migration: preserve frontend shell pages and styles

app/tests/preservation_helpers.py

@@ -0,0 +1,75 @@
+from __future__ import annotations
+
+import hashlib
+import re
+from pathlib import Path
+
+
+APP_ROOT = Path(__file__).resolve().parents[1]
+ORIGINAL_ROOT = APP_ROOT.parent
+FRONTEND_ROOT = APP_ROOT / "frontend"
+ORIGINAL_STATIC = ORIGINAL_ROOT / "static"
+
+SOURCE_RANGE = re.compile(
+    r"/\* PRESERVATION-SOURCE-BEGIN app\.js:(\d+)-(\d+) \*/\n"
+    r"(.*?)"
+    r"/\* PRESERVATION-SOURCE-END app\.js:\1-\2 \*/\n?",
+    re.DOTALL,
+)
+
+
+def sha256(path: Path) -> str:
+    return hashlib.sha256(path.read_bytes()).hexdigest()
+
+
+def reassembled_frontend_runtime() -> str:
+    chunks: dict[tuple[int, int], str] = {}
+    for path in FRONTEND_ROOT.rglob("*.js"):
+        for match in SOURCE_RANGE.finditer(path.read_text(encoding="utf-8")):
+            source_range = (int(match.group(1)), int(match.group(2)))
+            if source_range in chunks:
+                raise AssertionError(f"duplicate app.js source range: {source_range}")
+            chunks[source_range] = match.group(3)
+
+    assembled: list[str] = []
+    next_line = 1
+    for (start, end), content in sorted(chunks.items()):
+        if start != next_line:
+            raise AssertionError(
+                f"app.js source coverage gap: expected line {next_line}, got {start}"
+            )
+        if len(content.splitlines(keepends=True)) != end - start + 1:
+            raise AssertionError(f"app.js line count changed in range {start}-{end}")
+        assembled.append(content)
+        next_line = end + 1
+
+    original_line_count = len(
+        (ORIGINAL_STATIC / "app.js").read_text(encoding="utf-8").splitlines()
+    )
+    if next_line != original_line_count + 1:
+        raise AssertionError(
+            f"app.js source coverage ended at {next_line - 1}, expected {original_line_count}"
+        )
+    return "".join(assembled)
+
+
+def assert_moved_asset_matches(
+    testcase,
+    original_relative: str,
+    frontend_relative: str | None = None,
+) -> None:
+    target_relative = frontend_relative or original_relative
+    testcase.assertEqual(
+        sha256(FRONTEND_ROOT / target_relative),
+        sha256(ORIGINAL_STATIC / original_relative),
+        original_relative,
+    )
+
+
+def assert_page_prefix_matches(testcase, page_relative: str) -> None:
+    original = (ORIGINAL_STATIC / page_relative).read_text(encoding="utf-8")
+    migrated = (FRONTEND_ROOT / page_relative).read_text(encoding="utf-8")
+    testcase.assertTrue(
+        migrated.startswith(original.rstrip("\n") + "\n\n"),
+        page_relative,
+    )