const { set: lodashSet } = require("@11ty/lodash-custom");

const debug = require("debug")("Eleventy:ComputedDataTemplateString");

/* Calculates computed data in Template Strings.
 * Ideally we would use the Proxy approach but it doesn’t work
 * in some template languages that visit all available data even if
 * it isn’t used in the template (Nunjucks)
 */
class ComputedDataTemplateString {
  constructor(computedKeys) {
    if (Array.isArray(computedKeys)) {
      this.computedKeys = new Set(computedKeys);
    } else {
      this.computedKeys = computedKeys;
    }

    // is this ¯\_(lisp)_/¯
    // must be strings that won’t be escaped by template languages
    this.prefix = "(((11ty(((";
    this.suffix = ")))11ty)))";
  }

  getProxyData() {
    let proxyData = {};

    // use these special strings as a workaround to check the rendered output
    // can’t use proxies here as some template languages trigger proxy for all
    // keys in data
    for (let key of this.computedKeys) {
      // TODO don’t allow to set eleventyComputed.page? other disallowed computed things?
      lodashSet(proxyData, key, this.prefix + key + this.suffix);
    }

    return proxyData;
  }

  findVarsInOutput(output = "") {
    let vars = new Set();
    let splits = output.split(this.prefix);
    for (let split of splits) {
      let varName = split.slice(0, split.indexOf(this.suffix) < 0 ? 0 : split.indexOf(this.suffix));
      if (varName) {
        vars.add(varName);
      }
    }
    return Array.from(vars);
  }

  async findVarsUsed(fn) {
    let proxyData = this.getProxyData();
    let output;
    // Mitigation for #1061, errors with filters in the first pass shouldn’t fail the whole thing.
    try {
      output = await fn(proxyData);
    } catch (e) {
      debug("Computed Data first pass data resolution error: %o", e);
    }

    // page.outputPath on serverless urls returns false.
    if (typeof output === "string") {
      return this.findVarsInOutput(output);
    }
    return [];
  }
}

module.exports = ComputedDataTemplateString;