package openai

import (
	"fmt"
	"io"
	"mime/multipart"
	"net/textproto"
	"os"
	"path/filepath"
	"strings"
)

type FormBuilder interface {
	CreateFormFile(fieldname string, file *os.File) error
	CreateFormFileReader(fieldname string, r io.Reader, filename string) error
	WriteField(fieldname, value string) error
	Close() error
	FormDataContentType() string
}

type DefaultFormBuilder struct {
	writer *multipart.Writer
}

func NewFormBuilder(body io.Writer) *DefaultFormBuilder {
	return &DefaultFormBuilder{
		writer: multipart.NewWriter(body),
	}
}

func (fb *DefaultFormBuilder) CreateFormFile(fieldname string, file *os.File) error {
	return fb.createFormFile(fieldname, file, file.Name())
}

var quoteEscaper = strings.NewReplacer("\\", "\\\\", `"`, "\\\"")

func escapeQuotes(s string) string {
	return quoteEscaper.Replace(s)
}

// CreateFormFileReader creates a form field with a file reader.
// The filename in Content-Disposition is required.
func (fb *DefaultFormBuilder) CreateFormFileReader(fieldname string, r io.Reader, filename string) error {
	if filename == "" {
		if f, ok := r.(interface{ Name() string }); ok {
			filename = f.Name()
		}
	}
	var contentType string
	if f, ok := r.(interface{ ContentType() string }); ok {
		contentType = f.ContentType()
	}

	h := make(textproto.MIMEHeader)
	h.Set(
		"Content-Disposition",
		fmt.Sprintf(
			`form-data; name="%s"; filename="%s"`,
			escapeQuotes(fieldname),
			escapeQuotes(filepath.Base(filename)),
		),
	)
	// content type is optional, but it can be set
	if contentType != "" {
		h.Set("Content-Type", contentType)
	}

	fieldWriter, err := fb.writer.CreatePart(h)
	if err != nil {
		return err
	}

	_, err = io.Copy(fieldWriter, r)
	if err != nil {
		return err
	}

	return nil
}

func (fb *DefaultFormBuilder) createFormFile(fieldname string, r io.Reader, filename string) error {
	if filename == "" {
		return fmt.Errorf("filename cannot be empty")
	}

	fieldWriter, err := fb.writer.CreateFormFile(fieldname, filename)
	if err != nil {
		return err
	}

	_, err = io.Copy(fieldWriter, r)
	if err != nil {
		return err
	}

	return nil
}

func (fb *DefaultFormBuilder) WriteField(fieldname, value string) error {
	if fieldname == "" {
		return fmt.Errorf("fieldname cannot be empty")
	}
	return fb.writer.WriteField(fieldname, value)
}

func (fb *DefaultFormBuilder) Close() error {
	return fb.writer.Close()
}

func (fb *DefaultFormBuilder) FormDataContentType() string {
	return fb.writer.FormDataContentType()
}