from __future__ import annotations

from typing import Any, Callable, Type, TypeVar, Generic, Optional, Protocol, runtime_checkable, cast
from sqlalchemy import and_, func, inspect, or_, text
from sqlalchemy.engine import Engine, Connection
from sqlalchemy.orm import Load, Session, with_polymorphic, Mapper, RelationshipProperty
from sqlalchemy.orm.attributes import InstrumentedAttribute

from crudkit.core.base import Version
from crudkit.core.spec import CRUDSpec
from crudkit.core.types import OrderSpec, SeekWindow
from crudkit.backend import BackendInfo, make_backend_info
from crudkit.projection import compile_projection

import logging
log = logging.getLogger("crudkit.service")

def _is_rel(model_cls, name: str) -> bool:
    try:
        prop = model_cls.__mapper__.relationships.get(name)
        return isinstance(prop, RelationshipProperty)
    except Exception:
        return False

@runtime_checkable
class _HasID(Protocol):
    id: int

@runtime_checkable
class _HasTable(Protocol):
    __table__: Any

@runtime_checkable
class _HasADict(Protocol):
    def as_dict(self) -> dict: ...

@runtime_checkable
class _SoftDeletable(Protocol):
    is_deleted: bool

class _CRUDModelProto(_HasID, _HasTable, _HasADict, Protocol):
    """Minimal surface that our CRUD service relies on. Soft-delete is optional."""
    pass

T = TypeVar("T", bound=_CRUDModelProto)

def _is_truthy(val):
    return str(val).lower() in ('1', 'true', 'yes', 'on')

class CRUDService(Generic[T]):
    def __init__(
        self,
        model: Type[T],
        session_factory: Callable[[], Session],
        polymorphic: bool = False,
        *,
        backend: Optional[BackendInfo] = None
    ):
        self.model = model
        self._session_factory = session_factory
        self.polymorphic = polymorphic
        self.supports_soft_delete = hasattr(model, 'is_deleted')
        # Cache backend info once. If not provided, derive from session bind.
        bind = session_factory().get_bind()
        eng: Engine = bind.engine if isinstance(bind, Connection) else cast(Engine, bind)
        self.backend = backend or make_backend_info(eng)

    @property
    def session(self) -> Session:
        return self._session_factory()

    def get_query(self):
        if self.polymorphic:
            poly = with_polymorphic(self.model, "*")
            return self.session.query(poly), poly
        return self.session.query(self.model), self.model

    def _apply_not_deleted(self, query, root_alias, params) -> Any:
        if self.supports_soft_delete and not _is_truthy((params or {}).get("include_deleted")):
            return query.filter(getattr(root_alias, "is_deleted") == False)
        return query

    def _extract_order_spec(self, root_alias, given_order_by):
        """
        SQLAlchemy 2.x only:
        Normalize order_by into (cols, desc_flags). Supports plain columns and
        col.asc()/col.desc() (UnaryExpression). Avoids boolean evaluation of clauses.
        """
        from sqlalchemy.sql import operators
        from sqlalchemy.sql.elements import UnaryExpression

        given = self._stable_order_by(root_alias, given_order_by)

        cols, desc_flags = [], []
        for ob in given:
            # Unwrap column if this is a UnaryExpression produced by .asc()/.desc()
            elem = getattr(ob, "element", None)
            col = elem if elem is not None else ob

            # Detect direction in SA 2.x
            is_desc = False
            dir_attr = getattr(ob, "_direction", None)
            if dir_attr is not None:
                is_desc = (dir_attr is operators.desc_op) or (getattr(dir_attr, "name", "").upper() == "DESC")
            elif isinstance(ob, UnaryExpression):
                op = getattr(ob, "operator", None)
                is_desc = (op is operators.desc_op) or (getattr(op, "name", "").upper() == "DESC")

            cols.append(col)
            desc_flags.append(bool(is_desc))

        from crudkit.core.types import OrderSpec
        return OrderSpec(cols=tuple(cols), desc=tuple(desc_flags))

    def _key_predicate(self, spec: OrderSpec, key_vals: list[Any], backward: bool):
        if not key_vals:
            return None

        conds = []
        for i, col in enumerate(spec.cols):
            # If NULLs possible, normalize for comparison. Example using coalesce to a sentinel:
            # sent_col = func.coalesce(col, literal("-∞"))
            sent_col = col
            ties = [spec.cols[j] == key_vals[j] for j in range(i)]
            is_desc = spec.desc[i]
            if not backward:
                op = (sent_col < key_vals[i]) if is_desc else (sent_col > key_vals[i])
            else:
                op = (sent_col > key_vals[i]) if is_desc else (sent_col < key_vals[i])
            conds.append(and_(*ties, op))
        return or_(*conds)

    def _pluck_key(self, obj: Any, spec: OrderSpec) -> list[Any]:
        out = []
        for c in spec.cols:
            # Only simple mapped columns supported for key pluck
            key = getattr(c, "key", None) or getattr(c, "name", None)
            if key is None or not hasattr(obj, key):
                raise ValueError("Order includes non-mapped or related column; cannot pluck cursor key from row object.")
            out.append(getattr(obj, key))
        return out

    def seek_window(
        self,
        params: dict | None = None,
        *,
        key: list[Any] | None = None,
        backward: bool = False,
        include_total: bool = True,
    ) -> "SeekWindow[T]":
        """
        Transport-agnostic keyset pagination that preserves all the goodies from `list()`:
          - filters, includes, joins, field projection, eager loading, soft-delete
          - deterministic ordering (user sort + PK tiebreakers)
          - forward/backward seek via `key` and `backward`
        Returns a SeekWindow with items, first/last keys, order spec, limit, and optional total.
        """
        session = self.session
        fields = list((params or {}).get("fields", []))
        expanded_fields, proj_opts = compile_projection(self.model, fields) if fields else ([], [])
        query, root_alias = self.get_query()
        if proj_opts:
            query = query.options(*proj_opts)

        spec = CRUDSpec(self.model, params or {}, root_alias)

        filters = spec.parse_filters()
        order_by = spec.parse_sort()

        root_fields, rel_field_names, root_field_names = spec.parse_fields()

        # Soft delete filter
        # if self.supports_soft_delete and not _is_truthy((params or {}).get("include_deleted")):
        #     query = query.filter(getattr(root_alias, "is_deleted") == False)
        query = self._apply_not_deleted(query, root_alias, params)

        # Parse filters first
        if filters:
            query = query.filter(*filters)

        # Includes + joins (so relationship fields like brand.name, location.label work)
        spec.parse_includes()
        join_paths = tuple(spec.get_join_paths())

        for _, relationship_attr, target_alias in spec.get_join_paths():
            rel_attr = cast(InstrumentedAttribute, relationship_attr)
            target = cast(Any, target_alias)
            query = query.join(target, rel_attr.of_type(target), isouter=True)

        # Fields/projection: load_only for root columns, eager loads for relationships
        only_cols = [c for c in root_fields if isinstance(c, InstrumentedAttribute)]
        if only_cols:
            query = query.options(Load(root_alias).load_only(*only_cols))

        # Order + limit
        order_spec = self._extract_order_spec(root_alias, order_by)  # SA2-only helper
        limit, _ = spec.parse_pagination()
        if limit is None:
            effective_limit = 50
        elif limit == 0:
            effective_limit = None
        else:
            effective_limit = limit

        # Keyset predicate
        if key:
            pred = self._key_predicate(order_spec, key, backward)
            if pred is not None:
                query = query.filter(pred)

        # Apply ordering. For backward, invert SQL order then reverse in-memory for display.
        if not backward:
            clauses = [(c.desc() if is_desc else c.asc()) for c, is_desc in zip(order_spec.cols, order_spec.desc)]
            query = query.order_by(*clauses)
            if effective_limit is not None:
                query = query.limit(effective_limit)
            items = query.all()
        else:
            inv_clauses = [(c.asc() if is_desc else c.desc()) for c, is_desc in zip(order_spec.cols, order_spec.desc)]
            query = query.order_by(*inv_clauses)
            if effective_limit is not None:
                query = query.limit(effective_limit)
            items = list(reversed(query.all()))


        # Tag projection so your renderer knows what fields were requested
        if expanded_fields:
            proj = list(expanded_fields)
        else:
            proj = []
            if root_field_names:
                proj.extend(root_field_names)
            if root_fields:
                proj.extend(c.key for c in root_fields)
            for path, names in (rel_field_names or {}).items():
                prefix = ".".join(path)
                for n in names:
                    proj.append(f"{prefix}.{n}")
            if proj and "id" not in proj and hasattr(self.model, "id"):
                proj.insert(0, "id")

        if proj:
            for obj in items:
                try:
                    setattr(obj, "__crudkit_projection__", tuple(proj))
                except Exception:
                    pass

        # Boundary keys for cursor encoding in the API layer
        first_key = self._pluck_key(items[0], order_spec) if items else None
        last_key  = self._pluck_key(items[-1], order_spec) if items else None

        # Optional total that’s safe under JOINs (COUNT DISTINCT ids)
        total = None
        if include_total:
            base = session.query(getattr(root_alias, "id"))
            base = self._apply_not_deleted(base, root_alias, params)
            if filters:
                base = base.filter(*filters)
            for _, relationship_attr, target_alias in join_paths:   # reuse
                rel_attr = cast(InstrumentedAttribute, relationship_attr)
                target = cast(Any, target_alias)
                base = base.join(target, rel_attr.of_type(target), isouter=True)
            total = session.query(func.count()).select_from(
                base.order_by(None).distinct().subquery()
            ).scalar() or 0

        window_limit_for_body = 0 if effective_limit is None and limit == 0 else (effective_limit or 50)

        if log.isEnabledFor(logging.DEBUG):
            log.debug("QUERY: %s", str(query))

        from crudkit.core.types import SeekWindow  # avoid circulars at module top
        return SeekWindow(
            items=items,
            limit=window_limit_for_body,
            first_key=first_key,
            last_key=last_key,
            order=order_spec,
            total=total,
        )

    # Helper: default ORDER BY for MSSQL when paginating without explicit order
    def _default_order_by(self, root_alias):
        mapper: Mapper[Any] = cast(Mapper[Any], inspect(self.model))
        cols = []
        for col in mapper.primary_key:
            try:
                cols.append(getattr(root_alias, col.key))
            except AttributeError:
                cols.append(col)
        return cols or [text("1")]

    def _stable_order_by(self, root_alias, given_order_by):
        """
        Ensure deterministic ordering by appending PK columns as tiebreakers.
        If no order is provided, fall back to default primary-key order.
        """
        order_by = list(given_order_by or [])
        if not order_by:
            return self._default_order_by(root_alias)

        mapper: Mapper[Any] = cast(Mapper[Any], inspect(self.model))
        pk_cols = []
        for col in mapper.primary_key:
            try:
                pk_cols.append(getattr(root_alias, col.key))
            except AttributeError:
                pk_cols.append(col)

        return [*order_by, *pk_cols]

    def get(self, id: int, params=None) -> T | None:
        query, root_alias = self.get_query()

        include_deleted = False
        root_fields = []
        root_field_names = {}
        rel_field_names = {}

        spec = CRUDSpec(self.model, params or {}, root_alias)
        if params:
            if self.supports_soft_delete:
                include_deleted = _is_truthy(params.get('include_deleted'))
        if self.supports_soft_delete and not include_deleted:
            query = query.filter(getattr(root_alias, "is_deleted") == False)
        query = query.filter(getattr(root_alias, "id") == id)

        spec.parse_includes()

        for _, relationship_attr, target_alias in spec.get_join_paths():
            rel_attr = cast(InstrumentedAttribute, relationship_attr)
            target = cast(Any, target_alias)
            query = query.join(target, rel_attr.of_type(target), isouter=True)

        if params:
            root_fields, rel_field_names, root_field_names = spec.parse_fields()

        req_fields = list((params or {}).get("fields", []))
        expanded_fields, proj_opts = compile_projection(self.model, req_fields) if req_fields else ([], [])
        if proj_opts:
            query = query.options(*proj_opts)

        only_cols = [c for c in root_fields if isinstance(c, InstrumentedAttribute)]
        if only_cols:
            query = query.options(Load(root_alias).load_only(*only_cols))

        obj = query.first()

        if expanded_fields:
            proj = list(expanded_fields)
        else:
            proj = []
            if root_field_names:
                proj.extend(root_field_names)
            if root_fields:
                proj.extend(c.key for c in root_fields)
            for path, names in (rel_field_names or {}).items():
                prefix = ".".join(path)
                for n in names:
                    proj.append(f"{prefix}.{n}")
            if proj and "id" not in proj and hasattr(self.model, "id"):
                proj.insert(0, "id")

        if proj and obj is not None:
            try:
                setattr(obj, "__crudkit_projection__", tuple(proj))
            except Exception:
                pass

        if log.isEnabledFor(logging.DEBUG):
            log.debug("QUERY: %s", str(query))

        return obj or None

    def list(self, params=None) -> list[T]:
        query, root_alias = self.get_query()

        root_fields = []
        root_field_names = {}
        rel_field_names = {}

        if params:
            if self.supports_soft_delete:
                include_deleted = _is_truthy(params.get('include_deleted'))
                if not include_deleted:
                    query = query.filter(getattr(root_alias, "is_deleted") == False)

            spec = CRUDSpec(self.model, params or {}, root_alias)
            filters = spec.parse_filters()
            order_by = spec.parse_sort()
            limit, offset = spec.parse_pagination()
            spec.parse_includes()

            for _, relationship_attr, target_alias in spec.get_join_paths():
                rel_attr = cast(InstrumentedAttribute, relationship_attr)
                target = cast(Any, target_alias)
                query = query.join(target, rel_attr.of_type(target), isouter=True)

            if params:
                root_fields, rel_field_names, root_field_names = spec.parse_fields()

            only_cols = [c for c in root_fields if isinstance(c, InstrumentedAttribute)]
            if only_cols:
                query = query.options(Load(root_alias).load_only(*only_cols))

            if filters:
                query = query.filter(*filters)

            # MSSQL: requires ORDER BY when using OFFSET (and SQLA will use OFFSET for limit+offset).
            paginating = (limit is not None) or (offset is not None and offset != 0)
            if paginating and not order_by and self.backend.requires_order_by_for_offset:
                order_by = self._default_order_by(root_alias)

            if order_by:
                query = query.order_by(*order_by)

            # Only apply offset/limit when not None.
            if offset is not None and offset != 0:
                query = query.offset(offset)
            if limit is not None and limit > 0:
                query = query.limit(limit)

        req_fields = list((params or {}).get("fields", []))
        expanded_fields, proj_opts = compile_projection(self.model, req_fields) if req_fields else ([], [])
        if proj_opts:
            query = query.options(*proj_opts)

        rows = query.all()

        if expanded_fields:
            proj = list(expanded_fields)
        else:
            proj = []
            if root_field_names:
                proj.extend(root_field_names)
            if root_fields:
                proj.extend(c.key for c in root_fields)
            for path, names in (rel_field_names or {}).items():
                prefix = ".".join(path)
                for n in names:
                    proj.append(f"{prefix}.{n}")
            if proj and "id" not in proj and hasattr(self.model, "id"):
                proj.insert(0, "id")

        if proj:
            for obj in rows:
                try:
                    setattr(obj, "__crudkit_projection__", tuple(proj))
                except Exception:
                    pass

        if log.isEnabledFor(logging.DEBUG):
            log.debug("QUERY: %s", str(query))

        return rows

    def create(self, data: dict, actor=None) -> T:
        session = self.session
        obj = self.model(**data)
        session.add(obj)
        session.commit()
        self._log_version("create", obj, actor)
        return obj

    def update(self, id: int, data: dict, actor=None) -> T:
        session = self.session
        obj = self.get(id)
        if not obj:
            raise ValueError(f"{self.model.__name__} with ID {id} not found.")
        valid_fields = {c.name for c in self.model.__table__.columns}
        unknown = set(data) - valid_fields
        if unknown:
            raise ValueError(f"Unknown fields: {', '.join(sorted(unknown))}")
        for k, v in data.items():
            if k in valid_fields:
                setattr(obj, k, v)
        session.commit()
        self._log_version("update", obj, actor)
        return obj

    def delete(self, id: int, hard: bool = False, actor = None):
        session = self.session
        obj = session.get(self.model, id)
        if not obj:
            return None
        if hard or not self.supports_soft_delete:
            session.delete(obj)
        else:
            soft = cast(_SoftDeletable, obj)
            soft.is_deleted = True
        session.commit()
        self._log_version("delete", obj, actor)
        return obj

    def _log_version(self, change_type: str, obj: T, actor=None, metadata: dict | None = None):
        session = self.session
        try:
            data = obj.as_dict()
        except Exception:
            data = {"error": "Failed to serialize object."}
        version = Version(
            model_name=self.model.__name__,
            object_id=obj.id,
            change_type=change_type,
            data=data,
            actor=str(actor) if actor else None,
            meta=metadata
        )
        session.add(version)
        session.commit()