"""
Hermes Web UI -- Filesystem checkpoint (rollback) API.

Provides endpoints to list, diff, and restore filesystem checkpoints
created by the Hermes agent's CheckpointManager.  Checkpoints live at
``{hermes_home}/checkpoints/<hash>/`` as shadow git repositories.
"""

import hashlib
import json
import logging
import os
import shutil
import subprocess
from datetime import datetime, timezone
from pathlib import Path
from typing import Any

logger = logging.getLogger(__name__)


def _hermes_home() -> Path:
    """Return the active Hermes home directory."""
    try:
        from api.profiles import get_active_hermes_home
        return Path(get_active_hermes_home())
    except Exception:
        return Path(os.environ.get("HERMES_HOME", "~/.hermes")).expanduser()


def _workspace_hash(workspace: str) -> str:
    """Derive the checkpoint directory name from a workspace path.

    Matches the agent's CheckpointManager._get_checkpoint_dir logic:
    SHA-256 of the canonical workspace path.
    """
    try:
        canonical = os.path.realpath(workspace)
    except (OSError, ValueError):
        canonical = workspace
    return hashlib.sha256(canonical.encode()).hexdigest()[:12]


def _checkpoint_root() -> Path:
    return _hermes_home() / "checkpoints"


def _resolve_workspace(workspace: str) -> str:
    """Validate and return the canonical workspace path.

    Security: workspace must match a known configured workspace
    (from workspaces.json or session-attached workspaces).
    """
    if not workspace or not isinstance(workspace, str):
        raise ValueError("workspace is required")
    # Basic path validation
    resolved = os.path.realpath(workspace)
    if not os.path.isdir(resolved):
        raise ValueError(f"Workspace does not exist: {workspace}")
    # Security: confirm workspace is in the known list
    try:
        from api.workspace import load_workspaces
        known_paths = set()
        for ws in load_workspaces():
            p = ws.get("path", "")
            if p:
                known_paths.add(os.path.realpath(p))
        if resolved not in known_paths:
            raise ValueError(f"Workspace not in configured list: {workspace}")
    except ImportError:
        logger.warning("Could not load workspace list for rollback validation")
    return resolved


def _find_git() -> str:
    """Return the path to the git binary."""
    return shutil.which("git") or "git"


# ── Public API functions (called from routes.py) ────────────────────────────


def list_checkpoints(workspace: str) -> dict[str, Any]:
    """List all checkpoints for a workspace.

    Returns a dict with:
        checkpoints: list of checkpoint objects
        workspace: resolved workspace path
        checkpoint_dir: the checkpoint directory path
    """
    resolved = _resolve_workspace(workspace)
    ws_hash = _workspace_hash(resolved)
    ckpt_dir = _checkpoint_root() / ws_hash

    checkpoints = []
    if not ckpt_dir.is_dir():
        return {"checkpoints": [], "workspace": resolved, "checkpoint_dir": str(ckpt_dir)}

    # Each checkpoint is a git repo in <ckpt_dir>/<commit_hash>/
    git = _find_git()
    for entry in sorted(ckpt_dir.iterdir(), key=lambda p: p.stat().st_mtime if p.is_dir() else 0, reverse=True):
        if not entry.is_dir():
            continue
        ckpt_info = _inspect_checkpoint(entry, git)
        if ckpt_info:
            checkpoints.append(ckpt_info)

    return {
        "checkpoints": checkpoints,
        "workspace": resolved,
        "checkpoint_dir": str(ckpt_dir),
    }


def _inspect_checkpoint(ckpt_path: Path, git: str) -> dict[str, Any] | None:
    """Extract metadata from a single checkpoint directory."""
    git_dir = ckpt_path / ".git"
    if not git_dir.is_dir():
        return None

    name = ckpt_path.name
    try:
        result = subprocess.run(
            [git, "-C", str(ckpt_path), "log", "--format=%H%n%s%n%aI", "-1"],
            capture_output=True, text=True, timeout=5,
        )
        if result.returncode != 0 or not result.stdout.strip():
            return None

        lines = result.stdout.strip().split("\n")
        commit_hash = lines[0] if len(lines) > 0 else name
        message = lines[1] if len(lines) > 1 else "checkpoint"
        date_str = lines[2] if len(lines) > 2 else ""

        # Parse date for display
        date_display = ""
        if date_str:
            try:
                dt = datetime.fromisoformat(date_str)
                date_display = dt.strftime("%Y-%m-%d %H:%M")
            except (ValueError, TypeError):
                date_display = date_str

        # Count files
        files_result = subprocess.run(
            [git, "-C", str(ckpt_path), "ls-files"],
            capture_output=True, text=True, timeout=5,
        )
        file_count = len(files_result.stdout.strip().split("\n")) if files_result.stdout.strip() else 0

        return {
            "id": name,
            "commit": commit_hash[:12],
            "message": message,
            "date": date_str,
            "date_display": date_display,
            "files": file_count,
            "path": str(ckpt_path),
        }
    except (subprocess.TimeoutExpired, OSError, Exception) as e:
        logger.debug("Failed to inspect checkpoint %s: %s", ckpt_path, e)
        return None


def get_checkpoint_diff(workspace: str, checkpoint: str) -> dict[str, Any]:
    """Show the diff between a checkpoint and the current workspace state.

    Returns a dict with:
        diff: unified diff text
        files_changed: list of changed file paths
    """
    resolved = _resolve_workspace(workspace)
    ws_hash = _workspace_hash(resolved)
    ckpt_dir = _checkpoint_root() / ws_hash / checkpoint

    if not ckpt_dir.is_dir():
        raise ValueError(f"Checkpoint not found: {checkpoint}")

    git = _find_git()

    # Get list of files in the checkpoint
    ls_result = subprocess.run(
        [git, "-C", str(ckpt_dir), "ls-files"],
        capture_output=True, text=True, timeout=10,
    )
    if ls_result.returncode != 0:
        raise ValueError("Failed to list checkpoint files")

    ckpt_files = [f for f in ls_result.stdout.strip().split("\n") if f]
    files_changed = []
    diff_lines = []

    for rel_path in ckpt_files:
        ckpt_file = ckpt_dir / rel_path
        ws_file = Path(resolved) / rel_path

        if not ckpt_file.is_file():
            continue

        # Read checkpoint version
        try:
            ckpt_content = ckpt_file.read_text(errors="replace")
        except OSError:
            continue

        # Read workspace version (if exists)
        if ws_file.is_file():
            try:
                ws_content = ws_file.read_text(errors="replace")
            except OSError:
                ws_content = ""
        else:
            ws_content = None  # File was deleted in workspace

        if ws_content is None:
            # File exists in checkpoint but not in workspace (deleted)
            files_changed.append({"file": rel_path, "status": "deleted"})
            diff_lines.append(f"--- a/{rel_path}")
            diff_lines.append(f"+++ /dev/null")
            diff_lines.append("@@ -1,{lines} +0,0 @@".format(lines=len(ckpt_content.splitlines())))
            for line in ckpt_content.splitlines():
                diff_lines.append(f"-{line}")
        elif ckpt_content != ws_content:
            # File changed
            import difflib
            ckpt_lines = ckpt_content.splitlines(keepends=True)
            ws_lines = ws_content.splitlines(keepends=True)
            diff = list(difflib.unified_diff(ckpt_lines, ws_lines, fromfile=f"a/{rel_path}", tofile=f"b/{rel_path}", lineterm=""))
            if diff:
                files_changed.append({"file": rel_path, "status": "modified"})
                diff_lines.extend(diff)

    # Check for new files in workspace that aren't in checkpoint
    # (skip for performance — diff is primarily for seeing what the checkpoint captures)

    return {
        "checkpoint": checkpoint,
        "workspace": resolved,
        "diff": "\n".join(diff_lines) if diff_lines else "",
        "files_changed": files_changed,
        "total_changes": len(files_changed),
    }


def restore_checkpoint(workspace: str, checkpoint: str) -> dict[str, Any]:
    """Restore a checkpoint by copying files back to the workspace.

    Only restores files that exist in the checkpoint.  Does NOT delete
    files that were added after the checkpoint was created.

    Returns a dict with:
        ok: True
        files_restored: list of restored file paths
    """
    resolved = _resolve_workspace(workspace)
    ws_hash = _workspace_hash(resolved)
    ckpt_dir = _checkpoint_root() / ws_hash / checkpoint

    if not ckpt_dir.is_dir():
        raise ValueError(f"Checkpoint not found: {checkpoint}")

    git = _find_git()

    # Get list of files in the checkpoint
    ls_result = subprocess.run(
        [git, "-C", str(ckpt_dir), "ls-files"],
        capture_output=True, text=True, timeout=10,
    )
    if ls_result.returncode != 0:
        raise ValueError("Failed to list checkpoint files")

    ckpt_files = [f for f in ls_result.stdout.strip().split("\n") if f]
    restored = []
    errors = []

    for rel_path in ckpt_files:
        ckpt_file = ckpt_dir / rel_path
        ws_file = Path(resolved) / rel_path

        if not ckpt_file.is_file():
            continue

        try:
            ws_file.parent.mkdir(parents=True, exist_ok=True)
            shutil.copy2(str(ckpt_file), str(ws_file))
            restored.append(rel_path)
        except OSError as e:
            errors.append({"file": rel_path, "error": str(e)})
            logger.warning("Failed to restore %s: %s", rel_path, e)

    return {
        "ok": True,
        "checkpoint": checkpoint,
        "workspace": resolved,
        "files_restored": restored,
        "files_restored_count": len(restored),
        "errors": errors,
    }