local api = vim.api
local nvim_on = require('vim._core.util').nvim_on
local lsp = vim.lsp
local util = lsp.util
local method = 'textDocument/onTypeFormatting'

local schedule = vim.schedule
local current_buf = api.nvim_get_current_buf
local get_mode = api.nvim_get_mode

local ns = api.nvim_create_namespace('nvim.lsp.on_type_formatting')
local augroup = api.nvim_create_augroup('nvim.lsp.on_type_formatting', {})

local M = {}

--- @alias vim.lsp.on_type_formatting.BufTriggers table<string, table<integer, vim.lsp.Client>>

--- A map from bufnr -> trigger character -> client ID -> client
--- @type table<integer, vim.lsp.on_type_formatting.BufTriggers>
local buf_handles = {}

--- |lsp-handler| for the `textDocument/onTypeFormatting` method.
---
--- @param err? lsp.ResponseError
--- @param result? lsp.TextEdit[]
--- @param ctx lsp.HandlerContext
local function on_type_formatting(err, result, ctx)
  if err then
    lsp.log.error('on_type_formatting', err)
    return
  end

  local bufnr = assert(ctx.bufnr)

  -- A `null` result is equivalent to an empty `TextEdit[]` result; no work should be done.
  if not result or not api.nvim_buf_is_loaded(bufnr) or util.buf_versions[bufnr] ~= ctx.version then
    return
  end

  local client = assert(vim.lsp.get_client_by_id(ctx.client_id))

  util.apply_text_edits(result, ctx.bufnr, client.offset_encoding)
end

---@param bufnr integer
---@param typed string
---@param triggered_clients vim.lsp.Client[]
---@param idx integer?
---@param client vim.lsp.Client?
local function format_iter(bufnr, typed, triggered_clients, idx, client)
  if not idx or not client then
    return
  end
  ---@type lsp.DocumentOnTypeFormattingParams
  local params = vim.tbl_extend(
    'keep',
    util.make_formatting_params(),
    util.make_position_params(0, client.offset_encoding),
    { ch = typed }
  )
  client:request(method, params, function(...)
    on_type_formatting(...)
    format_iter(bufnr, typed, triggered_clients, next(triggered_clients, idx))
  end, bufnr)
end

---@param typed string
local function on_key(_, typed)
  local mode = get_mode()
  if mode.blocking or mode.mode ~= 'i' then
    return
  end

  local bufnr = current_buf()

  local buf_handle = buf_handles[bufnr]
  if not buf_handle then
    return
  end

  -- LSP expects '\n' for formatting on newline
  if typed == '\r' then
    typed = '\n'
  end

  local triggered_clients = buf_handle[typed]
  if not triggered_clients then
    return
  end

  -- Schedule the formatting to occur *after* the LSP is aware of the inserted character
  schedule(function()
    format_iter(bufnr, typed, triggered_clients, next(triggered_clients))
  end)
end

--- @param client vim.lsp.Client
--- @param bufnr integer
local function detach(client, bufnr)
  local buf_handle = buf_handles[bufnr]
  if not buf_handle then
    return
  end

  local client_id = client.id

  -- Remove this client from its associated trigger characters
  for trigger_char, attached_clients in pairs(buf_handle) do
    attached_clients[client_id] = nil

    -- Remove the trigger character if we detached its last client.
    if not next(attached_clients) then
      buf_handle[trigger_char] = nil
    end
  end

  -- Remove the buf handle and its autocmds if we removed its last client.
  if not next(buf_handle) then
    buf_handles[bufnr] = nil
    api.nvim_clear_autocmds({ group = augroup, buf = bufnr })

    -- Remove the on_key callback if we removed the last buf handle.
    if not next(buf_handles) then
      vim.on_key(nil, ns)
    end
  end
end

--- @param client vim.lsp.Client
--- @param bufnr integer
local function attach(client, bufnr)
  if not client:supports_method(method, bufnr) then
    return
  end

  local client_id = client.id
  ---@type lsp.DocumentOnTypeFormattingOptions
  local otf_capabilities =
    assert(vim.tbl_get(client.server_capabilities, 'documentOnTypeFormattingProvider'))

  -- Set on_key callback, clearing first in case it was already registered.
  vim.on_key(nil, ns)
  vim.on_key(on_key, ns)

  -- Populate the buf handle data. We cannot use defaulttable here because then an empty table will
  -- be created for each unique keystroke
  local buf_handle = buf_handles[bufnr] or {}
  buf_handles[bufnr] = buf_handle

  local trigger = buf_handle[otf_capabilities.firstTriggerCharacter] or {}
  buf_handle[otf_capabilities.firstTriggerCharacter] = trigger
  trigger[client_id] = client

  for _, char in ipairs(otf_capabilities.moreTriggerCharacter or {}) do
    trigger = buf_handle[char] or {}
    buf_handle[char] = trigger
    trigger[client_id] = client
  end

  api.nvim_clear_autocmds({ group = augroup, buf = bufnr })
  nvim_on('LspDetach', augroup, {
    buf = bufnr,
    desc = 'Detach on-type formatting module when the client detaches',
  }, function(ev)
    local detached_client = assert(lsp.get_client_by_id(ev.data.client_id))
    detach(detached_client, bufnr)
  end)
end

nvim_on('LspAttach', nil, {
  desc = 'Enable on-type formatting for all buffers with individually-enabled clients.',
}, function(ev)
  local buf = ev.buf
  local client = assert(lsp.get_client_by_id(ev.data.client_id))
  if client._otf_enabled then
    attach(client, buf)
  end
end)

---@param enable boolean
---@param client vim.lsp.Client
local function toggle_for_client(enable, client)
  local handler = enable and attach or detach

  -- Toggle for buffers already attached.
  for bufnr, _ in pairs(client.attached_buffers) do
    handler(client, bufnr)
  end

  client._otf_enabled = enable
end

---@param enable boolean
local function toggle_globally(enable)
  -- Toggle for clients that have already attached.
  local clients = lsp.get_clients({ method = method })
  for _, client in ipairs(clients) do
    toggle_for_client(enable, client)
  end

  -- If disabling, only clear the attachment autocmd. If enabling, create it as well.
  local group = api.nvim_create_augroup('nvim.lsp.on_type_formatting', { clear = true })
  if enable then
    nvim_on('LspAttach', group, {
      desc = 'Enable on-type formatting for ALL clients by default.',
    }, function(ev)
      local client = assert(lsp.get_client_by_id(ev.data.client_id))
      if client._otf_enabled ~= false then
        attach(client, ev.buf)
      end
    end)
  end
end

--- Optional filters |kwargs|:
--- @inlinedoc
--- @class vim.lsp.on_type_formatting.enable.Filter
--- @field client_id integer? Client ID, or `nil` for all.

--- Enables/disables on-type formatting globally or for the {filter}ed scope. The following are some
--- practical usage examples:
---
--- ```lua
--- -- Enable for all clients
--- vim.lsp.on_type_formatting.enable()
---
--- -- Enable for a specific client
--- vim.api.nvim_create_autocmd('LspAttach', {
---   callback = function(ev)
---     local client_id = ev.data.client_id
---     local client = assert(vim.lsp.get_client_by_id(client_id))
---     if client.name == 'rust-analyzer' then
---       vim.lsp.on_type_formatting.enable(true, { client_id = client_id })
---     end
---   end,
--- })
--- ```
---
--- @param enable? boolean true/nil to enable, false to disable.
--- @param filter vim.lsp.on_type_formatting.enable.Filter?
function M.enable(enable, filter)
  vim.validate('enable', enable, 'boolean', true)
  vim.validate('filter', filter, 'table', true)

  enable = enable ~= false
  filter = filter or {}

  if filter.client_id then
    local client =
      assert(lsp.get_client_by_id(filter.client_id), 'Client not found for id ' .. filter.client_id)
    toggle_for_client(enable, client)
  else
    toggle_globally(enable)
  end
end

return M
