feat: implement readExcel function with sheetName param

deno.json

@@ -6,6 +6,8 @@
     "dev": "deno run --watch main.ts"
   },
   "imports": {
+    "@std/assert": "jsr:@std/assert@^1.0.10",
+    "@std/fs": "jsr:@std/fs@^1.0.8",
     "@tinkie101/exceljs-wrapper": "jsr:@tinkie101/exceljs-wrapper@^1.0.2",
     "polars": "npm:nodejs-polars@^0.17.0"
   }

mod.ts

@@ -1,47 +1,7 @@
-import pl from "polars";
+import type pl from "polars";
 import ExcelJS from "@tinkie101/exceljs-wrapper";
-
-type RowData = Record<string, string | number | boolean | null | undefined>;
-
-/**
- * Reads an Excel file and returns its content as a Polars DataFrame.
- * This function loads the first sheet of the workbook and converts it into a DataFrame.
- *
- * @param filePath - The path to the Excel file to be read.
- * @returns A Promise resolving to a Polars DataFrame containing the data from the first sheet.
- */
-async function readExcel(filePath: string): Promise<pl.DataFrame> {
-  const workbook = new ExcelJS.Workbook();
-  await workbook.xlsx.readFile(filePath);
-
-  const worksheet = workbook.worksheets[0];
-  if (!worksheet) {
-    throw new Error("No sheets found in the Excel file.");
-  }
-
-  const jsonData: RowData[] = [];
-  const headers: string[] = [];
-
-  worksheet.eachRow((row, rowNumber) => {
-    const rowData: RowData = {};
-
-    row.eachCell((cell, colNumber) => {
-      const cellValue = cell.value as string | number | boolean | null;
-
-      if (rowNumber === 1) {
-        headers[colNumber - 1] = cellValue?.toString() || `Column${colNumber}`;
-      } else {
-        rowData[headers[colNumber - 1]] = cellValue;
-      }
-    });
-
-    if (rowNumber > 1) {
-      jsonData.push(rowData);
-    }
-  });
-
-  return pl.DataFrame(jsonData);
-}
+import { readExcel } from "./read_excel.ts";
+import type { RowData } from "./types.ts";
 
 /**
  * Writes a Polars DataFrame to an Excel file.

read_excel.ts

@@ -0,0 +1,44 @@
+import pl from "polars";
+import ExcelJS from "@tinkie101/exceljs-wrapper";
+import type { RowData } from "./types.ts";
+
+export async function readExcel(
+  filePath: string,
+  sheetName?: string,
+): Promise<pl.DataFrame> {
+  const workbook = new ExcelJS.Workbook();
+  await workbook.xlsx.readFile(filePath);
+
+  const worksheet = sheetName
+    ? workbook.getWorksheet(sheetName)
+    : workbook.worksheets[0];
+
+  if (!worksheet) {
+    throw new Error(
+      `Worksheet ${sheetName || "Sheet1"} not found in the Excel file.`,
+    );
+  }
+
+  const jsonData: RowData[] = [];
+  const headers: string[] = [];
+
+  worksheet.eachRow((row, rowNumber) => {
+    const rowData: RowData = {};
+
+    row.eachCell((cell, colNumber) => {
+      const cellValue = cell.value as string | number | boolean | null;
+
+      if (rowNumber === 1) {
+        headers[colNumber - 1] = cellValue?.toString() || `Column${colNumber}`;
+      } else {
+        rowData[headers[colNumber - 1]] = cellValue;
+      }
+    });
+
+    if (rowNumber > 1) {
+      jsonData.push(rowData);
+    }
+  });
+
+  return pl.DataFrame(jsonData);
+}

read_excel_test.ts

@@ -0,0 +1,66 @@
+import { assertEquals, assertRejects } from "@std/assert";
+import { readExcel } from "./read_excel.ts";
+import { createTestExcelFile, removeTestFile } from "./test_utils.ts";
+import ExcelJS from "@tinkie101/exceljs-wrapper";
+
+Deno.test({
+  name: "readExcel - Reads data from a valid Excel file",
+  async fn() {
+    const filePath = "./test-read-valid.xlsx";
+    const testData = {
+      headers: ["Name", "Age", "Country"],
+      rows: [
+        ["Alice", 30, "USA"],
+        ["Bob", 25, "Canada"],
+      ],
+    };
+    await createTestExcelFile(filePath, testData);
+
+    const df = await readExcel(filePath);
+
+    const expected = [
+      { Name: "Alice", Age: 30, Country: "USA" },
+      { Name: "Bob", Age: 25, Country: "Canada" },
+    ];
+    assertEquals(df.toRecords(), expected);
+
+    await removeTestFile(filePath);
+  },
+});
+
+Deno.test({
+  name: "readExcel - Throws error for missing sheet",
+  async fn() {
+    const filePath = "./test-read-missing-sheet.xlsx";
+    const testData = {
+      headers: ["Name", "Age"],
+      rows: [["Alice", 30]],
+    };
+    await createTestExcelFile(filePath, testData);
+
+    await assertRejects(
+      async () => {
+        await readExcel(filePath, "NonExistentSheet");
+      },
+      Error,
+      "Worksheet NonExistentSheet not found in the Excel file.",
+    );
+    await removeTestFile(filePath);
+  },
+});
+
+Deno.test({
+  name: "readExcel - Handles empty Excel file",
+  async fn() {
+    const filePath = "./test-empty.xlsx";
+    const workbook = new ExcelJS.Workbook();
+    workbook.addWorksheet("Sheet1");
+    await workbook.xlsx.writeFile(filePath);
+
+    const df = await readExcel(filePath);
+
+    assertEquals(df.shape, { height: 0, width: 0 });
+
+    await removeTestFile(filePath);
+  },
+});

test_utils.ts

@@ -0,0 +1,21 @@
+import ExcelJS from "jsr:@tinkie101/exceljs-wrapper@^1.0.2";
+import { exists } from "@std/fs";
+
+export async function createTestExcelFile(
+  filePath: string,
+  data: { headers: string[]; rows: (string | number | boolean)[][] },
+): Promise<void> {
+  const workbook = new ExcelJS.Workbook();
+  const worksheet = workbook.addWorksheet("Sheet1");
+
+  worksheet.addRow(data.headers);
+  data.rows.forEach((row) => worksheet.addRow(row));
+
+  await workbook.xlsx.writeFile(filePath);
+}
+
+export async function removeTestFile(filePath: string): Promise<void> {
+  if (await exists(filePath)) {
+    await Deno.remove(filePath);
+  }
+}

types.ts

@@ -0,0 +1,4 @@
+export type RowData = Record<
+  string,
+  string | number | boolean | null | undefined
+>;