--- The HTTP client, built on LuaSocket (and LuaSec for `https://`).
--
-- Each request opens a fresh TCP+TLS connection; nothing is pooled. For a
-- one-off lookup that is irrelevant. For thousands, **do not write a loop** —
-- use `Client:lookup_many`, which resolves up to 500 CEPs per request. A loop
-- of 500 calls pays 500 TLS handshakes; the batch pays one.
--
-- Retry policy: 429 and the transient 5xx, plus network failures, are retried
-- with exponentially backed-off, jittered waits. 400 and 404 are deliberately
-- absent from that set — both are definitive answers about the request, so
-- retrying returns the same thing more slowly while burning someone's quota.
--
-- @module cepis.client

local socket = require("socket")
local http = require("socket.http")
local ltn12 = require("ltn12")
local json = require("dkjson")

local errors = require("cepis.errors")
local models = require("cepis.models")
local csv = require("cepis.csv")

local M = {}

--- Library version, as it appears in the default `User-Agent`.
M.VERSION = "0.1.0"

--- Where the API lives unless `base_url` says otherwise.
M.DEFAULT_URL = "https://cep.is"

--- How many CEPs the batch endpoint accepts in one request.
M.MAX_BATCH = 500

local ACCEPT = "application/json, text/csv;q=0.9, */*;q=0.1"

local RETRIABLE_STATUS = {
  [429] = true,
  [500] = true,
  [502] = true,
  [503] = true,
  [504] = true,
}

local MONTHS = {
  Jan = 1,
  Feb = 2,
  Mar = 3,
  Apr = 4,
  May = 5,
  Jun = 6,
  Jul = 7,
  Aug = 8,
  Sep = 9,
  Oct = 10,
  Nov = 11,
  Dec = 12,
}

local ARRAY_MT = {}

if _VERSION < "Lua 5.4" then
  math.randomseed(os.time())
end

local function quote(value)
  local text = tostring(value)
  if #text > 60 then
    text = text:sub(1, 60) .. "..."
  end
  return "'" .. (text:gsub("%c", " ")) .. "'"
end

local function urlescape(value)
  return (value:gsub("[^%w%-%.%_%~]", function(char)
    return string.format("%%%02X", string.byte(char))
  end))
end

local function utc_to_epoch(fields)
  fields.isdst = false
  local as_local = os.time(fields)
  if not as_local then
    return nil
  end
  local utc = os.date("!*t", as_local)
  utc.isdst = false
  return as_local + os.difftime(as_local, os.time(utc))
end

--- Seconds to wait, from a `Retry-After` header value.
--
-- RFC 9110 allows two forms: a number of seconds (`"120"`) and an HTTP date
-- (`"Wed, 21 Oct 2026 07:28:00 GMT"`). Handling only the first is the common
-- bug, and it makes a client ignore exactly the wait request that matters
-- most.
--
-- @tparam string|nil value the raw header
-- @treturn number|nil seconds, never negative, or `nil` if unparseable
function M.retry_after_seconds(value)
  if type(value) ~= "string" then
    return nil
  end

  value = value:match("^%s*(.-)%s*$")
  if value == "" then
    return nil
  end

  local seconds = tonumber(value)
  if seconds then
    return math.max(0, seconds)
  end

  local day, month, year, hour, minute, second =
    value:match("^%a+,%s+(%d+)%s+(%a+)%s+(%d+)%s+(%d+):(%d+):(%d+)%s+GMT$")
  if not day then
    day, month, year, hour, minute, second =
      value:match("^(%d+)%s+(%a+)%s+(%d+)%s+(%d+):(%d+):(%d+)%s+GMT$")
  end
  if not day or not MONTHS[month] then
    return nil
  end

  local target = utc_to_epoch({
    year = tonumber(year),
    month = MONTHS[month],
    day = tonumber(day),
    hour = tonumber(hour),
    min = tonumber(minute),
    sec = tonumber(second),
  })
  if not target then
    return nil
  end

  return math.max(0, target - os.time())
end

--- Return the CEP's 8 digits, accepting the mask.
--
-- `"01001-000"`, `"01001000"` and `" 01001-000 "` all become `"01001000"`.
--
-- Returns `nil, err` with `err.kind == "invalid_cep"` unless exactly 8 digits
-- remain. This runs **before** any request: a 7-digit CEP is the caller's bug,
-- and spending a round trip for the server to say so wastes both sides' time.
--
-- @tparam string value masked or unmasked
-- @treturn[1] string the 8 digits
-- @treturn[2] nil
-- @treturn[2] table the error
function M.normalize_cep(value)
  if type(value) ~= "string" then
    return nil,
      errors.new(errors.INVALID_CEP, "CEP must be a string, got " .. type(value))
  end

  local cleaned = value:gsub("[%s%.%-]", "")
  if not cleaned:match("^%d%d%d%d%d%d%d%d$") then
    return nil,
      errors.new(
        errors.INVALID_CEP,
        "CEP must be 8 digits, got " .. quote(value)
      )
  end

  return cleaned
end

local function decode_object(body)
  local data = json.decode(body, 1, nil, nil, ARRAY_MT)
  if type(data) ~= "table" or getmetatable(data) == ARRAY_MT then
    return nil,
      errors.new(
        errors.INVALID_RESPONSE,
        "response is not a JSON object — something between you and the API is "
          .. "answering instead of it: "
          .. quote(body)
      )
  end
  return data
end

local function error_message(body, fallback)
  local ok, data = pcall(json.decode, body or "", 1, nil)
  if ok and type(data) == "table" and type(data.mensagem) == "string" then
    if data.mensagem ~= "" then
      return data.mensagem
    end
  end
  return fallback
end

local function transport(url)
  if url:lower():find("^https://") then
    local ok, https = pcall(require, "ssl.https")
    if not ok then
      return nil,
        "an https:// base_url needs LuaSec (luarocks install luasec); "
          .. "use an http:// base_url to avoid it"
    end
    return https.request
  end
  return http.request
end

--- Client for the cep.is API.
--
-- Reuse one instance: the configuration is not mutated and no method keeps
-- state between calls.
--
-- @type Client
-- @field base_url string
-- @field timeout number
-- @field max_attempts number
-- @field backoff_base number
-- @field backoff_max number
-- @field total_timeout number|nil
-- @field user_agent string
local Client = {}
Client.__index = Client
Client.__name = "cepis.Client"

M.Client = Client

--- Build a client.
--
-- Every option has a usable default, so `Client.new()` is valid. A bad option
-- raises through `error()` rather than returning one: it is a mistake in the
-- calling code, not a condition to handle at runtime.
--
-- @tparam[opt] table opts
-- @tparam[opt="https://cep.is"] string opts.base_url
--   Where the API lives. Point it at a local instance (the API repo brings one
--   up on `http://localhost:8080` with `just up`) or at a test server. It is
--   the only option that usually changes between environments. Trailing
--   slashes are stripped, so it cannot produce doubled separators that some
--   proxies normalise and others 404.
-- @tparam[opt=10] number opts.timeout
--   Seconds to wait **per socket operation** (connect, and each read) — this
--   is not a cap on the whole call. That cap is `total_timeout`.
-- @tparam[opt=3] number opts.max_attempts
--   How many attempts in total, counting the first. `1` disables retrying. The
--   default of `3` covers the common case (one transient failure) without
--   turning a real outage into a long wait.
-- @tparam[opt=0.5] number opts.backoff_base
--   Base of the exponential wait, in seconds. The actual wait is drawn from
--   `[0, base * 2^(n-1)]` — *full jitter*. The randomness is not decoration:
--   without it, N clients that fail together come back together and reproduce
--   the spike that took the service down.
-- @tparam[opt=8] number opts.backoff_max
--   Cap on each individual wait, in seconds. It applies to a server-sent
--   `Retry-After` too, or a `Retry-After: 3600` from a misconfigured proxy
--   would park the caller for an hour.
-- @tparam[opt] number opts.total_timeout
--   Cap on the whole call, attempts and waits included. `nil` leaves
--   `max_attempts` as the only bound. Set it in code serving a web request:
--   without it the worst case is `max_attempts * timeout` plus the sum of the
--   backoffs.
-- @tparam[opt] string opts.user_agent
--   Overrides the `User-Agent`. The default identifies the library and its
--   version, which is what lets the server diagnose an old client
--   misbehaving.
-- @treturn Client
function Client.new(opts)
  opts = opts or {}

  local base_url = opts.base_url or M.DEFAULT_URL
  local timeout = opts.timeout or 10.0
  local max_attempts = opts.max_attempts or 3
  local backoff_base = opts.backoff_base or 0.5
  local backoff_max = opts.backoff_max or 8.0
  local total_timeout = opts.total_timeout

  if type(base_url) ~= "string" or base_url == "" then
    error("base_url must be a non-empty string", 2)
  end
  if type(timeout) ~= "number" or timeout <= 0 then
    error("timeout must be a number > 0", 2)
  end
  if type(max_attempts) ~= "number" or max_attempts < 1 then
    error("max_attempts must be a number >= 1", 2)
  end
  if type(backoff_base) ~= "number" or backoff_base < 0 then
    error("backoff_base must be a number >= 0", 2)
  end
  if type(backoff_max) ~= "number" or backoff_max < 0 then
    error("backoff_max must be a number >= 0", 2)
  end
  if total_timeout ~= nil and (type(total_timeout) ~= "number" or total_timeout <= 0) then
    error("total_timeout must be a number > 0, or nil", 2)
  end
  if opts.user_agent ~= nil and type(opts.user_agent) ~= "string" then
    error("user_agent must be a string", 2)
  end

  return setmetatable({
    base_url = (base_url:gsub("/+$", "")),
    timeout = timeout,
    max_attempts = math.floor(max_attempts),
    backoff_base = backoff_base,
    backoff_max = backoff_max,
    total_timeout = total_timeout,
    user_agent = opts.user_agent
      or ("cepis-lua/" .. M.VERSION .. " (+https://cep.is)"),
  }, Client)
end

function Client:_perform(url, request)
  local chunks = {}
  local previous = http.TIMEOUT
  http.TIMEOUT = self.timeout

  local called, ok, code, headers = pcall(request, {
    url = url,
    method = "GET",
    headers = {
      ["user-agent"] = self.user_agent,
      ["accept"] = ACCEPT,
      ["accept-encoding"] = "identity",
    },
    sink = ltn12.sink.table(chunks),
    redirect = false,
  })

  http.TIMEOUT = previous

  if not called then
    return nil, tostring(ok)
  end
  if not ok or type(code) ~= "number" then
    return nil, tostring(code)
  end

  return code, table.concat(chunks), headers or {}
end

function Client:_backoff(attempt, retry_after)
  if retry_after then
    return math.min(retry_after, self.backoff_max)
  end
  local ceiling = math.min(self.backoff_base * 2 ^ (attempt - 1), self.backoff_max)
  return math.random() * ceiling
end

function Client:_request(path, accepted)
  accepted = accepted or { [200] = true }

  local url = self.base_url .. path

  local request, unavailable = transport(url)
  if not request then
    return nil, errors.new(errors.NETWORK_ERROR, "cannot reach " .. url .. ": " .. unavailable)
  end

  local deadline = nil
  if self.total_timeout then
    deadline = socket.gettime() + self.total_timeout
  end

  local last_status, last_retry_after, last_network

  for attempt = 1, self.max_attempts do
    if deadline and socket.gettime() >= deadline then
      break
    end

    local status, body, headers = self:_perform(url, request)

    if status then
      if accepted[status] or not RETRIABLE_STATUS[status] then
        return status, body, headers
      end
      last_status = status
      last_retry_after = M.retry_after_seconds(headers["retry-after"])
      last_network = nil
    else
      last_network = body
      last_status = nil
      last_retry_after = nil
    end

    if attempt == self.max_attempts then
      break
    end

    local wait = self:_backoff(attempt, last_retry_after)
    if deadline then
      local remaining = deadline - socket.gettime()
      if remaining <= 0 then
        break
      end
      if wait > remaining then
        wait = remaining
      end
    end
    socket.sleep(wait)
  end

  local suffix = string.format(" (after %d attempt(s))", self.max_attempts)

  if last_status == 429 then
    return nil,
      errors.new(errors.RATE_LIMITED, "rate limit reached at " .. url .. suffix, {
        status = 429,
        retry_after = last_retry_after,
      })
  end
  if last_status then
    return nil,
      errors.new(
        errors.SERVER_ERROR,
        string.format("the API answered %d at %s%s", last_status, url, suffix),
        { status = last_status }
      )
  end
  return nil,
    errors.new(
      errors.NETWORK_ERROR,
      "could not reach " .. url .. suffix .. ": " .. tostring(last_network)
    )
end

--- Look up a single CEP.
--
--     local address, err = client:lookup("01001-000")
--     print(address.localidade, address.uf)  --> São Paulo  SP
--
-- A 400 from the API surfaces as `invalid_cep` carrying the API's own message:
-- the format already passed local validation, so the server knows something
-- this client does not.
--
-- @tparam string cep masked or unmasked
-- @treturn[1] Address
-- @treturn[2] nil
-- @treturn[2] table the error; `kind` is one of `invalid_cep` (not 8 digits —
--   no request is made), `not_found` (well-formed, absent from the database),
--   `rate_limited`, `server_error`, `network_error`, `invalid_response`
function Client:lookup(cep)
  local number, invalid = M.normalize_cep(cep)
  if not number then
    return nil, invalid
  end

  local status, body = self:_request("/" .. number)
  if not status then
    return nil, body
  end

  if status == 404 then
    return nil,
      errors.new(
        errors.NOT_FOUND,
        "CEP " .. number .. " does not exist in the DNE database",
        { cep = number, status = 404 }
      )
  end
  if status == 400 then
    return nil,
      errors.new(
        errors.INVALID_CEP,
        error_message(body, "CEP " .. number .. " rejected by the API"),
        { cep = number, status = 400 }
      )
  end

  local data, malformed = decode_object(body)
  if not data then
    return nil, malformed
  end

  return models.new_address(data)
end

function Client:_lookup_chunk(ceps)
  local wanted = #ceps
  local query = "ceps=" .. urlescape(table.concat(ceps, ","))

  local status, body = self:_request("/csv?" .. query)
  if not status then
    return nil, body
  end

  local rows = csv.parse(body)
  local out = {}
  local count = 0

  if #rows > 0 then
    local header = rows[1]
    for index = 2, #rows do
      if count >= wanted then
        break
      end
      local record = {}
      for column = 1, #header do
        record[header[column]] = rows[index][column] or ""
      end
      count = count + 1
      if record.localidade == nil or record.localidade:match("^%s*$") then
        out[count] = false
      else
        out[count] = models.new_address(record)
      end
    end
  end

  for index = count + 1, wanted do
    out[index] = false
  end

  return out
end

--- Look up many CEPs in one batch.
--
-- Returns a list of **the same length and in the same order** as the input.
--
-- **A CEP that does not exist is `false` at its position, not `nil`.** This is
-- the one place where Lua forces a difference from the other clients in this
-- family, and it is not cosmetic: a `nil` inside a sequence truncates it at the
-- first hole, so `#result` and `ipairs` would silently stop at the first
-- missing CEP and drop every address after it. `false` keeps the sequence
-- dense, and `if address then` still reads as the natural test:
--
--     local result = client:lookup_many({ "01001000", "99999999", "20040020" })
--     for index, address in ipairs(result) do
--       if address then
--         print(ceps[index], address.localidade)
--       else
--         print(ceps[index], "not found")
--       end
--     end
--
-- A malformed CEP is `false` too, for the same reason, rather than failing the
-- call: in a batch of a thousand, one bad CEP must not cost the other nine
-- hundred and ninety-nine. If you need to know *which* one was malformed,
-- validate first with `normalize_cep`.
--
-- Input is chunked into blocks of 500 (the API's limit) automatically.
--
-- **The batch carries no coordinate.** The endpoint behind it is CSV, and the
-- CSV has no `geo` column. Every `Address` returned here has `geo == nil`,
-- including for CEPs that do have one. Need `geo`? Use `lookup`, one at a
-- time.
--
-- @tparam table ceps list of strings
-- @treturn[1] table list of `Address|false`, same length and order as `ceps`
-- @treturn[2] nil
-- @treturn[2] table the error, if the batch request itself failed
function Client:lookup_many(ceps)
  if type(ceps) ~= "table" then
    error("lookup_many expects a table of CEPs, got " .. type(ceps), 2)
  end

  local total = #ceps
  if total == 0 then
    return {}
  end

  local result = {}
  local filled = 0
  local start = 1

  while start <= total do
    local stop = math.min(start + M.MAX_BATCH - 1, total)
    local chunk = {}
    for index = start, stop do
      chunk[#chunk + 1] = tostring(ceps[index])
    end

    local rows, err = self:_lookup_chunk(chunk)
    if not rows then
      return nil, err
    end

    for index = 1, #chunk do
      filled = filled + 1
      result[filled] = rows[index]
    end
    start = stop + 1
  end

  return result
end

--- Query `GET /health`: does the API answer, and with which database.
--
-- An API reporting itself degraded is not an error — that arrives in
-- `health.status`, and checking health is exactly when you want the diagnosis
-- rather than a failure. Network failures still return `nil, err`.
--
-- @treturn[1] Health
-- @treturn[2] nil
-- @treturn[2] table the error
function Client:health()
  local status, body = self:_request("/health", { [200] = true, [503] = true })
  if not status then
    return nil, body
  end

  local data, malformed = decode_object(body)
  if not data then
    return nil, malformed
  end

  return models.new_health(data)
end

return M