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

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

---@type integer?
local task_bufnr = nil
---@type integer?
local task_winid = nil
local task_ns = vim.api.nvim_create_namespace('pending')
---@type 'category'|'priority'|nil
local current_view = nil
---@type pending.LineMeta[]
local _meta = {}
---@type table<integer, table<string, boolean>>
local _fold_state = {}

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

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

---@return integer?
function M.winid()
  return task_winid
end

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

function M.clear_winid()
  task_winid = nil
end

function M.close()
  if task_winid and vim.api.nvim_win_is_valid(task_winid) then
    vim.api.nvim_win_close(task_winid, false)
  end
  task_winid = nil
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 = 'pending'
  vim.bo[bufnr].modifiable = true
  vim.bo[bufnr].omnifunc = 'v:lua.require("pending.complete").omnifunc'
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
  vim.wo[winid].winfixheight = 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 /^## .*$/ contains=taskId
      syntax match taskCheckbox /\[!\]/ contained containedin=taskLine
      syntax match taskLine /^\/\d\+\/- \[.\] .*$/ contains=taskId,taskCheckbox
    ]])
  end)
end

---@param above boolean
function M.open_line(above)
  local bufnr = task_bufnr
  if not bufnr or not vim.api.nvim_buf_is_valid(bufnr) then
    return
  end
  local row = vim.api.nvim_win_get_cursor(0)[1]
  local insert_row = above and (row - 1) or row
  vim.bo[bufnr].modifiable = true
  vim.api.nvim_buf_set_lines(bufnr, insert_row, insert_row, false, { '- [ ] ' })
  vim.api.nvim_win_set_cursor(0, { insert_row + 1, 6 })
  vim.cmd('startinsert!')
end

---@return string
function M.get_fold()
  local lnum = vim.v.lnum
  local m = _meta[lnum]
  if not m then
    return '0'
  end
  if m.type == 'header' then
    return '>1'
  elseif m.type == 'task' then
    return '1'
  else
    return '0'
  end
end

---@param bufnr integer
---@param line_meta pending.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
      local due_hl = m.overdue and 'PendingOverdue' or 'PendingDue'
      local virt_parts = {}
      if m.show_category and m.category then
        table.insert(virt_parts, { m.category, 'PendingHeader' })
      end
      if m.recur then
        table.insert(virt_parts, { '\u{21bb} ' .. m.recur, 'PendingRecur' })
      end
      if m.due then
        table.insert(virt_parts, { m.due, due_hl })
      end
      if #virt_parts > 0 then
        for p = 1, #virt_parts - 1 do
          virt_parts[p][1] = virt_parts[p][1] .. '  '
        end
        vim.api.nvim_buf_set_extmark(bufnr, task_ns, row, 0, {
          virt_text = virt_parts,
          virt_text_pos = 'eol',
        })
      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+/')) or 0
        vim.api.nvim_buf_set_extmark(bufnr, task_ns, row, col_start, {
          end_col = #line,
          hl_group = 'PendingDone',
        })
      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 = 'PendingHeader',
      })
    end
  end
end

local function setup_highlights()
  vim.api.nvim_set_hl(0, 'PendingHeader', { link = 'Title', default = true })
  vim.api.nvim_set_hl(0, 'PendingDue', { link = 'DiagnosticHint', default = true })
  vim.api.nvim_set_hl(0, 'PendingOverdue', { link = 'DiagnosticError', default = true })
  vim.api.nvim_set_hl(0, 'PendingDone', { link = 'Comment', default = true })
  vim.api.nvim_set_hl(0, 'PendingPriority', { link = 'DiagnosticWarn', default = true })
  vim.api.nvim_set_hl(0, 'PendingRecur', { link = 'DiagnosticInfo', default = true })
end

local function snapshot_folds(bufnr)
  if current_view ~= 'category' then
    return
  end
  for _, winid in ipairs(vim.fn.win_findbuf(bufnr)) do
    local state = {}
    vim.api.nvim_win_call(winid, function()
      for lnum, m in ipairs(_meta) do
        if m.type == 'header' and m.category then
          if vim.fn.foldclosed(lnum) ~= -1 then
            state[m.category] = true
          end
        end
      end
    end)
    _fold_state[winid] = state
  end
end

local function restore_folds(bufnr)
  if current_view ~= 'category' then
    return
  end
  for _, winid in ipairs(vim.fn.win_findbuf(bufnr)) do
    local state = _fold_state[winid]
    if state and next(state) ~= nil then
      vim.api.nvim_win_call(winid, function()
        vim.cmd('normal! zx')
        local saved = vim.api.nvim_win_get_cursor(0)
        for lnum, m in ipairs(_meta) do
          if m.type == 'header' and m.category and state[m.category] then
            vim.api.nvim_win_set_cursor(0, { lnum, 0 })
            vim.cmd('normal! zc')
          end
        end
        vim.api.nvim_win_set_cursor(0, saved)
      end)
      _fold_state[winid] = nil
    end
  end
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
  vim.api.nvim_buf_set_name(bufnr, 'pending://' .. current_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

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

  setup_syntax(bufnr)
  apply_extmarks(bufnr, line_meta)

  for _, winid in ipairs(vim.fn.win_findbuf(bufnr)) do
    if current_view == 'category' then
      vim.wo[winid].foldmethod = 'expr'
      vim.wo[winid].foldexpr = 'v:lua.require("pending.buffer").get_fold()'
      vim.wo[winid].foldlevel = 99
      vim.wo[winid].foldenable = true
    else
      vim.wo[winid].foldmethod = 'manual'
      vim.wo[winid].foldenable = false
    end
  end
  restore_folds(bufnr)
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_winid and vim.api.nvim_win_is_valid(task_winid) then
    vim.api.nvim_set_current_win(task_winid)
    M.render(task_bufnr)
    return task_bufnr --[[@as integer]]
  end

  if not (task_bufnr and vim.api.nvim_buf_is_valid(task_bufnr)) then
    task_bufnr = vim.api.nvim_create_buf(true, false)
    set_buf_options(task_bufnr)
  end

  vim.cmd('botright new')
  task_winid = vim.api.nvim_get_current_win()
  vim.api.nvim_win_set_buf(task_winid, task_bufnr)
  local h = config.get().drawer_height
  if h and h > 0 then
    vim.api.nvim_win_set_height(task_winid, h)
  end
  set_win_options(task_winid)

  M.render(task_bufnr)

  return task_bufnr
end

return M