-- Custom hover for CljElixir .clje files
-- Resolves Module/function patterns against stub files in the project's stubs/ directory
local M = {}

--- Walk up from the current buffer's directory to find the stubs/ directory
local function find_stubs_dir()
  local bufpath = vim.api.nvim_buf_get_name(0)
  if bufpath == "" then return nil end
  local dir = vim.fn.fnamemodify(bufpath, ":p:h")
  for _ = 1, 20 do
    if dir == "/" or dir == "" then break end
    if vim.fn.isdirectory(dir .. "/stubs") == 1 then
      return dir .. "/stubs"
    end
    dir = vim.fn.fnamemodify(dir, ":h")
  end
  return nil
end

--- Extract the symbol under cursor, handling namespace/function patterns.
--- Returns (namespace, function_name) or nil.
local function symbol_under_cursor()
  local line = vim.api.nvim_get_current_line()
  local col = vim.api.nvim_win_get_cursor(0)[2] -- 0-indexed byte col

  -- Expand outward from cursor to find the full symbol (letters, digits, -, ?, !, ., /, _)
  local s, e = col + 1, col + 1
  local sym_chars = "[%w%-%?%!%.%/_><=*+]"
  while s > 1 and line:sub(s - 1, s - 1):match(sym_chars) do
    s = s - 1
  end
  while e < #line and line:sub(e + 1, e + 1):match(sym_chars) do
    e = e + 1
  end
  local word = line:sub(s, e)
  if not word or word == "" then return nil, nil end

  -- Must contain a / to be a qualified call
  local slash = word:find("/")
  if not slash then return nil, nil end

  local ns = word:sub(1, slash - 1)
  local fn_name = word:sub(slash + 1)
  if ns == "" or fn_name == "" then return nil, nil end

  return ns, fn_name
end

--- Resolve a namespace name to a stub file path
local function resolve_stub_file(stubs_dir, ns)
  -- Direct match (e.g., Process.clj, erlang.clj)
  local path = stubs_dir .. "/" .. ns .. ".clj"
  if vim.fn.filereadable(path) == 1 then return path end

  -- erl_ prefix for case-insensitive collisions (e.g., erl_io.clj for :io)
  path = stubs_dir .. "/erl_" .. ns .. ".clj"
  if vim.fn.filereadable(path) == 1 then return path end

  -- Subdirectory (e.g., clje/core.clj)
  path = stubs_dir .. "/clje/" .. ns .. ".clj"
  if vim.fn.filereadable(path) == 1 then return path end

  return nil
end

--- Find a (defn ...) or (defmacro ...) form in the file lines and return its text
local function find_defn(lines, fn_name)
  -- Escape special pattern chars in the function name
  local pat = fn_name:gsub("([%-%.%?%!%*%+%[%]%(%)%^%$%%])", "%%%1")

  local start_idx = nil
  for i, line in ipairs(lines) do
    -- Match (defn name or (defmacro name at the start of a line
    if line:match("^%(defn%s+" .. pat .. "$")
      or line:match("^%(defn%s+" .. pat .. "%s")
      or line:match("^%(defmacro%s+" .. pat .. "$")
      or line:match("^%(defmacro%s+" .. pat .. "%s") then
      start_idx = i
      break
    end
  end

  if not start_idx then return nil end

  -- Collect lines for this form by tracking paren depth
  local form_lines = {}
  local depth = 0
  for i = start_idx, #lines do
    local line = lines[i]
    table.insert(form_lines, line)
    for ch in line:gmatch(".") do
      if ch == "(" then depth = depth + 1
      elseif ch == ")" then depth = depth - 1 end
    end
    if depth <= 0 and i > start_idx then break end
  end

  return form_lines
end

--- Extract a vector [args] from a signature line, stripping outer parens and trailing junk
local function extract_sig(s)
  -- Match the innermost [args] vector
  local vec = s:match("%[(.-)%]")
  if vec then
    return "[" .. vec .. "]"
  end
  return nil
end

--- Extract docstring and signatures from defn form lines for a cleaner display
local function parse_defn(form_lines, ns, fn_name)
  local md = {}
  local docstring_parts = {}
  local signatures = {}
  local in_docstring = false

  for i, line in ipairs(form_lines) do
    if i == 1 then goto continue end -- skip (defn name line

    local trimmed = line:match("^%s*(.-)%s*$")

    -- Detect docstring (starts and/or ends with ")
    if not in_docstring and trimmed:match('^"') then
      in_docstring = true
      -- Single-line docstring
      if trimmed:match('^"(.*)"$') then
        table.insert(docstring_parts, trimmed:match('^"(.*)"$'))
        in_docstring = false
      else
        table.insert(docstring_parts, trimmed:match('^"(.*)$'))
      end
    elseif in_docstring then
      if trimmed:match('"[%)]*$') then
        table.insert(docstring_parts, trimmed:match('^(.-)"'))
        in_docstring = false
      else
        table.insert(docstring_parts, trimmed)
      end
    elseif trimmed:match("%[") then
      -- Signature line containing [args]
      local sig = extract_sig(trimmed)
      if sig then
        table.insert(signatures, sig)
      end
    end

    ::continue::
  end

  -- Build markdown
  table.insert(md, "### `" .. ns .. "/" .. fn_name .. "`")
  table.insert(md, "")

  if #signatures > 0 then
    table.insert(md, "```clojure")
    for _, sig in ipairs(signatures) do
      if sig == "[]" then
        table.insert(md, "(" .. ns .. "/" .. fn_name .. ")")
      else
        table.insert(md, "(" .. ns .. "/" .. fn_name .. " " .. sig .. ")")
      end
    end
    table.insert(md, "```")
    table.insert(md, "")
  end

  if #docstring_parts > 0 then
    for _, part in ipairs(docstring_parts) do
      table.insert(md, part)
    end
  end

  return md
end

--- Main hover function — looks up Module/function in stubs
function M.hover()
  local ns, fn_name = symbol_under_cursor()
  if not ns or not fn_name then
    vim.lsp.buf.hover()
    return
  end

  local stubs_dir = find_stubs_dir()
  if not stubs_dir then
    vim.lsp.buf.hover()
    return
  end

  local stub_file = resolve_stub_file(stubs_dir, ns)
  if not stub_file then
    vim.lsp.buf.hover()
    return
  end

  local lines = vim.fn.readfile(stub_file)
  if not lines or #lines == 0 then
    vim.lsp.buf.hover()
    return
  end

  local form_lines = find_defn(lines, fn_name)
  if not form_lines then
    -- Function not found in stub, fall back to LSP
    vim.lsp.buf.hover()
    return
  end

  local md = parse_defn(form_lines, ns, fn_name)

  vim.lsp.util.open_floating_preview(md, "markdown", {
    border = "rounded",
    focus_id = "clje-hover",
  })
end

return M