--- @type libmodal.globals
local globals = require 'libmodal/src/globals'

--- @type libmodal.collections.ParseTable
local ParseTable = require 'libmodal/src/collections/ParseTable'

--- @type libmodal.utils
local utils = require 'libmodal/src/utils'

--- @class libmodal.Mode
--- @field private exit libmodal.utils.Vars
--- @field private flush_input_timer unknown
--- @field private help? libmodal.utils.Help
--- @field private indicator libmodal.utils.Indicator
--- @field private input libmodal.utils.Vars
--- @field private instruction fun()|{[string]: fun()|string}
--- @field private mappings libmodal.collections.ParseTable
--- @field private name string
--- @field private popups libmodal.collections.Stack
--- @field private supress_exit boolean
--- @field private timeouts_enabled boolean
local Mode = utils.classes.new()

local InputBytes = utils.classes.new(
{
	clear = function(self)
		for i, _ in ipairs(self) do
			self[i] = nil
		end
	end
})

local HELP = '?'
local TIMEOUT =
{
	CHAR = 'ø',
	LEN  = vim.go.timeoutlen,
	SEND = function(self) vim.api.nvim_feedkeys(self.CHAR, 'nt', false) end
}
TIMEOUT.CHAR_NUMBER = string.byte(TIMEOUT.CHAR)

--- execute the `instruction`.
--- @param instruction fun()|string a Lua function or Vimscript command.
function Mode.execute_instruction(instruction)
	if type(instruction) == globals.TYPE_FUNC then
		instruction()
	else
		vim.api.nvim_command(instruction)
	end
end

--- check the user's input against the `self.instruction` mappings to see if there is anything to execute.
--- if there is nothing to execute, the user's input is rendered on the screen (as does Vim by default).
function Mode:check_input_for_mapping()
	-- stop any running timers
	self.flush_input_timer:stop()

	-- append the latest input to the locally stored input history.
	self.input_bytes[#self.input_bytes + 1] = self.input:get()

	-- get the command based on the users input.
	local cmd = self.mappings:get(self.input_bytes)

	-- get the type of the command.
	local command_type = type(cmd)

	-- if there was no matching command
	if not cmd then
		if #self.input_bytes < 2 and self.input_bytes[1] == string.byte(HELP) then
			self.help:show()
		end

		self.input_bytes:clear()
	elseif command_type == globals.TYPE_TBL and globals.is_true(self.timeouts_enabled) then -- the command was a table, meaning that it MIGHT match.
		self.flush_input_timer:start( -- start the timer
			TIMEOUT.LEN, 0, vim.schedule_wrap(function()
				-- send input to interrupt a blocking `getchar`
				TIMEOUT:SEND()
				-- if there is a command, execute it.
				if cmd[ParseTable.CR] then
					self.execute_instruction(cmd[ParseTable.CR])
				end
				-- clear input
				self.input_bytes:clear()
				self.popups:peek():refresh(self.input_bytes)
			end)
		)
	else -- the command was an actual vim command.
		--- @diagnostic disable-next-line:param-type-mismatch already checked `cmd` != `table`
		self.execute_instruction(cmd)
		self.input_bytes:clear()
	end

	self.popups:peek():refresh(self.input_bytes)
end

--- enter this mode.
function Mode:enter()
	-- intialize variables that are needed for each recurse of a function
	if type(self.instruction) == globals.TYPE_TBL then
		-- initialize the input history variable.
		self.popups:push(utils.Popup.new())
	end

	self.previous_mode_name = vim.g.libmodalActiveModeName
	vim.g.libmodalActiveModeName = self.name

	--[[ MODE LOOP. ]]
	local previous_mode = self.previous_mode_name or vim.api.nvim_get_mode().mode
	vim.api.nvim_exec_autocmds('ModeChanged', {pattern = previous_mode .. ':' .. self.name})

	local continue_mode = true
	while continue_mode do
		-- try (using pcall) to use the mode.
		local ok, mode_result = pcall(self.get_user_input, self)

		-- if there were errors, handle them.
		if not ok then
			--- @diagnostic disable-next-line:param-type-mismatch if `not ok` then `mode_result` is a string
			utils.notify_error('Error during nvim-libmodal mode', mode_result)
			continue_mode = false
		else
			continue_mode = mode_result
		end
	end

	self:tear_down()
	vim.api.nvim_exec_autocmds('ModeChanged', {pattern = self.name .. ':' .. previous_mode})
end

--- get input from the user.
--- @return boolean more_input
function Mode:get_user_input()
	-- if the mode is not handling exit events automatically and the global exit var is true.
	if self.supress_exit and globals.is_true(self.exit:get()) then
		return false
	end

	-- echo the indicator.
	utils.api.hi_echo(self.indicator)

	-- capture input.
	local user_input = vim.fn.getchar()

	-- return if there was a timeout event.
	if user_input == TIMEOUT.CHAR_NUMBER then
		return true
	end

	-- set the global input variable to the new input.
	self.input:set(user_input)

	if not self.supress_exit and user_input == globals.ESC_NR then -- the user wants to exit.
		return false -- as in, "I don't want to continue."
	else -- the user wants to continue.

		--[[ The instruction type is determined every cycle, because the user may be assuming a more direct control
			over the instruction and it may change over the course of execution. ]]
		local instruction_type = type(self.instruction)

		if instruction_type == globals.TYPE_TBL then -- the instruction was provided as a was a set of mappings.
			self:check_input_for_mapping()
		elseif instruction_type == globals.TYPE_STR then -- the instruction is the name of a Vimscript function.
			vim.fn[self.instruction]()
		else -- the instruction is a function.
			self.instruction()
		end
	end

	return true
end

--- uninitialize variables from after exiting the mode.
function Mode:tear_down()
	if type(self.instruction) == globals.TYPE_TBL then
		self.flush_input_timer:stop()
		self.input_bytes = nil

		self.popups:pop():close()
	end

	if self.previous_mode_name and #vim.trim(self.previous_mode_name) < 1 then
		vim.g.libmodalActiveModeName = nil
	else
		vim.g.libmodalActiveModeName = self.previous_mode_name
	end

	utils.api.redraw()
end

return
{
	--- create a new mode.
	--- @param name string the name of the mode.
	--- @param instruction fun()|string|table a Lua function, keymap dictionary, Vimscript command.
	--- @return libmodal.Mode
	new = function(name, instruction, supress_exit)
		name = vim.trim(name)

		-- inherit the metatable.
		local self = setmetatable(
			{
				exit = utils.Vars.new('exit', name),
				indicator = utils.Indicator.new('LibmodalPrompt', '-- ' .. name .. ' --'),
				input = utils.Vars.new('input', name),
				instruction = instruction,
				name = name,
			},
			Mode
		)

		-- define the exit flag
		self.supress_exit = supress_exit or false

		-- if the user provided keymaps
		if type(instruction) == globals.TYPE_TBL then
			-- create a timer to perform actions with.
			self.flush_input_timer = vim.loop.new_timer()

			-- determine if a default `Help` should be created.
			if not self.instruction[HELP] then
				--- @diagnostic disable-next-line:param-type-mismatch we checked that `instruction` is a table above
				self.help = utils.Help.new(self.instruction, 'KEY MAP')
			end

			self.input_bytes = setmetatable({}, InputBytes)

			-- build the parse tree.
			--- @diagnostic disable-next-line:param-type-mismatch already checked `self.instruction` != `table`
			self.mappings = ParseTable.new(self.instruction)

			-- create a table for mode-specific data.
			self.popups = require('libmodal/src/collections/Stack').new()

			-- create a variable for whether or not timeouts are enabled.
			self.timeouts = utils.Vars.new('timeouts', self.name)

			-- read the correct timeout variable.
			self.timeouts_enabled = self.timeouts:get() or vim.g.libmodalTimeouts
		end

		return self
	end
}