-- JSON Encoder/Decoder for LSP server
-- Minimal implementation supporting basic JSON parsing and encoding

local json = {}

--- Check if a table is an array (sequential numeric keys starting from 1)
--- @param t table Table to check
--- @return boolean True if table is an array
local function is_array(t)
  local i = 0
  for _ in pairs(t) do
    i = i + 1
    if t[i] == nil then
      return false
    end
  end
  return true
end

--- Escape special characters in string for JSON
--- @param s string String to escape
--- @return string Escaped string
local function escape(s)
  s = s:gsub("\\", "\\\\")
  s = s:gsub('"', '\\"')
  s = s:gsub("\n", "\\n")
  s = s:gsub("\r", "\\r")
  s = s:gsub("\t", "\\t")
  return s
end

--- Encode Lua value to JSON string
--- @param data any Value to encode
--- @return string JSON string
function json.encode(data)
  local t = type(data)
  if t == "nil" then
    return "null"
  elseif t == "boolean" then
    return data and "true" or "false"
  elseif t == "number" then
    return tostring(data)
  elseif t == "string" then
    return '"' .. escape(data) .. '"'
  elseif t == "table" then
    local parts = {}
    if is_array(data) then
      for _, v in ipairs(data) do
        table.insert(parts, json.encode(v))
      end
      return "[" .. table.concat(parts, ",") .. "]"
    else
      for k, v in pairs(data) do
        table.insert(parts, '"' .. escape(k) .. '":' .. json.encode(v))
      end
      return "{" .. table.concat(parts, ",") .. "}"
    end
  else
    return "null"
  end
end

--- Skip whitespace in string
--- @param s string JSON string
--- @param i number Current position
--- @return number New position after whitespace
local function skip_whitespace(s, i)
  while i <= #s and s:sub(i, i):match("%s") do
    i = i + 1
  end
  return i
end

--- Parse JSON string literal
--- @param s string JSON string
--- @param i number Current position (at opening quote)
--- @return string|nil Parsed string
--- @return number New position
local function parse_string(s, i)
  local result = {}
  i = i + 1
  while i <= #s do
    local c = s:sub(i, i)
    if c == '"' then
      return table.concat(result), i + 1
    elseif c == "\\" and i < #s then
      local next_c = s:sub(i + 1, i + 1)
      if next_c == "n" then
        table.insert(result, "\n")
      elseif next_c == "r" then
        table.insert(result, "\r")
      elseif next_c == "t" then
        table.insert(result, "\t")
      elseif next_c == '"' then
        table.insert(result, '"')
      elseif next_c == "\\" then
        table.insert(result, "\\")
      else
        table.insert(result, next_c)
      end
      i = i + 2
    else
      table.insert(result, c)
      i = i + 1
    end
  end
  return nil, i
end

--- Parse JSON number
--- @param s string JSON string
--- @param i number Current position
--- @return number Parsed number
--- @return number New position
local function parse_number(s, i)
  local start = i
  if s:sub(i, i) == "-" then
    i = i + 1
  end
  while i <= #s and s:sub(i, i):match("%d") do
    i = i + 1
  end
  if s:sub(i, i) == "." then
    i = i + 1
    while i <= #s and s:sub(i, i):match("%d") do
      i = i + 1
    end
  end
  if s:sub(i, i):match("[eE]") then
    i = i + 1
    if s:sub(i, i):match("[+-]") then
      i = i + 1
    end
    while i <= #s and s:sub(i, i):match("%d") do
      i = i + 1
    end
  end
  return tonumber(s:sub(start, i - 1)), i
end

local parse_value

--- Parse JSON array
--- @param s string JSON string
--- @param i number Current position (at opening bracket)
--- @return table|nil Parsed array
--- @return number New position
local function parse_array(s, i)
  local arr = {}
  i = i + 1
  while i <= #s do
    i = skip_whitespace(s, i)
    if s:sub(i, i) == "]" then
      return arr, i + 1
    end
    local val
    val, i = parse_value(s, i)
    table.insert(arr, val)
    i = skip_whitespace(s, i)
    if s:sub(i, i) == "]" then
      return arr, i + 1
    end
    if s:sub(i, i) == "," then
      i = i + 1
    end
  end
  return nil, i
end

--- Parse JSON object
--- @param s string JSON string
--- @param i number Current position (at opening brace)
--- @return table|nil Parsed object
--- @return number New position
local function parse_object(s, i)
  local obj = {}
  i = i + 1
  while i <= #s do
    i = skip_whitespace(s, i)
    if s:sub(i, i) == "}" then
      return obj, i + 1
    end
    if s:sub(i, i) == '"' then
      local key
      key, i = parse_string(s, i)
      i = skip_whitespace(s, i)
      if s:sub(i, i) ~= ":" then
        return nil, i
      end
      i = i + 1
      local val
      val, i = parse_value(s, i)
      obj[key] = val
      i = skip_whitespace(s, i)
      if s:sub(i, i) == "}" then
        return obj, i + 1
      end
      if s:sub(i, i) == "," then
        i = i + 1
      end
    else
      return nil, i
    end
  end
  return nil, i
end

parse_value = function(s, i)
  i = skip_whitespace(s, i)
  if i > #s then
    return nil, i
  end

  local c = s:sub(i, i)

  if c == "{" then
    return parse_object(s, i)
  elseif c == "[" then
    return parse_array(s, i)
  elseif c == '"' then
    return parse_string(s, i)
  elseif c == "t" then
    if s:sub(i, i + 3) == "true" then
      return true, i + 4
    end
    return nil, i
  elseif c == "f" then
    if s:sub(i, i + 4) == "false" then
      return false, i + 5
    end
    return nil, i
  elseif c == "n" then
    if s:sub(i, i + 3) == "null" then
      return nil, i + 4
    end
    return nil, i
  elseif c == "-" or c:match("%d") then
    return parse_number(s, i)
  else
    return nil, i
  end
end

--- Decode JSON string to Lua value
--- @param s string JSON string
--- @return any|nil Parsed value
--- @return number|nil Position after parsing or error
function json.decode(s)
  if type(s) ~= "string" then
    return nil, "invalid input"
  end
  local data, i = parse_value(s, 1)
  return data, i
end

return json