Add split command (#30)

README.md

@@ -60,6 +60,12 @@ go run . combine
 
 This looks for all files named `data/courses-{year}.json` and merges them.
 
+You can also do the inverse, splitting a single `data/courses.json` into multiple `data/courses-{year}.json`.
+
+```bash
+go run . split
+```
+
 ### Running the server
 
 The server listens for web requests on port 7500. (It also spawns a Redis instance, using Docker, on port 7501.)

main.go

@@ -7,6 +7,7 @@ import (
 	"log"
 	"os"
 	"path/filepath"
+	"sort"
 
 	"classes.wtf/datasource"
 	"classes.wtf/server"
@@ -78,6 +79,46 @@ func main() {
 		}
 		log.Printf("wrote %d courses to data/courses.json", len(courses))
 
+	case "split":
+		splitCmd := flag.NewFlagSet("split", flag.ExitOnError)
+		splitCmd.Parse(os.Args[2:])
+
+		filename := "data/courses.json"
+
+		log.Printf("parsing combined course data from %s", filename)
+		file, err := os.Open(filename)
+		if err != nil {
+			log.Fatalf("failed to open %s: %v", filename, err)
+		}
+		var courses []datasource.Course
+		if err = json.NewDecoder(file).Decode(&courses); err != nil {
+			log.Fatalf("failed to parse %s: %v", filename, err)
+		}
+
+		log.Printf("got %d courses; splitting by year", len(courses))
+		coursesByYear := make(map[uint32][]datasource.Course)
+		for _, course := range courses {
+			coursesByYear[course.AcademicYear] = append(coursesByYear[course.AcademicYear], course)
+		}
+		years := make([]uint32, 0, len(coursesByYear))
+		for year := range coursesByYear {
+			years = append(years, year)
+		}
+		sort.Slice(years, func(i, j int) bool { return years[i] < years[j] })
+
+		log.Printf("writing")
+		for _, year := range years {
+			filename := fmt.Sprintf("data/courses-%d.json", year)
+			yearCourses := coursesByYear[year]
+			log.Printf("  - %s  [len: %d]", filename, len(yearCourses))
+			yearCoursesJson, _ := json.Marshal(yearCourses)
+			if err := os.WriteFile(filename, yearCoursesJson, 0644); err != nil {
+				log.Fatalf("failed to write %s: %v", filename, err)
+			}
+		}
+
+		log.Printf("wrote %d courses", len(courses))
+
 	case "server":
 		serverCmd := flag.NewFlagSet("server", flag.ExitOnError)
 		data := serverCmd.String("data", "", "path or url for the data file")