auto-detect date format (DD/MM vs MM/DD) in CSV imports

src/utils/import.ts

@@ -9,6 +9,23 @@ export interface ImportEntry {
   tags?: string[]
 }
 
+export type DateFormat = 'DMY' | 'MDY'
+export type DateDetectResult = DateFormat | 'ambiguous'
+
+export function detectDateFormat(rows: string[][], dateColIndex: number): DateDetectResult {
+  if (dateColIndex < 0) return 'ambiguous'
+  for (let i = 1; i < rows.length; i++) {
+    const val = (rows[i]?.[dateColIndex] || '').trim()
+    const match = val.match(/^(\d{1,2})[\/.](\d{1,2})[\/.](\d{2,4})$/)
+    if (!match) continue
+    const a = parseInt(match[1])
+    const b = parseInt(match[2])
+    if (a > 12) return 'DMY'
+    if (b > 12) return 'MDY'
+  }
+  return 'ambiguous'
+}
+
 export function parseCSV(text: string): string[][] {
   const lines = text.split('\n').filter(l => l.trim())
   return lines.map(line => {
@@ -44,7 +61,7 @@ export function parseDurationString(dur: string): number {
 }
 
 // Parse locale-variable date strings into YYYY-MM-DD
-function parseFlexDate(dateStr: string): string {
+function parseFlexDate(dateStr: string, formatHint?: DateFormat): string {
   if (!dateStr) return new Date().toISOString().split('T')[0]
   const s = dateStr.trim()
 
@@ -63,7 +80,9 @@ function parseFlexDate(dateStr: string): string {
     if (parseInt(a) > 12) return `${year}-${b.padStart(2, '0')}-${a.padStart(2, '0')}`
     // If second part > 12, must be month-first (MM/DD/YYYY)
     if (parseInt(b) > 12) return `${year}-${a.padStart(2, '0')}-${b.padStart(2, '0')}`
-    // Ambiguous - assume MM/DD/YYYY (US default, most common Clockify setting)
+    // Use format hint if provided
+    if (formatHint === 'DMY') return `${year}-${b.padStart(2, '0')}-${a.padStart(2, '0')}`
+    // Default to MDY
     return `${year}-${a.padStart(2, '0')}-${b.padStart(2, '0')}`
   }
 
@@ -99,13 +118,13 @@ function parseFlexTime(timeStr: string): string {
   return '00:00:00'
 }
 
-function safeDateTime(date: string, time?: string): string {
-  const d = parseFlexDate(date)
+function safeDateTime(date: string, time?: string, dateFormat?: DateFormat): string {
+  const d = parseFlexDate(date, dateFormat)
   const t = time ? parseFlexTime(time) : '00:00:00'
   return `${d}T${t}`
 }
 
-function findCol(header: string[], ...terms: string[]): number {
+export function findCol(header: string[], ...terms: string[]): number {
   for (const term of terms) {
     const idx = header.findIndex(h => h === term)
     if (idx >= 0) return idx
@@ -121,7 +140,7 @@ function col(row: string[], idx: number): string {
   return idx >= 0 ? (row[idx] || '') : ''
 }
 
-export function mapTogglCSV(rows: string[][]): ImportEntry[] {
+export function mapTogglCSV(rows: string[][], dateFormat?: DateFormat): ImportEntry[] {
   const header = rows[0].map(h => h.toLowerCase().trim())
   const descIdx = findCol(header, 'description')
   const projIdx = findCol(header, 'project')
@@ -137,13 +156,13 @@ export function mapTogglCSV(rows: string[][]): ImportEntry[] {
     client_name: col(row, clientIdx) || undefined,
     task_name: col(row, taskIdx) || undefined,
     description: col(row, descIdx) || undefined,
-    start_time: safeDateTime(col(row, startDateIdx), col(row, startTimeIdx) || undefined),
+    start_time: safeDateTime(col(row, startDateIdx), col(row, startTimeIdx) || undefined, dateFormat),
     duration: parseDurationString(col(row, durationIdx)),
     tags: tagIdx >= 0 && row[tagIdx] ? row[tagIdx].split(',').map(t => t.trim()).filter(Boolean) : undefined,
   }))
 }
 
-export function mapClockifyCSV(rows: string[][]): ImportEntry[] {
+export function mapClockifyCSV(rows: string[][], dateFormat?: DateFormat): ImportEntry[] {
   const header = rows[0].map(h => h.toLowerCase().trim())
   const descIdx = findCol(header, 'description')
   const projIdx = findCol(header, 'project')
@@ -172,14 +191,14 @@ export function mapClockifyCSV(rows: string[][]): ImportEntry[] {
       client_name: col(row, clientIdx) || undefined,
       task_name: col(row, taskIdx) || undefined,
       description: col(row, descIdx) || undefined,
-      start_time: safeDateTime(col(row, startDateIdx), col(row, startTimeIdx) || undefined),
+      start_time: safeDateTime(col(row, startDateIdx), col(row, startTimeIdx) || undefined, dateFormat),
       duration,
       tags: tagIdx >= 0 && row[tagIdx] ? row[tagIdx].split(',').map(t => t.trim()).filter(Boolean) : undefined,
     }
   })
 }
 
-export function mapHarvestCSV(rows: string[][]): ImportEntry[] {
+export function mapHarvestCSV(rows: string[][], dateFormat?: DateFormat): ImportEntry[] {
   const header = rows[0].map(h => h.toLowerCase().trim())
   const dateIdx = findCol(header, 'date')
   const projIdx = header.findIndex(h => h === 'project')
@@ -193,7 +212,7 @@ export function mapHarvestCSV(rows: string[][]): ImportEntry[] {
     client_name: col(row, clientIdx) || undefined,
     task_name: col(row, taskIdx) || undefined,
     description: col(row, notesIdx) || undefined,
-    start_time: safeDateTime(col(row, dateIdx)),
+    start_time: safeDateTime(col(row, dateIdx), undefined, dateFormat),
     duration: hoursIdx >= 0 && row[hoursIdx] ? Math.round(parseFloat(row[hoursIdx]) * 3600) : 0,
   }))
 }