-- comms (gpio bridge)

function rpin(i) return peek(0x5f80+i) end
function wpin(i,v) poke(0x5f80+i,v) end

-- pin (byte) map
p_turn=0
p_state=1
p_fid=2
p_flen=3
p_dlen=4
p_op=5
p_arg=6
p_data=7
data_bytes=119

my_turn=0
their_turn=1

-- opcodes: cart -> js
op_req_timeline=0x10
op_req_thread=0x11
op_req_more=0x12
op_req_demo=0x13
op_req_demo_stop=0x14
op_post_create=0x20
op_post_reply=0x21
op_like=0x22 -- arg=refid, data "1"=like / "0"=unlike
op_repost=0x23 -- arg=refid, data "1"=repost / "0"=unrepost
op_post_quote=0x24 -- arg=refid (quoted post), data=comment text
-- opcodes: js -> cart
op_resp_post=0x30
op_resp_end=0x31
op_resp_error=0x32
op_resp_ok=0x33
op_resp_auth_lost=0x34
op_demo_stop=0x41
op_resp_fire=0x42
op_resp_image=0x35 -- pixelated 32x32 thumbnail (2px/byte, hi nibble first)
op_resp_image_fail=0x36 -- image fetch failed; arg=refid
op_resp_avatar=0x37 -- pixelated 16x16 avatar (2px/byte, 128 bytes, ~2 frames)
op_resp_avatar_fail=0x38 -- avatar fetch failed; arg=refid
op_resp_feeds=0x39 -- subscribed feed names (\1-joined); idx 1=following

fsep=255 -- field separator
rsep=254 -- record separator

outq={}   -- outbound frame queue
inbuf=""  -- inbound assembly buffer
imgbuf={}  -- raw byte accumulator for multi-frame image data
avbuf={}   -- raw byte accumulator for avatar data (always 1 frame)

-- split a string into <=119 byte frames and queue them
function enqueue(op,arg,s)
 s=s or ""
 local n=max(1,ceil(#s/data_bytes))
 for i=1,n do
  local chunk=sub(s,1,data_bytes)
  s=sub(s,#chunk+1)
  add(outq,{op=op,arg=arg or 0,fid=i,flen=n,data=chunk})
 end
end

function write_frame(f)
 wpin(p_op,f.op)
 wpin(p_arg,f.arg)
 wpin(p_fid,f.fid)
 wpin(p_flen,f.flen)
 wpin(p_dlen,#f.data)
 for i=1,#f.data do
  local c=sub(f.data,i,i)
  local b=ord(c) or 32
  if c=="\n" then b=0 end
  wpin(p_data+i-1,b)
 end
end

function clear_out()
 wpin(p_op,0) wpin(p_arg,0)
 wpin(p_fid,0) wpin(p_flen,0) wpin(p_dlen,0)
end

-- decode inbound bytes; field/record seps -> \1 / \2 markers
function read_frame()
 local op=rpin(p_op)
 if op==0 then return end
 -- firehose deltas arrive as raw bytes (no text decode / separators)
 if op==op_resp_fire then
  on_fire(
   rpin(p_data),rpin(p_data+1),
   rpin(p_data+2),rpin(p_data+3),
   rpin(p_data+4),rpin(p_arg))
  return
 end
 -- frame id / count / payload length, shared by every remaining branch
 local fid,flen,dlen=rpin(p_fid),rpin(p_flen),rpin(p_dlen)
 if ONLINE then
  if op==op_resp_image then
   for i=1,dlen do add(imgbuf,rpin(p_data+i-1)) end
   if fid>=flen then on_image(rpin(p_arg),imgbuf) imgbuf={} end
   return
  end
  if op==op_resp_image_fail then on_image_fail(rpin(p_arg)) return end
  if op==op_resp_avatar then
   for i=1,dlen do add(avbuf,rpin(p_data+i-1)) end
   if fid>=flen then on_avatar(rpin(p_arg),avbuf) avbuf={} end
   return
  end
  if op==op_resp_avatar_fail then return end
 end
 local s=""
 for i=1,dlen do
  local b=rpin(p_data+i-1)
  if b==0 then s=s.."\n"
  elseif b==fsep then s=s.."\1"
  elseif b==rsep then s=s.."\2"
  else s=s..chr(b) end
 end
 inbuf=inbuf..s
 if fid>=flen then
  local full=inbuf
  inbuf=""
  on_message(op,rpin(p_arg),full)
 end
end

function comms_update()
 if rpin(p_turn)!=my_turn then return end
 read_frame()
 if #outq>0 then
  write_frame(deli(outq,1))
 else
  clear_out()
 end
 wpin(p_state,scr)
 wpin(p_turn,their_turn)
end