llm-covers/make_cover_briefs.lua

#!/usr/bin/env luajit

package.path = (arg[0]:match("@?(.*/)") or arg[0]:match("@?(.*\\)")) .. "lib" .. package.config:sub(1, 1) .. "?.lua;" .. package.path
local utility = require "utility"

local default_model = "gemma4:12b-mlx"
local maximum_bytes = 40000

local partial_prompt = [[You are extracting information for a later cover design process.

This is only one section of a larger story.

Do NOT attempt to design a cover.
Do NOT decide what should appear on the cover.
Do NOT write a summary.

Extract only information that may be useful when creating a cover after all story sections have been analyzed.

Return:

GENRE:
- up to 5 items

SETTING:
- locations
- environments
- time period

CHARACTERS:
- names
- physical descriptions
- distinctive visual traits

CREATURES:
- notable creatures

OBJECTS:
- important recurring items

VISUAL MOTIFS:
- recurring imagery
- symbols
- repeated visual elements

THEMES:
- major themes

MOOD:
- emotional tone

COLORS:
- colors strongly associated with scenes or imagery

MEMORABLE VISUAL SCENES:
- 3-10 visually striking moments

CONFIDENCE:
- how central each item appears to be

]]

local squish_partials_prompt = [[Take the common portions from the following text and produce a single simplified list of information:

]]

local cover_brief_prompt = [[Generate a cover brief from the following:

]]

local segmented_cover_brief_prompt = [[Generate a single cover brief.

Prefer elements that:
- appear repeatedly across chunks
- have highest confidence
- best represent the entire story

Avoid minor plot events.

]]

local gemini_prompt = [[

Generate an ebook cover inset within an empty white border 10% larger than the cover using the following cover brief. It should be a flat graphic design file, with no artifacts of a physical object. The aspect ratio of an ebook is tall, not wide. The white border is very important, and should take up 10% of the area of the image. The title and author should only appear once on the cover. It must be sutiable for printing. Do not include the word "by" when adding the author's name to the cover.

]]

local read_all = function(file_name)
  return utility.open(file_name, "r", function(file)
    return file:read("*all")
  end)
end
local write_all = function(file_name, text)
  return utility.open(file_name, "w", function(file)
    file:write(text)
    file:write("\n")
  end)
end

local timings = {}
local timing_report = function()
  local minimum, maximum, sum = math.huge, 0, 0
  for _, delta in ipairs(timings) do
    if delta > maximum then maximum = delta end
    if delta < minimum then minimum = delta end
    sum = sum + delta
  end
  print("")
  print("Prompts took a total of " .. sum .. " minutes.")
  print("Average: " .. math.floor(sum / #timings) .. " minutes. Fastest: " .. minimum .. " minutes. Slowest: " .. maximum .. " minutes.")
end

local strip_reasoning = function(text, reasoning_lines)
  if not reasoning_lines then reasoning_lines = {} end
  local tab = text:split("\n")
  table.remove(tab, 1) -- remove "Thinking..."

  while true do
    local done = tab[1] == "...done thinking."
    local line = table.remove(tab, 1)
    if done then
      table.remove(tab, 1) -- remove newline after end of thinking
      return table.concat(tab, "\n")
    elseif #tab < 1 then
      return text -- no reasoning output
    else
      reasoning_lines[#reasoning_lines + 1] = line -- export thinking lines
    end
  end
end

local send_prompt = function(text, model)
  if type(text) == "table" then text = table.concat(text, "\n") end

  local tmp_file_name = utility.tmp_file_name()
  utility.open(tmp_file_name, "w", function(file)
    file:write(text)
  end)

  local start_time = os.time()
  -- word wrap breaks the raw output badly, so I need to implement my own for terminal output somehow
  local output = utility.capture_safe("cat " .. tmp_file_name:enquote() .. " | ollama run " .. (model or default_model) .. " --nowordwrap")
  os.execute("ollama stop " .. (model or default_model)) -- NOTE this makes things slower, but more stable
  local delta = math.floor( (os.time() - start_time) / 60 * 10 ) / 10
  print("Took " .. delta .. " minutes.")
  timings[#timings + 1] = delta
  os.execute("rm " .. tmp_file_name)
  if not output then error("ollama failed to generate output") end
  output = output:sub(1, -2) -- strip extra newline from utility.capture_safe

  output = strip_reasoning(output)

  return output
end

local tree
tree = function(path, fn)
  utility.list(path or ".", function(path_name)
    local blacklist = {
      [".git"] = true,
      [".gitkeep"] = true,
      [".gitignore"] = true,
      [".DS_Store"] = true,
    }
    if blacklist[path_name] then return end
    if utility.is_file(path_name) then
      fn(path_name)
    else
      tree(path .. utility.path_separator .. path_name, fn)
    end
  end)
end

tree("extracted_texts", function(file_name)
  local path, name, extension = utility.split_path_components(file_name)
  if utility.path_exists("cover_briefs/" .. name) then return end

  local text = read_all(file_name)
  local result

  print(name)
  local outputs = {}
  if #text > maximum_bytes then
    -- TODO check if this would work just as well starting from 1 instead..
    for i = 0, #text/maximum_bytes do
      print("Processing section " .. (i + 1) .. " of " .. math.floor(#text/maximum_bytes + 1))
      local piece = text:sub(i * maximum_bytes, (i + 1) * maximum_bytes - 1)
      result = send_prompt(partial_prompt .. piece)
      outputs[#outputs + 1] = result
      print(#result .. " characters added to intermediate context.")
    end

    text = table.concat(outputs, "\n\n")
    write_all("intermediates/" .. name, text)
  end

  -- handle too much context (works with up to 100 slices)
  if #outputs > 10 then
    local context_slices = {}
    while #outputs > 2 do
      local output_slices = {}
      for i = 1, 10 do
        if #outputs >= 1 then
          output_slices[#output_slices + 1] = table.remove(outputs, 1)
        end
      end

      print("Squishing context. " .. #outputs .. " samples remaining.")
      result = send_prompt(squish_partials_prompt .. table.concat(output_slices, "\n\n"))
      context_slices[#context_slices + 1] = result
      print(#result .. " characters added to final context.")
    end

    text = table.concat(context_slices, "\n\n")
    write_all("intermediates/" .. name:sub(1, -5) .. " CONDENSED.txt", text)
  end

  print("Generating cover brief.")
  result = send_prompt(cover_brief_prompt .. text)
  write_all("cover_briefs/" .. name, result)
  write_all("for_gemini/" .. name, "Title: " .. name:sub(1, -5) .. gemini_prompt .. result)
end)

timing_report()