iterm2_bg.go

package main

import (
	"fmt"
	"io"
	"os"
	"path/filepath"
)

const iterm2BGDir = "/tmp/dev-image-chat-bg"

// ITerm2BGPath returns the background image path for a given project key and slot.
func ITerm2BGPath(projectKey string, slot int) string {
	return filepath.Join(iterm2BGDir, fmt.Sprintf("%s_%d.png", projectKey, slot))
}

// chooseSlot picks the slot to write next by selecting the older of the two files.
// If neither exists, returns 0.
func chooseSlot(projectKey string) int {
	info0, err0 := os.Stat(ITerm2BGPath(projectKey, 0))
	info1, err1 := os.Stat(ITerm2BGPath(projectKey, 1))

	switch {
	case err0 != nil && err1 != nil:
		return 0 // neither exists
	case err0 != nil:
		return 0 // slot 0 doesn't exist, write there
	case err1 != nil:
		return 1 // slot 1 doesn't exist, write there
	default:
		// Both exist — overwrite the older one
		if info0.ModTime().Before(info1.ModTime()) {
			return 0
		}
		return 1
	}
}

// CopyImageForProject copies the generated image to a per-project path,
// alternating between two slots so that iTerm2 detects the path change
// and reloads the image.
func CopyImageForProject(srcPath, projectKey string) error {
	if err := os.MkdirAll(iterm2BGDir, 0700); err != nil {
		return fmt.Errorf("failed to create bg dir: %w", err)
	}

	src, err := os.Open(srcPath)
	if err != nil {
		return fmt.Errorf("failed to open source image: %w", err)
	}
	defer src.Close()

	slot := chooseSlot(projectKey)
	dstPath := ITerm2BGPath(projectKey, slot)
	dst, err := os.CreateTemp(iterm2BGDir, "tmp-*.png")
	if err != nil {
		return fmt.Errorf("failed to create temp file: %w", err)
	}
	tmpPath := dst.Name()

	if _, err := io.Copy(dst, src); err != nil {
		_ = dst.Close()
		os.Remove(tmpPath)
		return fmt.Errorf("failed to copy image: %w", err)
	}
	if err := dst.Close(); err != nil {
		os.Remove(tmpPath)
		return fmt.Errorf("failed to close temp file: %w", err)
	}

	// Atomic rename to avoid partial reads by the watcher.
	if err := os.Rename(tmpPath, dstPath); err != nil {
		os.Remove(tmpPath)
		return fmt.Errorf("failed to rename temp file: %w", err)
	}

	return nil
}