"""FlowDeck — offline synchronization engine (v6.0.0 PWA).

Reconciles offline mutations (queued on the client) with server state:

- ``get_delta`` — changes on the server since a given timestamp, for offline
  clients to pull before pushing their own batch.
- ``apply_batch`` — replays a batch of offline mutations with optimistic
  concurrency control. ``sync_version`` (auto-bumped by SQLite triggers added
  in migration v17) is the version token.

Conflict model (from docs/V6_PWA_Progressive_Web_App.md):
- edit-edit  → last-write-wins by default (applied + reported)
- edit-delete→ the page was deleted server-side → orphan copy created
- create-create → same title already exists server-side → renamed "… (copie offline)"
- delete     → soft-delete (idempotent)
"""
from __future__ import annotations

import datetime as _dt
import json
import logging
import time

from app.db import get_conn
from app.services.collection_lifecycle import delete_collections

logger = logging.getLogger(__name__)


class ConflictError(Exception):
    """Raised when a mutation conflicts with server state."""

    def __init__(self, detail: dict):
        super().__init__(detail.get("type"))
        self.details = detail


class SyncEngine:
    """Apply/read offline mutations. Stateless methods, thin sqlite access."""

    # ── helpers ────────────────────────────────────────────────────────────

    @staticmethod
    def _now_epoch() -> float:
        return time.time()

    @staticmethod
    def _can_access(conn, user_id: int, workspace_id: int | None) -> bool:
        """Owner or member of the workspace; legacy NULL workspace → allow."""
        if not workspace_id:
            return True
        ws = conn.execute(
            "SELECT owner_id FROM workspaces WHERE id=?", (workspace_id,)
        ).fetchone()
        if ws and ws["owner_id"] == user_id:
            return True
        member = conn.execute(
            "SELECT 1 FROM workspace_members WHERE workspace_id=? AND user_id=?",
            (workspace_id, user_id),
        ).fetchone()
        return bool(member)

    @staticmethod
    def _page_workspace_id(conn, page_id: int) -> int | None:
        row = conn.execute(
            "SELECT workspace_id FROM pages WHERE id=?", (page_id,)
        ).fetchone()
        return row["workspace_id"] if row else None

    # ── delta ─────────────────────────────────────────────────────────────

    async def get_delta(self, user_id: int, since: float, workspace_id: int | None) -> dict:
        """Return server-side changes since `since` (epoch seconds)."""
        if since and since > 1e12:
            since /= 1000.0  # accept epoch-millis from legacy clients

        changes: list[dict] = []
        with get_conn() as conn:
            if not self._can_access(conn, user_id, workspace_id):
                return {"error": "forbidden"}

            # ── pages (created / updated / soft-deleted) ──
            rows = conn.execute(
                """SELECT * FROM pages
                   WHERE (? IS NULL OR workspace_id = ?)
                     AND (CAST(strftime('%s', COALESCE(updated_at, created_at)) AS REAL) > ?
                          OR (deleted_at IS NOT NULL
                              AND CAST(strftime('%s', deleted_at) AS REAL) > ?))""",
                (workspace_id, workspace_id, since, since),
            ).fetchall()
            for r in rows:
                data = dict(r)
                deleted = data.get("deleted_at") is not None
                created_epoch = _iso_epoch(data.get("created_at"))
                created_after = bool(created_epoch and created_epoch > since)
                if deleted:
                    ctype = "page_deleted"
                elif created_after:
                    ctype = "page_created"
                else:
                    ctype = "page_updated"
                changes.append({"change_type": ctype, "data": data})

            # ── collections (created / updated) ──
            coll_rows = conn.execute(
                "SELECT * FROM collections WHERE CAST(strftime('%s', updated_at) AS REAL) > ?",
                (since,),
            ).fetchall()
            for r in coll_rows:
                data = dict(r)
                created_epoch = _iso_epoch(data.get("created_at"))
                changes.append({
                    "change_type": "collection_created" if created_epoch and created_epoch > since
                    else "collection_updated",
                    "data": data,
                })

            # ── collection rows (informational for offline reading) ──
            cp_rows = conn.execute(
                "SELECT * FROM collection_pages WHERE CAST(strftime('%s', updated_at) AS REAL) > ?",
                (since,),
            ).fetchall()
            for r in cp_rows:
                changes.append({"change_type": "collection_row_updated", "data": dict(r)})

        return {
            "changes": changes,
            "server_time": self._now_epoch(),
            "has_more": False,
        }

    # ── batch ──────────────────────────────────────────────────────────────

    async def apply_batch(self, user_id: int, mutations: list[dict], device_id: str) -> dict:
        """Apply a batch of offline mutations; returns per-mutation results.

        ``mutations`` = [{"id"|"mutation_id", "type", "payload", "client_timestamp"}]
        """
        results: list[dict] = []
        conflicts: list[dict] = []

        for mut in mutations:
            mut_id = mut.get("id") or mut.get("mutation_id") or f"m{len(results)}"
            mtype = mut.get("type", "")
            payload = mut.get("payload") or {}
            client_ts = float(mut.get("client_timestamp") or 0)
            result = {
                "mutation_id": mut_id,
                "type": mtype,
                "status": "synced",
                "server_version": None,
            }
            try:
                handler = getattr(self, f"_mut_{mtype}", None)
                if handler is None:
                    raise ValueError(f"unknown mutation type: {mtype}")
                outcome = handler(user_id, payload)
                result.update(outcome)
                status = "conflict" if outcome.get("conflict") else "synced"
                result["status"] = status
                if outcome.get("conflict"):
                    conflicts.append({
                        "mutation_id": mut_id,
                        "type": mtype,
                        **outcome["conflict"],
                    })
            except ConflictError as exc:
                result["status"] = "conflict"
                result["conflict"] = exc.details
                conflicts.append({"mutation_id": mut_id, "type": mtype, **exc.details})
            except Exception as exc:  # noqa: BLE001 — report, don't kill the batch
                logger.warning("sync mutation %s failed: %s", mut_id, exc)
                result["status"] = "failed"
                result["error"] = str(exc)
            finally:
                self._record(user_id, device_id, mtype, mut, client_ts, result)
            results.append(result)

        return {"results": results, "conflicts": conflicts}

    # ── page mutations ─────────────────────────────────────────────────────

    def _mut_page_create(self, user_id: int, payload: dict) -> dict:
        title = (payload.get("title") or "New page").strip() or "New page"
        workspace_id = payload.get("workspace_id")
        parent_id = payload.get("parent_id")

        with get_conn() as conn:
            if not self._can_access(conn, user_id, workspace_id):
                raise ConflictError({"type": "forbidden", "workspace_id": workspace_id})

            # create-create conflict: same title already present at same parent
            new_title = title
            dup = conn.execute(
                """SELECT id FROM pages
                   WHERE title=? AND (? IS NULL OR workspace_id = ?)
                     AND (? IS NULL OR parent_id IS ?)
                     AND deleted_at IS NULL
                   LIMIT 1""",
                (title, workspace_id, workspace_id, parent_id, parent_id),
            ).fetchone()
            if dup:
                new_title = f"{title} (copie offline)"

            cur = conn.execute(
                """INSERT INTO pages
                   (workspace, workspace_id, title, content, content_format,
                    parent_id, parent_section, sort_order)
                   VALUES ('', ?, ?, ?, ?, ?, 'Private', ?)""",
                (workspace_id, new_title,
                 payload.get("content", ""),
                 payload.get("content_format", "blocks"),
                 parent_id,
                 payload.get("sort_order", 0)),
            )
            conn.commit()
            page_id = cur.lastrowid
            synced = payload.get("client_page_id")
            return {"page_id": page_id, "server_version": 1, "client_page_id": synced,
                    "conflict": {"type": "create_create", "renamed": new_title != title}
                    if new_title != title else None}

    def _mut_page_update(self, user_id: int, payload: dict) -> dict:
        page_id = payload.get("page_id")
        base_version = payload.get("base_version")
        with get_conn() as conn:
            row = conn.execute("SELECT * FROM pages WHERE id=?", (page_id,)).fetchone()
            if not row:
                raise ConflictError({"type": "page_not_found", "page_id": page_id})

            ws_id = row["workspace_id"] or payload.get("workspace_id")
            if not self._can_access(conn, user_id, ws_id):
                raise ConflictError({"type": "forbidden", "page_id": page_id})

            # edit-delete: page soft-deleted server-side → orphan copy
            if row["deleted_at"] is not None:
                cur = conn.execute(
                    """INSERT INTO pages
                       (workspace, workspace_id, title, content, content_format, parent_section)
                       VALUES ('', ?, ?, ?, ?, 'Private')""",
                    (ws_id,
                     payload.get("title") or row["title"],
                     (payload.get("content")
                      if payload.get("content") is not None else row["content"]),
                     payload.get("content_format") or row["content_format"]),
                )
                conn.commit()
                orphan_id = cur.lastrowid
                raise ConflictError({
                    "type": "edit_delete",
                    "page_id": page_id,
                    "new_page_id": orphan_id,
                    "detail": "La page a été supprimée côté serveur — copie récréée en page orpheline",
                })

            # edit-edit: version mismatch → last-write-wins + conflict report
            server_version = row["sync_version"]
            conflict = None
            if base_version is not None and server_version != base_version:
                conflict = {
                    "type": "edit_edit",
                    "page_id": page_id,
                    "client_version": base_version,
                    "server_version": server_version,
                }

            sets, params = [], []
            if payload.get("title") is not None:
                sets.append("title=?")
                params.append(payload["title"])
            if payload.get("content") is not None:
                sets.append("content=?")
                params.append(payload["content"])
            if payload.get("content_format") is not None:
                sets.append("content_format=?")
                params.append(payload["content_format"])
            sets_str = ", ".join(sets) if sets else "updated_at=updated_at"
            params.append(page_id)
            conn.execute(
                f"UPDATE pages SET {sets_str}, updated_at=CURRENT_TIMESTAMP WHERE id=?",
                params,
            )
            conn.commit()
            new_version = conn.execute(
                "SELECT sync_version FROM pages WHERE id=?", (page_id,)
            ).fetchone()["sync_version"]
            return {"page_id": page_id, "server_version": new_version,
                    "conflict": conflict}

    def _mut_page_delete(self, user_id: int, payload: dict) -> dict:
        page_id = payload.get("page_id")
        with get_conn() as conn:
            row = conn.execute("SELECT id, workspace_id FROM pages WHERE id=?", (page_id,)).fetchone()
            if not row:
                return {"page_id": page_id, "server_version": None}  # idempotent / already hard-deleted
            ws_id = row["workspace_id"]
            if not self._can_access(conn, user_id, ws_id):
                raise ConflictError({"type": "forbidden", "page_id": page_id})
            conn.execute(
                "UPDATE pages SET deleted_at=CURRENT_TIMESTAMP, "
                "updated_at=CURRENT_TIMESTAMP WHERE id=? AND deleted_at IS NULL",
                (page_id,),
            )
            conn.commit()
            new_version = conn.execute(
                "SELECT sync_version FROM pages WHERE id=?", (page_id,)
            ).fetchone()["sync_version"]
            return {"page_id": page_id, "server_version": new_version}

    def _mut_page_move(self, user_id: int, payload: dict) -> dict:
        page_id = payload.get("page_id")
        with get_conn() as conn:
            row = conn.execute("SELECT id, workspace_id FROM pages WHERE id=?", (page_id,)).fetchone()
            if not row:
                return {"page_id": page_id, "server_version": None}
            ws_id = row["workspace_id"]
            if not self._can_access(conn, user_id, ws_id):
                raise ConflictError({"type": "forbidden", "page_id": page_id})
            sets, params = [], []
            if payload.get("parent_id") is not None:
                sets.append("parent_id=?")
                params.append(payload["parent_id"])
            if payload.get("sort_order") is not None:
                sets.append("sort_order=?")
                params.append(payload["sort_order"])
            if sets:
                params.append(page_id)
                conn.execute(
                    f"UPDATE pages SET {', '.join(sets)}, updated_at=CURRENT_TIMESTAMP WHERE id=?",
                    params,
                )
                conn.commit()
            new_version = conn.execute(
                "SELECT sync_version FROM pages WHERE id=?", (page_id,)
            ).fetchone()["sync_version"]
            return {"page_id": page_id, "server_version": new_version}

    # ── collection mutations ───────────────────────────────────────────────

    def _mut_collection_create(self, user_id: int, payload: dict) -> dict:
        with get_conn() as conn:
            cur = conn.execute(
                """INSERT INTO collections (name, description, icon, schema_json)
                   VALUES (?, ?, ?, ?)""",
                (payload.get("name", ""), payload.get("description", ""),
                 payload.get("icon", "📋"), json.dumps(payload.get("schema", []))),
            )
            conn.commit()
            return {"collection_id": cur.lastrowid, "server_version": 1}

    def _mut_collection_update(self, user_id: int, payload: dict) -> dict:
        cid = payload.get("collection_id")
        with get_conn() as conn:
            row = conn.execute("SELECT * FROM collections WHERE id=?", (cid,)).fetchone()
            if not row:
                raise ConflictError({"type": "collection_not_found", "collection_id": cid})
            sets, params = [], []
            if payload.get("name") is not None:
                sets.append("name=?")
                params.append(payload["name"])
            if payload.get("description") is not None:
                sets.append("description=?")
                params.append(payload["description"])
            if payload.get("icon") is not None:
                sets.append("icon=?")
                params.append(payload["icon"])
            if payload.get("schema") is not None:
                sets.append("schema_json=?")
                params.append(json.dumps(payload["schema"]))
            if sets:
                params.append(cid)
                conn.execute(
                    f"UPDATE collections SET {', '.join(sets)}, updated_at=CURRENT_TIMESTAMP WHERE id=?",
                    params,
                )
                conn.commit()
            new_version = conn.execute(
                "SELECT sync_version FROM collections WHERE id=?", (cid,)
            ).fetchone()["sync_version"]
            return {"collection_id": cid, "server_version": new_version}

    def _mut_collection_delete(self, user_id: int, payload: dict) -> dict:
        cid = payload.get("collection_id")
        with get_conn() as conn:
            delete_collections(conn, [cid])
            conn.commit()
            return {"collection_id": cid, "server_version": None}

    # ── audit ──────────────────────────────────────────────────────────────

    def _record(self, user_id: int, device_id: str, mtype: str, mut: dict,
                client_ts: float, result: dict) -> None:
        """Persist every mutation in the server-side audit queue."""
        try:
            with get_conn() as conn:
                conn.execute(
                    """INSERT INTO offline_sync_queue
                       (user_id, device_id, type, payload, client_timestamp,
                        server_version, status, error)
                       VALUES (?, ?, ?, ?, ?, ?, ?, ?)""",
                    (user_id, device_id, mtype, json.dumps(mut),
                     client_ts, result.get("server_version"),
                     result.get("status", "synced"),
                     result.get("error") or (json.dumps(result["conflict"], ensure_ascii=False)
                                             if result.get("conflict") else None)),
                )
                conn.commit()
        except Exception:  # noqa: BLE001 — audit must never break the batch
            logger.warning("failed to record sync audit row", exc_info=True)


def _iso_epoch(value) -> float | None:
    """Best-effort ISO→epoch. SQLite CURRENT_TIMESTAMP → 'YYYY-MM-DD HH:MM:SS'."""
    try:
        if value is None:
            return None
        # append a timezone so strptime behaves on naive timestamps
        text = str(value).replace("T", " ").split(".")[0]
        parsed = _dt.datetime.strptime(text, "%Y-%m-%d %H:%M:%S")
        return parsed.replace(tzinfo=_dt.UTC).timestamp()
    except ValueError:
        return None