Architecture

ViralUnity is a thin Python orchestration layer over Snakemake workflows. The Python code validates inputs, writes a YAML config, and launches one of six Snakemake workflows; all the bioinformatics lives in the .smk rule files.

Data flow

CLI (click)                       viralunity_cli.py  →  <subcommand>_cli.py
   │  parses options, configures logging (--log-level / --json-logs)
   ▼
main(args)                        viralunity_consensus.py / viralunity_meta.py
   │  thin wrapper around…
   ▼
_orchestrator.run_pipeline(...)   viralunity/_orchestrator.py
   │  resolve_paths → validate → generate_config → [run manifest] → run_workflow
   ▼
ConfigGenerator → YAML            viralunity/config_generator.py
   │  emits the exact keys the .smk files read (config["samples"], …)
   ▼
snakemake(workflow.smk, config)   viralunity/scripts/<pipeline>_<datatype>.smk
   │  rule all → _all_inputs() → include: rules/*.smk
   ▼
per-rule conda envs               viralunity/scripts/envs/*.yaml  (--use-conda)

Module map

Module	Responsibility
`viralunity_cli.py`	Top-level click group; wires `--log-level` / `--json-logs`.
`<sub>_cli.py`	Per-subcommand click options → plain `args` dict.
`viralunity_consensus.py`, `viralunity_meta.py`	Own `validate_args`, `generate_config_file`, `run_snakemake_workflow`; call the orchestrator.
`_orchestrator.py`	Shared `run_pipeline` skeleton (resolve → validate → config → manifest → run) with structured error handling.
`validators.py`	File/dir existence, sample-sheet parsing, cross-dependency checks, input sanitization.
`config_generator.py`	Writes the YAML config (the contract with the `.smk` files).
`constants.py`	`ConfigKeys`, `DataType`, `ResourceDefaults` (per-pipeline rule lists).
`exceptions.py`	Typed error hierarchy with machine-readable `code`s.
`logging_config.py`	Central logging (run id, text/JSON).
`provenance.py`	`run_manifest.json` (version, config, input checksums).
`_subprocess.py`	`run_command` for external tools (get-databases / build-deacon-index), with timeouts.
`scripts/.smk`, `scripts/rules/.smk`	The actual pipelines.
`scripts/python/*.py`	Helpers run via Snakemake’s `script:` directive.

The config is the contract

ConfigGenerator emits keys that are hard-coded as strings in the .smk files (e.g. config["samples"], config["output"], config["run_denovo_assembly"]). Adding a pipeline option means touching four places: the click option in the relevant *_cli.py, the validators.py check, a ConfigGenerator.add_* setter, and the rule(s) that read it. config["samples"] maps sample-<id> to a list of FASTQ paths (readers tolerate the legacy space-joined string form too).

Workflow selection

run_snakemake_workflow formats a path: scripts/{consensus,metagenomics}_{illumina,nanopore}[_segmented].smk. Segmentation is chosen when args["reference"] is a dict (from repeatable --segmented-reference SEGMENT=PATH). There is no segmented metagenomics variant.