package main

import (
	"encoding/csv"
	"encoding/json"
	"fmt"
	"log"
	"math/rand"
	"os"

	"github.com/brianvoe/gofakeit/v6"
)

var course_type = []string{
	"A",
	"B",
	"C",
	"D",
	"E",
}

type User struct {
	UID       string `json:"uid"`
	FirstName string `json:"first_name"`
	LastName  string `json:"last_name"`
	Status    string `json:"status"`
	ExamID    string `json:"exam_id"`
}

type Section struct {
	SectionID    string `json:"section_id"`
	CourseNumber string `json:"course_number"`
	Instructor   string `json:"course_instructor"`
	CourseTitle  string `json:"course_title"`
	CourseType   string `json:"course_type"`
}

type Config struct {
	NumberOfUsers int            `json:"number_of_users"`
	NumberOfSections int            `json:"number_of_sections"`
	NumberOfInstructors int `json:"number_of_instructors"`
	PercentStatus map[string]int `json:"percent_status"`
}

var statuses = []string{"JD", "LLM", "MCL", "PHD", "SJD", "MLS", "SPEC", "MNR", "CERT"}

func GenerateUserData (config Config) {
	// Build a weighted list of statuses
	weightedStatuses := make([]string, 0, 100)
	for status, pct := range config.PercentStatus {
		for i := 0; i < pct; i++ {
			weightedStatuses = append(weightedStatuses, status)
		}
	}

	// Generate unique ExamIDs and UIDs
	examIDs := uniqueNumericStrings(4, config.NumberOfUsers)
	uids := uniqueNumericStrings(10, config.NumberOfUsers)

	users := make([]User, config.NumberOfUsers)
	for i := range users {
		users[i] = User{
			UID:       uids[i],
			FirstName: gofakeit.FirstName(),
			LastName:  gofakeit.LastName(),
			Status:    weightedStatuses[rand.Intn(len(weightedStatuses))],
			ExamID:    examIDs[i],
		}
	}

	f, err := os.Create("users.csv")
	if err != nil {
		log.Fatalf("failed to create users.csv: %v", err)
	}
	defer f.Close()

	w := csv.NewWriter(f)
	if err := w.Write([]string{"uid", "first_name", "last_name", "status", "exam_id"}); err != nil {
		log.Fatalf("failed to write csv header: %v", err)
	}
	for _, u := range users {
		if err := w.Write([]string{u.UID, u.FirstName, u.LastName, u.Status, u.ExamID}); err != nil {
			log.Fatalf("failed to write csv row: %v", err)
		}
	}
	w.Flush()
	if err := w.Error(); err != nil {
		log.Fatalf("csv flush error: %v", err)
	}

	fmt.Printf("Generated %d users to users.csv\n", config.NumberOfUsers)
}

func GenerateSectionData(config Config) {
	// Generate unique instructor names: "LastName, X"
	instructorNames := make([]string, 0, config.NumberOfInstructors)
	seenInstructors := make(map[string]struct{}, config.NumberOfInstructors)
	for len(instructorNames) < config.NumberOfInstructors {
		name := fmt.Sprintf("%s, %c", gofakeit.LastName(), 'A'+rune(rand.Intn(26)))
		if _, exists := seenInstructors[name]; !exists {
			seenInstructors[name] = struct{}{}
			instructorNames = append(instructorNames, name)
		}
	}

	// Generate unique course numbers: one uppercase letter + 3 digits
	seenCourseNumbers := make(map[string]struct{}, config.NumberOfSections)
	courseNumbers := make([]string, 0, config.NumberOfSections)
	for len(courseNumbers) < config.NumberOfSections {
		cn := fmt.Sprintf("%c%03d", 'A'+rune(rand.Intn(26)), rand.Intn(1000))
		if _, exists := seenCourseNumbers[cn]; !exists {
			seenCourseNumbers[cn] = struct{}{}
			courseNumbers = append(courseNumbers, cn)
		}
	}

	sectionIDs := uniqueNumericStrings(5, config.NumberOfSections)

	sections := make([]Section, config.NumberOfSections)
	for i := range sections {
		sections[i] = Section{
			SectionID:    sectionIDs[i],
			CourseNumber: courseNumbers[i],
			Instructor:   instructorNames[rand.Intn(len(instructorNames))],
			CourseTitle:  gofakeit.BookTitle(),
			CourseType:   course_type[rand.Intn(len(course_type))],
		}
	}

	f, err := os.Create("sections.csv")
	if err != nil {
		log.Fatalf("failed to create sections.csv: %v", err)
	}
	defer f.Close()

	w := csv.NewWriter(f)
	if err := w.Write([]string{"section_id", "course_number", "course_instructor", "course_title", "course_type"}); err != nil {
		log.Fatalf("failed to write csv header: %v", err)
	}
	for _, s := range sections {
		if err := w.Write([]string{s.SectionID, s.CourseNumber, s.Instructor, s.CourseTitle, s.CourseType}); err != nil {
			log.Fatalf("failed to write csv row: %v", err)
		}
	}
	w.Flush()
	if err := w.Error(); err != nil {
		log.Fatalf("csv flush error: %v", err)
	}

	fmt.Printf("Generated %d sections to sections.csv\n", config.NumberOfSections)
}

func main() {
	data, err := os.ReadFile("config.json")
	if err != nil {
		log.Fatalf("failed to read config.json: %v", err)
	}

	var config Config
	if err := json.Unmarshal(data, &config); err != nil {
		log.Fatalf("failed to parse config.json: %v", err)
	}

	total := 0
	for _, v := range config.PercentStatus {
		total += v
	}
	if total != 100 {
		log.Fatalf("percent_status values must total 100, got %d", total)
	}

	GenerateUserData(config)
	GenerateSectionData(config)

}

// uniqueNumericStrings generates n unique zero-padded numeric strings of the given digit length.
func uniqueNumericStrings(digits, n int) []string {
	max := 1
	for i := 0; i < digits; i++ {
		max *= 10
	}
	if n > max {
		log.Fatalf("cannot generate %d unique %d-digit strings (max %d)", n, digits, max)
	}

	seen := make(map[int]struct{}, n)
	results := make([]string, 0, n)
	format := fmt.Sprintf("%%0%dd", digits)
	for len(results) < n {
		v := rand.Intn(max)
		if _, exists := seen[v]; !exists {
			seen[v] = struct{}{}
			results = append(results, fmt.Sprintf(format, v))
		}
	}
	return results
}