local domain = require("clever_f.domain")

local M = {}
local State = {}
M.State = State

local MAP_FIELDS = {
  "previous_descriptor",
  "previous_landing",
  "first_move",
  "previous_target",
}

local MAP_FIELD_SET = {}
for _, field in ipairs(MAP_FIELDS) do
  MAP_FIELD_SET[field] = true
end

local data = {
  previous_descriptor = {},
  previous_landing = {},
  first_move = {},
  previous_target = {},
  known_contexts = {},
  last_input_context = nil,
  moved_forward = false,
  moved_forward_initialized = false,
  migemo_cache = {},
  repeat_timestamp_ms = 0,
  highlight_timer = nil,
  target_overlays = {},
  temporary_overlays = {},
  finalizers = {},
}

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

local function normalize_context(context, name)
  if domain.ModeContext.is(context) then
    return domain.ModeContext.from_full_mode(context.full_mode)
  end
  if type(context) ~= "string" or context == "" then
    fail((name or "context") .. " must be a ModeContext or full mode string", 2)
  end
  return domain.ModeContext.from_full_mode(context)
end

local function copy_map(source)
  local result = {}
  for key, value in pairs(source) do
    result[key] = value
  end
  return result
end

local function copy_resource(resource)
  local result = {}
  for key, value in pairs(resource) do
    result[key] = value
  end
  return result
end

local function copy_resources(resources)
  local result = {}
  for index, resource in ipairs(resources) do
    result[index] = copy_resource(resource)
  end
  return result
end

local function sorted_contexts()
  local result = {}
  for context in pairs(data.known_contexts) do
    result[#result + 1] = context
  end
  table.sort(result, function(left, right)
    return left.key < right.key
  end)
  return result
end

local function context_record(context)
  return {
    context = context,
    previous_descriptor = data.previous_descriptor[context],
    previous_landing = data.previous_landing[context],
    first_move = data.first_move[context],
    previous_target = data.previous_target[context],
  }
end

local function context_records()
  local result = {}
  for _, context in ipairs(sorted_contexts()) do
    result[context.key] = context_record(context)
  end
  return result
end

function State:get_previous_descriptor(context)
  context = normalize_context(context)
  return data.previous_descriptor[context]
end

function State:get_previous_landing(context)
  context = normalize_context(context)
  return data.previous_landing[context]
end

function State:get_first_move(context)
  context = normalize_context(context)
  return data.first_move[context]
end

function State:get_previous_target(context)
  context = normalize_context(context)
  return data.previous_target[context]
end

function State:get_context(context)
  context = normalize_context(context)
  return context_record(context)
end

State.context = State.get_context

function State:has_previous_landing(context)
  return self:get_previous_landing(context) ~= nil
end

function State:get_migemo(encoding)
  if type(encoding) ~= "string" or encoding == "" then
    fail("encoding must be a nonempty string", 2)
  end
  return data.migemo_cache[encoding]
end

function State:target_overlay_identities()
  local result = {}
  for index, resource in ipairs(data.target_overlays) do
    result[index] = resource.identity
  end
  return result
end

function State:temporary_overlay_identities()
  local result = {}
  for index, resource in ipairs(data.temporary_overlays) do
    result[index] = resource.identity
  end
  return result
end

function State:finalizer_identities()
  local result = {}
  for index, resource in ipairs(data.finalizers) do
    result[index] = resource.identity
  end
  return result
end

function State:resources()
  return {
    highlight_timer = data.highlight_timer,
    target_overlays = copy_resources(data.target_overlays),
    temporary_overlays = copy_resources(data.temporary_overlays),
    finalizers = copy_resources(data.finalizers),
  }
end

function State:snapshot()
  local snapshot = {
    contexts = context_records(),
    last_input_context = data.last_input_context,
    moved_forward = data.moved_forward,
    moved_forward_initialized = data.moved_forward_initialized,
    migemo_cache = copy_map(data.migemo_cache),
    repeat_timestamp_ms = data.repeat_timestamp_ms,
    highlight_timer = data.highlight_timer,
    target_overlays = copy_resources(data.target_overlays),
    temporary_overlays = copy_resources(data.temporary_overlays),
    finalizers = copy_resources(data.finalizers),
  }
  for _, field in ipairs(MAP_FIELDS) do
    snapshot[field] = copy_map(data[field])
  end
  return snapshot
end

local function target_to_table(target)
  return target and target:to_table() or nil
end

function State:to_table()
  local contexts = {}
  for _, context in ipairs(sorted_contexts()) do
    local record = context_record(context)
    contexts[context.key] = {
      previous_descriptor = record.previous_descriptor
          and record.previous_descriptor.value
        or nil,
      previous_landing = record.previous_landing
          and record.previous_landing:to_table()
        or nil,
      first_move = record.first_move,
      previous_target = target_to_table(record.previous_target),
    }
  end

  local cache_keys = {}
  for encoding in pairs(data.migemo_cache) do
    cache_keys[#cache_keys + 1] = encoding
  end
  table.sort(cache_keys)

  return {
    contexts = contexts,
    last_input_context = data.last_input_context and data.last_input_context.key or nil,
    moved_forward = data.moved_forward,
    moved_forward_initialized = data.moved_forward_initialized,
    migemo_cache = cache_keys,
    repeat_timestamp_ms = data.repeat_timestamp_ms,
    highlight_timer = data.highlight_timer,
    target_overlays = self:target_overlay_identities(),
    temporary_overlays = self:temporary_overlay_identities(),
    finalizers = self:finalizer_identities(),
  }
end

local state
local state_metatable = {
  __index = function(_, key)
    local method = State[key]
    if method ~= nil then
      return method
    end
    if MAP_FIELD_SET[key] then
      return copy_map(data[key])
    end
    if key == "contexts" then
      return context_records()
    end
    if key == "last_input_context"
      or key == "moved_forward"
      or key == "moved_forward_initialized"
      or key == "highlight_timer"
    then
      return data[key]
    end
    if key == "repeat_timestamp" or key == "repeat_timestamp_ms" then
      return data.repeat_timestamp_ms
    end
    if key == "migemo_cache" then
      return copy_map(data.migemo_cache)
    end
    if key == "target_overlays"
      or key == "temporary_overlays"
      or key == "finalizers"
    then
      return copy_resources(data[key])
    end
    return nil
  end,
  __newindex = function()
    fail("SequenceState is read-only; use StateTransitions", 2)
  end,
  __metatable = "clever_f.sequence_state.State",
}
state = setmetatable({}, state_metatable)

function M.get()
  return state
end

function M.new()
  return state
end

function M.is(value)
  return value == state
end

M.global = state

function M._mutate(target, mutation)
  if target ~= state then
    fail("StateTransitions must use the plugin-global SequenceState", 2)
  end
  if type(mutation) ~= "function" then
    fail("state mutation must be a function", 2)
  end
  return mutation(data)
end

function M._normalize_context(context)
  return normalize_context(context)
end

return M