- https://github.com/rxi/json.lua

--

-- json.lua

--

-- Copyright (c) 2020 rxi

--

-- Permission is hereby granted, free of charge, to any person obtaining a copy of

-- this software and associated documentation files (the "Software"), to deal in

-- the Software without restriction, including without limitation the rights to

-- use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies

-- of the Software, and to permit persons to whom the Software is furnished to do

-- so, subject to the following conditions:

--

-- The above copyright notice and this permission notice shall be included in all

-- copies or substantial portions of the Software.

--

-- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

-- IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

-- FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

-- AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

-- LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

-- OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE

-- SOFTWARE.

--

local json = { _version = "0.1.2" }

-------------------------------------------------------------------------------

-- Encode

-------------------------------------------------------------------------------

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 function escape_char(c)

  return "\\" .. (escape_char_map[c] or string.format("u%04x", c:byte()))

end

local function encode_nil(val)

  return "null"

end

local function encode_table(val, stack)

  local res = {}

  stack = stack or {}

  -- Circular reference?

  if stack[val] then error("circular reference") end

  stack[val] = true

  if rawget(val, 1) ~= nil or next(val) == nil then

    -- Treat as array -- check keys are valid and it is not sparse

    local n = 0

    for k in pairs(val) do

      if type(k) ~= "number" then

        error("invalid table: mixed or invalid key types")

      end

      n = n + 1

    end

    if n ~= #val then

      error("invalid table: sparse array")

    end

    -- Encode

    for i, v in ipairs(val) do

      table.insert(res, encode(v, stack))

    end

    stack[val] = nil

    return "[" .. table.concat(res, ",") .. "]"

  else

    -- Treat as an object

    for k, v in pairs(val) do

      if type(k) ~= "string" then

        error("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 function encode_string(val)

  return '"' .. val:gsub('[%z\1-\31\\"]', escape_char) .. '"'

end

local function encode_number(val)

  -- Check for NaN, -inf and inf

  if val ~= val or val <= -math.huge or val >= math.huge then

    error("unexpected number value '" .. tostring(val) .. "'")

  end

  return string.format("%.14g", val)

end

local type_func_map = {

  [ "nil"     ] = encode_nil,

  [ "table"   ] = encode_table,

  [ "string"  ] = encode_string,

  [ "number"  ] = encode_number,

  [ "boolean" ] = tostring,

}

encode = function(val, stack)

  local t = type(val)

  local f = type_func_map[t]

  if f then

    return f(val, stack)

  end

  error("unexpected type '" .. t .. "'")

end

function json.encode(val)

  return ( encode(val) )

end

-------------------------------------------------------------------------------

-- Decode

-------------------------------------------------------------------------------

local parse

local function create_set(...)

  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 function next_char(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 function decode_error(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

  error( string.format("%s at line %d col %d", msg, line_count, col_count) )

end

local function codepoint_to_utf8(n)

  -- http://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&id=iws-appendixa

  local f = math.floor

  if n <= 0x7f then

    return string.char(n)

  elseif n <= 0x7ff then

    return string.char(f(n / 64) + 192, n % 64 + 128)

  elseif n <= 0xffff then

    return string.char(f(n / 4096) + 224, f(n % 4096 / 64) + 128, n % 64 + 128)

  elseif n <= 0x10ffff then

    return string.char(f(n / 262144) + 240, f(n % 262144 / 4096) + 128,

                       f(n % 4096 / 64) + 128, n % 64 + 128)

  end

  error( string.format("invalid unicode codepoint '%x'", n) )

end

local function parse_unicode_escape(s)

  local n1 = tonumber( s:sub(1, 4),  16 )

  local n2 = tonumber( s:sub(7, 10), 16 )

   -- Surrogate pair?

  if n2 then

    return codepoint_to_utf8((n1 - 0xd800) * 0x400 + (n2 - 0xdc00) + 0x10000)

  else

    return codepoint_to_utf8(n1)

  end

end

local function parse_string(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 -- `\`: Escape

      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 -- `"`: End of string

      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 function parse_number(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 function parse_literal(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 function parse_array(str, i)

  local res = {}

  local n = 1

  i = i + 1

  while 1 do

    local x

    i = next_char(str, i, space_chars, true)

    -- Empty / end of array?

    if str:sub(i, i) == "]" then

      i = i + 1

      break

    end

    -- Read token

    x, i = parse(str, i)

    res[n] = x

    n = n + 1

    -- Next token

    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 function parse_object(str, i)

  local res = {}

  i = i + 1

  while 1 do

    local key, val

    i = next_char(str, i, space_chars, true)

    -- Empty / end of object?

    if str:sub(i, i) == "}" then

      i = i + 1

      break

    end

    -- Read key

    if str:sub(i, i) ~= '"' then

      decode_error(str, i, "expected string for key")

    end

    key, i = parse(str, i)

    -- Read ':' delimiter

    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)

    -- Read value

    val, i = parse(str, i)

    -- Set

    res[key] = val

    -- Next token

    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,

}

parse = function(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" then

    error("expected argument of type string, got " .. type(str))

  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