-- This Module contains all of the reviewer code for diffview
local u = require("gitlab.utils")
local state = require("gitlab.state")
local async_ok, async = pcall(require, "diffview.async")
local diffview_lib = require("diffview.lib")

local M = {
  bufnr = nil,
  tabnr = nil,
}

local all_git_manged_files_unmodified = function()
  -- check local managed files are unmodified, matching the state in the MR
  -- TODO: ensure correct CWD?
  return vim.fn.trim(vim.fn.system({ "git", "status", "--short", "--untracked-files=no" })) == ""
end

M.open = function()
  local diff_refs = state.INFO.diff_refs
  if diff_refs == nil then
    u.notify("Gitlab did not provide diff refs required to review this MR", vim.log.levels.ERROR)
    return
  end

  if diff_refs.base_sha == "" or diff_refs.head_sha == "" then
    u.notify("Merge request contains no changes", vim.log.levels.ERROR)
    return
  end

  local diffview_open_command = "DiffviewOpen"
  local diffview_feature_imply_local = {
    user_requested = state.settings.reviewer_settings.diffview.imply_local,
    usable = all_git_manged_files_unmodified(),
  }
  if diffview_feature_imply_local.user_requested and diffview_feature_imply_local.usable then
    diffview_open_command = diffview_open_command .. " --imply-local"
  end

  vim.api.nvim_command(string.format("%s %s..%s", diffview_open_command, diff_refs.base_sha, diff_refs.head_sha))
  M.tabnr = vim.api.nvim_get_current_tabpage()

  if diffview_feature_imply_local.user_requested and not diffview_feature_imply_local.usable then
    u.notify(
      "There are uncommited changes in the working tree, cannot use 'imply_local' setting for gitlab reviews. Stash or commit all changes to use.",
      vim.log.levels.WARN
    )
  end

  if state.INFO.has_conflicts then
    u.notify("This merge request has conflicts!", vim.log.levels.WARN)
  end

  -- Register Diffview hook for close event to set tab page # to nil
  local on_diffview_closed = function(view)
    if view.tabpage == M.tabnr then
      M.tabnr = nil
    end
  end
  require("diffview.config").user_emitter:on("view_closed", function(_, ...)
    on_diffview_closed(...)
  end)

  if state.settings.discussion_tree.auto_open then
    local discussions = require("gitlab.actions.discussions")
    discussions.close()
    discussions.toggle()
  end
end

M.close = function()
  vim.cmd("DiffviewClose")
  local discussions = require("gitlab.actions.discussions")
  discussions.close()
end

M.jump = function(file_name, new_line, old_line, opts)
  if M.tabnr == nil then
    u.notify("Can't jump to Diffvew. Is it open?", vim.log.levels.ERROR)
    return
  end
  vim.api.nvim_set_current_tabpage(M.tabnr)
  vim.cmd("DiffviewFocusFiles")
  local view = diffview_lib.get_current_view()
  if view == nil then
    u.notify("Could not find Diffview view", vim.log.levels.ERROR)
    return
  end
  local files = view.panel:ordered_file_list()
  local layout = view.cur_layout
  for _, file in ipairs(files) do
    if file.path == file_name then
      if not async_ok then
        u.notify("Could not load Diffview async", vim.log.levels.ERROR)
        return
      end
      async.await(view:set_file(file))
      -- TODO: Ranged comments on unchanged lines will have both a
      -- new line and a old line.
      --
      -- The same is true when the user leaves a single-line comment
      -- on an unchanged line in the "b" buffer.
      --
      -- We need to distinguish them somehow from
      -- range comments (which also have this) so that we can know
      -- which buffer to jump to. Right now, we jump to the wrong
      -- buffer for ranged comments on unchanged lines.
      if new_line ~= nil and not opts.is_undefined_type then
        layout.b:focus()
        vim.api.nvim_win_set_cursor(0, { tonumber(new_line), 0 })
      elseif old_line ~= nil then
        layout.a:focus()
        vim.api.nvim_win_set_cursor(0, { tonumber(old_line), 0 })
      end
      break
    end
  end
end

---Get the location of a line within the diffview. If range is specified, then also the location
---of the lines in range.
---@param range LineRange | nil Line range to get location for
---@return ReviewerInfo | nil nil is returned only if error was encountered
M.get_location = function(range)
  if M.tabnr == nil then
    u.notify("Diffview reviewer must be initialized first", vim.log.levels.ERROR)
    return
  end

  -- If there's a range, use the start of the visual selection, not the current line
  local current_line = range and range.start_line or vim.api.nvim_win_get_cursor(0)[1]

  -- Check if we are in the diffview tab
  local tabnr = vim.api.nvim_get_current_tabpage()
  if tabnr ~= M.tabnr then
    u.notify("Line location can only be determined within reviewer window", vim.log.levels.ERROR)
    return
  end

  -- Check if we are in the diffview buffer
  local view = diffview_lib.get_current_view()
  if view == nil then
    u.notify("Could not find Diffview view", vim.log.levels.ERROR)
    return
  end

  local layout = view.cur_layout

  ---@type ReviewerInfo
  local reviewer_info = {
    file_name = layout.a.file.path,
    new_line = nil,
    old_line = nil,
    range_info = nil,
  }

  local a_win = u.get_window_id_by_buffer_id(layout.a.file.bufnr)
  local b_win = u.get_window_id_by_buffer_id(layout.b.file.bufnr)
  local current_win = vim.fn.win_getid()
  local is_current_sha = current_win == b_win

  if a_win == nil or b_win == nil then
    u.notify("Error retrieving window IDs for current files", vim.log.levels.ERROR)
    return
  end

  local current_file = M.get_current_file()
  if current_file == nil then
    u.notify("Error retrieving current file from Diffview", vim.log.levels.ERROR)
    return
  end

  local a_linenr = vim.api.nvim_win_get_cursor(a_win)[1]
  local b_linenr = vim.api.nvim_win_get_cursor(b_win)[1]

  local data = u.parse_hunk_headers(current_file, state.INFO.target_branch)

  if data.hunks == nil then
    u.notify("Could not parse hunks", vim.log.levels.ERROR)
    return
  end

  -- Will be different depending on focused window.
  local modification_type =
    M.get_modification_type(a_linenr, b_linenr, is_current_sha, data.hunks, data.all_diff_output)

  if modification_type == "bad_file_unmodified" then
    u.notify("Comments on unmodified lines will be placed in the old file", vim.log.levels.WARN)
  end

  -- Comment on new line: Include only new_line in payload.
  if modification_type == "added" then
    reviewer_info.old_line = nil
    reviewer_info.new_line = b_linenr
    -- Comment on deleted line: Include only new_line in payload.
  elseif modification_type == "deleted" then
    reviewer_info.old_line = a_linenr
    reviewer_info.new_line = nil
    -- The line was not found in any hunks, only send the old line number
  elseif modification_type == "unmodified" or modification_type == "bad_file_unmodified" then
    reviewer_info.old_line = a_linenr
    reviewer_info.new_line = b_linenr
  end

  if range == nil then
    return reviewer_info
  end

  -- If leaving a multi-line comment, we want to also add range_info to the payload.
  local is_new = reviewer_info.new_line ~= nil
  local current_line_info = is_new and u.get_lines_from_hunks(data.hunks, reviewer_info.new_line, is_new)
    or u.get_lines_from_hunks(data.hunks, reviewer_info.old_line, is_new)
  local type = is_new and "new" or "old"

  ---@type ReviewerRangeInfo
  local range_info = { start = {}, ["end"] = {} }

  if current_line == range.start_line then
    range_info.start.old_line = current_line_info.old_line
    range_info.start.new_line = current_line_info.new_line
    range_info.start.type = type
  else
    local start_line_info = u.get_lines_from_hunks(data.hunks, range.start_line, is_new)
    range_info.start.old_line = start_line_info.old_line
    range_info.start.new_line = start_line_info.new_line
    range_info.start.type = type
  end
  if current_line == range.end_line then
    range_info["end"].old_line = current_line_info.old_line
    range_info["end"].new_line = current_line_info.new_line
    range_info["end"].type = type
  else
    local end_line_info = u.get_lines_from_hunks(data.hunks, range.end_line, is_new)
    range_info["end"].old_line = end_line_info.old_line
    range_info["end"].new_line = end_line_info.new_line
    range_info["end"].type = type
  end

  reviewer_info.range_info = range_info
  return reviewer_info
end

---Return content between start_line and end_line
---@param start_line integer
---@param end_line integer
---@return string[]
M.get_lines = function(start_line, end_line)
  return vim.api.nvim_buf_get_lines(0, start_line - 1, end_line, false)
end

---Checks whether the lines in the two buffers are the same
---@return boolean
M.lines_are_same = function(layout, a_cursor, b_cursor)
  local line_a = u.get_line_content(layout.a.file.bufnr, a_cursor)
  local line_b = u.get_line_content(layout.b.file.bufnr, b_cursor)
  return line_a == line_b
end

---Get currently shown file
M.get_current_file = function()
  local view = diffview_lib.get_current_view()
  if not view then
    return
  end
  return view.panel.cur_file.path
end

---Place a sign in currently reviewed file. Use new line for identifing lines after changes, old
---line for identifing lines before changes and both if line was not changed.
---@param signs SignTable[] table of signs. See :h sign_placelist
---@param type string "new" if diagnostic should be in file after changes else "old"
M.place_sign = function(signs, type)
  local view = diffview_lib.get_current_view()
  if not view then
    return
  end
  if type == "new" then
    for _, sign in ipairs(signs) do
      sign.buffer = view.cur_layout.b.file.bufnr
    end
  elseif type == "old" then
    for _, sign in ipairs(signs) do
      sign.buffer = view.cur_layout.a.file.bufnr
    end
  end
  vim.fn.sign_placelist(signs)
end

---Set diagnostics in currently reviewed file.
---@param namespace integer namespace for diagnostics
---@param diagnostics table see :h vim.diagnostic.set
---@param type string "new" if diagnostic should be in file after changes else "old"
---@param opts table? see :h vim.diagnostic.set
M.set_diagnostics = function(namespace, diagnostics, type, opts)
  local view = diffview_lib.get_current_view()
  if not view then
    return
  end
  if type == "new" and view.cur_layout.b.file.bufnr then
    vim.diagnostic.set(namespace, view.cur_layout.b.file.bufnr, diagnostics, opts)
  elseif type == "old" and view.cur_layout.a.file.bufnr then
    vim.diagnostic.set(namespace, view.cur_layout.a.file.bufnr, diagnostics, opts)
  end
end

---Diffview exposes events which can be used to setup autocommands.
---@param callback fun(opts: table) - for more information about opts see callback in :h nvim_create_autocmd
M.set_callback_for_file_changed = function(callback)
  local group = vim.api.nvim_create_augroup("gitlab.diffview.autocommand.file_changed", {})
  vim.api.nvim_create_autocmd("User", {
    pattern = { "DiffviewDiffBufWinEnter", "DiffviewViewEnter" },
    group = group,
    callback = function(...)
      if M.tabnr == vim.api.nvim_get_current_tabpage() then
        callback(...)
      end
    end,
  })
end

---Diffview exposes events which can be used to setup autocommands.
---@param callback fun(opts: table) - for more information about opts see callback in :h nvim_create_autocmd
M.set_callback_for_reviewer_leave = function(callback)
  local group = vim.api.nvim_create_augroup("gitlab.diffview.autocommand.leave", {})
  vim.api.nvim_create_autocmd("User", {
    pattern = { "DiffviewViewLeave", "DiffviewViewClosed" },
    group = group,
    callback = function(...)
      if M.tabnr == vim.api.nvim_get_current_tabpage() then
        callback(...)
      end
    end,
  })
end

---Returns whether the comment is on a deleted line, added line, or unmodified line.
---This is in order to build the payload for Gitlab correctly by setting the old line and new line.
---@param a_linenr number
---@param b_linenr number
---@param is_current_sha boolean
---@param hunks Hunk[] A list of hunks
---@param all_diff_output table The raw diff output
function M.get_modification_type(a_linenr, b_linenr, is_current_sha, hunks, all_diff_output)
  for _, hunk in ipairs(hunks) do
    local old_line_end = hunk.old_line + hunk.old_range
    local new_line_end = hunk.new_line + hunk.new_range

    if is_current_sha then
      -- If it is a single line change and neither hunk has a range, then it's added
      if b_linenr >= hunk.new_line and b_linenr <= new_line_end then
        if hunk.new_range == 0 and hunk.old_range == 0 then
          return "added"
        end
        -- If leaving a comment on the new window, we may be commenting on an added line
        -- or on an unmodified line. To tell, we have to check whether the line itself is
        -- prefixed with "+" and only return "added" if it is.
        if M.line_was_added(b_linenr, hunk, all_diff_output) then
          return "added"
        end
      end
    else
      -- It's a deletion if it's in the range of the hunks and the new
      -- range is zero, since that is only a deletion hunk, or if we find
      -- a match in another hunk with a range, and the corresponding line is prefixed
      -- with a "-" only. If it is, then it's a deletion.
      if a_linenr >= hunk.old_line and a_linenr <= old_line_end and hunk.old_range == 0 then
        return "deleted"
      end
      if
        (a_linenr >= hunk.old_line and a_linenr <= old_line_end)
        or (a_linenr >= hunk.new_line and b_linenr <= new_line_end)
      then
        if M.line_was_removed(a_linenr, hunk, all_diff_output) then
          return "deleted"
        end
      end
    end
  end

  -- If we can't find the line, this means the user is either trying to leave
  -- a comment on an unchanged line in the new or old file SHA. This is only
  -- allowed in the old file
  return is_current_sha and "bad_file_unmodified" or "unmodified"
end

---@param linnr number
---@param hunk Hunk
---@param all_diff_output table
M.line_was_removed = function(linnr, hunk, all_diff_output)
  for matching_line_index, line in ipairs(all_diff_output) do
    local found_hunk = u.parse_possible_hunk_headers(line)
    if found_hunk ~= nil and vim.deep_equal(found_hunk, hunk) then
      -- We found a matching hunk, now we need to iterate over the lines from the raw diff output
      -- at that hunk until we reach the line we are looking for. When the indexes match we check
      -- to see if that line is deleted or not.
      for hunk_line_index = found_hunk.old_line, hunk.old_line + hunk.old_range - 1, 1 do
        local line_content = all_diff_output[matching_line_index + 1]
        if hunk_line_index == linnr then
          if string.match(line_content, "^%-") then
            return "deleted"
          end
        end
      end
    end
  end
end

---@param linnr number
---@param hunk Hunk
---@param all_diff_output table
M.line_was_added = function(linnr, hunk, all_diff_output)
  for matching_line_index, line in ipairs(all_diff_output) do
    local found_hunk = u.parse_possible_hunk_headers(line)
    if found_hunk ~= nil and vim.deep_equal(found_hunk, hunk) then
      -- For added lines, we only want to iterate over the part of the diff that has has new lines,
      -- so we skip over the old range. We then keep track of the increment to the original new line index,
      -- and iterate until we reach the end of the total range of this hunk. If we arrive at the matching
      -- index for the line number, we check to see if the line was added.
      local i = 0
      local old_range = (found_hunk.old_range == 0 and found_hunk.old_line ~= 0) and 1 or found_hunk.old_range
      for hunk_line_index = matching_line_index + old_range + 1, matching_line_index + old_range + found_hunk.new_range, 1 do
        local line_content = all_diff_output[hunk_line_index]
        if (found_hunk.new_line + i) == linnr then
          if string.match(line_content, "^%+") then
            return "added"
          end
        end
        i = i + 1
      end
    end
  end
end
return M