fix(key),test: simplify the input analysis code

key_sequences.go

@@ -0,0 +1,71 @@
+package tea
+
+import "sort"
+
+// extSequences is used by the map-based algorithm below. It contains
+// the sequences plus their alternatives with an escape character
+// prefixed, plus the control chars, plus the space.
+// It does not contain the NUL character, which is handled specially
+// by detectOneMsg.
+var extSequences = func() map[string]Key {
+	s := map[string]Key{}
+	for seq, key := range sequences {
+		key := key
+		s[seq] = key
+		if !key.Alt {
+			key.Alt = true
+			s["\x1b"+seq] = key
+		}
+	}
+	for i := keyNUL + 1; i <= keyDEL; i++ {
+		if i == keyESC {
+			continue
+		}
+		s[string([]byte{byte(i)})] = Key{Type: i}
+		s[string([]byte{'\x1b', byte(i)})] = Key{Type: i, Alt: true}
+		if i == keyUS {
+			i = keyDEL - 1
+		}
+	}
+	s[" "] = Key{Type: KeySpace, Runes: spaceRunes}
+	s["\x1b "] = Key{Type: KeySpace, Alt: true, Runes: spaceRunes}
+	s["\x1b\x1b"] = Key{Type: KeyEscape, Alt: true}
+	return s
+}()
+
+// seqLengths is the sizes of valid sequences, starting with the
+// largest size.
+var seqLengths = func() []int {
+	sizes := map[int]struct{}{}
+	for seq := range extSequences {
+		sizes[len(seq)] = struct{}{}
+	}
+	lsizes := make([]int, 0, len(sizes))
+	for sz := range sizes {
+		lsizes = append(lsizes, sz)
+	}
+	sort.Slice(lsizes, func(i, j int) bool { return lsizes[i] > lsizes[j] })
+	return lsizes
+}()
+
+// detectSequence uses a longest prefix match over the input
+// sequence and a hash map.
+func detectSequence(input []byte) (hasSeq bool, width int, msg Msg) {
+	seqs := extSequences
+	for _, sz := range seqLengths {
+		if sz > len(input) {
+			continue
+		}
+		prefix := input[:sz]
+		key, ok := seqs[string(prefix)]
+		if ok {
+			return true, sz, KeyMsg(key)
+		}
+	}
+	// Is this an unknown CSI sequence?
+	if loc := unknownCSIRe.FindIndex(input); loc != nil {
+		return true, loc[1], unknownCSISequenceMsg(input[:loc[1]])
+	}
+
+	return false, 0, nil
+}