claude-code/dashboard/internal/claude/history_tailer.go

package claude

import (
	"bufio"
	"encoding/json"
	"os"
	"time"
)

func TailHistoryFile(stop <-chan struct{}, hub *EventHub, path string) {
	var offset int64

	for {
		select {
		case <-stop:
			return
		default:
		}

		stat, err := os.Stat(path)
		if err != nil {
			if !os.IsNotExist(err) {
				hub.Publish(Event{
					TS:   time.Now(),
					Type: EventTypeServerError,
					Data: map[string]any{"error": err.Error()},
				})
			}
			time.Sleep(1 * time.Second)
			continue
		}

		size := stat.Size()
		if size > offset {
			if err := processNewBytes(path, offset, size, hub); err != nil {
				hub.Publish(Event{
					TS:   time.Now(),
					Type: EventTypeServerError,
					Data: map[string]any{"error": err.Error()},
				})
			}
			offset = size
		} else if size < offset {
			offset = 0
			hub.Publish(Event{
				TS:   time.Now(),
				Type: EventTypeServerNotice,
				Data: map[string]any{"msg": "file truncated, resetting offset"},
			})
		}

		time.Sleep(500 * time.Millisecond)
	}
}

func processNewBytes(path string, oldSize, newSize int64, hub *EventHub) error {
	f, err := os.Open(path)
	if err != nil {
		return err
	}
	defer f.Close()

	if _, err := f.Seek(oldSize, 0); err != nil {
		return err
	}

	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		line := scanner.Text()
		if line == "" {
			continue
		}

		data := map[string]any{
			"rawLine": line,
		}

		var jsonData map[string]any
		if err := json.Unmarshal([]byte(line), &jsonData); err != nil {
			data["parseError"] = err.Error()
		} else {
			data["json"] = jsonData

			summary := map[string]string{}
			if v, ok := jsonData["sessionId"].(string); ok {
				summary["sessionId"] = v
			}
			if v, ok := jsonData["project"].(string); ok {
				summary["project"] = v
			}
			if v, ok := jsonData["display"].(string); ok {
				summary["display"] = v
			}
			data["summary"] = summary
		}

		hub.Publish(Event{
			TS:   time.Now(),
			Type: EventTypeHistoryAppend,
			Data: data,
		})
	}

	return scanner.Err()
}