local domain = require("clever_f.domain")
local policy = require("clever_f.policy")
local sequence_state = require("clever_f.sequence_state")
local state_transitions = require("clever_f.state_transitions")
local text_topology = require("clever_f.text_topology")

local M = {}
local FeedbackService = {}
FeedbackService.__index = FeedbackService
M.FeedbackService = FeedbackService
local CursorPresentationLease = {}
M.CursorPresentationLease = CursorPresentationLease

M.DEFAULT_LABEL_GROUP = "CleverFDefaultLabel"
M.Priority = {
  HIGH = "high",
  ORDINARY = "ordinary",
}
M.FINALIZER_EVENTS = {
  "CursorMoved",
  "InsertEnter",
  "TextChanged",
}
M.FinalizerAction = {
  PRESERVE = "preserve",
  FINALIZE = "finalize",
}
M.MigrationReason = {
  LINE_CHANGE = "line_change",
  TILL_DIRECTION_CHANGE = "till_direction_change",
}

local OVERLAY_PRIORITIES = {
  CleverFCursor = M.Priority.HIGH,
  CleverFChar = M.Priority.HIGH,
  CleverFDirect = M.Priority.ORDINARY,
}

local service_records = setmetatable({}, { __mode = "k" })
local cursor_lease_records = setmetatable({}, { __mode = "k" })
local temporary_release_records = setmetatable({}, { __mode = "k" })

local FEATURE_GROUPS = {
  "CleverFCursor",
  "CleverFChar",
  "CleverFDirect",
}

local LEGACY_NORMAL_EX_CONTEXTS = {
  cv = true,
  cvr = true,
}

local DIRECT_FINALIZER_EVENTS = {
  InsertEnter = true,
  TextChanged = true,
}

local DEFAULT_LABEL_DEFINITION = {
  guifg = "red",
  guibg = "NONE",
  gui = {
    bold = true,
    underline = true,
  },
  ctermfg = "red",
  ctermbg = "NONE",
  cterm = {
    bold = true,
    underline = true,
  },
}

local function copy(value)
  if type(value) ~= "table" then
    return value
  end
  local result = {}
  for key, item in pairs(value) do
    result[key] = copy(item)
  end
  return result
end

function M.default_label_definition()
  return copy(DEFAULT_LABEL_DEFINITION)
end

function M.overlay_priority(group)
  local priority = OVERLAY_PRIORITIES[group]
  if priority == nil then
    error("unknown feedback overlay group '" .. tostring(group) .. "'", 2)
  end
  return priority
end

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

local function normalize_options(options)
  if type(options) ~= "table" then
    fail("FeedbackService options must be a table", 3)
  end
  if options.host == nil then
    return { host = options }
  end
  return options
end

local function require_host(host)
  if type(host) ~= "table"
    or type(host.read_highlight_group) ~= "function"
    or type(host.define_highlight_group) ~= "function"
    or type(host.create_highlight) ~= "function"
    or type(host.remove_highlight) ~= "function"
    or type(host.read_buffer) ~= "function"
    or type(host.read_cursor) ~= "function"
    or type(host.read_window) ~= "function"
    or type(host.register_events) ~= "function"
    or type(host.remove_event_registration) ~= "function"
    or type(host.stop_timer) ~= "function"
    or type(host.supports_cursor_presentation) ~= "function"
    or type(host.suppress_cursor_presentation) ~= "function"
    or type(host.restore_cursor_presentation) ~= "function"
  then
    fail("FeedbackService host must provide highlight groups", 3)
  end
  return host
end

local function require_transitions(transitions, state)
  transitions = transitions or state_transitions.new(state)
  if type(transitions) ~= "table"
    or type(transitions.AddTemporaryOverlay) ~= "function"
    or type(transitions.RemoveTemporaryOverlay) ~= "function"
    or type(transitions.AddTargetOverlay) ~= "function"
    or type(transitions.ClearTargetOverlays) ~= "function"
    or type(transitions.AddFinalizer) ~= "function"
    or type(transitions.RemoveFinalizer) ~= "function"
    or type(transitions.FullFinalization) ~= "function"
  then
    fail("FeedbackService transitions must manage overlay resources", 3)
  end
  return transitions
end

local function require_policy(service, host)
  service = service or policy.new(host)
  if type(service) ~= "table"
    or type(service.evaluate_highlight_links) ~= "function"
    or type(service.sample_acquisition) ~= "function"
  then
    fail("FeedbackService policy must evaluate highlight links", 3)
  end
  return service
end

function FeedbackService.new(options)
  if FeedbackService.is(options) then
    return options
  end
  options = normalize_options(options)
  local service = setmetatable({}, FeedbackService)
  local host = require_host(options.host)
  local state = options.state or sequence_state.get()
  if not sequence_state.is(state) then
    fail("FeedbackService state must be the plugin-global SequenceState", 2)
  end
  service_records[service] = {
    host = host,
    policy = require_policy(options.policy or options.policy_service, host),
    state = state,
    transitions = require_transitions(
      options.transitions or options.state_transitions,
      state
    ),
    persistent_requests = {},
    owned_finalizer = nil,
  }
  return service
end

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

local cursor_lease_metatable = {
  __index = function(lease, key)
    local method = CursorPresentationLease[key]
    if method ~= nil then
      return method
    end
    local record = cursor_lease_records[lease]
    if key == "identity" then
      return record.identity
    end
    if key == "active" then
      return record.active
    end
    return nil
  end,
  __newindex = function()
    fail("cursor presentation leases are read-only", 2)
  end,
  __metatable = "clever_f.feedback_service.CursorPresentationLease",
}

local function new_cursor_presentation_lease(host, suppress)
  local lease = setmetatable({}, cursor_lease_metatable)
  local identity = suppress and host:suppress_cursor_presentation() or nil
  cursor_lease_records[lease] = {
    host = host,
    identity = identity,
    active = identity ~= nil,
  }
  return lease
end

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

function CursorPresentationLease:release()
  local record = cursor_lease_records[self]
  if record == nil then
    fail("cursor presentation lease is invalid", 2)
  end
  if not record.active then
    return false
  end
  record.active = false
  record.host:restore_cursor_presentation(record.identity)
  return true
end

function FeedbackService:create_cursor_presentation_lease(enabled)
  local record = service_records[self]
  if enabled == nil then
    enabled = record.policy:sample_acquisition().hide_cursor_on_cmdline
  elseif type(enabled) ~= "boolean" then
    fail("cursor presentation policy must be a Boolean", 2)
  end
  local supported = enabled and record.host:supports_cursor_presentation()
  return new_cursor_presentation_lease(record.host, supported == true)
end

local function position_list(positions)
  if type(positions) ~= "table" then
    fail("direct marker positions must be a list", 3)
  end
  local result = {}
  local item_count = 0
  for key, position in pairs(positions) do
    if type(key) ~= "number"
      or key ~= math.floor(key)
      or key < 1
      or key > #positions
    then
      fail("direct marker positions must be a list", 3)
    end
    result[key] = domain.Position.coerce(position)
    item_count = item_count + 1
  end
  if item_count ~= #positions then
    fail("direct marker positions must be a list", 3)
  end
  return result
end

function FeedbackService:create_direct_markers(positions, window)
  positions = position_list(positions)
  if #positions == 0 then
    return nil
  end
  if window == nil then
    fail("direct marker window must identify its host window", 2)
  end

  local record = service_records[self]
  local identity = record.host:create_highlight({
    group = "CleverFDirect",
    window = window,
    positions = positions,
    priority = M.overlay_priority("CleverFDirect"),
  })
  record.transitions:AddTemporaryOverlay(identity, window, "CleverFDirect")
  local resource = {
    identity = identity,
    window = window,
    group = "CleverFDirect",
    positions = positions,
  }
  temporary_release_records[resource] = false
  return resource
end

function FeedbackService:create_cursor_marker(position, window)
  position = domain.Position.coerce(position)
  if window == nil then
    fail("cursor marker window must identify its host window", 2)
  end

  local record = service_records[self]
  local identity = record.host:create_highlight({
    group = "CleverFCursor",
    window = window,
    position = position,
    priority = M.overlay_priority("CleverFCursor"),
  })
  record.transitions:AddTemporaryOverlay(identity, window, "CleverFCursor")
  local resource = {
    identity = identity,
    window = window,
    group = "CleverFCursor",
    position = position,
  }
  temporary_release_records[resource] = false
  return resource
end

function FeedbackService:remove_temporary_overlay(resource)
  if type(resource) ~= "table" or resource.identity == nil then
    fail("temporary overlay resource must identify its highlight", 2)
  end
  if temporary_release_records[resource] == true then
    return false
  end
  temporary_release_records[resource] = true
  local record = service_records[self]
  local ok, removed = pcall(
    record.host.remove_highlight,
    record.host,
    resource.identity
  )
  record.transitions:RemoveTemporaryOverlay(resource.identity, resource.window)
  if not ok then
    error(removed, 0)
  end
  return removed
end

function M.persistent_context_eligible(context)
  context = domain.ModeContext.from_full_mode(context)
  return context.key == "n"
    or context.visual_kind ~= nil
    or context.select_kind ~= nil
    or LEGACY_NORMAL_EX_CONTEXTS[context.key] == true
end

function M.persistent_destination(
  view,
  target_position,
  descriptor,
  endpoint_policy
)
  if not text_topology.TextView.is(view) then
    fail("persistent feedback requires a TextView", 2)
  end
  target_position = domain.Position.coerce(target_position)
  descriptor = domain.Descriptor.from_string(descriptor)
  endpoint_policy = domain.EndpointPolicy.from_string(endpoint_policy)

  if endpoint_policy == domain.EndpointPolicy.VISUAL_EXCLUSIVE
    and descriptor.direction == domain.Direction.FORWARD
  then
    if descriptor.family == domain.Family.FIND then
      return view:successor(target_position)
    end
    return target_position
  end
  if descriptor.family == domain.Family.FIND then
    return target_position
  end
  if descriptor.direction == domain.Direction.FORWARD then
    return view:predecessor(target_position)
  end
  return view:successor(target_position)
end

function M.persistent_match_positions(
  view,
  match_start_line,
  target_plan,
  descriptor,
  endpoint_policy
)
  if not text_topology.TextView.is(view) then
    fail("persistent feedback requires a TextView", 2)
  end
  if not domain.TargetPlan.is(target_plan) then
    fail("persistent feedback requires a TargetPlan", 2)
  end
  local positions = {}
  local seen = {}
  local candidates = view:iter_line_forward(match_start_line)
  while true do
    local position, character = candidates()
    if position == nil then
      break
    end
    if target_plan:matches(character, position, view) then
      local destination = M.persistent_destination(
        view,
        position,
        descriptor,
        endpoint_policy
      )
      if destination ~= nil then
        local key = tostring(destination.line)
          .. ":"
          .. tostring(destination.byte_column)
        if not seen[key] then
          seen[key] = true
          positions[#positions + 1] = destination
        end
      end
    end
  end
  return positions
end

function FeedbackService:build_persistent(specification)
  if type(specification) ~= "table" then
    fail("persistent feedback request must be a table", 2)
  end
  local context = domain.ModeContext.from_full_mode(specification.context)
  if not M.persistent_context_eligible(context) then
    fail("persistent feedback request requires an eligible context", 2)
  end
  if not domain.TargetPlan.is(specification.target_plan) then
    fail("persistent feedback request requires a TargetPlan", 2)
  end
  if not domain.ResolvedMotionPlan.is(specification.motion_plan) then
    fail("persistent feedback request requires a ResolvedMotionPlan", 2)
  end
  if specification.motion_plan.target_plan ~= specification.target_plan then
    fail("persistent feedback must reuse the movement TargetPlan", 2)
  end
  local descriptor = domain.Descriptor.from_string(
    specification.descriptor or specification.motion_plan.descriptor
  )
  local endpoint_policy = domain.EndpointPolicy.from_string(
    specification.endpoint_policy or specification.motion_plan.endpoint_policy
  )
  local anchor = domain.Position.coerce(specification.anchor)
  local view = specification.text_view
    or text_topology.from_host(service_records[self].host)
  return {
    context = context,
    anchor = anchor,
    target_plan = specification.target_plan,
    motion_plan = specification.motion_plan,
    descriptor = descriptor,
    endpoint_policy = endpoint_policy,
    match_start_line = anchor.line,
    positions = M.persistent_match_positions(
      view,
      anchor.line,
      specification.target_plan,
      descriptor,
      endpoint_policy
    ),
    text_view = view,
    window = specification.window,
  }
end

local function release_target_overlays(record, resources)
  for _, resource in ipairs(resources) do
    record.host:remove_highlight(resource.identity)
  end
end

local function remove_target_overlays(record, window)
  local resources = record.transitions:ClearTargetOverlays(window)
  release_target_overlays(record, resources)
  return resources
end

function FeedbackService:remove_character_overlays(window)
  if window == nil then
    fail("character overlay window must identify its host window", 2)
  end
  return remove_target_overlays(service_records[self], window)
end

function FeedbackService:cursor_moved_decision()
  local record = service_records[self]
  local context = record.state.last_input_context
  local expected = context and record.state:get_previous_landing(context) or nil
  local actual = record.host:read_cursor()
  return {
    context = context,
    expected = expected,
    actual = actual,
    equal = expected ~= nil and domain.Position.equal(actual, expected),
  }
end

local function release_finalizers(record, resources)
  for _, resource in ipairs(resources) do
    record.host:remove_event_registration(resource.identity)
  end
end

local function release_highlight_timer(record, identity)
  if identity == nil then
    return false
  end
  return record.host:stop_timer(identity)
end

function FeedbackService:full_finalize(window)
  local record = service_records[self]
  window = window or record.host:read_window()
  local cleanup = record.transitions:FullFinalization(window)
  release_finalizers(record, cleanup.finalizers)
  release_highlight_timer(record, cleanup.highlight_timer)
  release_target_overlays(record, cleanup.target_overlays)
  record.owned_finalizer = nil
  return cleanup
end

function FeedbackService:handle_finalizer_event(name, payload)
  if name == "CursorMoved" then
    local decision = self:cursor_moved_decision()
    if decision.equal then
      decision.action = M.FinalizerAction.PRESERVE
    else
      decision.action = M.FinalizerAction.FINALIZE
      decision.cleanup = self:full_finalize(payload and payload.window)
    end
    return decision
  end
  if DIRECT_FINALIZER_EVENTS[name] then
    return {
      action = M.FinalizerAction.FINALIZE,
      cleanup = self:full_finalize(payload and payload.window),
    }
  end
  return false
end

local function register_finalizers(service, record)
  local buffer = record.host:read_buffer()
  local owned = record.owned_finalizer
  if owned ~= nil and owned.buffer == buffer then
    return owned
  end
  if owned ~= nil then
    record.host:remove_event_registration(owned.identity)
    record.transitions:RemoveFinalizer(owned.identity, owned.buffer)
  end

  local identity = record.host:register_events(
    M.FINALIZER_EVENTS,
    function(name, payload)
      service:handle_finalizer_event(name, payload)
    end,
    { buffer = buffer }
  )
  record.transitions:AddFinalizer(identity, buffer)
  owned = {
    identity = identity,
    buffer = buffer,
  }
  record.owned_finalizer = owned
  return owned
end

function FeedbackService:request_persistent(specification)
  local request = self:build_persistent(specification)
  if request.window == nil then
    fail("persistent feedback window must identify its host window", 2)
  end
  local record = service_records[self]
  remove_target_overlays(record, request.window)
  request.identity = record.host:create_highlight({
    group = "CleverFChar",
    window = request.window,
    positions = request.positions,
    priority = M.overlay_priority("CleverFChar"),
    target_plan = request.target_plan,
    descriptor = request.descriptor,
    endpoint_policy = request.endpoint_policy,
    match_start_line = request.match_start_line,
  })
  request.group = "CleverFChar"
  request.priority = M.overlay_priority("CleverFChar")
  record.transitions:AddTargetOverlay(
    request.identity,
    request.window,
    request.anchor.line
  )
  request.finalizers = register_finalizers(self, record)
  local requests = record.persistent_requests
  requests[#requests + 1] = request
  return request
end

function FeedbackService:persistent_requests()
  local result = {}
  for index, request in ipairs(service_records[self].persistent_requests) do
    result[index] = request
  end
  return result
end

function M.repeated_till_migration_candidate(request)
  if type(request) ~= "table" then
    fail("command feedback migration request must be a table", 2)
  end
  local plan = request.resolved_motion_plan or request.plan
  return domain.ResolvedMotionPlan.is(plan)
    and plan.descriptor.family == domain.Family.TILL
    and request.first_move == false
end

function M.till_direction_changed(request)
  if not M.repeated_till_migration_candidate(request) then
    return false
  end
  if type(request.moved_forward) ~= "boolean"
    or type(request.previous_moved_forward) ~= "boolean"
  then
    fail("TILL feedback migration requires movement directions", 2)
  end
  return request.moved_forward ~= request.previous_moved_forward
end

function M.command_migration_reason(request)
  if type(request) ~= "table" then
    fail("command feedback migration request must be a table", 2)
  end
  local origin = domain.Position.coerce(request.origin)
  local destination = domain.Position.coerce(request.destination)
  if request.outcome ~= nil and request.outcome.complete ~= true then
    return nil
  end
  if origin.line ~= destination.line then
    return M.MigrationReason.LINE_CHANGE
  end
  if M.till_direction_changed(request) then
    return M.MigrationReason.TILL_DIRECTION_CHANGE
  end
  return nil
end

local function has_target_overlay(record, window)
  for _, resource in ipairs(record.state.target_overlays) do
    if resource.window == window then
      return true
    end
  end
  return false
end

function FeedbackService:migrate_command(request)
  local reason = M.command_migration_reason(request)
  local record = service_records[self]
  local window = request.window or record.host:read_window()
  if reason == nil or not has_target_overlay(record, window) then
    return {
      migrated = false,
      reason = reason,
    }
  end

  local plan = request.resolved_motion_plan or request.plan
  if not domain.ResolvedMotionPlan.is(plan) then
    fail("command feedback migration requires a ResolvedMotionPlan", 2)
  end
  local overlay = self:request_persistent({
    context = request.context,
    anchor = request.destination,
    target_plan = plan.target_plan,
    motion_plan = plan,
    descriptor = plan.descriptor,
    endpoint_policy = plan.endpoint_policy,
    window = window,
  })
  return {
    migrated = true,
    reason = reason,
    overlay = overlay,
  }
end

function FeedbackService:evaluate_feature_links()
  local record = service_records[self]
  local rules = record.policy:evaluate_highlight_links()
  local results = {}
  for _, group in ipairs(FEATURE_GROUPS) do
    local rule = rules[group]
    if rule.enabled then
      if rule.configured_target ~= nil then
        record.host:define_highlight_group(
          group,
          { link = rule.configured_target },
          { force = true }
        )
        results[group] = {
          group = group,
          target = rule.configured_target,
          source = "configured",
          applied = true,
        }
      else
        local existing = record.host:read_highlight_group(group)
        if existing ~= nil then
          results[group] = {
            group = group,
            definition = existing,
            source = "colorscheme",
            applied = false,
          }
        else
          record.host:define_highlight_group(
            group,
            { link = rule.target },
            { default = true }
          )
          results[group] = {
            group = group,
            target = rule.target,
            source = "fallback",
            applied = true,
          }
        end
      end
    end
  end
  return results
end

function FeedbackService:ensure_default_label()
  local existing = service_records[self].host:read_highlight_group(
    M.DEFAULT_LABEL_GROUP
  )
  if existing ~= nil then
    return {
      group = M.DEFAULT_LABEL_GROUP,
      definition = existing,
      source = "colorscheme",
      applied = false,
    }
  end

  local definition = M.default_label_definition()
  service_records[self].host:define_highlight_group(
    M.DEFAULT_LABEL_GROUP,
    definition,
    { default = true }
  )
  return {
    group = M.DEFAULT_LABEL_GROUP,
    definition = definition,
    source = "fallback",
    applied = true,
  }
end

function FeedbackService:evaluate_highlights()
  return {
    default_label = self:ensure_default_label(),
    feature_links = self:evaluate_feature_links(),
  }
end

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

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

return M