-- Create the module table
local M = {}

-- Default configuration
local defaults = {
	filetypes = { "markdown", "text", "norg" }, -- Filetypes to activate the plugin for
}

-- Helper: Parses line details for a given line number (1-based)
-- Returns table: { line = str, indent = str, marker = str|nil, content = str, is_todo = bool } or nil
local function get_line_details(lnum)
  -- Use nvim_buf_get_lines which is 0-indexed for ranges
  local lines = vim.api.nvim_buf_get_lines(0, lnum - 1, lnum, false)
  if not lines or #lines == 0 then return nil end -- Handle potential errors getting line
  local line = lines[1]

  local indent = string.match(line, "^%s*") or ""
  -- Pattern captures marker '-', '*', or '+' followed by at least one space
  -- Returns: indent, marker, space_after_marker
  local marker_pattern = "^(%s*)([%-%*%+])(%s+)"
  -- Pattern captures marker, checkbox '[ ]' or '[x]', and optional space after checkbox
  -- Matches lines like: "- [ ] task", "* [x] task", "+ [ ] task"
  local todo_pattern = "^(%s*[%-%*%+]%s+)%[([ x])%]%s*" -- Capture prefix before checkbox

  local _, marker_match, _ = string.match(line, marker_pattern)
  local is_todo = (string.match(line, todo_pattern) ~= nil)
  local content = ""

  if is_todo then
    -- Content is everything after "[x] " or "[ ] " (including leading space)
    content = string.match(line, todo_pattern .. "(.*)") or ""
  elseif marker_match then
    -- Content is everything after "- " / "* " / "+ "
    content = string.match(line, marker_pattern .. "(.*)") or ""
  else
    -- No list marker, just the trimmed line content
    content = vim.trim(line)
  end

  return {
    line = line,
    indent = indent,
    marker = marker_match, -- '-', '*', '+', or nil
    content = content,
    is_todo = is_todo,
  }
end

-- Helper: Gets details for the current line
local function get_current_line_details()
    local cursor_pos = vim.api.nvim_win_get_cursor(0)
    local lnum = cursor_pos[1] -- 1-based line number
    return get_line_details(lnum), lnum
end

-- <leader>ti: Convert line to TODO, cursor after "] " (Normal mode)
local function add_todo_insert_mode()
    local details, lnum = get_current_line_details()
    -- Don't convert if already a TODO or if getting details failed
    if not details or details.is_todo then return end

    local use_marker = details.marker or "-" -- Default to '-' if no list marker found
    local text_content = details.content -- Content already extracted correctly by get_line_details

    local new_line = details.indent .. use_marker .. " [ ] " .. text_content
    -- Replace current line (lnum is 1-based, set_lines is 0-based)
    vim.api.nvim_buf_set_lines(0, lnum - 1, lnum, false, { new_line })

    -- Set cursor position: 1-based row, 0-based byte column
    -- Position cursor right after the "] "
    local cursor_col_bytes = #(details.indent .. use_marker .. " [ ] ") -- Use Lua # operator
    vim.api.nvim_win_set_cursor(0, { lnum, cursor_col_bytes })
end

-- <leader>ta: Convert line to TODO, cursor at end of line (Normal mode)
local function add_todo_append_mode()
    local details, lnum = get_current_line_details()
    if not details or details.is_todo then return end

    local use_marker = details.marker or "-"
    local text_content = details.content

    local new_line = details.indent .. use_marker .. " [ ] " .. text_content
    vim.api.nvim_buf_set_lines(0, lnum - 1, lnum, false, { new_line })

    -- Set cursor position: 1-based row, 0-based byte column
    -- Position cursor at the very end of the line content
    local cursor_col_bytes = #new_line -- Use Lua # operator
    vim.api.nvim_win_set_cursor(0, { lnum, cursor_col_bytes })
end


-- <leader>to: Insert new TODO line below, cursor after "] " (Normal mode)
local function add_todo_new_line_mode()
    local details, lnum = get_current_line_details()
    if not details then return end -- Should not happen usually, but check anyway

    -- Determine indent and marker based on current line, default to '-' if no marker
    local new_indent = details.indent
    local new_marker = details.marker or "-"

    local new_line_content = new_indent .. new_marker .. " [ ] "
    -- Insert after current line (lnum is 1-based, set_lines is 0-based for ranges)
    vim.api.nvim_buf_set_lines(0, lnum, lnum, false, { new_line_content })

    -- Set cursor position: 1-based row (lnum + 1), 0-based byte column
    -- Position cursor at the end of the new line (after "] ")
    local cursor_col_bytes = #new_line_content -- Use Lua # operator
    vim.api.nvim_win_set_cursor(0, { lnum + 1, cursor_col_bytes })
end

-- Internal function to set up buffer-local keymaps
local function setup_buffer_keymaps()
	-- Handles Enter key press in Insert mode
	local function press_enter()
        local details, lnum = get_current_line_details()
        if not details then
            -- Getting details failed, do nothing and let Neovim handle Enter.
            return
        end

        -- Check if the line is a TODO item and if it has content after the marker
        -- Use string.match with %S to check for any non-whitespace character
        local has_content = details.content and string.match(details.content, "%S")

        if details.is_todo and has_content then
            -- Case 1: Non-empty TODO line
            -- Create a new TODO line below with same indent/marker
            local new_marker = details.marker or "-" -- Should always have marker if is_todo, but safety check
            local new_line_content = details.indent .. new_marker .. " [ ] "

            -- Insert the new line below the current one
            vim.api.nvim_buf_set_lines(0, lnum, lnum, false, { new_line_content })

            -- Move cursor to the new line, after the "] "
            local cursor_col_bytes = #new_line_content
            vim.api.nvim_win_set_cursor(0, { lnum + 1, cursor_col_bytes })

            -- Action handled, do not fall through to default behavior.
            -- No return value needed as it's not an expr mapping anymore.

        elseif details.is_todo and not has_content then
            -- Case 2: Empty TODO line (e.g., "- [ ]") - Implement Outdenting
            local current_indent = details.indent
            local current_indent_len = #current_indent
            local sw = vim.bo.shiftwidth -- Get buffer's shiftwidth
            local et = vim.bo.expandtab -- Get buffer's expandtab setting

            if current_indent_len > 0 then
                -- Line is indented, calculate new indentation
                local new_indent = ""
                if et then -- Using spaces
                    local target_indent_len = math.max(0, current_indent_len - sw)
                    new_indent = string.rep(" ", target_indent_len)
                else -- Using tabs
                    -- Remove the first tab character found
                    new_indent = string.gsub(current_indent, "^\t", "", 1)
                    -- Safety check: if gsub didn't change anything (e.g., indent was spaces),
                    -- try removing spaces as a fallback, though this is less ideal with noexpandtab
                    if new_indent == current_indent and current_indent_len > 0 then
                       local target_indent_len = math.max(0, current_indent_len - sw)
                       new_indent = string.rep(" ", target_indent_len)
                    end
                end

                -- Replace the current line with the outdented version
                local new_marker = details.marker or "-"
                local new_line_content = new_indent .. new_marker .. " [ ] "
                vim.api.nvim_buf_set_lines(0, lnum - 1, lnum, false, { new_line_content })

                -- Move cursor after the "] " on the modified line
                local cursor_col_bytes = #new_line_content
                vim.api.nvim_win_set_cursor(0, { lnum, cursor_col_bytes })

                -- Action handled, do not fall through.

            else
                -- Line is not indented, terminate the list
                -- Replace the line with an empty string
                vim.api.nvim_buf_set_lines(0, lnum - 1, lnum, false, { "" })
                -- Now, manually insert a newline below using the API
                vim.api.nvim_buf_set_lines(0, lnum, lnum, false, { "" })
                -- Move cursor to the new empty line
                vim.api.nvim_win_set_cursor(0, { lnum + 1, 0 })

                -- Action handled, do not fall through.
            end

        else
            -- Case 3: Not a TODO line
            -- Do nothing. Neovim will automatically handle the Enter key press
            -- because this function didn't modify the buffer or explicitly handle it.
            return -- Explicitly return nothing to be clear
        end
	end

	-- indent line if tab is pressed when line is a todo (Will be refactored in Step 4)
	local function press_tab()
		local current_line = vim.api.nvim_get_current_line()
		-- Check if current line matches the patterns (Only checks '-' marker currently)
        -- TODO: Update pattern to match *, + as well
		local pattern = "^%s*%- %[[ x]%]"
		if string.match(current_line, pattern) then
			-- print("tab pressed, allegedly") -- Removed print
			vim.api.nvim_feedkeys(vim.api.nvim_replace_termcodes("<C-t>", true, false, true), "i", false)
            return "" -- Action handled by feedkeys
		else
            -- Return <Tab> to allow default behavior
            return vim.api.nvim_replace_termcodes("<Tab>", true, false, true)
        end
	end

	-- indent line if shift tab is pressed when line is a todo (Will be refactored in Step 4)
	local function press_shift_tab()
		local current_line = vim.api.nvim_get_current_line()
		-- Check if current line matches the patterns (Only checks '-' marker currently)
        -- TODO: Update pattern to match *, + as well
		local pattern = "^%s*%- %[[ x]%]"
		if string.match(current_line, pattern) then
			-- print("shift tab pressed, allegedly") -- Removed print
			vim.api.nvim_feedkeys(vim.api.nvim_replace_termcodes("<C-d>", true, false, true), "i", false)
            return "" -- Action handled by feedkeys
		else
            -- Return <S-Tab> to allow default behavior
            return vim.api.nvim_replace_termcodes("<S-Tab>", true, false, true)
        end
	end

	-- Toggles the checkbox [ ] <-> [x] for lines starting with -, *, +, or #
	local function toggle_todo()
		local line = vim.api.nvim_get_current_line()
        -- Pattern captures:
        -- 1: Prefix (indentation, marker '-', '*', '+', or '#', and whitespace)
        -- 2: State (' ' or 'x')
        -- 3: Rest of the line (after ']')
		local prefix, state, rest = string.match(line, "^([%s]*[%-#%*%+]%s*)%[([ x])%](.*)")

		if prefix then -- Check if the pattern matched (i.e., it's a toggleable line)
			-- Determine the new state
			local new_state = (state == ' ') and 'x' or ' '
			-- Reconstruct the line with the new state
			local new_line = prefix .. "[" .. new_state .. "]" .. rest
			-- Update the current line
			vim.api.nvim_set_current_line(new_line)
		end
        -- If the pattern didn't match, do nothing.
	end

	-- Set up buffer-local keymaps
	-- Use buffer = 0 to target the current buffer
	vim.keymap.set("n", "<leader>t", function() end, { desc = "+TODOs", buffer = 0 }) -- Placeholder
    -- Removed expr = true from <CR> mapping
	vim.keymap.set("i", "<CR>", press_enter, { desc = "Todoer: Handle Enter", buffer = 0 })
    -- Keep expr = true for Tab/S-Tab for now, until they are refactored
	vim.keymap.set("i", "<TAB>", press_tab, { desc = "Todoer: Handle Tab", expr = true, buffer = 0 })
	vim.keymap.set("i", "<S-Tab>", press_shift_tab, { desc = "Todoer: Handle Shift-Tab", expr = true, buffer = 0 })
	vim.keymap.set("n", "<leader>tt", toggle_todo, { desc = "Todoer: Toggle TODO", buffer = 0 })
	-- New mappings for adding TODOs
	vim.keymap.set("n", "<leader>ti", add_todo_insert_mode, { desc = "Todoer: Add TODO (cursor after marker)", buffer = 0, silent = true })
	vim.keymap.set("n", "<leader>ta", add_todo_append_mode, { desc = "Todoer: Add TODO (cursor at end)", buffer = 0, silent = true })
	vim.keymap.set("n", "<leader>to", add_todo_new_line_mode, { desc = "Todoer: Add new TODO line below", buffer = 0, silent = true })

	-- Optional: Notify that keymaps are set for this buffer
	-- vim.notify("Todoer keymaps activated for this buffer", vim.log.levels.INFO)
end

-- Setup function: Called by the user in their config
function M.setup(opts)
	-- Merge user options with defaults
	local config = vim.tbl_deep_extend("force", {}, defaults, opts or {})

	-- Create an autocommand group to ensure we can clear it later if needed
	local group = vim.api.nvim_create_augroup("TodoerUserSetup", { clear = true })

	-- Create the autocommand
	vim.api.nvim_create_autocmd("FileType", {
		group = group,
		pattern = config.filetypes, -- Use filetypes from config
		desc = "Setup Todoer keymaps for specific filetypes",
		callback = function()
			-- Call the function that sets up buffer-local keymaps
			setup_buffer_keymaps()
		end,
	})
end

-- Return the module table
return M