"""Delta-sync API for the local-first native clients (M8 sync hub).

Pull: `GET /api/sync/changes?since=<cursor>` returns every note + label the caller
owns whose sync_revision advanced past the cursor, newest-revision last, paginated.
Notes and labels both draw from ONE shared sequence (sync_revision_seq), so the
cursor is a single monotonic watermark across both entity types.

The web app does NOT use this — it stays on the live REST API. This surface exists
purely so a native client can mirror the server into its local store and resume
from where it left off (since=0 = full initial sync).
"""
from __future__ import annotations

import uuid
from datetime import datetime, timezone

from quart import Blueprint, g, jsonify, request
from sqlalchemy import delete as sa_delete
from sqlalchemy import func, select

from .auth import login_required
from .common import iso, parse_dt
from .db import session_scope
from .labeling import reconcile_manual_labels, resolve_owned_label_ids
from .models.label import Label, NoteLabel
from .models.note import Note
from .models.note_revision import NoteRevision
from .revisions import should_snapshot
from .notes import (
    _reconcile_tags,
    _serialize_notes,
    derive_display_title,
    normalize_color,
    normalize_recurrence,
)
from .retention import purge_note
from .serialize import serialize_label_sync
from .unfurl_queue import schedule as schedule_unfurls

bp = Blueprint("sync", __name__, url_prefix="/api/sync")

DEFAULT_LIMIT = 500
MAX_LIMIT = 1000
MAX_PUSH = 1000  # per-batch change cap

# --- protocol versioning (M10.6) --------------------------------------------
#
# The client<->server compatibility contract. These integers version the WIRE
# PROTOCOL, deliberately separate from the app's release version, so a client and
# server on different releases can still work out whether they can talk. Without
# that separation every protocol change would force app<->server lockstep.
#
#   SYNC_PROTOCOL_VERSION       what this server speaks.
#   MIN_CLIENT_PROTOCOL_VERSION the oldest client protocol it still accepts.
#
# Bump SYNC_PROTOCOL_VERSION for ANY wire change. Raise
# MIN_CLIENT_PROTOCOL_VERSION only for a genuinely BREAKING one: it is the switch
# that hard-blocks older clients, so additive changes must leave it alone.
# v2 (M13): `kind` and `title` both left the wire. Dropping a field a v1 client sends
# and expects back is breaking, so the FLOOR moves too — a v1 client would keep pushing
# both and would read back notes carrying neither.
#
# One bump for the pair: they landed in the same protocol generation, and nothing ever
# ran against a half-applied v2.
SYNC_PROTOCOL_VERSION = 3
MIN_CLIENT_PROTOCOL_VERSION = 3

# Named capabilities beyond the base protocol. An ADDITIVE change earns a name
# here rather than a min-version bump, so a newer client meeting an older server
# can degrade to "some features unavailable" instead of refusing to sync. Clients
# test for the name, never infer a capability from a version number — that's what
# keeps feature gating independent of release lockstep.
SYNC_FEATURES: tuple[str, ...] = (
    "notes",  # note delta sync (pull + push)
    "labels",  # the label catalog as its own entity
    "attachments",  # blob upload/download, deduped by sha256
    "tombstones",  # purge propagates as a content-less row
    "revisions",  # an overwritten version snapshots into note history
)


def protocol_advertisement() -> dict:
    """What the server publishes about the sync protocol, merged into `/api/config`.

    DB-free and unauthenticated on purpose: a client has to be able to ask "can I
    talk to you at all?" before it holds a device token — or even has an account.
    """
    return {
        "sync_protocol_version": SYNC_PROTOCOL_VERSION,
        "min_client_protocol_version": MIN_CLIENT_PROTOCOL_VERSION,
        "sync_features": list(SYNC_FEATURES),
    }


def _parse_since(raw: str | None) -> int:
    """The pull cursor: a non-negative revision watermark. Bad/absent → 0 (full sync)."""
    try:
        return max(int(raw), 0) if raw is not None else 0
    except (ValueError, TypeError):
        return 0


def _clamp_limit(raw: str | None) -> int:
    try:
        return max(1, min(int(raw), MAX_LIMIT)) if raw is not None else DEFAULT_LIMIT
    except (ValueError, TypeError):
        return DEFAULT_LIMIT


def _page_cursor(note_revs: list[int], label_revs: list[int], since: int, limit: int) -> tuple[int, bool]:
    """Compute the next cursor + has_more when paging TWO revision streams that share
    one sequence. Each stream is fetched `rev > since ORDER BY rev LIMIT limit`.

    If either stream came back FULL (== limit) we're truncating, so the safe cursor is
    the SMALLER of the two page boundaries — advancing only to where BOTH streams are
    fully drained, so nothing between the cursor and the next pull is skipped. If
    neither is full, everything ≤ max(returned) is drained. Both lists are ascending.
    """
    boundaries = []
    if len(note_revs) == limit:
        boundaries.append(note_revs[-1])
    if len(label_revs) == limit:
        boundaries.append(label_revs[-1])
    if boundaries:
        return min(boundaries), True
    all_revs = note_revs + label_revs
    return (max(all_revs) if all_revs else since), False


@bp.get("/changes")
@login_required
async def changes():
    since = _parse_since(request.args.get("since"))
    limit = _clamp_limit(request.args.get("limit"))
    async with session_scope() as db:
        # ALL of the owner's notes/labels (any state — active/archived/trash/purged),
        # since a client mirrors everything; ordered by the shared revision.
        note_rows = (
            await db.scalars(
                select(Note)
                .where(Note.owner_id == g.user_id, Note.sync_revision > since)
                .order_by(Note.sync_revision)
                .limit(limit)
            )
        ).all()
        label_rows = (
            await db.scalars(
                select(Label)
                .where(Label.owner_id == g.user_id, Label.sync_revision > since)
                .order_by(Label.sync_revision)
                .limit(limit)
            )
        ).all()

        cursor, has_more = _page_cursor(
            [n.sync_revision for n in note_rows],
            [lb.sync_revision for lb in label_rows],
            since,
            limit,
        )
        # Trim each stream to the shared watermark so the two feeds stay aligned.
        note_rows = [n for n in note_rows if n.sync_revision <= cursor]
        label_rows = [lb for lb in label_rows if lb.sync_revision <= cursor]

        # Note bodies come from the shared note serializer; sync adds the two
        # delta-only fields on top (folding these into the serializer itself waits on
        # the notes.py serialization split).
        notes_out = await _serialize_notes(db, note_rows)
        for data, n in zip(notes_out, note_rows):
            data["sync_revision"] = n.sync_revision
            data["purged_at"] = iso(n.purged_at)

        return jsonify(
            {
                "notes": notes_out,
                "labels": [serialize_label_sync(lb) for lb in label_rows],
                "cursor": cursor,
                "has_more": has_more,
            }
        )


# --- Push: apply client mutations (LWW by client edit-time, non-destructive) ---


def client_wins(client_edited_at: datetime | None, server_edited_at: datetime | None) -> bool:
    """Last-write-wins: the client's version is applied iff its edit-time is at least
    the server's. A missing client time never overwrites a real server edit; a missing
    server time (new/unknown row) always yields to a present client edit."""
    if client_edited_at is None:
        return server_edited_at is None
    if server_edited_at is None:
        return True
    return client_edited_at >= server_edited_at


def _assign_note_fields(note: Note, ch: dict) -> None:
    """Overwrite a note's scalar fields from a client's FULL-state change (sync is
    whole-note, not a partial patch — the client sends its authoritative version)."""
    note.body = ch["body"] if isinstance(ch.get("body"), str) else ""
    note.color = normalize_color(ch.get("color"))
    note.pinned = bool(ch.get("pinned"))
    note.archived = bool(ch.get("archived"))
    if ch.get("trashed"):
        if note.deleted_at is None:
            note.deleted_at = datetime.now(timezone.utc)
    else:
        note.deleted_at = None
    note.remind_at = parse_dt(ch.get("remind_at"))
    note.recurrence = normalize_recurrence(ch.get("recurrence"))
    if isinstance(ch.get("position"), int):
        note.position = ch["position"]


# `_first_item_text` and `_apply_note_items` lived here until M304. Both existed for
# one reason — a checklist was a table beside the body — and both are gone with it. A
# pushed change carries its items as `- [ ] ` lines inside `body`, so applying them is
# applying the body, and naming the note is reading its first line. A client that still
# sends an `items` array is a v2 client, and the version floor below turns it away
# before any of this runs.


async def _apply_note_manual_labels(db, note: Note, ch: dict) -> None:
    """Set the note's MANUAL (picker) label memberships from client label_ids, leaving
    tag-sourced (via_tag) rows to _reconcile_tags. Only labels the caller owns count."""
    raw = ch.get("label_ids")
    if not isinstance(raw, list):
        return
    wanted: set = set()
    for r in raw:
        try:
            wanted.add(uuid.UUID(str(r)))
        except (ValueError, TypeError):
            continue  # sync is lenient: skip a malformed id rather than reject the push
    owned = await resolve_owned_label_ids(db, wanted, g.user_id)
    await reconcile_manual_labels(db, note, owned)


async def _apply_note(db, ch: dict) -> dict:
    raw_id = ch.get("id")
    try:
        nid = uuid.UUID(str(raw_id))
    except (ValueError, TypeError):
        return {"id": raw_id, "entity": "note", "status": "rejected", "error": "invalid id"}
    op = ch.get("op", "upsert")
    edited_at = parse_dt(ch.get("edited_at"))

    note = await db.scalar(select(Note).where(Note.id == nid))
    if note is not None and note.owner_id != g.user_id:
        # A client only ever pushes ids of notes IT created, so this branch is only
        # reached by a probe (or a ~0-probability UUID collision). Reject with a
        # GENERIC message so the response doesn't confirm the id belongs to another
        # user (don't leak existence via a distinctive "not yours").
        return {"id": str(nid), "entity": "note", "status": "rejected", "error": "cannot apply"}

    if op == "delete":
        if note is None:
            return {"id": str(nid), "entity": "note", "status": "noop"}
        if not client_wins(edited_at, note.updated_at):
            return {"id": str(nid), "entity": "note", "status": "kept", "sync_revision": note.sync_revision}
        await purge_note(db, note, edited_at)
        await db.flush()
        await db.refresh(note, ["sync_revision"])
        return {"id": str(nid), "entity": "note", "status": "applied", "sync_revision": note.sync_revision}

    creating = note is None
    if creating:
        note = Note(id=nid, owner_id=g.user_id, body="", display_title="")
        created = parse_dt(ch.get("created_at"))
        if created is not None:
            note.created_at = created
        db.add(note)
    elif not client_wins(edited_at, note.updated_at):
        return {"id": str(nid), "entity": "note", "status": "kept", "sync_revision": note.sync_revision}
    elif note.purged_at is not None:
        note.purged_at = None  # client re-created/edited → clear the tombstone

    old_body = note.body
    _assign_note_fields(note, ch)
    note.display_title = derive_display_title(note.body)
    if edited_at is not None:
        note.updated_at = edited_at
    # Non-destructive LWW: snapshot the overwritten server body into history —
    # subject to the same session window as a direct edit (revisions.should_snapshot).
    # This path is why the window is a time rule rather than a flag on the wire: a
    # client autosaving every second pushes a body change every second, and without
    # the check the SERVER would snapshot each one no matter how restrained the
    # client's own store was being.
    if not creating and await should_snapshot(db, note.id, old_body, note.body):
        db.add(NoteRevision(note_id=note.id, body=old_body))
    await db.flush()  # assign note.id before items/labels/links
    await _reconcile_tags(db, note)
    await _apply_note_manual_labels(db, note, ch)
    await db.flush()
    await db.refresh(note, ["sync_revision"])
    # A note pushed from a linked client gets the same link previews as one typed into
    # the web app — the client picks them up on its next pull. Scheduled rather than
    # awaited: a push batch must not wait on somebody else's website.
    if creating or note.body != old_body:
        schedule_unfurls(note.id, note.body)
    return {
        "id": str(nid),
        "entity": "note",
        "status": "created" if creating else "applied",
        "sync_revision": note.sync_revision,
    }


async def _apply_label(db, ch: dict) -> dict:
    raw_id = ch.get("id")
    try:
        lid = uuid.UUID(str(raw_id))
    except (ValueError, TypeError):
        return {"id": raw_id, "entity": "label", "status": "rejected", "error": "invalid id"}
    op = ch.get("op", "upsert")
    edited_at = parse_dt(ch.get("edited_at"))

    label = await db.scalar(select(Label).where(Label.id == lid))
    if label is not None and label.owner_id != g.user_id:
        # Generic rejection (see _apply_note): don't confirm a foreign-owned id exists.
        return {"id": str(lid), "entity": "label", "status": "rejected", "error": "cannot apply"}

    if op == "delete":
        if label is None:
            return {"id": str(lid), "entity": "label", "status": "noop"}
        if not client_wins(edited_at, label.updated_at):
            return {"id": str(lid), "entity": "label", "status": "kept", "sync_revision": label.sync_revision}
        await db.execute(sa_delete(NoteLabel).where(NoteLabel.label_id == label.id))
        label.purged_at = datetime.now(timezone.utc)
        if edited_at is not None:
            label.updated_at = edited_at
        await db.flush()
        await db.refresh(label, ["sync_revision"])
        return {"id": str(lid), "entity": "label", "status": "applied", "sync_revision": label.sync_revision}

    name = (ch.get("name") or "").strip()
    creating = label is None
    if not creating and not client_wins(edited_at, label.updated_at):
        return {"id": str(lid), "entity": "label", "status": "kept", "sync_revision": label.sync_revision}
    # Names are unique per owner — a same-name clash on a DIFFERENT id can't be an insert.
    if name:
        clash = await db.scalar(
            select(Label.id).where(
                Label.owner_id == g.user_id, func.lower(Label.name) == name.lower(), Label.id != lid
            )
        )
        if clash is not None:
            return {"id": str(lid), "entity": "label", "status": "rejected", "error": "name in use"}

    if creating:
        if not name:
            return {"id": str(lid), "entity": "label", "status": "rejected", "error": "name required"}
        label = Label(id=lid, owner_id=g.user_id, name=name, color=normalize_color(ch.get("color")))
        db.add(label)
    else:
        if label.purged_at is not None:
            label.purged_at = None
        if name:
            label.name = name
        label.color = normalize_color(ch.get("color"))
    if edited_at is not None:
        label.updated_at = edited_at
    await db.flush()
    await db.refresh(label, ["sync_revision"])
    return {
        "id": str(lid),
        "entity": "label",
        "status": "created" if creating else "applied",
        "sync_revision": label.sync_revision,
    }


@bp.post("/push")
@login_required
async def push():
    """Apply a batch of client changes. Additive + owner-scoped; LWW by client
    edit-time with a version-history snapshot on any overwrite (nothing is lost)."""
    body = await request.get_json(silent=True) or {}
    changes = body.get("changes")
    if not isinstance(changes, list):
        return jsonify({"error": "changes must be a list"}), 400
    if len(changes) > MAX_PUSH:
        return jsonify({"error": f"too many changes in one push (max {MAX_PUSH})"}), 400

    results = []
    async with session_scope() as db:
        for ch in changes:
            if not isinstance(ch, dict):
                results.append({"status": "rejected", "error": "not an object"})
                continue
            entity = ch.get("entity")
            if entity == "note":
                results.append(await _apply_note(db, ch))
            elif entity == "label":
                results.append(await _apply_label(db, ch))
            else:
                results.append({"id": ch.get("id"), "status": "rejected", "error": "unknown entity"})
        await db.commit()
    return jsonify({"results": results})