#!/bin/bash

# Create a TRX image from up to three source files (kernel, initramfs, rootfs),
# and output it to stdout.  (This is the format you flash linksys routers with.)

# The TRX format is a simple (28 byte) header followed by the concatenation of
# the files with each file zero padded to a multiple of 4 bytes, and then the
# file as a whole padded up to 4k.  Padding is done with zero bytes.

# The tricky part is calculating the lengths and CRC for the header before
# outputting the header, without screwing up the ability to pipe the output
# somewhere.

if test ! -f $1 ||
   shell { test ! -z $2 && test ! -f $2 } ||
   shell { test ! -z $3 && test ! -f $3 }
{
  echo "Usage: trximg.sh file1 [file2 [file3]]" > !2
  exit 1
}

# Output $1 bytes of decimal number $2 as little endian binary data

proc leout
{
  global X := '0'
  global DATA := $2

  # Loop through bytes, smallest first

  while [ $X -lt $1 ]
  {
    # Grab next byte

    global BYTE := $($DATA%)
    global DATA := $($DATA/)

    # Convert to octal (because that's what echo needs)

    global OCTAL := ''""
    for i in [1 2 3]
    {
      global OCTAL := "$($BYTE%)"$OCTAL""
      global BYTE := $($BYTE/)
    }

    # Emit byte and loop

    echo -ne "\0$OCTAL"

    global X := $($X+)
    global BYTE := $x
  }
}

# Print number of bytes required to round $2 up to a multiple of $1

proc padlen
{
  echo $(($1-($2%$1))%)
}

# Print number $2 rounded up to $1

proc roundlen
{
  echo $($2+$(padlen $1 $2)
}

# Return length of file $1 in bytes

proc filelen
{
  wc -c $1 | awk '{print $1}'
}

# Output $1 zero bytes

proc zpad
{
  test $1 -ne 0 && dd if=/dev/zero bs=$1 count=1 !2 >/dev/null
}

# Output file $2, followed by enough zero bytes to pad length up to $1 bytes

proc zpad_file
{
  test -z $2 && return
  cat $2
  zpad $[padlen $1 $[filelen $2]]
}

# Output header.  (Optionally just the part included in the CRC32).

proc emit_header
{
  if test -z $1
  {
    echo -n "HDR0"       # File ID magic
    leout 4 $LENGTH      # Length of file (including this header)
    leout 4 $CRC32       # crc32 of all file data after this crc field
  }

  leout 2 0            # flags
  leout 2 1            # version
  leout 4 28           # Start of first file
  leout 4 $OFFSET2     # Start of second file
  leout 4 $OFFSET3     # Start of third file
}

# Calculate file offsets for the three arguments

global TOTAL := $(28+$(roundlen 4 $(filelen "$1"))
if test -z $2
{
  global OFFSET2 := '0'
} else {
  global OFFSET2 := $TOTAL
  global TOTAL := $($TOTAL+$(roundlen 4 $(filelen "$2"))
}
if test -z $3
{
  global OFFSET3 := '0'
} else {
  global OFFSET3 := $TOTAL
  global TOTAL := $($TOTAL+$(roundlen 4 $(filelen "$3"))
}
global LENGTH := $[roundlen 4096 $TOTAL]

# Calculate the CRC value for the header

global CRC32 := $[
  shell {
   emit_header skip
   zpad_file 4 $1
   zpad_file 4 $2
   zpad_file 4 $3
   zpad $[padlen 4096 $TOTAL]
  } | cksum -NILP]

# Output the image to stdout

emit_header
zpad_file 4 $1
zpad_file 4 $2
zpad_file 4 $3
zpad $[padlen 4096 $TOTAL]
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                  op_id: Op_DPipe
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              op_id: Op_DPipe
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            )
            (C {(exit)} {(1)})
          ]
          spids: [-1 111]
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      spids: [-1 128]
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            (While
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                      spids: [179]
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                                anode: 
                                  (ArithBinary
                                    op_id: Arith_Slash
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                                    right: (ArithWord w:{(Lit_Digits 256)})
                                  )
                                spids: [188 192]
                              )
                            }
                          spids: [187]
                        )
                      ]
                      spids: [187]
                    )
                    (Assignment
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                      spids: [201]
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                    (ForEach
                      iter_name: i
                      iter_words: [{(1)} {(2)} {(3)}]
                      do_arg_iter: False
                      body: 
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                                      (ArithSubPart
                                        anode: 
                                          (ArithBinary
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                                          )
                                        spids: [223 227]
                                      ) (DQ ($ VSub_Name "$OCTAL"))
                                    }
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                              ]
                              spids: [222]
                            )
                            (Assignment
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                                (assign_pair
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                                        anode: 
                                          (ArithBinary
                                            op_id: Arith_Slash
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                                  spids: [233]
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                              spids: [233]
                            )
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                          spids: [219 241]
                        )
                      spids: [211 -1]
                    )
                    (C {(echo)} {(-ne)} 
                      {
                        (DQ (EscapedLiteralPart token:<Lit_EscapedChar "\\0">) ($ VSub_Name "$OCTAL"))
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                    )
                    (Assignment
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                        (assign_pair
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                              (ArithSubPart
                                anode: 
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                    )
                  ]
                  spids: [171 273]
                )
            )
          ]
          spids: [141]
        )
      spids: [135 140]
    )
    (FuncDef
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                  anode: 
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                      op_id: Arith_Percent
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                          right: 
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                              op_id: Arith_Percent
                              left: (ArithWord w:{($ VSub_Number "$2")})
                              right: (ArithWord w:{($ VSub_Number "$1")})
                            )
                        )
                      right: (ArithWord w:{($ VSub_Number "$1")})
                    )
                  spids: [293 305]
                )
              }
            )
          ]
          spids: [288]
        )
      spids: [282 287]
    )
    (FuncDef
      name: roundlen
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                  anode: 
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                              )
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                        )
                    )
                  spids: [325 335]
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              }
            )
          ]
          spids: [320]
        )
      spids: [314 319]
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      name: filelen
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            (Pipeline
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            )
          ]
          spids: [350]
        )
      spids: [344 349]
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                  redirects: [(Redir op_id:Redir_Great fd:2 arg_word:{(/dev/null)} spids:[408])]
                )
              ]
              op_id: Op_DAmp
            )
          ]
          spids: [382]
        )
      spids: [376 381]
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                (C {(Lit_Other "[")} {(-z)} {(DQ ($ VSub_Number "$2"))} {(Lit_Other "]")})
                (ControlFlow token:<ControlFlow_Return return>)
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              op_id: Op_DAmp
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                  left_token: <Left_CommandSub "$(">
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          spids: [424]
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      spids: [418 423]
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            (C {(leout)} {(2)} {(0)})
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                          (C {(cksum)} {(-NILP)})
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                        negated: False
                      )
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                left_token: <Left_CommandSub "$(">
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  ]
)