{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE NoImplicitPrelude #-}

module Omni.Task.Core where

import Alpha
import Data.Aeson (FromJSON, ToJSON, decode, encode)
import qualified Data.ByteString.Lazy.Char8 as BLC
import qualified Data.Text as T
import qualified Data.Text.IO as TIO
import Data.Time (UTCTime, diffTimeToPicoseconds, getCurrentTime, utctDayTime)
import GHC.Generics ()
import System.Directory (createDirectoryIfMissing, doesFileExist)

-- Core data types
data Task = Task
  { taskId :: Text,
    taskTitle :: Text,
    taskType :: TaskType,
    taskParent :: Maybe Text, -- Parent epic ID
    taskNamespace :: Maybe Text, -- Optional namespace (e.g., "Omni/Task", "Biz/Cloud")
    taskStatus :: Status,
    taskDependencies :: [Text], -- List of task IDs this depends on
    taskCreatedAt :: UTCTime,
    taskUpdatedAt :: UTCTime
  }
  deriving (Show, Eq, Generic)

data TaskType = Epic | WorkTask
  deriving (Show, Eq, Generic)

data Status = Open | InProgress | Done
  deriving (Show, Eq, Generic)

instance ToJSON TaskType

instance FromJSON TaskType

instance ToJSON Status

instance FromJSON Status

instance ToJSON Task

instance FromJSON Task

-- Initialize the task database
initTaskDb :: IO ()
initTaskDb = do
  createDirectoryIfMissing True ".tasks"
  exists <- doesFileExist ".tasks/tasks.jsonl"
  unless exists <| do
    TIO.writeFile ".tasks/tasks.jsonl" ""
    putText "Initialized task database at .tasks/tasks.jsonl"

-- Generate a short ID using base62 encoding of timestamp
generateId :: IO Text
generateId = do
  now <- getCurrentTime
  -- Convert current time to microseconds since midnight
  let dayTime = utctDayTime now
      microseconds = diffTimeToPicoseconds dayTime `div` 1000000
      -- Convert to base62 for shorter IDs
      encoded = toBase62 (fromIntegral microseconds)
  pure <| "t-" <> T.pack encoded

-- Convert number to base62 (0-9, a-z, A-Z)
toBase62 :: Integer -> String
toBase62 0 = "0"
toBase62 n = reverse <| go n
  where
    alphabet = ['0' .. '9'] ++ ['a' .. 'z'] ++ ['A' .. 'Z']
    go 0 = []
    go x =
      let (q, r) = x `divMod` 62
          idx = fromIntegral r
          char = case drop idx alphabet of
            (c : _) -> c
            [] -> '0' -- Fallback (should never happen)
       in char : go q

-- Load all tasks from JSONL file
loadTasks :: IO [Task]
loadTasks = do
  exists <- doesFileExist ".tasks/tasks.jsonl"
  if exists
    then do
      content <- TIO.readFile ".tasks/tasks.jsonl"
      let taskLines = T.lines content
      pure <| mapMaybe decodeTask taskLines
    else pure []
  where
    decodeTask :: Text -> Maybe Task
    decodeTask line =
      if T.null line
        then Nothing
        else decode (BLC.pack <| T.unpack line)

-- Save a single task (append to JSONL)
saveTask :: Task -> IO ()
saveTask task = do
  let json = encode task
  BLC.appendFile ".tasks/tasks.jsonl" (json <> "\n")

-- Create a new task
createTask :: Text -> TaskType -> Maybe Text -> Maybe Text -> [Text] -> IO Task
createTask title taskType parent namespace deps = do
  tid <- generateId
  now <- getCurrentTime
  let task =
        Task
          { taskId = tid,
            taskTitle = title,
            taskType = taskType,
            taskParent = parent,
            taskNamespace = namespace,
            taskStatus = Open,
            taskDependencies = deps,
            taskCreatedAt = now,
            taskUpdatedAt = now
          }
  saveTask task
  pure task

-- Update task status
updateTaskStatus :: Text -> Status -> IO ()
updateTaskStatus tid newStatus = do
  tasks <- loadTasks
  now <- getCurrentTime
  let updatedTasks = map updateIfMatch tasks
      updateIfMatch t =
        if taskId t == tid
          then t {taskStatus = newStatus, taskUpdatedAt = now}
          else t
  -- Rewrite the entire file (simple approach for MVP)
  TIO.writeFile ".tasks/tasks.jsonl" ""
  traverse_ saveTask updatedTasks

-- List tasks, optionally filtered by type or parent
listTasks :: Maybe TaskType -> Maybe Text -> IO [Task]
listTasks maybeType maybeParent = do
  tasks <- loadTasks
  let filtered =
        tasks
          |> filterByType maybeType
          |> filterByParent maybeParent
  pure filtered
  where
    filterByType Nothing ts = ts
    filterByType (Just typ) ts = filter (\t -> taskType t == typ) ts
    filterByParent Nothing ts = ts
    filterByParent (Just pid) ts = filter (\t -> taskParent t == Just pid) ts

-- Get ready tasks (not blocked by dependencies)
getReadyTasks :: IO [Task]
getReadyTasks = do
  allTasks <- loadTasks
  let openTasks = filter (\t -> taskStatus t /= Done) allTasks
      doneIds = map taskId <| filter (\t -> taskStatus t == Done) allTasks
      isReady task = all (`elem` doneIds) (taskDependencies task)
  pure <| filter isReady openTasks

-- Show dependency tree for a task
showDependencyTree :: Text -> IO ()
showDependencyTree tid = do
  tasks <- loadTasks
  case filter (\t -> taskId t == tid) tasks of
    [] -> putText "Task not found"
    (task : _) -> printTree tasks task 0
  where
    printTree :: [Task] -> Task -> Int -> IO ()
    printTree allTasks task indent = do
      putText <| T.pack (replicate (indent * 2) ' ') <> taskId task <> ": " <> taskTitle task
      let deps = filter (\t -> taskId t `elem` taskDependencies task) allTasks
      traverse_ (\dep -> printTree allTasks dep (indent + 1)) deps

-- Helper to print a task
printTask :: Task -> IO ()
printTask t =
  putText
    <| taskId t
    <> " ["
    <> T.pack (show (taskType t))
    <> "] ["
    <> T.pack (show (taskStatus t))
    <> "] "
    <> taskTitle t
    <> parentInfo
    <> namespaceInfo
  where
    parentInfo = case taskParent t of
      Nothing -> ""
      Just p -> " (parent: " <> p <> ")"
    namespaceInfo = case taskNamespace t of
      Nothing -> ""
      Just ns -> " [" <> ns <> "]"

-- Export tasks: Consolidate JSONL file (remove duplicates, keep latest version)
exportTasks :: IO ()
exportTasks = do
  tasks <- loadTasks
  -- Rewrite the entire file with deduplicated tasks
  TIO.writeFile ".tasks/tasks.jsonl" ""
  traverse_ saveTask tasks

-- Import tasks: Read from another JSONL file and merge with existing tasks
importTasks :: FilePath -> IO ()
importTasks filePath = do
  exists <- doesFileExist filePath
  unless exists <| panic (T.pack filePath <> " does not exist")

  -- Load tasks from import file
  content <- TIO.readFile filePath
  let importLines = T.lines content
      importedTasks = mapMaybe decodeTask importLines

  -- Load existing tasks
  existingTasks <- loadTasks

  -- Create a map of existing task IDs for quick lookup
  let existingIds = map taskId existingTasks
      -- Filter to only new tasks (not already in our database)
      newTasks = filter (\t -> taskId t `notElem` existingIds) importedTasks
      -- For tasks that exist, update them with imported data
      updatedTasks = map (updateWithImported importedTasks) existingTasks
      -- Combine: updated existing tasks + new tasks
      allTasks = updatedTasks ++ newTasks

  -- Rewrite tasks.jsonl with merged data
  TIO.writeFile ".tasks/tasks.jsonl" ""
  traverse_ saveTask allTasks
  where
    decodeTask :: Text -> Maybe Task
    decodeTask line =
      if T.null line
        then Nothing
        else decode (BLC.pack <| T.unpack line)

    -- Update an existing task if there's a newer version in imported tasks
    updateWithImported :: [Task] -> Task -> Task
    updateWithImported imported existing =
      case filter (\t -> taskId t == taskId existing) imported of
        [] -> existing -- No imported version, keep existing
        (importedTask : _) ->
          -- Use imported version if it's newer (based on updatedAt)
          if taskUpdatedAt importedTask > taskUpdatedAt existing
            then importedTask
            else existing