// Package textsafe validates user free-text at the API boundary (Spec input-compliance).
package textsafe

import (
	"errors"
	"fmt"
	"strings"
	"unicode"
	"unicode/utf8"
)

// Kind selects length limits and whether empty is allowed.
type Kind int

const (
	Nickname Kind = iota
	DisplayName
	AskContent
	Note       // optional
	Title
	Focus      // optional
	Scene
)

// ErrRejected is returned for compliance failures (map to HTTP 400 / code 40060).
var ErrRejected = errors.New("文案不合规")

type limits struct {
	min, max int
	allowNL  bool
}

func lim(k Kind) limits {
	switch k {
	case Nickname:
		return limits{1, 16, false}
	case DisplayName:
		return limits{1, 24, false}
	case AskContent:
		return limits{1, 2000, true}
	case Note:
		return limits{0, 200, true}
	case Title:
		return limits{1, 40, false}
	case Focus:
		return limits{0, 40, false}
	case Scene:
		return limits{1, 80, false}
	default:
		return limits{1, 200, false}
	}
}

var banned = []string{
	"占卜", "算命", "改命", "测测",
	"疗效", "包治", "根治", "治疗疾病", "治愈癌症",
	"不测就有灾", "大师算卦", "神棍",
}

// Check normalizes and validates. Empty optional kinds return ("", nil).
func Check(kind Kind, raw string) (string, error) {
	s := Normalize(raw, lim(kind).allowNL)
	l := lim(kind)
	n := utf8.RuneCountInString(s)
	if n < l.min {
		if l.min == 0 {
			return "", nil
		}
		return "", reject("请填写内容")
	}
	if n > l.max {
		return "", reject("内容过长")
	}
	if err := rejectControls(s, l.allowNL); err != nil {
		return "", err
	}
	if err := rejectMarkup(s); err != nil {
		return "", err
	}
	if err := rejectBanned(s); err != nil {
		return "", err
	}
	if err := rejectSpam(s); err != nil {
		return "", err
	}
	return s, nil
}

// Normalize trims; optionally keeps internal newlines.
func Normalize(s string, allowNL bool) string {
	s = strings.TrimSpace(s)
	if !allowNL {
		s = strings.Map(func(r rune) rune {
			if r == '\n' || r == '\r' || r == '\t' {
				return ' '
			}
			return r
		}, s)
		s = strings.Join(strings.Fields(s), " ")
	}
	return s
}

func reject(msg string) error {
	return fmt.Errorf("%w：%s", ErrRejected, msg)
}

func rejectControls(s string, allowNL bool) error {
	for _, r := range s {
		if r == 0 {
			return reject("含非法字符")
		}
		if r == '\n' || r == '\r' || r == '\t' {
			if !allowNL {
				return reject("含非法空白")
			}
			continue
		}
		if r < 0x20 || r == 0x7f {
			return reject("含非法字符")
		}
	}
	return nil
}

func rejectMarkup(s string) error {
	low := strings.ToLower(s)
	if strings.Contains(low, "<script") || strings.Contains(low, "javascript:") {
		return reject("含不安全内容")
	}
	if strings.Contains(low, "onerror=") || strings.Contains(low, "onload=") {
		return reject("含不安全内容")
	}
	// bare tags like <img ...>
	for i := 0; i < len(s); i++ {
		if s[i] != '<' {
			continue
		}
		if i+1 < len(s) {
			c := s[i+1]
			if c == '/' || (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '!' {
				return reject("含不安全内容")
			}
		}
	}
	return nil
}

func rejectBanned(s string) error {
	for _, b := range banned {
		if b != "" && strings.Contains(s, b) {
			return reject("含不允许的表述，请换一种说法")
		}
	}
	return nil
}

func rejectSpam(s string) error {
	runes := []rune(s)
	if len(runes) >= 6 {
		allSame := true
		for i := 1; i < len(runes); i++ {
			if runes[i] != runes[0] {
				allSame = false
				break
			}
		}
		if allSame && !unicode.IsSpace(runes[0]) {
			return reject("请勿重复刷屏")
		}
	}
	streak := 1
	for i := 1; i < len(runes); i++ {
		if runes[i] == runes[i-1] && !unicode.IsSpace(runes[i]) {
			streak++
			if streak >= 8 {
				return reject("请勿重复刷屏")
			}
		} else {
			streak = 1
		}
	}
	return nil
}