{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE OverloadedStrings #-}
{-# 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.Aeson.KeyMap as KM
import Data.Aeson.Types (parseMaybe)
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 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
    taskCreatedAt :: UTCTime,
    taskUpdatedAt :: UTCTime
  }
  deriving (Show, Eq, Generic)

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

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

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

-- Get the tasks database file path (use test file if TASK_TEST_MODE is set)
getTasksFilePath :: IO FilePath
getTasksFilePath = do
  customPath <- lookupEnv "TASK_DB_PATH"
  testMode <- lookupEnv "TASK_TEST_MODE"
  pure <| case (customPath, testMode) of
    (Just path, _) -> path
    (_, Just "1") -> ".tasks/tasks-test.jsonl"
    _ -> ".tasks/tasks.jsonl"

-- Initialize the task database
initTaskDb :: IO ()
initTaskDb = do
  createDirectoryIfMissing True ".tasks"
  tasksFile <- getTasksFilePath
  exists <- doesFileExist tasksFile
  unless exists <| do
    TIO.writeFile tasksFile ""
    putText <| "Initialized task database at " <> T.pack tasksFile

-- Generate a short ID using base62 encoding of timestamp
generateId :: IO Text
generateId = do
  now <- getCurrentTime
  -- Convert current time to microseconds since epoch (using MJD)
  let day = utctDay now
      dayTime = utctDayTime now
      mjd = toModifiedJulianDay day
      micros = diffTimeToPicoseconds dayTime `div` 1000000
      -- Combine MJD and micros to ensure uniqueness across days.
      -- Multiplier 10^11 (100,000 seconds) is safe for any day length.
      totalMicros = (mjd * 100000000000) + micros
      encoded = toBase62 totalMicros
  pure <| "t-" <> T.pack encoded

-- Generate a child ID based on parent ID (e.g. "t-abc.1", "t-abc.1.2")
-- Finds the next available sequential suffix among existing children.
generateChildId :: Text -> IO Text
generateChildId parentId = do
  tasks <- loadTasks
  -- Find the max suffix among ALL tasks that look like children (to avoid ID collisions)
  -- We check all tasks, not just those with taskParent set, because we want to ensure
  -- ID uniqueness even if the parent link is missing.
  let suffixes = mapMaybe (getSuffix parentId <. taskId) tasks
      nextSuffix = case suffixes of
        [] -> 1
        s -> maximum s + 1
  pure <| 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 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 (with migration support)
loadTasks :: IO [Task]
loadTasks = do
  tasksFile <- getTasksFilePath
  exists <- doesFileExist tasksFile
  if exists
    then do
      content <- TIO.readFile tasksFile
      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 case decode (BLC.pack <| T.unpack line) of
          Just task -> Just task
          Nothing -> migrateOldTask line

    -- Migrate old task format (with taskProject field or missing priority) to new format
    migrateOldTask :: Text -> Maybe Task
    migrateOldTask line = case Aeson.decode (BLC.pack <| T.unpack line) :: Maybe Aeson.Object of
      Nothing -> Nothing
      Just obj ->
        let taskId' = KM.lookup "taskId" obj +> parseMaybe Aeson.parseJSON
            taskTitle' = KM.lookup "taskTitle" obj +> parseMaybe Aeson.parseJSON
            taskStatus' = KM.lookup "taskStatus" obj +> parseMaybe Aeson.parseJSON
            taskCreatedAt' = KM.lookup "taskCreatedAt" obj +> parseMaybe Aeson.parseJSON
            taskUpdatedAt' = KM.lookup "taskUpdatedAt" obj +> parseMaybe Aeson.parseJSON
            -- Extract old taskDependencies (could be [Text] or [Dependency])
            oldDeps = KM.lookup "taskDependencies" obj +> parseMaybe Aeson.parseJSON :: Maybe [Text]
            newDeps = maybe [] (map (\tid -> Dependency {depId = tid, depType = Blocks})) oldDeps
            -- taskProject is ignored in new format (use epics instead)
            taskType' = WorkTask -- Old tasks become WorkTask by default
            taskParent' = Nothing
            taskNamespace' = KM.lookup "taskNamespace" obj +> parseMaybe Aeson.parseJSON
            -- Default priority to P2 (medium) for old tasks
            taskPriority' = fromMaybe P2 (KM.lookup "taskPriority" obj +> parseMaybe Aeson.parseJSON)
         in case (taskId', taskTitle', taskStatus', taskCreatedAt', taskUpdatedAt') of
              (Just tid, Just title, Just status, Just created, Just updated) ->
                Just
                  Task
                    { taskId = tid,
                      taskTitle = title,
                      taskType = taskType',
                      taskParent = taskParent',
                      taskNamespace = taskNamespace',
                      taskStatus = status,
                      taskPriority = taskPriority',
                      taskDependencies = newDeps,
                      taskCreatedAt = created,
                      taskUpdatedAt = updated
                    }
              _ -> Nothing

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

-- Create a new task
createTask :: Text -> TaskType -> Maybe Text -> Maybe Text -> Priority -> [Dependency] -> IO Task
createTask title taskType parent namespace priority deps = do
  tid <- maybe generateId generateChildId parent
  now <- getCurrentTime
  let task =
        Task
          { taskId = tid,
            taskTitle = title,
            taskType = taskType,
            taskParent = parent,
            taskNamespace = namespace,
            taskStatus = Open,
            taskPriority = priority,
            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)
  tasksFile <- getTasksFilePath
  TIO.writeFile tasksFile ""
  traverse_ saveTask updatedTasks

-- List tasks, optionally filtered by type, parent, status, or namespace
listTasks :: Maybe TaskType -> Maybe Text -> Maybe Status -> Maybe Text -> IO [Task]
listTasks maybeType maybeParent maybeStatus maybeNamespace = do
  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 (not blocked by dependencies and not a parent)
getReadyTasks :: IO [Task]
getReadyTasks = do
  allTasks <- loadTasks
  let openTasks = filter (\t -> taskStatus t /= Done) allTasks
      doneIds = map taskId <| filter (\t -> taskStatus t == Done) allTasks

      -- Find all tasks that act as parents
      parentIds = mapMaybe taskParent allTasks
      isParent tid = tid `elem` parentIds

      -- Only Blocks and ParentChild dependencies block ready work
      blockingDepIds task = [depId dep | dep <- taskDependencies task, depType dep `elem` [Blocks, ParentChild]]
      isReady task =
        not (isParent (taskId task))
          && all (`elem` doneIds) (blockingDepIds task)
  pure <| filter isReady openTasks

-- Get dependency tree for a task (returns tasks)
getDependencyTree :: Text -> IO [Task]
getDependencyTree tid = do
  tasks <- loadTasks
  case filter (\t -> taskId t == tid) tasks of
    [] -> pure []
    (task : _) -> pure <| collectDeps tasks task
  where
    collectDeps :: [Task] -> Task -> [Task]
    collectDeps allTasks task =
      let depIds = map depId (taskDependencies task)
          deps = filter (\t -> taskId t `elem` depIds) allTasks
       in task : concatMap (collectDeps allTasks) deps

-- 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 depIds = map depId (taskDependencies task)
          deps = filter (\t -> taskId t `elem` depIds) allTasks
      traverse_ (\dep -> printTree allTasks dep (indent + 1)) deps

-- Get task tree (returns tasks hierarchically)
getTaskTree :: Maybe Text -> IO [Task]
getTaskTree maybeId = do
  tasks <- loadTasks
  case maybeId of
    Nothing -> do
      -- Return all epics with their children
      let epics = filter (\t -> taskType t == Epic) tasks
       in pure <| concatMap (collectChildren tasks) epics
    Just tid -> do
      -- Return specific task/epic with its children
      case filter (\t -> taskId t == tid) tasks of
        [] -> pure []
        (task : _) -> pure <| collectChildren tasks task
  where
    collectChildren :: [Task] -> Task -> [Task]
    collectChildren allTasks task =
      let children = filter (\t -> taskParent t == Just (taskId task)) allTasks
       in task : concatMap (collectChildren allTasks) children

-- Show task tree (epic with children, or all epics if no ID given)
showTaskTree :: Maybe Text -> IO ()
showTaskTree maybeId = do
  tasks <- loadTasks
  case maybeId of
    Nothing -> do
      -- Show all epics with their children
      let epics = filter (\t -> taskType t == Epic) tasks
      if null epics
        then putText "No epics found"
        else traverse_ (printEpicTree tasks) epics
    Just tid -> do
      -- Show specific task/epic with its children
      case filter (\t -> taskId t == tid) tasks of
        [] -> putText "Task not found"
        (task : _) -> printEpicTree tasks task
  where
    printEpicTree :: [Task] -> Task -> IO ()
    printEpicTree allTasks task = printTreeNode allTasks task 0

    printTreeNode :: [Task] -> Task -> Int -> IO ()
    printTreeNode allTasks task indent = printTreeNode' allTasks task indent []

    printTreeNode' :: [Task] -> Task -> Int -> [Bool] -> IO ()
    printTreeNode' allTasks task indent ancestry = do
      let children = filter (\t -> taskParent t == Just (taskId task)) allTasks
          -- Build tree prefix using box-drawing characters
          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
          -- For epics, show progress count [completed/total]; for tasks, show status checkbox
          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) <> "]"
            WorkTask -> case taskStatus task of
              Open -> "[ ]"
              InProgress -> "[~]"
              Review -> "[?]"
              Done -> "[✓]"
          nsStr = case taskNamespace task of
            Nothing -> ""
            Just ns -> "[" <> ns <> "] "
          -- Calculate available width for title (80 cols - prefix - id - labels)
          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
      putText <| prefix <> taskId task <> " " <> statusStr <> " " <> nsStr <> truncatedTitle

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

-- Helper to print a task
printTask :: Task -> IO ()
printTask t = do
  tasks <- loadTasks
  let progressInfo =
        if taskType t == Epic
          then
            let children = filter (\child -> taskParent child == Just (taskId t)) 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 <> "]"
  putText
    <| taskId t
    <> " ["
    <> T.pack (show (taskType t))
    <> "] ["
    <> T.pack (show (taskStatus t))
    <> "]"
    <> progressInfo
    <> " "
    <> taskTitle t
    <> parentInfo
    <> namespaceInfo

-- Show detailed task information (human-readable)
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

  -- Show epic progress if this is an epic
  when (taskType t == Epic) <| do
    let children = filter (\child -> taskParent child == Just (taskId t)) 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))

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

  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)) <> "]"

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

-- Task statistics
data TaskStats = TaskStats
  { totalTasks :: Int,
    openTasks :: Int,
    inProgressTasks :: Int,
    reviewTasks :: 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

-- Get task statistics
getTaskStats :: IO TaskStats
getTaskStats = do
  tasks <- loadTasks
  ready <- getReadyTasks
  let 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
      done = length <| filter (\t -> taskStatus t == Done) tasks
      epics = length <| filter (\t -> taskType t == Epic) tasks
      readyCount = length ready
      blockedCount = total - readyCount - done
      -- Count tasks by priority
      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)
        ]
      -- Count tasks by namespace
      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,
        doneTasks = done,
        totalEpics = epics,
        readyTasks = readyCount,
        blockedTasks = blockedCount,
        tasksByPriority = byPriority,
        tasksByNamespace = byNamespace
      }

-- Show task statistics (human-readable)
showTaskStats :: IO ()
showTaskStats = do
  stats <- getTaskStats
  putText ""
  putText "Task Statistics"
  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 <| "  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 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
  tasksFile <- getTasksFilePath
  TIO.writeFile tasksFile ""
  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