{-# 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 :: [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 | Done
  deriving (Show, Eq, 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 DependencyType

instance FromJSON DependencyType

instance ToJSON Dependency

instance FromJSON Dependency

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 -> [Dependency] -> 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
      -- Only Blocks and ParentChild dependencies block ready work
      blockingDepIds task = [depId dep | dep <- taskDependencies task, depType dep `elem` [Blocks, ParentChild]]
      isReady task = all (`elem` doneIds) (blockingDepIds 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 depIds = map depId (taskDependencies task)
          deps = filter (\t -> taskId t `elem` depIds) 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