swaf/src/frontend/SvelteViewEngine.ts

import "./register_svelte/register_svelte.js";

import clearModule from "clear-module";
import config from "config";
import crypto from "crypto";
import {promises as fs} from 'fs';
import path from "path";
import requireFromString from "require-from-string";
import {compile, preprocess} from "svelte/compiler";
import {sveltePreprocess} from "svelte-preprocess/dist/autoProcess.js";

import {publicUrl, routes} from "../common/Routing.js";
import {logger} from "../Logger.js";
import FileCache from "../utils/FileCache.js";
import ViewEngine from "./ViewEngine.js";

const BACKEND_CODE_PREFIX = '$locals.';
const BACKEND_CODE_PREFIX_TEMPORARY_HOLDER = '$$locals$$';
const COMPILED_SVELTE_EXTENSION = '.precompiled';

export default class SvelteViewEngine extends ViewEngine {
    public static getPreCompileSeparator(canonicalViewName: string): string {
        return '\n---' +
            crypto.createHash('sha1')
                .update(path.basename(path.resolve(canonicalViewName)))
                .digest('base64') +
            '---\n';
    }


    private readonly fileCache: FileCache = new FileCache();
    private readonly dependencyCache: Record<string, Set<string>> = {};
    private readonly preprocessingCache: Record<string, PreprocessingCacheEntry> = {};
    private readonly cssCache: Record<string, string[] | undefined> = {};

    public constructor(
        targetDir: string,
        ...additionalViewPaths: string[]
    ) {
        super(targetDir, 'views', 'svelte', true, ...additionalViewPaths);
    }

    public async onFileChange(file: string): Promise<void> {
        delete this.preprocessingCache[this.toCanonicalName(file)];
        await super.onFileChange(file);
    }

    public async onFileRemove(file: string): Promise<void> {
        const canonicalName = this.toCanonicalName(file);
        delete this.preprocessingCache[canonicalName];
        delete this.dependencyCache[canonicalName];
        Object.values(this.dependencyCache).forEach(set => set.delete(canonicalName));
        await super.onFileRemove(file);
    }

    public async render(
        file: string,
        locals: Record<string, unknown>,
    ): Promise<string> {
        const canonicalViewName = this.toCanonicalName(file);

        // View
        const actualFile = path.join(this.targetDir, canonicalViewName + COMPILED_SVELTE_EXTENSION);
        const view = await this.fileCache.get(actualFile, !config.get<boolean>('view.cache'));

        // Root template
        const templateFile = await this.resolveFileFromCanonicalNameOrFail('layouts/svelte_layout.html');
        const rawOutput = await this.fileCache.get(templateFile, !config.get<boolean>('view.cache'));

        // Pre-compiled parts
        const [
            backendCalls,
            head,
            html,
            css,
        ] = view.split(SvelteViewEngine.getPreCompileSeparator(canonicalViewName));

        const localMap: Record<string, unknown> = this.compileBackendCalls(backendCalls.split('\n'), locals, false);
        const actualLocals = JSON.stringify(localMap, (key, value) => {
            if (key.startsWith('_')) return undefined;
            return typeof value === 'function' ?
                value.toString() :
                value;
        });

        // Replaces
        const replaceMap: Record<string, string> = {
            canonicalViewName: canonicalViewName,
            locals: actualLocals,
            head: head,
            html: html,
            css: css,

            routes: JSON.stringify(routes),
            publicUrl: publicUrl,
        };
        return rawOutput.replace(
            new RegExp(Object.keys(replaceMap).map(str => `%${str}%`).join('|'), 'g'),
            (substring) => replaceMap[substring.slice(1, substring.length - 1)],
        );
    }

    public async preCompile(canonicalName: string, alsoCompileDependents: boolean): Promise<void> {
        const targetFile = path.join(this.targetDir, canonicalName);
        logger.info(canonicalName + ' > ', 'Pre-compiling', canonicalName, '->', targetFile);

        const {backendCalls} = await this.preprocess(canonicalName);

        // Server Side Render (initial HTML and CSS, no-js)
        const ssr = await this.compileSsr(canonicalName);

        const separator = SvelteViewEngine.getPreCompileSeparator(canonicalName);
        const finalCode = [
            [...new Set<string>(backendCalls).values()].join('\n'),
            ssr.head,
            ssr.html,
            ssr.css,
        ].join(separator);

        const swafViewFile = path.join(this.targetDir, canonicalName + COMPILED_SVELTE_EXTENSION);
        await fs.mkdir(path.dirname(swafViewFile), {recursive: true});
        await fs.writeFile(swafViewFile, finalCode);

        if (alsoCompileDependents && Object.keys(this.dependencyCache).indexOf(canonicalName) >= 0) {
            logger.info(canonicalName + ' > ', 'Compiling dependents...');
            for (const dependent of [...this.dependencyCache[canonicalName]]) {
                await this.preCompile(dependent, true);
            }
        }
    }

    private resolveDependencies(source: string, canonicalViewName: string): string[] {
        const dependencies: string[] = [];

        for (const match of source.matchAll(/import .+ from ['"](.+?\.svelte)['"];/gm)) {
            dependencies.push(path.join(path.dirname(canonicalViewName), match[1]));
        }

        // Clear existing links from cache
        for (const dependency of Object.keys(this.dependencyCache)) {
            this.dependencyCache[dependency].delete(canonicalViewName);
        }

        // Add new links to cache
        for (const dependency of dependencies) {
            if (Object.keys(this.dependencyCache).indexOf(dependency) < 0) {
                this.dependencyCache[dependency] = new Set<string>();
            }
            this.dependencyCache[dependency].add(canonicalViewName);
        }

        return dependencies;
    }

    private async preprocess(canonicalName: string): Promise<PreprocessingCacheEntry> {
        // Cache
        if (Object.keys(this.preprocessingCache).indexOf(canonicalName) >= 0) {
            return this.preprocessingCache[canonicalName];
        }

        const file = await this.resolveFileFromCanonicalNameOrFail(canonicalName);
        logger.info(canonicalName + ' > ', `Preprocessing ${file}`);

        // mkdir output file dir
        const outputFile = path.join(this.targetDir, canonicalName);
        await fs.mkdir(path.dirname(outputFile), {recursive: true});

        // Read source file if code was not already provided
        const code = await this.fileCache.get(file, !config.get<boolean>('view.cache'));

        // Replace backend calls
        const replacedBackendCalls = await this.replaceBackendCalls(canonicalName, code);

        // Preprocess svelte
        logger.info(canonicalName + ' > ', 'Svelte preprocessing');
        const preprocessed = await preprocess(
            replacedBackendCalls.code,
            sveltePreprocess({
                typescript: {
                    tsconfigFile: 'src/assets/views/tsconfig.json',
                },
            }),
            {
                filename: outputFile,
            },
        );

        // Write to output file
        await fs.writeFile(outputFile, preprocessed.code);

        // Preprocess dependencies
        const backendCalls: string[] = replacedBackendCalls.backendCalls;
        for (const dependency of this.resolveDependencies(code, canonicalName)) {
            backendCalls.push(...(await this.preprocess(dependency)).backendCalls);
        }

        return this.preprocessingCache[canonicalName] = {
            backendCalls: backendCalls,
            code: preprocessed.code,
        };
    }

    private async replaceBackendCalls(canonicalName: string, code: string): Promise<PreprocessingCacheEntry> {
        logger.info(canonicalName + ' > ', 'Replacing backend calls');

        // Skip replace if there is no swaf export
        if (!code.match(/import[ \n]+{[ \n]*locals[ \n]*}[ \n]+from[ \n]+["'](\.\.\/)+ts\/stores(\.js)?["']/)) {
            return {
                backendCalls: [],
                code: code,
            };
        }


        let output = code;
        const backendCalls = new Set<string>();

        let index = 0;
        while ((index = output.indexOf(BACKEND_CODE_PREFIX, index + 1)) >= 0) {
            // Escaping
            if (index > 0 && output[index - 1] === '\\') {
                const isEscapingEscaped: boolean = index > 1 && output[index - 2] === '\\';
                output = output.substring(0, index - 1 - (isEscapingEscaped ? 1 : 0)) +
                    output.substring(index, output.length);
                continue;
            }

            const startIndex = index + BACKEND_CODE_PREFIX.length;
            let endIndex = startIndex;
            let struct = 0;

            while (endIndex < output.length) {
                if (['(', '[', '{'].indexOf(output[endIndex]) >= 0) struct++;
                if ([')', ']', '}'].indexOf(output[endIndex]) >= 0) {
                    struct--;
                    if (struct <= 0) {
                        if (struct === 0) endIndex++;
                        break;
                    }
                }
                if ([' ', '\n', '<', '.', '\'', '"', '?', ','].indexOf(output[endIndex]) >= 0 && struct === 0) break;
                endIndex++;
            }

            let backendCall = output.substring(startIndex, endIndex);
            if (backendCall.match(/([^()]+)\((.*?)\)/)) {
                backendCall = backendCall.replace(/([^()]+)\((.*?)\)/, "'$1', `[$2]`");
            } else {
                backendCall = backendCall.replace(/([^()]+)(\(\))?/, "'$1'");
            }
            backendCalls.add(backendCall);

            output = output.substring(0, index) +
                '$locals(' + backendCall.split(BACKEND_CODE_PREFIX).join(BACKEND_CODE_PREFIX_TEMPORARY_HOLDER) + ')' +
                output.substring(endIndex, output.length);
        }
        output = output.split(BACKEND_CODE_PREFIX_TEMPORARY_HOLDER).join(BACKEND_CODE_PREFIX);

        return {
            backendCalls: [...backendCalls],
            code: output,
        };
    }

    private async compileSsr(canonicalName: string): Promise<{
        head: string,
        css: string,
        html: string,
    }> {
        const targetFile = path.join(this.targetDir, canonicalName);
        const {backendCalls, code} = await this.preprocess(canonicalName);

        // Get dependencies css
        const dependenciesCss: string[] = [];
        for (const dependency of this.resolveDependencies(code, canonicalName)) {
            if (this.cssCache[dependency] === undefined) {
                await this.compileSsr(dependency);
            }
            const css = this.cssCache[dependency];
            if (css === undefined) {
                logger.error(typeof this.cssCache[dependency], !!this.cssCache[dependency]);
                throw new Error(`Compiling ssr of ${dependency} didn't cache its css.`);
            }
            dependenciesCss.push(...css);
        }

        logger.info(canonicalName + ' > ', 'Compiling svelte ssr', targetFile);

        // Svelte compile
        const svelteSsr = compile(code, {
            dev: config.get<boolean>('view.dev'),
            generate: 'ssr',
            format: 'cjs',
            cssOutputFilename: targetFile + '.css',
        });

        // Load locals into locals store
        const localsModulePath = "../../intermediates/assets/ts/stores.js";
        const localsModule = await import(localsModulePath);
        const locals = this.getGlobals().get();
        const localMap = this.compileBackendCalls(backendCalls, locals, true);
        localsModule.locals.set((key: string, args: string) => {
            return localMap[args ?
                `'${key}', \`${args}\``
                : `'${key}'`];
        });

        // Load module and render
        const moduleId = path.resolve(targetFile);
        clearModule.single(moduleId);
        const {
            head,
            css,
            html,
        } = requireFromString(svelteSsr.js.code, moduleId).default.render();
        const cssFragments = css.code === '' ?
            dependenciesCss :
            [...dependenciesCss, css.code];
        this.cssCache[canonicalName] = cssFragments;
        return {
            head,
            css: [...new Set(cssFragments)].join(''),
            html,
        };
    }

    private compileBackendCalls(
        backendCalls: string[],
        locals: Record<string, unknown>,
        isPreRender: boolean,
    ): Record<string, unknown> {
        locals = {...locals, isPreRender};

        const localMap: Record<string, unknown> = {};
        backendCalls.forEach(code => {
            const key = code.substring(1, code.indexOf(',') >= 0 ? code.indexOf(',') - 1 : code.length - 1);
            if (code.indexOf('`[') >= 0) {
                const args = code.substring(code.indexOf('`[') + 2, code.length - 2)
                    .split(/, *?/)
                    .map(arg => {
                        if (arg.startsWith("'")) return '"' + arg.substring(1, arg.length - 1) + '"';
                        return arg;
                    })
                    .filter(arg => arg.length > 0)
                    .map(arg => {
                        return Function(`"use strict";const $locals = arguments[0];return (${arg});`)(locals);
                    }); // Uses named parameter locals

                const f = locals[key];
                if (typeof f !== 'function') throw new Error(key + ' is not a function.');
                localMap[`'${key}', \`[${code.substring(code.indexOf('`[') + 2, code.length - 2)}]\``] = f.call(locals, ...args);
            } else {
                localMap[`'${key}'`] = locals[key];
            }
        });
        return localMap;
    }
}

type PreprocessingCacheEntry = {
    backendCalls: string[],
    code: string,
};