local json = {_version = "0.1.2"}
local tag = "json"
local encode
local escape_char_map = {
  ["\\"] = "\\",
  ["\""] = "\"",
  ["\b"] = "b",
  ["\f"] = "f",
  ["\n"] = "n",
  ["\r"] = "r",
  ["\t"] = "t"
}
local escape_char_map_inv = {
  ["/"] = "/"
}
for k, v in pairs(escape_char_map) do
  escape_char_map_inv[v] = k
end
local escape_char = function(c)
  return "\\" .. (escape_char_map[c] or string.format("u%04x", c:byte()))
end
local encode_nil = function(val)
  return "null"
end
local encode_table = function(val, stack)
  local res = {}
  stack = stack or {}
  if stack[val] then
    errorf("circular reference")
  end
  stack[val] = true
  if rawget(val, 1) ~= nil or next(val) == nil then
    local n = 0
    for k in pairs(val) do
      if type(k) ~= "number" then
        errorf("invalid table: mixed or invalid key types")
      end
      n = n + 1
    end
    if n ~= #val then
      errorf("invalid table: sparse array")
    end
    for i, v in ipairs(val) do
      table.insert(res, encode(v, stack))
    end
    stack[val] = nil
    return "[" .. table.concat(res, ",") .. "]"
  else
    for k, v in pairs(val) do
      if type(k) ~= "string" then
        errorf("invalid table: mixed or invalid key types")
      end
      table.insert(res, encode(k, stack) .. ":" .. encode(v, stack))
    end
    stack[val] = nil
    return "{" .. table.concat(res, ",") .. "}"
  end
end
local encode_string = function(val)
  return "\"" .. val:gsub("[%z\001-\031\\\"]", escape_char) .. "\""
end
local encode_number = function(val)
  if val ~= val or val <= -math.huge or val >= math.huge then
    errorf("unexpected number value '" .. tostring(val) .. "'")
  end
  return tostring(val)
end
local type_func_map = {
  ["nil"] = encode_nil,
  table = encode_table,
  string = encode_string,
  number = encode_number,
  boolean = tostring
}

function encode(val, stack)
  local t = type(val)
  local f = type_func_map[t]
  if f then
    return f(val, stack)
  end
  errorf("unexpected type '" .. t .. "'")
end

function json.encode(val)
  return (encode(val))
end

local parse
local create_set = function(...)
  local res = {}
  for i = 1, select("#", ...) do
    res[select(i, ...)] = true
  end
  return res
end
local space_chars = create_set(" ", "\t", "\r", "\n")
local delim_chars = create_set(" ", "\t", "\r", "\n", "]", "}", ",")
local escape_chars = create_set("\\", "/", "\"", "b", "f", "n", "r", "t", "u")
local literals = create_set("true", "false", "null")
local literal_map = {
  ["true"] = true,
  ["false"] = false,
  null = nil
}
local next_char = function(str, idx, set, negate)
  for i = idx, #str do
    if set[str:sub(i, i)] ~= negate then
      return i
    end
  end
  return #str + 1
end
local decode_error = function(str, idx, msg)
  local line_count = 1
  local col_count = 1
  for i = 1, idx - 1 do
    col_count = col_count + 1
    if str:sub(i, i) == "\n" then
      line_count = line_count + 1
      col_count = 1
    end
  end
  errorf(string.format("%s at line %d col %d", msg, line_count, col_count))
end
local codepoint_to_utf8 = function(n)
  local f = math.floor
  if n <= 127 then
    return string.char(n)
  elseif n <= 2047 then
    return string.char(f(n / 64) + 192, n % 64 + 128)
  elseif n <= 65535 then
    return string.char(f(n / 4096) + 224, f(n % 4096 / 64) + 128, n % 64 + 128)
  elseif n <= 1114111 then
    return string.char(f(n / 262144) + 240, f(n % 262144 / 4096) + 128, f(n % 4096 / 64) + 128, n % 64 + 128)
  end
  errorf(string.format("invalid unicode codepoint '%x'", n))
end
local parse_unicode_escape = function(s)
  local n1 = tonumber(s:sub(1, 4), 16)
  local n2 = tonumber(s:sub(7, 10), 16)
  if n2 then
    return codepoint_to_utf8((n1 - 55296) * 1024 + (n2 - 56320) + 65536)
  else
    return codepoint_to_utf8(n1)
  end
end
local parse_string = function(str, i)
  local res = ""
  local j = i + 1
  local k = j
  while j <= #str do
    local x = str:byte(j)
    if x < 32 then
      decode_error(str, j, "control character in string")
    elseif x == 92 then
      res = res .. str:sub(k, j - 1)
      j = j + 1
      local c = str:sub(j, j)
      if c == "u" then
        local hex = str:match("^[dD][89aAbB]%x%x\\u%x%x%x%x", j + 1) or str:match("^%x%x%x%x", j + 1) or decode_error(str, j - 1, "invalid unicode escape in string")
        res = res .. parse_unicode_escape(hex)
        j = j + #hex
      else
        if not escape_chars[c] then
          decode_error(str, j - 1, "invalid escape char '" .. c .. "' in string")
        end
        res = res .. escape_char_map_inv[c]
      end
      k = j + 1
    elseif x == 34 then
      res = res .. str:sub(k, j - 1)
      return res, j + 1
    end
    j = j + 1
  end
  decode_error(str, i, "expected closing quote for string")
end
local parse_number = function(str, i)
  local x = next_char(str, i, delim_chars)
  local s = str:sub(i, x - 1)
  local n = tonumber(s)
  if not n then
    decode_error(str, i, "invalid number '" .. s .. "'")
  end
  return n, x
end
local parse_literal = function(str, i)
  local x = next_char(str, i, delim_chars)
  local word = str:sub(i, x - 1)
  if not literals[word] then
    decode_error(str, i, "invalid literal '" .. word .. "'")
  end
  return literal_map[word], x
end
local parse_array = function(str, i)
  local res = {}
  local n = 1
  i = i + 1
  while true do
    local x
    i = next_char(str, i, space_chars, true)
    if str:sub(i, i) == "]" then
      i = i + 1
      break
    end
    x, i = parse(str, i)
    res[n] = x
    n = n + 1
    i = next_char(str, i, space_chars, true)
    local chr = str:sub(i, i)
    i = i + 1
    if chr == "]" then
      break
    end
    if chr ~= "," then
      decode_error(str, i, "expected ']' or ','")
    end
  end
  return res, i
end
local parse_object = function(str, i)
  local res = {}
  i = i + 1
  while true do
    local key, val
    i = next_char(str, i, space_chars, true)
    if str:sub(i, i) == "}" then
      i = i + 1
      break
    end
    if str:sub(i, i) ~= "\"" then
      decode_error(str, i, "expected string for key")
    end
    key, i = parse(str, i)
    i = next_char(str, i, space_chars, true)
    if str:sub(i, i) ~= ":" then
      decode_error(str, i, "expected ':' after key")
    end
    i = next_char(str, i + 1, space_chars, true)
    val, i = parse(str, i)
    res[key] = val
    i = next_char(str, i, space_chars, true)
    local chr = str:sub(i, i)
    i = i + 1
    if chr == "}" then
      break
    end
    if chr ~= "," then
      decode_error(str, i, "expected '}' or ','")
    end
  end
  return res, i
end
local char_func_map = {
  ["\""] = parse_string,
  ["0"] = parse_number,
  ["1"] = parse_number,
  ["2"] = parse_number,
  ["3"] = parse_number,
  ["4"] = parse_number,
  ["5"] = parse_number,
  ["6"] = parse_number,
  ["7"] = parse_number,
  ["8"] = parse_number,
  ["9"] = parse_number,
  ["-"] = parse_number,
  t = parse_literal,
  f = parse_literal,
  n = parse_literal,
  ["["] = parse_array,
  ["{"] = parse_object
}

function parse(str, idx)
  local chr = str:sub(idx, idx)
  local f = char_func_map[chr]
  if f then
    return f(str, idx)
  end
  decode_error(str, idx, "unexpected character '" .. chr .. "'")
end

function json.decode(str)
  if type(str) ~= "string" or str == "" then
    errorf("expected argument of type string, got " .. type(str))
    return nil
  end
  local res, idx = parse(str, next_char(str, 1, space_chars, true))
  idx = next_char(str, idx, space_chars, true)
  if idx <= #str then
    decode_error(str, idx, "trailing garbage")
  end
  return res
end

return json
