"""Application database schema definition and initialisation.

BanGUI maintains its own SQLite database that stores configuration, session
state, blocklist source definitions, and import run logs.  This module is
the single source of truth for the schema — all ``CREATE TABLE`` statements
live here and are applied on first run via :func:`init_db`.

The fail2ban database is separate and is accessed read-only by the history
and ban services.
"""

import aiosqlite
import structlog

log: structlog.stdlib.BoundLogger = structlog.get_logger()

# ---------------------------------------------------------------------------
# DDL statements
# ---------------------------------------------------------------------------

_CREATE_SETTINGS: str = """
CREATE TABLE IF NOT EXISTS settings (
    id          INTEGER PRIMARY KEY AUTOINCREMENT,
    key         TEXT    NOT NULL UNIQUE,
    value       TEXT    NOT NULL,
    created_at  TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
    updated_at  TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now'))
);
"""

_CREATE_SESSIONS: str = """
CREATE TABLE IF NOT EXISTS sessions (
    id              INTEGER PRIMARY KEY AUTOINCREMENT,
    token_hash      TEXT    NOT NULL UNIQUE,
    created_at      TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
    expires_at      TEXT    NOT NULL
);
"""

_CREATE_SESSIONS_TOKEN_INDEX: str = """
CREATE UNIQUE INDEX IF NOT EXISTS idx_sessions_token_hash ON sessions (token_hash);
"""

_CREATE_BLOCKLIST_SOURCES: str = """
CREATE TABLE IF NOT EXISTS blocklist_sources (
    id          INTEGER PRIMARY KEY AUTOINCREMENT,
    name        TEXT    NOT NULL,
    url         TEXT    NOT NULL UNIQUE,
    enabled     INTEGER NOT NULL DEFAULT 1,
    created_at  TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
    updated_at  TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now'))
);
"""

_CREATE_IMPORT_LOG: str = """
CREATE TABLE IF NOT EXISTS import_log (
    id              INTEGER PRIMARY KEY AUTOINCREMENT,
    source_id       INTEGER REFERENCES blocklist_sources(id) ON DELETE SET NULL,
    source_url      TEXT    NOT NULL,
    timestamp       TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
    ips_imported    INTEGER NOT NULL DEFAULT 0,
    ips_skipped     INTEGER NOT NULL DEFAULT 0,
    errors          TEXT
);
"""

_CREATE_GEO_CACHE: str = """
CREATE TABLE IF NOT EXISTS geo_cache (
    ip              TEXT    PRIMARY KEY,
    country_code    TEXT,
    country_name    TEXT,
    asn             TEXT,
    org             TEXT,
    cached_at       TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now'))
);
"""

_CREATE_HISTORY_ARCHIVE: str = """
CREATE TABLE IF NOT EXISTS history_archive (
    id          INTEGER PRIMARY KEY AUTOINCREMENT,
    jail        TEXT    NOT NULL,
    ip          TEXT    NOT NULL,
    timeofban   INTEGER NOT NULL,
    bancount    INTEGER NOT NULL,
    data        TEXT    NOT NULL,
    action      TEXT    NOT NULL CHECK(action IN ('ban', 'unban')),
    created_at  TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
    UNIQUE(ip, jail, action, timeofban)
);
"""

_CREATE_SCHEMA_MIGRATIONS: str = """
CREATE TABLE IF NOT EXISTS schema_migrations (
    version     INTEGER PRIMARY KEY,
    migrated_at TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now'))
);
"""

# Ordered list of DDL statements to execute on initialisation.
_SCHEMA_STATEMENTS: list[str] = [
    _CREATE_SETTINGS,
    _CREATE_SESSIONS,
    _CREATE_SESSIONS_TOKEN_INDEX,
    _CREATE_BLOCKLIST_SOURCES,
    _CREATE_IMPORT_LOG,
    _CREATE_GEO_CACHE,
    _CREATE_HISTORY_ARCHIVE,
]

_CURRENT_SCHEMA_VERSION: int = 6

_MIGRATIONS: dict[int, str] = {
    1: "\n".join(_SCHEMA_STATEMENTS),
    2: """
-- Migration 2: Hash session tokens for security.
-- Drop the old sessions table and recreate with token_hash column.
-- This invalidates all existing sessions, which is acceptable as the DB
-- contents were exposed in plaintext.
DROP TABLE IF EXISTS sessions;
CREATE TABLE sessions (
    id              INTEGER PRIMARY KEY AUTOINCREMENT,
    token_hash      TEXT    NOT NULL UNIQUE,
    created_at      TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
    expires_at      TEXT    NOT NULL
);
CREATE UNIQUE INDEX idx_sessions_token_hash ON sessions (token_hash);
""",
    3: """
-- Migration 3: Add last_seen timestamp to geo_cache for retention policy.
-- Tracks when each IP was last referenced to enable purging of stale entries.
-- Default to current timestamp for existing rows.
ALTER TABLE geo_cache ADD COLUMN last_seen TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now'));
""",
    4: """
-- Migration 4: Add scheduler_lock table for multi-worker safety.
-- Implements database-backed locking to ensure only one worker runs the scheduler.
-- Uses atomic transactions to prevent race conditions in container orchestration.
-- Lock is held by the process that successfully inserts the singleton row (id=1).
CREATE TABLE scheduler_lock (
    id INTEGER PRIMARY KEY CHECK (id = 1),
    pid INTEGER NOT NULL,
    hostname TEXT NOT NULL,
    created_at REAL NOT NULL,
    heartbeat_at REAL NOT NULL
);
""",
    5: """
-- Migration 5: Add indexes to history_archive table for query performance.
-- The history_archive table supports filtering by jail, IP, action, and time range,
-- combined with pagination (ORDER BY timeofban DESC LIMIT/OFFSET).
-- These indexes accelerate common dashboard and API queries.
-- See Docs/Backend-Development.md § Database Performance for details.

-- Composite index for common queries: jail + timeofban ordering (dashboard filter).
CREATE INDEX IF NOT EXISTS idx_history_archive_jail_timeofban
    ON history_archive (jail, timeofban DESC);

-- Composite index for time-range + jail queries (history timeline filters).
CREATE INDEX IF NOT EXISTS idx_history_archive_timeofban_jail_action
    ON history_archive (timeofban DESC, jail, action);

-- Index for single-column filters: supports IP prefix searches and exact matches.
CREATE INDEX IF NOT EXISTS idx_history_archive_ip
    ON history_archive (ip);

-- Index for action-based queries: supports ban/unban filtering.
CREATE INDEX IF NOT EXISTS idx_history_archive_action
    ON history_archive (action);
""",
    6: """
-- Migration 6: Add import_runs table for tracking blocklist import idempotency.
-- Tracks unique imports by source and content hash to enable idempotent retries.
-- On import crash, retry will detect the operation_id and skip duplicate bans.
-- This prevents duplicate IP bans if the scheduler retries after a failure.
CREATE TABLE IF NOT EXISTS import_runs (
    id              INTEGER PRIMARY KEY AUTOINCREMENT,
    source_id       INTEGER NOT NULL REFERENCES blocklist_sources(id) ON DELETE CASCADE,
    content_hash    TEXT    NOT NULL,
    status          TEXT    NOT NULL CHECK(status IN ('pending', 'completed', 'failed')),
    imported_count  INTEGER NOT NULL DEFAULT 0,
    skipped_count   INTEGER NOT NULL DEFAULT 0,
    error_message   TEXT,
    created_at      TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
    updated_at      TEXT    NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
    UNIQUE(source_id, content_hash)
);
-- Index for looking up completed imports by source
CREATE INDEX IF NOT EXISTS idx_import_runs_source_status
    ON import_runs (source_id, status);
""",
}


# ---------------------------------------------------------------------------
# Public API
# ---------------------------------------------------------------------------


async def _configure_connection(db: aiosqlite.Connection) -> None:
    """Apply hardening pragmas to a newly-opened SQLite connection."""
    await db.execute("PRAGMA journal_mode=WAL;")
    await db.execute("PRAGMA foreign_keys=ON;")
    await db.execute("PRAGMA busy_timeout=5000;")


async def _get_current_schema_version(db: aiosqlite.Connection) -> int:
    """Return the highest applied schema version for the given database."""
    await db.execute(_CREATE_SCHEMA_MIGRATIONS)
    async with db.execute("SELECT MAX(version) FROM schema_migrations;") as cursor:
        row = await cursor.fetchone()
    if row is None or row[0] is None:
        return 0
    return int(row[0])


async def _parse_migration_statements(script: str) -> list[str]:
    """Parse a migration script into individual SQL statements.

    Splits on semicolons but ignores semicolons inside string literals and
    comments. Handles both block (-- comment) and line comments.

    Args:
        script: The raw migration script.

    Returns:
        List of SQL statements (stripped of whitespace and comments).
    """
    statements: list[str] = []
    current_stmt: list[str] = []
    i = 0

    while i < len(script):
        char = script[i]

        # Skip block comments (-- ...)
        if i < len(script) - 1 and script[i:i+2] == "--":
            while i < len(script) and script[i] != "\n":
                i += 1
            i += 1
            continue

        # Skip line comments (/* ... */)
        if i < len(script) - 1 and script[i:i+2] == "/*":
            i += 2
            while i < len(script) - 1:
                if script[i:i+2] == "*/":
                    i += 2
                    break
                i += 1
            continue

        # Handle string literals (single or double quotes)
        if char in ("'", '"'):
            quote = char
            current_stmt.append(char)
            i += 1
            while i < len(script):
                if script[i] == quote:
                    if i + 1 < len(script) and script[i + 1] == quote:
                        # Escaped quote
                        current_stmt.append(quote)
                        current_stmt.append(quote)
                        i += 2
                    else:
                        # End of string
                        current_stmt.append(quote)
                        i += 1
                        break
                else:
                    current_stmt.append(script[i])
                    i += 1
            continue

        # Statement separator
        if char == ";":
            stmt = "".join(current_stmt).strip()
            if stmt:
                statements.append(stmt)
            current_stmt = []
            i += 1
            continue

        current_stmt.append(char)
        i += 1

    # Add any remaining statement
    stmt = "".join(current_stmt).strip()
    if stmt:
        statements.append(stmt)

    return statements


async def _apply_migration(db: aiosqlite.Connection, version: int) -> None:
    """Apply a single migration step and record its completion atomically.

    Wraps all DDL statements and the schema_migrations insert in a single
    BEGIN IMMEDIATE ... COMMIT transaction to ensure atomicity. If any
    statement fails, the entire migration is rolled back.

    Args:
        db: An open aiosqlite.Connection.
        version: The migration version number.

    Raises:
        Any exception from executing the migration statements or inserting
        the schema migration record will cause a rollback.
    """
    migration_script = _MIGRATIONS[version]
    statements = await _parse_migration_statements(migration_script)

    try:
        await db.execute("BEGIN IMMEDIATE;")

        for statement in statements:
            await db.execute(statement)

        await db.execute("INSERT INTO schema_migrations (version) VALUES (?);", (version,))

        await db.commit()
    except Exception:
        await db.rollback()
        raise


async def _migrate_schema(db: aiosqlite.Connection) -> None:
    """Migrate the database schema to the latest supported version."""
    current_version = await _get_current_schema_version(db)
    if current_version == _CURRENT_SCHEMA_VERSION:
        return

    if current_version > _CURRENT_SCHEMA_VERSION:
        raise RuntimeError(
            f"database schema version {current_version} is newer than supported "
            f"version {_CURRENT_SCHEMA_VERSION}"
        )

    log.info("migrating_database_schema", from_version=current_version, to_version=_CURRENT_SCHEMA_VERSION)
    for next_version in range(current_version + 1, _CURRENT_SCHEMA_VERSION + 1):
        await _apply_migration(db, next_version)
    log.info("database_schema_ready", schema_version=_CURRENT_SCHEMA_VERSION)


async def init_db(db: aiosqlite.Connection) -> None:
    """Create or migrate the BanGUI application database schema.

    This function is idempotent — calling it on an already-initialised
    database has no effect.  It should be called once during application
    startup inside the FastAPI lifespan handler.

    Args:
        db: An open :class:`aiosqlite.Connection` to the application database.
    """
    log.info("initialising_database_schema")
    await _configure_connection(db)
    await _migrate_schema(db)


async def open_db(database_path: str) -> aiosqlite.Connection:
    """Open a new application SQLite connection with the standard settings.

    Args:
        database_path: Path to the BanGUI SQLite database.

    Returns:
        A configured :class:`aiosqlite.Connection` instance.
    """
    db = await aiosqlite.connect(database_path)
    db.row_factory = aiosqlite.Row
    await _configure_connection(db)
    return db