-- lua/c/utils.lua
local M = {}

-- Find the project root (same markers clangd likes)
local function project_root(buf)
  return vim.fs.root(buf or 0, { "compile_commands.json", ".git", "Makefile", "makefile" })
end

local function relpath(abs, root)
  if not abs or not root then return nil end
  if abs:sub(1, #root) ~= root then return nil end
  local r = abs:sub(#root + 1)
  if r:sub(1, 1) == "/" then r = r:sub(2) end
  return r
end

local function dirpart(p) return p:match("^(.*)/") end

-- Build the alternate path (header <-> source), preserving nested subdirs
local function alternate_rel(rel)
  local first = rel:match("^([^/]+)/")
  local ext   = rel:match("%.([^.]+)$") or ""
  local rest  = rel:gsub("^" .. (first or "") .. "/", "")

  if first == "include" and ext == "h" then
    return "src/" .. rest:gsub("%.h$", ".c")
  elseif first == "src" and ext == "c" then
    return "include/" .. rest:gsub("%.c$", ".h")
  end

  -- Fallbacks if file isn’t directly under include/ or src/
  if ext == "h" then
    return ("src/" .. rel):gsub("^src/include/", "src/"):gsub("%.h$", ".c")
  elseif ext == "c" then
    return ("include/" .. rel):gsub("^include/src/", "include/"):gsub("%.c$", ".h")
  end

  return nil
end

function M.toggle_header_source()
  local buf  = 0
  local abs  = vim.api.nvim_buf_get_name(buf)
  if abs == "" then
    vim.notify("No file name (unsaved buffer).", vim.log.levels.WARN)
    return
  end

  local root = project_root(buf)
  if not root then
    vim.notify("Couldn’t locate project root (no .git/Makefile/compile_commands.json).", vim.log.levels.WARN)
    return
  end

  local rel = relpath(abs, root)
  if not rel then
    vim.notify("File not under project root: " .. abs, vim.log.levels.WARN)
    return
  end

  local alt_rel = alternate_rel(rel)
  if not alt_rel then
    vim.notify("Not a .c/.h under include/ or src/: " .. rel, vim.log.levels.WARN)
    return
  end

  local alt_abs = root .. "/" .. alt_rel
  if vim.loop.fs_stat(alt_abs) then
    vim.cmd.edit(vim.fn.fnameescape(alt_abs))
    return
  end

  -- Prompt to create
  local choice = vim.fn.confirm(("Create %s?\n\n%s"):format(alt_rel, alt_abs), "&Yes\n&No", 2)
  if choice ~= 1 then return end

  -- Ensure dirs exist, then open the new file (unsaved until you write)
  local dir = dirpart(alt_abs)
  if dir and not vim.loop.fs_stat(dir) then
    vim.fn.mkdir(dir, "p")
  end
  vim.cmd.edit(vim.fn.fnameescape(alt_abs))
  -- Optional: write an empty file immediately. Comment out if you prefer unsaved buffer.
  -- vim.cmd.write()
end

return M