local M={}


local P={}
do
local greys={0x0F0F0F,0x1E1E1E,0x2D2D2D,0x3C3C3C,0x4B4B4B,0x5A5A5A,0x696969,0x787878,0x878787,0x969696,0xA5A5A5,
0xB4B4B4,0xC3C3C3,0xD2D2D2,0xE1E1E1,0xF0F0F0}
local gi,n=1,0
for r=0,5 do
for g=0,7 do
for b=0,4 do
P[n]=(r*51)<<16|((g*255+3)//7)<<8|((b*255+2)//4)
n=n+1
end
end

if r<5 then for _=1,(r==2 and 4 or 3)do if greys[gi]then P[n]=greys[gi];gi=gi+1;n=n+1 end end end
end
end

local cache={}

function M.load(path,nocache)
local c=not nocache and cache[path]
if c then return c end
local f=io.open(path,"rb")
if not f then return nil,"cannot open "..path end
local d=f:read("*a")
f:close()
if not d or d:sub(1,4)~="OCIF"then return nil,"not an OCIF image"end
local pos=5
local byte,codepoint=string.byte,utf8.codepoint
local function b1()local v=byte(d,pos)pos=pos+1 return v end
local function b2()local a,b=byte(d,pos,pos+1)pos=pos+2 return a<<8|b end
local function uc()
local c0=byte(d,pos)
local n=c0>=0xF0 and 4 or c0>=0xE0 and 3 or c0>=0xC0 and 2 or 1
local cp=codepoint(d,pos)
pos=pos+n
return cp
end
local m=b1()
local w,h,cells=0,0,{}
if m==5 then
w,h=b2(),b2()
for i=1,w*h do
local bg,fg,a=P[b1()],P[b1()],b1()
local k=i*3
cells[k-2],cells[k-1],cells[k]=uc(),fg,a<128 and bg or-1
end
elseif m>=6 and m<=8 then
local is7,is8=m>=7 and 1 or 0,m>=8 and 1 or 0
w,h=b1()+is8,b1()+is8
for i=1,w*h do cells[i*3-2],cells[i*3-1],cells[i*3]=32,0,-1 end
for _=1,b1()+is7 do
local a=b1()
for _=1,b2()+is7 do
local ch=uc()
for _=1,b1()+is7 do
local bg=P[b1()]
for _=1,b1()+is7 do
local fg=P[b1()]
for _=1,b1()+is7 do
local y=b1()+is8
for _=1,b1()+is7 do
local x=b1()+is8
local k=((y-1)*w+x)*3
cells[k-2],cells[k-1],cells[k]=ch,fg,a<128 and bg or-1
end
end
end
end
end
end
else
return nil,"unsupported OCIF encoding "..tostring(m)
end
c={w,h,cells}
if not nocache then cache[path]=c end
return c
end


local near={}
local function to8(c)
local i=near[c]
if i then return i end
local best,bd=0,math.huge
for k=0,255 do
local p=P[k]
local d=((p>>16)-(c>>16))^2+(((p>>8)&255)-((c>>8)&255))^2+((p&255)-(c&255))^2
if d<bd then best,bd=k,d end
end
near[c]=best
return best
end


function M.save(path,img)
local w,h,d=img[1],img[2],img[3]
local out={"OCIF",string.char(5,w>>8,w&255,h>>8,h&255)}
for i=1,w*h do
local k=i*3
local bg=d[k]
out[#out+1]=string.char(to8(bg>=0 and bg or 0),to8(d[k-1]),bg>=0 and 0 or 255)..utf8.char(d[k-2])
end
local f,err=io.open(path,"wb")
if not f then return nil,err end
f:write(table.concat(out))
f:close()
cache[path]=nil
return true
end
function M.forget(path)cache[path]=nil end

return M