--[[
  auto_pic.lua - Auto-fit image to monitor
  Usage: auto_pic <fill|fit> <image_url>
  fill: stretch to fill entire screen (may distort)
  fit: keep aspect ratio, fill as much as possible, center
]]

local args = {...}
if #args < 2 then
    print("Usage: auto_pic <fill|fit> <image_url>")
    return
end

local mode = args[1]
local url = args[2]

-- 1. Find monitor
local mon = peripheral.find("monitor")
if not mon then
    print("ERROR: No monitor found")
    return
end

-- 2. Get monitor grid size
local cols, rows = mon.getSize()
print("Monitor: " .. cols .. " x " .. rows)

-- 3. Download image via imgon-cc as .bimg (400x400 to get enough data)
local bimgFile = "/tmp/pic.bimg"
local dlCmd = "wget https://imgon.cyberbit.dev/400x400:bimg/" .. url .. " " .. bimgFile
print("Downloading image...")
shell.run(dlCmd)
if not fs.exists(bimgFile) then
    print("ERROR: Download failed, check URL")
    return
end

-- 4. Parse .bimg format
local function parseBimg(filename)
    local f = fs.open(filename, "rb")
    if not f then return nil end
    -- .bimg: first 4 bytes width (little-endian), next 4 bytes height
    local wBytes = f.read(4)
    local hBytes = f.read(4)
    if not wBytes or #wBytes < 4 or not hBytes or #hBytes < 4 then
        f.close()
        return nil
    end
    local w = string.byte(wBytes, 1) + string.byte(wBytes, 2)*256 + string.byte(wBytes, 3)*65536 + string.byte(wBytes, 4)*16777216
    local h = string.byte(hBytes, 1) + string.byte(hBytes, 2)*256 + string.byte(hBytes, 3)*65536 + string.byte(hBytes, 4)*16777216
    local data = f.readAll()
    f.close()
    if #data < w * h then
        print("WARNING: Incomplete image data")
        return nil
    end
    return {width = w, height = h, pixels = data}
end

local img = parseBimg(bimgFile)
if not img then
    print("ERROR: Failed to parse image")
    return
end
print("Original image: " .. img.width .. " x " .. img.height)

-- 5. Calculate scaling
local function calcScale(imgW, imgH, screenW, screenH, mode)
    local scaleX = screenW / imgW
    local scaleY = screenH / imgH
    if mode == "fill" then
        return scaleX, scaleY, 1, 1
    else -- fit
        local scale = math.min(scaleX, scaleY)
        local outW = math.floor(imgW * scale)
        local outH = math.floor(imgH * scale)
        local offX = math.floor((screenW - outW) / 2) + 1
        local offY = math.floor((screenH - outH) / 2) + 1
        return scale, scale, offX, offY
    end
end

local sx, sy, offX, offY
if mode == "fill" then
    sx, sy, offX, offY = calcScale(img.width, img.height, cols, rows, "fill")
    offX, offY = 1, 1
else
    sx, sy, offX, offY = calcScale(img.width, img.height, cols, rows, "fit")
end

print("Scale: " .. sx .. ", " .. sy)
print("Offset: " .. offX .. ", " .. offY)

-- 6. Draw to monitor (nearest neighbor)
mon.clear()

local function drawScaled()
    local pixels = img.pixels
    local imgW, imgH = img.width, img.height
    for y = 0, rows - 1 do
        for x = 0, cols - 1 do
            local srcX = math.floor((x - offX + 1) / sx)
            local srcY = math.floor((y - offY + 1) / sy)
            if srcX >= 0 and srcX < imgW and srcY >= 0 and srcY < imgH then
                local idx = srcY * imgW + srcX + 1
                local color = string.byte(pixels, idx)  -- 0-15
                mon.setCursorPos(x + 1, y + 1)
                mon.blit(" ", string.char(color + 32), " ")
            end
        end
    end
end

drawScaled()
fs.delete(bimgFile)
print("Done")