import path from "path";
import fs from "fs";
import chokidar, {FSWatcher} from "chokidar";
import {logger} from "../Logger";
import {afs, readdirRecursively} from "../Utils";
import {Express} from "express";

export default abstract class ViewEngine {
    private static readonly globals: Record<string, unknown> = {};

    public static getGlobals(): Record<string, unknown> {
        return {...this.globals};
    }

    public static setGlobal(key: string, value: unknown): void {
        this.globals[key] = value;
    }


    protected readonly viewPaths: string[];
    private watcher?: FSWatcher;

    /**
     * @param devWatchedViewDir The directory that should be watched in dev environment.
     * @param additionalViewPaths By order of priority, the directories that contain all the views of the app.
     * Swaf provided views and default ./view directory are automatically added (don't add them yourself).
     * @protected
     */
    protected constructor(
        private readonly devWatchedViewDir: string,
        ...additionalViewPaths: string[]
    ) {
        this.viewPaths = [
            ...additionalViewPaths.map(p => path.resolve(p)),
            path.resolve(__dirname, '../../../views'),
            path.resolve(__dirname, '../../views'),
            path.resolve(__dirname, '../views'),
        ].filter(dir => fs.existsSync(dir));
    }

    public abstract getExtension(): string;


    public abstract render(
        file: string,
        locals: Record<string, unknown>,
    ): Promise<string>;

    public setup(app: Express, main: boolean): void {
        app.engine(this.getExtension(), (path, options, callback) => {
            // Props (locals)
            const locals = Object.assign(options, ViewEngine.getGlobals());

            this.render(path, locals)
                .then(value => callback(null, value))
                .catch(err => callback(err));
        });

        const existingViewPaths = app.get('views');
        app.set('views', existingViewPaths ?
            [...new Set([
                ...typeof existingViewPaths === 'string' ?
                    [existingViewPaths] :
                    existingViewPaths,
                ...this.getViewPaths(),
            ])] :
            this.getViewPaths());

        if (main) {
            app.set('view engine', this.getExtension());
        }
    }

    public getViewPaths(): string[] {
        return this.viewPaths;
    }

    public preCompile?(canonicalName: string, alsoCompileDependents: boolean): Promise<void>;

    public afterPreCompile?(watch: boolean): Promise<void>;

    public async preCompileAll(watch: boolean): Promise<void> {
        if (this.preCompile) {
            logger.info(`Pre-compiling ${this.getExtension()} views...`);

            // List all views
            const views: string[] = [];
            for (const viewPath of this.viewPaths) {
                await readdirRecursively(viewPath, async file => {
                    if (file.endsWith('.' + this.getExtension())) {
                        views.push(this.toCanonicalName(file));
                    }
                });
            }

            // Deduplicate and pre-compile
            for (const canonicalName of [...new Set<string>(views)]) {
                await this.preCompile(canonicalName, false);
            }
        }

        await this.afterPreCompile?.(watch);

        if (watch) {
            await this.watch();
        }
    }

    public onNewFile?(file: string): Promise<void>;

    public onFileChange?(file: string): Promise<void>;

    public onFileRemove?(file: string): Promise<void>;

    public async watch(): Promise<void> {
        this.watcher = chokidar.watch(this.devWatchedViewDir, {persistent: true});
        this.watcher.on('ready', () => {
            if (!this.watcher) return;

            logger.info(`Watching ${this.getExtension()} assets for changes`);

            this.watcher.on('add', (file) => {
                if (file.endsWith('.' + this.getExtension())) {
                    (this.onNewFile ? this.onNewFile(file) : Promise.resolve())
                        .then(() => this.preCompile?.(this.toCanonicalName(file), true))
                        .then(() => this.afterPreCompile?.(true))
                        .catch(err => logger.error(err));
                }
            });

            this.watcher.on('change', (file) => {
                if (file.endsWith('.' + this.getExtension())) {
                    (this.onFileChange ? this.onFileChange(file) : Promise.resolve())
                        .then(() => this.preCompile?.(this.toCanonicalName(file), true))
                        .then(() => this.afterPreCompile?.(true))
                        .catch(err => logger.error(err));
                }
            });

            this.watcher.on('unlink', (file) => {
                if (file.endsWith('.' + this.getExtension())) {
                    (this.onFileRemove ? this.onFileRemove(file) : Promise.resolve())
                        .catch(err => logger.error(err));
                }
            });
        });
    }

    public async stop(): Promise<void> {
        if (this.watcher) {
            await this.watcher.close();
            this.watcher = undefined;
        }
    }

    protected toCanonicalName(file: string): string {
        const resolvedFilePath = path.resolve(file);

        let canonicalViewName: string | null = null;
        for (const viewPath of this.viewPaths) {
            if (resolvedFilePath.startsWith(viewPath)) {
                canonicalViewName = resolvedFilePath.substring(viewPath.length + 1);
            }
        }

        if (!canonicalViewName) throw new Error('view ' + file + ' not found');
        return canonicalViewName;
    }

    protected async resolveFileFromCanonicalName(canonicalName: string): Promise<string> {
        for (const viewPath of this.viewPaths) {
            const tryPath = path.join(viewPath, canonicalName);
            if (await afs.exists(tryPath)) {
                return tryPath;
            }
        }

        throw new Error('View not found from canonical name ' + canonicalName);
    }
}