//
//  SQLiteDatabase.swift
//
//  Copyright 2026 Brendan Szymanski <hello@bscubed.dev>
//
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with this program.  If not, see <https://www.gnu.org/licenses/>.
//
//  SPDX-License-Identifier: GPL-3.0-or-later
//

import CSQLite
import Foundation
import LuminateCore

/// A synchronous SQLite connection owned by the storage actor.
package final class SQLiteDatabase {
    package let handle: OpaquePointer

    /// Opens or creates a private SQLite database at `url` and configures local durability.
    ///
    /// - Parameter url: The database file location.
    /// - Throws: ``PreferenceStoreError/cannotOpen(path:message:)`` when SQLite cannot open it.
    package init(url: URL) throws {
        let directory = url.deletingLastPathComponent()
        try FileManager.default.createDirectory(
            at: directory,
            withIntermediateDirectories: true,
            attributes: [.posixPermissions: 0o700]
        )

        var opened: OpaquePointer?
        let result = url.path.withCString { path in
            sqlite3_open_v2(
                path,
                &opened,
                SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE | SQLITE_OPEN_NOMUTEX,
                nil
            )
        }
        guard result == SQLITE_OK, let opened else {
            let message = opened.map { String(cString: sqlite3_errmsg($0)) } ?? "SQLite returned no handle"
            if let opened { sqlite3_close_v2(opened) }
            throw PreferenceStoreError.cannotOpen(path: url.path, message: message)
        }
        handle = opened
        try? FileManager.default.setAttributes([.posixPermissions: 0o600], ofItemAtPath: url.path)
        try exec("PRAGMA journal_mode = WAL;")
        try exec("PRAGMA synchronous = NORMAL;")
        try exec("PRAGMA foreign_keys = ON;")
        // SQLite has no busy handler by default, so concurrent writers would fail immediately.
        try exec("PRAGMA busy_timeout = 5000;")
    }

    deinit {
        sqlite3_close_v2(handle)
    }

    /// The latest SQLite diagnostic for this connection.
    package var errorMessage: String {
        String(cString: sqlite3_errmsg(handle))
    }

    /// Executes SQL that does not return rows.
    ///
    /// - Parameter sql: The SQL statements to execute.
    /// - Throws: ``PreferenceStoreError/sqlite(message:)`` when execution fails.
    package func exec(_ sql: String) throws {
        var errorPointer: UnsafeMutablePointer<CChar>?
        let result = sqlite3_exec(handle, sql, nil, nil, &errorPointer)
        defer {
            if let errorPointer { sqlite3_free(errorPointer) }
        }
        guard result == SQLITE_OK else {
            let message = errorPointer.map { String(cString: $0) } ?? errorMessage
            throw PreferenceStoreError.sqlite(message: message)
        }
    }

    /// Runs a closure inside one SQLite transaction and rolls back failures.
    ///
    /// - Parameter body: Statements to execute while the transaction is open.
    /// - Throws: The first error raised by the body or transaction control statements.
    package func transaction(_ body: () throws -> Void) throws {
        try exec("BEGIN;")
        do {
            try body()
            try exec("COMMIT;")
        } catch {
            try? exec("ROLLBACK;")
            throw error
        }
    }

    /// Reads SQLite's schema version pragma.
    package var userVersion: Int32 {
        get throws {
            let statement = try SQLiteStatement(database: self, sql: "PRAGMA user_version;")
            guard try statement.step() else { throw PreferenceStoreError.sqlite(message: errorMessage) }
            return statement.integer(at: 0)
        }
    }

    /// Sets SQLite's schema version pragma.
    ///
    /// - Parameter version: The non-negative schema version.
    /// - Throws: ``PreferenceStoreError/sqlite(message:)`` when SQLite rejects the pragma.
    package func setUserVersion(_ version: Int32) throws {
        try exec("PRAGMA user_version = \(version);")
    }

    /// Reads SQLite's application identifier pragma.
    package var applicationID: Int32 {
        get throws {
            let statement = try SQLiteStatement(database: self, sql: "PRAGMA application_id;")
            guard try statement.step() else { throw PreferenceStoreError.sqlite(message: errorMessage) }
            return statement.integer(at: 0)
        }
    }

    /// Sets SQLite's application identifier pragma.
    ///
    /// - Parameter applicationID: The application identifier to persist in the file header.
    /// - Throws: ``PreferenceStoreError/sqlite(message:)`` when SQLite rejects the pragma.
    package func setApplicationID(_ applicationID: Int32) throws {
        try exec("PRAGMA application_id = \(applicationID);")
    }

}