feat(oo): sheet-aware spreadsheet export (docs csv/json)

- lib: WorkbookSheetNames/CSV/JSON (excelize) — sheet selection + JSON rows
- oo docs csv  SRC... [--sheet N] [--delimiter ,|;|||tab] [--out]
- oo docs json SRC... [--sheet N] [--out]
- SRC = OO file id or local path; --sheet is 1-based (default first)
- DS csv output is first-sheet-only (verified) -> local reader for selection/JSON
- test: TestWorkbookSheetExport

sheets.go

@@ -0,0 +1,123 @@
+package onlyoffice
+
+// Spreadsheet (XLS/XLSX/ODS) sheet-aware export to CSV / JSON.
+//
+// The OnlyOffice DocumentServer converter can emit CSV, but only for the first
+// worksheet and it ignores any sheet selector (verified against a live DS).
+// So sheet selection and JSON use a local reader (excelize). This is data
+// extraction, not a document-format conversion pipeline.
+
+import (
+	"bytes"
+	"encoding/csv"
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/xuri/excelize/v2"
+)
+
+// WorkbookSheetNames returns worksheet names in workbook order.
+func WorkbookSheetNames(data []byte) ([]string, error) {
+	f, err := excelize.OpenReader(bytes.NewReader(data))
+	if err != nil {
+		return nil, fmt.Errorf("open workbook: %w", err)
+	}
+	defer f.Close()
+	return f.GetSheetList(), nil
+}
+
+// workbookSheet resolves a 0-based sheet index to its name. A negative index
+// selects the first sheet; an out-of-range index is an error.
+func workbookSheet(f *excelize.File, index int) (string, error) {
+	names := f.GetSheetList()
+	if len(names) == 0 {
+		return "", fmt.Errorf("workbook has no sheets")
+	}
+	if index < 0 {
+		index = 0
+	}
+	if index >= len(names) {
+		return "", fmt.Errorf("sheet index %d out of range (0..%d)", index, len(names)-1)
+	}
+	return names[index], nil
+}
+
+// WorkbookSheetCSV renders one worksheet as CSV. sheetIndex is 0-based
+// (negative = first). delimiter 0 keeps the default comma. header, when true,
+// is kept as the first CSV row (it is always kept; the flag only affects JSON).
+func WorkbookSheetCSV(data []byte, sheetIndex int, delimiter rune) (string, error) {
+	f, err := excelize.OpenReader(bytes.NewReader(data))
+	if err != nil {
+		return "", fmt.Errorf("open workbook: %w", err)
+	}
+	defer f.Close()
+	name, err := workbookSheet(f, sheetIndex)
+	if err != nil {
+		return "", err
+	}
+	rows, err := f.GetRows(name)
+	if err != nil {
+		return "", err
+	}
+	var b strings.Builder
+	w := csv.NewWriter(&b)
+	if delimiter != 0 {
+		w.Comma = delimiter
+	}
+	for _, row := range rows {
+		_ = w.Write(row)
+	}
+	w.Flush()
+	return b.String(), w.Error()
+}
+
+// WorkbookSheetJSON renders one worksheet as a list of row objects, using the
+// first row as the field names (blank headers become col1, col2, …). sheetIndex
+// is 0-based (negative = first).
+func WorkbookSheetJSON(data []byte, sheetIndex int) ([]map[string]any, error) {
+	f, err := excelize.OpenReader(bytes.NewReader(data))
+	if err != nil {
+		return nil, fmt.Errorf("open workbook: %w", err)
+	}
+	defer f.Close()
+	name, err := workbookSheet(f, sheetIndex)
+	if err != nil {
+		return nil, err
+	}
+	rows, err := f.GetRows(name)
+	if err != nil {
+		return nil, err
+	}
+	if len(rows) == 0 {
+		return nil, nil
+	}
+	header := rows[0]
+	out := make([]map[string]any, 0, len(rows)-1)
+	for _, row := range rows[1:] {
+		m := make(map[string]any, len(header))
+		for i, h := range header {
+			key := strings.TrimSpace(h)
+			if key == "" {
+				key = fmt.Sprintf("col%d", i+1)
+			}
+			if i < len(row) {
+				m[key] = row[i]
+			} else {
+				m[key] = ""
+			}
+		}
+		out = append(out, m)
+	}
+	return out, nil
+}
+
+// WorkbookSheetCSVTo is WorkbookSheetCSV writing into w.
+func WorkbookSheetCSVTo(data []byte, sheetIndex int, delimiter rune, w io.Writer) error {
+	s, err := WorkbookSheetCSV(data, sheetIndex, delimiter)
+	if err != nil {
+		return err
+	}
+	_, err = io.WriteString(w, s)
+	return err
+}