; Read a named file from beginning to end, one block at a time.
;
;   DP0 = filename
;   CALL fileStreamOpen       Q = 0, or the osFileInfo error
;   CALL fileStreamNext       Q = 0, or the osFileBlock error
;                             DP3 = bytes in FileStreamBlock; zero means EOF
;
; This is application-side machinery built on CosmOS services, not a filesystem and not
; yet an OS stream. Open remembers the address of the caller's filename, which must remain
; valid until the one stream is finished.
;
; Written by ChatGPT for Anachronaut's SplitBit

#Program
fileStreamOpen:
  SETD.3 FileStreamName
  STD.0.3
  SWI osFileInfo
  BNQ fileStreamReturn
  PSHD.3
  POPB
  POPA
  SETD.3 FileStreamBlocks
  STA.3
  INCD.3
  STB.3
  SETD.3 FileStreamIndex
  RSTA
  STA.3
  INCD.3
  STA.3
fileStreamReturn:
  RET

fileStreamNext:
  SETD.3 FileStreamBlocks
  LDA.3
  INCD.3
  LDB.3
  OR
  BRQ fileStreamEnd
  SETD.3 FileStreamName
  LDD.0.3
  SETD.1 FileStreamBlock
  SETD.3 FileStreamIndex
  LDA.3
  INCD.3
  LDB.3
  SWI osFileBlock
  BNQ fileStreamReturn

  ; DP3 is the service's return value and also the pointer this routine uses for all of
  ; its bookkeeping. Keep the value before touching the pointer, then restore it at the
  ; one successful return below.
  PSHD.3
  POPB
  POPA
  SETD.3 FileStreamCount
  STA.3
  INCD.3
  STB.3

  ; Index++.
  SETD.3 FileStreamIndex
  INCD.3
  LDA.3
  INCA
  STA.3
  BNC fileStreamTakeBlock
  DECD.3
  LDA.3
  INCA
  STA.3
fileStreamTakeBlock:
  ; Blocks--.
  SETD.3 FileStreamBlocks
  INCD.3
  LDA.3
  BRA fileStreamBlocksBorrow
  DECA
  STA.3
  BRI fileStreamReadReturn
fileStreamBlocksBorrow:
  INIA 0xFF
  STA.3
  DECD.3
  LDA.3
  DECA
  STA.3
fileStreamReadReturn:
  SETD.3 FileStreamCount
  LDD.3.3
  RET
fileStreamEnd:
  ; There is no reset-pointer instruction. Two zero bytes through the Stack are the
  ; literal construction of a zero Data Pointer.
  RSTA
  PSHA
  PSHA
  POPD.3
  RET

; DP2 names a big-endian sixteen-bit byte count. Decrement it, returning Q = 0 when it
; reached zero and nonzero while bytes remain. This is shared because correctly counting
; a full 0x0100-byte block is the least interesting part of both applications to duplicate.
fileStreamTakeRemaining:
  INCD.2
  LDA.2
  BRA fileStreamRemainingBorrow
  DECA
  STA.2
  DECD.2
  LDB.2
  INCD.2
  LDA.2
  OR
  RET
fileStreamRemainingBorrow:
  INIA 0xFF
  STA.2
  DECD.2
  LDA.2
  DECA
  STA.2
  LDB.2
  INCD.2
  LDA.2
  OR
  RET

#Data
FileStreamName:
  0x00 0x00
FileStreamBlocks:
  0x00 0x00
FileStreamIndex:
  0x00 0x00
FileStreamCount:
  0x00 0x00
FileStreamBlock:
  #Reserve 0d256