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src/engine/rocketExportImport.js

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+import { downloadBlob } from './exportImport.js'
+
+export { downloadBlob }
+
+/**
+ * Build a rocket design JSON Blob for download.
+ * Schema version 1: inputs section is re-importable; results is reference-only.
+ */
+export function exportRocketJSON({ outerRadius, tankConfig, propDensities, payload, structure, engineData, geometry }) {
+  const payload_ = {
+    version: 1,
+    type: 'rocket_design',
+    exportedAt: new Date().toISOString(),
+    inputs: {
+      outerRadius,
+      tankConfig,
+      propDensities,
+      payload,
+      structure,
+    },
+    engineData: engineData ?? null,
+    results: geometry ?? null,
+  }
+  return new Blob([JSON.stringify(payload_, null, 2)], { type: 'application/json' })
+}
+
+/**
+ * Parse an imported rocket design JSON string and return the inputs section.
+ * Throws a descriptive Error if the file is invalid.
+ */
+export function parseRocketImport(jsonString) {
+  let data
+  try {
+    data = JSON.parse(jsonString)
+  } catch {
+    throw new Error('File is not valid JSON.')
+  }
+
+  if (data.type !== 'rocket_design') {
+    throw new Error('This file is not a rocket design export.')
+  }
+  if (data.version !== 1) {
+    throw new Error(`Unsupported export version: ${data.version}`)
+  }
+
+  const { outerRadius, tankConfig, propDensities, payload, structure } = data.inputs ?? {}
+
+  return {
+    outerRadius: outerRadius ?? null,
+    tankConfig:  tankConfig  ?? null,
+    propDensities: propDensities ?? null,
+    payload:     payload     ?? null,
+    structure:   structure   ?? null,
+    engineData:  data.engineData ?? null,
+  }
+}