-- Copyright (C) 2018-2021 by KittenOS NEO contributors
--
-- Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted.
--
-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
-- THIS SOFTWARE.

-- This library helps in crunching down the installer a bit further.
local sequences = {
 {"\n", " "},
 {"  ", " "},
 {" #", "#"},
 {"# ", "#"},
 {" ,", ","},
 {", ", ","},
 {" (", "("},
 {"( ", "("},
 {" )", ")"},
 {") ", ")"},
 {" {", "{"},
 {"{ ", "{"},
 {" }", "}"},
 {"} ", "}"},
 {" <", "<"},
 {"< ", "<"},
 {" >", ">"},
 {"> ", ">"},
 {" *", "*"},
 {"* ", "*"},
 {" ~", "~"},
 {"~ ", "~"},
 {" /", "/"},
 {"/ ", "/"},
 {" %", "%"},
 {"% ", "%"},
 {" =", "="},
 {"= ", "="},
 {" -", "-"},
 {"- ", "-"},
 {" +", "+"},
 {"+ ", "+"},
 {".. ", ".."},
 {" ..", ".."},
 {"\"\" ", "\"\""},
 {"=0 t", "=0t"},
 {">0 t", ">0t"},
 {">1 t", ">1t"},
 {"=1 w", "=1w"},
 {"=380 l", "=380l"},
 {"=127 t", "=127t"},
 {"<128 t", "<128t"},
 {"=128 t", "=128t"},
 {">255 t", ">255t"},
 {"=512 t", "=512t"}
}

local function pass(buffer)
 local ob = ""
 local smode = false
 while #buffer > 0 do
  if not smode then
   local ds = true
   while ds do
    ds = false
    for _, v in ipairs(sequences) do
     if buffer:sub(1, #(v[1])) == v[1] then
      buffer = v[2] .. buffer:sub(#(v[1]) + 1)
      ds = true
     end
    end
   end
  end
  local ch = buffer:sub(1, 1)
  buffer = buffer:sub(2)
  ob = ob .. ch
  if ch == "\"" then
   smode = not smode
  end
 end
 return ob
end

-- Context creation --
return function ()
 local forwardSymTab = {}
 local reverseSymTab = {}

 local temporaryPool = {}

 local stackFrames = {}

 local log = {}

 local possible = {}
 for i = 1, 52 do
  possible[i] = ("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"):sub(i, i)
 end

 local function allocate(reason)
  for _, v in pairs(possible) do
   if not reverseSymTab[v] then
    reverseSymTab[v] = reason
    return v
   end
  end
 end

 local function allocTmp(id)
  assert(not forwardSymTab[id], "var already exists: " .. id)
  local val = table.remove(temporaryPool, 1)
  if not val then val = allocate("temporary") end
  forwardSymTab[id] = val
  table.insert(log, "allocTmp " .. id .. " -> " .. val)
  return val
 end

 local lexCrunch = {}
 function lexCrunch.dump(file)
  file:write("forward table:\n")
  for k, v in pairs(forwardSymTab) do
   file:write(k .. " -> " .. v .. "\n")
  end
  file:write("reverse table (where differing):\n")
  for k, v in pairs(reverseSymTab) do
   if forwardSymTab[v] ~= k then
    file:write(v .. " -> " .. k .. "\n")
   end
  end
  file:write("log:\n")
  for k, v in ipairs(log) do
   file:write(v .. "\n")
  end
 end
 function lexCrunch.process(op, defines)
  -- symbol replacement
  op = op:gsub("%$[%$a-z%{%}%|A-Z0-9]*", function (str)
   if str:sub(2, 2) == "$" then
    -- defines
    assert(defines[str], "no define " .. str)
    return defines[str]
   end
   local com = {}
   for v in str:sub(2):gmatch("[^%|]*") do
    table.insert(com, v)
   end
   if com[1] == "L" then
    assert(#com == 2)
    local id = "$" .. com[2]
    assert(stackFrames[1], "allocation of " .. id .. " outside of stack frame")
    table.insert(stackFrames[1], id)
    return allocTmp(id)
   elseif com[1] == "{" then
    assert(#com == 1)
    table.insert(stackFrames, 1, {})
    return ""
   elseif com[1] == "}" then
    assert(#com == 1)
    for _, id in ipairs(table.remove(stackFrames, 1)) do
     table.insert(temporaryPool, forwardSymTab[id])
     forwardSymTab[id] = nil
    end
    return ""
   else
    assert(#com == 1)
    local id = "$" .. com[1]
    -- normal handling
    if forwardSymTab[id] then
     return forwardSymTab[id]
    end
    local v = allocate(id)
    forwardSymTab[id] = v
    return v
   end
  end)
  -- comment removal
  while true do
   local np = op:gsub("%-%-[^\n]*\n", " ")
   np = np:gsub("%-%-[^\n]*$", "")
   if np == op then
    break
   end
   op = np
  end
  -- stripping
  while true do
   local np = pass(op)
   if np == op then
    return np
   end
   op = np
  end
  return op
 end
 return lexCrunch
end