{-# LANGUAGE OverloadedStrings #-}

module Main where

import System.IO
import System.Directory
import Data.Text (Text, pack, unpack, isInfixOf, lines, unlines)
import qualified Data.Text.IO as TIO
import Control.Monad (when)
import Data.List (sortBy)
import Data.Ord (comparing)
import Data.Char (isAlpha)

todoFile :: FilePath
todoFile = "todo.txt"

main :: IO ()
main = do
    putStrLn "Welcome to the Haskell Todo App"
    putStrLn "1. Display tasks"
    putStrLn "2. Add task"
    putStrLn "3. Filter tasks by tag"
    putStrLn "4. Sort tasks by priority"
    putStrLn "5. Exit"
    putStr "Choose an option: "
    hFlush stdout
    option <- getLine
    case option of
        "1" -> displayTasks
        "2" -> addTask
        "3" -> filterTasksByTag
        "4" -> sortTasksByPriority
        "5" -> putStrLn "Goodbye!"
        _   -> putStrLn "Invalid option" >> main

displayTasks :: IO ()
displayTasks = do
    exists <- doesFileExist todoFile
    if exists
        then do
            contents <- TIO.readFile todoFile
            putStrLn "Tasks:"
            TIO.putStrLn contents
        else putStrLn "No tasks found."
    main

addTask :: IO ()
addTask = do
    putStr "Enter the task: "
    hFlush stdout
    task <- getLine
    TIO.appendFile todoFile (pack task <> "\n")
    putStrLn "Task added."
    main

filterTasksByTag :: IO ()
filterTasksByTag = do
    putStr "Enter the tag to filter by (e.g., +chapelShelving): "
    hFlush stdout
    tag <- getLine
    exists <- doesFileExist todoFile
    if exists
        then do
            contents <- TIO.readFile todoFile
            let tasks = Data.Text.lines contents
                filteredTasks = filter (isInfixOf (pack tag)) tasks
            putStrLn "Filtered tasks:"
            TIO.putStrLn (Data.Text.unlines filteredTasks)
        else putStrLn "No tasks found."
    main

sortTasksByPriority :: IO ()
sortTasksByPriority = do
    exists <- doesFileExist todoFile
    if exists
        then do
            contents <- TIO.readFile todoFile
            let tasks = Data.Text.lines contents
                sortedTasks = sortBy comparePriority tasks
            putStrLn "Sorted tasks by priority:"
            TIO.putStrLn (Data.Text.unlines sortedTasks)
        else putStrLn "No tasks found."
    main

comparePriority :: Text -> Text -> Ordering
comparePriority t1 t2 = comparing getPriority t1 t2

getPriority :: Text -> Maybe Char
getPriority t = case unpack t of
    ('(':p:')':_) | isAlpha p -> Just p
    _                         -> Nothing