `nbd graph` command (see CLI ticket) needs to traverse `Ticket.dependencies` edges to produce an ordered, tree-structured representation of the dependency DAG. This module isolates that logic from I/O and rendering.
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## Data structures
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```rust
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/// A node in the dependency graph.
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pub struct GraphNode<'a> {
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pub ticket: &'a Ticket,
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/// Direct dependents (tickets that list this ticket as a dependency).
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pub dependents: Vec<&'a str>,
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/// Direct dependencies (tickets this ticket depends on).
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pub dependencies: Vec<&'a str>,
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}
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/// A directed dependency graph built from a flat list of tickets.
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pub struct TicketGraph<'a> {
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nodes: IndexMap<&'a str, GraphNode<'a>>,
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}
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```
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## Functions to implement
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### `TicketGraph::build(tickets: &[Ticket]) -> TicketGraph`
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- Constructs `nodes` map keyed by ticket ID.
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- Iterates `ticket.dependencies` to populate both `dependencies` (forward) and `dependents` (reverse) edges.
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- IDs in `dependencies` that do not correspond to a known ticket are silently ignored (dangling references are tolerated).
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### `TicketGraph::roots(&self) -> Vec<&Ticket>`
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- Returns tickets with no dependencies (or whose dependencies are all outside the graph).
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- Sorted by priority descending (same ordering as `list_tickets`).
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- These become the starting points for the recursive ASCII tree renderer.
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### `TicketGraph::subtree(&self, root_id: &str) -> Vec<&str>`
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- Returns all ticket IDs reachable from `root_id` by following `dependencies` edges in depth-first order, including `root_id` itself.
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- Cycles: track visited set; stop recursion when an ID has been visited. This makes the function safe even if the data contains cycles.
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### `TicketGraph::to_json_value(&self) -> serde_json::Value`
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- Returns an object like:
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```json
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{
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"nodes": [
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{"id": "a3f9c2", "title": "...", "status": "todo", "dependencies": ["b7d41e"]},
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...
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],
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"edges": [
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{"from": "a3f9c2", "to": "b7d41e"},
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...
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]
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}
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```
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## Crate dependencies
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No new crates needed. If `IndexMap` insertion-order is useful, `indexmap` can be added — but a `HashMap` with a separate sorted `Vec<&str>` of keys also works. Prefer whatever avoids adding a new crate dependency.
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## Files touched
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- `src/graph.rs` — new file, public module
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- `src/main.rs` — `mod graph;` declaration
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## Tests (unit, in `src/tests.rs`)
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- `build` with an empty slice returns an empty graph.
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- `roots` returns only tickets with no in-graph dependencies.
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- `subtree` returns the correct set of IDs for a linear chain.
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- `subtree` does not infinite-loop when the data contains a cycle.
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- `to_json_value` contains all expected IDs in `nodes` and all edges in `edges`. |