kit/internal/core/truncate.go

package core

import (
	"fmt"
	"strings"
)

const (
	defaultMaxLines   = 2000
	defaultMaxBytes   = 50 * 1024 // 50KB
	defaultMaxLineLen = 2000      // max characters per line before truncation
	grepMaxLineLen    = 500

	// DefaultMaxLines is the exported default line limit for truncation.
	DefaultMaxLines = defaultMaxLines
	// DefaultMaxBytes is the exported default byte limit for truncation.
	DefaultMaxBytes = defaultMaxBytes
	// DefaultMaxLineLen is the exported default per-line character limit.
	DefaultMaxLineLen = defaultMaxLineLen
)

// TruncationResult describes how output was truncated.
type TruncationResult struct {
	Content   string
	Truncated bool
	TruncBy   string // "lines", "bytes", or ""
	Total     int    // total lines before truncation
	Kept      int    // lines kept after truncation
}

// TruncateTail keeps the last maxLines lines and at most maxBytes bytes.
// Individual lines longer than defaultMaxLineLen are truncated to prevent
// extremely long single lines from blowing up the TUI when wrapped.
// Used for bash output where the tail is most relevant.
func TruncateTail(content string, maxLines, maxBytes int) TruncationResult {
	if maxLines <= 0 {
		maxLines = defaultMaxLines
	}
	if maxBytes <= 0 {
		maxBytes = defaultMaxBytes
	}

	lines := strings.Split(content, "\n")
	total := len(lines)

	// Truncate individual long lines first to prevent single lines from
	// wrapping into hundreds of visual lines in the TUI.
	lines = truncateLongLines(lines, defaultMaxLineLen)

	// Truncate by lines (keep tail)
	truncBy := ""
	if total > maxLines {
		lines = lines[total-maxLines:]
		truncBy = "lines"
	}

	result := strings.Join(lines, "\n")

	// Then truncate by bytes if still too large
	if len(result) > maxBytes {
		// Find a line boundary near the byte limit
		result = result[len(result)-maxBytes:]
		// Discard partial first line
		if idx := strings.Index(result, "\n"); idx >= 0 {
			result = result[idx+1:]
		}
		truncBy = "bytes"
	}

	kept := strings.Count(result, "\n") + 1
	if truncBy != "" {
		header := fmt.Sprintf("[truncated %d/%d lines, showing last %d lines]\n", total-kept, total, kept)
		result = header + result
	}

	return TruncationResult{
		Content:   result,
		Truncated: truncBy != "",
		TruncBy:   truncBy,
		Total:     total,
		Kept:      kept,
	}
}

// truncateHead keeps the first maxLines lines and at most maxBytes bytes.
// Individual lines longer than defaultMaxLineLen are truncated.
// Used for read, grep, find, ls output where the head is most relevant.
func truncateHead(content string, maxLines, maxBytes int) TruncationResult {
	if maxLines <= 0 {
		maxLines = defaultMaxLines
	}
	if maxBytes <= 0 {
		maxBytes = defaultMaxBytes
	}

	lines := strings.Split(content, "\n")
	total := len(lines)

	// Truncate individual long lines first.
	lines = truncateLongLines(lines, defaultMaxLineLen)

	truncBy := ""
	if total > maxLines {
		lines = lines[:maxLines]
		truncBy = "lines"
	}

	result := strings.Join(lines, "\n")

	if len(result) > maxBytes {
		result = result[:maxBytes]
		// Discard partial last line
		if idx := strings.LastIndex(result, "\n"); idx >= 0 {
			result = result[:idx]
		}
		truncBy = "bytes"
	}

	kept := strings.Count(result, "\n") + 1
	if truncBy != "" {
		result += fmt.Sprintf("\n[truncated %d/%d lines, showing first %d lines]", total-kept, total, kept)
	}

	return TruncationResult{
		Content:   result,
		Truncated: truncBy != "",
		TruncBy:   truncBy,
		Total:     total,
		Kept:      kept,
	}
}

// truncateLongLines caps each line to maxLen characters, appending a
// "[...N chars truncated]" marker to any line that exceeds the limit.
// This prevents a single very long line (e.g. minified JSON/JS) from
// wrapping into hundreds of visual rows and blowing up the TUI.
func truncateLongLines(lines []string, maxLen int) []string {
	for i, line := range lines {
		if len(line) > maxLen {
			lines[i] = line[:maxLen] + fmt.Sprintf("... [%d chars truncated]", len(line)-maxLen)
		}
	}
	return lines
}

// truncateLine truncates a single line to maxChars, appending "..." if cut.
func truncateLine(line string, maxChars int) string {
	if maxChars <= 0 {
		maxChars = grepMaxLineLen
	}
	if len(line) <= maxChars {
		return line
	}
	return line[:maxChars] + "..."
}