Build Flask WAF log converter app

app/services/exporter.py

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+import csv
+import io
+from dataclasses import dataclass
+
+from app.constants import VENDOR_FIELDS
+
+
+@dataclass(slots=True)
+class ExportResult:
+    content: str
+    columns: list[str]
+    output_format: str
+
+    def preview(self, record_limit: int) -> str:
+        """Build a small preview string for the result page."""
+        if self.output_format == "text":
+            marker = f"--- record {record_limit + 1} ---"
+            if marker in self.content:
+                return self.content.split(marker, 1)[0].rstrip()
+            return self.content
+
+        lines = self.content.splitlines()
+        if len(lines) <= record_limit + 1:
+            return self.content
+        return "\n".join(lines[: record_limit + 1])
+
+
+def build_export(
+    records: list[dict[str, str]],
+    union_keys: list[str],
+    mode: str,
+    output_format: str,
+) -> ExportResult:
+    columns = VENDOR_FIELDS if mode == "vendor" else union_keys
+
+    if output_format == "text":
+        return ExportResult(
+            content=_render_text(records, columns),
+            columns=columns,
+            output_format=output_format,
+        )
+
+    return ExportResult(
+        content=_render_csv(records, columns),
+        columns=columns,
+        output_format=output_format,
+    )
+
+
+def _render_text(records: list[dict[str, str]], columns: list[str]) -> str:
+    max_key_length = max((len(column) for column in columns), default=0)
+    chunks: list[str] = []
+
+    for index, record in enumerate(records, start=1):
+        chunks.append(f"--- record {index} ---")
+        for column in columns:
+            value = record.get(column, "")
+            chunks.append(f"  {column.ljust(max_key_length)} = {value}")
+
+    return "\n".join(chunks)
+
+
+def _render_csv(records: list[dict[str, str]], columns: list[str]) -> str:
+    buffer = io.StringIO()
+    writer = csv.DictWriter(buffer, fieldnames=columns, extrasaction="ignore")
+    writer.writeheader()
+    for record in records:
+        writer.writerow({column: record.get(column, "") for column in columns})
+    return buffer.getvalue()