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

local M = {}
local HostAdapter = {}
HostAdapter.__index = HostAdapter
M.HostAdapter = HostAdapter

M.ActionEffect = {
  NONE = "none",
  ESCAPE = "escape",
  ERROR = "error",
}

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" and options.runtime ~= nil then
    return options.runtime
  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 = {},
    event_order = {},
    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_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

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
    resource.active = false
    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
  resource.active = false
  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

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()
  return adapter_records[self].event_queue:begin_transition()
end

function HostAdapter:commit_action_transition(token)
  return adapter_records[self].event_queue:commit_transition(token)
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)
  local runtime = self: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 nil
  runtime.notify(text, levels and levels.ERROR or nil, { title = "clever-f" })
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
    self:emit_action_error(outcome.diagnostic)
    return M.ActionEffect.ERROR
  end
  return M.ActionEffect.NONE
end

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

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

return M