Name the municipality when the CEP does not existv0.2.0

Answering only "não encontrei" wastes the trip. A CEP that fails is
almost never a random number: it is someone who knows the city and
guessed the rest, most often at the "-000" that 957 municipalities never
received. The API now names that municipality on the 404, so the reply
names it too.

It stays an answer to a failure. No 📮, no address block, and no CEP
suggested from inside the range — the range is sparse (Areal's 118 CEPs
span nearly five thousand numbers), so the reply gives the count and says
so instead of letting the two ends read as a list of valid CEPs.

cep.is/go v0.1.0 discards the 404 body, so internal/lookup reads it with
one extra GET, on that path alone and never inside a retry. Everything
that can go wrong there — a slow answer, broken JSON, a faixa naming no
municipality — falls back to the reply the bot has always given. The
wrapper goes away the day the library exposes the field.

1 files changed, 141 insertions, 0 deletions

diff --git a/internal/bot/format_test.go b/internal/bot/format_test.go
index 56b8dda..513db36 100644
--- a/internal/bot/format_test.go
+++ b/internal/bot/format_test.go
@@ -7,6 +7,8 @@ import (
 	"testing"
 
 	cepis "cep.is/go"
+
+	"cep.is/telegrambot/internal/lookup"
 )
 
 func decodeAddress(t *testing.T, body string) *cepis.Address {
@@ -116,6 +118,145 @@ func TestErrorMessagesAreDistinct(t *testing.T) {
 	}
 }
 
+func notFound(faixa *lookup.Faixa) error {
+	return &lookup.NotFoundError{Faixa: faixa, Err: cepis.ErrCEPNotFound}
+}
+
+var areal = &lookup.Faixa{
+	Localidade: "Areal", UF: "RJ", Estado: "Rio de Janeiro", Regiao: "Sudeste",
+	IBGE: "3300225", CEPIni: "25845001", CEPFim: "25849899", CEPs: 118,
+}
+
+func TestNotFoundNamesTheMunicipality(t *testing.T) {
+	text := ErrorMessage(notFound(areal))
+
+	for _, needed := range []string{
+		"não encontrado", "Areal/RJ", "118 CEPs", "25845-001", "25849-899",
+		"esparsa", "Confira os oito dígitos",
+	} {
+		if !strings.Contains(text, needed) {
+			t.Fatalf("reply is missing %q:\n%s", needed, text)
+		}
+	}
+}
+
+// The municipality is context on a failure. A reply that looks like a hit would
+// have someone write the city down as the answer.
+func TestNotFoundDoesNotLookLikeAnAnswer(t *testing.T) {
+	text := ErrorMessage(notFound(areal))
+
+	if strings.Contains(text, "📮") {
+		t.Fatalf("the found-address marker leaked into a failure:\n%s", text)
+	}
+	if !strings.HasPrefix(text, notFoundHead) {
+		t.Fatalf("the reply must open by saying the CEP does not exist:\n%s", text)
+	}
+	if !strings.HasSuffix(text, notFoundAdvice) {
+		t.Fatalf("the reply must close with the usual advice:\n%s", text)
+	}
+	if strings.Contains(text, "25845-000") {
+		t.Fatalf("the reply suggests the CEP that just failed:\n%s", text)
+	}
+}
+
+// Absence of a faixa must be indistinguishable from the day before this
+// existed, byte for byte.
+func TestNotFoundWithoutFaixaIsUnchanged(t *testing.T) {
+	const want = "🔍 CEP não encontrado na base dos Correios (DNE).\n" +
+		"Confira os oito dígitos — a base é atualizada a cada quinze dias."
+
+	for name, err := range map[string]error{
+		"plain sentinel": cepis.ErrCEPNotFound,
+		"no faixa":       notFound(nil),
+		"empty faixa":    notFound(&lookup.Faixa{}),
+	} {
+		if got := ErrorMessage(err); got != want {
+			t.Fatalf("%s:\n got %q\nwant %q", name, got, want)
+		}
+	}
+}
+
+func TestNotFoundEscapesTheMunicipality(t *testing.T) {
+	text := ErrorMessage(notFound(&lookup.Faixa{
+		Localidade: "Santa <b>Rita</b> & Cia", UF: "M&G",
+		CEPIni: "25845001", CEPFim: "25849899", CEPs: 2,
+	}))
+
+	if strings.Contains(text, "<b>Rita</b>") {
+		t.Fatalf("the municipality name must be escaped:\n%s", text)
+	}
+	if !strings.Contains(text, "Santa &lt;b&gt;Rita&lt;/b&gt; &amp; Cia/M&amp;G") {
+		t.Fatalf("escaping is wrong:\n%s", text)
+	}
+}
+
+// Every field of the faixa is optional in practice, and a missing one may not
+// take the sentence down with it.
+func TestNotFoundDegradesFieldByField(t *testing.T) {
+	cases := map[string]struct {
+		faixa   *lookup.Faixa
+		present []string
+		absent  []string
+	}{
+		"no count": {
+			faixa:   &lookup.Faixa{Localidade: "Areal", UF: "RJ", CEPIni: "25845001", CEPFim: "25849899"},
+			present: []string{"Areal/RJ", "25845-001", "25849-899", "esparsa"},
+			absent:  []string{"CEPs,"},
+		},
+		"no range": {
+			faixa:   &lookup.Faixa{Localidade: "Areal", UF: "RJ", CEPs: 118},
+			present: []string{"Areal/RJ", "118 CEPs"},
+			absent:  []string{"<code>", "esparsa"},
+		},
+		"only the name": {
+			faixa:   &lookup.Faixa{Localidade: "Areal"},
+			present: []string{"cairia em <b>Areal</b>."},
+			absent:  []string{"<code>", "esparsa", "Areal/"},
+		},
+		"single CEP": {
+			faixa:   &lookup.Faixa{Localidade: "Vila", UF: "SP", CEPIni: "12345678", CEPFim: "12345678", CEPs: 1},
+			present: []string{"1 CEP."},
+			absent:  []string{"12345-678"},
+		},
+		"unusable range": {
+			faixa:   &lookup.Faixa{Localidade: "Areal", UF: "RJ", CEPIni: "abc", CEPFim: "2584", CEPs: 118},
+			present: []string{"118 CEPs."},
+			absent:  []string{"abc", "2584"},
+		},
+	}
+
+	for name, tc := range cases {
+		t.Run(name, func(t *testing.T) {
+			text := ErrorMessage(notFound(tc.faixa))
+			for _, needed := range tc.present {
+				if !strings.Contains(text, needed) {
+					t.Fatalf("missing %q:\n%s", needed, text)
+				}
+			}
+			for _, unwanted := range tc.absent {
+				if strings.Contains(text, unwanted) {
+					t.Fatalf("should not carry %q:\n%s", unwanted, text)
+				}
+			}
+		})
+	}
+}
+
+func TestInlineErrorDescriptionNamesTheMunicipality(t *testing.T) {
+	if got := inlineErrorDescription(notFound(areal)); got != "Cairia em Areal/RJ — toque para ver" {
+		t.Fatalf("description = %q", got)
+	}
+	if got := inlineErrorDescription(cepis.ErrCEPNotFound); got != "Toque para enviar o motivo" {
+		t.Fatalf("description without a faixa = %q", got)
+	}
+	// Titles and descriptions are plain text: escaping them would show the
+	// entities to the user.
+	got := inlineErrorDescription(notFound(&lookup.Faixa{Localidade: "Santa & Cia", UF: "SP"}))
+	if !strings.Contains(got, "Santa & Cia/SP") {
+		t.Fatalf("description = %q", got)
+	}
+}
+
 func TestHelpMentionsEveryEntryPoint(t *testing.T) {
 	text := HelpMessage("cepisbot")
 	for _, needed := range []string{"01001-000", "/cep 01001000", "@cepisbot 01001000", "https://cep.is"} {