local globals = require 'libmodal.globals'
local ParseTable = require 'libmodal.collections.ParseTable'
local utils = require 'libmodal.utils' --- @type libmodal.utils

--- @alias CursorPosition {[1]: integer, [2]: integer} see `nvim_win_get_cursor`

--- @class libmodal.Mode
--- @field private autocmds integer[]
--- @field private changedtick integer
--- @field private cursor CursorPosition
--- @field private flush_input_timer unknown
--- @field private help? libmodal.utils.Help
--- @field private input libmodal.utils.Var[integer]
--- @field private input_bytes? integer[] local `input` history
--- @field private instruction fun()|{[string]: fun()|string}
--- @field private mappings libmodal.collections.ParseTable
--- @field private modeline string[][]
--- @field private name string
--- @field private popups libmodal.collections.Stack
--- @field private supress_exit boolean
--- @field public count libmodal.utils.Var[integer]
--- @field public exit libmodal.utils.Var[boolean]
--- @field public timeouts? libmodal.utils.Var[boolean]
local Mode = utils.classes.new()

local C_v = utils.api.replace_termcodes '<C-v>'
local C_s = utils.api.replace_termcodes '<C-s>'

--- Event groups organized by modes
local EVENTS_BY_MODE = {
	--- Cursor events triggered by which modes
	CURSOR_MOVED = {
		CursorMoved = {
			n = true,
			nt = true,
			ntT = true,
			s = true,
			S = true,
			[C_s] = true,
			v = true,
			V = true,
			[C_v] = true,
			vs = true,
			Vs = true,
			[C_v .. 's'] = true,
		},

		CursorMovedI = {
			i = true,
			niI = true,
			niR = true,
			R = true,
			Rv = true,
		},
	},

	TEXT_CHANGED = {
		TextChanged = {
			n = true,
			nt = true,
			ntT = true,
		},

		TextChangedI = {
			i = true,
			niI = true,
			niR = true,
			R = true,
			Rv = true,
		},

		TextChangedP = {
			ic = true,
			ix = true,
			Rc = true,
			Rvc = true,
			Rx = true,
			Rvx = true,
		},

		TextChangedT = {
			t = true,
		},
	},
}

--- The namespaces used by modes
local NS = {
	--- The virtual cursor namespace. Used to workaround neovim/neovim#20793
	CURSOR = vim.api.nvim_create_namespace('libmodal-mode-virtual_cursor'),
}

local HELP_CHAR = '?'
local TIMEOUT =
{
	CHAR = ' ',
	SEND = function(self) vim.api.nvim_feedkeys(self.CHAR, 'nt', false) end
}
TIMEOUT.CHAR_NUMBER = TIMEOUT.CHAR:byte()

--- Byte for 0
local ZERO = string.byte(0)

--- Byte for 9
local NINE = string.byte(9)

--- Execute events depending on current mode
--- @param events_by_mode {[string]: {[string]: true}}
local function execute_event_by_mode(events_by_mode)
	local mode = vim.api.nvim_get_mode().mode
	for event, modes in pairs(events_by_mode) do
		if modes[mode] then
			vim.api.nvim_exec_autocmds(event, {})
			break
		end
	end
end

--- execute the `instruction`.
--- @private
--- @param instruction fun(libmodal.Mode)|string a Lua function or Vimscript command.
--- @return nil
function Mode:execute_instruction(instruction)
	if type(instruction) == 'function' then
		instruction(self)
	else
		vim.api.nvim_command(instruction)
	end

	self.count:set(0)
	self:render_virtual_cursor(0, true)
	self:execute_text_changed_events()
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).
--- @private
--- @return nil
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] == HELP_CHAR:byte() then
			self.help:show()
		end

		self.input_bytes = {}
	elseif command_type == 'table' and globals.is_true(self.timeouts:get()) then -- the command was a table, meaning that it MIGHT match.
		local timeout = vim.api.nvim_get_option_value('timeoutlen', {})
		self.flush_input_timer:start( -- start the timer
			timeout, 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 = {}
				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 = {}
	end

	local input_bytes = self.input_bytes or {}

	local count = self.count:get()
	if count > 0 then
		local count_bytes = { tostring(count):byte(1, -1) }
		input_bytes = vim.list_extend(count_bytes, input_bytes)
	end

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

--- clears the virtual cursor from the screen
--- @param bufnr integer to clear the cursor on
--- @private
function Mode:clear_virtual_cursor(bufnr)
	vim.api.nvim_buf_clear_namespace(bufnr, NS.CURSOR, 0, -1);
end

--- Runs CursorMoved* events, if applicable
--- @param cursor CursorPosition the current cursor position
function Mode:execute_cursor_moved_events(cursor)
	if not vim.deep_equal(self.cursor, cursor) then
		execute_event_by_mode(EVENTS_BY_MODE.CURSOR_MOVED)
		self.cursor = cursor
	end
end

--- Runs TextChanged* events, if applicable
function Mode:execute_text_changed_events()
	local changedtick = vim.api.nvim_buf_get_changedtick(0)
	if self.changedtick ~= changedtick then
		execute_event_by_mode(EVENTS_BY_MODE.TEXT_CHANGED)
		self.changedtick = changedtick
	end
end

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

	self.count:set(0)
	self.exit:set(false)

	--- HACK: neovim/neovim#20793
	vim.api.nvim_command 'highlight Cursor blend=100'
	vim.schedule(function() vim.opt.guicursor:append { 'a:Cursor/lCursor' } end)
	self.cursor = self:cursor_in(0)
	self:render_virtual_cursor(0)

	do
		local augroup = vim.api.nvim_create_augroup('libmodal-mode-' .. self.name, { clear = false })
		self.autocmds = {
			vim.api.nvim_create_autocmd('BufLeave', {
				callback = function(ev)
					local bufnr = ev.buf
					self:clear_virtual_cursor(bufnr)
				end,
				group = augroup,
			}),

			vim.api.nvim_create_autocmd('BufEnter', {
				callback = function(ev)
					local bufnr = ev.buf
					self.changedtick = vim.api.nvim_buf_get_changedtick(bufnr)
				end,
			});
		}
	end

	self.changedtick = vim.api.nvim_buf_get_changedtick(0)

	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})

	repeat
		-- try (using pcall) to use the mode.
		local ok, 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', result)
			self.exit:set_local(true)
		end
	until globals.is_true(self.exit:get())

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

--- get input from the user.
--- @private
function Mode:get_user_input()
	-- echo the indicator.
	self:show_mode()

	-- 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 type(user_input) == "number" and ZERO <= user_input and user_input <= NINE then
		local oldCount = self.count:get()
		local newCount = tonumber(oldCount .. string.char(user_input))
		self.count:set(newCount)
	end

	if not self.supress_exit and user_input == globals.ESC_NR then -- the user wants to exit.
		if self.count:get() < 1 then -- exit
			return self.exit:set_local(true)
		end

		self.count:set(0) -- reset count count
	end

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

--- @param winid integer
--- @return CursorPosition line_and_col
function Mode:cursor_in(winid)
	local cursor = vim.api.nvim_win_get_cursor(winid)
	cursor[1] = cursor[1] - 1 -- win_get_cursor returns +1 for our purpose
	return cursor
end

--- render the virtual cursor using extmarks
--- @param winid integer
--- @param clear? boolean if true, clear other virtual cursors before rendering the new one
--- @private
function Mode:render_virtual_cursor(winid, clear)
	local bufnr = vim.api.nvim_win_get_buf(winid)
	if clear then
		self:clear_virtual_cursor(bufnr)
	end

	local cursor = self:cursor_in(winid)
	vim.highlight.range(bufnr, NS.CURSOR, 'Cursor', cursor, cursor, { inclusive = true })

	self:execute_cursor_moved_events(cursor)
end

--- show the mode indicator, if it is enabled
function Mode:show_mode()
	utils.api.redraw()

	local showmode = vim.api.nvim_get_option_value('showmode', {})
	if showmode then
		vim.api.nvim_echo({{'-- ' .. self.name .. ' --', 'LibmodalPrompt'}}, false, {})
	end
end

--- `enter` a `Mode` using the arguments given, and then flag the current mode to exit.
--- @param ... unknown arguments to `Mode.new`
--- @return nil
--- @see libmodal.Mode.enter which `...` shares the layout of
--- @see libmodal.Mode.exit
function Mode:switch(...)
	local mode = Mode.new(...)
	mode:enter()
	self.exit:set_local(true)
end

--- uninitialize variables from after exiting the mode.
--- @private
--- @return nil
function Mode:tear_down()
	--- HACK: neovim/neovim#20793
	self:clear_virtual_cursor(0)
	vim.schedule(function() vim.opt.guicursor:remove { 'a:Cursor/lCursor' } end)
	vim.api.nvim_command 'highlight Cursor blend=0'
	for _, autocmd in ipairs(self.autocmds) do
		vim.api.nvim_del_autocmd(autocmd)
	end
	self.cursor = nil

	if type(self.instruction) == 'table' 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

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

	-- inherit the metatable.
	local self = setmetatable(
		{
			count = utils.Var.new(name, 'count'),
			exit = utils.Var.new(name, 'exit'),
			input = utils.Var.new(name, 'input'),
			instruction = instruction,
			name = name,
			modeline = {{'-- ' .. name .. ' --', 'LibmodalPrompt'}},
		},
		Mode
	)

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

	-- if the user provided keymaps
	if type(instruction) == 'table' 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_CHAR] then
			self.help = utils.Help.new(instruction, 'KEY MAP')
		end

		self.input_bytes = {}

		-- build the parse tree.
		self.mappings = ParseTable.new(instruction)

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

		-- create a variable for whether or not timeouts are enabled.
		self.timeouts = utils.Var.new(self.name, 'timeouts', vim.g.libmodalTimeouts)
	end

	return self
end

return Mode