Add a simple CLI for use in unified UI

Adds a simple CLI that:
- reads input JSON (of type `ScenarioData`) from a specified input path
- runs the model by calling into `run.ts`
- writes output JSON (of type `AlgorithmResult`) into the specified output path

This allows the model to be run in a unified model UI.
Having this as part of the model repo enables the unified interface to keep up with model changes.

src/algorithms/cli.ts

@@ -0,0 +1,77 @@
+import * as fs from 'fs'
+import { run } from './run'
+import { ScenarioFlat, ScenarioData } from './types/Param.types'
+import { getAgeDistribution } from '../components/Main/state/getAgeDistribution'
+import { getSeverityDistribution } from '../components/Main/state/getSeverityDistribution'
+import { toInternal } from '../components/Main/state/getScenario'
+
+const handleRejection: NodeJS.UnhandledRejectionListener = (err) => {
+  console.error(err)
+  process.exit(1)
+}
+
+process.on('unhandledRejection', handleRejection)
+
+function readJsonFromFile<T>(arg: number) {
+  const inputFilename = process.argv[arg]
+  if (!inputFilename) {
+    usage()
+  }
+  console.log(`Reading data from file ${inputFilename}`)
+  const inputData = fs.readFileSync(inputFilename, 'utf8')
+  const inputJson = JSON.parse(inputData) as T
+  console.log(`Read input data`)
+  return inputJson
+}
+
+async function main() {
+  const scenarioData = readJsonFromFile<ScenarioData>(2)
+  const outputFile = process.argv[3]
+  if (!outputFile) {
+    usage()
+  }
+  console.log(`Will write model output to ${outputFile}`)
+
+  const scenario = toInternal(scenarioData.data)
+
+  const params: ScenarioFlat = {
+    ...scenario.population,
+    ...scenario.epidemiological,
+    ...scenario.simulation,
+    ...scenario.mitigation,
+  }
+  // Read data from severityDistributions.json and perform JSON validation.
+  // Use the model's default (and only) severity distribution.
+  console.log(`Reading severity distribution data`)
+  const DEFAULT_SEVERITY_DISTRIBUTION = 'China CDC'
+  const severity = getSeverityDistribution(DEFAULT_SEVERITY_DISTRIBUTION)
+  // Read data from ageDistribution.json and perform JSON validation.
+  console.log(`Reading age distribution data`)
+  const ageDistribution = getAgeDistribution(params.ageDistributionName)
+
+  try {
+    console.log('Running the model')
+    const result = await run({ params, severity, ageDistribution })
+    console.log('Run complete')
+    console.log(result)
+    console.log(`Writing output to ${outputFile}`)
+    fs.writeFileSync(outputFile, JSON.stringify(result))
+  } catch (error) {
+    console.error(`Run failed: ${error}`)
+    process.exit(1)
+  }
+}
+
+function usage() {
+  console.log(
+    `
+Usage:
+    cli <input-file> <output-file>
+        Manually perform a single model run with the given input, writing the results to the given output file.
+    `.trim(),
+  )
+
+  process.exit(1)
+}
+
+main()