Refactor `run` function to reduce complexity by extracting helper functions

[sourcery-ai]

The current implementation of the run function in the CLI module is becoming complex due to the inlining of multiple steps, especially within the Build command arm. This complexity makes the function harder to read and maintain.

Suggested Refactor:

• Extract the key steps in the Build command into small, well-named helper functions. For example:
  • handle_build(cli, targets) to encapsulate the build process
  • resolve_manifest_path(cli) to handle manifest path resolution
  • write_ninja_file(cli, graph) to handle writing the Ninja build file
• This approach will flatten out the Build arm, remove nested map_or_else calls, and keep the run function shallow and easy to follow.
• All existing functionality should be preserved.

Example Refactored Code:

pub fn run(cli: &Cli) -> io::Result<()> {
    match cli.command.clone().unwrap_or_default() {
        Commands::Build { targets } => handle_build(cli, &targets),
        Commands::Clean => { println!("Clean requested"); Ok(()) }
        Commands::Graph => { println!("Graph requested"); Ok(()) }
    }
}

fn handle_build(cli: &Cli, targets: &[String]) -> io::Result<()> {
    let manifest_path = resolve_manifest_path(cli);
    let manifest      = manifest::from_path(&manifest_path).map_err(io::Error::other)?;
    debug!("AST:\n{}", serde_json::to_string_pretty(&manifest).unwrap());

    let graph      = BuildGraph::from_manifest(&manifest).map_err(io::Error::other)?;
    let ninja_path = write_ninja_file(cli, &graph)?;
    info!("Generated Ninja file at {}", ninja_path.display());

    run_ninja(Path::new("ninja"), cli, targets)
}

fn resolve_manifest_path(cli: &Cli) -> PathBuf {
    cli.directory
       .as_ref()
       .map(|dir| dir.join(&cli.file))
       .unwrap_or_else(|| cli.file.clone())
}

fn write_ninja_file(cli: &Cli, graph: &BuildGraph) -> io::Result<PathBuf> {
    let content = ninja_gen::generate(graph);
    let path = cli
        .directory
        .as_ref()
        .map(|d| d.join("build.ninja"))
        .unwrap_or_else(|| PathBuf::from("build.ninja"));

    fs::write(&path, content)
        .map(|_| path)
        .map_err(io::Error::other)
}

Action Items:

• Refactor the run function as described above.
• Ensure all tests pass and functionality is preserved.
• Review for further simplification opportunities if possible.

References

• Issue: Refactor run function to reduce complexity by extracting helper functions #47

---

I created this issue for @leynos from #45 (comment).

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