import {Container, ContainerBlueprint} from '../di'
import {
    ErrorWithContext,
    globalRegistry,
    infer,
    isLoggingLevel,
    PathLike,
    StandardLogger,
    universalPath,
    UniversalPath,
} from '../util'

import {Logging} from '../service/Logging'
import {RunLevelErrorHandler} from './RunLevelErrorHandler'
import {Unit, UnitStatus} from './Unit'
import * as dotenv from 'dotenv'
import {CacheFactory} from '../support/cache/CacheFactory'
import {FileLogger} from '../util/logging/FileLogger'

/**
 * Helper function that resolves and infers environment variable values.
 *
 * If none is found, returns `defaultValue`.
 *
 * @param key
 * @param defaultValue
 */
export function env(key: string, defaultValue?: unknown): any {
    return Application.getApplication().env(key, defaultValue)
}

/**
 * Helper function for fetching a universal path relative to the root of the application.
 * @param parts
 */
export function basePath(...parts: PathLike[]): UniversalPath {
    return Application.getApplication().path(...parts)
}

/**
 * Helper function for fetching a universal path relative to the `app/` directory.
 * @param parts
 */
export function appPath(...parts: PathLike[]): UniversalPath {
    return Application.getApplication().appPath(...parts)
}

/**
 * The main application container.
 */
export class Application extends Container {
    public static readonly NODE_MODULES_INJECTION = 'extollo/npm'

    public static get NODE_MODULES_PROVIDER(): string {
        return process.env.EXTOLLO_NPM || 'pnpm'
    }

    public static getContainer(): Container {
        const existing = <Container | undefined> globalRegistry.getGlobal('extollo/injector')
        if ( !existing ) {
            const container = new Application()

            ContainerBlueprint.getContainerBlueprint()
                .resolve()
                .map(factory => container.registerFactory(factory))

            globalRegistry.setGlobal('extollo/injector', container)
            return container
        }

        return existing as Container
    }

    /**
     * Get the global application instance.
     */
    public static getApplication(): Application {
        const existing = <Container | undefined> globalRegistry.getGlobal('extollo/injector')
        if ( existing instanceof Application ) {
            return existing
        } else if ( existing ) {
            const app = new Application()
            existing.cloneTo(app)

            globalRegistry.setGlobal('extollo/injector', app)
            return app
        } else {
            const app = new Application()

            ContainerBlueprint.getContainerBlueprint()
                .resolve()
                .map(factory => app.registerFactory(factory))

            globalRegistry.setGlobal('extollo/injector', app)
            return app
        }
    }

    /**
     * The fully-qualified path to the base directory of the app.
     * @protected
     */
    protected baseDir!: string

    /**
     * Resolved universal path to the base directory of the app.
     * @protected
     */
    protected basePath!: UniversalPath

    /**
     * The Unit classes registered with the app.
     * @protected
     */
    protected applicationUnits: (typeof Unit)[] = []

    /**
     * Instances of the units registered with this app.
     * @protected
     */
    protected instantiatedUnits: Unit[] = []

    /**
     * If true, the "Starting Extollo..." messages will always
     * be logged.
     */
    public forceStartupMessage = true

    constructor() {
        super()

        if ( !this.hasKey(Application) ) {
            this.register(Application)
            this.instances.push({
                key: Application,
                value: this,
            })
        }

        if ( !this.hasKey('app') ) {
            this.registerSingleton('app', this)
        }
    }

    /**
     * Returns true if the given unit class is registered with the application.
     * @param unitClass
     */
    public hasUnit(unitClass: typeof Unit): boolean {
        return this.applicationUnits.includes(unitClass)
    }

    /**
     * Return a UniversalPath to the root of the application.
     */
    get root(): UniversalPath {
        return this.basePath.concat()
    }

    /**
     * Returns a UniversalPath to the `app/` directory in the application.
     */
    get appRoot(): UniversalPath {
        return this.basePath.concat('app')
    }

    /**
     * Resolve a path relative to the root of the application.
     * @param parts
     */
    path(...parts: PathLike[]): UniversalPath {
        return this.basePath.concat(...parts)
    }

    /**
     * Resolve a path relative to the `app/` directory in the application.
     * @param parts
     */
    appPath(...parts: PathLike[]): UniversalPath {
        return this.basePath.concat('app', ...parts)
    }

    /**
     * Get an instance of the RunLevelErrorHandler.
     */
    get errorHandler(): (e: Error) => void {
        const rleh: RunLevelErrorHandler = this.make<RunLevelErrorHandler>(RunLevelErrorHandler)
        return rleh.handle
    }

    /**
     * Wrap a base Error instance into an ErrorWithContext.
     * @param e
     * @param context
     */
    errorWrapContext(e: Error, context: {[key: string]: any}): ErrorWithContext {
        const rleh: RunLevelErrorHandler = this.make<RunLevelErrorHandler>(RunLevelErrorHandler)
        return rleh.wrapContext(e, context)
    }

    /**
     * Set up the bare essentials to get the application up and running.
     * @param absolutePathToApplicationRoot
     * @param applicationUnits
     */
    scaffold(absolutePathToApplicationRoot: string, applicationUnits: (typeof Unit)[]): void {
        this.baseDir = absolutePathToApplicationRoot
        this.basePath = universalPath(absolutePathToApplicationRoot)
        this.applicationUnits = applicationUnits

        this.bootstrapEnvironment()
        this.setupLogging()

        this.registerFactory(new CacheFactory())  // FIXME move this somewhere else?
        this.registerSingleton(Application.NODE_MODULES_INJECTION, Application.NODE_MODULES_PROVIDER)

        this.make<Logging>(Logging).debug(`Application root: ${this.baseDir}`)
    }

    /**
     * Initialize the logger and load the logging level from the environment.
     * @protected
     */
    protected setupLogging(): void {
        const standard: StandardLogger = this.make<StandardLogger>(StandardLogger)
        const logging: Logging = this.make<Logging>(Logging)

        logging.registerLogger(standard)

        if ( this.env('EXTOLLO_LOGGING_ENABLE_FILE') ) {
            const file: FileLogger = this.make<FileLogger>(FileLogger)
            logging.registerLogger(file)
        }

        logging.verbose('Attempting to load logging level from the environment...')

        const envLevel = this.env('EXTOLLO_LOGGING_LEVEL')
        logging.verbose(`Read logging level: ${envLevel}`)

        if ( isLoggingLevel(envLevel) ) {
            logging.verbose('Logging level is valid.')
            logging.level = envLevel
            logging.debug(`Set logging level from environment: ${envLevel}`)
        }
    }

    /**
     * Initialize the environment variable library and read from the `.env` file.
     * @protected
     */
    protected bootstrapEnvironment(): void {
        dotenv.config({
            path: this.basePath.concat('.env').toLocal,
        })
    }

    /**
     * Get a value from the loaded environment variables.
     * If no value could be found, the default value will be returned.
     * @param key
     * @param defaultValue
     */
    public env(key: string, defaultValue?: unknown): any {
        return infer(process.env[key] ?? '') ?? defaultValue
    }

    /**
     * Run the application by starting all units in order, then stopping them in reverse order.
     */
    async run(): Promise<void> {
        try {
            await this.up()
            await this.down()
        } catch (e) {
            this.errorHandler(e)
        }
    }

    /**
     * Start all units in the application, one at a time, in order.
     */
    async up(): Promise<void> {
        const logging: Logging = this.make<Logging>(Logging)

        logging.info('Starting Extollo...', this.forceStartupMessage)
        for ( const unitClass of this.applicationUnits ) {
            const unit: Unit = this.make<Unit>(unitClass)
            this.instantiatedUnits.push(unit)
            await this.startUnit(unit)
        }
    }

    /**
     * Stop all units in the application, one at a time, in reverse order.
     */
    async down(): Promise<void> {
        const logging: Logging = this.make<Logging>(Logging)

        logging.info('Stopping Extollo...', this.forceStartupMessage)
        for ( const unit of [...this.instantiatedUnits].reverse() ) {
            if ( !unit ) {
                continue
            }
            await this.stopUnit(unit)
        }
    }

    /**
     * Start a single unit, setting its status.
     * @param unit
     */
    public async startUnit(unit: Unit): Promise<void> {
        const logging: Logging = this.make<Logging>(Logging)

        try {
            logging.debug(`Starting ${unit.constructor.name}...`)
            unit.status = UnitStatus.Starting
            await unit.up()
            unit.status = UnitStatus.Started
            logging.info(`Started ${unit.constructor.name}.`)
        } catch (e) {
            unit.status = UnitStatus.Error
            throw this.errorWrapContext(e, {unitName: unit.constructor.name})
        }
    }

    /**
     * Stop a single unit, setting its status.
     * @param unit
     */
    public async stopUnit(unit: Unit): Promise<void> {
        const logging: Logging = this.make<Logging>(Logging)

        try {
            logging.debug(`Stopping ${unit.constructor.name}...`)
            unit.status = UnitStatus.Stopping
            await unit.down()
            unit.status = UnitStatus.Stopped
            logging.info(`Stopped ${unit.constructor.name}.`)
        } catch (e) {
            unit.status = UnitStatus.Error
            throw this.errorWrapContext(e, {unitName: unit.constructor.name})
        }
    }
}