import { Injectable, OnModuleInit } from '@nestjs/common';
import * as fs from 'fs';
import * as path from 'path';
import Handlebars from 'handlebars';

import {
  interpolateTemplateText,
  parseArticleBody,
  RenderedArticle,
} from './contract-article.util';
import { ContractViewModel } from './contract-view-model.builder';

@Injectable()
export class ContractRendererService implements OnModuleInit {
  private readonly templatesDir = path.join(__dirname, 'templates');
  private readonly compiled = new Map<string, Handlebars.TemplateDelegate>();

  onModuleInit(): void {
    Handlebars.registerHelper('eq', (a: unknown, b: unknown) => a === b);

    const partialsDir = path.join(this.templatesDir, '_partials');
    if (fs.existsSync(partialsDir)) {
      for (const file of fs.readdirSync(partialsDir)) {
        if (!file.endsWith('.hbs')) continue;
        const name = file.replace(/\.hbs$/, '');
        const content = fs.readFileSync(path.join(partialsDir, file), 'utf-8');
        Handlebars.registerPartial(name, content);
      }
    }
  }

  render(view: ContractViewModel): string {
    const fileName =
      view.template.templateFile ?? 'generic.hbs';
    const template = this.getCompiled(fileName);
    return template({
      ...view,
      paymentArticle: view.pricing.currency === 'ETB' ? 'ETB' : 'USD',
      ...this.buildDynamicSections(view),
    });
  }

  /**
   * Turn the DB-backed dynamic template (when present) into render-ready data:
   * interpolate placeholders against the view model, then parse each article
   * body into numbered clauses with nested bullets.
   */
  private buildDynamicSections(view: ContractViewModel): {
    dynamicDocumentTitle?: string;
    dynamicWhereas?: string[];
    dynamicArticles?: RenderedArticle[];
  } {
    const dyn = view.dynamicTemplate;
    if (!dyn || dyn.articles.length === 0) return {};

    const articles = [...dyn.articles]
      .sort((a, b) => (a.order ?? 0) - (b.order ?? 0))
      .map((article, index) => ({
        number: index + 1,
        id: article.id,
        title: interpolateTemplateText(article.title, view),
        ...parseArticleBody(interpolateTemplateText(article.body, view)),
      }));

    return {
      dynamicDocumentTitle: interpolateTemplateText(dyn.documentTitle, view),
      dynamicWhereas: dyn.whereasClauses.map((clause) =>
        interpolateTemplateText(clause, view),
      ),
      dynamicArticles: articles,
    };
  }

  private getCompiled(fileName: string): Handlebars.TemplateDelegate {
    const cached = this.compiled.get(fileName);
    if (cached) return cached;

    const filePath = path.join(this.templatesDir, fileName);
    const fallbackPath = path.join(this.templatesDir, 'generic.hbs');
    const source = fs.existsSync(filePath)
      ? fs.readFileSync(filePath, 'utf-8')
      : fs.readFileSync(fallbackPath, 'utf-8');

    const compiled = Handlebars.compile(source);
    this.compiled.set(fileName, compiled);
    return compiled;
  }
}