patterm/internal/app/keymatch.go

package app

import (
	"strconv"
	"strings"
)

// csiLen returns the byte length of the CSI sequence starting at
// chunk[i], or 0 if chunk[i:] doesn't begin a complete CSI. A CSI is
// ESC '[' followed by parameter bytes (0x30..0x3F), intermediate bytes
// (0x20..0x2F), and one final byte (0x40..0x7E).
func csiLen(chunk []byte, i int) int {
	if i+1 >= len(chunk) || chunk[i] != 0x1b || chunk[i+1] != '[' {
		return 0
	}
	end := i + 2
	for end < len(chunk) && chunk[end] >= 0x30 && chunk[end] <= 0x3F {
		end++
	}
	for end < len(chunk) && chunk[end] >= 0x20 && chunk[end] <= 0x2F {
		end++
	}
	if end >= len(chunk) {
		return 0
	}
	if final := chunk[end]; final < 0x40 || final > 0x7E {
		return 0
	}
	return end - i + 1
}

// csiuKey is the decoded form of a CSI u key event. key is the kitty
// keycode (the unshifted unicode codepoint for character keys, or a
// kitty functional-key constant). mods is the kitty modifier value
// (1 + bitfield: shift=1, alt=2, ctrl=4, super=8, …). event is the
// event type (1=press, 2=repeat, 3=release).
type csiuKey struct {
	key   int
	mods  int
	event int
}

// decodeCSIu parses the parameter string of a `CSI ... u` sequence.
// The kitty shape is:
//
//	<key>[:<shifted>[:<base>]] [;<mods>[:<event>][;<text>...]]
//
// Unspecified groups default to mods=1, event=1.
func decodeCSIu(params string) (csiuKey, bool) {
	parts := strings.SplitN(params, ";", 3)

	keyGroup := parts[0]
	if i := strings.IndexByte(keyGroup, ':'); i >= 0 {
		keyGroup = keyGroup[:i]
	}
	if keyGroup == "" {
		return csiuKey{}, false
	}
	key, err := strconv.Atoi(keyGroup)
	if err != nil {
		return csiuKey{}, false
	}

	mods, event := 1, 1
	if len(parts) > 1 {
		modGroup := parts[1]
		eventGroup := ""
		if i := strings.IndexByte(modGroup, ':'); i >= 0 {
			eventGroup = modGroup[i+1:]
			modGroup = modGroup[:i]
		}
		if modGroup != "" {
			m, err := strconv.Atoi(modGroup)
			if err != nil {
				return csiuKey{}, false
			}
			mods = m
		}
		if eventGroup != "" {
			e, err := strconv.Atoi(eventGroup)
			if err != nil {
				return csiuKey{}, false
			}
			event = e
		}
	}
	return csiuKey{key: key, mods: mods, event: event}, true
}

// matchCtrlK reports whether chunk[i:] starts with a Ctrl-K keystroke
// in any of the encodings we accept on input, and returns the number of
// bytes consumed.
//
// Three encodings are recognised:
//
//   - Legacy: the single byte 0x0B.
//   - Kitty keyboard CSI u: ESC '[' 107 ';' 5 'u' (optionally with sub-
//     parameters and trailing groups, see [kitty]). The kitty protocol
//     fires when a child PTY pushes it onto the host terminal's flag
//     stack; codex/ratatui does this on startup, which is what motivated
//     this matcher.
//   - xterm modifyOtherKeys: ESC '[' 27 ';' 5 ';' 107 '~'.
//
// Only an unmodified Ctrl-K (modifier value exactly 5 — i.e. Ctrl with
// no Shift/Alt/Meta) and a key-press event (event-type 1 or omitted)
// match. That mirrors the legacy 0x0B byte, which only fires on plain
// Ctrl-K too.
//
// [kitty]: https://sw.kovidgoyal.net/kitty/keyboard-protocol/
func matchCtrlK(chunk []byte, i int) (matched bool, advance int) {
	if i >= len(chunk) {
		return false, 0
	}
	if chunk[i] == keyCtrlK {
		return true, 1
	}
	n := csiLen(chunk, i)
	if n == 0 {
		return false, 0
	}
	final := chunk[i+n-1]
	params := string(chunk[i+2 : i+n-1])
	switch final {
	case 'u':
		k, ok := decodeCSIu(params)
		if ok && k.key == 107 && k.mods == 5 && k.event == 1 {
			return true, n
		}
	case '~':
		if isModifyOtherKeysCtrlK(params) {
			return true, n
		}
	}
	return false, 0
}

// isModifyOtherKeysCtrlK parses xterm's CSI 27;<mods>;<key>~ form.
func isModifyOtherKeysCtrlK(params string) bool {
	parts := strings.Split(params, ";")
	if len(parts) != 3 {
		return false
	}
	return parts[0] == "27" && parts[1] == "5" && parts[2] == "107"
}