--[=[  The function formatting module for pretty.

How is one supposed to pretty print functions? Well, there are many different
formats, and no "best" one, only "best for the purpose". Lets first look at how
you could display the most raw data about a function.

1.	The default Lua format: "function: 0x41f71c60"
	This is the default, and by far the easiest. Also, very uninformative. We
	only get a unique id for the function.
2.	Include the arguments: "function (t, str) ... end"
	This is slightly more advanced, as it requires using the debug library to
	discover the names of the arguments. In addition it adds a pseudo-correct
	formatting for the function. Now we know the arguments, and if they possess
	descriptive names, we can learn a lot about the function.
3.	Include some documentation: "function (x) --[[math.cosh: Returns the hyperbolic cosine of x.]] ... end"
	We retain the arguments and pseudo-correct formatting from above, and add
	documentation taken from elsewhere (for example the Lua Reference Manual, or
	LuaJIT webpage), as comments. This is great for explorative programming, as
	we can read about the language from within the language.
4.	Short names: "math.min"
	Rather than giving an overly descriptive overview of some inbuilt, we assume
	that we can find it by its standard name. With this one we gain complete
	native representation, assuming the standard enviroment, of course. It won't
	work at all with custom functions.
5.	Include source code: "function (a, b) return (a + b)/2 end"
	Now we find the source code somehow, and use it as the representation. This
	is powerful because we can directly inspect the code. It won't work with
	builtins, closured functions, or when fucking around with the source files.
6.	Include closures: "(function () local i = 5; return function () i = i + 1; return i end end)()"
	In cases where a function has a closure, we can use debug.getinfo to get
	the names and values of the upvalues. We can then represent the closure, by
	creating the closure itself. Iterators like the example above works nicely,
	but more complex chains of closures break down. For example:

		local val_a  = 1
		local func_a = function () val_a = val_a + 1; return val_a end
		local val_a  = val_a
		local func_c = function () return func_a() + val_a end

	Here we have two functions, both with their own upvalue, both named "val_a",
	yet those names refer to two different "slots". Successive calls to
	`func_c` should produce the list: 2, 3, 4, 5, 6, 7, ...
	To break through this barrier, we need to parse the Lua AST, and that is
	beyond this project.
--]=]

-- Import

local LIBRARY
do
	local thispath = ... and select('1', ...):match('.+%.') or ''
	local was_loaded, library  =  pcall(require, thispath..'library')
    LIBRARY  =  was_loaded and library or {}
end

-- Constants

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

local function get_function_info (f)
    -- NOTE: Works best in LuaJIT or Lua 5.2+

    -- Regarding get-info:
    -- *  No need to includ 'f'. Function is already known
    -- *  No need to include 'L' (active lines) option. Ignored
    -- *  No need to include 'n' (name and namewhat). Won't work.
    local info = debug.getinfo(f, 'Su')
          info.params = {}
          info.ups = {}
          info.env = debug.getfenv and debug.getfenv(f)
          info.builtin = (info.source == '=[C]')
    for i = 1, info.nparams or 0 do  info.params[i] = debug.getlocal(f, i)  end
    if info.isvararg or not info.nparams then  info.params[#info.params+1] = '...'  end
    -- Get upvalues
    for i = 1, info.nups do
        local k, v = debug.getupvalue(f, i)
        if k == '_ENV' and not debug.getfenv then
            info.env = v
        else
            info.ups[k] = v
        end
    end

    if     info.source:sub(1,1) == '=' then  info.defined_how = 'C'
    elseif info.source:sub(1,1) == '@' then  info.defined_how = 'file'
    else                                     info.defined_how = 'string'
    end

    if info.builtin and LIBRARY[f] then
        info.name       = LIBRARY[f].name
        info.params[1]  = LIBRARY[f].para
        info.doc        = LIBRARY[f].docs
    end

    return info
end

local function get_line_index (str, line_nr)
    local index = 0
    for _ = 2, line_nr do
        index = str:find('\n', index, true)
        if not index then  return #str  end
        index = index + 1
    end
    return index
end

local function get_full_function_str (str, start_line, end_line)
	-- Will attempt to find a string which refer to a function starting on
	-- line `start_line` and ending on line `end_line`.
    local start_line_index  =  get_line_index(str, start_line)
    local end_line_index    =  get_line_index(str, end_line + 1)

    local function_body  =  str:sub(start_line_index, end_line_index):match('function%s*[a-zA-Z0-9_.]*%s*(.+)end')
    return 'function '..function_body..'end'
end

local function get_function_str_from_file (filename, start_line, end_line)
	local file = io.open(filename, 'r')
	local str = file:read('*all')
	file:close()
	return get_full_function_str(str, start_line, end_line)
end

local function width_of_strings_in_l (l, start_i, end_i)
	-- FIXME: Copy of the one in pretty.lua
    local  width = 0
    for i = start_i or 1, (end_i or #l) do
        width = width + #l[i]
    end
    return width
end

local function add_indent_to_string (str, indent)
	local l = {}
	for line in string.gmatch(str, '\n', true) do
		l[#l+1] = indent
		l[#l+1] = line
	end
	return table.concat(l, '\n')
end

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

local function format_function_with_closure (value, options, depth, l, format_value)
	local info = get_function_info(value)

	local function_str = nil
	if (info.defined_how == 'string') then
		function_str = get_full_function_str(info.source, info.linedefined, info.lastlinedefined)
	else
		function_str = get_function_str_from_file(info.short_src, info.linedefined, info.lastlinedefined)
	end

	if info.nups > 0 then l[#l+1] = '(function () ' end
	-- Upvalues
	for k, v in pairs(info.ups) do
		l[#l+1] = 'local '
		l[#l+1] = tostring(k)
		l[#l+1] = ' = '
		format_value(v, options, depth + 1, l)
		l[#l+1] = '; '
	end
	-- Return function
	if info.nups > 0 then l[#l+1] = 'return ' end
	l[#l+1] = function_str
	--
	if info.nups > 0 then l[#l+1] = ' end)()' end
end

return function (value, options, depth, l, format_value)
    local info = get_function_info(value)

	if options.include_closure and not info.builtin then
		return format_function_with_closure(value, options, depth, l, format_value)
	end

    if info.defined_how == 'string' then
        -- Function was defined as a string.
        l[#l+1] = get_full_function_str(info.source, info.linedefined, info.lastlinedefined)
        return;
    end

	if info.builtin and options.short_builtins then
		l[#l+1] = info.name
		return;
	end

    -- Include function modifier, and alignment info.
    l[#l+1] = info.builtin and 'builtin ' or ''
    l[#l+1] = { 'align', 'func_mod', #l[#l]}

    -- Build rest of function signature
    l[#l+1] = 'function ('
    local top_before = #l
    for _, param in ipairs(info.params) do  l[#l+1], l[#l+2] = param, ', '  end
    if l[#l] == ', ' then  l[#l] = nil  end
    l[#l+1] = ')'
    l[#l+1] = { 'align', 'func_def', width_of_strings_in_l(l, top_before) }

    -- Cleanup and finish
    if not options.more_function_info or depth ~= 0  then
        l[#l+1] = ' ... end'
		return;
    end

	-- More info! --

	local indent = '\n' .. options.indent

	-- Name
    if info.name then
        l[#l+1] = indent
        l[#l+1] = '-- '
        l[#l+1] = info.name
    end

    -- Doc
    if info.doc then
        for doc_line in info.doc:gmatch('[^\n]+') do
            l[#l+1] = indent
            l[#l+1] = '-- '

            l[#l+1] = doc_line
        end
    end

    -- source
    if not info.builtin then
        l[#l+1] = indent
        l[#l+1] = ('-- source_file: \'%s\' '):format(info.short_src)
        if info.linedefined == info.lastlinedefined then
			l[#l+1] = ('[Line: %i]'):format(info.linedefined)
        else
			l[#l+1] = ('[Lines: %i - %i]'):format(info.linedefined, info.lastlinedefined)
        end
    end

    -- upvalues
    if info.nups > 0 and not info.builtin then
        l[#l+1] = indent
        l[#l+1] = '-- up_values:   '
        format_value(info.ups, options, depth + 1, l)
    end

	if options._all_function_info then
        -- NOTE: This is for testing/debugging/experimentation purposes, and is
		-- not designed to be pretty.

		l[#l+1] = indent
        l[#l+1] = '--[[ Function Body:\n\t'
        l[#l+1] = add_indent_to_string(get_function_str_from_file(info.short_src, info.linedefined, info.lastlinedefined), options.indent)
		l[#l+1] = indent
        l[#l+1] = '--]]'

		l[#l+1] = indent
        l[#l+1] = '--[[\n\tNative repr:'
        l[#l+1] = tostring(value)
		l[#l+1] = indent
        format_value(info, options, depth + 1, l)
		l[#l+1] = indent
        l[#l+1] = '--]]'
    end

    l[#l+1] = '\n'
	l[#l+1] = indent
    l[#l+1] = '...\nend'
end