lua-scripts-w-api/contrib/darktable-api/json.lua

-- Minimal JSON encoder/decoder (pure Lua, no dependencies)
local M = {}

-- ── Encoder ──────────────────────────────────────────────────────────────────

-- Iterate byte-by-byte to avoid null-byte issues in Lua pattern ranges.
local function encode_str(s)
  local buf = {'"'}
  for i = 1, #s do
    local b = s:byte(i)
    if     b == 34  then buf[#buf+1] = '\\"'
    elseif b == 92  then buf[#buf+1] = '\\\\'
    elseif b == 10  then buf[#buf+1] = '\\n'
    elseif b == 13  then buf[#buf+1] = '\\r'
    elseif b == 9   then buf[#buf+1] = '\\t'
    elseif b < 32 or b == 127 then
      buf[#buf+1] = string.format('\\u%04x', b)
    else
      buf[#buf+1] = s:sub(i, i)
    end
  end
  buf[#buf+1] = '"'
  return table.concat(buf)
end

local function enc(v, depth)
  if depth > 64 then error("json.encode: table too deeply nested") end
  local t = type(v)
  if t == "nil"     then return "null"
  elseif t == "boolean" then return tostring(v)
  elseif t == "number" then
    if v ~= v or math.abs(v) == math.huge then return "null" end
    return v == math.floor(v) and string.format("%d", v) or string.format("%.10g", v)
  elseif t == "string" then
    return encode_str(v)
  elseif t == "table" then
    -- Treat as array when it has a consecutive integer key sequence from 1
    if #v > 0 then
      local parts = {}
      for i = 1, #v do parts[i] = enc(v[i], depth + 1) end
      return "[" .. table.concat(parts, ",") .. "]"
    end
    local parts = {}
    for k, x in pairs(v) do
      if type(k) == "string" then
        parts[#parts+1] = encode_str(k) .. ":" .. enc(x, depth + 1)
      end
    end
    return "{" .. table.concat(parts, ",") .. "}"
  end
  return "null"
end

function M.encode(v) return enc(v, 0) end

-- ── Decoder ───────────────────────────────────────────────────────────────────

function M.decode(src)
  local pos = 1

  local function skip()
    while pos <= #src and src:byte(pos) <= 32 do pos = pos + 1 end
  end

  local parse  -- forward declaration

  local function parse_string()
    pos = pos + 1          -- consume opening "
    local buf = {}
    while pos <= #src do
      local c = src:sub(pos, pos)
      if c == '"' then pos = pos + 1; return table.concat(buf) end
      if c == '\\' then
        pos = pos + 1
        c = src:sub(pos, pos)
        if     c == '"'  then buf[#buf+1] = '"'
        elseif c == '\\' then buf[#buf+1] = '\\'
        elseif c == '/'  then buf[#buf+1] = '/'
        elseif c == 'n'  then buf[#buf+1] = '\n'
        elseif c == 'r'  then buf[#buf+1] = '\r'
        elseif c == 't'  then buf[#buf+1] = '\t'
        elseif c == 'b'  then buf[#buf+1] = '\b'
        elseif c == 'f'  then buf[#buf+1] = '\f'
        elseif c == 'u'  then
          local hex = tonumber(src:sub(pos+1, pos+4), 16) or 0
          -- Only emit ASCII; multi-byte unicode emits a placeholder
          buf[#buf+1] = hex < 128 and string.char(hex) or '\xEF\xBF\xBD'
          pos = pos + 4
        end
      else
        buf[#buf+1] = c
      end
      pos = pos + 1
    end
    error("json.decode: unterminated string near pos " .. pos)
  end

  local function parse_object()
    pos = pos + 1          -- consume '{'
    local obj = {}
    skip()
    if src:sub(pos, pos) == '}' then pos = pos + 1; return obj end
    while true do
      skip()
      local key = parse_string()
      skip()
      if src:sub(pos, pos) ~= ':' then error("json.decode: expected ':' near pos " .. pos) end
      pos = pos + 1
      skip()
      obj[key] = parse()
      skip()
      local ch = src:sub(pos, pos); pos = pos + 1
      if ch == '}' then return obj end
      if ch ~= ',' then error("json.decode: expected ',' or '}' near pos " .. pos) end
    end
  end

  local function parse_array()
    pos = pos + 1          -- consume '['
    local arr = {}
    skip()
    if src:sub(pos, pos) == ']' then pos = pos + 1; return arr end
    while true do
      skip()
      arr[#arr+1] = parse()
      skip()
      local ch = src:sub(pos, pos); pos = pos + 1
      if ch == ']' then return arr end
      if ch ~= ',' then error("json.decode: expected ',' or ']' near pos " .. pos) end
    end
  end

  parse = function()
    skip()
    local c = src:sub(pos, pos)
    if     c == '"' then return parse_string()
    elseif c == '{' then return parse_object()
    elseif c == '[' then return parse_array()
    elseif c == 't' then pos = pos + 4; return true
    elseif c == 'f' then pos = pos + 5; return false
    elseif c == 'n' then pos = pos + 4; return nil
    else
      -- Parentheses create the capture; without them find returns only start/end.
      local _, e, n = src:find("^(-?%d+%.?%d*[eE]?[+-]?%d*)", pos)
      if n then pos = e + 1; return tonumber(n) end
      error("json.decode: unexpected token '" .. c .. "' at pos " .. pos)
    end
  end

  local ok, result = pcall(parse)
  if not ok then return nil, result end
  return result
end

return M