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fn_registry/functions/tui/vt_render.go
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2026-06-04 23:44:39 +02:00

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package tui
import (
"strings"
"github.com/hinshun/vt10x"
)
// VTRender emulates a terminal of size cols×rows, feeds raw into it,
// and returns the resulting screen as plain text preserving the visual layout.
//
// Unlike strip_ansi which removes escape sequences from sequential output,
// VTRender correctly handles TUIs that use absolute cursor positioning
// (ESC[row;colH, ESC[colG, etc.) by maintaining a 2D grid and reconstructing
// real spaces between columns.
//
// Defaults: rows<=0 → 40, cols<=0 → 120.
// Trailing spaces on each line are trimmed. Trailing empty lines are removed.
func VTRender(raw string, rows, cols int) string {
if rows <= 0 {
rows = 40
}
if cols <= 0 {
cols = 120
}
// Create a fresh terminal emulator for each call — no shared state.
term := vt10x.New(vt10x.WithSize(cols, rows))
term.Write([]byte(raw)) //nolint:errcheck // Write on vt10x never returns a meaningful error
// String() returns all rows joined by '\n', one row per terminal line.
// Each row is exactly `cols` runes wide (padded with NUL/space for empty cells).
raw = term.String()
lines := strings.Split(raw, "\n")
// Trim trailing spaces from every line (cells that were never written
// contain NUL '\x00' in some versions, so we trim both NUL and space).
for i, line := range lines {
// Replace NUL characters (unwritten cells) with spaces first.
line = strings.ReplaceAll(line, "\x00", " ")
lines[i] = strings.TrimRight(line, " ")
}
// Remove trailing empty lines — the TUI probably only used the top portion
// of the grid. Keep intermediate empty lines (real visual separators).
last := len(lines) - 1
for last >= 0 && lines[last] == "" {
last--
}
lines = lines[:last+1]
return strings.Join(lines, "\n")
}