text: // @flow
  import * as t from "@babel/types";
  
  import type { TemplateReplacements } from "./options";
  import type { Metadata, Placeholder } from "./parse";
  
  export default function populatePlaceholders(
    metadata: Metadata,
    replacements: TemplateReplacements,
  ): BabelNodeFile {
    const ast = t.cloneNode(metadata.ast);
  
    if (replacements) {
      metadata.placeholders.forEach(placeholder => {
        if (
          !Object.prototype.hasOwnProperty.call(replacements, placeholder.name)
        ) {
          const placeholderName = placeholder.name;
  
          throw new Error(
            `Error: No substitution given for "${placeholderName}". If this is not meant to be a
              placeholder you may want to consider passing one of the following options to @babel/template:
              - { placeholderPattern: false, placeholderWhitelist: new Set(['${placeholderName}'])}
              - { placeholderPattern: /^${placeholderName}$/ }`,
          );
        }
      });
      Object.keys(replacements).forEach(key => {
        if (!metadata.placeholderNames.has(key)) {
          throw new Error(`Unknown substitution "${key}" given`);
        }
      });
    }
  
    // Process in reverse order to AST mutation doesn't change indices that
    // will be needed for later calls to `placeholder.resolve()`.
    metadata.placeholders
      .slice()
      .reverse()
      .forEach(placeholder => {
        try {
          applyReplacement(
            placeholder,
            ast,
            (replacements && replacements[placeholder.name]) || null,
          );
        } catch (e) {
          e.message = `@babel/template placeholder "${placeholder.name}": ${
            e.message
          }`;
          throw e;
        }
      });
  
    return ast;
  }
  
  function applyReplacement(
    placeholder: Placeholder,
    ast: BabelNodeFile,
    replacement: any,
  ) {
    // Track inserted nodes and clone them if they are inserted more than
    // once to avoid injecting the same node multiple times.
    if (placeholder.isDuplicate) {
      if (Array.isArray(replacement)) {
        replacement = replacement.map(node => t.cloneNode(node));
      } else if (typeof replacement === "object") {
        replacement = t.cloneNode(replacement);
      }
    }
  
    const { parent, key, index } = placeholder.resolve(ast);
  
    if (placeholder.type === "string") {
      if (typeof replacement === "string") {
        replacement = t.stringLiteral(replacement);
      }
      if (!replacement || !t.isStringLiteral(replacement)) {
        throw new Error("Expected string substitution");
      }
    } else if (placeholder.type === "statement") {
      if (index === undefined) {
        if (!replacement) {
          replacement = t.emptyStatement();
        } else if (Array.isArray(replacement)) {
          replacement = t.blockStatement(replacement);
        } else if (typeof replacement === "string") {
          replacement = t.expressionStatement(t.identifier(replacement));
        } else if (!t.isStatement(replacement)) {
          replacement = t.expressionStatement((replacement: any));
        }
      } else {
        if (replacement && !Array.isArray(replacement)) {
          if (typeof replacement === "string") {
            replacement = t.identifier(replacement);
          }
          if (!t.isStatement(replacement)) {
            replacement = t.expressionStatement((replacement: any));
          }
        }
      }
    } else if (placeholder.type === "param") {
      if (typeof replacement === "string") {
        replacement = t.identifier(replacement);
      }
  
      if (index === undefined) throw new Error("Assertion failure.");
    } else {
      if (typeof replacement === "string") {
        replacement = t.identifier(replacement);
      }
      if (Array.isArray(replacement)) {
        throw new Error("Cannot replace single expression with an array.");
      }
    }
  
    if (index === undefined) {
      t.validate(parent, key, replacement);
  
      (parent: any)[key] = replacement;
    } else {
      const items: Array<BabelNode> = (parent: any)[key].slice();
  
      if (placeholder.type === "statement" || placeholder.type === "param") {
        if (replacement == null) {
          items.splice(index, 1);
        } else if (Array.isArray(replacement)) {
          items.splice(index, 1, ...replacement);
        } else {
          items[index] = replacement;
        }
      } else {
        items[index] = replacement;
      }
  
      t.validate(parent, key, items);
      (parent: any)[key] = items;
    }
  }
  