"""Talk to the diora server: pull the book list and reading state, push queued positions,
download a book when it is opened.

Reading state follows docs/progress-sync.md (progress.py holds the rules). Books are listed
from the server's list and fetched only when opened (the file is encrypted: decrypted here
with the account's key and stored as a plain .epub in the library folder).
"""

from __future__ import annotations

import json
import os
import re
from dataclasses import dataclass, field
from pathlib import Path

import requests

from . import api, crypto, library, library_meta, progress
from .config import RemoteConfig
from .epub import server_key


class SyncError(Exception):
    pass


@dataclass
class SyncResult:
    books: int = 0
    skipped_pdf: list[str] = field(default_factory=list)
    failed: list[str] = field(default_factory=list)
    pushed: int = 0
    new_titles: list[str] = field(default_factory=list)


def _sanitize_filename(name: str) -> str:
    name = re.sub(r"[^\w\s.-]", "_", name).strip()
    return (name or "buch")[:80]


def local_path(library_dir: Path, server_id: int) -> Path | None:
    return next(library_dir.glob(f"{server_id:04d} - *.epub"), None)


def flush_pending(cfg: RemoteConfig) -> int:
    """Send every queued position. Stops quietly at the first network trouble (the rest stays
    queued); a book the server no longer has drops its queue."""
    store = progress.default()
    pushed = 0
    for key in store.pending_keys():
        st = store.get(key)
        if not (key.startswith("s") and key[1:].isdigit() and st and st.pending):
            continue
        body = dict(st.pending)
        try:
            answer = api.post_progress(
                cfg.server_url, cfg.api_token, int(key[1:]), anchor=body["anchor"], fraction=body["fraction"],
                read_at=body["read_at"], device=progress.DEVICE_NAME, force=bool(body.get("force")),
            )
        except api.ApiError as e:
            if "nicht gefunden" in str(e):
                store.sent(key, body, None)
                continue
            raise SyncError(str(e)) from e
        except requests.RequestException:
            break
        store.sent(key, body, answer)
        pushed += 1
    return pushed


def sync_library(library_dir: Path, cfg: RemoteConfig) -> SyncResult:
    """Push what is queued, then pull the book list and every book's reading state."""
    result = SyncResult()
    try:
        result.pushed = flush_pending(cfg)
        books, server_now, device_now = api.fetch_books(cfg.server_url, cfg.api_token)
    except api.ApiError as e:
        raise SyncError(str(e)) from e
    except requests.RequestException as e:
        raise SyncError(f"Verbindung zu {cfg.server_url} fehlgeschlagen: {e}") from e

    store = progress.default()
    store.set_server_now(server_now, device_now)
    known = library_meta.remote_entries()
    entries: dict[str, dict] = {}
    for b in books:
        try:
            meta = json.loads(crypto.decrypt(cfg.enc_key_b64, b["meta_iv"], b["meta_ct"]).decode("utf-8"))
        except (crypto.DecryptError, ValueError):
            result.failed.append(f"#{b['id']}")
            continue
        title = meta.get("title") or f"Buch {b['id']}"
        if meta.get("type") == "pdf":
            result.skipped_pdf.append(title)
            continue
        key = server_key(b["id"])
        entries[key] = {"server_id": b["id"], "title": title, "author": meta.get("author") or "",
                        "is_read": bool(b.get("is_read")), "uploaded_at": b.get("uploaded_at") or "",
                        "folders": library.folders_of_meta(meta), "pages": int(meta.get("pages") or 0),
                        "magazine": meta.get("magazine") if isinstance(meta.get("magazine"), bool) else None}
        if key not in known:
            result.new_titles.append(title)
        store.apply_server(key, b)
    library_meta.set_remote(entries)
    result.books = len(entries)
    _pull_folder_order(cfg)
    return result


def _pull_folder_order(cfg: RemoteConfig) -> None:
    """The folders' order: encrypted library prefs {folder_order: [...]}. Best effort."""
    try:
        prefs = api.fetch_prefs(cfg.server_url, cfg.api_token)
        if not prefs.get("prefs_ct"):
            return
        plain = json.loads(crypto.decrypt(cfg.enc_key_b64, prefs["prefs_iv"], prefs["prefs_ct"]).decode("utf-8"))
        order = plain.get("folder_order")
        if isinstance(order, list):
            library_meta.set_extra("folder_order", [f for f in order if isinstance(f, str)])
    except (api.ApiError, crypto.DecryptError, ValueError, requests.RequestException):
        pass


def download_book(library_dir: Path, cfg: RemoteConfig, server_id: int, title: str) -> Path:
    existing = local_path(library_dir, server_id)
    if existing is not None:
        return existing
    try:
        data = api.fetch_book_data(cfg.server_url, cfg.api_token, server_id)
        raw = crypto.decrypt(cfg.enc_key_b64, data["data_iv"], data["data_ct"])
    except api.ApiError as e:
        raise SyncError(str(e)) from e
    except crypto.DecryptError as e:
        raise SyncError("Das Buch lässt sich mit dem gespeicherten Schlüssel nicht entschlüsseln.") from e
    except requests.RequestException as e:
        raise SyncError(f"Verbindung zu {cfg.server_url} fehlgeschlagen: {e}") from e
    library_dir.mkdir(parents=True, exist_ok=True)
    dest = library_dir / f"{server_id:04d} - {_sanitize_filename(title)}.epub"
    tmp = dest.with_suffix(".part")
    tmp.write_bytes(raw)
    os.replace(tmp, dest)
    return dest