Add database helpers. Comment it.

core/database.go

@@ -26,24 +26,76 @@ type Row struct {
 type EventType int
 
 const (
-	EventService = iota
+	// represents when a servire's status changes
+	EventService EventType = iota
+	// represents when this program starts 
 	EventSelfUp
+	// represents when this program stops
 	EventSelfDown
 )
 
-// either EventSelfUp or EventSelfDown
-// I want real enum...
-type SelfStatusUpdate EventType
 
 type Database interface {
 	// dump data to disk
 	Persist() error
+
 	// get all records after some time (`cutoff`)
-	QueryAllAfter(url string, cutoff time.Time) ([]Row, error)
+	//
+	// Usage: (get past 7 days of history)
+	// db.QueryAllAfter(time.Now().Add(-7 * 24 * time.Hour))
+	//
+	// Then, parse the result with `GetServiceStatusSpans(rows, service_url)`
+	QueryAllAfter(cutoff time.Time) ([]Row, error)
+	
 	// store service status records with timestamp
 	StoreServiceStatusBatch(entries scanner.ServiceStatusBatch, when time.Time) error
+	
 	// store self up/down event with timestamp
-	StoreSelfStatus(status SelfStatusUpdate, when time.Time) error
+	// 
+	// `status` is EventSelfUp or EventSelfDown
+	StoreSelfStatus(status EventType, when time.Time) error
+}
+
+type Span struct {
+	start  time.Time
+	stop   time.Time
+	status scanner.ServiceStatus
+}
+
+func append_close_span(res *[]Span, rows []Row, start_i, stop_i int, status scanner.ServiceStatus) {
+	var stop_time time.Time
+	if stop_i < 0 {
+		stop_time = time.Now()
+	} else {
+		stop_time = rows[stop_i].time
+	}
+	start_time := rows[start_i].time
+	*res = append(*res, Span{start_time, stop_time, status})
+}
+
+// Find when the service is up, and when the service is down
+// returns timespans. There might be gaps between two spans, meaning that we don't know the state of that service
+func CalculateServiceStatusSpans(rows []Row, service_url string) []Span {
+	res := []Span{}
+	start_i := -1
+	var status scanner.ServiceStatus
+
+	for i, v := range rows {
+		switch v.kind {
+		case EventSelfDown:
+			append_close_span(&res, rows, start_i, i, status)
+			start_i = -1
+		case EventService:
+			if v.data.Url == service_url {
+				append_close_span(&res, rows, start_i, i, status)
+				start_i = i
+				status = v.data
+			}
+		}
+	}
+	append_close_span(&res, rows, start_i, -1, status)
+
+	return res
 }
 
 type dumbDatabase struct {
@@ -52,6 +104,7 @@ type dumbDatabase struct {
 	mutex   sync.Mutex
 }
 
+// Load the newest backup, or start anew
 func OpenDatabase(dir string) (Database, error) {
 	if dir == "" {
 		return nil, fmt.Errorf("database path is empty. did you set it in config file?")
@@ -75,7 +128,7 @@ func OpenDatabase(dir string) (Database, error) {
 		}
 		_, err := ulid.Parse(filename)
 		if err != nil {
-			continue
+			continue // because database files have ULID as names
 		}
 		fullpath := path.Join(dir, filename)
 		content, err := os.ReadFile(fullpath)
@@ -103,12 +156,16 @@ func (db *dumbDatabase) sortRows() {
 	})
 }
 
+// Dump data to file
+//
+// Steps:
+// create -> write -> fsync -> rename
 func (db *dumbDatabase) Persist() error {
 	db.mutex.Lock()
 	defer db.mutex.Unlock()
 
 	db.sortRows()
-	id := ulid.Make().String()
+	id := ulid.Make().String() // checkpoint filename is ULID
 
 	filename_final := path.Join(db.rootDir, id)
 	filename_tmp := path.Join(db.rootDir, id+".tmp")
@@ -117,7 +174,7 @@ func (db *dumbDatabase) Persist() error {
 		return err
 	}
 	defer file.Close()
-	err = json.NewEncoder(file).Encode(db.rows)
+	err = json.NewEncoder(file).Encode(db.rows) // file content is JSON
 	if err != nil {
 		return err
 	}
@@ -133,10 +190,10 @@ func (db *dumbDatabase) Persist() error {
 	return nil
 }
 
-func (db *dumbDatabase) QueryAllAfter(url string, cutoff time.Time) ([]Row, error) {
+func (db *dumbDatabase) QueryAllAfter(cutoff time.Time) ([]Row, error) {
 	db.mutex.Lock()
 	defer db.mutex.Unlock()
-	
+
 	db.sortRows()
 
 	var start int = -1
@@ -156,7 +213,7 @@ func (db *dumbDatabase) QueryAllAfter(url string, cutoff time.Time) ([]Row, erro
 func (db *dumbDatabase) StoreServiceStatusBatch(entries scanner.ServiceStatusBatch, when time.Time) error {
 	db.mutex.Lock()
 	defer db.mutex.Unlock()
-	
+
 	for _, v := range entries {
 		new_row := Row{when, EventService, v}
 
@@ -183,10 +240,10 @@ func (db *dumbDatabase) StoreServiceStatusBatch(entries scanner.ServiceStatusBat
 
 const max_rows = 10000
 
-func (db *dumbDatabase) StoreSelfStatus(status SelfStatusUpdate, when time.Time) error {
+func (db *dumbDatabase) StoreSelfStatus(status EventType, when time.Time) error {
 	db.mutex.Lock()
 	defer db.mutex.Unlock()
-	
+
 	if status != EventSelfUp && status != EventSelfDown {
 		log.Panicf("(StoreSelfStatus) invalid value: %v", status)
 	}