local fs=require("filesystem")
local byte,concat,floor=string.byte,table.concat,math.floor

local L={}
local HEADER_SIZE=64
local OP_BG,OP_FG,OP_BOTH,OP_TEXT=1,2,3,4
L.CODES={[0]=0x20,0x2584,0x2580,0x2588}

local function u16(s,o)return byte(s,o)*0x100+byte(s,o+1)end
local function u32(s,o)return u16(s,o)*0x10000+u16(s,o+2)end

function L.isVideo(dir)return fs.exists(fs.concat(dir,"index.ocv"))end

function L.readIndex(dir)
local f,err=io.open(fs.concat(dir,"index.ocv"),"rb")
if not f then return nil,"cannot open index.ocv: "..tostring(err)end
local h=f:read(HEADER_SIZE)
f:close()
if not h or#h<HEADER_SIZE or h:sub(1,4)~="OCV5"then return nil,"not an OCV5 video"end
local v={dir=dir,width=u16(h,5),height=u16(h,7),fps=u16(h,9)/100,
frames=u32(h,11),parts=u16(h,15),header=h}
if v.width<1 or v.height<1 or v.fps<=0 or v.frames<1 or v.parts<1 then return nil,"empty or damaged video"end
v.duration=v.frames/v.fps
v.bytes=0
for i=1,v.parts do v.bytes=v.bytes+(fs.size(fs.concat(dir,string.format("part%04d.ocv",i)))or 0)end
v.name=fs.name(dir)
return v
end


function L.colors(video)
local h,rgb=video.header,{}
for i=0,15 do
local o=17+i*3
rgb[i]=byte(h,o)*0x10000+byte(h,o+1)*0x100+byte(h,o+2)
end
for i=0,239 do
local r=floor(floor(i/40)*255/5+0.5)
local g=floor(floor(i/5)%8*255/7+0.5)
local b=floor(i%5*255/4+0.5)
rgb[16+i]=r*0x10000+g*0x100+b
end
return rgb
end


function L.openStream(video,capacity)
local part,file=0,nil
local queue,head,tail,bytes={},1,0,0
local eof=false
local s={}
local function readFrame()
while true do
if not file then
part=part+1
if part>video.parts then return nil end
local path=fs.concat(video.dir,string.format("part%04d.ocv",part))
local err
file,err=io.open(path,"rb")
if not file then error("cannot open "..path..": "..tostring(err),0)end
end
local h4=file:read(4)
if h4 and#h4==4 then
local len=u32(h4,1)
if len==0 then return""end
local data=file:read(len)
if not data or#data<len then error("truncated frame in part "..part,0)end
return data
end
file:close()
file=nil
end
end
function s.fill(maxFrames)
local n=0
while not eof and bytes<capacity and n<maxFrames do
local data=readFrame()
if not data then eof=true;break end
tail=tail+1
queue[tail]=data
bytes=bytes+#data
n=n+1
end
return n
end
function s.next()
if head>tail then s.fill(1)end
if head>tail then return nil end
local data=queue[head]
queue[head]=nil
head=head+1
bytes=bytes-#data
return data
end
function s.buffered()return tail-head+1,bytes end
function s.close()
if file then file:close();file=nil end
queue,head,tail,bytes={},1,0,0
end
return s
end



function L.newGrid(w,h,black)
local g={}
local v=0x20|(black<<21)|(black<<29)
for i=1,w*h do g[i]=v end
return g
end


function L.decodeToGrid(data,grid,gw,idx,st)
local codes=L.CODES
local p,n,sets=1,#data,0
local fg,bg=st.fg or idx[0],st.bg or idx[0]
while p<=n do
local op=byte(data,p)
if op==OP_TEXT then
local x,y,len=byte(data,p+1,p+3)
local q=p+4
local i=(y-1)*gw+x
local colors=(fg<<21)|(bg<<29)
local cnt=(len+3)//4
for k=0,cnt-1 do
local b=byte(data,q+k)
local m=math.min(4,len-k*4)
for j=1,m do
grid[i]=codes[(b>>(2*(4-j)))&3]|colors
i=i+1
end
end
p=q+cnt
sets=sets+1
elseif op==OP_BOTH then bg,fg=idx[byte(data,p+1)],idx[byte(data,p+2)];p=p+3
elseif op==OP_BG then bg=idx[byte(data,p+1)];p=p+2
elseif op==OP_FG then fg=idx[byte(data,p+1)];p=p+2
else error(string.format("corrupted frame: op %d at %d",op,p),0)end
end
st.fg,st.bg=fg,bg
return sets
end


function L.glyphs()
local chars={[0]=" ","▄","▀","█"}
local t={}
for n=1,4 do
t[n]={}
for b=0,255 do
local s={}
for i=1,n do s[i]=chars[floor(b/4^(4-i))%4]end
t[n][b]=concat(s)
end
end
return t
end


function L.gpuRenderer(gpu,colors,glyphs)
local setBg,setFg,set=gpu.setBackground,gpu.setForeground,gpu.set
local g4=glyphs[4]
local parts={}
return function(data)
local p,n=1,#data
while p<=n do
local op=byte(data,p)
if op==OP_TEXT then
local x,y,len=byte(data,p+1,p+3)
local q=p+4
if len<=4 then
set(x,y,glyphs[len][byte(data,q)])
p=q+1
else
local full=floor(len/4)
for i=1,full do parts[i]=g4[byte(data,q+i-1)]end
local cnt,rest=full,len-full*4
if rest>0 then cnt=cnt+1;parts[cnt]=glyphs[rest][byte(data,q+full)]end
set(x,y,concat(parts,"",1,cnt))
p=q+cnt
end
elseif op==OP_BOTH then setBg(colors[byte(data,p+1)]);setFg(colors[byte(data,p+2)]);p=p+3
elseif op==OP_BG then setBg(colors[byte(data,p+1)]);p=p+2
elseif op==OP_FG then setFg(colors[byte(data,p+1)]);p=p+2
else error(string.format("corrupted frame: op %d at %d",op,p),0)end
end
end
end



function L.paintGrid(gpu,grid,gw,gh,rgbOf)
local curF,curB
for y=1,gh do
local x=1
local base=(y-1)*gw
while x<=gw do
local v=grid[base+x]
local f,b=(v>>21)&255,(v>>29)&255
local chars,x2={},x
while x2<=gw do
local v2=grid[base+x2]
if((v2>>21)&255)~=f or((v2>>29)&255)~=b then break end
chars[#chars+1]=utf8.char(v2&0x1FFFFF)
x2=x2+1
end
if b~=curB then gpu.setBackground(rgbOf(b));curB=b end
if f~=curF then gpu.setForeground(rgbOf(f));curF=f end
gpu.set(x,y,table.concat(chars))
x=x2
end
end
end


function L.find(roots,depth)
local found,seen={},{}
local function walk(dir,d)
dir=fs.canonical(dir)
if seen[dir]or not fs.isDirectory(dir)then return end
seen[dir]=true
if L.isVideo(dir)then found[#found+1]=dir return end
if d<=0 then return end
for name in fs.list(dir)do
if name:sub(-1)=="/"then walk(fs.concat(dir,name),d-1)end
end
end
for _,r in ipairs(roots)do pcall(walk,r,depth or 2)end
table.sort(found)
return found
end

return L