--- Conceal `[[NODEID|Name]]` links down to a styled "Name" hyperlink in node
--- buffers (tech-spec §8.4). The node id is structural noise to a reader, so we
--- hide the `[[id|` prefix and the `]]` suffix with conceal extmarks, leaving
--- the label visible and highlighted. `conceallevel=2` + an empty
--- `concealcursor` reveal the raw `[[id|Name]]` on the line the cursor is on, so
--- it stays directly editable. A bare `[[id]]` (briefly, before save→reload
--- canonicalises it) just hides its brackets.

local M = {}

local ns = vim.api.nvim_create_namespace("heph_link_conceal")

--- Recompute conceal extmarks for every `[[…]]` span in `buf`.
function M.refresh(buf)
  if not vim.api.nvim_buf_is_valid(buf) then
    return
  end
  vim.api.nvim_buf_clear_namespace(buf, ns, 0, -1)
  local lines = vim.api.nvim_buf_get_lines(buf, 0, -1, false)
  for lnum, line in ipairs(lines) do
    local row = lnum - 1
    local from = 1
    while true do
      local s = line:find("[[", from, true) -- 1-based byte of first `[`
      if not s then
        break
      end
      local e = line:find("]]", s + 2, true) -- 1-based byte of `]]`
      if not e then
        break
      end
      local inner = line:sub(s + 2, e - 1)
      local pipe = inner:find("|", 1, true)
      -- Byte columns are 0-based for extmarks; end_col is exclusive.
      local open_end -- exclusive end of the hidden prefix (`[[` or `[[id|`)
      if pipe then
        open_end = (s + 1 + pipe) -- 0-based col just past the `|`
      else
        open_end = s + 1 -- 0-based col just past `[[`
      end
      -- Hide the prefix, highlight the visible label, hide the closing `]]`.
      vim.api.nvim_buf_set_extmark(buf, ns, row, s - 1, { end_col = open_end, conceal = "" })
      vim.api.nvim_buf_set_extmark(buf, ns, row, open_end, { end_col = e - 1, hl_group = "HephLink" })
      vim.api.nvim_buf_set_extmark(buf, ns, row, e - 1, { end_col = e + 1, conceal = "" })
      from = e + 2
    end
  end
end

--- Enable link conceal for the current window + `buf`: define the highlight,
--- set the window conceal options, refresh now, and refresh on edits.
function M.attach(buf)
  vim.api.nvim_set_hl(0, "HephLink", { link = "Underlined", default = true })
  vim.wo.conceallevel = 2
  vim.wo.concealcursor = "" -- reveal the raw link on the cursor's line
  M.refresh(buf)
  vim.api.nvim_create_autocmd({ "TextChanged", "TextChangedI" }, {
    buffer = buf,
    callback = function()
      M.refresh(buf)
    end,
    desc = "heph: refresh [[link]] conceal",
  })
end

return M