; Read a text file one screen at a time.
;
; Twenty two lines are shown before a prompt. Space advances another screen, Return one
; line, and q gives the machine back to CosmOS. This is forward-only on purpose: the file
; stream holds one block and never asks the whole document to fit in memory.
;
; Written by ChatGPT for Anachronaut's SplitBit

#Include services.asm
#Program
  #Base 0x4000

start:
  SETD.0 Name
  INIB 0d29
  SWI osArgument
  SETD.0 Name
  LDA.0
  BRA noName
  CALL fileStreamOpen
  BNQ openFailed
  CALL fullPage

nextBlock:
  CALL fileStreamNext
  BNQ readFailed
  PSHD.3
  POPB
  POPA
  SETD.2 Remaining
  STA.2
  INCD.2
  STB.2
  OR
  BRQ finished
  SETD.1 FileStreamBlock
  SETD.2 Remaining

printLoop:
  LDA.1
  OUTA 0x00
  INIB 0x0A
  XOR
  BNQ bytePrinted
  SETD.3 LinesLeft
  LDA.3
  DECA
  STA.3
  BNA bytePrinted
  CALL pause
  BNQ finished
bytePrinted:
  INCD.1
  CALL fileStreamTakeRemaining
  BRQ nextBlock
  BRI printLoop

; Ask for one key without asking for Return. The console is put back immediately,
; including on q and end of redirected input.
pause:
  SETD.0 MorePrompt
  SWI osPrintString
  INIA 0x01
  OUTA 0x02
  INA 0x00
  PSHA                      ; Keep the key while A is used to restore line mode.
  RSTA
  OUTA 0x02
  POPA
  SETD.0 ClearPrompt
  SWI osPrintString

  INIB 0x71                 ; q
  XOR
  BRQ pauseQuit
  INIB 0xFF                 ; end of redirected input
  XOR
  BRQ pauseQuit
  INIB 0x0A                 ; Return: one more line.
  XOR
  BRQ oneLine
  INIB 0x20                 ; Space: one more screen.
  XOR
  BNQ pause                 ; Ignore every other key.
  CALL fullPage
  RSTA
  RSTB
  OR
  RET
oneLine:
  SETD.3 LinesLeft
  INIA 0x01
  STA.3
  RSTA
  RSTB
  OR
  RET
pauseQuit:
  RSTA
  INIB 0x01
  OR
  RET
fullPage:
  SETD.3 LinesLeft
  INIA 0d22
  STA.3
  RET

noName:
  SETD.0 Usage
  SWI osPrintString
  INIA 0d2
  SWI osExit
openFailed:
  SETD.0 OpenError
  SWI osPrintString
  BRI printError
readFailed:
  SETD.0 ReadError
  SWI osPrintString
printError:
  RSTA
  MVQB
  SWI osPrintNumber
  SETD.0 NewLine
  SWI osPrintString
  ; ITS OWN EXIT, and it did not have one. This fell through into finished and reported
  ; that everything was fine, having just printed the reason it was not - which nobody
  ; noticed while the only reader was a person, who could see both.
  INIA 0d1
  SWI osExit

finished:
  RSTA
  SWI osExit

#Data
  #Base 0x2000
Usage:
"more: give me a file name
"
OpenError:
"more: cannot find the file, error "
ReadError:
"more: cannot read the file, error "
NewLine:
  0x0A 0x00
MorePrompt:
"-- more --"
ClearPrompt:
  0x0A 0x00
Name:
  #Reserve 0d29
Remaining:
  0x00 0x00
LinesLeft:
  0x00

#Include fileStream.asm