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

module Omni.Task.Core where

import Alpha
import Data.Aeson (FromJSON, ToJSON, decode, encode)
import qualified Data.Aeson as Aeson
import qualified Data.ByteString.Lazy.Char8 as BLC
import qualified Data.List as List
import qualified Data.Text as T
import qualified Data.Text.IO as TIO
import Data.Time (UTCTime, diffTimeToPicoseconds, getCurrentTime, utctDay, utctDayTime)
import Data.Time.Calendar (toModifiedJulianDay)
import qualified Database.SQLite.Simple as SQL
import qualified Database.SQLite.Simple.FromField as SQL
import qualified Database.SQLite.Simple.Ok as SQLOk
import qualified Database.SQLite.Simple.ToField as SQL
import GHC.Generics ()
import System.Directory (createDirectoryIfMissing, doesFileExist)
import System.Environment (lookupEnv)

-- 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,
    taskPriority :: Priority, -- Priority level (0-4)
    taskDependencies :: [Dependency], -- List of dependencies with types
    taskDescription :: Maybe Text, -- Optional detailed description
    taskCreatedAt :: UTCTime,
    taskUpdatedAt :: UTCTime
  }
  deriving (Show, Eq, Generic)

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

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

-- Priority levels (matching beads convention)
data Priority = P0 | P1 | P2 | P3 | P4
  deriving (Show, Eq, Ord, Read, Generic)

data Dependency = Dependency
  { depId :: Text, -- ID of the task this depends on
    depType :: DependencyType -- Type of dependency relationship
  }
  deriving (Show, Eq, Generic)

data DependencyType
  = Blocks -- Hard dependency, blocks ready work queue
  | DiscoveredFrom -- Work discovered during other work
  | ParentChild -- Epic/subtask relationship
  | Related -- Soft relationship, doesn't block
  deriving (Show, Eq, Read, Generic)

data TaskProgress = TaskProgress
  { progressTaskId :: Text,
    progressTotal :: Int,
    progressCompleted :: Int,
    progressPercentage :: Int
  }
  deriving (Show, Eq, Generic)

instance ToJSON TaskType

instance FromJSON TaskType

instance ToJSON Status

instance FromJSON Status

instance ToJSON Priority

instance FromJSON Priority

instance ToJSON DependencyType

instance FromJSON DependencyType

instance ToJSON Dependency

instance FromJSON Dependency

instance ToJSON Task

instance FromJSON Task

instance ToJSON TaskProgress

instance FromJSON TaskProgress

-- SQLite Instances

instance SQL.FromField TaskType where
  fromField f = do
    t <- SQL.fromField f :: SQLOk.Ok String
    case readMaybe t of
      Just x -> pure x
      Nothing -> SQL.returnError SQL.ConversionFailed f "Invalid TaskType"

instance SQL.ToField TaskType where
  toField x = SQL.toField (show x :: String)

instance SQL.FromField Status where
  fromField f = do
    t <- SQL.fromField f :: SQLOk.Ok String
    case readMaybe t of
      Just x -> pure x
      Nothing -> SQL.returnError SQL.ConversionFailed f "Invalid Status"

instance SQL.ToField Status where
  toField x = SQL.toField (show x :: String)

instance SQL.FromField Priority where
  fromField f = do
    t <- SQL.fromField f :: SQLOk.Ok String
    case readMaybe t of
      Just x -> pure x
      Nothing -> SQL.returnError SQL.ConversionFailed f "Invalid Priority"

instance SQL.ToField Priority where
  toField x = SQL.toField (show x :: String)

-- Store dependencies as JSON text
instance SQL.FromField [Dependency] where
  fromField f = do
    t <- SQL.fromField f :: SQLOk.Ok String
    case Aeson.decode (BLC.pack t) of
      Just x -> pure x
      Nothing -> pure [] -- Default to empty if parse fail or null

instance SQL.ToField [Dependency] where
  toField deps = SQL.toField (BLC.unpack (encode deps))

instance SQL.FromRow Task where
  fromRow =
    Task
      </ SQL.field
      <*> SQL.field
      <*> SQL.field
      <*> SQL.field
      <*> SQL.field
      <*> SQL.field
      <*> SQL.field
      <*> SQL.field
      <*> SQL.field
      <*> SQL.field
      <*> SQL.field

instance SQL.ToRow Task where
  toRow t =
    [ SQL.toField (taskId t),
      SQL.toField (taskTitle t),
      SQL.toField (taskType t),
      SQL.toField (taskParent t),
      SQL.toField (taskNamespace t),
      SQL.toField (taskStatus t),
      SQL.toField (taskPriority t),
      SQL.toField (taskDependencies t),
      SQL.toField (taskDescription t),
      SQL.toField (taskCreatedAt t),
      SQL.toField (taskUpdatedAt t)
    ]

-- | Case-insensitive ID comparison
matchesId :: Text -> Text -> Bool
matchesId id1 id2 = normalizeId id1 == normalizeId id2

-- | Normalize ID to lowercase
normalizeId :: Text -> Text
normalizeId = T.toLower

-- | Find a task by ID (case-insensitive)
findTask :: Text -> [Task] -> Maybe Task
findTask tid = List.find (\t -> matchesId (taskId t) tid)

-- | Normalize task IDs (self, parent, dependencies) to lowercase
normalizeTask :: Task -> Task
normalizeTask t =
  t
    { taskId = normalizeId (taskId t),
      taskParent = fmap normalizeId (taskParent t),
      taskDependencies = map normalizeDependency (taskDependencies t)
    }

normalizeDependency :: Dependency -> Dependency
normalizeDependency d = d {depId = normalizeId (depId d)}

-- Get the tasks database file path
getTasksDbPath :: IO FilePath
getTasksDbPath = do
  customPath <- lookupEnv "TASK_DB_PATH"
  testMode <- lookupEnv "TASK_TEST_MODE"
  let path = case (customPath, testMode) of
        (Just p, _) -> p
        (_, Just "1") -> ".tasks/tasks-test.db"
        _ -> ".tasks/tasks.db"
  pure path

-- DB Helper
withDb :: (SQL.Connection -> IO a) -> IO a
withDb action = do
  dbPath <- getTasksDbPath
  SQL.withConnection dbPath <| \conn -> do
    SQL.execute_ conn "PRAGMA busy_timeout = 5000"
    action conn

-- Initialize the task database
initTaskDb :: IO ()
initTaskDb = do
  createDirectoryIfMissing True ".tasks"
  withDb <| \conn -> do
    SQL.execute_
      conn
      "CREATE TABLE IF NOT EXISTS tasks (\
      \ id TEXT PRIMARY KEY, \
      \ title TEXT NOT NULL, \
      \ type TEXT NOT NULL, \
      \ parent TEXT, \
      \ namespace TEXT, \
      \ status TEXT NOT NULL, \
      \ priority TEXT NOT NULL, \
      \ dependencies TEXT NOT NULL, \
      \ description TEXT, \
      \ created_at TIMESTAMP NOT NULL, \
      \ updated_at TIMESTAMP NOT NULL \
      \)"

-- Generate a short ID using base36 encoding of timestamp (lowercase)
generateId :: IO Text
generateId = do
  now <- getCurrentTime
  let day = utctDay now
      dayTime = utctDayTime now
      mjd = toModifiedJulianDay day
      micros = diffTimeToPicoseconds dayTime `div` 1000000
      totalMicros = (mjd * 100000000000) + micros
      encoded = toBase36 totalMicros
  pure <| "t-" <> T.pack encoded

-- Generate a child ID based on parent ID
generateChildId :: Text -> IO Text
generateChildId parentId = do
  tasks <- loadTasks
  pure <| computeNextChildId tasks (normalizeId parentId)

computeNextChildId :: [Task] -> Text -> Text
computeNextChildId tasks parentId =
  let suffixes = mapMaybe (getSuffix parentId <. taskId) tasks
      nextSuffix = case suffixes of
        [] -> 1
        s -> maximum s + 1
   in parentId <> "." <> T.pack (show nextSuffix)

getSuffix :: Text -> Text -> Maybe Int
getSuffix parent childId =
  if parent `T.isPrefixOf` childId && T.length childId > T.length parent
    then
      let rest = T.drop (T.length parent) childId
       in if T.head rest == '.'
            then readMaybe (T.unpack (T.tail rest))
            else Nothing
    else Nothing

-- Convert number to base36 (0-9, a-z)
toBase36 :: Integer -> String
toBase36 0 = "0"
toBase36 n = reverse <| go n
  where
    alphabet = ['0' .. '9'] ++ ['a' .. 'z']
    go 0 = []
    go x =
      let (q, r) = x `divMod` 36
          idx = fromIntegral r
          char = case drop idx alphabet of
            (c : _) -> c
            [] -> '0'
       in char : go q

-- Load all tasks from DB
loadTasks :: IO [Task]
loadTasks =
  withDb <| \conn -> do
    SQL.query_ conn "SELECT id, title, type, parent, namespace, status, priority, dependencies, description, created_at, updated_at FROM tasks"

-- Save a single task (UPSERT)
saveTask :: Task -> IO ()
saveTask task =
  withDb <| \conn -> do
    SQL.execute
      conn
      "INSERT OR REPLACE INTO tasks \
      \ (id, title, type, parent, namespace, status, priority, dependencies, description, created_at, updated_at) \
      \ VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)"
      task

-- Create a new task
createTask :: Text -> TaskType -> Maybe Text -> Maybe Text -> Priority -> [Dependency] -> Maybe Text -> IO Task
createTask title taskType parent namespace priority deps description = do
  let parent' = fmap normalizeId parent
      deps' = map normalizeDependency deps

  tid <- case parent' of
    Nothing -> generateUniqueId
    Just pid -> do
      tasks <- loadTasks
      pure <| computeNextChildId tasks pid
  now <- getCurrentTime
  let task =
        Task
          { taskId = normalizeId tid,
            taskTitle = title,
            taskType = taskType,
            taskParent = parent',
            taskNamespace = namespace,
            taskStatus = Open,
            taskPriority = priority,
            taskDependencies = deps',
            taskDescription = description,
            taskCreatedAt = now,
            taskUpdatedAt = now
          }
  saveTask task
  pure task

-- Generate a unique ID
generateUniqueId :: IO Text
generateUniqueId = do
  -- We can query DB directly to check existence
  go
  where
    go = do
      tid <- generateId
      exists <-
        withDb <| \conn -> do
          [SQL.Only c] <- SQL.query conn "SELECT COUNT(*) FROM tasks WHERE id = ?" (SQL.Only tid) :: IO [SQL.Only Int]
          pure (c > 0)
      if exists then go else pure tid

-- Update task status
updateTaskStatus :: Text -> Status -> [Dependency] -> IO ()
updateTaskStatus tid newStatus newDeps =
  withDb <| \conn -> do
    now <- getCurrentTime
    -- If newDeps is empty, we need to preserve existing deps.
    -- If newDeps is NOT empty, we replace them.
    -- This logic is slightly tricky in SQL. We fetch first.
    rows <- SQL.query conn "SELECT dependencies FROM tasks WHERE id = ?" (SQL.Only tid) :: IO [SQL.Only [Dependency]]
    case rows of
      [] -> pure () -- Task not found
      (SQL.Only existingDeps : _) -> do
        let finalDeps = if null newDeps then existingDeps else newDeps
        SQL.execute
          conn
          "UPDATE tasks SET status = ?, updated_at = ?, dependencies = ? WHERE id = ?"
          (newStatus, now, finalDeps, tid)

-- Edit a task
editTask :: Text -> (Task -> Task) -> IO Task
editTask tid modifyFn = do
  tasks <- loadTasks
  case findTask tid tasks of
    Nothing -> panic "Task not found"
    Just original -> do
      now <- getCurrentTime
      let modified = modifyFn original
          finalTask = modified {taskUpdatedAt = now}
      saveTask finalTask
      pure finalTask

-- List tasks
listTasks :: Maybe TaskType -> Maybe Text -> Maybe Status -> Maybe Text -> IO [Task]
listTasks maybeType maybeParent maybeStatus maybeNamespace = do
  -- Implementing specific filters in SQL would be more efficient, but for MVP and API compat:
  tasks <- loadTasks
  let filtered =
        tasks
          |> filterByType maybeType
          |> filterByParent maybeParent
          |> filterByStatus maybeStatus
          |> filterByNamespace maybeNamespace
  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
    filterByStatus Nothing ts = ts
    filterByStatus (Just status) ts = filter (\t -> taskStatus t == status) ts
    filterByNamespace Nothing ts = ts
    filterByNamespace (Just ns) ts = filter (\t -> taskNamespace t == Just ns) ts

-- Get ready tasks
getReadyTasks :: IO [Task]
getReadyTasks = do
  allTasks <- loadTasks
  let openTasks = filter (\t -> taskStatus t == Open || taskStatus t == InProgress) allTasks
      doneIds = map taskId <| filter (\t -> taskStatus t == Done) allTasks

      parentIds = mapMaybe taskParent allTasks
      isParent tid = tid `elem` parentIds

      blockingDepIds task = [depId dep | dep <- taskDependencies task, depType dep `elem` [Blocks, ParentChild]]
      isReady task =
        taskType task
          /= Epic
          && not (isParent (taskId task))
          && all (`elem` doneIds) (blockingDepIds task)
          && taskType task
          /= HumanTask
  pure <| filter isReady openTasks

-- Get dependency tree
getDependencyTree :: Text -> IO [Task]
getDependencyTree tid = do
  tasks <- loadTasks
  case findTask tid tasks of
    Nothing -> pure []
    Just task -> pure <| collectDeps tasks task
  where
    collectDeps allTasks task =
      let depIds = map depId (taskDependencies task)
          deps = filter (\t -> any (matchesId (taskId t)) depIds) allTasks
       in task : concatMap (collectDeps allTasks) deps

-- Get task progress
getTaskProgress :: Text -> IO TaskProgress
getTaskProgress tidRaw = do
  let tid = normalizeId tidRaw
  -- Could be SQL optimized
  tasks <- loadTasks
  case findTask tid tasks of
    Nothing -> panic "Task not found"
    Just _ -> do
      let children = filter (\child -> taskParent child == Just tid) tasks
          total = length children
          completed = length <| filter (\child -> taskStatus child == Done) children
          percentage = if total == 0 then 0 else (completed * 100) `div` total
      pure
        TaskProgress
          { progressTaskId = tid,
            progressTotal = total,
            progressCompleted = completed,
            progressPercentage = percentage
          }

showTaskProgress :: Text -> IO ()
showTaskProgress tid = do
  progress <- getTaskProgress tid
  putText <| "Progress for " <> tid <> ": " <> T.pack (show (progressCompleted progress)) <> "/" <> T.pack (show (progressTotal progress)) <> " (" <> T.pack (show (progressPercentage progress)) <> "%)"

showDependencyTree :: Text -> IO ()
showDependencyTree tid = do
  tasks <- loadTasks
  case findTask tid tasks of
    Nothing -> putText "Task not found"
    Just 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 depIds = map depId (taskDependencies task)
          deps = filter (\t -> any (matchesId (taskId t)) depIds) allTasks
      traverse_ (\dep -> printTree allTasks dep (indent + 1)) deps

getTaskTree :: Maybe Text -> IO [Task]
getTaskTree maybeId = do
  tasks <- loadTasks
  case maybeId of
    Nothing -> do
      let epics = filter (\t -> taskType t == Epic) tasks
       in pure <| concatMap (collectChildren tasks) epics
    Just tid -> do
      case findTask tid tasks of
        Nothing -> pure []
        Just task -> pure <| collectChildren tasks task
  where
    collectChildren allTasks task =
      let children = filter (maybe False (`matchesId` taskId task) <. taskParent) allTasks
       in task : concatMap (collectChildren allTasks) children

showTaskTree :: Maybe Text -> IO ()
showTaskTree maybeId = do
  tasks <- loadTasks
  case maybeId of
    Nothing -> do
      let epics = filter (\t -> taskType t == Epic) tasks
      if null epics
        then putText "No epics found"
        else traverse_ (printEpicTree tasks) epics
    Just tid -> do
      case findTask tid tasks of
        Nothing -> putText "Task not found"
        Just task -> printEpicTree tasks task
  where
    printEpicTree allTasks task = printTreeNode allTasks task (0 :: Int)

    printTreeNode allTasks task indent = printTreeNode' allTasks task indent []

    printTreeNode' allTasks task indent ancestry = do
      let children = filter (maybe False (`matchesId` taskId task) <. taskParent) allTasks
          prefix =
            if indent == 0
              then ""
              else
                let ancestorPrefixes = map (\hasMore -> if hasMore then "│   " else "    ") (List.init ancestry)
                    myPrefix = if List.last ancestry then "├── " else "└── "
                 in T.pack <| concat ancestorPrefixes ++ myPrefix
          statusStr = case taskType task of
            Epic ->
              let total = length children
                  completed = length <| filter (\t -> taskStatus t == Done) children
               in "[" <> T.pack (show completed) <> "/" <> T.pack (show total) <> "]"
            _ -> case taskStatus task of
              Open -> "[ ]"
              InProgress -> "[~]"
              Review -> "[?]"
              Approved -> "[+]"
              Done -> "[✓]"

          coloredStatusStr = case taskType task of
            Epic -> magenta statusStr
            _ -> case taskStatus task of
              Open -> bold statusStr
              InProgress -> yellow statusStr
              Review -> magenta statusStr
              Approved -> green statusStr
              Done -> green statusStr

          nsStr = case taskNamespace task of
            Nothing -> ""
            Just ns -> "[" <> ns <> "] "

          coloredNsStr = case taskNamespace task of
            Nothing -> ""
            Just _ -> gray nsStr

          usedWidth = T.length prefix + T.length (taskId task) + T.length statusStr + T.length nsStr + 2
          availableWidth = max 20 (80 - usedWidth)
          truncatedTitle =
            if T.length (taskTitle task) > availableWidth
              then T.take (availableWidth - 3) (taskTitle task) <> "..."
              else taskTitle task

          coloredTitle = if taskType task == Epic then bold truncatedTitle else truncatedTitle

      putText <| prefix <> cyan (taskId task) <> " " <> coloredStatusStr <> " " <> coloredNsStr <> coloredTitle

      let indexedChildren = zip [1 ..] children
          totalChildren = length children
      traverse_
        ( \(idx, child) ->
            let hasMoreSiblings = idx < totalChildren
             in printTreeNode' allTasks child (indent + 1) (ancestry ++ [hasMoreSiblings])
        )
        indexedChildren

printTask :: Task -> IO ()
printTask t = do
  tasks <- loadTasks
  let progressInfo =
        if taskType t == Epic
          then
            let children = filter (maybe False (`matchesId` taskId t) <. taskParent) tasks
                total = length children
                completed = length <| filter (\child -> taskStatus child == Done) children
             in " [" <> T.pack (show completed) <> "/" <> T.pack (show total) <> "]"
          else ""

      parentInfo = case taskParent t of
        Nothing -> ""
        Just p -> " (parent: " <> p <> ")"

      namespaceInfo = case taskNamespace t of
        Nothing -> ""
        Just ns -> " [" <> ns <> "]"

      coloredStatus =
        let s = "[" <> T.pack (show (taskStatus t)) <> "]"
         in case taskStatus t of
              Open -> bold s
              InProgress -> yellow s
              Review -> magenta s
              Approved -> green s
              Done -> green s

      coloredTitle = if taskType t == Epic then bold (taskTitle t) else taskTitle t
      coloredProgress = if taskType t == Epic then magenta progressInfo else progressInfo
      coloredNamespace = case taskNamespace t of
        Nothing -> ""
        Just _ -> gray namespaceInfo
      coloredParent = case taskParent t of
        Nothing -> ""
        Just _ -> gray parentInfo

  putText
    <| cyan (taskId t)
    <> " ["
    <> T.pack (show (taskType t))
    <> "] "
    <> coloredStatus
    <> coloredProgress
    <> " "
    <> coloredTitle
    <> coloredParent
    <> coloredNamespace

showTaskDetailed :: Task -> IO ()
showTaskDetailed t = do
  tasks <- loadTasks
  putText ""
  putText <| "Task: " <> taskId t
  putText ""
  putText <| "Title:      " <> taskTitle t
  putText <| "Type:       " <> T.pack (show (taskType t))
  putText <| "Status:     " <> T.pack (show (taskStatus t))
  putText <| "Priority:   " <> T.pack (show (taskPriority t)) <> priorityDesc

  when (taskType t == Epic) <| do
    let children = filter (maybe False (`matchesId` taskId t) <. taskParent) tasks
        total = length children
        completed = length <| filter (\child -> taskStatus child == Done) children
        percentage = if total == 0 then 0 else (completed * 100) `div` total
    putText <| "Progress:   " <> T.pack (show completed) <> "/" <> T.pack (show total) <> " (" <> T.pack (show percentage) <> "%)"

  case taskParent t of
    Nothing -> pure ()
    Just p -> putText <| "Parent:     " <> p
  case taskNamespace t of
    Nothing -> pure ()
    Just ns -> putText <| "Namespace:  " <> ns
  putText <| "Created:    " <> T.pack (show (taskCreatedAt t))
  putText <| "Updated:    " <> T.pack (show (taskUpdatedAt t))

  unless (null (taskDependencies t)) <| do
    putText ""
    putText "Dependencies:"
    traverse_ printDependency (taskDependencies t)

  case taskDescription t of
    Nothing -> pure ()
    Just desc -> do
      putText ""
      putText "Description:"
      let indented = T.unlines <| map ("  " <>) (T.lines desc)
      putText indented

  putText ""
  where
    priorityDesc = case taskPriority t of
      P0 -> " (Critical)"
      P1 -> " (High)"
      P2 -> " (Medium)"
      P3 -> " (Low)"
      P4 -> " (Backlog)"

    printDependency dep =
      putText <| "  - " <> depId dep <> " [" <> T.pack (show (depType dep)) <> "]"

red, green, yellow, blue, magenta, cyan, gray, bold :: Text -> Text
red t = "\ESC[31m" <> t <> "\ESC[0m"
green t = "\ESC[32m" <> t <> "\ESC[0m"
yellow t = "\ESC[33m" <> t <> "\ESC[0m"
blue t = "\ESC[34m" <> t <> "\ESC[0m"
magenta t = "\ESC[35m" <> t <> "\ESC[0m"
cyan t = "\ESC[36m" <> t <> "\ESC[0m"
gray t = "\ESC[90m" <> t <> "\ESC[0m"
bold t = "\ESC[1m" <> t <> "\ESC[0m"

-- Export tasks: Dump SQLite to JSONL
exportTasks :: Maybe FilePath -> IO ()
exportTasks maybePath = do
  tasks <- loadTasks
  case maybePath of
    Just path -> do
      TIO.writeFile path ""
      traverse_ (saveTaskToJsonl path) tasks
    Nothing ->
      -- Stream to stdout
      traverse_ (BLC.putStrLn <. encode) tasks

saveTaskToJsonl :: FilePath -> Task -> IO ()
saveTaskToJsonl path task = do
  let json = encode task
  BLC.appendFile path (json <> "\n")

data TaskStats = TaskStats
  { totalTasks :: Int,
    openTasks :: Int,
    inProgressTasks :: Int,
    reviewTasks :: Int,
    approvedTasks :: Int,
    doneTasks :: Int,
    totalEpics :: Int,
    readyTasks :: Int,
    blockedTasks :: Int,
    tasksByPriority :: [(Priority, Int)],
    tasksByNamespace :: [(Text, Int)]
  }
  deriving (Show, Eq, Generic)

instance ToJSON TaskStats

instance FromJSON TaskStats

getTaskStats :: Maybe Text -> IO TaskStats
getTaskStats maybeEpicId = do
  allTasks <- loadTasks

  targetTasks <- case maybeEpicId of
    Nothing -> pure allTasks
    Just epicId ->
      case findTask epicId allTasks of
        Nothing -> panic "Epic not found"
        Just task -> pure <| getAllDescendants allTasks (taskId task)

  globalReady <- getReadyTasks
  let readyIds = map taskId globalReady
      readyCount = length <| filter (\t -> taskId t `elem` readyIds) targetTasks

      tasks = targetTasks
      total = length tasks
      open = length <| filter (\t -> taskStatus t == Open) tasks
      inProg = length <| filter (\t -> taskStatus t == InProgress) tasks
      review = length <| filter (\t -> taskStatus t == Review) tasks
      approved = length <| filter (\t -> taskStatus t == Approved) tasks
      done = length <| filter (\t -> taskStatus t == Done) tasks
      epics = length <| filter (\t -> taskType t == Epic) tasks
      readyCount' = readyCount
      blockedCount = total - readyCount' - done
      byPriority =
        [ (P0, length <| filter (\t -> taskPriority t == P0) tasks),
          (P1, length <| filter (\t -> taskPriority t == P1) tasks),
          (P2, length <| filter (\t -> taskPriority t == P2) tasks),
          (P3, length <| filter (\t -> taskPriority t == P3) tasks),
          (P4, length <| filter (\t -> taskPriority t == P4) tasks)
        ]
      namespaces = mapMaybe taskNamespace tasks
      uniqueNs = List.nub namespaces
      byNamespace = map (\ns -> (ns, length <| filter (\t -> taskNamespace t == Just ns) tasks)) uniqueNs
  pure
    TaskStats
      { totalTasks = total,
        openTasks = open,
        inProgressTasks = inProg,
        reviewTasks = review,
        approvedTasks = approved,
        doneTasks = done,
        totalEpics = epics,
        readyTasks = readyCount',
        blockedTasks = blockedCount,
        tasksByPriority = byPriority,
        tasksByNamespace = byNamespace
      }

getAllDescendants :: [Task] -> Text -> [Task]
getAllDescendants allTasks parentId =
  let children = filter (maybe False (`matchesId` parentId) <. taskParent) allTasks
   in children ++ concatMap (getAllDescendants allTasks <. taskId) children

showTaskStats :: Maybe Text -> IO ()
showTaskStats maybeEpicId = do
  stats <- getTaskStats maybeEpicId
  putText ""
  case maybeEpicId of
    Nothing -> putText "Task Statistics"
    Just epicId -> putText <| "Task Statistics for Epic " <> epicId
  putText ""
  putText <| "Total tasks:       " <> T.pack (show (totalTasks stats))
  putText <| "  Open:            " <> T.pack (show (openTasks stats))
  putText <| "  In Progress:     " <> T.pack (show (inProgressTasks stats))
  putText <| "  Review:          " <> T.pack (show (reviewTasks stats))
  putText <| "  Approved:        " <> T.pack (show (approvedTasks stats))
  putText <| "  Done:            " <> T.pack (show (doneTasks stats))
  putText ""
  putText <| "Epics:             " <> T.pack (show (totalEpics stats))
  putText ""
  putText <| "Ready to work:     " <> T.pack (show (readyTasks stats))
  putText <| "Blocked:           " <> T.pack (show (blockedTasks stats))
  putText ""
  putText "By Priority:"
  traverse_ printPriority (tasksByPriority stats)
  unless (null (tasksByNamespace stats)) <| do
    putText ""
    putText "By Namespace:"
    traverse_ printNamespace (tasksByNamespace stats)
  putText ""
  where
    printPriority (p, count) =
      let label = case p of
            P0 -> "P0 (Critical)"
            P1 -> "P1 (High)"
            P2 -> "P2 (Medium)"
            P3 -> "P3 (Low)"
            P4 -> "P4 (Backlog)"
       in putText <| "  " <> T.pack (show count) <> " " <> label
    printNamespace (ns, count) =
      putText <| "  " <> T.pack (show count) <> " " <> ns

-- Import tasks: Read from JSONL and insert/update DB
importTasks :: FilePath -> IO ()
importTasks filePath = do
  exists <- doesFileExist filePath
  unless exists <| panic (T.pack filePath <> " does not exist")

  content <- TIO.readFile filePath
  let importLines = T.lines content
      importedTasks = map normalizeTask (mapMaybe decodeTask importLines)

  -- Save all imported tasks (UPSERT logic handles updates)
  traverse_ saveTask importedTasks
  where
    decodeTask :: Text -> Maybe Task
    decodeTask line =
      if T.null line
        then Nothing
        else decode (BLC.pack <| T.unpack line)