path: root/lua/clever_f/host_adapter.lua

local capabilities = require("clever_f.capabilities")
local domain = require("clever_f.domain")

local M = {}
local unpack_values = table.unpack or unpack
local HostAdapter = {}
HostAdapter.__index = HostAdapter
M.HostAdapter = HostAdapter

M.ActionEffect = {
  NONE = "none",
  ESCAPE = "escape",
  ERROR = "error",
}
M.CONFIGURATION_PREFIX = "clever_f_"
M.CONFIGURATION_GLOBALS = {
  suppress_default_mappings = "clever_f_not_overwrites_standard_mappings",
}

local BOOLEAN_CONFIGURATION = {
  search_current_line_only = true,
  ignore_case = true,
  smart_case = true,
  use_migemo = true,
  fix_key_direction = true,
  show_prompt = true,
  mark_cursor = true,
  hide_cursor_on_cmdline = true,
  mark_char = true,
  mark_direct = true,
  clean_labels_eagerly = true,
}

local adapter_records = setmetatable({}, { __mode = "k" })

local function fail(message, level)
  error(message, (level or 1) + 1)
end

local function current_runtime(options)
  if type(options) == "table" then
    if options.runtime ~= nil then
      return options.runtime
    end
    if options.api ~= nil then
      return options
    end
    return rawget(_G, "vim")
  end
  if options ~= nil and options ~= HostAdapter then
    return options
  end
  return rawget(_G, "vim")
end

local function require_runtime(runtime)
  if type(runtime) ~= "table" or type(runtime.api) ~= "table" then
    fail("HostAdapter requires the Nvim Lua runtime", 3)
  end
  return runtime
end

function HostAdapter.new(options)
  if HostAdapter.is(options) then
    return options
  end
  local adapter = setmetatable({}, HostAdapter)
  local record = {
    runtime = require_runtime(current_runtime(options)),
    next_identity = 1,
    highlights = {},
    timers = {},
    cursor_presentations = {},
    events = {},
    actions = {},
    mappings = {},
    dot_repeat = nil,
    dot_bridge = nil,
    event_order = {},
    action_diagnostics = nil,
    augroup = nil,
  }
  record.event_queue = capabilities.EventQueue.new(function(_, delivery)
    delivery.callback(delivery.name, delivery.payload)
  end)
  adapter_records[adapter] = record
  return adapter
end

function HostAdapter.is(value)
  return type(value) == "table" and adapter_records[value] ~= nil
end

function HostAdapter:runtime()
  return adapter_records[self].runtime
end

function HostAdapter:read_text()
  local lines = self:runtime().api.nvim_buf_get_lines(0, 0, -1, true)
  if #lines == 0 then
    lines = { "" }
  end
  return domain.TextSnapshot.new(lines)
end

function HostAdapter:read_buffer()
  return self:runtime().api.nvim_get_current_buf()
end

function HostAdapter:read_window()
  return self:runtime().api.nvim_get_current_win()
end

function HostAdapter:read_cursor()
  local position = self:runtime().api.nvim_win_get_cursor(0)
  return domain.Position.new(position[1], position[2] + 1)
end

function HostAdapter:read_mode()
  return self:runtime().api.nvim_get_mode().mode
end

local function selection_option(runtime)
  local value = runtime.api.nvim_get_option_value(
    "selection",
    { scope = "global" }
  )
  if value == "exclusive" then
    return domain.SelectionOption.EXCLUSIVE
  end
  return domain.SelectionOption.INCLUSIVE
end

function HostAdapter:read_selection()
  local runtime = self:runtime()
  local context = domain.ModeContext.from_full_mode(self:read_mode())
  local kind = context.visual_kind or context.select_kind
  local option = selection_option(runtime)
  if kind == nil then
    return domain.Selection.inactive(option)
  end
  local raw_anchor = runtime.fn.getpos("v")
  local focus = self:read_cursor()
  local anchor
  if type(raw_anchor) == "table"
    and type(raw_anchor[2]) == "number"
    and raw_anchor[2] > 0
    and type(raw_anchor[3]) == "number"
    and raw_anchor[3] > 0
  then
    anchor = domain.Position.new(raw_anchor[2], raw_anchor[3])
  else
    anchor = focus
  end
  return domain.Selection.active(kind, anchor, focus, option)
end

function HostAdapter:read_count()
  local runtime = self:runtime()
  local count = runtime.v.count1
  if type(count) ~= "number" or count < 1 then
    count = 1
  end
  return domain.Count.new(count)
end

local function configuration_global(name)
  if type(name) ~= "string" or name == "" then
    fail("configuration name must be a nonempty string", 3)
  end
  return M.CONFIGURATION_GLOBALS[name] or M.CONFIGURATION_PREFIX .. name
end

function M.configuration_global(name)
  return configuration_global(name)
end

function HostAdapter:configuration_present(name)
  local global = configuration_global(name)
  return self:runtime().fn.exists("g:" .. global) == 1
end

local function normalize_configuration(name, value)
  if BOOLEAN_CONFIGURATION[name] and type(value) == "number" then
    return value ~= 0
  end
  return value
end

function HostAdapter:read_configuration(name)
  local global = configuration_global(name)
  return normalize_configuration(name, self:runtime().g[global])
end

function HostAdapter:write_configuration(name, value)
  local global = configuration_global(name)
  self:runtime().g[global] = value
end

function HostAdapter:read_encoding()
  local runtime = self:runtime()
  return runtime.api.nvim_get_option_value(
    "encoding",
    { scope = "global" }
  )
end

function HostAdapter:lowercase(value)
  if type(value) ~= "string" then
    fail("case conversion value must be a string", 2)
  end
  local result = self:runtime().fn.tolower(value)
  if type(result) ~= "string" then
    fail("Nvim case conversion must return a string", 2)
  end
  return result
end

function HostAdapter:read_macro_state()
  local register = self:runtime().fn.reg_executing()
  return domain.MacroState.new(register ~= "" and register or nil)
end

local function fold_open_policies(value)
  local result = {}
  for item in tostring(value):gmatch("[^,]+") do
    if item == "hor" then
      item = "horizontal"
    end
    result[#result + 1] = item
  end
  return result
end

function HostAdapter:read_fold_state()
  local runtime = self:runtime()
  local foldopen = runtime.api.nvim_get_option_value(
    "foldopen",
    { scope = "global" }
  )
  local line = self:read_cursor().line
  local closed_levels = runtime.fn.foldclosed(line) == -1 and 0 or 1
  return domain.FoldState.new(
    fold_open_policies(foldopen),
    closed_levels
  )
end

function HostAdapter:read_time_ms()
  local runtime = self:runtime()
  local uv = runtime.uv or runtime.loop
  if type(uv) ~= "table" or type(uv.hrtime) ~= "function" then
    fail("HostAdapter runtime must provide a monotonic clock", 2)
  end
  return uv.hrtime() / 1000000
end

function HostAdapter:read_pending_operator()
  local operator = self:runtime().v.operator
  if operator == nil then
    return ""
  end
  return operator
end

function HostAdapter:apply_cursor(position)
  position = domain.Position.coerce(position)
  self:runtime().api.nvim_win_set_cursor(
    0,
    { position.line, position.byte_column - 1 }
  )
end

function HostAdapter:apply_selection(position)
  if domain.Selection.is(position) then
    if not position.active then
      fail("selection movement requires an active selection", 2)
    end
    position = position.focus
  end
  return self:apply_cursor(position)
end

function HostAdapter:set_operator_inclusive(enabled)
  if type(enabled) ~= "boolean" then
    fail("operator inclusivity must be a Boolean", 2)
  end
  if not enabled then
    return
  end

  local runtime = self:runtime()
  local api = runtime.api
  local selection
  if type(api.nvim_get_option_value) == "function" then
    selection = api.nvim_get_option_value("selection", { scope = "global" })
  end
  if selection ~= "exclusive" then
    api.nvim_cmd({
      cmd = "normal",
      bang = true,
      args = { "v" },
    }, {})
    return
  end
  if type(api.nvim_set_option_value) ~= "function"
    or type(runtime.schedule) ~= "function"
  then
    fail("HostAdapter cannot preserve exclusive selection during an operator", 2)
  end

  api.nvim_set_option_value("selection", "inclusive", { scope = "global" })
  local ok, command_error = pcall(api.nvim_cmd, {
    cmd = "normal",
    bang = true,
    args = { "v" },
  }, {})
  if not ok then
    api.nvim_set_option_value("selection", selection, { scope = "global" })
    error(command_error, 0)
  end
  runtime.schedule(function()
    api.nvim_set_option_value("selection", selection, { scope = "global" })
  end)
end

local function string_bytes(value)
  local bytes = {}
  for index = 1, #value do
    bytes[index] = string.byte(value, index)
  end
  return bytes
end

function HostAdapter:read_input()
  local runtime = self:runtime()
  local value = runtime.fn.getcharstr()
  if type(value) ~= "string" or value == "" then
    fail("Nvim target input must be a nonempty string", 2)
  end
  local bytes = string_bytes(value)
  if #bytes == 3
    and bytes[1] == 0x80
    and bytes[2] == 0xfd
    and bytes[3] == 0x60
  then
    return domain.InputPacket.raw_bytes(bytes)
  end
  if #bytes == 1 and bytes[1] == 27 then
    return domain.InputPacket.special_key("Escape", bytes)
  end
  if bytes[1] == 0x80 then
    local name = type(runtime.fn.keytrans) == "function"
        and runtime.fn.keytrans(value)
      or "Special"
    return domain.InputPacket.special_key(name, value)
  end
  return domain.InputPacket.text(value)
end

function HostAdapter:open_fold(position)
  position = position and domain.Position.coerce(position) or self:read_cursor()
  local runtime = self:runtime()
  if runtime.fn.foldclosed(position.line) == -1 then
    return false
  end
  runtime.api.nvim_cmd({
    cmd = "normal",
    bang = true,
    args = { "zo" },
  }, {})
  return true
end

function HostAdapter:show_prompt(text)
  if type(text) ~= "string" then
    fail("prompt must be a string", 2)
  end
  self:runtime().api.nvim_echo({ { text } }, false, {})
end

function HostAdapter:redraw(kind)
  if kind == "suppressed" then
    return false
  end
  if kind ~= "screen" and kind ~= "full" then
    fail("redraw kind must be screen, full, or suppressed", 2)
  end
  self:runtime().api.nvim_cmd({
    cmd = "redraw",
    bang = kind == "full",
  }, {})
  return true
end

local DIAGNOSTIC_LEVELS = {
  error = "ERROR",
  warning = "WARN",
  info = "INFO",
}

function HostAdapter:emit_diagnostic(level, text)
  local level_name = DIAGNOSTIC_LEVELS[level]
  if level_name == nil then
    fail("diagnostic level must be error, warning, or info", 2)
  end
  if type(text) ~= "string" or text == "" then
    fail("diagnostic text must be a nonempty string", 2)
  end
  local record = adapter_records[self]
  local runtime = record.runtime
  if type(runtime.notify) ~= "function" then
    fail("HostAdapter runtime must provide notify", 2)
  end
  local levels = type(runtime.log) == "table" and runtime.log.levels or {}
  runtime.notify(text, levels[level_name], { title = "clever-f" })
  if record.action_diagnostics ~= nil then
    record.action_diagnostics[level .. "\0" .. text] = true
  end
end

local install_dot_bridge

function HostAdapter:register_dot_repeat(payload, callback)
  if not domain.DotPayload.is(payload) then
    fail("dot-repeat payload must be a DotPayload", 2)
  end
  if callback ~= nil and type(callback) ~= "function" then
    fail("dot-repeat callback must be a function", 2)
  end
  local record = adapter_records[self]
  record.dot_repeat = {
    payload = payload,
    callback = callback,
    operator = self:read_pending_operator(),
  }
  if install_dot_bridge ~= nil then
    install_dot_bridge(self)
  end
  if record.dot_bridge ~= nil then
    record.dot_bridge.awaiting_change = true
  end
  return payload
end

function HostAdapter:dot_repeat_payload()
  local registration = adapter_records[self].dot_repeat
  return registration and registration.payload or nil
end

function HostAdapter:replay_dot(count)
  local registration = adapter_records[self].dot_repeat
  if registration == nil or registration.callback == nil then
    fail("dot repeat is not executable", 2)
  end
  return registration.callback(
    registration.payload,
    domain.Count.new(count)
  )
end

local function next_identity(adapter, prefix)
  local record = adapter_records[adapter]
  local identity = prefix .. "-" .. tostring(record.next_identity)
  record.next_identity = record.next_identity + 1
  return identity
end

local function highlight_exists(runtime, name)
  if type(runtime.fn) == "table" and type(runtime.fn.hlexists) == "function" then
    return runtime.fn.hlexists(name) == 1
  end
  local definition = runtime.api.nvim_get_hl(0, {
    name = name,
    link = true,
    create = false,
  })
  return next(definition) ~= nil
end

function HostAdapter:read_highlight_group(name)
  if type(name) ~= "string" or name == "" then
    fail("highlight group name must be a nonempty string", 2)
  end
  local runtime = self:runtime()
  if not highlight_exists(runtime, name) then
    return nil
  end
  return runtime.api.nvim_get_hl(0, {
    name = name,
    link = true,
    create = false,
  })
end

local function native_highlight_definition(definition, options)
  if type(definition) ~= "table" then
    fail("highlight group definition must be a table", 3)
  end
  options = options or {}
  if type(options) ~= "table" then
    fail("highlight group options must be a table", 3)
  end
  local native = {}
  for key, value in pairs(definition) do
    if key ~= "guifg" and key ~= "guibg" and key ~= "gui" then
      native[key] = value
    end
  end
  if definition.guifg ~= nil then
    native.fg = definition.guifg
  end
  if definition.guibg ~= nil then
    native.bg = definition.guibg
  end
  for key, value in pairs(definition.gui or {}) do
    native[key] = value
  end
  if options.default ~= nil then
    native.default = options.default
  end
  if options.force ~= nil then
    native.force = options.force
  end
  return native
end

function HostAdapter:define_highlight_group(name, definition, options)
  if type(name) ~= "string" or name == "" then
    fail("highlight group name must be a nonempty string", 2)
  end
  options = options or {}
  local runtime = self:runtime()
  if options.default and highlight_exists(runtime, name) then
    return false
  end
  runtime.api.nvim_set_hl(
    0,
    name,
    native_highlight_definition(definition, options)
  )
  return true
end

local function overlay_positions(specification)
  local positions = specification.positions
  if positions == nil and specification.position ~= nil then
    positions = { specification.position }
  end
  if type(positions) ~= "table" then
    fail("highlight positions must be a list", 3)
  end
  local native = {}
  for index, position in ipairs(positions) do
    position = domain.Position.coerce(position)
    native[index] = { position.line, position.byte_column }
  end
  if #native == 0 then
    native[1] = { 0 }
  end
  return native
end

local function overlay_priority(value)
  if value == "high" then
    return 100
  end
  if value == "ordinary" or value == nil then
    return 10
  end
  if type(value) == "number" then
    return value
  end
  fail("highlight priority must be high, ordinary, or numeric", 3)
end

function HostAdapter:create_highlight(specification)
  if type(specification) ~= "table" then
    fail("highlight specification must be a table", 2)
  end
  if type(specification.group) ~= "string" or specification.group == "" then
    fail("highlight group must be a nonempty string", 2)
  end
  if specification.window == nil then
    fail("highlight window must identify its Nvim window", 2)
  end
  local record = adapter_records[self]
  local identity = specification.identity or next_identity(self, "highlight")
  if record.highlights[identity] ~= nil then
    fail("highlight identity is already active", 2)
  end
  local match_id = record.runtime.fn.matchaddpos(
    specification.group,
    overlay_positions(specification),
    overlay_priority(specification.priority),
    -1,
    { window = specification.window }
  )
  if type(match_id) ~= "number" or match_id < 0 then
    fail("Nvim could not create the window-local highlight", 2)
  end
  record.highlights[identity] = {
    match_id = match_id,
    window = specification.window,
  }
  return identity
end

function HostAdapter:remove_highlight(identity)
  local record = adapter_records[self]
  local resource = record.highlights[identity]
  if resource == nil then
    return false
  end
  record.highlights[identity] = nil
  record.runtime.fn.matchdelete(resource.match_id, resource.window)
  return true
end

local function nonnegative_integer(value, name)
  if type(value) ~= "number"
    or value < 0
    or value ~= math.floor(value)
    or value == math.huge
  then
    fail((name or "value") .. " must be a nonnegative integer", 3)
  end
  return value
end

function HostAdapter:supports_timers()
  local fn = self:runtime().fn
  return type(fn) == "table"
    and type(fn.timer_start) == "function"
    and type(fn.timer_stop) == "function"
end

function HostAdapter:start_timer(delay_ms, callback)
  nonnegative_integer(delay_ms, "timer delay")
  if type(callback) ~= "function" then
    fail("timer callback must be a function", 2)
  end
  if not self:supports_timers() then
    return nil
  end
  local record = adapter_records[self]
  local identity = next_identity(self, "timer")
  local timer_id = record.runtime.fn.timer_start(delay_ms, function()
    local resource = record.timers[identity]
    if resource == nil or not resource.active then
      return
    end
    record.timers[identity] = nil
    callback(identity)
  end)
  if type(timer_id) ~= "number" or timer_id < 0 then
    fail("Nvim could not start the timer", 2)
  end
  record.timers[identity] = {
    timer_id = timer_id,
    active = true,
  }
  return identity
end

function HostAdapter:stop_timer(identity)
  local record = adapter_records[self]
  local resource = record.timers[identity]
  if resource == nil or not resource.active then
    return false
  end
  record.timers[identity] = nil
  record.runtime.fn.timer_stop(resource.timer_id)
  return true
end

local function event_names(value)
  if type(value) == "string" then
    value = { value }
  end
  if type(value) ~= "table" or #value == 0 then
    fail("event names must be a nonempty list", 3)
  end
  local names = {}
  local set = {}
  for index, name in ipairs(value) do
    if type(name) ~= "string" or name == "" then
      fail("event name must be a nonempty string", 3)
    end
    if not set[name] then
      names[#names + 1] = name
      set[name] = true
    end
  end
  return names, set
end

local function event_payload(adapter, event)
  local payload = {
    buffer = event.buf,
    file = event.file,
    match = event.match,
    data = event.data,
  }
  local api = adapter:runtime().api
  if type(api.nvim_get_current_win) == "function" then
    payload.window = api.nvim_get_current_win()
  end
  return payload
end

local function event_augroup(record)
  if record.augroup == nil then
    record.augroup = record.runtime.api.nvim_create_augroup(
      "clever_f",
      { clear = true }
    )
  end
  return record.augroup
end

local function queue_event(record, name, payload, callback)
  return record.event_queue:emit(name, {
    name = name,
    payload = payload,
    callback = callback,
  })
end

function HostAdapter:register_events(names, callback, options)
  local name_set
  names, name_set = event_names(names)
  if type(callback) ~= "function" then
    fail("event callback must be a function", 2)
  end
  options = options or {}
  if type(options) ~= "table" then
    fail("event registration options must be a table", 2)
  end
  local record = adapter_records[self]
  local identity = next_identity(self, "event-registration")
  local autocmd_options = {
    group = event_augroup(record),
    desc = "clever-f " .. table.concat(names, "/"),
    callback = function(event)
      local resource = record.events[identity]
      if resource ~= nil and resource.active then
        queue_event(
          record,
          event.event,
          event_payload(self, event),
          resource.callback
        )
      end
    end,
  }
  if options.buffer ~= nil then
    autocmd_options.buffer = options.buffer
  end
  local autocmd_id = record.runtime.api.nvim_create_autocmd(
    names,
    autocmd_options
  )
  record.events[identity] = {
    autocmd_id = autocmd_id,
    names = names,
    name_set = name_set,
    callback = callback,
    buffer = options.buffer,
    active = true,
  }
  record.event_order[#record.event_order + 1] = identity
  return identity
end

function HostAdapter:remove_event_registration(identity)
  local record = adapter_records[self]
  local resource = record.events[identity]
  if resource == nil or not resource.active then
    return false
  end
  resource.active = false
  record.runtime.api.nvim_del_autocmd(resource.autocmd_id)
  return true
end

local DOT_MOTION_MAPPING = "<Plug>(clever-f-dot-motion)"

local function dot_bridge_supported(runtime)
  return type(runtime.keymap) == "table"
    and type(runtime.keymap.set) == "function"
    and type(runtime.keymap.del) == "function"
    and type(runtime.fn.maparg) == "function"
    and type(runtime.fn.mapset) == "function"
    and type(runtime.api.nvim_feedkeys) == "function"
end

local function restore_dot_mapping(record)
  local bridge = record.dot_bridge
  if bridge == nil or not bridge.active then
    return false
  end
  bridge.active = false
  pcall(record.runtime.keymap.del, "n", ".")
  if type(bridge.previous_mapping) == "table"
    and next(bridge.previous_mapping) ~= nil
  then
    record.runtime.fn.mapset("n", false, bridge.previous_mapping)
  end
  return true
end

local function dot_replay_keys(runtime, count, operator)
  local prefix = count > 0 and tostring(count) or ""
  local keys = prefix .. operator .. DOT_MOTION_MAPPING
  if type(runtime.keycode) == "function" then
    return runtime.keycode(keys)
  end
  return runtime.api.nvim_replace_termcodes(keys, true, false, true)
end

install_dot_bridge = function(adapter)
  local record = adapter_records[adapter]
  local runtime = record.runtime
  if not dot_bridge_supported(runtime) then
    return nil
  end
  local bridge = record.dot_bridge
  if bridge == nil then
    bridge = {
      active = false,
      awaiting_change = false,
      previous_mapping = nil,
    }
    record.dot_bridge = bridge
    runtime.keymap.set("o", DOT_MOTION_MAPPING, function()
      local registration = record.dot_repeat
      if registration == nil or registration.callback == nil then
        return
      end
      local outcome = registration.callback(
        registration.payload,
        adapter:read_count()
      )
      if domain.ActionOutcome.is(outcome) then
        adapter:translate_action_outcome(outcome)
      end
    end, {
      silent = true,
      remap = false,
      desc = "clever-f dot motion",
    })
    local has_cmd_atom = type(runtime.fn.exists) == "function"
      and runtime.fn.exists("##CmdAtom") == 1
    local ownership_events = has_cmd_atom
        and "CmdAtom"
      or { "TextChanged", "TextChangedI", "TextChangedP" }
    runtime.api.nvim_create_autocmd(ownership_events, {
      group = event_augroup(record),
      desc = "clever-f dot ownership",
      callback = function(event)
        if has_cmd_atom and not (event.data and event.data.changed) then
          return
        end
        if bridge.awaiting_change then
          bridge.awaiting_change = false
          return
        end
        restore_dot_mapping(record)
      end,
    })
  end
  if not bridge.active then
    bridge.previous_mapping = runtime.fn.maparg(".", "n", false, true)
    runtime.keymap.set("n", ".", function()
      local registration = record.dot_repeat
      if registration == nil or registration.operator == "" then
        restore_dot_mapping(record)
        runtime.api.nvim_feedkeys(".", "n", false)
        return
      end
      bridge.awaiting_change = true
      local count = runtime.v.count or 0
      runtime.api.nvim_feedkeys(
        dot_replay_keys(runtime, count, registration.operator),
        "n",
        false
      )
    end, {
      silent = true,
      remap = false,
      desc = "clever-f dot repeat",
    })
    bridge.active = true
  end
  return bridge
end

function HostAdapter:deliver_event(name, payload)
  if type(name) ~= "string" or name == "" then
    fail("event name must be a nonempty string", 2)
  end
  payload = payload or {}
  local record = adapter_records[self]
  local event_buffer = payload.buffer
  for _, identity in ipairs(record.event_order) do
    local resource = record.events[identity]
    if resource.active
      and resource.name_set[name]
      and (resource.buffer == nil
        or event_buffer == nil
        or resource.buffer == event_buffer)
    then
      queue_event(record, name, payload, resource.callback)
    end
  end
end

function HostAdapter:begin_action_transition()
  local record = adapter_records[self]
  record.action_diagnostics = {}
  return record.event_queue:begin_transition()
end

function HostAdapter:commit_action_transition(token)
  local record = adapter_records[self]
  local result = record.event_queue:commit_transition(token)
  record.action_diagnostics = nil
  return result
end

local function terminal_cursor_option(runtime)
  return runtime.fn.eval("&t_ve")
end

local function set_terminal_cursor_option(runtime, value)
  runtime.api.nvim_cmd({
    cmd = "let",
    args = { "&t_ve", "=", runtime.fn.string(value) },
  }, {})
end

function HostAdapter:supports_cursor_presentation()
  local runtime = self:runtime()
  return type(runtime.api.nvim_get_option_value) == "function"
    and type(runtime.api.nvim_set_option_value) == "function"
    and type(runtime.api.nvim_cmd) == "function"
    and type(runtime.fn) == "table"
    and type(runtime.fn.exists) == "function"
    and runtime.fn.exists("+t_ve") == 1
    and type(runtime.fn.eval) == "function"
    and type(runtime.fn.string) == "function"
end

function HostAdapter:suppress_cursor_presentation()
  if not self:supports_cursor_presentation() then
    return nil
  end
  local record = adapter_records[self]
  local runtime = record.runtime
  local identity = next_identity(self, "cursor-presentation")
  local saved = {
    guicursor = runtime.api.nvim_get_option_value(
      "guicursor",
      { scope = "global" }
    ),
    terminal_cursor = terminal_cursor_option(runtime),
  }
  runtime.api.nvim_set_option_value(
    "guicursor",
    "a:ver1",
    { scope = "global" }
  )
  local ok, failure = pcall(set_terminal_cursor_option, runtime, "")
  if not ok then
    runtime.api.nvim_set_option_value(
      "guicursor",
      saved.guicursor,
      { scope = "global" }
    )
    error(failure, 0)
  end
  record.cursor_presentations[identity] = saved
  return identity
end

function HostAdapter:restore_cursor_presentation(identity)
  local record = adapter_records[self]
  local saved = record.cursor_presentations[identity]
  if saved == nil then
    return false
  end
  record.cursor_presentations[identity] = nil
  record.runtime.api.nvim_set_option_value(
    "guicursor",
    saved.guicursor,
    { scope = "global" }
  )
  set_terminal_cursor_option(record.runtime, saved.terminal_cursor)
  return true
end

local function escape_key(runtime)
  if type(runtime.keycode) == "function" then
    return runtime.keycode("<Esc>")
  end
  if type(runtime.api.nvim_replace_termcodes) == "function" then
    return runtime.api.nvim_replace_termcodes("<Esc>", true, false, true)
  end
  return string.char(27)
end

function HostAdapter:return_escape()
  local runtime = self:runtime()
  if type(runtime.api.nvim_feedkeys) ~= "function" then
    fail("HostAdapter runtime must provide nvim_feedkeys", 2)
  end
  runtime.api.nvim_feedkeys(escape_key(runtime), "n", false)
end

function HostAdapter:emit_action_error(text)
  return self:emit_diagnostic("error", text)
end

function HostAdapter:translate_action_outcome(outcome)
  if not domain.ActionOutcome.is(outcome) then
    fail("host action translation requires an ActionOutcome", 2)
  end
  if outcome.kind == domain.ActionKind.ESCAPE then
    self:return_escape()
    return M.ActionEffect.ESCAPE
  end
  if outcome.kind == domain.ActionKind.ERROR then
    local diagnostics = adapter_records[self].action_diagnostics
    local key = "error\0" .. outcome.diagnostic
    if diagnostics == nil or not diagnostics[key] then
      self:emit_action_error(outcome.diagnostic)
    end
    return M.ActionEffect.ERROR
  end
  return M.ActionEffect.NONE
end

local function packed(...)
  return { n = select("#", ...), ... }
end

local function invoke_callback(adapter, callback, ...)
  local arguments = packed(...)
  local token = adapter:begin_action_transition()
  local results = packed(pcall(function()
    local values = packed(callback(unpack_values(arguments, 1, arguments.n)))
    if domain.ActionOutcome.is(values[1]) then
      adapter:translate_action_outcome(values[1])
    end
    return unpack_values(values, 1, values.n)
  end))
  local commit = packed(pcall(adapter.commit_action_transition, adapter, token))
  if not results[1] then
    error(results[2], 0)
  end
  if not commit[1] then
    error(commit[2], 0)
  end
  return unpack_values(results, 2, results.n)
end

function HostAdapter:register_action(name, callback)
  if type(name) ~= "string" or name == "" then
    fail("action name must be a nonempty string", 2)
  end
  if type(callback) ~= "function" then
    fail("action callback must be a function", 2)
  end
  local actions = adapter_records[self].actions
  if actions[name] ~= nil then
    fail("action is already registered", 2)
  end
  actions[name] = callback
  return name
end

function HostAdapter:invoke_action(name, ...)
  local callback = adapter_records[self].actions[name]
  if callback == nil then
    fail("action is not registered", 2)
  end
  return invoke_callback(self, callback, ...)
end

function HostAdapter:invoke_callback(callback, ...)
  if type(callback) ~= "function" then
    fail("action callback must be a function", 2)
  end
  return invoke_callback(self, callback, ...)
end

local function mapping_modes(value)
  if type(value) == "string" then
    value = { value }
  end
  if type(value) ~= "table" or #value == 0 then
    fail("mapping modes must be a nonempty list", 3)
  end
  local result = {}
  for index, mode in ipairs(value) do
    if type(mode) ~= "string" or mode == "" then
      fail("mapping mode must be a nonempty string", 3)
    end
    result[index] = mode
  end
  return result
end

function HostAdapter:register_mapping(modes, lhs, action, options)
  modes = mapping_modes(modes)
  if type(lhs) ~= "string" or lhs == "" then
    fail("mapping lhs must be a nonempty string", 2)
  end
  if type(action) ~= "string" and type(action) ~= "function" then
    fail("mapping action must be an action name or function", 2)
  end
  options = options or {}
  if type(options) ~= "table" then
    fail("mapping options must be a table", 2)
  end
  local callback
  if type(action) == "string" then
    callback = function()
      return self:invoke_action(action)
    end
  else
    callback = function(...)
      return invoke_callback(self, action, ...)
    end
  end
  local native_options = {
    silent = options.silent == true,
    remap = options.remap == true,
    desc = options.desc
      or ("clever-f " .. (type(action) == "string" and action or lhs)),
  }
  self:runtime().keymap.set(modes, lhs, callback, native_options)
  local identity = next_identity(self, "mapping")
  adapter_records[self].mappings[identity] = {
    modes = modes,
    lhs = lhs,
    action = action,
    options = options,
    callback = callback,
  }
  return identity
end

function M.new(options)
  return HostAdapter.new(options)
end

setmetatable(M, {
  __call = function(_, options)
    return HostAdapter.new(options)
  end,
})

return M