fix(google-sheets): normalise header case and fix monthly COUNTIFS formula

packages/destination-google-sheets/__tests__/examples.test.ts

@@ -41,9 +41,9 @@ describe('buildExampleSections', () => {
     expect(s.rows).toHaveLength(6) // last 6 months
     // Formulas should reference customers.created (column C = index 2)
     expect(s.rows[0][1]).toContain("'customers'!C2:C")
-    // Formula should use EDATE for Unix timestamp conversion
+    // Formula should use EDATE for month boundaries and DATEVALUE for ISO string parsing
     expect(s.rows[0][1]).toContain('EDATE')
-    expect(s.rows[0][1]).toContain('DATE(1970,1,1)')
+    expect(s.rows[0][1]).toContain('DATEVALUE')
   })
 
   it('includes payment volume section when payment_intents has status and amount', () => {

packages/destination-google-sheets/src/index.test.ts

@@ -10,6 +10,8 @@ import {
 } from './index.js'
 import {
   applyBatch,
+  displayToField,
+  fieldToDisplay,
   MAX_CELLS_PER_SPREADSHEET,
   readEnumValidations,
   readSheet,
@@ -2051,3 +2053,48 @@ describe('enum constraints on any column', () => {
     ).toBeUndefined()
   })
 })
+
+describe('fieldToDisplay / displayToField', () => {
+  it('roundtrip — lowercase snake_case fields survive display conversion', () => {
+    const fields = ['id', 'created_at', 'customer_id', 'object', 'invoice_item_id']
+    for (const f of fields) {
+      expect(displayToField(fieldToDisplay(f))).toBe(f)
+    }
+  })
+
+  it('fieldToDisplay — single word gets sentence case', () => {
+    expect(fieldToDisplay('id')).toBe('Id')
+    expect(fieldToDisplay('object')).toBe('Object')
+  })
+
+  it('fieldToDisplay — multi-word snake_case becomes sentence case with spaces', () => {
+    expect(fieldToDisplay('created_at')).toBe('Created at')
+    expect(fieldToDisplay('customer_id')).toBe('Customer id')
+  })
+
+  it('fieldToDisplay — uppercase in input is normalised to lowercase (no case leakage)', () => {
+    expect(fieldToDisplay('API_version')).toBe('Api version')
+    expect(fieldToDisplay('UPPER_case')).toBe('Upper case')
+  })
+
+  it('fieldToDisplay — system fields (leading underscore) are returned as-is', () => {
+    expect(fieldToDisplay('_idx')).toBe('_idx')
+    expect(fieldToDisplay('_updated_at')).toBe('_updated_at')
+  })
+
+  it('displayToField — reverses sentence case label back to snake_case', () => {
+    expect(displayToField('Created at')).toBe('created_at')
+    expect(displayToField('Customer id')).toBe('customer_id')
+    expect(displayToField('Id')).toBe('id')
+  })
+
+  it('displayToField — system fields (leading underscore) are returned as-is', () => {
+    expect(displayToField('_idx')).toBe('_idx')
+    expect(displayToField('_updated_at')).toBe('_updated_at')
+  })
+
+  it('displayToField — idempotent on already-snake_case strings', () => {
+    expect(displayToField('customer_id')).toBe('customer_id')
+    expect(displayToField('id')).toBe('id')
+  })
+})

packages/destination-google-sheets/src/writer.ts

@@ -53,7 +53,7 @@ function colIndexToLetter(idx: number): string {
 /** snake_case field name → "Sentence case" display label. System fields (_x) are returned as-is. */
 export function fieldToDisplay(field: string): string {
   if (field.startsWith('_')) return field
-  const words = field.split('_')
+  const words = field.split('_').map((w) => w.toLowerCase())
   words[0] = words[0].charAt(0).toUpperCase() + words[0].slice(1)
   return words.join(' ')
 }
@@ -763,10 +763,12 @@ export function buildExampleSections(
     for (let i = 5; i >= 0; i--) {
       // EDATE shifts the first-of-month by N months; negative = past
       const monthLabel = `=TEXT(EDATE(DATE(YEAR(TODAY()),MONTH(TODAY()),1),${-i}),"YYYY-MM")`
-      // Unix timestamp boundaries for each month
-      const startUnix = `(EDATE(DATE(YEAR(TODAY()),MONTH(TODAY()),1),${-i})-DATE(1970,1,1))*86400`
-      const endUnix = `(EDATE(DATE(YEAR(TODAY()),MONTH(TODAY()),1),${-(i - 1)})-DATE(1970,1,1))*86400`
-      rows.push([monthLabel, `=COUNTIFS(${createdRange},">="&${startUnix},${createdRange},"<"&${endUnix})`])
+      // COUNTIFS >=/<  only works on numbers/dates, not text strings.
+      // DATEVALUE(LEFT(cell,10)) parses the "yyyy-mm-dd" prefix of the ISO string into a Sheets date serial.
+      const start = `EDATE(DATE(YEAR(TODAY()),MONTH(TODAY()),1),${-i})`
+      const end = `EDATE(DATE(YEAR(TODAY()),MONTH(TODAY()),1),${-(i - 1)})`
+      const parsed = `IFERROR(DATEVALUE(LEFT(${createdRange},10)),0)`
+      rows.push([monthLabel, `=SUMPRODUCT((${parsed}>=${start})*(${parsed}<${end}))`])
     }
     sections.push({
       title: 'New Customers by Month',