local M = {}

local commands = require('diffs.commands')
local git = require('diffs.git')
local dbg = require('diffs.log').dbg

---@alias diffs.FugitiveSection 'staged' | 'unstaged' | 'untracked' | nil

---@param bufnr integer
---@param lnum integer
---@return diffs.FugitiveSection
function M.get_section_at_line(bufnr, lnum)
  local lines = vim.api.nvim_buf_get_lines(bufnr, 0, lnum, false)

  for i = #lines, 1, -1 do
    local line = lines[i]
    if line:match('^Staged ') then
      return 'staged'
    elseif line:match('^Unstaged ') then
      return 'unstaged'
    elseif line:match('^Untracked ') then
      return 'untracked'
    end
  end

  return nil
end

---@param line string
---@return string?
local function parse_file_line(line)
  local renamed = line:match('^R[%s%d]*[^%s]+%s*->%s*(.+)$')
  if renamed then
    return vim.trim(renamed)
  end

  local filename = line:match('^[MADRCU?][MADRCU%s]*%s+(.+)$')
  if filename then
    return vim.trim(filename)
  end

  return nil
end

---@param bufnr integer
---@param lnum integer
---@return string?, diffs.FugitiveSection
function M.get_file_at_line(bufnr, lnum)
  local lines = vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
  local current_line = lines[lnum]

  if not current_line then
    return nil, nil
  end

  local filename = parse_file_line(current_line)
  if filename then
    local section = M.get_section_at_line(bufnr, lnum)
    return filename, section
  end

  local prefix = current_line:sub(1, 1)
  if prefix == '+' or prefix == '-' or prefix == ' ' then
    for i = lnum - 1, 1, -1 do
      local prev_line = lines[i]
      filename = parse_file_line(prev_line)
      if filename then
        local section = M.get_section_at_line(bufnr, i)
        return filename, section
      end
      if prev_line:match('^%w+ %(') or prev_line == '' then
        break
      end
    end
  end

  return nil, nil
end

---@param bufnr integer
---@return string?
local function get_repo_root_from_fugitive(bufnr)
  local bufname = vim.api.nvim_buf_get_name(bufnr)
  local fugitive_path = bufname:match('^fugitive://(.+)///')
  if fugitive_path then
    return fugitive_path
  end

  local cwd = vim.fn.getcwd()
  local root = git.get_repo_root(cwd .. '/.')
  return root
end

---@param vertical boolean
function M.diff_file_under_cursor(vertical)
  local bufnr = vim.api.nvim_get_current_buf()
  local lnum = vim.api.nvim_win_get_cursor(0)[1]

  local filename, section = M.get_file_at_line(bufnr, lnum)

  if not filename then
    vim.notify('[diffs.nvim]: no file under cursor', vim.log.levels.WARN)
    return
  end

  local repo_root = get_repo_root_from_fugitive(bufnr)
  if not repo_root then
    vim.notify('[diffs.nvim]: could not determine repository root', vim.log.levels.ERROR)
    return
  end

  local filepath = repo_root .. '/' .. filename

  dbg('diff_file_under_cursor: %s (section: %s)', filename, section or 'unknown')

  if section == 'untracked' then
    vim.notify('[diffs.nvim]: cannot diff untracked file (no base version)', vim.log.levels.WARN)
    return
  end

  commands.gdiff_file(filepath, {
    vertical = vertical,
    staged = section == 'staged',
  })
end

---@param bufnr integer
---@param config { horizontal: string|false, vertical: string|false }
function M.setup_keymaps(bufnr, config)
  if config.horizontal and config.horizontal ~= '' then
    vim.keymap.set('n', config.horizontal, function()
      M.diff_file_under_cursor(false)
    end, { buffer = bufnr, desc = 'Unified diff (horizontal)' })
    dbg('set keymap %s for buffer %d', config.horizontal, bufnr)
  end

  if config.vertical and config.vertical ~= '' then
    vim.keymap.set('n', config.vertical, function()
      M.diff_file_under_cursor(true)
    end, { buffer = bufnr, desc = 'Unified diff (vertical)' })
    dbg('set keymap %s for buffer %d', config.vertical, bufnr)
  end
end

return M