feat: add Excel export functionality with support for metadata and customizable sheets

services/export_serializers.py

@@ -1,13 +1,14 @@
 from __future__ import annotations
 
 import csv
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 from datetime import date, datetime, timezone
 from decimal import Decimal, InvalidOperation, ROUND_HALF_UP
 from enum import Enum
-from io import StringIO
-from typing import Any, Callable, Iterable, Iterator, Sequence
+from io import BytesIO, StringIO
+from typing import Any, Callable, Iterable, Iterator, Mapping, Sequence
 
+from openpyxl import Workbook
 CSVValueFormatter = Callable[[Any], str]
 Accessor = Callable[[Any], Any]
 
@@ -18,6 +19,9 @@ __all__ = [
     "default_scenario_columns",
     "stream_projects_to_csv",
     "stream_scenarios_to_csv",
+    "ExcelExporter",
+    "export_projects_to_excel",
+    "export_scenarios_to_excel",
     "default_formatter",
     "format_datetime_utc",
     "format_date_iso",
@@ -34,13 +38,13 @@ class CSVExportColumn:
     formatter: CSVValueFormatter | None = None
     required: bool = False
 
-    def resolve_accessor(self) -> Accessor:
-        if isinstance(self.accessor, str):
-            return _coerce_accessor(self.accessor)
-        return self.accessor
+    _accessor: Accessor = field(init=False, repr=False)
+
+    def __post_init__(self) -> None:
+        object.__setattr__(self, "_accessor", _coerce_accessor(self.accessor))
 
     def value_for(self, entity: Any) -> Any:
-        accessor = self.resolve_accessor()
+        accessor = object.__getattribute__(self, "_accessor")
         try:
             return accessor(entity)
         except Exception:  # pragma: no cover - defensive safeguard
@@ -85,8 +89,7 @@ class CSVExporter:
     def _format_row(self, record: Any) -> list[str]:
         formatted: list[str] = []
         for column in self._columns:
-            accessor = column.resolve_accessor()
-            raw_value = accessor(record)
+            raw_value = column.value_for(record)
             formatter = column.formatter or default_formatter
             formatted.append(formatter(raw_value))
         return formatted
@@ -216,6 +219,114 @@ def format_decimal(value: Any) -> str:
     return default_formatter(value)
 
 
+class ExcelExporter:
+    """Produce Excel workbooks via write-only streaming."""
+
+    def __init__(
+        self,
+        columns: Sequence[CSVExportColumn],
+        *,
+        sheet_name: str = "Export",
+        workbook_title: str | None = None,
+        include_header: bool = True,
+        metadata: Mapping[str, Any] | None = None,
+        metadata_sheet_name: str = "Metadata",
+    ) -> None:
+        if not columns:
+            raise ValueError(
+                "At least one column is required for Excel export.")
+        self._columns: tuple[CSVExportColumn, ...] = tuple(columns)
+        self._sheet_name = sheet_name or "Export"
+        self._include_header = include_header
+        self._metadata = dict(metadata) if metadata else None
+        self._metadata_sheet_name = metadata_sheet_name or "Metadata"
+        self._workbook = Workbook(write_only=True)
+        if workbook_title:
+            self._workbook.properties.title = workbook_title
+
+    def export(self, records: Iterable[Any]) -> bytes:
+        sheet = self._workbook.create_sheet(title=self._sheet_name)
+        if self._include_header:
+            sheet.append([column.header for column in self._columns])
+
+        for record in records:
+            sheet.append(self._format_row(record))
+
+        self._append_metadata_sheet()
+        return self._finalize()
+
+    def _format_row(self, record: Any) -> list[Any]:
+        row: list[Any] = []
+        for column in self._columns:
+            raw_value = column.value_for(record)
+            formatter = column.formatter or default_formatter
+            row.append(formatter(raw_value))
+        return row
+
+    def _append_metadata_sheet(self) -> None:
+        if not self._metadata:
+            return
+
+        sheet_name = self._metadata_sheet_name
+        existing = set(self._workbook.sheetnames)
+        if sheet_name in existing:
+            index = 1
+            while True:
+                candidate = f"{sheet_name}_{index}"
+                if candidate not in existing:
+                    sheet_name = candidate
+                    break
+                index += 1
+
+        meta_ws = self._workbook.create_sheet(title=sheet_name)
+        meta_ws.append(["Key", "Value"])
+        for key, value in self._metadata.items():
+            meta_ws.append([
+                str(key),
+                "" if value is None else str(value),
+            ])
+
+    def _finalize(self) -> bytes:
+        buffer = BytesIO()
+        self._workbook.save(buffer)
+        buffer.seek(0)
+        return buffer.getvalue()
+
+
+def export_projects_to_excel(
+    projects: Iterable[Any],
+    *,
+    columns: Sequence[CSVExportColumn] | None = None,
+    sheet_name: str = "Projects",
+    workbook_title: str | None = None,
+    metadata: Mapping[str, Any] | None = None,
+) -> bytes:
+    exporter = ExcelExporter(
+        columns or default_project_columns(),
+        sheet_name=sheet_name,
+        workbook_title=workbook_title,
+        metadata=metadata,
+    )
+    return exporter.export(projects)
+
+
+def export_scenarios_to_excel(
+    scenarios: Iterable[Any],
+    *,
+    columns: Sequence[CSVExportColumn] | None = None,
+    sheet_name: str = "Scenarios",
+    workbook_title: str | None = None,
+    metadata: Mapping[str, Any] | None = None,
+) -> bytes:
+    exporter = ExcelExporter(
+        columns or default_scenario_columns(),
+        sheet_name=sheet_name,
+        workbook_title=workbook_title,
+        metadata=metadata,
+    )
+    return exporter.export(scenarios)
+
+
 def _coerce_accessor(accessor: Accessor | str) -> Accessor:
     if callable(accessor):
         return accessor