/**
 * Module dependencies.
 */

var mime = require('send').mime;
var crc32 = require('buffer-crc32');
var crypto = require('crypto');
var basename = require('path').basename;
var proxyaddr = require('proxy-addr');
var typer = require('media-typer');

/**
 * Return strong ETag for `body`.
 *
 * @param {String|Buffer} body
 * @param {String} [encoding]
 * @return {String}
 * @api private
 */

exports.etag = function etag(body, encoding){
  if (body.length === 0) {
    // fast-path empty body
    return '"1B2M2Y8AsgTpgAmY7PhCfg=="'
  }

  var hash = crypto
    .createHash('md5')
    .update(body, encoding)
    .digest('base64')
  return '"' + hash + '"'
};

/**
 * Return weak ETag for `body`.
 *
 * @param {String|Buffer} body
 * @param {String} [encoding]
 * @return {String}
 * @api private
 */

exports.wetag = function wetag(body, encoding){
  if (body.length === 0) {
    // fast-path empty body
    return 'W/"0-0"'
  }

  var buf = Buffer.isBuffer(body)
    ? body
    : new Buffer(body, encoding)
  var len = buf.length
  return 'W/"' + len.toString(16) + '-' + crc32.unsigned(buf) + '"'
};

/**
 * Check if `path` looks absolute.
 *
 * @param {String} path
 * @return {Boolean}
 * @api private
 */

exports.isAbsolute = function(path){
  if ('/' == path[0]) return true;
  if (':' == path[1] && '\\' == path[2]) return true;
  if ('\\\\' == path.substring(0, 2)) return true; // Microsoft Azure absolute path
};

/**
 * Flatten the given `arr`.
 *
 * @param {Array} arr
 * @return {Array}
 * @api private
 */

exports.flatten = function(arr, ret){
  ret = ret || [];
  var len = arr.length;
  for (var i = 0; i < len; ++i) {
    if (Array.isArray(arr[i])) {
      exports.flatten(arr[i], ret);
    } else {
      ret.push(arr[i]);
    }
  }
  return ret;
};

/**
 * Normalize the given `type`, for example "html" becomes "text/html".
 *
 * @param {String} type
 * @return {Object}
 * @api private
 */

exports.normalizeType = function(type){
  return ~type.indexOf('/')
    ? acceptParams(type)
    : { value: mime.lookup(type), params: {} };
};

/**
 * Normalize `types`, for example "html" becomes "text/html".
 *
 * @param {Array} types
 * @return {Array}
 * @api private
 */

exports.normalizeTypes = function(types){
  var ret = [];

  for (var i = 0; i < types.length; ++i) {
    ret.push(exports.normalizeType(types[i]));
  }

  return ret;
};

/**
 * Generate Content-Disposition header appropriate for the filename.
 * non-ascii filenames are urlencoded and a filename* parameter is added
 *
 * @param {String} filename
 * @return {String}
 * @api private
 */

exports.contentDisposition = function(filename){
  var ret = 'attachment';
  if (filename) {
    filename = basename(filename);
    // if filename contains non-ascii characters, add a utf-8 version ala RFC 5987
    ret = /[^\040-\176]/.test(filename)
      ? 'attachment; filename="' + encodeURI(filename) + '"; filename*=UTF-8\'\'' + encodeURI(filename)
      : 'attachment; filename="' + filename + '"';
  }

  return ret;
};

/**
 * Parse accept params `str` returning an
 * object with `.value`, `.quality` and `.params`.
 * also includes `.originalIndex` for stable sorting
 *
 * @param {String} str
 * @return {Object}
 * @api private
 */

function acceptParams(str, index) {
  var parts = str.split(/ *; */);
  var ret = { value: parts[0], quality: 1, params: {}, originalIndex: index };

  for (var i = 1; i < parts.length; ++i) {
    var pms = parts[i].split(/ *= */);
    if ('q' == pms[0]) {
      ret.quality = parseFloat(pms[1]);
    } else {
      ret.params[pms[0]] = pms[1];
    }
  }

  return ret;
}

/**
 * Compile "etag" value to function.
 *
 * @param  {Boolean|String|Function} val
 * @return {Function}
 * @api private
 */

exports.compileETag = function(val) {
  var fn;

  if (typeof val === 'function') {
    return val;
  }

  switch (val) {
    case true:
      fn = exports.wetag;
      break;
    case false:
      break;
    case 'strong':
      fn = exports.etag;
      break;
    case 'weak':
      fn = exports.wetag;
      break;
    default:
      throw new TypeError('unknown value for etag function: ' + val);
  }

  return fn;
}

/**
 * Compile "proxy trust" value to function.
 *
 * @param  {Boolean|String|Number|Array|Function} val
 * @return {Function}
 * @api private
 */

exports.compileTrust = function(val) {
  if (typeof val === 'function') return val;

  if (val === true) {
    // Support plain true/false
    return function(){ return true };
  }

  if (typeof val === 'number') {
    // Support trusting hop count
    return function(a, i){ return i < val };
  }

  if (typeof val === 'string') {
    // Support comma-separated values
    val = val.split(/ *, */);
  }

  return proxyaddr.compile(val || []);
}

/**
 * Set the charset in a given Content-Type string.
 *
 * @param {String} type
 * @param {String} charset
 * @return {String}
 * @api private
 */

exports.setCharset = function(type, charset){
  if (!type || !charset) return type;

  // parse type
  var parsed = typer.parse(type);

  // set charset
  parsed.parameters.charset = charset;

  // format type
  return typer.format(parsed);
};
