Add layout linear-gene

src/scripts/layout/linear-gene.ts

+import { GeneData, PositionedGeneData } from "../component/sequence/gene";
+import { scaleLinear } from "d3-scale";
+
+export default function linearGene(
+  data: Array<GeneData>,
+  width: number,
+  geneOffset: number
+) {
+  const sumLength = data.reduce((accum, gene) => accum + gene.length, 0);
+  const sumGeneOffset = (data.length - 1) * geneOffset;
+  const xScale = scaleLinear().domain([0, sumLength - sumGeneOffset]).range([0, width])
+
+  return data.reduce(function (
+    accum: PositionedGeneData[],
+    gene: GeneData,
+    i: number,
+    data: GeneData[]
+  ) {
+    if (i > 0) {
+      const previousGene = accum[i - 1];
+      accum.push({
+        ...gene,
+        position: {
+          x: previousGene.position.x + previousGene.position.width + geneOffset,
+          y: 0,
+          width: xScale(gene.length)
+        }
+      });
+      return accum;
+
+    }
+    else {
+      accum.push({
+        ...gene,
+        position: {
+          x: 0,
+          y: 0,
+          width: xScale(gene.length)
+        }
+      });
+      return accum;
+
+    }
+
+  }, []);
+
+}
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