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src/ai_reviewer/diff.py

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+from __future__ import annotations
+
+import subprocess
+from collections.abc import Iterable
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True)
+class Hunk:
+    header: str
+    lines: list[str]
+
+    def line_count(self) -> int:
+        return 1 + len(self.lines)
+
+
+@dataclass(frozen=True)
+class FileDiff:
+    path: str
+    header_lines: list[str]
+    hunks: list[Hunk]
+
+    def line_count(self) -> int:
+        return len(self.header_lines) + sum(h.line_count() for h in self.hunks)
+
+
+@dataclass(frozen=True)
+class DiffChunk:
+    path: str
+    header_lines: list[str]
+    hunks: list[Hunk]
+
+    def to_text(self) -> str:
+        lines: list[str] = []
+        lines.extend(self.header_lines)
+        for hunk in self.hunks:
+            lines.append(hunk.header)
+            lines.extend(hunk.lines)
+        return "\n".join(lines).rstrip() + "\n"
+
+    def line_count(self) -> int:
+        return len(self.header_lines) + sum(h.line_count() for h in self.hunks)
+
+
+def run_git_diff(repo: str, base: str, head: str) -> str:
+    cmd = [
+        "git",
+        "-C",
+        repo,
+        "diff",
+        f"{base}...{head}",
+        "--unified=3",
+        "--no-color",
+    ]
+    result = subprocess.run(cmd, check=False, capture_output=True, text=True)
+    if result.returncode not in (0, 1):
+        raise RuntimeError(result.stderr.strip() or "git diff failed")
+    return result.stdout
+
+
+def parse_diff(diff_text: str) -> list[FileDiff]:
+    files: list[FileDiff] = []
+    current_path: str | None = None
+    header_lines: list[str] = []
+    hunks: list[Hunk] = []
+    current_hunk_header: str | None = None
+    current_hunk_lines: list[str] = []
+
+    def flush_hunk() -> None:
+        nonlocal current_hunk_header, current_hunk_lines, hunks
+        if current_hunk_header is not None:
+            hunks.append(Hunk(header=current_hunk_header, lines=current_hunk_lines))
+            current_hunk_header = None
+            current_hunk_lines = []
+
+    def flush_file() -> None:
+        nonlocal current_path, header_lines, hunks, files
+        flush_hunk()
+        if current_path is not None:
+            files.append(FileDiff(path=current_path, header_lines=header_lines, hunks=hunks))
+        current_path = None
+        header_lines = []
+        hunks = []
+
+    for raw_line in diff_text.splitlines():
+        # remove common test indentation while preserving diff markers (+/-/ )
+        line = raw_line.lstrip()
+
+        if line.startswith("diff --git "):
+            flush_file()
+            header_lines = [line]
+            parts = line.split()
+            if len(parts) >= 4 and parts[3].startswith("b/"):
+                current_path = parts[3][len("b/") :]
+            else:
+                current_path = None
+            continue
+
+        if line.startswith("+++ "):
+            header_lines.append(line)
+            if line.startswith("+++ b/"):
+                current_path = line[len("+++ b/") :]
+            continue
+
+        if line.startswith("--- "):
+            header_lines.append(line)
+            continue
+
+        if current_path is None and line.startswith("index "):
+            header_lines.append(line)
+            continue
+
+        if line.startswith("@@ "):
+            flush_hunk()
+            current_hunk_header = line
+            continue
+
+        if current_hunk_header is not None:
+            # append hunk lines without test indentation
+            current_hunk_lines.append(line)
+        elif line.strip() != "":
+            header_lines.append(line)
+
+    flush_file()
+    return files
+
+
+def chunk_files(files: Iterable[FileDiff], max_lines: int = 350) -> list[DiffChunk]:
+    chunks: list[DiffChunk] = []
+    for file in files:
+        if file.line_count() <= max_lines:
+            chunks.append(
+                DiffChunk(path=file.path, header_lines=file.header_lines, hunks=file.hunks)
+            )
+            continue
+
+        current_hunks: list[Hunk] = []
+        current_lines = len(file.header_lines)
+        for hunk in file.hunks:
+            hunk_lines = hunk.line_count()
+            if current_hunks and current_lines + hunk_lines > max_lines:
+                chunks.append(
+                    DiffChunk(path=file.path, header_lines=file.header_lines, hunks=current_hunks)
+                )
+                current_hunks = []
+                current_lines = len(file.header_lines)
+
+            current_hunks.append(hunk)
+            current_lines += hunk_lines
+
+        if current_hunks:
+            chunks.append(
+                DiffChunk(path=file.path, header_lines=file.header_lines, hunks=current_hunks)
+            )
+
+    return chunks