import GRDB
import os.log

/// `AppDatabase` lets the application access the database.
///
/// You create an `AppDatabase` with a connection to an SQLite database
/// (see <https://swiftpackageindex.com/groue/grdb.swift/documentation/grdb/databaseconnections>).
///
/// Create those connections with a configuration returned from
/// `AppDatabase/makeConfiguration(_:)`.
///
/// For example:
///
/// ```swift
/// // Create an in-memory AppDatabase
/// let config = AppDatabase.makeConfiguration()
/// let dbQueue = try DatabaseQueue(configuration: config)
/// let appDatabase = try AppDatabase(dbQueue)
/// ```
struct AppDatabase {
    /// Creates an `AppDatabase`, and makes sure the database schema
    /// is ready.
    ///
    /// - important: Create the `DatabaseWriter` with a configuration
    ///   returned by ``makeConfiguration(_:)``.
    init(_ dbWriter: any DatabaseWriter) throws {
        self.dbWriter = dbWriter
        try migrator.migrate(dbWriter)
    }
    
    /// Provides access to the database.
    ///
    /// Application can use a `DatabasePool`, and tests can use a fast
    /// in-memory `DatabaseQueue`.
    ///
    /// See <https://swiftpackageindex.com/groue/grdb.swift/documentation/grdb/databaseconnections>
    private let dbWriter: any DatabaseWriter
}

// MARK: - Database Configuration

extension AppDatabase {
    private static let sqlLogger = OSLog(subsystem: Bundle.main.bundleIdentifier!, category: "SQL")
    
    /// Returns a database configuration suited for `PlayerRepository`.
    ///
    /// SQL statements are logged if the `SQL_TRACE` environment variable
    /// is set.
    ///
    /// - parameter base: A base configuration.
    public static func makeConfiguration(_ base: Configuration = Configuration()) -> Configuration {
        var config = base
        
        // An opportunity to add required custom SQL functions or
        // collations, if needed:
        // config.prepareDatabase { db in
        //     db.add(function: ...)
        // }
        
        // Log SQL statements if the `SQL_TRACE` environment variable is set.
        // See <https://swiftpackageindex.com/groue/grdb.swift/documentation/grdb/database/trace(options:_:)>
        if ProcessInfo.processInfo.environment["SQL_TRACE"] != nil {
            config.prepareDatabase { db in
                db.trace {
                    // It's ok to log statements publicly. Sensitive
                    // information (statement arguments) are not logged
                    // unless config.publicStatementArguments is set
                    // (see below).
                    os_log("%{public}@", log: sqlLogger, type: .debug, String(describing: $0))
                }
            }
        }
        
#if DEBUG
        // Protect sensitive information by enabling verbose debugging in
        // DEBUG builds only.
        // See <https://swiftpackageindex.com/groue/grdb.swift/documentation/grdb/configuration/publicstatementarguments>
        config.publicStatementArguments = true
#endif
        
        return config
    }
}

// MARK: - Database Migrations

extension AppDatabase {
    /// The DatabaseMigrator that defines the database schema.
    ///
    /// See <https://swiftpackageindex.com/groue/grdb.swift/documentation/grdb/migrations>
    private var migrator: DatabaseMigrator {
        var migrator = DatabaseMigrator()
        
#if DEBUG
        // Speed up development by nuking the database when migrations change
        // See <https://swiftpackageindex.com/groue/grdb.swift/documentation/grdb/migrations>
        migrator.eraseDatabaseOnSchemaChange = true
#endif
        
        migrator.registerMigration("createPlayer") { db in
            // Create a table
            // See <https://swiftpackageindex.com/groue/grdb.swift/documentation/grdb/databaseschema>
            try db.create(table: "player") { t in
                t.autoIncrementedPrimaryKey("id")
                t.column("name", .text).notNull()
                t.column("score", .integer).notNull()
            }
        }
        
        // Migrations for future application versions will be inserted here:
        // migrator.registerMigration(...) { db in
        //     ...
        // }
        
        return migrator
    }
}

// MARK: - Database Access: Writes
// The write methods execute invariant-preserving database transactions.

extension AppDatabase {
    /// Saves (inserts or updates) a player. When the method returns, the
    /// player is present in the database, and its id is not nil.
    func savePlayer(_ player: inout Player) throws {
        try dbWriter.write { db in
            try player.save(db)
        }
    }
    
    /// Delete the specified players
    func deletePlayers(ids: [Int64]) throws {
        try dbWriter.write { db in
            _ = try Player.deleteAll(db, ids: ids)
        }
    }
    
    /// Delete all players
    func deleteAllPlayers() throws {
        try dbWriter.write { db in
            _ = try Player.deleteAll(db)
        }
    }
    
    /// Refresh all players (by performing some random changes, for demo purpose).
    func refreshPlayers() throws {
        try dbWriter.write { db in
            if try Player.all().isEmpty(db) {
                // When database is empty, insert new random players
                try createRandomPlayers(db)
            } else {
                // Insert a player
                if Bool.random() {
                    _ = try Player.makeRandom().inserted(db) // insert but ignore inserted id
                }
                
                // Delete a random player
                if Bool.random() {
                    try Player.order(sql: "RANDOM()").limit(1).deleteAll(db)
                }
                
                // Update some players
                for var player in try Player.fetchAll(db) where Bool.random() {
                    try player.updateChanges(db) {
                        $0.score = Player.randomScore()
                    }
                }
            }
        }
    }
    
    /// Create random players if the database is empty.
    func createRandomPlayersIfEmpty() throws {
        try dbWriter.write { db in
            if try Player.all().isEmpty(db) {
                try createRandomPlayers(db)
            }
        }
    }
    
    /// Support for `createRandomPlayersIfEmpty()` and `refreshPlayers()`.
    private func createRandomPlayers(_ db: Database) throws {
        for _ in 0..<8 {
            _ = try Player.makeRandom().inserted(db) // insert but ignore inserted id
        }
    }
}

// MARK: - Database Access: Reads

// This demo app does not provide any specific reading method, and instead
// gives an unrestricted read-only access to the rest of the application.
// In your app, you are free to choose another path, and define focused
// reading methods.
extension AppDatabase {
    /// Provides a read-only access to the database
    var reader: DatabaseReader {
        dbWriter
    }
}