fyp/logic/utils/utils.go

package utils

import (
	"database/sql"
	"errors"
	"fmt"
	"io"
	"mime"
	"net/http"
	"net/url"
	"reflect"
	"strconv"
	"strings"

	"github.com/google/uuid"
)

func CheckEmpty(f url.Values, path string) bool {
	return !f.Has(path) || f.Get(path) == ""
}

func CheckNumber(f url.Values, path string, number *int) bool {
	if CheckEmpty(f, path) {
		fmt.Println("here", path)
		fmt.Println(f.Get(path))
		return false
	}
	n, err := strconv.Atoi(f.Get(path))
	if err != nil {
		fmt.Println(err)
		return false
	}
	*number = n
	return true
}

func CheckFloat64(f url.Values, path string, number *float64) bool {
	if CheckEmpty(f, path) {
		fmt.Println("here", path)
		fmt.Println(f.Get(path))
		return false
	}
	n, err := strconv.ParseFloat(f.Get(path), 64)
	if err != nil {
		fmt.Println(err)
		return false
	}
	*number = n
	return true
}

func CheckId(f url.Values, path string) bool {
	return !CheckEmpty(f, path) && IsValidUUID(f.Get(path))
}

func IsValidUUID(u string) bool {
	_, err := uuid.Parse(u)
	return err == nil
}

func GetIdFromUrl(r *http.Request, target string) (string, error) {
	if !r.URL.Query().Has(target) {
		return "", errors.New("Query does not have " + target)
	}

	id := r.URL.Query().Get("id")
	if len(id) == 0 {
		return "", errors.New("Query is empty for " + target)
	}

	if !IsValidUUID(id) {
		return "", errors.New("Value of query is not a valid uuid for " + target)
	}

	return id, nil
}

type maxBytesReader struct {
	w   http.ResponseWriter
	r   io.ReadCloser // underlying reader
	i   int64         // max bytes initially, for MaxBytesError
	n   int64         // max bytes remaining
	err error         // sticky error
}

type MaxBytesError struct {
	Limit int64
}

func (e *MaxBytesError) Error() string {
	// Due to Hyrum's law, this text cannot be changed.
	return "http: request body too large"
}

func (l *maxBytesReader) Read(p []byte) (n int, err error) {
	if l.err != nil {
		return 0, l.err
	}
	if len(p) == 0 {
		return 0, nil
	}
	// If they asked for a 32KB byte read but only 5 bytes are
	// remaining, no need to read 32KB. 6 bytes will answer the
	// question of the whether we hit the limit or go past it.
	// 0 < len(p) < 2^63
	if int64(len(p))-1 > l.n {
		p = p[:l.n+1]
	}
	n, err = l.r.Read(p)

	if int64(n) <= l.n {
		l.n -= int64(n)
		l.err = err
		return n, err
	}

	n = int(l.n)
	l.n = 0

	// The server code and client code both use
	// maxBytesReader. This "requestTooLarge" check is
	// only used by the server code. To prevent binaries
	// which only using the HTTP Client code (such as
	// cmd/go) from also linking in the HTTP server, don't
	// use a static type assertion to the server
	// "*response" type. Check this interface instead:
	type requestTooLarger interface {
		requestTooLarge()
	}
	if res, ok := l.w.(requestTooLarger); ok {
		res.requestTooLarge()
	}
	l.err = &MaxBytesError{l.i}
	return n, l.err
}

func (l *maxBytesReader) Close() error {
	return l.r.Close()
}

func MyParseForm(r *http.Request) (vs url.Values, err error) {
	if r.Body == nil {
		err = errors.New("missing form body")
		return
	}
	ct := r.Header.Get("Content-Type")
	// RFC 7231, section 3.1.1.5 - empty type
	//   MAY be treated as application/octet-stream
	if ct == "" {
		ct = "application/octet-stream"
	}
	ct, _, err = mime.ParseMediaType(ct)
	switch {
	case ct == "application/x-www-form-urlencoded":
		var reader io.Reader = r.Body
		maxFormSize := int64(1<<63 - 1)
		if _, ok := r.Body.(*maxBytesReader); !ok {
			maxFormSize = int64(10 << 20) // 10 MB is a lot of text.
			reader = io.LimitReader(r.Body, maxFormSize+1)
		}
		b, e := io.ReadAll(reader)
		if e != nil {
			if err == nil {
				err = e
			}
			break
		}
		if int64(len(b)) > maxFormSize {
			err = errors.New("http: POST too large")
			return
		}
		vs, e = url.ParseQuery(string(b))
		if err == nil {
			err = e
		}
	case ct == "multipart/form-data":
		// handled by ParseMultipartForm (which is calling us, or should be)
		// TODO(bradfitz): there are too many possible
		// orders to call too many functions here.
		// Clean this up and write more tests.
		// request_test.go contains the start of this,
		// in TestParseMultipartFormOrder and others.
	}
	return
}

type JustId struct { Id string }

type Generic struct{ reflect.Type }

var NotFoundError = errors.New("Not found")

func generateQuery(t reflect.Type) (query string, nargs int) {
	nargs = t.NumField()
	query = ""

	for i := 0; i < nargs; i += 1 {
        field := t.Field(i)
        name, ok := field.Tag.Lookup("db")
        if !ok {
            name = field.Name;
        }
        query += strings.ToLower(name) + ","
	}
    
    // Remove the last comma
	query = query[0 : len(query)-1]
    
    return
}

func GetDbMultitple[T interface{}](c *Context, tablename string, args ...any) ([]*T, error) {
    t := reflect.TypeFor[T]()

    query, nargs := generateQuery(t)

	rows, err := c.Db.Query(fmt.Sprintf("select %s from %s", query, tablename), args...)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

    list := []*T{}

    for rows.Next() {
        item := new(T)
        if err = mapRow(item, rows, nargs); err != nil {
            return nil, err
        }
        list = append(list, item)
    }

    return list, nil
}

func mapRow(store interface{}, rows *sql.Rows, nargs int) (err error) {
    err = nil 

    val := reflect.Indirect(reflect.ValueOf(store))
	scan_args := make([]interface{}, nargs);
    for i := 0; i < nargs; i++ {
        valueField := val.Field(i)
        scan_args[i] = valueField.Addr().Interface()
    }

	err = rows.Scan(scan_args...)
	if err != nil {
		return
	}

    return nil
}

func GetDBOnce(c *Context, store interface{}, tablename string, args ...any) error {
    t := reflect.TypeOf(store).Elem()

    query, nargs := generateQuery(t)

	rows, err := c.Db.Query(fmt.Sprintf("select %s from %s", query, tablename), args...)
	if err != nil {
		return err
	}
	defer rows.Close()

	if !rows.Next() {
		return NotFoundError
	}

    err = nil 

    val := reflect.ValueOf(store).Elem()
	scan_args := make([]interface{}, nargs);
    for i := 0; i < nargs; i++ {
        valueField := val.Field(i)
        scan_args[i] = valueField.Addr().Interface()
    }

	err = rows.Scan(scan_args...)
	if err != nil {
		return err
	}

    return nil
}