fix(worked-before): a prefixed call is one operator, not a whole country

Reported from a screenshot: working ZA/OE8NDR, the worked-before list showed
ZA/IZ2DPX and ZA/IW2JOP beside him and the header counted all four as contacts
"with this call".

callMatch folded portable forms together by taking the part before the slash.
That is right when the slash carries a suffix — RK3DWA/3, RK3DWA/P are one
person — and exactly wrong when it carries a prefix: ZA/OE8NDR became the
station "ZA", and the predicate `callsign LIKE 'ZA/%'` then selected every other
visitor to Albania.

The operator's own call is now picked out properly: drop the known qualifiers
(P, M, MM, AM, QRP, a bare call-area digit) and of what remains take the longest
part — a country prefix is short by nature, ZA, F, KH6, VP2E, and a callsign is
not. The predicate matches the prefixed forms too, so ZA/OE8NDR and a plain
OE8NDR still find each other, which is the whole point of the fold.

A base under three characters falls back to an exact match: a malformed entry
must not produce a LIKE that selects half the logbook.

internal/qso/callmatch_test.go

@@ -2,6 +2,32 @@ package qso
 
 import "testing"
 
+// baseCall picks the operator's OWN callsign out of a portable form. The slash
+// carries a qualifier on either side and which side depends on what it is, so
+// this is the whole difficulty.
+func TestBaseCall(t *testing.T) {
+	for in, want := range map[string]string{
+		"RK3DWA":      "RK3DWA",
+		"RK3DWA/3":    "RK3DWA", // call-area digit
+		"RK3DWA/P":    "RK3DWA", // portable
+		"RK3DWA/QRP":  "RK3DWA",
+		"RK3DWA/MM":   "RK3DWA",
+		"ZA/OE8NDR":   "OE8NDR", // an Austrian in Albania — the case that prompted this
+		"ZA/IZ2DPX":   "IZ2DPX",
+		"F/DL1ABC":    "DL1ABC",
+		"F/DL1ABC/P":  "DL1ABC",
+		"KH6/K6ABC":   "K6ABC",
+		"VP2E/W1ABC":  "W1ABC",
+		"3DA0/ZS1ABC": "ZS1ABC",
+		"9A/S51AB":    "S51AB",
+		"/RK3DWA":     "RK3DWA",
+	} {
+		if got := baseCall(in); got != want {
+			t.Errorf("baseCall(%q) = %q, want %q", in, got, want)
+		}
+	}
+}
+
 // The predicate behind "Worked before". Exact when folding is off; with it on,
 // a station's portable forms are one operator — and the fold has to work from
 // either end, because you may type the base call or the portable one.
@@ -10,25 +36,61 @@ func TestCallMatch(t *testing.T) {
 		t.Errorf("exact: got %q %v", pred, args)
 	}
 
-	// Typing the base call: match it and everything suffixed off it.
-	pred, args := callMatch("RK3DWA", true)
-	if pred != "(callsign = ? OR callsign LIKE ?)" {
-		t.Errorf("variants predicate = %q", pred)
-	}
-	if len(args) != 2 || args[0] != "RK3DWA" || args[1] != "RK3DWA/%" {
-		t.Errorf("variants args = %v, want [RK3DWA RK3DWA/%%]", args)
-	}
+	// Typing the base call: match it, everything suffixed off it, and every
+	// prefixed form of it.
+	_, args := callMatch("RK3DWA", true)
+	want := []any{"RK3DWA", "RK3DWA/%", "%/RK3DWA", "%/RK3DWA/%"}
+	assertArgs(t, "base call", args, want)
 
-	// Typing a portable form must reach the plain call too — the suffix is
+	// Typing a portable form must reach the plain call too — the qualifier is
 	// stripped from the INPUT, not just matched in the column.
 	_, args = callMatch("RK3DWA/3", true)
-	if len(args) != 2 || args[0] != "RK3DWA" || args[1] != "RK3DWA/%" {
-		t.Errorf("portable input args = %v, want [RK3DWA RK3DWA/%%]", args)
+	assertArgs(t, "portable input", args, want)
+}
+
+// A prefixed call is the same operator, and NOT every other visitor to that
+// country.
+//
+// Matching on the part before the slash made ZA/OE8NDR the station "ZA", so the
+// worked-before list for one Austrian operating from Albania showed every other
+// ZA/ guest — two Italians — and counted them as four contacts "with this
+// call". Reported from a screenshot of exactly that.
+func TestCallMatchPrefixedIsTheOperatorNotTheCountry(t *testing.T) {
+	_, args := callMatch("ZA/OE8NDR", true)
+	assertArgs(t, "ZA/OE8NDR", args, []any{"OE8NDR", "OE8NDR/%", "%/OE8NDR", "%/OE8NDR/%"})
+
+	for _, a := range args {
+		if s, _ := a.(string); s == "ZA" || s == "ZA/%" {
+			t.Fatalf("the country prefix is still being matched as a station: %v", args)
+		}
 	}
 
-	// A leading slash is not a suffix marker — dropping to "" there would match
-	// the entire logbook.
-	if _, args := callMatch("/RK3DWA", true); args[0] != "/RK3DWA" {
-		t.Errorf("leading slash: args[0] = %v, want the call unchanged", args[0])
+	// And the two are not each other: nothing in one operator's predicate can
+	// select the other's call.
+	_, other := callMatch("ZA/IZ2DPX", true)
+	assertArgs(t, "ZA/IZ2DPX", other, []any{"IZ2DPX", "IZ2DPX/%", "%/IZ2DPX", "%/IZ2DPX/%"})
+}
+
+// A base too short to be a callsign falls back to an exact match. "F/DL1ABC"
+// resolves fine, but a malformed entry must never produce a LIKE that selects
+// half the logbook.
+func TestCallMatchRefusesAShortBase(t *testing.T) {
+	for _, call := range []string{"F/", "9A", "/P", "K/M"} {
+		pred, args := callMatch(call, true)
+		if pred != "callsign = ?" || len(args) != 1 {
+			t.Errorf("%q produced %q %v — want an exact match", call, pred, args)
+		}
+	}
+}
+
+func assertArgs(t *testing.T, what string, got, want []any) {
+	t.Helper()
+	if len(got) != len(want) {
+		t.Fatalf("%s: args %v, want %v", what, got, want)
+	}
+	for i := range want {
+		if got[i] != want[i] {
+			t.Fatalf("%s: args %v, want %v", what, got, want)
+		}
 	}
 }