//
//  SQLitePreferenceStore.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 Foundation
import Logging
import LuminateCore

private let logger = Logger(label: "\(AppInfo.identifier).store")

/// A SQLite-backed preference store with an ordered asynchronous write queue.
package actor SQLitePreferenceStore: PreferenceStoring {
    private let database: SQLiteDatabase
    package nonisolated let initialSnapshot: [String: StoredPreference]
    private nonisolated let continuation: AsyncStream<PreferenceWrite>.Continuation
    private var pendingFailure: PreferenceStoreError?

    /// Opens, migrates, and snapshots the preference database at `url`.
    ///
    /// - Parameter url: The database file location.
    /// - Throws: ``PreferenceStoreError`` when the database cannot be opened or migrated.
    package init(url: URL) throws {
        let database = try SQLiteDatabase(url: url)
        try SchemaMigrator.migrate(database)
        initialSnapshot = try Self.loadAllPreferences(from: database)
        self.database = database
        let (stream, continuation) = AsyncStream<PreferenceWrite>.makeStream(bufferingPolicy: .unbounded)
        self.continuation = continuation
        Task { [weak self] in
            for await write in stream {
                guard let self else { break }
                await self.apply(write)
            }
        }
    }

    deinit {
        continuation.finish()
    }

    /// Queues a value update or deletion without blocking the caller.
    package nonisolated func enqueue(_ key: String, _ value: StoredPreference?) {
        continuation.yield(.set(key: key, value: value))
    }

    /// Returns after queued writes have been committed to SQLite.
    ///
    /// - Throws: The first write failure recorded since the previous flush.
    package nonisolated func flush() async throws {
        try await withCheckedThrowingContinuation { (continuation: CheckedContinuation<Void, any Error>) in
            self.continuation.yield(
                .barrier { error in
                    if let error {
                        continuation.resume(throwing: error)
                    } else {
                        continuation.resume(returning: ())
                    }
                })
        }
    }

    private func apply(_ write: PreferenceWrite) {
        switch write {
        case .set(let key, let value):
            do {
                try Self.writePreference(to: database, key: key, value: value)
            } catch {
                let failure = (error as? PreferenceStoreError) ?? .sqlite(message: "\(error)")
                logger.error("Preference write failed", error: failure, metadata: ["key": "\(key)"])
                if pendingFailure == nil {
                    pendingFailure = failure
                }
            }
        case .barrier(let resume):
            let failure = pendingFailure
            pendingFailure = nil
            resume(failure)
        }
    }

    /// Reads every non-NULL row from the preference table.
    ///
    /// - Parameter database: The open SQLite connection containing the preference table.
    /// - Returns: Raw preference values keyed by their stable row names.
    /// - Throws: ``PreferenceStoreError`` when querying the table fails.
    private static func loadAllPreferences(from database: SQLiteDatabase) throws -> [String: StoredPreference] {
        let statement = try SQLiteStatement(database: database, sql: "SELECT key, value FROM preference;")
        var values: [String: StoredPreference] = [:]
        while try statement.step() {
            guard let key = statement.text(at: 0), let value = statement.preference(at: 1) else { continue }
            values[key] = value
        }
        return values
    }

    /// Inserts or updates one preference row, or deletes it when `value` is `nil`.
    ///
    /// - Parameters:
    ///   - database: The open SQLite connection containing the preference table.
    ///   - key: The stable row key.
    ///   - value: The scalar value to store, or `nil` to delete the row.
    /// - Throws: ``PreferenceStoreError`` when the statement fails.
    private static func writePreference(
        to database: SQLiteDatabase,
        key: String,
        value: StoredPreference?
    ) throws {
        if let value {
            let statement = try SQLiteStatement(
                database: database,
                sql: "INSERT INTO preference (key, value) VALUES (?1, ?2) "
                    + "ON CONFLICT(key) DO UPDATE SET value = excluded.value;"
            )
            try statement.bind(1, text: key)
            try statement.bind(2, value)
            _ = try statement.step()
        } else {
            let statement = try SQLiteStatement(database: database, sql: "DELETE FROM preference WHERE key = ?1;")
            try statement.bind(1, text: key)
            _ = try statement.step()
        }
    }
}