-------------------------------------------------------------------------------
-- Tools to deal with tasks
-------------------------------------------------------------------------------
local Tasks = {}
local Configuration = require('configuration')
local Notes = require('notes')
local Util = require('util')
local api = vim.api
-------------------------------------------------------------------------------
-- Internal Functions
-------------------------------------------------------------------------------
local unchecked_pattern = '^(%s*)%- %[ %]'
local unchecked_important_pattern = '^(%s*)%* %[ %]'
local checked_pattern = '^(%s*)%- %[x%]'
local checked_important_pattern = '^(%s*)%* %[x%]'

local function is_open_task(line)
  return line:match(unchecked_pattern) or line:match(unchecked_important_pattern)
end

local function is_completed_task(line)
  return line:match(checked_pattern) or line:match(checked_important_pattern)
end

local function is_task(line)
    return is_open_task(line) or is_completed_task(line)
end

local function open(path)
  local parent = Util.directory_name(path)
  Util.ensure_directory_exists(parent)
  vim.cmd('edit ' .. path)
end

local function open_inbox()
  local path = Configuration.path_for(Configuration.configuration.tasks.inbox)
  open(path)
end

local function open_someday()
  local path = Configuration.path_for(Configuration.configuration.tasks.someday)
  open(path)
end

local function parse_tags(tag_string)
  local tags = {}
  for tag in tag_string:gmatch('([^,]+)') do
    table.insert(tags, tag)
  end
  return tags
end

local function table_contains_value(target_table, value)
  for _, table_value in ipairs(target_table) do
    if table_value == value then
        return true
    end
  end
  return false
end

local function remove_value(target_table, value)
  for i, table_value in ipairs(target_table) do
    if table_value == value then
      table.remove(target_table, i)
    end
  end
end

-------------------------------------------------------------------------------
-- Public Interface
-------------------------------------------------------------------------------

--- Toggles a task completion status
function Tasks.toggle()
    local line_number = api.nvim_win_get_cursor(0)[1]
    local line = api.nvim_get_current_line()

    if line:match(unchecked_pattern) then
        line = line:gsub(unchecked_pattern, '%1- [x]', 1)
    elseif line:match(unchecked_important_pattern) then
        line = line:gsub(unchecked_important_pattern, '%1* [x]', 1)
    elseif line:match(checked_pattern) then
        line = line:gsub(checked_pattern, '%1- [ ]', 1)
    elseif line:match(checked_important_pattern) then
        line = line:gsub(checked_important_pattern, '%1* [ ]', 1)
    else
      api.nvim_err_writeln('Toggle completion only works on tasks')
    end

    api.nvim_buf_set_lines(0, line_number - 1, line_number, false, {line})
end

--- Toggles a task completion status
function Tasks.toggle_importance()
    local line_number = api.nvim_win_get_cursor(0)[1]
    local line = api.nvim_get_current_line()

    if line:match(unchecked_pattern) then
        line = line:gsub(unchecked_pattern, '%1* [ ]', 1)
    elseif line:match(unchecked_important_pattern) then
        line = line:gsub(unchecked_important_pattern, '%1- [ ]', 1)
    elseif line:match(checked_pattern) then
        line = line:gsub(checked_pattern, '%1* [x]', 1)
    elseif line:match(checked_important_pattern) then
        line = line:gsub(checked_important_pattern, '%1- [x]', 1)
    else
      api.nvim_err_writeln('Toggle importance only works on tasks')
    end

    api.nvim_buf_set_lines(0, line_number - 1, line_number, false, {line})
end

--- Inserts a new task at the cursor location
function Tasks.insert()
  vim.cmd('normal! o- [ ] ')
  vim.cmd('startinsert!')
end

--- Captures a new task into the inbox
function Tasks.capture()
  local prefix = '- [ ] '
  open_inbox()
  vim.cmd('normal! Go'..prefix)
  vim.cmd('startinsert!')
end

--- Tag a task
function Tasks.tag(tag)
  local line_number = api.nvim_win_get_cursor(0)[1]
  local line = api.nvim_get_current_line()
  if is_task(line) then
    local pattern = ':(.*):$'
    local tag_string = line:match(pattern) or ''
    if not tag or tag == '' then
      tag = vim.fn.input('Add new tag for task (' .. tag_string .. '): ')
      if not tag or tag == '' then
        return
      end
    end
    local tags = parse_tags(tag_string)
    if not table_contains_value(tags, tag) then
      table.insert(tags, tag)
      local new_tags = table.concat(tags, ',')
      if line:match(pattern) then
        line = line:gsub(pattern, ':' .. new_tags .. ':', 1)
      else
        line = line .. '    :' .. new_tags .. ':'
      end
      api.nvim_buf_set_lines(0, line_number - 1, line_number, false, {line})
    end
  else
    api.nvim_err_writeln('Tagging only works on tasks')
  end
end

--- Remove tag on a task
function Tasks.remove_tag(tag)
  local line_number = api.nvim_win_get_cursor(0)[1]
  local line = api.nvim_get_current_line()
  if is_task(line) then
    local pattern = ':(.*):$'
    local tag_string = line:match(pattern)
    if not tag_string then
      api.nvim_err_writeln('No tags to remove')
      return
    end

    if not tag or tag == '' then
      tag = vim.fn.input('Pick tag to remove (' .. tag_string .. '): ')
    end

    local tags = parse_tags(tag_string)
    remove_value(tags, tag)
    local new_tags = ''

    if #tags > 0 then
      new_tags = ':' .. table.concat(tags, ',') .. ':'
    end

    line = line:gsub(pattern, new_tags, 1):gsub('%s+$', '')
    api.nvim_buf_set_lines(0, line_number - 1, line_number, false, {line})
  else
    api.nvim_err_writeln('Tagging only works on tasks')
  end
end

--- Reschedule a task for today
function Tasks.reschedule_for_today()
  local today = os.date('%Y-%m-%d')
  Tasks.reschedule(today)
end

--- Reschedule a task for tomorrow
function Tasks.reschedule_for_tomorrow()
  local tomorrow = os.date('%Y-%m-%d', os.time() + 24*60*60)
  Tasks.reschedule(tomorrow)
end

--- Reschedule a task for someday
function Tasks.reschedule_for_someday()
  Tasks.reschedule('someday')
end

--- Reschedule a task for an arbitrary date
function Tasks.reschedule(new_date)

  if not new_date or new_date == '' then
    new_date = vim.fn.input('Reschedule for which date (YYYY-mm-dd): ')
  end

  if not Util.is_valid_date(new_date) and new_date ~= 'someday' then
    api.nvim_err_writeln(new_date .. ' is not a valid date in the format YYYY-mm-dd')
    return
  end

  local line_number = api.nvim_win_get_cursor(0)[1]
  local buffer = api.nvim_get_current_buf()
  local line = api.nvim_get_current_line()
  local filename = vim.fn.expand('%:t:r')

  if is_open_task(line) then
    if Util.is_before_today(filename) and line:match(unchecked_pattern) then
      local rescheduled_line = line:gsub(unchecked_pattern, '%1- [>' .. new_date .. ']', 1)
      api.nvim_buf_set_lines(0, line_number - 1, line_number, false, {rescheduled_line})
    elseif Util.is_before_today(filename) and line:match(unchecked_important_pattern) then
      local rescheduled_line = line:gsub(unchecked_important_pattern, '%1* [>' .. new_date .. ']', 1)
      api.nvim_buf_set_lines(0, line_number - 1, line_number, false, {rescheduled_line})
    else
      api.nvim_buf_set_lines(buffer, line_number - 1, line_number, false, {})
    end

    vim.cmd('write')

    if new_date == 'someday' then
      open_someday()
    else
      Notes.open_daily(new_date)
    end

    local line_count = api.nvim_buf_line_count(0)
    api.nvim_buf_set_lines(0, line_count, line_count, false, {line})
    api.nvim_win_set_cursor(0, {line_count, 0})
  else
    api.nvim_err_writeln('Reschedule only works on open tasks')
  end
end

return Tasks