local my_utf8 = require 'my_utf8'

local colorize = {}

local I = {}
colorize.internal = I

-- State transitions while colorizing a single line.
-- Just for comments and strings.
-- Limitation: each fragment gets a uniform color so we can only change color
-- at word boundaries.
local Next_state = {
  normal={
    {prefix='--[[', target='block_comment'},  -- only single-line for now
    {prefix='--', target='comment'},
    {prefix='"', target='dstring'},
    {prefix="'", target='sstring'},
    {prefix='[[', target='block_string'},  -- only single line for now
  },
  dstring={
    {suffix='"', target='normal'},
  },
  sstring={
    {suffix="'", target='normal'},
  },
  block_string={
    {suffix=']]', target='normal'},
  },
  block_comment={
    {suffix=']]', target='normal'},
  },
  -- comments are a sink
}

local Comment_color = {0, 0, 1}
local String_color = {0, 0.5, 0.5}

local Colors = {
  normal=Foreground_color,
  comment=Comment_color,
  sstring=String_color,
  dstring=String_color,
  block_string=String_color,
  block_comment=Comment_color,
}

function colorize.configure(comment_color, string_color)
  Colors.comment = comment_color
  Colors.block_comment = comment_color
  Colors.sstring = string_color
  Colors.dstring = string_color
  Colors.block_string = string_color
end

function colorize.reset()
  Colors.comment = Comment_color
  Colors.block_comment = Comment_color
  Colors.sstring = String_color
  Colors.dstring = String_color
  Colors.block_string = String_color
end

-- This part doesn't scale. We parse the entire file on every frame.
-- Carousel is intended for small buffers that can be edited comfortably on
-- a phone.
function colorize.all(editor)
  editor.colors = {}
  local current_state = 'normal'
  for line_index, line in ipairs(editor.lines) do
    editor.colors[line_index] = {}
    for pos in my_utf8.chars(line.data) do
      local offset = my_utf8.offset(line.data, pos)
      local prefix_match = false
      if Next_state[current_state] then
        for _, cand in ipairs(Next_state[current_state]) do
          if cand.prefix and I.prefix_match(line.data, offset, cand.prefix) then
            current_state = cand.target
            prefix_match = true
            break
          end
        end
      end
      editor.colors[line_index][pos] = Colors[current_state]
      if not prefix_match and Next_state[current_state] then
        for _, cand in ipairs(Next_state[current_state]) do
          if cand.suffix and I.suffix_match(line.data, offset, cand.suffix) then
            current_state = cand.target
            break
          end
        end
      end
    end
    if current_state == 'comment' then current_state = 'normal' end  -- comments end on newline
  end
end

function I.prefix_match(str, offset, prefix)
  return str:sub(offset, offset+#prefix-1) == prefix
end

function I.suffix_match(str, offset, suffix)
  return str:sub(offset-#suffix+1, offset) == suffix
end

return colorize