---@class ProblemContext
---@field contest string Contest name (e.g. "atcoder", "codeforces")
---@field contest_id string Contest ID (e.g. "abc123", "1933")
---@field problem_id? string Problem ID for AtCoder/Codeforces (e.g. "a", "b")
---@field source_file string Source filename (e.g. "abc123a.cpp")
---@field binary_file string Binary output path (e.g. "build/abc123a.run")
---@field input_file string Input test file path (e.g. "io/abc123a.in")
---@field output_file string Output file path (e.g. "io/abc123a.out")
---@field expected_file string Expected output path (e.g. "io/abc123a.expected")
---@field problem_name string Canonical problem identifier (e.g. "abc123a")

local M = {}

---@param contest string
---@param contest_id string
---@param problem_id? string
---@param config cp.Config
---@param language? string
---@return ProblemContext
function M.create_context(contest, contest_id, problem_id, config, language)
  vim.validate({
    contest = { contest, 'string' },
    contest_id = { contest_id, 'string' },
    problem_id = { problem_id, { 'string', 'nil' }, true },
    config = { config, 'table' },
    language = { language, { 'string', 'nil' }, true },
  })

  local contest_config = config.contests[contest]
  if not contest_config then
    error(("No contest config found for '%s'"):format(contest))
  end

  local target_language = language or contest_config.default_language
  local language_config = contest_config[target_language]
  if not language_config then
    error(("No language config found for '%s' in contest '%s'"):format(target_language, contest))
  end
  if not language_config.extension then
    error(
      ("No extension configured for language '%s' in contest '%s'"):format(target_language, contest)
    )
  end

  local base_name
  if config.filename then
    local source_file = config.filename(contest, contest_id, problem_id, config, language)
    base_name = vim.fn.fnamemodify(source_file, ':t:r')
  else
    local default_filename = require('cp.config').default_filename
    base_name = default_filename(contest_id, problem_id)
  end

  local source_file = base_name .. '.' .. language_config.extension

  return {
    contest = contest,
    contest_id = contest_id,
    problem_id = problem_id,
    source_file = source_file,
    binary_file = ('build/%s.run'):format(base_name),
    input_file = ('io/%s.cpin'):format(base_name),
    output_file = ('io/%s.cpout'):format(base_name),
    expected_file = ('io/%s.expected'):format(base_name),
    problem_name = base_name,
  }
end

return M