import {Unit} from '../lifecycle/Unit'
import {Inject, Singleton} from '../di'
import {Config} from './Config'
import {Logging} from './Logging'
import {Filesystem, ErrorWithContext} from '../util'

/**
 * Error thrown when a function is called on a filesystem that does not exists in code.
 */
export class FilesystemDoesNotExist extends ErrorWithContext {
    constructor(
        message = 'The specified filesystem does not exist.',
        context: {[key: string]: any} = {},
    ) {
        super(message, context)
    }
}

/**
 * Unit service that loads and creates Filesystem drivers from config. The filesystems
 * will automatically be opened when the app starts, and closed when it stops.
 *
 * @example
 * Filesystems can be defined in the `server.filesystems` config. For example:
 *
 * ```typescript
 * import {basePath} from "@extollo/lib"
 * import {LocalFilesystem, LocalFilesystemConfig} from "@extollo/util"
 *
 * export default {
 *     // ... other configs ...
 *     filesystems: {
 *         default: {
 *             driver: LocalFilesystem,
 *             config: {
 *                 baseDir: basePath('..', 'uploads').toLocal,
 *             } as LocalFilesystemConfig,
 *         },
 *     },
 * }
 * ```
 *
 * The `config` key should be an instance of the config interface for the driver
 * in question.
 *
 * @example
 * Filesystems can then be accessed from the Files service:
 *
 * ```typescript
 * if ( files.hasFilesystem('default') ) {
 *     const filesystem = files.getFilesystem('default')
 *     // ... do something with the filesystem ...
 * }
 * ```
 *
 */
@Singleton()
export class Files extends Unit {
    protected filesystems: {[key: string]: Filesystem} = {}

    protected defaultFilesystem?: Filesystem

    @Inject()
    protected readonly config!: Config

    @Inject()
    protected readonly logging!: Logging

    async up(): Promise<void> {
        const config = this.config.get('server.filesystems', {})
        const promises = []
        for ( const key in config ) {
            if ( !Object.prototype.hasOwnProperty.call(config, key) ) {
                continue
            }

            if ( config[key]?.driver?.prototype instanceof Filesystem ) {
                this.logging.verbose(`Registering filesystem '${key}' with driver ${config[key].driver.name}...`)

                const inst = <Filesystem> this.make(config[key].driver, config[key].config || {})
                promises.push(inst.open())

                if ( this.filesystems[key] ) {
                    this.logging.warn(`Overwriting filesystem with duplicate name: ${key}`)
                }

                this.filesystems[key] = inst

                if ( config[key]?.isDefault ) {
                    this.defaultFilesystem = inst
                }
            }
        }

        await Promise.all(promises)

        // Once they have initialized, register the DI token for the default filesystem
        this.app().registerProducer(Filesystem, () => {
            // This will throw FilesystemDoesNotExistError if no default filesystem was created
            // Such behavior is desired as it is clearer than an invalid injection error, e.g.
            return this.getFilesystem()
        })

        // If file uploads are enabled, ensure that the default upload prefix exists
        if ( this.defaultFilesystem ) {
            const upload = this.config.get('server.uploads', {})
            if ( upload?.enable && upload?.filesystemPrefix ) {
                await this.defaultFilesystem.mkdir({
                    storePath: upload.filesystemPrefix,
                })
            }
        }
    }

    async down(): Promise<void> {
        await Promise.all(Object.values(this.filesystems).map(fs => fs.close()))
    }

    /**
     * Returns true if a filesystem with the given name exists.
     * @param key
     */
    hasFilesystem(key?: string): boolean {
        if ( !key ) {
            return Boolean(this.defaultFilesystem)
        }

        return Boolean(this.filesystems[key])
    }

    /**
     * Given the name of a filesystem registered in the system, get that filesystem.
     * @param key
     */
    getFilesystem(key?: string): Filesystem {
        if ( !key ) {
            if ( !this.defaultFilesystem ) {
                throw new FilesystemDoesNotExist()
            }

            return this.defaultFilesystem
        }

        if ( !this.hasFilesystem(key) ) {
            throw new FilesystemDoesNotExist()
        }

        return this.filesystems[key]
    }

    /**
     * Register the given filesystem with this service by name.
     * @param key
     * @param fs
     */
    registerFilesystem(key: string, fs: Filesystem): void {
        if ( this.hasFilesystem(key) ) {
            this.logging.warn(`Overwriting filesystem with duplicate name: ${key}`)
        }

        this.filesystems[key] = fs
    }
}