import {AppClass} from '../lifecycle/AppClass'
import {Config} from '../service/Config'
import {Container} from '../di'
import {ErrorWithContext, UniversalPath} from '../util'

/**
 * Abstract base class for rendering views via different view engines.
 */
export abstract class ViewEngine extends AppClass {
    protected readonly config: Config

    protected readonly debug: boolean

    protected readonly namespaces: {[key: string]: UniversalPath} = {}

    constructor() {
        super()
        this.config = Container.getContainer().make(Config)
        this.debug = (this.config.get('server.mode', 'production') === 'development'
                        || this.config.get('server.debug', false))
    }

    /**
     * Get the UniversalPath to the base directory where views are loaded from.
     */
    public get path(): UniversalPath {
        return this.app().appPath(...['resources', 'views'])  // FIXME allow configuring
    }

    /**
     * Given a template string and a set of variables for the view, render the string to HTML and return it.
     * @param templateString
     * @param locals
     */
    public abstract renderString(templateString: string, locals: {[key: string]: any}): string | Promise<string>

    /**
     * Given the canonical name of a template file, render the file using the provided variables.
     * @param templateName
     * @param locals
     */
    public abstract renderByName(templateName: string, locals: {[key: string]: any}): string | Promise<string>

    public registerNamespace(namespace: string, basePath: UniversalPath): this {
        if ( namespace.startsWith('@') ) {
            namespace = namespace.substr(1)
        }

        this.namespaces[namespace] = basePath
        return this
    }

    public resolveName(templateName: string): UniversalPath {
        let path = this.path
        if ( templateName.startsWith('@') ) {
            const [namespace, ...parts] = templateName.split(':')
            path = this.namespaces[namespace.substr(1)]

            if ( !path ) {
                throw new ErrorWithContext('Invalid template namespace: ' + namespace, {
                    namespace,
                    templateName,
                })
            }

            templateName = parts.join(':')
        }

        if ( !templateName.endsWith('.pug') ) {
            templateName += '.pug'
        }

        return path.concat(...templateName.split(':'))
    }

    public resolveBasePath(templateName: string): UniversalPath {
        let path = this.path
        if ( templateName.startsWith('@') ) {
            const [namespace] = templateName.split(':')
            path = this.namespaces[namespace.substr(1)]

            if ( !path ) {
                throw new ErrorWithContext('Invalid template namespace: ' + namespace, {
                    namespace,
                    templateName,
                })
            }
        }

        return path
    }
}