sebmck/6to5

// @flow

import {
  merge,
  validate,
  type TemplateOpts,
  type PublicOpts,
  type PublicReplacements,
} from "./options";
import type { Formatter } from "./formatters";

import stringTemplate from "./string";
import literalTemplate from "./literal";

export type TemplateBuilder<T> = {
  // Build a new builder, merging the given options with the previous ones.
  (opts: PublicOpts): TemplateBuilder<T>,

  // Building from a string produces an AST builder function by default.
  (tpl: string, opts: ?PublicOpts): (?PublicReplacements) => T,

  // Building from a template literal produces an AST builder function by default.
  (tpl: Array<string>, ...args: Array<mixed>): (?PublicReplacements) => T,

  // Allow users to explicitly create templates that produce ASTs, skipping
  // the need for an intermediate function.
  ast: {
    (tpl: string, opts: ?PublicOpts): T,
    (tpl: Array<string>, ...args: Array<mixed>): T,
  },
};

// Prebuild the options that will be used when parsing a `.ast` template.
// These do not use a pattern because there is no way for users to pass in
// replacement patterns to begin with, and disabling pattern matching means
// users have more flexibility in what type of content they have in their
// template JS.
const NO_PLACEHOLDER: TemplateOpts = validate({
  placeholderPattern: false,
});

export default function createTemplateBuilder<T>(
  formatter: Formatter<T>,
  defaultOpts?: TemplateOpts,
): TemplateBuilder<T> {
  const templateFnCache = new WeakMap();
  const templateAstCache = new WeakMap();
  const cachedOpts = defaultOpts || validate(null);

  return Object.assign(
    ((tpl, ...args) => {
      if (typeof tpl === "string") {
        if (args.length > 1) throw new Error("Unexpected extra params.");
        return extendedTrace(
          stringTemplate(formatter, tpl, merge(cachedOpts, validate(args[0]))),
        );
      } else if (Array.isArray(tpl)) {
        let builder = templateFnCache.get(tpl);
        if (!builder) {
          builder = literalTemplate(formatter, tpl, cachedOpts);
          templateFnCache.set(tpl, builder);
        }
        return extendedTrace(builder(args));
      } else if (typeof tpl === "object" && tpl) {
        if (args.length > 0) throw new Error("Unexpected extra params.");
        return createTemplateBuilder(
          formatter,
          merge(cachedOpts, validate(tpl)),
        );
      }
      throw new Error(`Unexpected template param ${typeof tpl}`);
    }: Function),
    {
      ast: (tpl, ...args) => {
        if (typeof tpl === "string") {
          if (args.length > 1) throw new Error("Unexpected extra params.");
          return stringTemplate(
            formatter,
            tpl,
            merge(merge(cachedOpts, validate(args[0])), NO_PLACEHOLDER),
          )();
        } else if (Array.isArray(tpl)) {
          let builder = templateAstCache.get(tpl);
          if (!builder) {
            builder = literalTemplate(
              formatter,
              tpl,
              merge(cachedOpts, NO_PLACEHOLDER),
            );
            templateAstCache.set(tpl, builder);
          }
          return builder(args)();
        }

        throw new Error(`Unexpected template param ${typeof tpl}`);
      },
    },
  );
}

function extendedTrace<Arg, Result>(fn: Arg => Result): Arg => Result {
  // Since we lazy parse the template, we get the current stack so we have the
  // original stack to append if it errors when parsing
  let rootStack = "";
  try {
    // error stack gets populated in IE only on throw
    // (https://msdn.microsoft.com/en-us/library/hh699850(v=vs.94).aspx)
    throw new Error();
  } catch (error) {
    if (error.stack) {
      // error.stack does not exists in IE <= 9
      // We slice off the top 3 items in the stack to remove the call to
      // 'extendedTrace', and the anonymous builder function, with the final
      // stripped line being the error message itself since we threw it
      // in the first place and it doesn't matter.
      rootStack = error.stack.split("\n").slice(3).join("\n");
    }
  }

  return (arg: Arg) => {
    try {
      return fn(arg);
    } catch (err) {
      err.stack += `\n    =============\n${rootStack}`;
      throw err;
    }
  };
}