-- Check for possible loading errors

local string_dist
do
    local thispath = ... and (...):match('.+%.') or ''
    local function import (name, ignore_failure)
        local was_loaded, lib_or_error      =  pcall(require, thispath..name)
        if not was_loaded then
            if ignore_failure then  return nil  end
            error('['..thispath..']: Could not load vital library: '..name..'.lua:\n\t'..lib_or_error)
        end
        return lib_or_error
    end

    string_dist = import 'string_distance'
end

if not debug then
    error('[errors/loading]: Expected the debug library to be available in _G.')
elseif not debug.getinfo then
    error('[errors/loading]: Expected debug.getinfo to be available in the debug library.')
end

--------------------------------------------------------------------------------
-- Constants

local DEFAULT_ERROR_MSG_NORMAL    =  'Unknown error occured'
local DEFAULT_ERROR_MSG_INTERNAL  =  'Unknown internal error occured'
local DEFAULT_ERROR_MSG_CORRECT   =  'Unexpected input "%s", maybe you meant %s?'

--------------------------------------------------------------------------------
-- Util

local function format_probable_strings (probable_strings, amount)
    assert(type(probable_strings) == 'table')
    assert(#probable_strings > 0)
    assert(type(amount) == 'number')

    local l = {}
    for i = 1, math.min(amount, #probable_strings) do
        l[#l+1] = probable_strings[i]
        l[#l+1] = ', '
    end
    if l[#l] == ', ' then  l[#l] = nil  end
    if #l >= 3 then  l[#l-1] = ' or ' end
    return table.concat(l, '')
end

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

local function internal_error (self, module_suffix, format_msg, ...)
    -- internal_error(error_handler, module_suffix [, format_msg, ...])

    -- Error check
    assert(type(self)          == 'table' and self.is_error_handler)
    assert(type(module_suffix) == 'string')
    format_msg = format_msg or DEFAULT_ERROR_MSG_NORMAL
    assert(type(format_msg)    == 'string')
    -- Format
    return error(('[%s%s]: '..format_msg):format(self.module_name, module_suffix, ...), 3)
end

local function external_error (self, module_suffix, format_msg, ...)
    -- external_error(error_handler, module_suffix [, format_msg, ...])

    -- Error check
    assert(type(self)          == 'table' and self.is_error_handler)
    assert(type(module_suffix) == 'string')
    format_msg = format_msg or DEFAULT_ERROR_MSG_INTERNAL
    assert(type(format_msg)    == 'string')
    -- Find error level
    local level = 3
    while self.registered[debug.getinfo(level, 'f').func] do
        level = level + 1
    end
    -- Format
    return error(('[%s%s]: '..format_msg):format(self.module_name, module_suffix, ...), level -1)
end

local function correct_error (self, module_suffix, format_msg, gotten_string, possible_strings)
    -- correct_error(error_handler, module_suffix [, format_msg], gotten_string, possible_strings)

    -- Error check
    assert(type(self)          == 'table' and self.is_error_handler)
    assert(type(module_suffix) == 'string')
    format_msg = format_msg or DEFAULT_ERROR_MSG_CORRECT
    assert(type(format_msg)    == 'string')
    assert(type(gotten_string) == 'string')
    assert(type(possible_strings) == 'table')

    -- Do stuff
    local possible_strings = string_dist.strings_with_highest_similarity(gotten_string, possible_strings)
    local list_string = format_probable_strings(possible_strings, 3)
    -- Format
    return error(('[%s%s]: '..format_msg):format(self.module_name, module_suffix, gotten_string, list_string), 3)
end


local ErrorHandler_mt = {__call = function (self, ...) internal_error(self, '', ...)  end}


return function (module_name)
    assert(type(module_name) == 'string')

    local  err_hdl = setmetatable({}, ErrorHandler_mt)
           err_hdl.is_error_handler = true
           err_hdl.module_name      = module_name
           err_hdl.registered       = {}
           err_hdl.any_registered   = false

    function err_hdl.internal (...)
        local args = {...}
        if args[1] == err_hdl then  table.remove(args, 1)  end
        internal_error(err_hdl, '/internal', unpack(args))
    end

    function err_hdl.external (...)
        local args = {...}
        if args[1] == err_hdl then  table.remove(args, 1)  end
        external_error(err_hdl, '', unpack(args))
    end

    function err_hdl.correct (...)
        local args = {...}
        if args[1] == err_hdl then  table.remove(args, 1)  end
        if #args == 2 then  table.insert(args, 1, DEFAULT_ERROR_MSG_CORRECT)  end
        correct_error(err_hdl, '', unpack(args))
    end

    function err_hdl.register (...)
        local args = {...}
        if args[1] == err_hdl then  table.remove(args, 1)  end
        assert(#args > 0)
        for i = 1, #args do
            assert(type(args[i]) == 'function')
            err_hdl.registered[args[i]]  =  true
            err_hdl.any_registered       =  true
        end
    end

    function err_hdl.strict_table (...)
        local args = {...}
        if args[1] == err_hdl then  table.remove(args, 1)  end
        return setmetatable(args[1] or {}, {
            __index = function (t, k)
                local keys = {}
                for k in pairs(t) do  keys[#keys+1] = tostring(k)  end
                if #keys == 0 then  external_error(err_hdl, '', 'Attempting to index unknown key %s in an empty table.', k)  end
                correct_error(err_hdl, '', 'Attempting to index unknown key %s, maybe you meant %s?', k, keys)
            end
        })
    end

    return err_hdl
end