package handlers

import (
	"errors"
	"fmt"
	"mime/multipart"
	"path/filepath"
	"strings"

	"go_blog/models"
)

// ErrUploadsDisabled is returned when the global upload switch is off.
var ErrUploadsDisabled = errors.New("uploads are disabled")

// FileValidationError describes why an uploaded file was rejected.
type FileValidationError struct {
	Reason string
}

func (e *FileValidationError) Error() string { return e.Reason }

// FileCheck is the outcome of validating an uploaded file header.
type FileCheck struct {
	OK      bool
	Type    *models.UploadFileType // matched type, nil if not found
	MaxSize int64                  // effective byte limit applied
}

// ValidateUpload checks a file header against the cached platform upload
// policy: master switch, extension whitelist, and per-type size limit. The
// reported MaxSize is the effective limit (per-type override, else default).
func ValidateUpload(header *multipart.FileHeader) FileCheck {
	cfg := models.GetUploadConfig()

	if !cfg.Enabled {
		return FileCheck{OK: false}
	}

	ext := strings.ToLower(filepath.Ext(header.Filename))
	def := cfg.DefaultMaxSize
	for i := range models.GetUploadFileTypes() {
		t := &models.GetUploadFileTypes()[i]
		if !t.Enabled {
			continue
		}
		if strings.EqualFold(t.Extension, ext) {
			max := t.EffectiveMaxSize(def)
			if header.Size > max {
				return FileCheck{OK: false, Type: t, MaxSize: max}
			}
			return FileCheck{OK: true, Type: t, MaxSize: max}
		}
	}

	// Extension not in the whitelist.
	return FileCheck{OK: false, MaxSize: def}
}

// formatSize renders a byte count as a human-readable string.
func formatSize(b int64) string {
	const unit = 1024
	if b < unit {
		return fmt.Sprintf("%d B", b)
	}
	div, exp := int64(unit), 0
	for n := b / unit; n >= unit; n /= unit {
		div *= unit
		exp++
	}
	return fmt.Sprintf("%.1f %ciB", float64(b)/float64(div), "KMGTPE"[exp])
}