local policy = require("clever_f.policy")

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

M.DEFAULT_LABEL_GROUP = "CleverFDefaultLabel"
M.Priority = {
  HIGH = "high",
  ORDINARY = "ordinary",
}

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

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

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

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"
  then
    fail("FeedbackService host must provide highlight groups", 3)
  end
  return host
end

local function require_policy(service, host)
  service = service or policy.new(host)
  if type(service) ~= "table"
    or type(service.evaluate_highlight_links) ~= "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)
  service_records[service] = {
    host = host,
    policy = require_policy(options.policy or options.policy_service, host),
  }
  return service
end

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

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

return M