import LifecycleUnit from '../lifecycle/Unit.ts'
import Config from './Config.ts'
import {isViewEngine, ViewEngine as Types, ViewFileExtension} from '../const/view_engines.ts'
import {views, handlebars} from '../external/http.ts'
import {Unit} from '../lifecycle/decorators.ts'
import {Logging} from '../service/logging/Logging.ts'
import {ConfigError} from '../error/ConfigError.ts'
import {path, fs} from '../external/std.ts'

/**
 * Error thrown when an action requiring a view engine is attempted, but no view
 * engine has been configured properly.
 */
export class MissingViewEngineError extends Error {
    constructor(message = 'Missing or invalid view engine type config.') {
        super(message)
    }
}

/**
 * Error thrown when an action requiring a template base directory is attempted,
 * but no such directory has been configured.
 */
export class MissingTemplateDirectoryError extends Error {
    constructor(message = 'Missing or invalid path to template base directory.') {
        super(message)
    }
}

/**
 * Lifecycle unit which manages the initialization of the configured rendering
 * engine, as well as utilities for rendering template files and strings.
 * @extends LifecycleUnit
 */
@Unit()
export default class ViewEngine extends LifecycleUnit {
    protected engine?: Types
    protected template_dir?: string

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

    public async up() {
        const config: unknown = this.config.get('app.views.engine')
        const base_dir: unknown = this.config.get('app.views.base_dir')

        if ( !isViewEngine(config) ) {
            throw new ConfigError('app.views.engine', config)
        }

        if ( !String(base_dir) ) {
            throw new ConfigError('app.views.base_dir', base_dir)
        }

        this.template_dir = this.app.app_path(base_dir)
        this.engine = config
        this.logger.info(`Determined view engine from config: ${config}`)
        this.logger.info(`Determined base directory for templates: ${this.template_dir}`)

        await this.init_engine()
    }

    /**
     * Render a template file using the configured engine.
     * @param {string} template_path - the relative path of the template w/in the template dir.
     * @param {object} [data = {}]
     * @return Promise<string>
     */
    public async template(template_path: string, data: { [key: string]: any } = {}) {
        const file_path = `${this.template_path(template_path.replace(/:/g, '/'))}${this.get_file_extension()}`

        this.logger.debug(`Rendering template "${template_path}" from file: ${file_path}`)

        // TODO cache this
        // TODO replace with fs.readFileStr
        const content = await Deno.readTextFile(file_path)
        const engine: views.Engine = this.get_engine()

        return engine(
            content,
            data,
            this.get_render_context(),
            `${template_path}${this.get_file_extension()}`
        )
    }

    /**
     * Resolve a path within the template base directory.
     * @param {...string} parts
     * @return string
     */
    public template_path(...parts: string[]): string {
console.log('template path parts', parts)
        if ( !this.template_dir ) throw new MissingTemplateDirectoryError()
        let template_dir = this.template_dir
        if ( template_dir.startsWith('file://') ) template_dir = template_dir.slice(7)

console.log('template path dir', template_dir)

        const resolved_path = path.resolve(template_dir, ...parts)

console.log('template path resolved 1', resolved_path)

        if ( resolved_path.startsWith('/') ) {
            return `file://${resolved_path}`
        } else {
            return resolved_path
        }
    }

    /**
     * Render a template string using the configured engine.
     * @param {string} template
     * @param {object} [data = {}]
     * @return Promise<string>
     */
    public async render(template: string, data: { [key: string]: any } = {}) {
        const engine: views.Engine = this.get_engine()
        return engine(template, data)
    }

    /**
     * Get the rendering engine for the configured backend.
     */
    public get_engine(): views.Engine {
        if ( this.engine === Types.Denjuck ) {
            return views.engineFactory.getDenjuckEngine()
        } else if ( this.engine === Types.Ejs ) {
            return views.engineFactory.getEjsEngine()
        } else if ( this.engine === Types.Handlebars ) {
            return views.engineFactory.getHandlebarsEngine()
        }

        throw new MissingViewEngineError()
    }

    /**
     * Get the file extension expected by the currently configured render engine.
     */
    public get_file_extension(): ViewFileExtension {
        if ( this.engine === Types.Denjuck ) {
            return ViewFileExtension.Denjuck
        } else if ( this.engine === Types.Ejs ) {
            return ViewFileExtension.Ejs
        } else if ( this.engine === Types.Handlebars ) {
            return ViewFileExtension.Handlebars
        }

        throw new MissingViewEngineError()
    }

    /**
     * Get the rendering context to pass to the render engine. This is here
     * for compatibility with the view_engine library.
     */
    public get_render_context() {
        if ( !this.template_dir ) throw new MissingTemplateDirectoryError()

        return {
            viewExt: this.get_file_extension(),
            viewEngine: this.get_engine(),
            viewRoot: this.template_dir,
            useCache: false, // TODO better value here
            cache: undefined,
        }
    }

    /**
     * Initialize the appropriate rendering engine.
     */
    protected async init_engine() {
        if ( this.engine === Types.Handlebars ) {
            await this.init_engine_handlebars()
        }
    }

    /**
     * Initialize the Handlebars rendering engine by loading and registering partial views
     * from the configured partials directory, if one exists.
     */
    protected async init_engine_handlebars() {
        const partials_dir: unknown = this.config.get('app.views.partials_dir')
        if ( String(partials_dir) ) {
            const partials_path = this.template_path(String(partials_dir))
console.log({ partials_path, partials_dir })
            this.logger.info(`Registering Handlebars partials from: ${partials_path}`)

            for await ( const entry of fs.walk(partials_path) ) {
                if ( !entry.isFile || !entry.path.endsWith(this.get_file_extension()) ) {
                    if ( entry.isFile ) this.logger.debug(`Skipping file in Handlebars partials path with invalid suffix: ${entry.path}`)
                    continue
                }

                const content = await Deno.readTextFile(entry.path)

                // Generate the partial name.
                // This is done by taking the relative path from the partials dir, removing the suffix,
                // and replacing directory separators with the standard : identifier.
                let partial_name = entry.path.replace(partials_path, '').slice(0, -1 * (this.get_file_extension()).length)
                if ( partial_name.startsWith('/') ) partial_name = partial_name.slice(1)
                partial_name = partial_name.replace(/\//g, ':')

                this.logger.debug(`Registering handlebars partial: ${partial_name}`)
                handlebars.registerPartial(partial_name, content)
            }
        }
    }
}