"""Unified database backend configuration.

Controls BOTH the LangGraph checkpointer and the DeerFlow application
persistence layer (runs, threads metadata, users, etc.). The user
configures one backend; the system handles physical separation details.

SQLite mode: checkpointer and app share a single .db file
({sqlite_dir}/deerflow.db) with WAL journal mode enabled on every
connection. WAL allows concurrent readers and a single writer without
blocking, making a unified file safe for both workloads.  Writers
that contend for the lock wait via the default 5-second sqlite3
busy timeout rather than failing immediately.

Postgres mode: both use the same database URL but maintain independent
connection pools with different lifecycles.

Memory mode: checkpointer uses MemorySaver, app uses in-memory stores.
No database is initialized.

Sensitive values (postgres_url) should use $VAR syntax in config.yaml
to reference environment variables from .env:

    database:
      backend: postgres
      postgres_url: $DATABASE_URL

The $VAR resolution is handled by AppConfig.resolve_env_variables()
before this config is instantiated -- DatabaseConfig itself does not
need to do any environment variable processing.
"""

from __future__ import annotations

import os
from typing import Literal

from pydantic import BaseModel, Field

CheckpointChannelMode = Literal["full", "delta"]


class DatabaseConfig(BaseModel):
    backend: Literal["memory", "sqlite", "postgres"] = Field(
        default="memory",
        description=("Storage backend for both checkpointer and application data. 'memory' for development (no persistence across restarts), 'sqlite' for single-node deployment, 'postgres' for production multi-node deployment."),
    )
    checkpoint_channel_mode: CheckpointChannelMode = Field(
        default="full",
        description=(
            "Checkpoint representation for accumulating channels. "
            "'full' preserves full-value message checkpoints; 'delta' uses "
            "LangGraph DeltaChannel for messages. Restart is required, and all "
            "processes sharing one checkpoint database must use the same value."
        ),
    )
    checkpoint_delta_snapshot_frequency: int = Field(
        default=1000,
        ge=1,
        description=(
            "DeltaChannel snapshot frequency used in checkpoint 'delta' mode: "
            "every N message-channel writes the saver stores a full snapshot "
            "instead of a delta sentinel. Restart-required, and all processes "
            "sharing one checkpoint database must use the same value."
        ),
    )
    sqlite_dir: str = Field(
        default=".deer-flow/data",
        description=("Directory for the SQLite database file. Both checkpointer and application data share {sqlite_dir}/deerflow.db."),
    )
    postgres_url: str = Field(
        default="",
        description=(
            "PostgreSQL connection URL, shared by checkpointer and app. "
            "Use $DATABASE_URL in config.yaml to reference .env. "
            "Example: postgresql://user:pass@host:5432/deerflow "
            "(the +asyncpg driver suffix is added automatically where needed)."
        ),
    )
    echo_sql: bool = Field(
        default=False,
        description="Echo all SQL statements to log (debug only).",
    )
    pool_size: int = Field(
        default=5,
        description="Connection pool size for the app ORM engine (postgres only).",
    )
    pool_recycle: int = Field(
        default=300,
        gt=0,
        description="Seconds before app ORM PostgreSQL connections are recycled.",
    )
    command_timeout: float | None = Field(
        default=30,
        gt=0,
        description="Timeout in seconds for app ORM PostgreSQL commands. Set to null to disable the command timeout.",
    )

    # -- Derived helpers (not user-configured) --

    @property
    def _resolved_sqlite_dir(self) -> str:
        """Resolve sqlite_dir to an absolute path (relative to CWD)."""
        from pathlib import Path

        return str(Path(self.sqlite_dir).resolve())

    @property
    def sqlite_path(self) -> str:
        """Unified SQLite file path shared by checkpointer and app."""
        return os.path.join(self._resolved_sqlite_dir, "deerflow.db")

    # Backward-compatible aliases
    @property
    def checkpointer_sqlite_path(self) -> str:
        """SQLite file path for the LangGraph checkpointer (alias for sqlite_path)."""
        return self.sqlite_path

    @property
    def app_sqlite_path(self) -> str:
        """SQLite file path for application ORM data (alias for sqlite_path)."""
        return self.sqlite_path

    @property
    def app_sqlalchemy_url(self) -> str:
        """SQLAlchemy async URL for the application ORM engine."""
        if self.backend == "sqlite":
            return f"sqlite+aiosqlite:///{self.sqlite_path}"
        if self.backend == "postgres":
            url = self.postgres_url
            if url.startswith("postgresql://"):
                url = url.replace("postgresql://", "postgresql+asyncpg://", 1)
            elif url.startswith("postgres://"):
                # libpq's short alias: accepted by the psycopg checkpointer, but not a SQLAlchemy dialect.
                url = url.replace("postgres://", "postgresql+asyncpg://", 1)
            return url
        raise ValueError(f"No SQLAlchemy URL for backend={self.backend!r}")

    @property
    def app_sync_sqlalchemy_url(self) -> str:
        """SQLAlchemy *synchronous* URL for the application ORM data.

        Used by the ``agent_storage.backend: db`` store, whose consumers (the
        LangGraph graph factory, the setup/update tools) are synchronous and may
        run on the event loop or in a separate process from the gateway, where an
        async engine cannot be driven. Points at the same database file/server as
        :meth:`app_sqlalchemy_url`; only the driver differs (both drivers —
        stdlib sqlite3 and psycopg — ship with the app, so this adds no
        dependency).
        """
        if self.backend == "sqlite":
            return f"sqlite:///{self.sqlite_path}"
        if self.backend == "postgres":
            url = self.postgres_url
            if url.startswith("postgresql+asyncpg://"):
                url = url.replace("postgresql+asyncpg://", "postgresql+psycopg://", 1)
            elif url.startswith("postgresql://"):
                url = url.replace("postgresql://", "postgresql+psycopg://", 1)
            elif url.startswith("postgres://"):
                url = url.replace("postgres://", "postgresql+psycopg://", 1)
            return url
        raise ValueError(f"No SQLAlchemy URL for backend={self.backend!r}")