import chokidar, {FSWatcher} from "chokidar";
import {existsSync, mkdirSync, promises as fs} from "fs";
import path from "path";

import {logger} from "../Logger.js";
import {doesFileExist, listFilesRecursively} from "../Utils.js";
import Globals from "./Globals.js";

export default abstract class AssetPreCompiler {
    protected readonly assetPaths: string[];
    private globals?: Globals;
    private watcher?: FSWatcher;
    private afterPreCompileHandlers: ((watch: boolean) => Promise<void>)[] = [];
    private inputChangeHandler?: (restart: boolean) => Promise<void>;

    private hadError: boolean = false;

    /**
     * @param targetDir The directory to put pre-compiled assets into.
     * @param assetType This must be the assets sub-directory name of the asset type this pre-compiler will handle.
     * Example: ts
     * Example: views
     * @param extension The asset files extension.
     * @param outputToPublicDir should the assets be compiled into the publicly served directory?
     * @param additionalFallbackAssetPaths By order of priority, fallback asset directories.
     * Swaf provided assets and default ./assets directory are automatically added (don't add them yourself).
     */
    protected constructor(
        protected readonly targetDir: string,
        protected readonly assetType: string,
        protected readonly extension: string,
        private readonly outputToPublicDir: boolean,
        ...additionalFallbackAssetPaths: string[]
    ) {
        this.assetPaths = [
            ...additionalFallbackAssetPaths,
            'src/assets',
            'node_modules/swaf/assets',
        ].map(p => path.resolve(p, assetType))
            .filter(dir => existsSync(dir));
        this.targetDir = path.join(targetDir, assetType);

        if (!existsSync(this.targetDir)) {
            mkdirSync(this.targetDir, {recursive: true});
        }
    }

    public getExtension(): string {
        return this.extension;
    }

    public isPublic(): boolean {
        return this.outputToPublicDir;
    }

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

    protected getGlobals(): Globals {
        if (!this.globals) throw new Error('globals field not intialized.');
        return this.globals;
    }

    public setGlobals(globals: Globals): void {
        this.globals = globals;
    }

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

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

    public onPreCompile(afterPreCompileHandler: (watch: boolean) => Promise<void>): void {
        this.afterPreCompileHandlers.push(afterPreCompileHandler);
    }

    protected async afterPreCompile(watch: boolean): Promise<void> {
        await Promise.all(this.afterPreCompileHandlers.map(handler => handler(watch)));
    }

    public async preCompileAll(watch: boolean): Promise<void> {
        if (watch) {
            await this.watch();
        }

        logger.info(`Pre-compiling ${this.extension} views...`);

        // List all views
        const views: string[] = [];
        for (const viewPath of this.assetPaths) {
            for (const file of await listFilesRecursively(viewPath)) {
                if (file.endsWith('.' + this.extension)) {
                    views.push(this.toCanonicalName(file));
                }
            }
        }

        // Deduplicate and pre-compile
        const hasInputChanged = this.hadError;
        this.hadError = false;
        for (const canonicalName of [...new Set<string>(views)]) {
            try {
                await this.preCompile(canonicalName, false);
            } catch (e) {
                logger.error(e);
                this.hadError = true;
            }
        }

        // If previous preCompileAll had errors, not all output files were generated.
        if (hasInputChanged) {
            await this.inputChangeHandler?.(false);
        }

        await this.afterPreCompile(watch);

        if (this.hadError && !watch) throw new Error('Errors while precompiling assets.');
    }

    public async watch(): Promise<void> {
        const watchedPaths = this.assetPaths.map(p => `${p}/**/*.${this.getExtension()}`);
        this.watcher = chokidar.watch(watchedPaths, {persistent: true});
        this.watcher.on('ready', () => {
            if (!this.watcher) return;

            logger.info(`Watching ${this.extension} assets for changes in ${watchedPaths}`);

            this.watcher.on('add', (file) => {
                this.onNewFile(file)
                    .catch(err => logger.error(err));
            });

            this.watcher.on('change', (file) => {
                this.onFileChange(file)
                    .catch(err => logger.error(err));
            });

            this.watcher.on('unlink', (file) => {
                this.onFileRemove(file)
                    .catch(err => logger.error(err));
            });
        });
    }

    public async onNewFile(file: string): Promise<void> {
        logger.silly('a', file);
        const canonicalName = this.toCanonicalName(file);
        await this.preCompile(canonicalName, true);
        await this.afterPreCompile(true);

        await this.inputChangeHandler?.(false);
    }

    public async onFileChange(file: string): Promise<void> {
        logger.silly('c', file);
        const canonicalName = this.toCanonicalName(file);
        await this.preCompile(canonicalName, true);
        await this.afterPreCompile(true);
    }

    public async onFileRemove(file: string): Promise<void> {
        logger.silly('r', file);
        const canonicalName = this.toCanonicalName(file);
        const replacementSourceFile = await this.resolveFileFromCanonicalName(canonicalName);
        if (replacementSourceFile) {
            await this.preCompile(canonicalName, true);
            await this.afterPreCompile(true);
        } else {
            const targetFile = path.resolve(this.targetDir, canonicalName);
            await fs.rm(targetFile);
        }

        await this.inputChangeHandler?.(true);
    }

    public onInputChange(inputChangeHandler: (restart: boolean) => Promise<void>): void {
        this.inputChangeHandler = inputChangeHandler;
    }

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

        let canonicalViewName: string | null = null;
        for (const viewPath of this.assetPaths) {
            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 | null> {
        for (const viewPath of this.assetPaths) {
            const tryPath = path.join(viewPath, canonicalName);
            if (await doesFileExist(tryPath)) {
                return tryPath;
            }
        }

        return null;
    }

    protected async resolveFileFromCanonicalNameOrFail(canonicalName: string): Promise<string> {
        const file = await this.resolveFileFromCanonicalName(canonicalName);
        if (file) return file;
        else throw new Error('View not found from canonical name ' + canonicalName);
    }
}