import { EventEmitter } from "events";
import {
  getMinimumPackageAgeExclusions,
  getMinimumPackageAgeHours,
} from "../../../../config/settings.js";
import { ui } from "../../../../environment/userInteraction.js";
import { clearCachingHeaders, getHeaderValueAsString } from "../../http-utils.js";

/** @type {EventEmitter<{ versionsRemoved: [{packageName: string, packageVersions: string[]}] }>} */
export const modifyResponseEventEmitter = new EventEmitter();

/**
 * @param {NodeJS.Dict<string | string[]>} headers
 * @returns {NodeJS.Dict<string | string[]>}
 */
export function modifyNpmInfoRequestHeaders(headers) {
  const accept = getHeaderValueAsString(headers, "accept");
  if (accept?.includes("application/vnd.npm.install-v1+json")) {
    // The npm registry sometimes serves a more compact format that lacks
    // the time metadata we need to filter out too new packages.
    // Force the registry to return the full metadata by changing the Accept header.
    headers["accept"] = "application/json";
  }
  return headers;
}

/**
 * @param {string} url
 * @returns {boolean}
 */
export function isPackageInfoUrl(url) {
  // Remove query string and fragment to get the actual path
  const urlWithoutParams = url.split("?")[0].split("#")[0];

  // Tarball downloads end with .tgz
  if (urlWithoutParams.endsWith(".tgz")) return false;

  // Special endpoints start with /-/ and should not be modified
  // Examples: /-/npm/v1/security/advisories/bulk, /-/v1/search, /-/package/foo/access
  if (urlWithoutParams.includes("/-/")) return false;

  // Everything else is package metadata that can be modified
  return true;
}
/**
 *
 * @param {Buffer} body
 * @param {NodeJS.Dict<string | string[]> | undefined} headers
 * @returns Buffer
 */
export function modifyNpmInfoResponse(body, headers) {
  try {
    const contentType = getHeaderValueAsString(headers, "content-type");
    if (!contentType?.toLowerCase().includes("application/json")) {
      return body;
    }

    if (body.byteLength === 0) {
      return body;
    }

    // utf-8 is default encoding for JSON, so we don't check if charset is defined in content-type header
    const bodyContent = body.toString("utf8");
    const bodyJson = JSON.parse(bodyContent);

    if (!bodyJson.time || !bodyJson["dist-tags"] || !bodyJson.versions) {
      // Just return the current body if the format is not
      return body;
    }

    // Check if this package is excluded from minimum age filtering
    const packageName = bodyJson.name;
    const exclusions = getMinimumPackageAgeExclusions();
    if (
      packageName &&
      exclusions.some((pattern) =>
        matchesExclusionPattern(packageName, pattern),
      )
    ) {
      ui.writeVerbose(
        `Safe-chain: ${packageName} is excluded from minimum package age filtering (minimumPackageAgeExclusions setting).`,
      );
      return body;
    }

    const cutOff = new Date(
      new Date().getTime() - getMinimumPackageAgeHours() * 3600 * 1000,
    );

    const hasLatestTag = !!bodyJson["dist-tags"]["latest"];

    const versions = Object.entries(bodyJson.time)
      .map(([version, timestamp]) => ({
        version,
        timestamp,
      }))
      .filter((x) => x.version !== "created" && x.version !== "modified");

    const removedVersions = [];

    for (const { version, timestamp } of versions) {
      const timestampValue = new Date(timestamp);
      if (timestampValue > cutOff) {
        removedVersions.push(version);

        deleteVersionFromJson(bodyJson, version);
        clearCachingHeaders(headers);
      }
    }

    if (hasLatestTag && !bodyJson["dist-tags"]["latest"]) {
      // The latest tag was removed because it contained a package younger than the treshold.
      // A new latest tag needs to be calculated
      bodyJson["dist-tags"]["latest"] = calculateLatestTag(bodyJson.time);
    }

    if (removedVersions.length > 0) {
      modifyResponseEventEmitter.emit("versionsRemoved", {
        packageName: packageName,
        packageVersions: removedVersions,
      });
    }

    return Buffer.from(JSON.stringify(bodyJson));
  } catch (/** @type {any} */ err) {
    ui.writeVerbose(
      `Safe-chain: Package metadata not in expected format - bypassing modification. Error: ${err.message}`,
    );
    return body;
  }
}

/**
 * @param {any} json
 * @param {string} version
 */
function deleteVersionFromJson(json, version) {
  const packageName = typeof json?.name === "string" ? json.name : "(unknown)";

  ui.writeVerbose(
    `Safe-chain: ${packageName}@${version} is newer than ${getMinimumPackageAgeHours()} hours and was removed (minimumPackageAgeInHours setting).`,
  );

  delete json.time[version];
  delete json.versions[version];

  for (const [tag, distVersion] of Object.entries(json["dist-tags"])) {
    if (version == distVersion) {
      delete json["dist-tags"][tag];
    }
  }
}

/**
 * @param {Record<string, string>} tagList
 * @returns {string | undefined}
 */
function calculateLatestTag(tagList) {
  const entries = Object.entries(tagList).filter(
    ([version, _]) => version !== "created" && version !== "modified",
  );

  const latestFullRelease = getMostRecentTag(
    Object.fromEntries(
      entries.filter(([version, _]) => !version.includes("-")),
    ),
  );
  if (latestFullRelease) {
    return latestFullRelease;
  }

  const latestPrerelease = getMostRecentTag(
    Object.fromEntries(entries.filter(([version, _]) => version.includes("-"))),
  );
  return latestPrerelease;
}

/**
 * @param {Record<string, string>} tagList
 * @returns {string | undefined}
 */
function getMostRecentTag(tagList) {
  let current, currentDate;

  for (const [version, timestamp] of Object.entries(tagList)) {
    if (!currentDate || currentDate < timestamp) {
      current = version;
      currentDate = timestamp;
    }
  }

  return current;
}

/**
 * Checks if a package name matches an exclusion pattern.
 * Supports trailing wildcard (*) for prefix matching.
 * @param {string} packageName
 * @param {string} pattern
 * @returns {boolean}
 */
function matchesExclusionPattern(packageName, pattern) {
  if (pattern.endsWith("/*")) {
    return packageName.startsWith(pattern.slice(0, -1));
  }
  return packageName === pattern;
}

/**
 * @param {Buffer} body
 * @param {NodeJS.Dict<string | string[]> | undefined} headers
 * @returns {string | undefined}
 */
export function getPackageNameFromMetadataResponse(body, headers) {
  try {
    const contentType = getHeaderValueAsString(headers, "content-type");
    if (!contentType?.toLowerCase().includes("application/json")) {
      return undefined;
    }

    const bodyJson = JSON.parse(body.toString("utf8"));
    return typeof bodyJson.name === "string" ? bodyJson.name : undefined;
  } catch {
    return undefined;
  }
}