from __future__ import annotations

import json
import shutil
from datetime import datetime, timezone
from pathlib import Path


def _safe_path(root: Path, relative: str) -> Path | None:
    target = (root / relative).resolve()
    if not target.is_relative_to(root.resolve()):
        return None
    return target


def bootstrap_media_store(source_root: Path, target_root: Path) -> dict[str, int]:
    """Merge the immutable image baseline into the persistent media volume.

    Existing decisions and files in the volume always win. New baseline assets
    are copied in on release, so a recreated container cannot reset decisions
    while a newer Git baseline can still add assets.
    """
    source_manifest_path = source_root / "manifest.json"
    target_manifest_path = target_root / "manifest.json"
    source = json.loads(source_manifest_path.read_text(encoding="utf-8"))
    target = json.loads(target_manifest_path.read_text(encoding="utf-8")) if target_manifest_path.exists() else {"version": 1, "assets": []}
    target_by_url = {item.get("asset_url"): item for item in target.get("assets", [])}
    added = 0
    copied = 0
    target_root.mkdir(parents=True, exist_ok=True)

    for source_item in source.get("assets", []):
        url = source_item.get("asset_url")
        if not url or url in target_by_url:
            continue
        item = dict(source_item)
        target_by_url[url] = item
        target.setdefault("assets", []).append(item)
        added += 1

    for item in target.get("assets", []):
        for relative in [item.get("local_path"), *[variant.get("local_path") for variant in item.get("derivatives", [])]]:
            if not isinstance(relative, str):
                continue
            source_path = _safe_path(source_root, relative)
            target_path = _safe_path(target_root, relative)
            if not source_path or not target_path or not source_path.is_file() or target_path.exists():
                continue
            target_path.parent.mkdir(parents=True, exist_ok=True)
            shutil.copy2(source_path, target_path)
            copied += 1

    target["version"] = max(int(source.get("version", 1)), int(target.get("version", 1)))
    if added or copied or not target_manifest_path.exists():
        target["updated_at"] = datetime.now(timezone.utc).isoformat()
        temporary = target_manifest_path.with_suffix(".json.tmp")
        temporary.write_text(json.dumps(target, ensure_ascii=False, indent=2) + "\n", encoding="utf-8")
        temporary.replace(target_manifest_path)
    return {"added_assets": added, "copied_files": copied}