import sqlite3
from contextlib import contextmanager
from flask import current_app

class DB:
    def __init__(self):
        self._transaction_depth = 0
        self._connection = None


    @contextmanager
    def _get_connection(self):
        if self._connection and self._transaction_depth > 0:
            yield self._connection
            return

        conn = sqlite3.connect(current_app.config["DB_PATH"])
        conn.row_factory = sqlite3.Row
        conn.execute("PRAGMA FOREIGN_KEYS = 1")

        try:
            yield conn
        finally:
            if self._transaction_depth == 0:
                conn.close()


    @contextmanager
    def transaction(self):
        """Transaction context."""
        self.begin()
        try:
            yield
            self.commit()
        except Exception:
            self.rollback()
            raise


    def begin(self):
        """Begins a new transaction."""
        if self._transaction_depth == 0:
            if not self._connection:
                self._connection = sqlite3.connect(current_app.config["DB_PATH"])
                self._connection.row_factory = sqlite3.Row
                self._connection.execute("PRAGMA FOREIGN_KEYS = 1")
            self._connection.execute("BEGIN")
        self._transaction_depth += 1


    def commit(self):
        """Commits the current transaction."""
        if self._transaction_depth > 0:
            self._transaction_depth -= 1
            if self._transaction_depth == 0:
                self._connection.commit()


    def rollback(self):
        """Rolls back the current transaction."""
        if self._transaction_depth > 0:
            self._transaction_depth = 0
            self._connection.rollback()


    def query(self, sql, *args):
        """Executes a query and returns a list of dictionaries."""
        with self._get_connection() as conn:
            rows = conn.execute(sql, args).fetchall()
            return [dict(row) for row in rows]


    def insert(self, table, columns, *values):
        if isinstance(columns, (list, tuple)):
            columns = ", ".join(columns)

        placeholders = ", ".join(["?"] * len(values))
        sql = f"""
            INSERT INTO {table} ({columns})
            VALUES ({placeholders})
            RETURNING *
        """

        with self._get_connection() as conn:
            result = conn.execute(sql, values).fetchone()
            conn.commit()
            return dict(result) if result else None


    def execute(self, sql, *args):
        """Executes a query without returning."""
        with self._get_connection() as conn:
            conn.execute(sql, args)
            conn.commit()


    def fetch_one(self, sql, *args):
        """Grabs the first row of a query."""
        with self._get_connection() as conn:
            row = conn.execute(sql, args).fetchone()
            return dict(row) if row else None


    class QueryBuilder:
        def __init__(self, table):
            self.table = table
            self._where = {}
            self._select = "*"
            self._params = []


        def select(self, columns = "*"):
            self._select = columns
            return self


        def where(self, condition):
            self._where.update(condition)
            return self


        def build_select(self):
            sql = f"SELECT {self._select} FROM {self.table}"
            if self._where:
                conditions = " AND ".join(f"{k} = ?" for k in self._where.keys())
                sql += f" WHERE {conditions}"
            return sql, list(self._where.values())


        def build_update(self, data):
            columns = ", ".join(f"{k} = ?" for k in data.keys())
            sql = f"UPDATE {self.table} SET {columns}"
            if self._where:
                conditions = " AND ".join(f"{k} = ?" for k in self._where.keys())
                sql += f" WHERE {conditions}"
            params = list(data.values()) + list(self._where.values())
            return sql, params


        def build_delete(self):
            sql = f"DELETE FROM {self.table}"
            if self._where:
                conditions = " AND ".join(f"{k} = ?" for k in self._where.keys())
                sql += f" WHERE {conditions}"
            return sql, list(self._where.values())


        def first(self):
            sql, params = self.build_select()
            return db.fetch_one(f"{sql} LIMIT 1", *params)


        def all(self):
            sql, params = self.build_select()
            return db.query(sql, *params)


class Model:
    def __init__(self, table):
        self.table = table
        self._data = {}


    def __getitem__(self, key):
        return self._data[key]


    def __getattr__(self, key):
        try:
            return self._data[key]
        except KeyError:
            raise AttributeError(f"No column '{key}'")


    @classmethod
    def find(cls, condition):
        row = db.QueryBuilder(cls.table)\
            .where(condition)\
            .first()
        if not row:
            return None
        instance = cls(cls.table)
        instance._data = dict(row)
        return instance


    @classmethod
    def create(cls, values):
        if not values:
            return None

        columns = list(values.keys())
        row = db.insert(cls.table, columns, *values.values())

        if row:
            instance = cls(cls.table)
            instance._data = row
            return instance
        return None


    @classmethod
    def count(cls, conditions = None):
        qb = db.QueryBuilder(cls.table).select("COUNT(*) AS c")
        if conditions is not None:
            qb.where(conditions)

        result = qb.first()
        return result["c"] if result else 0


    def update(self, data):
        qb = db.QueryBuilder(self.table)\
            .where({"id": self._data["id"]})
        sql, params = qb.build_update(data)
        db.execute(sql, *params)
        self._data.update(data)


    def delete(self):
        qb = db.QueryBuilder(self.table)\
            .where({"id": self._data["id"]})
        sql, params = qb.build_delete()
        db.execute(sql, *params)
        self._data = {}

db = DB()