local api = vim.api
local tsutils = require "nvim-treesitter.ts_utils"
local query = require "nvim-treesitter.query"
local parsers = require "nvim-treesitter.parsers"

local M = {}

-- This is cached on buf tick to avoid computing that multiple times
-- Especially not for every line in the file when `zx` is hit
local folds_levels = tsutils.memoize_by_buf_tick(function(bufnr)
  local max_fold_level = api.nvim_win_get_option(0, "foldnestmax")
  local trim_level = function(level)
    if level > max_fold_level then
      return max_fold_level
    end
    return level
  end

  local parser = parsers.get_parser(bufnr)

  if not parser then
    return {}
  end

  local matches = query.get_capture_matches_recursively(bufnr, function(lang)
    if query.has_folds(lang) then
      return "@fold", "folds"
    elseif query.has_locals(lang) then
      return "@scope", "locals"
    end
  end)

  -- start..stop is an inclusive range
  local start_counts = {}
  local stop_counts = {}

  local prev_start = -1
  local prev_stop = -1

  local min_fold_lines = api.nvim_win_get_option(0, "foldminlines")

  for _, node in ipairs(matches) do
    local start, _, stop, stop_col = node.node:range()

    if stop_col == 0 then
      stop = stop - 1
    end

    local fold_length = stop - start + 1
    local should_fold = fold_length > min_fold_lines

    -- Fold only multiline nodes that are not exactly the same as previously met folds
    -- Checking against just the previously found fold is sufficient if nodes
    -- are returned in preorder or postorder when traversing tree
    if should_fold and not (start == prev_start and stop == prev_stop) then
      start_counts[start] = (start_counts[start] or 0) + 1
      stop_counts[stop] = (stop_counts[stop] or 0) + 1
      prev_start = start
      prev_stop = stop
    end
  end

  local levels = {}
  local current_level = 0

  -- We now have the list of fold opening and closing, fill the gaps and mark where fold start
  for lnum = 0, api.nvim_buf_line_count(bufnr) do
    local prefix = ""

    local last_trimmed_level = trim_level(current_level)
    current_level = current_level + (start_counts[lnum] or 0)
    local trimmed_level = trim_level(current_level)
    current_level = current_level - (stop_counts[lnum] or 0)
    local next_trimmed_level = trim_level(current_level)

    -- Determine if it's the start/end of a fold
    -- NB: vim's fold-expr interface does not have a mechanism to indicate that
    -- two (or more) folds start at this line, so it cannot distinguish between
    --  ( \n ( \n )) \n (( \n ) \n )
    -- versus
    --  ( \n ( \n ) \n ( \n ) \n )
    -- If it did have such a mechanism, (trimmed_level - last_trimmed_level)
    -- would be the correct number of starts to pass on.
    if trimmed_level - last_trimmed_level > 0 then
      prefix = ">"
    elseif trimmed_level - next_trimmed_level > 0 then
      -- Ending marks tend to confuse vim more than it helps, particularly when
      -- the fold level changes by at least 2; we can uncomment this if
      -- vim's behavior gets fixed.
      -- prefix = "<"
      prefix = ""
    end

    levels[lnum + 1] = prefix .. tostring(trimmed_level)
  end

  return levels
end)

function M.get_fold_indic(lnum)
  if not parsers.has_parser() or not lnum then
    return "0"
  end

  local buf = api.nvim_get_current_buf()

  local levels = folds_levels(buf) or {}

  return levels[lnum] or "0"
end

return M
