from datetime import date, datetime
from decimal import Decimal
from typing import Any

from fastapi import HTTPException, status
from sqlalchemy import select, text
from sqlalchemy.engine import Engine, RowMapping
from sqlalchemy.exc import SQLAlchemyError
from sqlalchemy.orm import Session

from app.core.constants import ActorValue, ApiStatus
from app.core.config import get_settings
from app.core.database import legacy_engine
from app.core.http.pagination import bounded_limit
from app.core.utils.time import utc_now
from app.modules.audit.constants import AuditAction, AuditRiskLevel, AuditSource, AuditStatus
from app.modules.audit.schemas import AuditLogCreate
from app.modules.audit.service import AuditService
from app.modules.business.constants import BusinessDomain, SourceSystem, StatusValue
from app.modules.business.models import LegacySyncRun, Project, WorkTask
from app.modules.business.service import serialize_model
from app.modules.events.constants import (
    EventAggregateType,
    EventPayloadKey,
    EventSource,
    EventType,
)
from app.modules.events.service import EventService
from app.modules.legacy_mysql.constants import (
    LEGACY_PROJECT_QUERY_SOURCE,
    LEGACY_PROJECT_SYNC_NOTE,
    LEGACY_SYNC_MISSING_ID_REASON,
    LEGACY_SYNC_RUN_CODE_PREFIX,
    LEGACY_TASK_CODE_TEMPLATE,
    LEGACY_TASK_QUERY_SOURCE,
    LEGACY_TASK_SYNC_NOTE,
    LEGACY_TASK_SYNC_RUN_CODE_PREFIX,
    LEGACY_HEALTH_SQL,
    LEGACY_LIMIT_CLAUSE,
    LEGACY_LIMIT_MARKER,
    LEGACY_MYSQL_CONNECTION_FAILED_TEMPLATE,
    LEGACY_PROJECT_CODE_TEMPLATE,
    LEGACY_SELECT_PREFIX,
    LEGACY_SQL_TRAILING_TERMINATOR,
    LEGACY_UNNAMED_TASK,
    LEGACY_UNNAMED_PROJECT,
    LegacyProjectField,
    LegacyQueryError,
    LegacyQueryName,
    LegacyResponseKey,
    LegacySyncAction,
    LegacyTaskField,
)

FORBIDDEN_SQL_TOKENS = {
    "insert",
    "update",
    "delete",
    "drop",
    "alter",
    "truncate",
    "create",
    "replace",
    "grant",
    "revoke",
}


def _jsonable(value: Any) -> Any:
    """Convert database scalar values into JSON-friendly values."""

    if isinstance(value, (datetime, date)):
        return value.isoformat()
    if isinstance(value, Decimal):
        return float(value)
    return value


def _row_to_dict(row: RowMapping) -> dict[str, Any]:
    """Convert a SQLAlchemy row mapping to a serializable dictionary."""

    return {key: _jsonable(value) for key, value in row.items()}


def _normalize_sql(sql: str) -> str:
    return " ".join(sql.strip().rstrip(LEGACY_SQL_TRAILING_TERMINATOR).split()).lower()


def _query_name_text(query_name: str | LegacyQueryName | None) -> str:
    if query_name is None:
        return LegacyQueryName.PROJECTS.value
    if isinstance(query_name, LegacyQueryName):
        return query_name.value
    return str(query_name)


class LegacyMySQLService:
    """Read legacy MySQL data and sync projects into the internal ledger."""

    def __init__(self, db: Session | None):
        self.db = db

    @staticmethod
    def _ensure_engine() -> Engine:
        if legacy_engine is None:
            raise HTTPException(
                status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
                detail=LegacyQueryError.DATABASE_NOT_CONFIGURED,
            )
        return legacy_engine

    @staticmethod
    def _ensure_readonly(sql: str) -> None:
        stripped = sql.strip().lower()
        if not stripped.startswith(LEGACY_SELECT_PREFIX):
            raise HTTPException(
                status_code=status.HTTP_400_BAD_REQUEST,
                detail=LegacyQueryError.ONLY_SELECT_ALLOWED,
            )
        tokens = {token.strip(" ;,\n\t") for token in stripped.replace("(", " ").split()}
        if tokens & FORBIDDEN_SQL_TOKENS:
            raise HTTPException(
                status_code=status.HTTP_400_BAD_REQUEST,
                detail=LegacyQueryError.FORBIDDEN_SQL_TOKEN,
            )

    @staticmethod
    def _allowed_queries() -> dict[str, str]:
        settings = get_settings()
        queries = {
            _query_name_text(name): sql
            for name, sql in settings.legacy_allowed_queries.items()
        }
        if settings.legacy_project_query:
            queries.setdefault(LegacyQueryName.PROJECTS.value, settings.legacy_project_query)
        if settings.legacy_task_query:
            queries.setdefault(LegacyQueryName.TASKS.value, settings.legacy_task_query)
        return queries

    def health(self) -> dict[str, str]:
        engine = self._ensure_engine()
        try:
            with engine.connect() as conn:
                conn.execute(text(LEGACY_HEALTH_SQL))
        except SQLAlchemyError as exc:
            raise HTTPException(
                status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
                detail=LEGACY_MYSQL_CONNECTION_FAILED_TEMPLATE.format(error=exc),
            ) from exc
        return {LegacyResponseKey.STATUS: ApiStatus.OK}

    def execute_readonly(
        self,
        sql: str,
        params: dict[str, Any] | None = None,
        limit: int = 100,
    ) -> dict[str, Any]:
        """Execute a readonly SQL statement only when it matches the allowlist."""

        normalized_sql = _normalize_sql(sql)
        for allowed_sql in self._allowed_queries().values():
            if _normalize_sql(allowed_sql) == normalized_sql:
                return self._execute_readonly_sql(allowed_sql, params, limit)
        raise HTTPException(
            status_code=status.HTTP_403_FORBIDDEN,
            detail=LegacyQueryError.QUERY_NOT_ALLOWED,
        )

    def execute_allowed_query(
        self,
        query_name: str | None,
        params: dict[str, Any] | None = None,
        limit: int = 100,
    ) -> dict[str, Any]:
        queries = self._allowed_queries()
        normalized_name = _query_name_text(query_name)
        sql = queries.get(normalized_name)
        if not sql:
            raise HTTPException(
                status_code=status.HTTP_403_FORBIDDEN,
                detail=LegacyQueryError.QUERY_NOT_ALLOWED,
            )
        return self._execute_readonly_sql(sql, params, limit)

    def _execute_readonly_sql(
        self,
        sql: str,
        params: dict[str, Any] | None = None,
        limit: int = 100,
    ) -> dict[str, Any]:
        self._ensure_readonly(sql)
        engine = self._ensure_engine()
        params = dict(params or {})
        try:
            params[LegacyResponseKey.LIMIT] = bounded_limit(
                params.get(LegacyResponseKey.LIMIT, limit)
            )
        except (TypeError, ValueError) as exc:
            raise HTTPException(
                status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
                detail=LegacyQueryError.INVALID_LIMIT,
            ) from exc
        limited_sql = sql
        if LEGACY_LIMIT_MARKER not in sql.lower():
            limited_sql = f"{sql.rstrip(LEGACY_SQL_TRAILING_TERMINATOR)}{LEGACY_LIMIT_CLAUSE}"
        with engine.connect() as conn:
            result = conn.execute(text(limited_sql), params)
            rows = [_row_to_dict(row) for row in result.mappings().all()]
        columns = list(rows[0].keys()) if rows else []
        return {
            LegacyResponseKey.COLUMNS: columns,
            LegacyResponseKey.ROWS: rows,
            LegacyResponseKey.ROW_COUNT: len(rows),
        }

    def fetch_default_projects(self, limit: int = 100) -> dict[str, Any]:
        settings = get_settings()
        if not settings.legacy_project_query:
            raise HTTPException(
                status_code=status.HTTP_400_BAD_REQUEST,
                detail=LegacyQueryError.PROJECT_QUERY_NOT_CONFIGURED,
            )
        return self.execute_allowed_query(
            LegacyQueryName.PROJECTS,
            {LegacyResponseKey.LIMIT: limit},
            limit=limit,
        )

    def fetch_default_tasks(self, limit: int = 100) -> dict[str, Any]:
        settings = get_settings()
        if not settings.legacy_task_query:
            raise HTTPException(
                status_code=status.HTTP_400_BAD_REQUEST,
                detail=LegacyQueryError.TASK_QUERY_NOT_CONFIGURED,
            )
        return self.execute_allowed_query(
            LegacyQueryName.TASKS,
            {LegacyResponseKey.LIMIT: limit},
            limit=limit,
        )

    @staticmethod
    def _value(
        row: dict[str, Any],
        field_map: dict[str, str],
        internal_name: str,
        fallback: Any = None,
    ) -> Any:
        source_name = field_map.get(internal_name, internal_name)
        if source_name in row:
            return row[source_name]
        return fallback

    def _project_payload(self, row: dict[str, Any], field_map: dict[str, str]) -> dict[str, Any]:
        settings = get_settings()
        external_id = self._value(
            row,
            field_map,
            LegacyProjectField.EXTERNAL_ID,
            row.get(LegacyProjectField.ID),
        )
        raw_code = self._value(row, field_map, LegacyProjectField.CODE, None)
        code = None
        if raw_code:
            code = str(raw_code)
        elif external_id is not None:
            code = LEGACY_PROJECT_CODE_TEMPLATE.format(
                prefix=settings.legacy_project_code_prefix,
                external_id=external_id,
            )
        return {
            LegacyProjectField.CODE: code,
            LegacyProjectField.EXTERNAL_ID: str(external_id) if external_id is not None else code,
            LegacyProjectField.SOURCE_SYSTEM: SourceSystem.LEGACY_MYSQL,
            LegacyProjectField.NAME: self._value(
                row,
                field_map,
                LegacyProjectField.NAME,
                LEGACY_UNNAMED_PROJECT,
            ),
            LegacyProjectField.OWNER: self._value(row, field_map, LegacyProjectField.OWNER, None),
            LegacyProjectField.STATUS: self._value(row, field_map, LegacyProjectField.STATUS, StatusValue.UNKNOWN),
            LegacyProjectField.PROGRESS_PERCENT: int(
                self._value(
                    row,
                    field_map,
                    LegacyProjectField.PROGRESS_PERCENT,
                    row.get(LegacyProjectField.PROGRESS) or 0,
                )
                or 0
            ),
            LegacyProjectField.START_DATE: self._value(row, field_map, LegacyProjectField.START_DATE, None),
            LegacyProjectField.DUE_DATE: self._value(row, field_map, LegacyProjectField.DUE_DATE, None),
            LegacyProjectField.BUDGET_AMOUNT: (
                self._value(row, field_map, LegacyProjectField.BUDGET_AMOUNT, row.get(LegacyProjectField.BUDGET) or 0) or 0
            ),
            LegacyProjectField.ACTUAL_AMOUNT: (
                self._value(row, field_map, LegacyProjectField.ACTUAL_AMOUNT, row.get(LegacyProjectField.ACTUAL_COST) or 0) or 0
            ),
            LegacyProjectField.DESCRIPTION: self._value(row, field_map, LegacyProjectField.DESCRIPTION, None),
        }

    def _task_payload(self, row: dict[str, Any], field_map: dict[str, str]) -> dict[str, Any]:
        settings = get_settings()
        external_id = self._value(
            row,
            field_map,
            LegacyTaskField.EXTERNAL_ID,
            row.get(LegacyTaskField.ID),
        )
        raw_code = self._value(row, field_map, LegacyTaskField.CODE, None)
        code = None
        if raw_code:
            code = str(raw_code)
        elif external_id is not None:
            code = LEGACY_TASK_CODE_TEMPLATE.format(
                prefix=settings.legacy_task_code_prefix,
                external_id=external_id,
            )
        return {
            LegacyTaskField.CODE: code,
            LegacyTaskField.EXTERNAL_ID: str(external_id) if external_id is not None else code,
            LegacyTaskField.SOURCE_SYSTEM: SourceSystem.LEGACY_MYSQL,
            LegacyTaskField.TITLE: self._value(
                row,
                field_map,
                LegacyTaskField.TITLE,
                LEGACY_UNNAMED_TASK,
            ),
            LegacyTaskField.PROJECT_CODE: self._value(
                row,
                field_map,
                LegacyTaskField.PROJECT_CODE,
                None,
            ),
            LegacyTaskField.OWNER: self._value(row, field_map, LegacyTaskField.OWNER, None),
            LegacyTaskField.STATUS: self._value(
                row,
                field_map,
                LegacyTaskField.STATUS,
                StatusValue.TODO,
            ),
            LegacyTaskField.PRIORITY: self._value(
                row,
                field_map,
                LegacyTaskField.PRIORITY,
                "P2",
            ),
            LegacyTaskField.DUE_DATE: self._value(row, field_map, LegacyTaskField.DUE_DATE, None),
            LegacyTaskField.COMPLETED_AT: self._value(
                row,
                field_map,
                LegacyTaskField.COMPLETED_AT,
                None,
            ),
            LegacyTaskField.BLOCKER: self._value(row, field_map, LegacyTaskField.BLOCKER, None),
            LegacyTaskField.DESCRIPTION: self._value(
                row,
                field_map,
                LegacyTaskField.DESCRIPTION,
                None,
            ),
        }

    def sync_projects(
        self,
        source_query: str | None = None,
        source_query_name: str | None = None,
        field_map: dict[str, str] | None = None,
        limit: int = 100,
        dry_run: bool = True,
        actor: str = ActorValue.API,
    ) -> dict[str, Any]:
        if self.db is None:
            raise HTTPException(
                status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
                detail=LegacyQueryError.APP_DB_UNAVAILABLE,
            )

        query_name = source_query_name or LegacyQueryName.PROJECTS
        if source_query:
            rows = self.execute_readonly(
                source_query,
                {LegacyResponseKey.LIMIT: limit},
                limit=limit,
            )[LegacyResponseKey.ROWS]
            query_ref = LegacySyncAction.ALLOWLISTED_INLINE_SQL
        else:
            rows = self.execute_allowed_query(
                query_name,
                {LegacyResponseKey.LIMIT: limit},
                limit=limit,
            )[LegacyResponseKey.ROWS]
            query_ref = _query_name_text(query_name)
        field_map = field_map or {}
        created = 0
        updated = 0
        skipped = 0
        items: list[dict[str, Any]] = []

        for row in rows:
            payload = self._project_payload(row, field_map)
            if not payload[LegacyProjectField.EXTERNAL_ID] and not payload[LegacyProjectField.CODE]:
                skipped += 1
                items.append(
                    {
                        LegacyResponseKey.ACTION: LegacySyncAction.SKIPPED,
                        LegacyResponseKey.REASON: LEGACY_SYNC_MISSING_ID_REASON,
                        LegacyResponseKey.SOURCE: row,
                    }
                )
                continue

            stmt = select(Project).where(
                Project.source_system == SourceSystem.LEGACY_MYSQL,
                Project.external_id == payload[LegacyProjectField.EXTERNAL_ID],
            )
            record = self.db.execute(stmt).scalar_one_or_none()
            if record is None:
                record = self.db.execute(
                    select(Project).where(Project.code == payload[LegacyProjectField.CODE])
                ).scalar_one_or_none()

            if record is None:
                created += 1
                action = LegacySyncAction.CREATE
                result = payload
                if not dry_run:
                    record = Project(**payload)
                    self.db.add(record)
                    self.db.flush()
                    result = serialize_model(record)
            else:
                updated += 1
                action = LegacySyncAction.UPDATE
                if not dry_run:
                    for key, value in payload.items():
                        setattr(record, key, value)
                    self.db.flush()
                    result = serialize_model(record)
                else:
                    result = payload
            items.append(
                {
                    LegacyResponseKey.ACTION: action,
                    LegacyResponseKey.PROJECT: result,
                    LegacyResponseKey.SOURCE: row,
                }
            )

        if not dry_run:
            self.db.commit()

        result = {
            LegacyResponseKey.DRY_RUN: dry_run,
            LegacyResponseKey.CREATED: created,
            LegacyResponseKey.UPDATED: updated,
            LegacyResponseKey.SKIPPED: skipped,
            LegacyResponseKey.ITEMS: items,
        }
        sync_run = LegacySyncRun(
            code=f"{LEGACY_SYNC_RUN_CODE_PREFIX}-{utc_now():%Y%m%d%H%M%S%f}",
            domain=BusinessDomain.PROJECTS,
            source_table=LEGACY_PROJECT_QUERY_SOURCE,
            status=StatusValue.DRY_RUN if dry_run else AuditStatus.SUCCESS,
            finished_at=utc_now(),
            created_count=created,
            updated_count=updated,
            skipped_count=skipped,
            note=LEGACY_PROJECT_SYNC_NOTE,
        )
        self.db.add(sync_run)
        self.db.commit()
        self.db.refresh(sync_run)
        result[LegacyResponseKey.SYNC_RUN_CODE] = sync_run.code

        AuditService(self.db).log(
            AuditLogCreate(
                actor=actor,
                source=AuditSource.LEGACY_MYSQL,
                action=AuditAction.LEGACY_SYNC_PROJECTS,
                target_type=BusinessDomain.PROJECTS,
                risk_level=AuditRiskLevel.MEDIUM,
                request_payload={
                    LegacyResponseKey.SOURCE_QUERY: query_ref,
                    LegacyResponseKey.FIELD_MAP: field_map,
                    LegacyResponseKey.LIMIT: limit,
                    LegacyResponseKey.DRY_RUN: dry_run,
                },
                response_payload={
                    key: result[key]
                    for key in [
                        LegacyResponseKey.DRY_RUN,
                        LegacyResponseKey.CREATED,
                        LegacyResponseKey.UPDATED,
                        LegacyResponseKey.SKIPPED,
                    ]
                },
            )
        )
        EventService(self.db).emit(
            event_type=EventType.LEGACY_SYNC_COMPLETED,
            source=EventSource.LEGACY_MYSQL,
            aggregate_type=EventAggregateType.LEGACY_SYNC_RUN,
            aggregate_id=sync_run.code,
            actor=actor,
            payload={
                EventPayloadKey.CODE: sync_run.code,
                EventPayloadKey.DOMAIN: BusinessDomain.PROJECTS,
                EventPayloadKey.STATUS: sync_run.status,
                EventPayloadKey.CREATED: created,
                EventPayloadKey.UPDATED: updated,
                EventPayloadKey.SKIPPED: skipped,
            },
            idempotency_key=f"legacy-sync:{sync_run.code}",
        )
        return result

    def sync_tasks(
        self,
        source_query: str | None = None,
        source_query_name: str | None = None,
        field_map: dict[str, str] | None = None,
        limit: int = 100,
        dry_run: bool = True,
        actor: str = ActorValue.API,
    ) -> dict[str, Any]:
        if self.db is None:
            raise HTTPException(
                status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
                detail=LegacyQueryError.APP_DB_UNAVAILABLE,
            )

        query_name = source_query_name or LegacyQueryName.TASKS
        if source_query:
            rows = self.execute_readonly(
                source_query,
                {LegacyResponseKey.LIMIT: limit},
                limit=limit,
            )[LegacyResponseKey.ROWS]
            query_ref = LegacySyncAction.ALLOWLISTED_INLINE_SQL
        else:
            rows = self.execute_allowed_query(
                query_name,
                {LegacyResponseKey.LIMIT: limit},
                limit=limit,
            )[LegacyResponseKey.ROWS]
            query_ref = _query_name_text(query_name)
        field_map = field_map or {}
        created = 0
        updated = 0
        skipped = 0
        items: list[dict[str, Any]] = []

        for row in rows:
            payload = self._task_payload(row, field_map)
            if not payload[LegacyTaskField.EXTERNAL_ID] and not payload[LegacyTaskField.CODE]:
                skipped += 1
                items.append(
                    {
                        LegacyResponseKey.ACTION: LegacySyncAction.SKIPPED,
                        LegacyResponseKey.REASON: LEGACY_SYNC_MISSING_ID_REASON,
                        LegacyResponseKey.SOURCE: row,
                    }
                )
                continue

            stmt = select(WorkTask).where(
                WorkTask.source_system == SourceSystem.LEGACY_MYSQL,
                WorkTask.external_id == payload[LegacyTaskField.EXTERNAL_ID],
            )
            record = self.db.execute(stmt).scalar_one_or_none()
            if record is None:
                record = self.db.execute(
                    select(WorkTask).where(WorkTask.code == payload[LegacyTaskField.CODE])
                ).scalar_one_or_none()

            if record is None:
                created += 1
                action = LegacySyncAction.CREATE
                result = payload
                if not dry_run:
                    record = WorkTask(**payload)
                    self.db.add(record)
                    self.db.flush()
                    result = serialize_model(record)
            else:
                updated += 1
                action = LegacySyncAction.UPDATE
                if not dry_run:
                    for key, value in payload.items():
                        setattr(record, key, value)
                    self.db.flush()
                    result = serialize_model(record)
                else:
                    result = payload
            items.append(
                {
                    LegacyResponseKey.ACTION: action,
                    LegacyResponseKey.TASK: result,
                    LegacyResponseKey.SOURCE: row,
                }
            )

        if not dry_run:
            self.db.commit()

        result = {
            LegacyResponseKey.DRY_RUN: dry_run,
            LegacyResponseKey.CREATED: created,
            LegacyResponseKey.UPDATED: updated,
            LegacyResponseKey.SKIPPED: skipped,
            LegacyResponseKey.ITEMS: items,
        }
        sync_run = LegacySyncRun(
            code=f"{LEGACY_TASK_SYNC_RUN_CODE_PREFIX}-{utc_now():%Y%m%d%H%M%S%f}",
            domain=BusinessDomain.TASKS,
            source_table=LEGACY_TASK_QUERY_SOURCE,
            status=StatusValue.DRY_RUN if dry_run else AuditStatus.SUCCESS,
            finished_at=utc_now(),
            created_count=created,
            updated_count=updated,
            skipped_count=skipped,
            note=LEGACY_TASK_SYNC_NOTE,
        )
        self.db.add(sync_run)
        self.db.commit()
        self.db.refresh(sync_run)
        result[LegacyResponseKey.SYNC_RUN_CODE] = sync_run.code

        AuditService(self.db).log(
            AuditLogCreate(
                actor=actor,
                source=AuditSource.LEGACY_MYSQL,
                action=AuditAction.LEGACY_SYNC_TASKS,
                target_type=BusinessDomain.TASKS,
                risk_level=AuditRiskLevel.MEDIUM,
                request_payload={
                    LegacyResponseKey.SOURCE_QUERY: query_ref,
                    LegacyResponseKey.FIELD_MAP: field_map,
                    LegacyResponseKey.LIMIT: limit,
                    LegacyResponseKey.DRY_RUN: dry_run,
                },
                response_payload={
                    key: result[key]
                    for key in [
                        LegacyResponseKey.DRY_RUN,
                        LegacyResponseKey.CREATED,
                        LegacyResponseKey.UPDATED,
                        LegacyResponseKey.SKIPPED,
                    ]
                },
            )
        )
        EventService(self.db).emit(
            event_type=EventType.LEGACY_SYNC_COMPLETED,
            source=EventSource.LEGACY_MYSQL,
            aggregate_type=EventAggregateType.LEGACY_SYNC_RUN,
            aggregate_id=sync_run.code,
            actor=actor,
            payload={
                EventPayloadKey.CODE: sync_run.code,
                EventPayloadKey.DOMAIN: BusinessDomain.TASKS,
                EventPayloadKey.STATUS: sync_run.status,
                EventPayloadKey.CREATED: created,
                EventPayloadKey.UPDATED: updated,
                EventPayloadKey.SKIPPED: skipped,
            },
            idempotency_key=f"legacy-sync:{sync_run.code}",
        )
        return result