module MusicalDocuments where

import Data.Maybe

-- A document comprises some number of openings (double page spreads)
data Document = Document [Opening]

-- An opening comprises one or two pages (usually two)
data Opening = Opening (Page, Maybe Page)

-- A page comprises multiple systems
data Page = Page [System]

-- Each part is the line for a particular voice
data Voice = Superius | Discantus | Tenor | Contratenor | Bassus

-- A part comprises a list of musical sybmols, but it may span mutliple systems
--(including partial systems)
data Part = Part [MusicalSymbol]

-- A piece comprises some number of sections
data Piece = Piece [Section]

-- A system is a collection of staves
data System = System [Staff]

-- A staff is a list of atomic graphical symbols
data Staff = Staff [Glyph]

-- A section is a collection of parts
data Section = Section [Part]

-- These are the atomic components, MusicalSymbols are semantic and Glyphs are
--syntactic (i.e. just image elements)
data MusicalSymbol = MusicalSymbol
data Glyph = Glyph

-- If this were real, Image would abstract over some kind of binary format
data Image = Image

-- One of the important properties we need in order to be able to construct pieces
-- from the scanned components is to be able to say when objects of the some of the
-- types are strictly contiguous, i.e. this staff immediately follows that staff
class Contiguous a where
  immediatelyFollows :: a -> a -> Bool
  immediatelyPrecedes :: a -> a -> Bool
  immediatelyPrecedes a b = b `immediatelyFollows` a

instance Contiguous Staff where
  immediatelyFollows :: Staff -> Staff -> Bool
  immediatelyFollows = undefined

-- Another interesting property of this data set is that there are a number of
-- duplicate scans of openings, but nothing in the metadata that indicates this,
-- so our workflow needs to recognise duplicates
instance Eq Opening where
  (==) :: Opening -> Opening -> Bool
  (==) a b = undefined

-- Maybe it would also be useful to have equality for staves too?
instance Eq Staff where
  (==) :: Staff -> Staff -> Bool
  (==) a b = undefined

-- The following functions actually represent the workflow

collate :: [Document]
collate = undefined

scan :: Document -> [Image]
scan = undefined

split :: Image -> Opening
split = undefined

paginate :: Opening -> [Page]
paginate = undefined

omr :: Page -> [System]
omr = undefined

segment :: System -> [Staff]
segment = undefined

tokenize :: Staff -> [Glyph]
tokenize = undefined

recogniseMusicalSymbol :: Glyph -> Maybe MusicalSymbol
recogniseMusicalSymbol = undefined

part :: [Glyph] -> Maybe Part
part gs =
  if null symbols then Nothing else Just $ Part symbols
  where symbols = mapMaybe recogniseMusicalSymbol gs

alignable :: Part -> Part -> Bool
alignable = undefined

piece :: [Part] -> Maybe Piece
piece = undefined