FirstSteps.hs

module Jira where
  
-- data Maybe a = Nothing | Just a

--instance Show Event where
--  show (IssueOpened id)          = "IssueOpened " ++ id
--  show (IssueResolved id)        = "IssueResolved " ++ id
--  show (IssueClosed id)          = "IssueClosed " ++ id
--  show (IssueReopened id)        = "IssueReopened " ++ id
--  show (IssueProgressStarted id) = "IssueProgressStarted " ++ id
--  show (IssueProgressStopped id) = "IssueProgressStopped " ++ id

--instance Eq Status where 
--  (==) Open Open             = True
--  (==) Resolved Resolved     = True
--  (==) Closed Closed         = True
--  (==) Reopened Reopened     = True
--  (==) InProgress InProgress = True
--  (==) _ _                   = False

--instance Show Status where
--  show Open       = "Open"
--  show Resolved   = "Resolved"
--  show Closed     = "Closed"
--  show Reopened   = "Reopened"
--  show InProgress = "InProgress"

--instance Show Issue where
--  show (Issue id status) = "Issue " ++ id ++ " " ++ (show status)

-- types

type IssueId = String

data Event = IssueOpened IssueId | 
             IssueResolved IssueId | 
             IssueClosed IssueId|         
             IssueReopened IssueId |
             IssueProgressStarted IssueId |
             IssueProgressStopped IssueId deriving (Show, Eq)
 
data Command = CreateIssue IssueId |      
               ResolveIssue IssueId |   
               CloseIssue IssueId |
               ReopenIssue IssueId |      
               StartIssueProgress IssueId |
               StopIssueProgress IssueId deriving (Show, Eq)
               
type History = [Event]

data Status = Open | 
              Resolved | 
              Closed | 
              Reopened | 
              InProgress deriving (Show, Eq)

data Issue = Issue { issueId :: IssueId
                   , status  :: Status 
                   } deriving Show


-- command handler

handle :: Command -> History -> History
handle command events =
  handle' command issue
  where issue = apply events


-- aggregate
-- TODO: better errors over empty array?

handle' :: Command -> Maybe Issue -> History
handle' (CreateIssue issueId) Nothing =
  [IssueOpened issueId]

handle' (CloseIssue issueId) (Just issue)
  | canClose  = [IssueClosed issueId]
  | otherwise = []
  where canClose = any (== (status issue)) [Open, Resolved]
  
handle' (CloseIssue issueId) Nothing =
  []


-- projecting events into Issue record

apply :: History -> Maybe Issue
apply events = foldl apply' Nothing events

apply' :: Maybe Issue -> Event -> Maybe Issue
apply' _ (IssueOpened issueId) =
  Just (Issue issueId Open)

apply' _ (IssueResolved issueId) =
  Just (Issue issueId Resolved)

apply' _ (IssueClosed issueId) =
  Just (Issue issueId Closed)

apply' _ (IssueReopened issueId) =
  Just (Issue issueId Reopened)
  
apply' _ (IssueProgressStarted issueId) =
  Just (Issue issueId InProgress)
  
apply' _ (IssueProgressStopped issueId) =
  Just (Issue issueId Open)
  

-- event handler

react :: Event -> IO ()
react event =
  print event


-- process

--process :: History -> Event -> Maybe Command
--process events event
--  | complete  = Just (CreateIssue "19d7e8c0-ee9d-4aaa-9129-a2d850d5be51")
--  | otherwise = Nothing
--  where complete = events ++ [event] == []
--  
--