/**
 * ES-module emitter for the optional view compiler.
 *
 * Turns a {@link CompiledView} into an importable side-effect module that
 * registers the precompiled expressions at startup. The emitted code contains
 * no `with` and no `new Function()`, so importing it is safe under a strict CSP.
 *
 * @module bquery/view/compiler
 */

import { compileViews } from './compile';
import type { CompiledView, CompileOptions, CompileStats } from './types';

/** Default module specifier the emitted code imports the runtime hook from. */
export const DEFAULT_IMPORT_SPECIFIER = '@bquery/bquery/view';

/** Options for {@link emitModule} / {@link compileToModule}. */
export type EmitOptions = CompileOptions & {
  /**
   * Module specifier to import `registerCompiledExpressions` from. Defaults to
   * `'@bquery/bquery/view'`; override it for monorepos or custom aliases.
   */
  importSpecifier?: string;
};

/**
 * Emits an importable ES module from an already-compiled view.
 */
export const emitModule = (
  compiled: CompiledView,
  importSpecifier: string = DEFAULT_IMPORT_SPECIFIER
): string => {
  const entries = Object.keys(compiled.expressions);
  const lines = entries.map(
    (expression) => `  ${JSON.stringify(expression)}: ${compiled.expressions[expression]},`
  );

  const header =
    '// Auto-generated by @bquery/bquery/view/compiler. Do not edit by hand.\n' +
    `// Compiled ${compiled.stats.compiled}/${compiled.stats.total} expression(s); ` +
    `${compiled.stats.skipped.length} fall back to the runtime evaluator.\n`;

  if (entries.length === 0) {
    // Nothing compiled — emit a valid no-op module so the build step never
    // produces a broken import.
    return `${header}export {};\n`;
  }

  return (
    `${header}import { registerCompiledExpressions } from ${JSON.stringify(importSpecifier)};\n\n` +
    `registerCompiledExpressions({\n${lines.join('\n')}\n});\n`
  );
};

/**
 * Compiles a template and emits an importable ES module in one step.
 *
 * @returns The module source and the compile statistics (so a build tool can
 *   report or assert on coverage).
 *
 * @example
 * ```ts
 * import { compileToModule } from '@bquery/bquery/view/compiler';
 *
 * const { code, stats } = compileToModule('<p bq-text="count"></p>');
 * // write `code` next to your template and import it before mounting
 * ```
 */
export const compileToModule = (
  template: string,
  options: EmitOptions = {}
): { code: string; stats: CompileStats } => {
  const compiled = compileViews(template, options);
  return {
    code: emitModule(compiled, options.importSpecifier),
    stats: compiled.stats,
  };
};