--[[ NOTHING INSIDE THIS FILE NEEDS TO BE EDITED BY THE USER. ]]

--- A Neovim plugin to create more straightforward syntax for Lua `:map`ping and `:unmap`ping.
--- @module nvim-cartographer
--- @alias highlite table

--[[/* IMPORTS */]]

local vim = vim
local api = vim.api
local exe = api.nvim_command
local fn  = vim.fn
local go = vim.go

--[[/* VARS */]]

--- Which set of colors to use.
local _USE_256 = tonumber(go.t_Co) > 255 or string.find(vim.env.TERM, '256')

--- Indicating nothing for a highlight field.
local _NONE = 'NONE'

--- Which index to use for `cterm` highlights.
local _PALETTE_CTERM = _USE_256 and 2 or 3

--- Which index to use for `gui` highlights.
local _PALETTE_HEX  = 1

--- The `string` type.
local _TYPE_STRING = 'string'

--- The `table` type.
local _TYPE_TABLE  = 'table'

--[[/* HELPER FUNCTIONS */]]

--- Filter out information not pertaining to styles
--- @param key string the field from `nvim_get_hl_by_name`
--- @return boolean should_not_filter `true` if the field should not be filtered
local function filter_group_style(key)
	return key ~= 'background'
		and key ~= 'blend'
		and key ~= 'foreground'
		and key ~= 'special'
end

--- @param color string|table the color name or definition
--- @param index number
--- @return number|string color_value a hex, 16-bit, or ANSI color. "NONE" by default
local function get(color, index) -- {{{ †
	if type(color) == _TYPE_TABLE and color[index] then
		return color[index]
	elseif type(color) == _TYPE_STRING then
		return color
	else
		return _NONE
	end
end --}}} ‡

--- Take a `command` and add color-specifying components to it.
--- @param command table the in-progress `:highlight` command
--- @param attributes table the definition of the highlight group
local function colorize(command, attributes) -- {{{ †
	command[#command+1]=' guibg='..get(attributes.bg, _PALETTE_HEX)..' guifg='..get(attributes.fg, _PALETTE_HEX)
		..' ctermbg='..get(attributes.bg, _PALETTE_CTERM)..' ctermfg='..get(attributes.fg, _PALETTE_CTERM)

	-- Add the `blend` parameter if it is present
	if attributes.blend then -- There is a value for the `highlight-blend` field.
		command[#command+1]=' blend='..attributes.blend
	end
end --}}} ‡

--- This function appends `selected_attributes` to the end of `highlight_cmd`.
--- @param command table the in-progress `:highlight` command
--- @param style string the `gui`/`cterm` arguments to apply
--- @param color string|table a `guisp` argument; same arg as `get`
--- @see get
local function stylize(command, style, color)
	command[#command+1]=' gui='..style..' cterm='..style

	if color then -- There is an undercurl color.
		command[#command+1]=' guisp='..get(color, _PALETTE_HEX)
	end
end

--- @param rgb string some string of RGB colors.
--- @return string hex
local function tohex(rgb) return string.format('#%06x', rgb) end

--- Create a metatable which prioritizes entries in the `&bg` index of `attributes`
--- @param attributes table the definition of the highlight group
--- @return table
local function use_background_with(attributes)
	return setmetatable(
		attributes[go.background],
		{['__index'] = attributes}
	)
end

--[[/* MODULE */]]

local highlite = {}

--- @param group_name string
--- @return table attributes a nvim-highlite compliant table describing `group_name`
function highlite.group(group_name)
	local no_errors, group_definition = pcall(api.nvim_get_hl_by_name, group_name, go.termguicolors)

	if not no_errors then group_definition = {} end

	-- the style of the highlight group
	local style = vim.tbl_filter(filter_group_style, vim.tbl_keys(group_definition))
	if group_definition.special then
		style.color = tohex(group_definition.special)
	end

	return
	{
		['fg'] = group_definition.foreground and tohex(group_definition.foreground) or _NONE,
		['bg'] = group_definition.background and tohex(group_definition.background) or _NONE,
		['blend'] = group_definition.blend,
		['style'] = style or _NONE
	}
end

-- Generate a `:highlight` command from a group and some attributes.

--- Generate and execute `:highlight` command from a group and some attributes.
--- @param highlight_group string the `{group-name}` argument for `:highlight`
--- @param attributes table the definition of the highlight group
function highlite.highlight(highlight_group, attributes) -- {{{ †
	-- The base highlight command
	local highlight_cmd = {'hi! ', highlight_group}

	if type(attributes) == _TYPE_STRING then -- `highlight_group` is a link to another group.
		highlight_cmd[3] = highlight_cmd[2]
		highlight_cmd[2] = 'link '
		highlight_cmd[4] = ' '
		highlight_cmd[5] = attributes
	else -- The `highlight_group` is uniquely defined.
		-- Take care of special instructions for certain background colors.
		if attributes[go.background] then
			attributes = use_background_with(attributes)
		end

		colorize(highlight_cmd, attributes)

		local style = attributes.style or _NONE

		if type(style) == _TYPE_TABLE then
			-- Concat all of the entries together with a comma between before styling.
			stylize(highlight_cmd, table.concat(style, ','), style.color)
		else -- The style is just a single entry.
			stylize(highlight_cmd, style)
		end
	end

	exe(table.concat(highlight_cmd))
end --}}} ‡

--- Set `g:terminal_color_`s based on `terminal_colors`.
--- @param terminal_colors table a list 1..16 of colors to use in the terminal
function highlite:highlight_terminal(terminal_colors)
	for index, color in ipairs(terminal_colors) do vim.g['terminal_color_'..(index-1)] =
		go.termguicolors and color[_PALETTE_HEX] or color[_PALETTE_CTERM]
	end
end

return setmetatable(highlite, {['__call'] = function(self, normal, highlights, terminal_colors)
	-- function to resolve function highlight groups being defined by function calls.
	local function resolve(tbl, key, resolve_links)
		local value = tbl[key]
		local value_type = type(value)
		if value_type == 'function' then -- call and cache the result; next time, if it isn't a function this step will be skipped
			tbl[key] = value(setmetatable({},
			{
				['__index'] = function(_, inner_key) return resolve(tbl, inner_key, true) end
			}))
		elseif resolve_links and value_type == _TYPE_STRING and not string.find(value, '^#') then
			return resolve(tbl, value, resolve_links)
		end

		return tbl[key]
	end

	-- save the colors_name before syntax reset
	local color_name = vim.g.colors_name

	-- If the syntax has been enabled, reset it.
	if fn.exists 'syntax_on' then exe 'syntax reset' end

	-- replace the colors_name
	vim.g.colors_name = color_name
	color_name = nil

	-- If we aren't using hex nor 256 colorsets.
	if not (go.termguicolors or _USE_256) then go.t_Co = '16' end

	-- Highlight the baseline.
	self.highlight('Normal', normal)

	-- Highlight everything else.
	for highlight_group, _ in pairs(highlights) do
		self.highlight(highlight_group, resolve(highlights, highlight_group, false))
	end

	-- Set the terminal highlight colors.
	self:highlight_terminal(terminal_colors)
end})