--=============================================================================
-- browser.lua --- browser zknotes
-- Copyright (c) 2019-2024 Wang Shidong & Contributors
-- Author: Wang Shidong < wsdjeg@outlook.com >
-- URL: https://spacevim.org
-- License: GPLv3
--=============================================================================
local M = {}
local fn = vim.fn

local config = require('zettelkasten.config')

local ZK_FULL_TITLE_PATTERN = '# %d+-%d+-%d+-%d+-%d+-%d+ .+'
local ZK_ID_PATTERN = '%d+-%d+-%d+-%d+-%d+-%d+'
local ZK_FILE_NAME_PATTERN = '%d+-%d+-%d+-%d+-%d+-%d+.md'

local s_note_cache_with_file_path = {}
local s_note_cache_with_id = {}


-- list all zettelkasten notes in specific folder
local function get_files(folder)
  local files = fn.split(fn.globpath(folder, '*.md'), '\\n')
  files = vim.tbl_filter(function(file)
    return string.match(file, ZK_FILE_NAME_PATTERN) ~= nil
  end, files)

  return files
end

local function extract_id_and_title(line)
  local zk_id = string.match(line, ZK_FULL_TITLE_PATTERN)
  if zk_id == nil then
    return nil
  end

  zk_id = string.gsub(zk_id, '# ', '')
  local note_id = string.match(zk_id, ZK_ID_PATTERN)
  local title = vim.trim(string.gsub(zk_id, ZK_ID_PATTERN, ''))

  return { id = note_id, title = string.gsub(title, '\r', '') }
end

local function extract_references(line, linenr)
  assert(line ~= nil)

  local references = {}
  for ref in string.gmatch(line, '(%[%[' .. ZK_ID_PATTERN .. '%]%])') do
    ref = string.gsub(ref, '%[%[', '')
    ref = string.gsub(ref, '%]%]', '')
    table.insert(references, { id = ref, linenr = linenr })
  end

  return references
end

local function extract_back_references(notes, note_id)
  assert(note_id ~= nil)

  local back_references = {}
  for _, note in ipairs(notes) do
    if note.id == note_id then
      goto continue
    end

    local references = note.references
    for _, ref in ipairs(references) do
      if ref.id == note_id then
        table.insert(back_references, {
          id = note.id,
          title = note.title,
          file_name = note.file_name,
          linenr = ref.linenr,
        })

        break
      end
    end

    ::continue::
  end

  return back_references
end

local function extract_tags(line, linenr)
  assert(line ~= nil)

  local tags = {}
  for tag in string.gmatch(line, '(%#%a[%w-]+)') do
    local start_pos, _ = string.find(line, tag, 1, true)
    local previous_char = string.sub(line, start_pos - 1, start_pos - 1)
    if previous_char == '' or previous_char == ' ' then
      table.insert(tags, { linenr = linenr, name = tag })
    end
  end

  return tags
end

local function get_note_information(file_path)
  local last_modified = fn.strftime('%Y-%m-%d.%H:%M:%S', fn.getftime(file_path))
  if
    s_note_cache_with_file_path[file_path] ~= nil
    and s_note_cache_with_file_path[file_path].last_modified == last_modified
  then
    return s_note_cache_with_file_path[file_path]
  end

  local file = io.open(file_path, 'r')
  if file:read(0) == nil then
    return nil
  end

  local info = {
    id = '',
    title = '',
    file_name = file_path,
    last_modified = last_modified,
    tags = {},
    references = {},
    back_references = {},
  }

  local linenr = 0
  while true do
    linenr = linenr + 1
    local line = file:read('*line')
    if line == nil then
      break
    end

    if line == '' then
      goto continue
    end

    if info.id == '' then
      local id_title = extract_id_and_title(line)
      if id_title then
        info = vim.tbl_extend('force', info, id_title)
        goto continue
      end
    end

    local refs = extract_references(line, linenr)
    if refs then
      vim.list_extend(info.references, refs)
    end

    local tags = extract_tags(line, linenr)
    if tags then
      vim.list_extend(info.tags, tags)
    end

    ::continue::
  end

  if info.id ~= nil then
    s_note_cache_with_file_path[file_path] = info
    s_note_cache_with_id[info.id] = info
  end
  return info
end

function M.get_note(id)
  if s_note_cache_with_id[id] ~= nil then
    return s_note_cache_with_id[id]
  end

  local _ = M.get_notes()

  if s_note_cache_with_id[id] ~= nil then
    return s_note_cache_with_id[id]
  end

  return nil
end

function M.get_notes()
  local folder = config.zettel_dir
  local files = get_files(folder)
  local all_notes = {}
  for _, file in ipairs(files) do
    table.insert(all_notes, get_note_information(file))
  end

  for _, note in ipairs(all_notes) do
    if note.id == nil then
      goto continue
    end

    local back_references = extract_back_references(all_notes, note.id)
    if back_references then
      -- When notes are cached, `back_references` field will have the references from before.
      -- Since the files that refer to this one might have changed, we'll overwrite it here.
      -- extract_back_references() already re-processes the references.
      note.back_references = back_references
    end

    ::continue::
  end

  return all_notes
end

function M.get_tags()
  local notes = M.get_notes()
  local tags = {}
  for _, note in ipairs(notes) do
    if #note.tags == 0 then
      goto continue
    end

    for _, tag in ipairs(note.tags) do
      table.insert(tags, {
        linenr = tag.linenr,
        name = tag.name,
        file_name = note.file_name,
      })
    end

    ::continue::
  end

  return tags
end

return M