-------------------------------------------------------------------------------
--         FILE:  luaotfload-configuration.lua
--  DESCRIPTION:  part of luaotfload / luaotfload-tool / config file reader
--       AUTHOR:  Philipp Gesang, <phg@phi-gamma.net>
--       AUTHOR:  Dohyun Kim <nomosnomos@gmail.com>
-------------------------------------------------------------------------------

local ProvidesLuaModule = { 
    name          = "luaotfload-configuration",
    version       = "2.94",       --TAGVERSION
    date          = "2018-12-19", --TAGDATE
    description   = "luaotfload submodule / config file reader",
    license       = "GPL v2.0"
}

if luatexbase and luatexbase.provides_module then
  luatexbase.provides_module (ProvidesLuaModule)
end  

------------------------------

local status_file             = "luaotfload-status"
local luaotfloadstatus        = require (status_file)

local string                  = string
local stringfind              = string.find
local stringformat            = string.format
local stringstrip             = string.strip
local stringsub               = string.sub

local tableappend             = table.append
local tableconcat             = table.concat
local tablecopy               = table.copy
local table                   = table
local tabletohash             = table.tohash

local math                    = math
local mathfloor               = math.floor

local io                      = io
local ioloaddata              = io.loaddata
local iopopen                 = io.popen
local iowrite                 = io.write

local os                      = os
local osdate                  = os.date
local osgetenv                = os.getenv

local lpeg                    = require "lpeg"
local lpegmatch               = lpeg.match
local commasplitter           = lpeg.splitat ","
local equalssplitter          = lpeg.splitat "="

local kpseexpand_path         = kpse.expand_path

local lfs                     = lfs
local lfsisfile               = lfs.isfile
local lfsisdir                = lfs.isdir

local file                    = file
local filejoin                = file.join
local filereplacesuffix       = file.replacesuffix

local logreport               = print -- overloaded later
local getwritablepath         = caches.getwritablepath


local config_parser -- set later during init
local stripslashes  -- set later during init

-------------------------------------------------------------------------------
---                                SETTINGS
-------------------------------------------------------------------------------

local path_t = 0
local kpse_t = 1

local val_home            = kpseexpand_path "~"
local val_xdg_config_home = kpseexpand_path "$XDG_CONFIG_HOME"

if val_xdg_config_home == "" then val_xdg_config_home = "~/.config" end

local config_paths = {
  --- needs adapting for those other OS
  { path_t, "./luaotfload.conf" },
  { path_t, "./luaotfloadrc" },
  { path_t, filejoin (val_xdg_config_home, "luaotfload/luaotfload.conf") },
  { path_t, filejoin (val_xdg_config_home, "luaotfload/luaotfloadrc") },
  { path_t, filejoin (val_home, ".luaotfloadrc") },
  { kpse_t, "luaotfloadrc" },
  { kpse_t, "luaotfload.conf" },
}

local valid_formats = tabletohash {
  "otf", "ttc", "ttf", "afm", "pfb"
}

local default_anon_sequence = {
  "tex", "path", "name"
}

local valid_resolvers = tabletohash {
  "tex", "path", "name", "file", "my"
}

local feature_presets = {
  arab = tabletohash {
    "ccmp", "locl", "isol", "fina", "fin2",
    "fin3", "medi", "med2", "init", "rlig",
    "calt", "liga", "cswh", "mset", "curs",
    "kern", "mark", "mkmk",
  },
  deva = tabletohash {
    "ccmp", "locl", "init", "nukt", "akhn",
    "rphf", "blwf", "half", "pstf", "vatu",
    "pres", "blws", "abvs", "psts", "haln",
    "calt", "blwm", "abvm", "dist", "kern",
    "mark", "mkmk",
  },
  khmr = tabletohash {
    "ccmp", "locl", "pref", "blwf", "abvf",
    "pstf", "pres", "blws", "abvs", "psts",
    "clig", "calt", "blwm", "abvm", "dist",
    "kern", "mark", "mkmk",
  },
  thai = tabletohash {
    "ccmp", "locl", "liga", "kern", "mark",
    "mkmk",
  },
}

--[[doc--

  We allow loading of arbitrary fontloaders. Nevertheless we maintain a
  list of the “official” ones shipped with Luaotfload so we can emit a
  different log message.

--doc]]--

local default_fontloader = function ()
  return luaotfloadstatus and luaotfloadstatus.notes.loader or "reference"
end

local registered_loaders = {
  default    = default_fontloader (),
  reference  = "reference",
  unpackaged = "unpackaged",
  context    = "context",
}

local pick_fontloader = function (s)
  local ldr = registered_loaders[s]
  if ldr ~= nil and type (ldr) == "string" then
    logreport ("log", 2, "conf", "Using predefined fontloader \"%s\".", ldr)
    return ldr
  end
  local idx = stringfind (s, ":")
  if idx and idx > 2 then
    if stringsub (s, 1, idx - 1) == "context" then
      local pth = stringsub (s, idx + 1)
      pth = stringstrip (pth)
      logreport ("log", 2, "conf", "Context base path specified at \"%s\".", pth)
      if lfsisdir (pth) then
        logreport ("log", 5, "conf", "Context base path exists at \"%s\".", pth)
        return pth
      end
      pth = kpseexpand_path (pth)
      if lfsisdir (pth) then
        logreport ("log", 5, "conf", "Context base path exists at \"%s\".", pth)
        return pth
      end
      logreport ("both", 0, "conf", "Context base path not found at \"%s\".", pth)
    end
  end
  return nil
end

--[[doc--

  The ``post_linebreak_filter`` has been made the default callback for
  hooking the colorizer into. This helps with the linebreaking whose
  inserted hyphens would remain unaffected by the coloring otherwise.

  http://tex.stackexchange.com/q/238539/14066

--doc]]--

local permissible_color_callbacks = {
  default               = "post_linebreak_filter",
  pre_linebreak_filter  = "pre_linebreak_filter",
  post_linebreak_filter = "post_linebreak_filter",
  pre_output_filter     = "pre_output_filter",
}


-------------------------------------------------------------------------------
---                                DEFAULTS
-------------------------------------------------------------------------------

local default_config = {
  db = {
    formats         = "otf,ttf,ttc",
    scan_local      = false,
    skip_read       = false,
    strip           = true,
    update_live     = true,
    compress        = true,
    max_fonts       = 2^51,
    designsize_dimen= "bp",
  },
  run = {
    anon_sequence  = default_anon_sequence,
    resolver       = "cached",
    definer        = "patch",
    log_level      = 0,
    color_callback = "post_linebreak_filter",
    fontloader     = default_fontloader (),
  },
  misc = {
    bisect         = false,
    version        = luaotfload.version,
    statistics     = false,
    termwidth      = nil,
  },
  paths = {
    names_dir           = "names",
    cache_dir           = "fonts",
    index_file          = "luaotfload-names.lua",
    lookups_file        = "luaotfload-lookup-cache.lua",
    lookup_path_lua     = nil,
    lookup_path_luc     = nil,
    index_path_lua      = nil,
    index_path_luc      = nil,
  },
  default_features = {
    global = { mode = "node" },
    dflt = tabletohash {
      "ccmp", "locl", "rlig", "liga", "clig",
      "kern", "mark", "mkmk", 'itlc',
    },

    arab = feature_presets.arab,
    syrc = feature_presets.arab,
    mong = feature_presets.arab,
    nko  = feature_presets.arab,

    deva = feature_presets.deva,
    beng = feature_presets.deva,
    guru = feature_presets.deva,
    gujr = feature_presets.deva,
    orya = feature_presets.deva,
    taml = feature_presets.deva,
    telu = feature_presets.deva,
    knda = feature_presets.deva,
    mlym = feature_presets.deva,
    sinh = feature_presets.deva,

    khmr = feature_presets.khmr,
    tibt = feature_presets.khmr,
    thai = feature_presets.thai,
    lao  = feature_presets.thai,

    hang = tabletohash { "ccmp", "ljmo", "vjmo", "tjmo", },
  },
}

-------------------------------------------------------------------------------
---                          RECONFIGURATION TASKS
-------------------------------------------------------------------------------

--[[doc--

    Procedures to be executed in order to put the new configuration into effect.

--doc]]--

local reconf_tasks = nil

local min_terminal_width = 40

--- The “termwidth” value is only considered when printing
--- short status messages, e.g. when building the database
--- online.
local check_termwidth = function ()
  if config.luaotfload.misc.termwidth == nil then
      local tw = 79
      if not (   os.type == "windows" --- Assume broken terminal.
              or osgetenv "TERM" == "dumb")
      then
          local p = iopopen "tput cols"
          if p then
              result = tonumber (p:read "*all")
              p:close ()
              if result then
                  tw = result
              else
                  logreport ("log", 2, "db", "tput returned non-number.")
              end
          else
              logreport ("log", 2, "db", "Shell escape disabled or tput executable missing.")
              logreport ("log", 2, "db", "Assuming 79 cols terminal width.")
          end
      end
      config.luaotfload.misc.termwidth = tw
  end
  return true
end

local set_font_filter = function ()
  local names = fonts.names
  if names and names.set_font_filter then
    local formats = config.luaotfload.db.formats
    if not formats or formats == "" then
      formats = default_config.db.formats
    end
    names.set_font_filter (formats)
  end
  return true
end

local set_size_dimension = function ()
  local names = fonts.names
  if names and names.set_size_dimension then
    local dim = config.luaotfload.db.designsize_dimen
    if not dim or dim == "" then
      dim = default_config.db.designsize_dimen
    end
    names.set_size_dimension (dim)
  end
  return true
end

local set_name_resolver = function ()
  local names = fonts.names
  if names and names.resolve_cached then
    --- replace the resolver from luatex-fonts
    if config.luaotfload.db.resolver == "cached" then
        logreport ("both", 2, "cache", "Caching of name: lookups active.")
        names.resolvespec  = fonts.names.lookup_font_name_cached
    else
        names.resolvespec  = fonts.names.lookup_font_name
    end
  end
  return true
end

local set_loglevel = function ()
  if luaotfload then
    luaotfload.log.set_loglevel (config.luaotfload.run.log_level)
    return true
  end
  return false
end

local build_cache_paths = function ()
  local paths  = config.luaotfload.paths
  local prefix = getwritablepath (paths.names_dir, "")

  if not prefix then
    luaotfload.error ("Impossible to find a suitable writeable cache...")
    return false
  end

  prefix = lpegmatch (stripslashes, prefix)
  logreport ("log", 0, "conf", "Root cache directory is %s.", prefix)

  local index_file      = filejoin (prefix, paths.index_file)
  local lookups_file    = filejoin (prefix, paths.lookups_file)

  paths.prefix          = prefix
  paths.index_path_lua  = filereplacesuffix (index_file,   "lua")
  paths.index_path_luc  = filereplacesuffix (index_file,   "luc")
  paths.lookup_path_lua = filereplacesuffix (lookups_file, "lua")
  paths.lookup_path_luc = filereplacesuffix (lookups_file, "luc")
  return true
end


local set_default_features = function ()
  local default_features = config.luaotfload.default_features
  luaotfload.features    = luaotfload.features or {
                             global   = { },
                             defaults = { },
                           }
  current_features       = luaotfload.features
  for var, val in next, default_features do
    if var == "global" then
      current_features.global = val
    else
      current_features.defaults[var] = val
    end
  end
  return true
end

reconf_tasks = {
  { "Set the log level"         , set_loglevel         },
  { "Build cache paths"         , build_cache_paths    },
  { "Check terminal dimensions" , check_termwidth      },
  { "Set the font filter"       , set_font_filter      },
  { "Set design size dimension" , set_size_dimension   },
  { "Install font name resolver", set_name_resolver    },
  { "Set default features"      , set_default_features },
}

-------------------------------------------------------------------------------
---                          OPTION SPECIFICATION
-------------------------------------------------------------------------------

local string_t    = "string"
local table_t     = "table"
local number_t    = "number"
local boolean_t   = "boolean"
local function_t  = "function"

local tointeger = function (n)
  n = tonumber (n)
  if n then
    return mathfloor (n + 0.5)
  end
end

local toarray = function (s)
  local fields = { lpegmatch (commasplitter, s) }
  local ret    = { }
  for i = 1, #fields do
    local field = stringstrip (fields[i])
    if field and field ~= "" then
      ret[#ret + 1] = field
    end
  end
  return ret
end

local tohash = function (s)
  local result = { }
  local fields = toarray (s)
  for _, field in next, fields do
    local var, val
    if stringfind (field, "=") then
      local tmp
      var, tmp = lpegmatch (equalssplitter, field)
      if tmp == "true" or tmp == "yes" then val = true else val = tmp end
    else
      var, val = field, true
    end
    result[var] = val
  end
  return result
end

local option_spec = {
  db = {
    formats      = {
      in_t  = string_t,
      out_t = string_t,
      transform = function (f)
        local fields = toarray (f)

        --- check validity
        if not fields then
          logreport ("both", 0, "conf",
                     "Expected list of identifiers, got %q.", f)
          return nil
        end

        --- strip dupes
        local known  = { }
        local result = { }
        for i = 1, #fields do
          local field = fields[i]
          if known[field] ~= true then
            --- yet unknown, tag as seen
            known[field] = true
            --- include in output if valid
            if valid_formats[field] == true then
              result[#result + 1] = field
            else
              logreport ("both", 4, "conf",
                         "Invalid font format identifier %q, ignoring.",
                         field)
            end
          end
        end
        if #result == 0 then
          --- force defaults
          return nil
        end
        return tableconcat (result, ",")
      end
    },
    scan_local   = { in_t = boolean_t, },
    skip_read    = { in_t = boolean_t, },
    strip        = { in_t = boolean_t, },
    update_live  = { in_t = boolean_t, },
    compress     = { in_t = boolean_t, },
    max_fonts    = {
      in_t      = number_t,
      out_t     = number_t, --- TODO int_t from 5.3.x on
      transform = tointeger,
    },
    designsize_dimen = {
      in_t  = string_t,
      out_t = string_t,
    },
  },
  run = {
    anon_sequence = {
      in_t      = string_t,
      out_t     = table_t,
      transform = function (s)
        if s ~= "default" then
          local bits = { lpegmatch (commasplitter, s) }
          if next (bits) then
            local seq = { }
            local done = { }
            for i = 1, #bits do
              local bit = bits [i]
              if valid_resolvers [bit] then
                if not done [bit] then
                  done [bit] = true
                  seq [#seq + 1] = bit
                else
                  logreport ("both", 0, "conf",
                             "ignoring duplicate resolver %s at position %d \z
                              in lookup sequence",
                             bit, i)
                end
              else
                logreport ("both", 0, "conf",
                           "lookup sequence contains invalid item %s \z
                            at position %d.",
                           bit, i)
              end
            end
            if next (seq) then
              logreport ("both", 2, "conf",
                         "overriding anon lookup sequence %s.",
                         tableconcat (seq, ","))
              return seq
            end
          end
        end
        return default_anon_sequence
      end
    },
    live = { in_t = boolean_t, }, --- false for the tool, true for TeX run
    resolver = {
      in_t      = string_t,
      out_t     = string_t,
      transform = function (r) return r == "normal" and r or "cached" end,
    },
    definer = {
      in_t      = string_t,
      out_t     = string_t,
      transform = function (d)
        if   d == "generic"      or d == "patch"
          or d == "info_generic" or d == "info_patch"
        then
          return d
        end
        return "patch"
      end,
    },
    fontloader = {
      in_t      = string_t,
      out_t     = string_t,
      transform = function (id)
        local ldr = pick_fontloader (id)
        if ldr ~= nil then
          return ldr
        end
        logreport ("log", 0, "conf",
                    "Requested fontloader \"%s\" not defined, "
                    .. "use at your own risk.",
                    id)
        return id
      end,
    },
    log_level = {
      in_t      = number_t,
      out_t     = number_t, --- TODO int_t from 5.3.x on
      transform = tointeger,
    },
    color_callback = {
      in_t      = string_t,
      out_t     = string_t,
      transform = function (cb_spec)
        --- These are the two that make sense.
        local cb = permissible_color_callbacks[cb_spec]
        if cb then
          logreport ("log", 3, "conf",
                     "Using callback \"%s\" for font colorization.",
                     cb)
          return cb
        end
        logreport ("log", 0, "conf",
                    "Requested callback identifier \"%s\" invalid, "
                    .. "falling back to default.",
                    cb_spec)
        return permissible_color_callbacks.default
      end,
    },
  },
  misc = {
    bisect          = { in_t = boolean_t, }, --- doesn’t make sense in a config file
    version         = { in_t = string_t,  },
    statistics      = { in_t = boolean_t, },
    termwidth       = {
      in_t      = number_t,
      out_t     = number_t,
      transform = function (w)
        w = tointeger (w)
        if w < min_terminal_width then
          return min_terminal_width
        end
        return w
      end,
    },
  },
  paths = {
    names_dir           = { in_t = string_t, },
    cache_dir           = { in_t = string_t, },
    index_file          = { in_t = string_t, },
    lookups_file        = { in_t = string_t, },
    lookup_path_lua     = { in_t = string_t, },
    lookup_path_luc     = { in_t = string_t, },
    index_path_lua      = { in_t = string_t, },
    index_path_luc      = { in_t = string_t, },
  },
  default_features = {
    __default = { in_t  = string_t, out_t = table_t, transform = tohash, },
  },
}

-------------------------------------------------------------------------------
---                               FORMATTERS
-------------------------------------------------------------------------------

local commented = function (str)
  return ";" .. str
end

local underscore_replacer = lpeg.replacer ("_", "-", true)

local dashed = function (var)
  --- INI spec dictates that dashes are valid in variable names, not
  --- underscores.
  return underscore_replacer (var) or var
end

local indent = "  "
local format_string = function (var, val)
  return stringformat (indent .. "%s = %s", var, val)
end

local format_integer = function (var, val)
  return stringformat (indent .. "%s = %d", var, val)
end

local format_boolean = function (var, val)
  return stringformat (indent .. "%s = %s", var, val == true and "true" or "false")
end

local format_keyval = function (var, val)
  local list = { }
  local keys = table.sortedkeys (val)
  for i = 1, #keys do
    local key    = keys[i]
    local subval = val[key]
    if subval == true then
      list[#list + 1] = stringformat ("%s", key)
    else
      list[#list + 1] = stringformat ("%s=%s", key, val[key])
    end
  end
  if next (list) then
    return stringformat (indent .. "%s = %s",
                         var,
                         tableconcat (list, ","))
  end
end

local format_list = function (var, val)
  local elts = { }
  for i = 1, #val do elts [i] = val [i] end
  if next (elts) then
    return stringformat (indent .. "%s = %s",
                         var, tableconcat (elts, ","))
  end
end

local format_section = function (title)
  return stringformat ("[%s]", dashed (title))
end

local conf_header = [==[
;;-----------------------------------------------------------------------------
;; Luaotfload Configuration
;;-----------------------------------------------------------------------------
;;
;; This file was generated by luaotfload-tool
;; on %s. Configuration variables
;; are documented in the manual to luaotfload.conf(5).
;;
;;-----------------------------------------------------------------------------

]==]

local conf_footer = [==[

;; vim:filetype=dosini:expandtab:shiftwidth=2
]==]

--- Each dumpable variable (the ones mentioned in the man page) receives a
--- formatter that will be used in dumping the variable. Each value receives a
--- “commented” flag that indicates whether or not the line should be printed
--- as a comment.

local formatters = {
  db = {
    compress         = { false, format_boolean },
    designsize_dimen = { false, format_string  },
    formats          = { false, format_string  },
    max_fonts        = { false, format_integer },
    scan_local       = { false, format_boolean },
    skip_read        = { false, format_boolean },
    strip            = { false, format_boolean },
    update_live      = { false, format_boolean },
  },
  default_features = {
    __default = { true, format_keyval },
  },
  misc = {
    bisect     = { false, format_boolean },
    statistics = { false, format_boolean },
    termwidth  = { true , format_integer },
    version    = { true , format_string  },
  },
  paths = {
    cache_dir    = { false, format_string },
    names_dir    = { false, format_string },
    index_file   = { false, format_string },
    lookups_file = { false, format_string },
  },
  run = {
    anon_sequence   = { false, format_list    },
    color_callback  = { false, format_string  },
    definer         = { false, format_string  },
    fontloader      = { false, format_string  },
    log_level       = { false, format_integer },
    resolver        = { false, format_string  },
  },
}

-------------------------------------------------------------------------------
---                           MAIN FUNCTIONALITY
-------------------------------------------------------------------------------

--[[doc--

  tilde_expand -- Rudimentary tilde expansion; covers just the “substitute ‘~’
  by the current users’s $HOME” part.

--doc]]--

local tilde_expand = function (p)
  if #p > 2 then
    if stringsub (p, 1, 2) == "~/" then
      local homedir = osgetenv "HOME"
      if homedir and lfsisdir (homedir) then
        p = filejoin (homedir, stringsub (p, 3))
      end
    end
  end
  return p
end

local resolve_config_path = function ()
  for i = 1, #config_paths do
    local t, p = unpack (config_paths[i])
    local fullname
    if t == kpse_t then
      fullname = kpse.find_file (p)
      logreport ("both", 6, "conf", "kpse lookup: %s -> %s.", p, fullname)
    elseif t == path_t then
      local expanded = tilde_expand (p)
      if lfsisfile (expanded) then
        fullname = expanded
      end
      logreport ("both", 6, "conf", "path lookup: %s -> %s.", p, fullname)
    end
    if fullname then
      logreport ("both", 3, "conf", "Reading configuration file at %q.", fullname)
      return fullname
    end
  end
  logreport ("both", 2, "conf", "No configuration file found.")
  return false
end

local add_config_paths = function (t)
  if not next (t) then
    return
  end
  local result = { }
  for i = 1, #t do
    local path = t[i]
    result[#result + 1] = { path_t, path }
  end
  config_paths = tableappend (result, config_paths)
end

local process_options = function (opts)
  local new = { }
  for i = 1, #opts do
    local section = opts[i]
    local title = section.section.title
    local vars  = section.variables

    if not title then --- trigger warning: arrow code ahead
      logreport ("both", 2, "conf", "Section %d lacks a title; skipping.", i)
    elseif not vars then
      logreport ("both", 2, "conf", "Section %d (%s) lacks a variable section; skipping.", i, title)
    else
      local spec = option_spec[title]
      if not spec then
        logreport ("both", 2, "conf", "Section %d (%s) unknown; skipping.", i, title)
      else
        local newsection = new[title]
        if not newsection then
          newsection = { }
          new[title] = newsection
        end

        for var, val in next, vars do
          local vspec = spec[var] or spec.__default
          local t_val = type (val)
          if not vspec then
            logreport ("both", 2, "conf",
                       "Section %d (%s): invalid configuration variable %q (%q); ignoring.",
                       i, title,
                       var, tostring (val))
          elseif t_val ~= vspec.in_t then
            logreport ("both", 2, "conf",
                       "Section %d (%s): type mismatch of input value %q (%q, %s != %s); ignoring.",
                       i, title,
                       var, tostring (val), t_val, vspec.in_t)
          else --- type matches
            local transform = vspec.transform
            if transform then
              local dval
              local t_transform = type (transform)
              if t_transform == function_t then
                dval = transform (val)
              elseif t_transform == table_t then
                dval = transform[val]
              end
              if dval then
                local out_t = vspec.out_t
                if out_t then
                  local t_dval = type (dval)
                  if t_dval == out_t then
                    newsection[var] = dval
                  else
                    logreport ("both", 2, "conf",
                               "Section %d (%s): type mismatch of derived value of %q (%q, %s != %s); ignoring.",
                               i, title,
                               var, tostring (dval), t_dval, out_t)
                  end
                else
                  newsection[var] = dval
                end
              else
                logreport ("both", 2, "conf",
                           "Section %d (%s): value of %q could not be derived via %s from input %q; ignoring.",
                           i, title, var, t_transform, tostring (val))
              end
            else --- insert as is
              newsection[var] = val
            end
          end
        end
      end
    end
  end
  return new
end

local apply
apply = function (old, new)
  if not new then
    if not old then
      return false
    end
    return tablecopy (old)
  elseif not old then
    return tablecopy (new)
  end
  local result = tablecopy (old)
  for name, section in next, new do
    local t_section = type (section)
    if t_section ~= table_t then
      logreport ("both", 1, "conf",
                 "Error applying configuration: entry %s is %s, expected table.",
                 section, t_section)
      --- ignore
    else
      local currentsection = result[name]
      for var, val in next, section do
        currentsection[var] = val
      end
    end
  end
  result.status = luaotfloadstatus
  return result
end

local reconfigure = function ()
  for i = 1, #reconf_tasks do
    local name, task = unpack (reconf_tasks[i])
    logreport ("both", 3, "conf", "Launch post-configuration task %q.", name)
    if not task () then
      logreport ("both", 0, "conf", "Post-configuration task %q failed.", name)
      return false
    end
  end
  return true
end

local read = function (extra)
  if extra then
    add_config_paths (extra)
  end

  local readme = resolve_config_path ()
  if readme == false then
    logreport ("both", 2, "conf", "No configuration file.")
    return false
  end

  local raw = ioloaddata (readme)
  if not raw then
    logreport ("both", 2, "conf", "Error reading the configuration file %q.", readme)
    return false
  end

  local parsed = lpegmatch (config_parser, raw)
  if not parsed then
    logreport ("both", 2, "conf", "Error parsing configuration file %q.", readme)
    return false
  end

  local ret, msg = process_options (parsed)
  if not ret then
    logreport ("both", 2, "conf", "File %q is not a valid configuration file.", readme)
    logreport ("both", 2, "conf", "Error: %s", msg)
    return false
  end
  return ret
end

local apply_defaults = function ()
  local defaults      = default_config
  local vars          = read ()
  --- Side-effects galore ...
  config.luaotfload   = apply (defaults, vars)
  return reconfigure ()
end

local dump = function ()
  local sections = table.sortedkeys (config.luaotfload)
  local confdata = { }
  for i = 1, #sections do
    local section    = sections[i]
    local vars       = config.luaotfload[section]
    local varnames   = table.sortedkeys (vars)
    local sformats   = formatters[section]
    if sformats then
      confdata[#confdata + 1] = format_section (section)
      for j = 1, #varnames do
        local var = varnames[j]
        local val = vars[var]
        local comment, sformat = unpack (sformats[var] or { })
        if not sformat then
          comment, sformat = unpack (sformats.__default or { })
        end

        if sformat then
          local dashedvar = dashed (var)
          if comment then
            confdata[#confdata + 1] = commented (sformat (dashedvar, val))
          else
            confdata[#confdata + 1] = sformat (dashedvar, val)
          end
        end

      end
      confdata[#confdata + 1] = ""
    end
  end
  if next(confdata) then
    iowrite (stringformat (conf_header,
                           osdate ("%Y-%m-d %H:%M:%S", os.time ())))
    iowrite (tableconcat (confdata, "\n"))
    iowrite (conf_footer)
  end
end

-------------------------------------------------------------------------------
---                                 EXPORTS
-------------------------------------------------------------------------------

return {
  init = function ()
    config.luaotfload = { }
    logreport         = luaotfload.log.report
    local parsers     = luaotfload.parsers
    config_parser     = parsers.config
    stripslashes      = parsers.stripslashes

    luaotfload.default_config = default_config
    config.actions = {
      read             = read,
      apply            = apply,
      apply_defaults   = apply_defaults,
      reconfigure      = reconfigure,
      dump             = dump,
    }
    if not apply_defaults () then
      logreport ("log", 0, "load",
                 "Configuration unsuccessful: error loading default settings.")
    end
    return true
  end
}