import LifecycleUnit from '../lifecycle/Unit.ts'
import {Unit} from '../lifecycle/decorators.ts'
import {Handlebars} from '../external/http.ts'
import {Logging} from '../service/logging/Logging.ts'
import {fs} from '../external/std.ts'

/**
 * Lifecycle unit which sets up and provides basic view engine services.
 * @extends LifecycleUnit
 */
@Unit()
export default class ViewEngine extends LifecycleUnit {
    /**
     * The Handlebars instance.
     * @type Handlebars
     */
    protected _handlebars!: Handlebars

    // TODO include basic app info in view data

    constructor(
        protected readonly logger: Logging,
    ) {
        super()
    }

    async up() {
        this.logger.info(`Setting views base dir: ${this.app.app_path('http', 'views')}`)
        this._handlebars = new Handlebars({
            baseDir: this.app.app_path('http', 'views'),
            extname: '.hbs',
            layoutsDir: 'layouts',
            partialsDir: 'partials',
            defaultLayout: 'main',
            helpers: undefined,
            compilerOptions: undefined,
        })

        const main_layout_path = this.app.app_path('http', 'views', 'layouts', 'main.hbs')
        if ( !(await fs.exists(main_layout_path)) ) {
            this.logger.warn(`Unable to open main view layout file: ${main_layout_path}`)
            this.logger.warn(`Unless you are using a custom layout, this could cause errors.`)
        }

        const partials_path = this.app.app_path('http', 'views', 'partials')
        if ( !(await fs.exists(partials_path)) ) {
            this.logger.warn(`Unable to open view partials directory: ${partials_path}`)
            this.logger.warn(`This directory must exist for the view engine to function, even if it is empty.`)
        }
    }

    /**
     * The handlebars instance.
     * @type Handlebars
     */
    get handlebars(): Handlebars {
        return this._handlebars
    }

    /**
     * Render a view with the given name, using the specified arguments and layout.
     * @param {string} view
     * @param [args]
     * @param {string} [layout]
     * @return Promise<string>
     */
    async render(view: string, args?: any, layout?: string): Promise<string> {
        this.logger.debug(`Rendering view: ${view}`)
        return this.handlebars.renderView(view, args, layout)
    }

    /**
     * Render a partial view with the given name, using the specified arguments.
     * @param {string} view
     * @param [args]
     */
    async partial(view: string, args?: any) {
        const parts = `${view}.hbs`.split(':')
        const resolved = this.app.app_path('http', 'views', ...parts)

        this.logger.debug(`Rendering partial: ${view} from ${resolved}`)
        return this.handlebars.render(resolved, args)
    }
}