#!/usr/bin/env python3
"""Assemble the context packet for a-review.

Reads CLAUDE.md, latest session notes, expanded diff, and diff stat
from the current git repository. Outputs a structured context document
to stdout for piping to the reviewer model.

Usage:
    python scripts/assemble_context.py              # diff against HEAD~1
    python scripts/assemble_context.py --staged     # diff of staged changes
    python scripts/assemble_context.py --context 15 # 15 lines of context
"""

from __future__ import annotations

import argparse
import subprocess
import sys
from pathlib import Path


def _run(cmd: list[str], cwd: Path | None = None) -> str:
    """Run a command and return stdout, or empty string on failure."""
    try:
        result = subprocess.run(
            cmd,
            capture_output=True,
            text=True,
            cwd=cwd,
            check=False,
        )
        return result.stdout.strip()
    except FileNotFoundError:
        return ""


def _find_project_root() -> Path:
    """Find the git repository root."""
    root = _run(["git", "rev-parse", "--show-toplevel"])
    if root:
        return Path(root)
    return Path.cwd()


def _read_file_if_exists(path: Path) -> str:
    """Read a file if it exists, return empty string otherwise."""
    if path.exists():
        return path.read_text()
    return ""


def _find_latest_session_entry(project_root: Path) -> str:
    """Find and return the latest session notes entry."""
    sessions_dir = project_root / "sessions"
    if not sessions_dir.exists():
        return ""

    # Find session note files
    session_files = sorted(sessions_dir.glob("*.md"), key=lambda f: f.stat().st_mtime, reverse=True)
    if not session_files:
        return ""

    content = session_files[0].read_text()

    # Extract the last ## Session entry
    sections = content.split("\n## Session")
    if len(sections) < 2:
        return content  # Return full file if no session headers

    last_section = "## Session" + sections[-1]
    return last_section.strip()


def assemble(staged: bool = False, context_lines: int = 10) -> str:
    """Assemble the full context packet."""
    root = _find_project_root()
    parts: list[str] = []

    # Header
    project_name = root.name
    parts.append(f"# Code Review Context: {project_name}")
    parts.append("")

    # CLAUDE.md
    claude_md = _read_file_if_exists(root / "CLAUDE.md")
    if claude_md:
        parts.append("## Project Documentation (CLAUDE.md)")
        parts.append("")
        parts.append(claude_md)
        parts.append("")
    else:
        parts.append("## Project Documentation")
        parts.append("No CLAUDE.md found in project root.")
        parts.append("")

    # Session notes
    session = _find_latest_session_entry(root)
    if session:
        parts.append("## Latest Session Notes")
        parts.append("")
        parts.append(session)
        parts.append("")
    else:
        parts.append("## Session Notes")
        parts.append("No session notes found.")
        parts.append("")

    # Diff stat
    diff_ref = ["--cached"] if staged else ["HEAD~1"]
    stat = _run(["git", "diff", "--stat", *diff_ref], cwd=root)
    if stat:
        parts.append("## Diff Summary")
        parts.append("```")
        parts.append(stat)
        parts.append("```")
        parts.append("")

    # Expanded diff (with surrounding context)
    expanded = _run(
        ["git", "diff", f"-U{context_lines}", *diff_ref],
        cwd=root,
    )
    if expanded:
        parts.append(f"## Expanded Diff ({context_lines} lines context)")
        parts.append("```diff")
        parts.append(expanded)
        parts.append("```")
        parts.append("")

    # Standard diff
    diff = _run(["git", "diff", *diff_ref], cwd=root)
    if diff:
        parts.append("## Diff")
        parts.append("```diff")
        parts.append(diff)
        parts.append("```")
    elif not expanded:
        parts.append("## Diff")
        parts.append("No changes found.")

    return "\n".join(parts)


def main() -> None:
    parser = argparse.ArgumentParser(description="Assemble a-review context packet")
    parser.add_argument("--staged", action="store_true", help="Review staged changes instead of HEAD~1")
    parser.add_argument("--context", type=int, default=10, help="Lines of surrounding context (default: 10)")
    args = parser.parse_args()

    output = assemble(staged=args.staged, context_lines=args.context)
    sys.stdout.write(output)


if __name__ == "__main__":
    main()