Server Framework

/**
 * Creates an embedded server with the specified engine factory
 * @param factory The engine factory to use (Netty, CIO, Jetty, Tomcat)
 * @param port The port to bind to
 * @param host The host to bind to
 * @param watchPaths Paths to watch for reloading
 * @param configure Configuration block for the server environment
 * @param module Application module to install
 * @return Configured ApplicationEngine instance
 */
fun <TEngine : ApplicationEngine, TConfiguration : ApplicationEngine.Configuration> embeddedServer(
    factory: ApplicationEngineFactory<TEngine, TConfiguration>,
    port: Int = 80,
    host: String = "0.0.0.0",
    watchPaths: List<String> = listOf(WORKING_DIRECTORY_PATH),
    configure: ApplicationEngineEnvironmentBuilder.() -> Unit = {},
    module: suspend Application.() -> Unit
): TEngine

/**
 * Creates an embedded server from environment
 * @param factory The engine factory to use
 * @param environment Pre-configured application environment
 * @return Configured ApplicationEngine instance
 */
fun <TEngine : ApplicationEngine, TConfiguration : ApplicationEngine.Configuration> embeddedServer(
    factory: ApplicationEngineFactory<TEngine, TConfiguration>,
    environment: ApplicationEnvironment
): TEngine

import io.ktor.server.engine.*
import io.ktor.server.netty.*
import io.ktor.server.application.*
import io.ktor.server.routing.*
import io.ktor.server.response.*

// Basic embedded server
fun main() {
    embeddedServer(Netty, port = 8080) {
        routing {
            get("/") {
                call.respondText("Hello World!")
            }
        }
    }.start(wait = true)
}

// Custom configuration
fun main() {
    embeddedServer(Netty, port = 8080, host = "127.0.0.1") {
        // Configure environment
        developmentMode = true
        watchPaths = listOf("build")
    } {
        // Application module
        install(Routing) {
            get("/health") {
                call.respondText("OK")
            }
        }
    }.start(wait = true)
}

/**
 * Main application interface for Ktor server applications
 */
public class Application internal constructor(
    environment: ApplicationEnvironment,
    developmentMode: Boolean,
    public var rootPath: String,
    public val monitor: Events,
    public val parentCoroutineContext: CoroutineContext,
    private val engineProvider: () -> ApplicationEngine
) : ApplicationCallPipeline, CoroutineScope {
    
    /**
     * The engine instance this application is running on
     */
    val engine: ApplicationEngine
    
    /**
     * Application environment containing configuration and other resources
     */
    val environment: ApplicationEnvironment
    
    /**
     * Event monitor for application lifecycle events
     */
    val monitor: Events
    
    /**
     * Application-scoped attributes storage
     */
    val attributes: Attributes
    
    /**
     * Parent coroutine context for the application
     */
    override val coroutineContext: CoroutineContext
}

/**
 * Application environment provides access to configuration and other resources
 */
interface ApplicationEnvironment {
    /**
     * Application configuration from config files
     */
    val config: ApplicationConfig
    
    /**
     * Logger instance for the application
     */
    val log: Logger
    
    /**
     * Development mode flag
     */
    val developmentMode: Boolean
    
    /**
     * Application root path
     */
    val rootPath: String
    
    /**
     * Class loader for loading application resources
     */
    val classLoader: ClassLoader
    
    /**
     * Monitor for application lifecycle events
     */
    val monitor: Events
}

/**
 * Base class for applications and routes that provides call processing pipeline
 */
open class ApplicationCallPipeline(
    val developmentMode: Boolean = false,
    val environment: ApplicationEnvironment? = null
) : Pipeline<Unit, ApplicationCall> {
    
    /**
     * Pipeline for processing incoming calls
     */
    val call: PipelinePhase = PipelinePhase("Call")
    
    /**
     * Interceptors for handling specific functionality
     */
    fun intercept(
        phase: PipelinePhase,
        block: suspend PipelineContext<Unit, ApplicationCall>.(Unit) -> Unit
    )
}

/**
 * Application configuration interface
 */
interface ApplicationConfig {
    /**
     * Get property value by path
     */
    fun property(path: String): ApplicationConfigValue
    
    /**
     * Get property value or null if not found
     */
    fun propertyOrNull(path: String): ApplicationConfigValue?
    
    /**
     * Get list of property values
     */
    fun configList(path: String): List<ApplicationConfig>
    
    /**
     * Get nested configuration
     */
    fun config(path: String): ApplicationConfig
    
    /**
     * Check if property exists
     */
    fun hasProperty(path: String): Boolean
    
    /**
     * Get all property keys
     */
    fun keys(): Set<String>
}

/**
 * Configuration value wrapper
 */
interface ApplicationConfigValue {
    fun getString(): String
    fun getList(): List<String>
}

// application.conf (HOCON format)
/*
ktor {
    application {
        modules = [ com.example.ApplicationKt.module ]
    }
    deployment {
        port = 8080
        host = "0.0.0.0"
    }
    database {
        url = "jdbc:postgresql://localhost/mydb"
        driver = "org.postgresql.Driver"
    }
}
*/

// Using configuration in application
fun Application.module() {
    val dbUrl = environment.config.property("database.url").getString()
    val dbDriver = environment.config.property("database.driver").getString()
    
    // Configure database connection
    connectToDatabase(dbUrl, dbDriver)
}

/**
 * Netty engine factory for high-performance applications
 */
object Netty : ApplicationEngineFactory<NettyApplicationEngine, NettyApplicationEngine.Configuration> {
    override fun create(
        environment: ApplicationEnvironment,
        configure: NettyApplicationEngine.Configuration.() -> Unit
    ): NettyApplicationEngine
}

/**
 * CIO (Coroutine I/O) engine factory for pure Kotlin implementation
 */
object CIO : ApplicationEngineFactory<CIOApplicationEngine, CIOApplicationEngine.Configuration> {
    override fun create(
        environment: ApplicationEnvironment,
        configure: CIOApplicationEngine.Configuration.() -> Unit
    ): CIOApplicationEngine
}

/**
 * Jetty engine factory for servlet container compatibility
 */
object Jetty : ApplicationEngineFactory<JettyApplicationEngine, JettyApplicationEngine.Configuration> {
    override fun create(
        environment: ApplicationEnvironment,
        configure: JettyApplicationEngine.Configuration.() -> Unit
    ): JettyApplicationEngine
}

/**
 * Tomcat engine factory for servlet container compatibility
 */
object Tomcat : ApplicationEngineFactory<TomcatApplicationEngine, TomcatApplicationEngine.Configuration> {
    override fun create(
        environment: ApplicationEnvironment,
        configure: TomcatApplicationEngine.Configuration.() -> Unit
    ): TomcatApplicationEngine
}

/**
 * Base interface for all application engines
 */
interface ApplicationEngine {
    /**
     * Engine environment
     */
    val environment: ApplicationEnvironment
    
    /**
     * Application instance
     */
    val application: Application
    
    /**
     * Start the engine
     */
    fun start(wait: Boolean = false): ApplicationEngine
    
    /**
     * Stop the engine
     */
    fun stop(gracePeriodMillis: Long, timeoutMillis: Long)
    
    /**
     * Engine configuration
     */
    interface Configuration {
        var parallelism: Int
        var connectionGroupSize: Int
        var workerGroupSize: Int
        var callGroupSize: Int
    }
}