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

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

--- Normalizes a `buffer = true|false|0` argument into a number.
--- @param buffer boolean|number the argument to normalize
--- @return nil|number
local function normalize_buffer(buffer)
	if buffer == true or buffer == 0 then
		return vim.api.nvim_get_current_buf()
	elseif buffer == false then
		return nil
	end

	--- @diagnostic disable-next-line:return-type-mismatch `true` and `false are already checked
	return buffer
end

--- Normalizes a keymap from `vim.api.nvim_get_keymap` so it can be passed to `vim.keymap.set`
--- @param keymap table
--- @return table normalized
local function normalize_keymap(keymap)
	local to_return = {}
	-- Keys which must be manually edited
	to_return.buffer = keymap.buffer > 0 and keymap.buffer or nil
	to_return.rhs = keymap.callback or keymap.rhs

	-- Keys which are `v:true` or `v:false`
	to_return.expr = globals.is_true(keymap.expr)
	to_return.noremap = globals.is_true(keymap.noremap)
	to_return.nowait = globals.is_true(keymap.nowait)
	to_return.script = globals.is_true(keymap.script)
	to_return.silent = globals.is_true(keymap.silent)

	to_return.desc = keymap.desc
	return to_return
end

--- remove and return the right-hand side of a `keymap`.
--- @param keymap table the keymap to unpack
--- @return fun()|string rhs, table options
local function unpack_keymap_rhs(keymap)
	local rhs = keymap.rhs
	keymap.rhs = nil

	return rhs, keymap
end

--- @class libmodal.Layer
--- @field private active boolean whether the layer is currently applied
--- @field private existing_keymaps_by_mode table the keymaps to restore when exiting the mode; generated automatically
--- @field private layer_keymaps_by_mode table the keymaps to apply when entering the mode; provided by user
local Layer = require('libmodal.src.utils.classes').new()

--- apply the `Layer`'s keymaps buffer.
--- @return nil
function Layer:enter()
	if self:is_active() then
		vim.notify(
			'nvim-libmodal layer: This layer has already been entered. `:exit()` before entering again.',
			vim.log.levels.ERROR,
			{title = 'nvim-libmodal'}
		)
		return
	end

	self.active = true

	for mode, new_keymaps in pairs(self.layer_keymaps_by_mode) do
		for lhs, options in pairs(new_keymaps) do
			local rhs, unpacked = unpack_keymap_rhs(options)
			self:map(mode, lhs, rhs, unpacked)
		end
	end
end

--- exit the layer, restoring all previous keymaps.
--- @return nil
function Layer:exit()
	if not self.active then
		vim.notify(
			'nvim-libmodal layer: you cannot exit a layer without entering it first.',
			vim.log.levels.ERROR,
			{title = 'nvim-libmodal'}
		)
		return
	end

	for mode, keymaps in pairs(self.layer_keymaps_by_mode) do
		for lhs, keymap in pairs(keymaps) do
			self:unmap(keymap.buffer, mode, lhs)
		end
	end

	self.active = false
end

--- Check whether the layer has been `:enter`ed previously but not `:exit`ed.
--- @return boolean
function Layer:is_active()
	return self.active
end

--- add a keymap to the mode.
--- @param mode string the mode that this keymap for.
--- @param lhs string the left hand side of the keymap.
--- @param rhs fun()|string the right hand side of the keymap.
--- @param options table options for the keymap.
--- @return nil
--- @see vim.keymap.set
function Layer:map(mode, lhs, rhs, options)
	lhs = utils.api.replace_termcodes(lhs)
	options.buffer = normalize_buffer(options.buffer)

	if self.active then -- the layer has been activated
		if not self.existing_keymaps_by_mode[mode] then -- this is the first time that a keymap with this mode is being set
			self.existing_keymaps_by_mode[mode] = {}
		end

		if not self.existing_keymaps_by_mode[mode][lhs] then -- the keymap's state has not been saved.
			for _, existing_keymap in ipairs(
				options.buffer and
				vim.api.nvim_buf_get_keymap(options.buffer, mode) or
				vim.api.nvim_get_keymap(mode)
			) do -- check if this keymap will overwrite something
				if utils.api.replace_termcodes(existing_keymap.lhs) == lhs then -- mapping this will overwrite something; log the old mapping
					self.existing_keymaps_by_mode[mode][lhs] = normalize_keymap(existing_keymap)
					break
				end
			end
		end

		vim.keymap.set(mode, lhs, rhs, options)
	end

	-- add the new mapping to the layer's keymap
	options.rhs = rhs
	if self.layer_keymaps_by_mode[mode] then
		self.layer_keymaps_by_mode[mode][lhs] = options
	else
		self.layer_keymaps_by_mode[mode] = {[lhs] = options}
	end
end

--- @param keymaps_by_mode table the keymaps (e.g. `{n = {gg = {rhs = 'G', silent = true}}}`)
--- @return libmodal.Layer
function Layer.new(keymaps_by_mode)
	return setmetatable({existing_keymaps_by_mode = {}, layer_keymaps_by_mode = keymaps_by_mode, active = false}, Layer)
end

--- restore one keymapping to its original state.
--- @param buffer? number the buffer to unmap from (`nil` if it is not buffer-local)
--- @param mode string the mode of the keymap.
--- @param lhs string the keys which invoke the keymap.
--- @return nil
--- @see vim.api.nvim_del_keymap
function Layer:unmap(buffer, mode, lhs)
	lhs = utils.api.replace_termcodes(lhs)

	if self.active then
		if self.existing_keymaps_by_mode[mode][lhs] then -- there is an older keymap to go back to; restore it
			local rhs, options = unpack_keymap_rhs(self.existing_keymaps_by_mode[mode][lhs])
			-- WARN: nvim can fail to restore the original keybinding here unless schedule
			vim.schedule(function() vim.keymap.set(mode, lhs, rhs, options) end)
		else -- there was no older keymap; just delete the one set by this layer
			local ok, err = pcall(function()
				if buffer then
					vim.api.nvim_buf_del_keymap(buffer, mode, lhs)
				else
					vim.api.nvim_del_keymap(mode, lhs)
				end
			end)

			if not ok and err:match 'E31: No such mapping' then
				require('libmodal.src.utils').notify_error('nvim-libmodal encountered an error while unmapping from layer', err)
				return
			end
		end

		-- remove this keymap from the list of ones to restore
		self.existing_keymaps_by_mode[mode][lhs] = nil
	end

	-- remove this keymap from the list of ones managed by the layer
	self.layer_keymaps_by_mode[mode][lhs] = nil
end

return Layer