"""Per-app version history, stored the way git stores history: content-addressed.

Each unique file's bytes are written ONCE to a per-app blob store (sha256 name,
zlib-compressed); a version is a tiny manifest mapping path -> blob digest. So a
run that changes one file out of fifty costs one new blob, not fifty, and 500
versions of a barely-changing app stay small. That keeps this feature from
making OpenSwarm feel heavier than it already is. We reuse the .swarm app
serializer (captures flat-inline AND webapp_template workspace apps; skips
node_modules/.venv/dist/.git, excludes .env), but never .swarm's pack() (it
refuses on secret-shaped fields, and a local snapshot must never decline to save
the user's own app). No git binary: it isn't guaranteed on a packaged Mac/Win."""
from __future__ import annotations

import hashlib
import json
import logging
import os
import shutil
import zlib
from datetime import datetime
from uuid import uuid4

from backend.apps.outputs.models import Output, OutputVersion
from backend.apps.outputs.workspace_io import WALK_SKIP_DIRS, save, load_output
from backend.apps.swarm.entities.apps import AppExportable
from backend.config.paths import OUTPUTS_VERSIONS_DIR, OUTPUTS_WORKSPACE_DIR

logger = logging.getLogger(__name__)

P_MAX_FILE_BYTES = 25 * 1024 * 1024  # don't snapshot giant build artifacts


class p_NullExportCtx:
    """serialize() wants an ExportContext but apps have no cross-refs to rewrite."""

    def bundle_id_for(self, etype, local_id):  # noqa: ARG002
        return None


P_NULL_CTX = p_NullExportCtx()


def p_app_dir(output_id: str) -> str:
    return os.path.join(OUTPUTS_VERSIONS_DIR, output_id)


def blobs_dir(output_id: str) -> str:
    return os.path.join(p_app_dir(output_id), "blobs")


def p_manifests_dir(output_id: str) -> str:
    return os.path.join(p_app_dir(output_id), "manifests")


def p_digest(data: bytes) -> str:
    return hashlib.sha256(data).hexdigest()


def p_safe_join(folder: str, rel: str) -> str:
    dest = os.path.realpath(os.path.join(folder, rel))
    root = os.path.realpath(folder)
    if dest != root and not dest.startswith(root + os.sep):
        raise ValueError("version file path escapes the workspace")
    return dest


def p_write_blob(output_id: str, data: bytes, digest: str) -> None:
    """Store bytes once, content-addressed. A blob that already exists is the
    whole point: that's a file unchanged since an earlier version, stored zero
    extra times."""
    path = os.path.join(blobs_dir(output_id), digest)
    if os.path.exists(path):
        return
    os.makedirs(blobs_dir(output_id), exist_ok=True)
    tmp = path + ".tmp"
    with open(tmp, "wb") as f:
        f.write(zlib.compress(data, 6))
    os.replace(tmp, path)


def p_read_blob(output_id: str, digest: str) -> bytes | None:
    try:
        with open(os.path.join(blobs_dir(output_id), digest), "rb") as f:
            return zlib.decompress(f.read())
    except (OSError, zlib.error):
        return None


def read_manifest(output_id: str, version_id: str) -> dict | None:
    try:
        with open(os.path.join(p_manifests_dir(output_id), f"{version_id}.json"), encoding="utf-8") as f:
            return json.load(f)
    except (OSError, json.JSONDecodeError, UnicodeDecodeError):
        return None


def p_latest_manifest(output_id: str) -> dict | None:
    """Newest manifest by write time; only read for the dedupe check so capture
    stays O(1) reads rather than scanning every version's content."""
    folder = p_manifests_dir(output_id)
    if not os.path.isdir(folder):
        return None
    js = [os.path.join(folder, f) for f in os.listdir(folder) if f.endswith(".json")]
    if not js:
        return None
    newest = max(js, key=os.path.getmtime)
    try:
        with open(newest, encoding="utf-8") as f:
            return json.load(f)
    except (OSError, json.JSONDecodeError, UnicodeDecodeError):
        return None


def p_tree_hash(app_meta: dict, file_map: dict[str, str]) -> str:
    """Dedupe key over the snapshot's content: app metadata + path->digest map.
    Cheap because the per-file hashing already happened to name the blobs."""
    h = hashlib.sha256()
    h.update(json.dumps(app_meta, sort_keys=True).encode("utf-8"))
    h.update(b"\0")
    for path in sorted(file_map):
        h.update(path.encode("utf-8"))
        h.update(b"\0")
        h.update(file_map[path].encode("utf-8"))
        h.update(b"\0")
    return h.hexdigest()


def p_snapshot(output: Output) -> tuple[dict, dict[str, bytes]]:
    app = AppExportable(output)
    return app.serialize(P_NULL_CTX), app.files()  # files keyed workspace/<rel>


def list_versions(output_id: str) -> list[OutputVersion]:
    folder = p_manifests_dir(output_id)
    if not os.path.isdir(folder):
        return []
    out: list[OutputVersion] = []
    for fname in os.listdir(folder):
        if not fname.endswith(".json"):
            continue
        m = read_manifest(output_id, fname[:-5])
        if m is None:
            continue
        try:
            out.append(OutputVersion(**m))  # ignores the heavy keys (app_meta, files)
        except Exception:
            logger.warning("skipping unreadable version manifest %s", fname)
    out.sort(key=lambda v: v.created_at, reverse=True)
    return out


def capture(
    output_id: str,
    *,
    source: str = "auto",
    label: str = "",
    thumbnail: str | None = None,
) -> OutputVersion | None:
    """Snapshot current app state. Returns the existing latest version (no new
    manifest) when nothing changed, so unchanged runs don't pile up. None only if
    the app is gone."""
    output = load_output(output_id)
    if output is None:
        return None
    app_meta, files = p_snapshot(output)

    file_map: dict[str, str] = {}
    for path, data in files.items():
        if len(data) > P_MAX_FILE_BYTES:
            continue
        file_map[path] = p_digest(data)
    tree = p_tree_hash(app_meta, file_map)

    latest = p_latest_manifest(output_id)
    parent_id = latest.get("id") if latest else None
    if latest is not None and latest.get("tree_hash") == tree:
        try:
            return OutputVersion(**latest)
        except Exception:
            pass  # corrupt latest: fall through and write a fresh manifest

    for path, data in files.items():
        d = file_map.get(path)
        if d is not None:
            p_write_blob(output_id, data, d)

    vid = uuid4().hex
    manifest = {
        "id": vid,
        "created_at": datetime.now().isoformat(),
        "label": label or "",
        "source": source,
        "parent_id": parent_id,
        "thumbnail": thumbnail if thumbnail is not None else output.thumbnail,
        "tree_hash": tree,
        "app_meta": app_meta,
        "files": file_map,
    }
    os.makedirs(p_manifests_dir(output_id), exist_ok=True)
    dest = os.path.join(p_manifests_dir(output_id), f"{vid}.json")
    tmp = dest + ".tmp"
    with open(tmp, "w", encoding="utf-8") as f:
        json.dump(manifest, f)
    os.replace(tmp, dest)
    return OutputVersion(**manifest)


def p_restore_workspace(output_id: str, workspace_id: str, file_map: dict[str, str]) -> None:
    """Make the workspace match the snapshot. Deletes current authored files not
    in it, then writes the rest FROM BLOBS, skipping any file already byte-correct
    (so a restore writes only the diff). Keeps the live .env and build/cache dirs.
    Per-file writes: a crash mid-restore leaves a mixed tree, but the pre_restore
    backup restore() takes first is the real safety net."""
    folder = os.path.join(OUTPUTS_WORKSPACE_DIR, workspace_id)
    os.makedirs(folder, exist_ok=True)
    targets: dict[str, str] = {
        key[len("workspace/"):]: dig for key, dig in file_map.items() if key.startswith("workspace/")
    }

    for root, dirs, fnames in os.walk(folder):
        dirs[:] = [d for d in dirs if d not in WALK_SKIP_DIRS]
        for fname in fnames:
            if fname == ".env":
                continue
            full = os.path.join(root, fname)
            rel = os.path.relpath(full, folder).replace(os.sep, "/")
            if rel not in targets:
                try:
                    os.remove(full)
                except OSError:
                    pass

    for rel, digest in targets.items():
        dest = p_safe_join(folder, rel)
        if os.path.exists(dest):
            try:
                with open(dest, "rb") as f:
                    if p_digest(f.read()) == digest:
                        continue  # already correct: don't rewrite
            except OSError:
                pass
        data = p_read_blob(output_id, digest)
        if data is None:
            continue
        os.makedirs(os.path.dirname(dest), exist_ok=True)
        with open(dest, "wb") as f:
            f.write(data)


def restore(output_id: str, version_id: str) -> Output | None:
    """Bring the app back to an earlier version, in place. Saves the current
    state as a pre_restore version first so this is always undoable."""
    output = load_output(output_id)
    if output is None:
        return None
    manifest = read_manifest(output_id, version_id)
    if manifest is None:
        return None

    target_label = manifest.get("label") or "an earlier version"
    capture(output_id, source="pre_restore", label=f"Before restoring '{target_label}'")

    app_meta = manifest.get("app_meta") or {}
    output.name = app_meta.get("name", output.name)
    output.description = app_meta.get("description", output.description)
    output.icon = app_meta.get("icon", output.icon)
    # Presence, not truthiness: a snapshot's empty {} schema must restore as empty.
    if app_meta.get("input_schema") is not None:
        output.input_schema = app_meta["input_schema"]
    output.files = app_meta.get("files") or {}
    if manifest.get("thumbnail") is not None:
        output.thumbnail = manifest["thumbnail"]
    now = datetime.now().isoformat()
    output.updated_at = now
    output.preview_updated_at = now

    if output.workspace_id:
        p_restore_workspace(output_id, output.workspace_id, manifest.get("files") or {})
    save(output)
    return output


def branch(output_id: str, version_id: str) -> str | None:
    """Make a brand-new app from an earlier version. Reuses the .swarm importer,
    which mints a fresh output id + workspace id and localizes a fresh .env."""
    manifest = read_manifest(output_id, version_id)
    if manifest is None:
        return None
    app_meta = dict(manifest.get("app_meta") or {})
    app_meta["name"] = f"{app_meta.get('name') or 'App'} (copy)"
    files: dict[str, bytes] = {}
    for path, digest in (manifest.get("files") or {}).items():
        data = p_read_blob(output_id, digest)
        if data is not None:
            files[path] = data
    from backend.apps.swarm.exportable import RemapTable
    try:
        return AppExportable.import_(app_meta, files, RemapTable())
    except Exception:
        # A partial import leaves an orphan workspace dir (small); better than a 500.
        logger.exception("branch import failed for %s/%s", output_id, version_id)
        return None


def delete_all(output_id: str) -> None:
    shutil.rmtree(p_app_dir(output_id), ignore_errors=True)