-----------------------------------------------------------------------------
-- URI parsing, composition and relative URL resolution
-- LuaSocket toolkit.
-- Author: Diego Nehab
-----------------------------------------------------------------------------

-----------------------------------------------------------------------------
-- Declare module
-----------------------------------------------------------------------------
local string = require("string")
local base = _G
local table = require("table")
local socket = require("socket")

socket.url = {}
local _M = socket.url

-----------------------------------------------------------------------------
-- Module version
-----------------------------------------------------------------------------
_M._VERSION = "URL 1.0.3"

-----------------------------------------------------------------------------
-- Encodes a string into its escaped hexadecimal representation
-- Input
--   s: binary string to be encoded
-- Returns
--   escaped representation of string binary
-----------------------------------------------------------------------------
function _M.escape(s)
  return (string.gsub(s, "([^A-Za-z0-9_])", function(c)
    return string.format("%%%02x", string.byte(c))
  end))
end

-----------------------------------------------------------------------------
-- Protects a path segment, to prevent it from interfering with the
-- url parsing.
-- Input
--   s: binary string to be encoded
-- Returns
--   escaped representation of string binary
-----------------------------------------------------------------------------
local function make_set(t)
  local s = {}
  for i,v in base.ipairs(t) do
    s[t[i]] = 1
  end
  return s
end

-- these are allowed withing a path segment, along with alphanum
-- other characters must be escaped
local segment_set = make_set {
  "-", "_", ".", "!", "~", "*", "'", "(",
  ")", ":", "@", "&", "=", "+", "$", ",",
}

local function protect_segment(s)
  return string.gsub(s, "([^A-Za-z0-9_])", function (c)
    if segment_set[c] then return c
     else return string.format("%%%02x", string.byte(c)) end
  end)
end

-----------------------------------------------------------------------------
-- Encodes a string into its escaped hexadecimal representation
-- Input
--   s: binary string to be encoded
-- Returns
--   escaped representation of string binary
-----------------------------------------------------------------------------
function _M.unescape(s)
  return (string.gsub(s, "%%(%x%x)", function(hex)
    return string.char(base.tonumber(hex, 16))
  end))
end

-----------------------------------------------------------------------------
-- Builds a path from a base path and a relative path
-- Input
--   base_path
--   relative_path
-- Returns
--   corresponding absolute path
-----------------------------------------------------------------------------
local function absolute_path(base_path, relative_path)
  if string.sub(relative_path, 1, 1) == "/" then return relative_path end
  local path = string.gsub(base_path, "[^/]*$", "")
  path = path .. relative_path
  path = string.gsub(path, "([^/]*%./)", function (s)
    if s ~= "./" then return s else return "" end
  end)
  path = string.gsub(path, "/%.$", "/")
  local reduced
  while reduced ~= path do
    reduced = path
    path = string.gsub(reduced, "([^/]*/%.%./)", function (s)
      if s ~= "../../" then return "" else return s end
    end)
  end
  path = string.gsub(reduced, "([^/]*/%.%.)$", function (s)
    if s ~= "../.." then return "" else return s end
  end)
  return path
end

-----------------------------------------------------------------------------
-- Parses a url and returns a table with all its parts according to RFC 2396
-- The following grammar describes the names given to the URL parts
-- <url> ::= <scheme>://<authority>/<path>;<params>?<query>#<fragment>
-- <authority> ::= <userinfo>@<host>:<port>
-- <userinfo> ::= <user>[:<password>]
-- <path> :: = {<segment>/}<segment>
-- Input
--   url: uniform resource locator of request
--   default: table with default values for each field
-- Returns
--   table with the following fields, where RFC naming conventions have
--   been preserved:
--     scheme, authority, userinfo, user, password, host, port,
--     path, params, query, fragment
-- Obs:
--   the leading '/' in {/<path>} is considered part of <path>
-----------------------------------------------------------------------------
function _M.parse(url, def)
  -- initialize default parameters
  local parsed = {}
  for i,v in base.pairs(def or parsed) do parsed[i] = v end
  -- empty url is parsed to nil
  if not url or url == "" then return nil, "invalid url" end
  -- remove whitespace
  -- url = string.gsub(url, "%s", "")
  -- get fragment
  url = string.gsub(url, "#(.*)$", function(f)
    parsed.fragment = f
    return ""
  end)
  -- get scheme
  url = string.gsub(url, "^([%w][%w%+%-%.]*)%:",
  function(s) parsed.scheme = s; return "" end)
  -- get authority
  url = string.gsub(url, "^//([^/]*)", function(n)
    parsed.authority = n
    return ""
  end)
  -- get query string
  url = string.gsub(url, "%?(.*)", function(q)
    parsed.query = q
    return ""
  end)
  -- get params
  url = string.gsub(url, "%;(.*)", function(p)
    parsed.params = p
    return ""
  end)
  -- path is whatever was left
  if url ~= "" then parsed.path = url end
  local authority = parsed.authority
  if not authority then return parsed end
  authority = string.gsub(authority,"^([^@]*)@",
  function(u) parsed.userinfo = u; return "" end)
  authority = string.gsub(authority, ":([^:%]]*)$",
  function(p) parsed.port = p; return "" end)
  if authority ~= "" then
    -- IPv6?
    parsed.host = string.match(authority, "^%[(.+)%]$") or authority
  end
  local userinfo = parsed.userinfo
  if not userinfo then return parsed end
  userinfo = string.gsub(userinfo, ":([^:]*)$",
  function(p) parsed.password = p; return "" end)
  parsed.user = userinfo
  return parsed
end

-----------------------------------------------------------------------------
-- Rebuilds a parsed URL from its components.
-- Components are protected if any reserved or unallowed characters are found
-- Input
--   parsed: parsed URL, as returned by parse
-- Returns
--   a stringing with the corresponding URL
-----------------------------------------------------------------------------
function _M.build(parsed)
  local ppath = _M.parse_path(parsed.path or "")
  local url = _M.build_path(ppath)
  if parsed.params then url = url .. ";" .. parsed.params end
  if parsed.query then url = url .. "?" .. parsed.query end
  local authority = parsed.authority
  if parsed.host then
    authority = parsed.host
    if string.find(authority, ":") then -- IPv6?
      authority = "[" .. authority .. "]"
    end
    if parsed.port then authority = authority .. ":" .. parsed.port end
    local userinfo = parsed.userinfo
    if parsed.user then
      userinfo = parsed.user
      if parsed.password then
        userinfo = userinfo .. ":" .. parsed.password
      end
    end
    if userinfo then authority = userinfo .. "@" .. authority end
  end
  if authority then url = "//" .. authority .. url end
  if parsed.scheme then url = parsed.scheme .. ":" .. url end
  if parsed.fragment then url = url .. "#" .. parsed.fragment end
  -- url = string.gsub(url, "%s", "")
  return url
end

-----------------------------------------------------------------------------
-- Builds a absolute URL from a base and a relative URL according to RFC 2396
-- Input
--   base_url
--   relative_url
-- Returns
--   corresponding absolute url
-----------------------------------------------------------------------------
function _M.absolute(base_url, relative_url)
  if base.type(base_url) == "table" then
    base_parsed = base_url
    base_url = _M.build(base_parsed)
   else
    base_parsed = _M.parse(base_url)
  end
  local relative_parsed = _M.parse(relative_url)
  if not base_parsed then return relative_url
   elseif not relative_parsed then return base_url
   elseif relative_parsed.scheme then return relative_url
   else
    relative_parsed.scheme = base_parsed.scheme
    if not relative_parsed.authority then
      relative_parsed.authority = base_parsed.authority
      if not relative_parsed.path then
        relative_parsed.path = base_parsed.path
        if not relative_parsed.params then
          relative_parsed.params = base_parsed.params
          if not relative_parsed.query then
            relative_parsed.query = base_parsed.query
          end
        end
       else
        relative_parsed.path = absolute_path(base_parsed.path or "",
        relative_parsed.path)
      end
    end
    return _M.build(relative_parsed)
  end
end

-----------------------------------------------------------------------------
-- Breaks a path into its segments, unescaping the segments
-- Input
--   path
-- Returns
--   segment: a table with one entry per segment
-----------------------------------------------------------------------------
function _M.parse_path(path)
  local parsed = {}
  path = path or ""
  --path = string.gsub(path, "%s", "")
  string.gsub(path, "([^/]+)", function (s) table.insert(parsed, s) end)
  for i = 1, #parsed do
    parsed[i] = _M.unescape(parsed[i])
  end
  if string.sub(path, 1, 1) == "/" then parsed.is_absolute = 1 end
  if string.sub(path, -1, -1) == "/" then parsed.is_directory = 1 end
  return parsed
end

-----------------------------------------------------------------------------
-- Builds a path component from its segments, escaping protected characters.
-- Input
--   parsed: path segments
--   unsafe: if true, segments are not protected before path is built
-- Returns
--   path: corresponding path stringing
-----------------------------------------------------------------------------
function _M.build_path(parsed, unsafe)
  local path = ""
  local n = #parsed
  if unsafe then
    for i = 1, n-1 do
      path = path .. parsed[i]
      path = path .. "/"
    end
    if n > 0 then
      path = path .. parsed[n]
      if parsed.is_directory then path = path .. "/" end
    end
   else
    for i = 1, n-1 do
      path = path .. protect_segment(parsed[i])
      path = path .. "/"
    end
    if n > 0 then
      path = path .. protect_segment(parsed[n])
      if parsed.is_directory then path = path .. "/" end
    end
  end
  if parsed.is_absolute then path = "/" .. path end
  return path
end

return _M
