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

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

---@type pending.Store?
local _store = nil

---@type integer?
local task_bufnr = nil
---@type integer?
local task_winid = nil
local ns_eol = vim.api.nvim_create_namespace('pending_eol')
local ns_inline = vim.api.nvim_create_namespace('pending_inline')
---@type 'category'|'priority'|nil
local current_view = nil
---@type pending.LineMeta[]
local _meta = {}
---@type table<integer, table<string, boolean>>
local _fold_state = {}
---@type boolean
local _initial_fold_loaded = false
---@type string[]
local _filter_predicates = {}
---@type table<integer, true>
local _hidden_ids = {}
---@type table<integer, true>
local _dirty_rows = {}
---@type boolean
local _on_bytes_active = false
---@type boolean
local _rendering = false

---@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

---@param s pending.Store?
---@return nil
function M.set_store(s)
  _store = s
end

---@return pending.Store?
function M.store()
  return _store
end

---@return string[]
function M.filter_predicates()
  return _filter_predicates
end

---@return table<integer, true>
function M.hidden_ids()
  return _hidden_ids
end

---@param predicates string[]
---@param hidden table<integer, true>
---@return nil
function M.set_filter(predicates, hidden)
  _filter_predicates = predicates
  _hidden_ids = hidden
end

---@return nil
function M.clear_winid()
  task_winid = nil
end

---@param winid integer
---@return nil
function M.update_winid(winid)
  task_winid = winid
end

---@param b? integer
---@return nil
function M.clear_marks(b)
  local bufnr = b or task_bufnr
  vim.api.nvim_buf_clear_namespace(bufnr, ns_eol, 0, -1)
  vim.api.nvim_buf_clear_namespace(bufnr, ns_inline, 0, -1)
end

---@param b integer
---@param row integer
---@return nil
function M.clear_inline_row(b, row)
  vim.api.nvim_buf_clear_namespace(b, ns_inline, row - 1, row)
end

---@return table<integer, true>
function M.dirty_rows()
  return _dirty_rows
end

---@return nil
function M.clear_dirty_rows()
  _dirty_rows = {}
end

---@param bufnr integer
---@param row integer
---@param m pending.LineMeta
---@param icons table
local function apply_inline_row(bufnr, row, m, icons)
  if m.type == 'filter' then
    local line = vim.api.nvim_buf_get_lines(bufnr, row, row + 1, false)[1] or ''
    vim.api.nvim_buf_set_extmark(bufnr, ns_inline, row, 0, {
      end_col = #line,
      hl_group = 'PendingFilter',
    })
  elseif m.type == 'task' then
    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, ns_inline, row, col_start, {
        end_col = #line,
        hl_group = 'PendingDone',
      })
    elseif m.status == 'blocked' 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, ns_inline, row, col_start, {
        end_col = #line,
        hl_group = 'PendingBlocked',
      })
    end
    local line = vim.api.nvim_buf_get_lines(bufnr, row, row + 1, false)[1] or ''
    local bracket_col = (line:find('%[') or 1) - 1
    local icon, icon_hl
    if m.status == 'done' then
      icon, icon_hl = icons.done, 'PendingDone'
    elseif m.status == 'wip' then
      icon, icon_hl = icons.wip or '>', 'PendingWip'
    elseif m.status == 'blocked' then
      icon, icon_hl = icons.blocked or '=', 'PendingBlocked'
    elseif m.priority and m.priority >= 3 then
      icon, icon_hl = icons.priority, 'PendingPriority3'
    elseif m.priority and m.priority == 2 then
      icon, icon_hl = icons.priority, 'PendingPriority2'
    elseif m.priority and m.priority > 0 then
      icon, icon_hl = icons.priority, 'PendingPriority'
    else
      icon, icon_hl = icons.pending, 'Normal'
    end
    vim.api.nvim_buf_set_extmark(bufnr, ns_inline, row, bracket_col, {
      virt_text = { { '[' .. icon .. ']', icon_hl } },
      virt_text_pos = 'overlay',
      priority = 100,
    })
  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, ns_inline, row, 0, {
      end_col = #line,
      hl_group = 'PendingHeader',
    })
    vim.api.nvim_buf_set_extmark(bufnr, ns_inline, row, 0, {
      virt_text = { { icons.category .. ' ', 'PendingHeader' } },
      virt_text_pos = 'overlay',
      priority = 100,
    })
  end
end

---@param line string
---@return string?
local function infer_status(line)
  local ch = line:match('^/%d+/- %[(.)%]') or line:match('^- %[(.)%]')
  if not ch then
    return nil
  end
  if ch == 'x' then
    return 'done'
  elseif ch == '>' then
    return 'wip'
  elseif ch == '=' then
    return 'blocked'
  end
  return 'pending'
end

---@param bufnr integer
---@return nil
function M.reapply_dirty_inline(bufnr)
  if not next(_dirty_rows) then
    return
  end
  local icons = config.get().icons
  for row in pairs(_dirty_rows) do
    local m = _meta[row]
    if m and m.type == 'task' then
      local line = vim.api.nvim_buf_get_lines(bufnr, row - 1, row, false)[1] or ''
      m.status = infer_status(line) or m.status
    end
    if m then
      vim.api.nvim_buf_clear_namespace(bufnr, ns_inline, row - 1, row)
      apply_inline_row(bufnr, row - 1, m, icons)
    end
  end
  _dirty_rows = {}
end

---@param bufnr integer
---@return nil
function M.attach_bytes(bufnr)
  if _on_bytes_active then
    return
  end
  _on_bytes_active = true
  vim.api.nvim_buf_attach(bufnr, false, {
    on_bytes = function(_, buf, _, start_row, _, _, old_end_row, _, _, new_end_row, _, _)
      if buf ~= task_bufnr then
        _on_bytes_active = false
        return true
      end
      if _rendering then
        return
      end
      local delta = new_end_row - old_end_row
      if delta > 0 then
        for _ = 1, delta do
          table.insert(_meta, start_row + 2, { type = 'task' })
        end
      elseif delta < 0 then
        for _ = 1, -delta do
          if _meta[start_row + 2] then
            table.remove(_meta, start_row + 2)
          end
        end
      end
      for r = start_row + 1, start_row + 1 + math.max(0, new_end_row) do
        _dirty_rows[r] = true
      end
    end,
  })
end

---@return nil
function M.persist_folds()
  log.debug(
    ('persist_folds: view=%s store=%s'):format(tostring(current_view), tostring(_store ~= nil))
  )
  if current_view ~= 'category' or not _store then
    log.debug('persist_folds: early return (view or store)')
    return
  end
  local bufnr = task_bufnr
  if not bufnr or not vim.api.nvim_buf_is_valid(bufnr) then
    log.debug('persist_folds: early return (no valid bufnr)')
    return
  end
  local folded = {}
  local seen = {}
  local wins = vim.fn.win_findbuf(bufnr)
  log.debug(
    ('persist_folds: checking %d windows for bufnr=%d, meta has %d entries'):format(
      #wins,
      bufnr,
      #_meta
    )
  )
  for _, winid in ipairs(wins) do
    if vim.api.nvim_win_is_valid(winid) then
      vim.api.nvim_win_call(winid, function()
        for lnum, m in ipairs(_meta) do
          if m.type == 'header' and m.category and not seen[m.category] then
            local closed = vim.fn.foldclosed(lnum)
            log.debug(
              ('persist_folds: win=%d lnum=%d cat=%s foldclosed=%d'):format(
                winid,
                lnum,
                m.category,
                closed
              )
            )
            if closed ~= -1 then
              seen[m.category] = true
              table.insert(folded, m.category)
            end
          end
        end
      end)
    end
  end
  log.debug(
    ('persist_folds: saving %d folded categories: %s'):format(#folded, table.concat(folded, ', '))
  )
  _store:set_folded_categories(folded)
end

---@return nil
function M.close()
  if not task_winid or not vim.api.nvim_win_is_valid(task_winid) then
    task_winid = nil
    return
  end
  M.persist_folds()
  if _store then
    _store:save()
  end
  local wins = vim.api.nvim_list_wins()
  if #wins == 1 then
    vim.cmd.enew()
  else
    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].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
---@return nil
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
  local meta_pos = insert_row + 1

  _rendering = true
  vim.bo[bufnr].modifiable = true
  vim.api.nvim_buf_set_lines(bufnr, insert_row, insert_row, false, { '- [ ] ' })
  _rendering = false

  table.insert(_meta, meta_pos, { type = 'task' })

  local icons = config.get().icons
  local total = vim.api.nvim_buf_line_count(bufnr)
  for r = meta_pos, math.min(meta_pos + 1, total) do
    vim.api.nvim_buf_clear_namespace(bufnr, ns_inline, r - 1, r)
    local m = _meta[r]
    if m then
      apply_inline_row(bufnr, r - 1, m, icons)
    end
  end

  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

---@class pending.EolSegment
---@field type 'specifier'|'literal'
---@field key? 'c'|'r'|'d'
---@field text? string

---@param fmt string
---@return pending.EolSegment[]
local function parse_eol_format(fmt)
  local segments = {}
  local pos = 1
  local len = #fmt
  while pos <= len do
    if fmt:sub(pos, pos) == '%' and pos + 1 <= len then
      local key = fmt:sub(pos + 1, pos + 1)
      if key == 'c' or key == 'r' or key == 'd' then
        table.insert(segments, { type = 'specifier', key = key })
        pos = pos + 2
      else
        table.insert(segments, { type = 'literal', text = '%' .. key })
        pos = pos + 2
      end
    else
      local next_pct = fmt:find('%%', pos + 1)
      local chunk = next_pct and fmt:sub(pos, next_pct - 1) or fmt:sub(pos)
      table.insert(segments, { type = 'literal', text = chunk })
      pos = pos + #chunk
    end
  end
  return segments
end

---@param segments pending.EolSegment[]
---@param m pending.LineMeta
---@param icons pending.Icons
---@return string[][]
local function build_eol_virt(segments, m, icons)
  local due_hl = m.overdue and 'PendingOverdue' or 'PendingDue'
  local resolved = {}
  for i, seg in ipairs(segments) do
    if seg.type == 'specifier' then
      local text, hl
      if seg.key == 'c' and m.show_category and m.category then
        text = icons.category .. ' ' .. m.category
        hl = 'PendingHeader'
      elseif seg.key == 'r' and m.recur then
        text = icons.recur .. ' ' .. m.recur
        hl = 'PendingRecur'
      elseif seg.key == 'd' and m.due then
        text = icons.due .. ' ' .. m.due
        hl = due_hl
      end
      resolved[i] = text and { text = text, hl = hl, present = true } or { present = false }
    else
      resolved[i] = { text = seg.text, hl = 'Normal', literal = true }
    end
  end

  local virt_parts = {}
  for i, r in ipairs(resolved) do
    if r.literal then
      local prev_present, next_present = false, false
      for j = i - 1, 1, -1 do
        if not resolved[j].literal then
          prev_present = resolved[j].present
          break
        end
      end
      for j = i + 1, #resolved do
        if not resolved[j].literal then
          next_present = resolved[j].present
          break
        end
      end
      if prev_present and next_present then
        table.insert(virt_parts, { r.text, r.hl })
      end
    elseif r.present then
      table.insert(virt_parts, { r.text, r.hl })
    end
  end
  return virt_parts
end

---@param bufnr integer
---@param line_meta pending.LineMeta[]
local function apply_extmarks(bufnr, line_meta)
  local cfg = config.get()
  local icons = cfg.icons
  local eol_segments = parse_eol_format(cfg.view.eol_format or '%c  %r  %d')
  vim.api.nvim_buf_clear_namespace(bufnr, ns_eol, 0, -1)
  vim.api.nvim_buf_clear_namespace(bufnr, ns_inline, 0, -1)
  for i, m in ipairs(line_meta) do
    local row = i - 1
    if m.type == 'task' then
      local virt_parts = build_eol_virt(eol_segments, m, icons)
      if #virt_parts > 0 then
        vim.api.nvim_buf_set_extmark(bufnr, ns_eol, row, 0, {
          virt_text = virt_parts,
          virt_text_pos = 'eol',
        })
      end
    end
    apply_inline_row(bufnr, row, m, icons)
  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, 'PendingPriority2', { link = 'DiagnosticError', default = true })
  vim.api.nvim_set_hl(0, 'PendingPriority3', { link = 'DiagnosticError', default = true })
  vim.api.nvim_set_hl(0, 'PendingWip', { link = 'DiagnosticInfo', default = true })
  vim.api.nvim_set_hl(0, 'PendingBlocked', { link = 'DiagnosticError', default = true })
  vim.api.nvim_set_hl(0, 'PendingRecur', { link = 'DiagnosticInfo', default = true })
  vim.api.nvim_set_hl(0, 'PendingFilter', { link = 'DiagnosticWarn', default = true })
end

---@return string
function M.get_foldtext()
  local folding = config.resolve_folding()
  if not folding.foldtext then
    return vim.fn.foldtext()
  end
  local line = vim.fn.getline(vim.v.foldstart)
  local cat = line:match('^#%s+(.+)$') or line
  local task_count = vim.v.foldend - vim.v.foldstart
  local icons = config.get().icons
  local result = folding.foldtext
    :gsub('%%c', cat)
    :gsub('%%n', tostring(task_count))
    :gsub('(%d+) (%w+)s%)', function(n, word)
      if n == '1' then
        return n .. ' ' .. word .. ')'
      end
      return n .. ' ' .. word .. 's)'
    end)
  return icons.category .. ' ' .. result
end

local function snapshot_folds(bufnr)
  if current_view ~= 'category' or not config.resolve_folding().enabled then
    return
  end
  for _, winid in ipairs(vim.fn.win_findbuf(bufnr)) do
    if _fold_state[winid] == nil and _initial_fold_loaded then
      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
end

local function restore_folds(bufnr)
  log.debug(
    ('restore_folds: view=%s folding_enabled=%s'):format(
      tostring(current_view),
      tostring(config.resolve_folding().enabled)
    )
  )
  if current_view ~= 'category' or not config.resolve_folding().enabled then
    return
  end
  for _, winid in ipairs(vim.fn.win_findbuf(bufnr)) do
    local state = _fold_state[winid]
    _fold_state[winid] = nil
    log.debug(
      ('restore_folds: win=%d has_fold_state=%s initial_loaded=%s has_store=%s'):format(
        winid,
        tostring(state ~= nil),
        tostring(_initial_fold_loaded),
        tostring(_store ~= nil)
      )
    )
    if not state and not _initial_fold_loaded and _store then
      _initial_fold_loaded = true
      local cats = _store:get_folded_categories()
      log.debug(
        ('restore_folds: loaded %d categories from store: %s'):format(
          #cats,
          table.concat(cats, ', ')
        )
      )
      if #cats > 0 then
        state = {}
        for _, cat in ipairs(cats) do
          state[cat] = true
        end
      end
    end
    if state and next(state) ~= nil then
      local applying = {}
      for k in pairs(state) do
        table.insert(applying, k)
      end
      log.debug(('restore_folds: applying folds for: %s'):format(table.concat(applying, ', ')))
      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
            log.debug(('restore_folds: folding lnum=%d cat=%s'):format(lnum, m.category))
            vim.api.nvim_win_set_cursor(0, { lnum, 0 })
            vim.cmd('normal! zc')
          end
        end
        vim.api.nvim_win_set_cursor(0, saved)
      end)
    end
  end
end

---@param bufnr? integer
---@return nil
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().view.default
  local view_label = current_view == 'priority' and 'queue' or current_view
  vim.api.nvim_buf_set_name(bufnr, 'pending://' .. view_label)
  local all_tasks = _store and _store:active_tasks() or {}
  local tasks = {}
  for _, task in ipairs(all_tasks) do
    if not _hidden_ids[task.id] then
      table.insert(tasks, task)
    end
  end

  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

  if #lines == 0 and #_filter_predicates == 0 then
    local default_cat = config.get().default_category
    lines = { '# ' .. default_cat }
    line_meta = { { type = 'header', category = default_cat } }
  end

  if #_filter_predicates > 0 then
    table.insert(lines, 1, 'FILTER: ' .. table.concat(_filter_predicates, ' '))
    table.insert(line_meta, 1, { type = 'filter' })
  end

  _meta = line_meta
  _dirty_rows = {}

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

  setup_syntax(bufnr)
  apply_extmarks(bufnr, line_meta)

  local folding = config.resolve_folding()
  for _, winid in ipairs(vim.fn.win_findbuf(bufnr)) do
    if current_view == 'category' and folding.enabled 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
      if folding.foldtext then
        vim.wo[winid].foldtext = 'v:lua.require("pending.buffer").get_foldtext()'
      else
        vim.wo[winid].foldtext = 'foldtext()'
      end
    else
      vim.wo[winid].foldmethod = 'manual'
      vim.wo[winid].foldenable = false
    end
  end
  restore_folds(bufnr)
end

---@return nil
function M.toggle_view()
  snapshot_folds(task_bufnr)
  if current_view == 'category' then
    current_view = 'priority'
  else
    current_view = 'category'
  end
  M.render()
end

---@return integer bufnr
function M.open()
  setup_highlights()
  if _store then
    _store:load()
  end

  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)
    M.attach_bytes(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