import Foundation

// MARK: - HTML Escaping

func escapeHTML(_ text: String) -> String {
    text.replacingOccurrences(of: "&", with: "&")
        .replacingOccurrences(of: "<", with: "&lt;")
        .replacingOccurrences(of: ">", with: "&gt;")
        .replacingOccurrences(of: "\"", with: "&quot;")
}

func escapeHTMLAttribute(_ text: String) -> String {
    escapeHTML(text).replacingOccurrences(of: "'", with: "&#39;")
}

// MARK: - URL Sanitization

func sanitizedReadmeLinkURLString(_ rawURL: String) -> String? {
    sanitizeReadmeURLString(
        rawURL,
        allowedSchemes: ["http", "https", "mailto"],
        allowsFragmentOnly: true
    )
}

func sanitizedReadmeImageURLString(_ rawURL: String) -> String? {
    sanitizeReadmeURLString(
        rawURL,
        allowedSchemes: ["http", "https"],
        allowsFragmentOnly: false
    )
}

private func sanitizeReadmeURLString(
    _ rawURL: String,
    allowedSchemes: Set<String>,
    allowsFragmentOnly: Bool
) -> String? {
    let trimmedURL = rawURL.trimmingCharacters(in: .whitespacesAndNewlines)
    guard !trimmedURL.isEmpty else { return nil }

    if allowsFragmentOnly, trimmedURL.hasPrefix("#"), trimmedURL.count > 1 {
        return escapeHTMLAttribute(trimmedURL)
    }

    if let scheme = URLComponents(string: trimmedURL)?.scheme?.lowercased() {
        guard allowedSchemes.contains(scheme),
              let sanitizedURL = URLComponents(string: trimmedURL)?.url?.absoluteString else {
            return nil
        }
        return escapeHTMLAttribute(sanitizedURL)
    }

    // No scheme → a relative reference (`diagram.png`, `docs/x`). It cannot carry a
    // `javascript:`/`data:` payload, so it is safe to keep as-is; apps that supply a
    // resolver turn these into absolute URLs before they reach here. Reject only the
    // protocol-relative `//host` form, which points off-origin.
    guard !trimmedURL.hasPrefix("//") else { return nil }
    return escapeHTMLAttribute(trimmedURL)
}

// MARK: - Regex Helpers

func orgKeywordDirective(in line: String) -> (keyword: String, value: String)? {
    guard let match = line.firstMatch(of: /^#\+([A-Za-z][A-Za-z0-9_-]*):\s*(.*)$/) else {
        return nil
    }
    return (
        keyword: String(match.1).lowercased(),
        value: String(match.2).trimmingCharacters(in: .whitespaces)
    )
}

func isOrgHorizontalRule(_ line: String) -> Bool {
    matchesRegex(line, pattern: #"^\s*-{5,}\s*$"#)
}

func matchesRegex(_ text: String, pattern: String) -> Bool {
    guard let regex = try? NSRegularExpression(pattern: pattern) else { return false }
    let range = NSRange(location: 0, length: (text as NSString).length)
    return regex.firstMatch(in: text, range: range) != nil
}