local config = require('todo.config')
local store = require('todo.store')
local views = require('todo.views')

---@class todo.buffer
local M = {}

---@type integer?
local task_bufnr = nil
local task_ns = vim.api.nvim_create_namespace('todo')
---@type 'category'|'priority'|nil
local current_view = nil
---@type todo.LineMeta[]
local _meta = {}

---@return todo.LineMeta[]
function M.meta()
  return _meta
end

---@return integer?
function M.bufnr()
  return task_bufnr
end

---@return string?
function M.current_view_name()
  return current_view
end

---@param bufnr integer
local function set_buf_options(bufnr)
  vim.bo[bufnr].buftype = 'acwrite'
  vim.bo[bufnr].bufhidden = 'hide'
  vim.bo[bufnr].swapfile = false
  vim.bo[bufnr].filetype = 'todo'
  vim.bo[bufnr].modifiable = true
end

---@param winid integer
local function set_win_options(winid)
  vim.wo[winid].conceallevel = 3
  vim.wo[winid].concealcursor = 'nvic'
  vim.wo[winid].wrap = false
  vim.wo[winid].number = false
  vim.wo[winid].relativenumber = false
  vim.wo[winid].signcolumn = 'no'
  vim.wo[winid].foldcolumn = '0'
  vim.wo[winid].spell = false
  vim.wo[winid].cursorline = true
end

---@param bufnr integer
local function setup_syntax(bufnr)
  vim.api.nvim_buf_call(bufnr, function()
    vim.cmd([[
      syntax clear
      syntax match taskId /^\/\d\+\// conceal
      syntax match taskHeader /^\S.*$/ contains=taskId
      syntax match taskPriority /! / contained containedin=taskLine
      syntax match taskLine /^\/\d\+\/  .*$/ contains=taskId,taskPriority
    ]])
  end)
end

---@param bufnr integer
local function setup_indentexpr(bufnr)
  vim.bo[bufnr].indentexpr = 'v:lua.require("todo.buffer").get_indent()'
end

---@return integer
function M.get_indent()
  local lnum = vim.v.lnum
  if lnum <= 1 then
    return 0
  end
  local prev = vim.fn.getline(lnum - 1)
  if prev == '' or prev:match('^%S') then
    return 0
  end
  return 2
end

---@param bufnr integer
---@param line_meta todo.LineMeta[]
local function apply_extmarks(bufnr, line_meta)
  vim.api.nvim_buf_clear_namespace(bufnr, task_ns, 0, -1)
  for i, m in ipairs(line_meta) do
    local row = i - 1
    if m.type == 'task' then
      if m.due then
        vim.api.nvim_buf_set_extmark(bufnr, task_ns, row, 0, {
          virt_text = { { m.due, 'TodoDue' } },
          virt_text_pos = 'right_align',
        })
      end
      if m.status == 'done' then
        local line = vim.api.nvim_buf_get_lines(bufnr, row, row + 1, false)[1] or ''
        local col_start = line:find('/%d+/') and select(2, line:find('/%d+/')) + 2 or 0
        vim.api.nvim_buf_set_extmark(bufnr, task_ns, row, col_start, {
          end_col = #line,
          hl_group = 'TodoDone',
        })
      end
    elseif m.type == 'header' then
      local line = vim.api.nvim_buf_get_lines(bufnr, row, row + 1, false)[1] or ''
      vim.api.nvim_buf_set_extmark(bufnr, task_ns, row, 0, {
        end_col = #line,
        hl_group = 'TodoHeader',
      })
    end
  end
end

local function setup_highlights()
  local function hl(name, opts)
    if vim.fn.hlexists(name) == 0 or vim.tbl_isempty(vim.api.nvim_get_hl(0, { name = name })) then
      vim.api.nvim_set_hl(0, name, opts)
    end
  end
  hl('TodoHeader', { bold = true })
  hl('TodoDue', { fg = '#888888', italic = true })
  hl('TodoDone', { strikethrough = true, fg = '#666666' })
  hl('TodoPriority', { fg = '#e06c75', bold = true })
end

---@param bufnr? integer
function M.render(bufnr)
  bufnr = bufnr or task_bufnr
  if not bufnr or not vim.api.nvim_buf_is_valid(bufnr) then
    return
  end

  current_view = current_view or config.get().default_view
  local tasks = store.active_tasks()

  local lines, line_meta
  if current_view == 'priority' then
    lines, line_meta = views.priority_view(tasks)
  else
    lines, line_meta = views.category_view(tasks)
  end

  _meta = line_meta

  vim.bo[bufnr].modifiable = true
  vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, lines)
  vim.bo[bufnr].modified = false

  setup_syntax(bufnr)
  apply_extmarks(bufnr, line_meta)
end

function M.toggle_view()
  if current_view == 'category' then
    current_view = 'priority'
  else
    current_view = 'category'
  end
  M.render()
end

---@return integer bufnr
function M.open()
  setup_highlights()
  store.load()

  if task_bufnr and vim.api.nvim_buf_is_valid(task_bufnr) then
    local wins = vim.fn.win_findbuf(task_bufnr)
    if #wins > 0 then
      vim.api.nvim_set_current_win(wins[1])
      M.render(task_bufnr)
      return task_bufnr
    end
    vim.api.nvim_set_current_buf(task_bufnr)
    set_win_options(vim.api.nvim_get_current_win())
    M.render(task_bufnr)
    return task_bufnr
  end

  task_bufnr = vim.api.nvim_create_buf(true, false)
  vim.api.nvim_buf_set_name(task_bufnr, 'todo://')

  set_buf_options(task_bufnr)
  setup_indentexpr(task_bufnr)
  vim.api.nvim_set_current_buf(task_bufnr)
  set_win_options(vim.api.nvim_get_current_win())

  M.render(task_bufnr)

  return task_bufnr
end

return M