// Package stringutil provides string utility functions.
package stringutil

import (
	"crypto/rand"
	"fmt"
	"net/mail"
	"path"
	"regexp"
	"strings"
	"time"
	"unicode"

	"github.com/inbucket/html2text"
	"github.com/yuin/goldmark"
	"github.com/yuin/goldmark/extension"
	"github.com/yuin/goldmark/renderer/html"
	"golang.org/x/text/unicode/norm"
)

const (
	PasswordDummy = "•"
)

var (
	regexpUnsafeFileChars = regexp.MustCompile(`[\x00-\x1f\x7f\x{80}-\x{9f}]+`)
	regexpSpaces          = regexp.MustCompile(`[\s]+`)
	uuidV4Regex           = regexp.MustCompile(`[a-fA-F0-9]{8}-[a-fA-F0-9]{4}-4[a-fA-F0-9]{3}-[89abAB][a-fA-F0-9]{3}-[a-fA-F0-9]{12}`)
	regexpRefNumber       = regexp.MustCompile(`#(\d+)`)
	regexpSlugChars       = regexp.MustCompile(`[^a-z0-9\-_]+`)
	regexpHyphens         = regexp.MustCompile(`-+`)
	regexpConvUUID        = regexp.MustCompile(`(?i)\+conv-[a-f0-9]{8}-[a-f0-9]{4}-4[a-f0-9]{3}-[a-f0-9]{4}-[a-f0-9]{12}@`)

	// markdownRenderer escapes raw HTML in the input; single newlines render as <br>.
	markdownRenderer = goldmark.New(
		goldmark.WithExtensions(extension.GFM),
		goldmark.WithRendererOptions(html.WithHardWraps()),
	)
)

// SanitizeUTF8 removes NUL bytes and replaces invalid UTF-8 byte sequences with the Unicode replacement character.
func SanitizeUTF8(s string) string {
	if s == "" {
		return s
	}
	s = strings.ReplaceAll(s, "\x00", "")
	return strings.ToValidUTF8(s, "�")
}

// GenerateSlug generates a URL-friendly slug from a title; a script with no ASCII form falls back to a random slug.
func GenerateSlug(title string) string {
	slug := strings.ToLower(strings.TrimSpace(foldAccents(title)))
	slug = regexpSpaces.ReplaceAllString(slug, "-")
	slug = regexpSlugChars.ReplaceAllString(slug, "")
	slug = regexpHyphens.ReplaceAllString(slug, "-")
	slug = strings.Trim(slug, "-")

	if slug == "" {
		randomSlug, err := RandomAlphanumeric(12)
		if err != nil {
			slug = "untitled"
		} else {
			slug = strings.ToLower(randomSlug)
		}
	}

	return slug
}

// HTML2Text converts HTML to plain text, dropping link URLs.
func HTML2Text(html string) string {
	return htmlToText(html, html2text.Options{TextOnly: true})
}

// Markdown2HTML converts markdown to HTML, falling back to the input on error.
func Markdown2HTML(md string) string {
	var b strings.Builder
	if err := markdownRenderer.Convert([]byte(md), &b); err != nil {
		return md
	}
	return b.String()
}

// SanitizeFilename removes control characters and path separators, preserving Unicode.
func SanitizeFilename(fName string) string {
	name := strings.TrimSpace(SanitizeUTF8(fName))
	name = path.Base(strings.ReplaceAll(name, `\`, "/"))
	name = regexpSpaces.ReplaceAllString(name, "-")
	name = regexpUnsafeFileChars.ReplaceAllString(name, "")
	if name == "" || name == "." || name == ".." || name == "/" {
		return "attachment"
	}
	return name
}

// RandomAlphanumeric generates a random alphanumeric string of length n.
func RandomAlphanumeric(n int) (string, error) {
	const dictionary = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"

	bytes := make([]byte, n)

	if _, err := rand.Read(bytes); err != nil {
		return "", err
	}

	for k, v := range bytes {
		bytes[k] = dictionary[v%byte(len(dictionary))]
	}

	return string(bytes), nil
}

// RandomNumeric generates a random numeric string of length n.
func RandomNumeric(n int) (string, error) {
	const dictionary = "0123456789"

	bytes := make([]byte, n)

	if _, err := rand.Read(bytes); err != nil {
		return "", err
	}

	for k, v := range bytes {
		bytes[k] = dictionary[v%byte(len(dictionary))]
	}

	return string(bytes), nil
}

// RemoveEmpty removes empty strings from a slice of strings.
func RemoveEmpty(s []string) []string {
	var r []string
	for _, str := range s {
		if str != "" {
			r = append(r, str)
		}
	}
	return r
}

// NormalizeMessageID strips surrounding whitespace and the optional angle brackets from an RFC 5322 Message-ID, and rejects values containing line breaks (which would produce malformed In-Reply-To/References headers). source_id is stored unbracketed; BuildEmailThreadingHeaders re-adds the brackets when composing them.
func NormalizeMessageID(id string) string {
	id = strings.Trim(strings.TrimSpace(id), "<>")
	if strings.ContainsAny(id, "\r\n") {
		return ""
	}
	return id
}

// GenerateEmailMessageID generates an RFC-compliant Message-ID for an email without angle brackets.
func GenerateEmailMessageID(uuid string, fromAddress string) (string, error) {
	if uuid == "" {
		return "", fmt.Errorf("uuid cannot be empty")
	}

	// Parse from address
	addr, err := mail.ParseAddress(fromAddress)
	if err != nil {
		return "", fmt.Errorf("invalid from address: %w", err)
	}

	// Extract domain with validation
	parts := strings.Split(addr.Address, "@")
	if len(parts) != 2 || parts[1] == "" {
		return "", fmt.Errorf("invalid domain in from address")
	}
	domain := parts[1]

	// Random component
	randomStr, err := RandomAlphanumeric(11)
	if err != nil {
		return "", fmt.Errorf("failed to generate random string: %w", err)
	}

	return fmt.Sprintf("%s-%d-%s@%s",
		uuid,
		time.Now().UnixNano(),
		randomStr,
		domain,
	), nil
}

// RemoveItemByValue removes all instances of a value from a slice of strings.
func RemoveItemByValue(slice []string, value string) []string {
	result := []string{}
	for _, v := range slice {
		if v != value {
			result = append(result, v)
		}
	}
	return result
}

// FormatDuration formats a duration as a string.
func FormatDuration(d time.Duration, includeSeconds bool) string {
	d = d.Round(time.Second)
	h := int64(d.Hours())
	d -= time.Duration(h) * time.Hour
	m := int64(d.Minutes())
	d -= time.Duration(m) * time.Minute
	s := int64(d.Seconds())

	var parts []string
	if h > 0 {
		parts = append(parts, fmt.Sprintf("%d hours", h))
	}
	if m >= 0 {
		parts = append(parts, fmt.Sprintf("%d minutes", m))
	}
	if s > 0 && includeSeconds {
		parts = append(parts, fmt.Sprintf("%d seconds", s))
	}
	return strings.Join(parts, " ")
}

// ValidEmail returns true if it's a valid email else return false.
func ValidEmail(email string) bool {
	addr, err := mail.ParseAddress(email)
	if err != nil {
		return false
	}
	return addr.Name == "" && addr.Address == email
}

// ExtractEmail extracts the email address from a string.
// E.g. "Name <john@example.com>" -> "john@example.com", "john@example.com" -> "john@example.com".
func ExtractEmail(s string) (string, error) {
	addr, err := mail.ParseAddress(s)
	if err != nil {
		return "", err
	}
	return addr.Address, nil
}

// DedupAndExcludeString returns a deduplicated []string excluding empty and a specific value.
func DedupAndExcludeString(list []string, exclude string) []string {
	seen := make(map[string]struct{}, len(list))
	cleaned := make([]string, 0, len(list))
	for _, s := range list {
		if s == "" || s == exclude {
			continue
		}
		if _, ok := seen[s]; !ok {
			seen[s] = struct{}{}
			cleaned = append(cleaned, s)
		}
	}
	return cleaned
}

// ExtractConvUUID extracts the conversation UUID from a plus-addressed email.
// e.g., support+conv-abc12345-1234-4123-1234-123456789abc@domain.com -> abc12345-1234-4123-1234-123456789abc
// Returns empty string if no valid UUIDv4 found.
func ExtractConvUUID(email string) string {
	match := regexpConvUUID.FindString(email)
	if match == "" {
		return ""
	}
	// match is "+conv-{uuid}@", extract just the UUID (skip "+conv-" prefix and "@" suffix)
	return match[6 : len(match)-1]
}

// ExtractUUID finds and returns the first valid UUID v4 in the given text.
// Returns empty string if no valid UUID is found.
func ExtractUUID(text string) string {
	return uuidV4Regex.FindString(text)
}

// ExtractReferenceNumber extracts the last reference number from a subject line.
// For example, "RE: Test - #392" returns "392".
// If multiple numbers exist (e.g., "Order #123 - #392"), returns the last one ("392").
func ExtractReferenceNumber(subject string) string {
	matches := regexpRefNumber.FindAllStringSubmatch(subject, -1)
	if len(matches) > 0 {
		// Return the last match's captured group.
		lastMatch := matches[len(matches)-1]
		if len(lastMatch) >= 2 {
			return lastMatch[1]
		}
	}
	return ""
}

// SplitName splits a full name; the first word is the first name, the rest is the last name.
func SplitName(name string) (string, string) {
	fields := strings.Fields(name)
	if len(fields) == 0 {
		return "", ""
	}
	if len(fields) == 1 {
		return fields[0], ""
	}
	return fields[0], strings.Join(fields[1:], " ")
}

func htmlToText(html string, opts html2text.Options) string {
	out, err := html2text.FromString(html, opts)
	if err != nil {
		return ""
	}
	return strings.TrimSpace(out)
}

func foldAccents(s string) string {
	var b strings.Builder
	for _, r := range norm.NFD.String(s) {
		if unicode.Is(unicode.Mn, r) {
			continue
		}
		b.WriteRune(r)
	}
	return norm.NFC.String(b.String())
}