; Copy one file to another without asking either file to fit in Data Memory.
;
; The two paths are the two words in the argument. Filesystem names can contain spaces,
; but the CosmOS command line has no quoting yet, so this deliberately has the same rule
; as the shell: a space separates things.
;
; osFileInfo reports how many disk blocks the source occupies, while osFileStart wants the
; shape stored in an SBFS entry: whole blocks and a possible tail. Reading the last block
; first recovers that distinction. The ordinary copy then walks forward one block at a
; time, through one 256-byte buffer.
;
; Written by ChatGPT for Anachronaut's SplitBit

#Include services.asm

#Program
  #Base 0x4000

start:
  SETD.0 Arguments
  INIB 0xFF
  SWI osArgument
  SETD.0 Arguments
  LDA.0
  BRA usage
  CALL textSplit
  SETD.0 TextRest
  LDD.0.0
  LDA.0
  BRA usage

  ; How many occupied blocks the source has. Keep it as both the loop bound and the
  ; distinction between an empty file and one whose last block must be inspected.
  SETD.0 Arguments
  SWI osFileInfo
  BNQ sourceFailed
  SETD.0 SourceBlocks
  STD.3.0
  PSHD.3
  POPB
  POPA
  OR
  BRQ emptySource

  ; Read the final occupied block. DP3 says how many bytes of it belong to the file:
  ; 0x0100 for a whole block, or 0x0001 through 0x00FF for a tail.
  SETD.0 SourceBlocks
  LDD.3.0
  DECD.3
  SETD.0 Index
  STD.3.0
  SETD.0 Arguments
  SETD.1 Block
  SETD.2 Index
  LDA.2
  INCD.2
  LDB.2
  SWI osFileBlock
  BNQ readFailed
  SETD.0 LastCount
  STD.3.0

  ; A full final block means every occupied block is whole. A short final block means
  ; there is one fewer whole block and its low-byte count is the tail.
  SETD.0 LastCount
  LDA.0
  BNA wholeEnding
  SETD.0 Index
  SETD.1 OutputWhole
  CALL copyWord
  SETD.0 LastCount
  INCD.0
  LDA.0
  SETD.1 OutputTail
  STA.1
  BRI sizeKnown

wholeEnding:
  SETD.0 SourceBlocks
  SETD.1 OutputWhole
  CALL copyWord
  RSTA
  SETD.0 OutputTail
  STA.0

sizeKnown:
  BRI startOutput

emptySource:
  RSTA
  SETD.0 OutputWhole
  STA.0
  INCD.0
  STA.0
  SETD.0 OutputTail
  STA.0

startOutput:
  SETD.0 TextRest
  LDD.0.0
  SETD.2 OutputWhole
  LDD.3.2
  SETD.2 OutputTail
  LDA.2
  SWI osFileStart
  BNQ startFailed

  ; Empty files have no blocks to transfer, but still need committing so that an existing
  ; destination becomes an empty file.
  SETD.0 SourceBlocks
  SETD.1 RemainingBlocks
  CALL copyWord
  RSTA
  SETD.0 Index
  STA.0
  INCD.0
  STA.0

copyNext:
  SETD.0 RemainingBlocks
  LDA.0
  INCD.0
  LDB.0
  OR
  BRQ copyDone

  SETD.0 Arguments
  SETD.1 Block
  SETD.2 Index
  LDA.2
  INCD.2
  LDB.2
  SWI osFileBlock
  BNQ readFailed

  SETD.1 Block
  SETD.2 Index
  LDA.2
  INCD.2
  LDB.2
  SWI osFileWrite
  BNQ writeFailed

  CALL stepIndex
  CALL takeBlock
  BRI copyNext

copyDone:
  SETD.2 OutputWhole
  LDD.3.2
  SETD.2 OutputTail
  LDA.2
  SWI osFileDone
  BNQ doneFailed
  SETD.0 Copied
  SWI osPrintString
  RSTA
  SWI osExit

; DP0 names the source word and DP1 the destination word.
copyWord:
  LDA.0
  STA.1
  INCD.0
  INCD.1
  LDA.0
  STA.1
  RET

; Increment the big-endian sixteen-bit Index.
stepIndex:
  SETD.0 Index
  INCD.0
  LDA.0
  INCA
  STA.0
  BNC stepDone
  DECD.0
  LDA.0
  INCA
  STA.0
stepDone:
  RET

; Decrement the big-endian sixteen-bit RemainingBlocks.
takeBlock:
  SETD.0 RemainingBlocks
  INCD.0
  LDA.0
  BRA takeBorrow
  DECA
  STA.0
  RET
takeBorrow:
  INIA 0xFF
  STA.0
  DECD.0
  LDA.0
  DECA
  STA.0
  RET

usage:
  SETD.0 Usage
  SWI osPrintString
  INIA 0d2
  SWI osExit
sourceFailed:
  SETD.0 SourceError
  SWI osPrintString
  INIA 0d1
  SWI osExit
readFailed:
  SETD.0 ReadError
  SWI osPrintString
  INIA 0d1
  SWI osExit
startFailed:
  SETD.0 StartError
  SWI osPrintString
  INIA 0d1
  SWI osExit
writeFailed:
  SETD.0 WriteError
  SWI osPrintString
  INIA 0d1
  SWI osExit
doneFailed:
  SETD.0 DoneError
  SWI osPrintString
  INIA 0d1
  SWI osExit

#Data
  #Base 0x2000

Arguments:
  #Reserve 0d256
SourceBlocks:
  0x00 0x00
RemainingBlocks:
  0x00 0x00
Index:
  0x00 0x00
LastCount:
  0x00 0x00
OutputWhole:
  0x00 0x00
OutputTail:
  0x00
Block:
  #Reserve 0d256

Usage:
"copy: give me a source and destination
"
SourceError:
"copy: cannot find the source
"
ReadError:
"copy: cannot read the source
"
StartError:
"copy: cannot create the destination
"
WriteError:
"copy: cannot write the destination
"
DoneError:
"copy: cannot finish the destination
"
Copied:
"copied
"

#Include text.asm