Implement 3-way merge on concurrent saves using git merge-file

edit/server.py

@@ -6,7 +6,9 @@ import asyncio
 import os
 import re
 import secrets
+import shutil
 import sqlite3
+import tempfile
 import time
 from contextlib import contextmanager
 from dataclasses import dataclass
@@ -74,6 +76,42 @@ async def _git_file_hash(file_path: Path) -> str:
         return ""
 
 
+async def _three_way_merge(
+    file_path: Path, user_content: str, base_hash: str, handle: str
+) -> tuple[str, bool]:
+    """Returns (merged_content, has_conflict). Falls back to user_content on error."""
+    rel = str(file_path.relative_to(_ROOT))
+    env = _git_env()
+    proc = await asyncio.create_subprocess_exec(
+        "git", "show", f"{base_hash}:{rel}",
+        cwd=str(_ROOT), env=env,
+        stdout=asyncio.subprocess.PIPE, stderr=asyncio.subprocess.DEVNULL,
+    )
+    stdout, _ = await proc.communicate()
+    if proc.returncode != 0:
+        return user_content, False
+    base_content    = stdout.decode()
+    current_content = file_path.read_text(encoding="utf-8")
+    tmpdir = tempfile.mkdtemp()
+    try:
+        p_current = Path(tmpdir) / "current.md"
+        p_base    = Path(tmpdir) / "base.md"
+        p_user    = Path(tmpdir) / "user.md"
+        p_current.write_text(current_content, encoding="utf-8")
+        p_base.write_text(base_content,       encoding="utf-8")
+        p_user.write_text(user_content,       encoding="utf-8")
+        proc = await asyncio.create_subprocess_exec(
+            "git", "merge-file",
+            "-L", "attuale", "-L", "base", "-L", handle,
+            str(p_current), str(p_base), str(p_user),
+            stdout=asyncio.subprocess.DEVNULL, stderr=asyncio.subprocess.DEVNULL,
+        )
+        await proc.wait()
+        return p_current.read_text(encoding="utf-8"), proc.returncode > 0
+    finally:
+        shutil.rmtree(tmpdir, ignore_errors=True)
+
+
 async def _git_commit(file_path: Path, handle: str, verb: str) -> None:
     rel = str(file_path.relative_to(_ROOT))
     env = _git_env()
@@ -319,13 +357,22 @@ async def get_page(slug: str, user: User = Depends(require_auth)) -> JSONRespons
 @app.post("/pages/{slug:path}")
 async def save_page(slug: str, body: PageBody, user: User = Depends(require_auth)) -> JSONResponse:
     path = _slug_to_path(slug, pages_dir)
-    if body.base_hash is not None:
-        current = await _git_file_hash(path)
-        if current and current != body.base_hash:
-            raise HTTPException(409, "Pagina modificata da qualcun altro — ricarica prima di salvare")
-    result = _save(slug, body, pages_dir)
+    content = body.content
+    if body.base_hash and path.exists():
+        current_hash = await _git_file_hash(path)
+        if current_hash and current_hash != body.base_hash:
+            merged, conflict = await _three_way_merge(path, body.content, body.base_hash, user.handle)
+            if conflict:
+                raise HTTPException(409, detail={
+                    "message": "Conflitto — risolvi i marcatori e salva di nuovo",
+                    "content": merged,
+                    "base_hash": current_hash,
+                })
+            content = merged
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_text(content, encoding="utf-8")
     await _git_commit(path, user.handle, "edited")
-    return result
+    return JSONResponse({"slug": str(path.relative_to(pages_dir).with_suffix("")), "saved": True})
 
 @app.delete("/pages/{slug:path}")
 async def delete_page(slug: str, user: User = Depends(require_auth)) -> JSONResponse:
@@ -348,13 +395,22 @@ async def get_story(slug: str, user: User = Depends(require_auth)) -> JSONRespon
 @app.post("/stories/{slug:path}")
 async def save_story(slug: str, body: PageBody, user: User = Depends(require_auth)) -> JSONResponse:
     path = _slug_to_path(slug, stories_dir)
-    if body.base_hash is not None:
-        current = await _git_file_hash(path)
-        if current and current != body.base_hash:
-            raise HTTPException(409, "Pagina modificata da qualcun altro — ricarica prima di salvare")
-    result = _save(slug, body, stories_dir)
+    content = body.content
+    if body.base_hash and path.exists():
+        current_hash = await _git_file_hash(path)
+        if current_hash and current_hash != body.base_hash:
+            merged, conflict = await _three_way_merge(path, body.content, body.base_hash, user.handle)
+            if conflict:
+                raise HTTPException(409, detail={
+                    "message": "Conflitto — risolvi i marcatori e salva di nuovo",
+                    "content": merged,
+                    "base_hash": current_hash,
+                })
+            content = merged
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_text(content, encoding="utf-8")
     await _git_commit(path, user.handle, "edited")
-    return result
+    return JSONResponse({"slug": str(path.relative_to(stories_dir).with_suffix("")), "saved": True})
 
 @app.delete("/stories/{slug:path}")
 async def delete_story(slug: str, user: User = Depends(require_auth)) -> JSONResponse: