dorfteich/apps/api/src/import-export/pandoc.converter.ts

import { Injectable } from '@nestjs/common';

import { AppConfig } from '../config/app-config.service';

/** A single pandoc conversion request (ADR 0009). `input` is the raw source
 * bytes; the converter base64-encodes it for pandoc when `from` is a binary
 * format (docx/odt/…) and passes it as text otherwise. */
export interface ConversionRequest {
  from: string;
  to: string;
  input: Buffer;
  standalone?: boolean;
  /** Inline referenced/embedded resources (images) as `data:` URIs in the
   * output. Used by the import pipeline (#63): pandoc-server is stateless and
   * will not hand back a document's media bytes any other way. */
  embedResources?: boolean;
  /** Line-wrapping of the writer's output. Import uses `none` so a paragraph
   * stays on one line (no soft breaks inside image alt text or links). */
  wrap?: 'none' | 'auto' | 'preserve';
}

export interface ConversionResult {
  output: Buffer;
  mimeType: string;
}

export type ConversionErrorCode =
  | 'converter_unavailable'
  | 'converter_timeout'
  | 'conversion_failed'
  // The pond ran out of storage while an import stored the document's media
  // (#63) — final, and surfaced the same way through the worker.
  | 'quota_exceeded'
  // Vault import (#117): rejected archive / unpacked ceiling exceeded.
  | 'import_vault_invalid_zip'
  | 'import_vault_too_large';

/** A conversion failure with a stable, localizable code. `retryable` marks
 * the transient causes (sidecar down / timed out) the worker retries before
 * giving up; a genuine `conversion_failed` (bad/unsupported content) is not
 * retried. */
export class ConversionError extends Error {
  constructor(
    readonly code: ConversionErrorCode,
    readonly retryable: boolean,
    message?: string,
  ) {
    super(message ?? code);
    this.name = 'ConversionError';
  }
}

/** Server-side conversion limits (ADR 0009). Input is checked before the
 * sidecar call; output is capped while reading the response so a runaway
 * conversion can't exhaust memory. */
export const MAX_CONVERSION_INPUT_BYTES = 25 * 1024 * 1024;
export const MAX_CONVERSION_OUTPUT_BYTES = 50 * 1024 * 1024;
/** Per ADR 0009 / issue #62: a single conversion may run for at most 60 s. */
export const CONVERSION_TIMEOUT_MS = 60_000;

/** Formats pandoc reads as binary — their bytes are base64-encoded in the
 * request `text` field; text formats are sent verbatim. */
const BINARY_INPUT_FORMATS = new Set(['docx', 'odt', 'epub', 'pptx']);

/** Served content type per pandoc output format. */
const OUTPUT_MIME_TYPES: Readonly<Record<string, string>> = {
  html: 'text/html',
  markdown: 'text/markdown',
  gfm: 'text/markdown',
  commonmark: 'text/markdown',
  plain: 'text/plain',
  docx: 'application/vnd.openxmlformats-officedocument.wordprocessingml.document',
  odt: 'application/vnd.oasis.opendocument.text',
};

/**
 * Typed client for the pandoc-server sidecar (ADR 0009). Abstract so the job
 * worker and its tests depend on the contract, not the HTTP transport — the
 * queue-mechanics tests inject a fake, this real implementation is exercised
 * against a running container in the integration test.
 */
export abstract class PandocConverter {
  abstract convert(request: ConversionRequest): Promise<ConversionResult>;
  abstract reachable(): Promise<boolean>;
}

@Injectable()
export class PandocServerConverter extends PandocConverter {
  /** Overridable so the timeout path is testable without a 60 s wait. */
  protected timeoutMs = CONVERSION_TIMEOUT_MS;

  constructor(private readonly config: AppConfig) {
    super();
  }

  private get baseUrl(): string {
    return this.config.env.PANDOC_URL;
  }

  async reachable(): Promise<boolean> {
    try {
      const response = await fetch(`${this.baseUrl}/version`);
      return response.ok;
    } catch {
      return false;
    }
  }

  async convert(request: ConversionRequest): Promise<ConversionResult> {
    if (request.input.byteLength > MAX_CONVERSION_INPUT_BYTES) {
      throw new ConversionError('conversion_failed', false, 'input exceeds size limit');
    }
    const text = BINARY_INPUT_FORMATS.has(request.from)
      ? request.input.toString('base64')
      : request.input.toString('utf8');

    const controller = new AbortController();
    const timer = setTimeout(() => controller.abort(), this.timeoutMs);
    let response: Response;
    try {
      response = await fetch(`${this.baseUrl}/`, {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({
          text,
          from: request.from,
          to: request.to,
          standalone: request.standalone ?? true,
          // pandoc-server uses hyphenated option keys; unknown keys are ignored,
          // so these are only present when the import pipeline sets them.
          ...(request.embedResources ? { 'embed-resources': true } : {}),
          ...(request.wrap ? { wrap: request.wrap } : {}),
        }),
        signal: controller.signal,
      });
    } catch (error) {
      // AbortController.abort() surfaces as an AbortError → the run timed out;
      // anything else means the sidecar could not be reached.
      if (error instanceof Error && error.name === 'AbortError') {
        throw new ConversionError('converter_timeout', true, 'pandoc timed out');
      }
      throw new ConversionError('converter_unavailable', true, shortMessage(error));
    } finally {
      clearTimeout(timer);
    }

    if (!response.ok) {
      // Non-200 = pandoc rejected the content (unknown format, malformed
      // document). Not retryable — the same input fails the same way.
      const detail = (await response.text().catch(() => '')).slice(0, 300);
      throw new ConversionError('conversion_failed', false, detail || `pandoc ${response.status}`);
    }

    const output = Buffer.from(await response.arrayBuffer());
    if (output.byteLength > MAX_CONVERSION_OUTPUT_BYTES) {
      throw new ConversionError('conversion_failed', false, 'output exceeds size limit');
    }
    return { output, mimeType: OUTPUT_MIME_TYPES[request.to] ?? 'application/octet-stream' };
  }
}

function shortMessage(error: unknown): string {
  const message = error instanceof Error ? error.message : String(error);
  return message.split('\n')[0]?.slice(0, 200) ?? 'unknown error';
}