//
//  URIFixup.swift
//  Gemini
//
//  Created by Shadowfacts on 8/30/21.
//
// This file is based on URIFixup & co. from the firefox-ios project, licensed under MPLv2.
// https://github.com/mozilla-mobile/firefox-ios/blob/8e796aa8ed70395f104ed83ac72c32fc2aba54ea/Client/Frontend/Browser/URIFixup.swift

import Foundation

class URIFixup {
    static func getURL(_ entry: String) -> URL? {

        let trimmed = entry.trimmingCharacters(in: .whitespacesAndNewlines)
        guard var escaped = trimmed.addingPercentEncoding(withAllowedCharacters: .URLAllowed) else {
            return nil
        }
        escaped = replaceBrackets(url: escaped)

        // Then check if the URL includes a scheme. This will handle
        // all valid requests starting with "http://", "about:", etc.
        // However, we ensure that the scheme is one that is listed in
        // the official URI scheme list, so that other such search phrases
        // like "filetype:" are recognised as searches rather than URLs.
        if let url = punycodedURL(escaped), url.schemeIsValid {
            return url
        }

        // If there's no scheme, we're going to prepend "gemini://". First,
        // make sure there's at least one "." in the host. This means
        // we'll allow single-word searches (e.g., "foo") at the expense
        // of breaking single-word hosts without a scheme (e.g., "localhost").
        if trimmed.range(of: ".") == nil {
            return nil
        }

        if trimmed.range(of: " ") != nil {
            return nil
        }

        // If there is a ".", prepend "gemini://" and try again. Since this
        // is strictly an "gemini://" URL, we also require a host.
        if let url = punycodedURL("gemini://\(escaped)"), url.host != nil {
            return url
        }

        return nil
    }

    static func punycodedURL(_ string: String) -> URL? {
        var string = string
        if string.filter({ $0 == "#" }).count > 1 {
            string = replaceHashMarks(url: string)
        }

        guard let url = URL(string: string) else { return nil }

        var components = URLComponents(url: url, resolvingAgainstBaseURL: false)
        let host = components?.host?.utf8HostToAscii()
        components?.host = host
        return components?.url
    }

    static func replaceBrackets(url: String) -> String {
        return url.replacingOccurrences(of: "[", with: "%5B").replacingOccurrences(of: "]", with: "%5D")
    }

    static func replaceHashMarks(url: String) -> String {
        guard let firstIndex = url.firstIndex(of: "#") else { return String() }
        let start = url.index(firstIndex, offsetBy: 1)
        return url.replacingOccurrences(of: "#", with: "%23", range: start..<url.endIndex)
    }
}

private extension CharacterSet {
    static let URLAllowed = CharacterSet(charactersIn: "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-._~:/?#[]@!$&'()*+,;=%")
}

// The list of permanent URI schemes has been taken from http://www.iana.org/assignments/uri-schemes/uri-schemes.xhtml
private let permanentURISchemes = ["aaa", "aaas", "about", "acap", "acct", "cap", "cid", "coap", "coaps", "crid", "data", "dav", "dict", "dns", "example", "file", "ftp", "geo", "go", "gopher", "h323", "http", "https", "iax", "icap", "im", "imap", "info", "ipp", "ipps", "iris", "iris.beep", "iris.lwz", "iris.xpc", "iris.xpcs", "jabber", "javascript", "ldap", "mailto", "mid", "msrp", "msrps", "mtqp", "mupdate", "news", "nfs", "ni", "nih", "nntp", "opaquelocktoken", "pkcs11", "pop", "pres", "reload", "rtsp", "rtsps", "rtspu", "service", "session", "shttp", "sieve", "sip", "sips", "sms", "snmp", "soap.beep", "soap.beeps", "stun", "stuns", "tag", "tel", "telnet", "tftp", "thismessage", "tip", "tn3270", "turn", "turns", "tv", "urn", "vemmi", "vnc", "ws", "wss", "xcon", "xcon-userid", "xmlrpc.beep", "xmlrpc.beeps", "xmpp", "z39.50r", "z39.50s"]

private extension URL {
    var schemeIsValid: Bool {
        guard let scheme = scheme else { return false }
        let lowercasedScheme = scheme.lowercased()
        // we care about gemini, unlike firefox
        let schemeMatches = lowercasedScheme == "gemini" || permanentURISchemes.contains(lowercasedScheme)
        return schemeMatches && self.absoluteURL.absoluteString.lowercased() != scheme + ":"
    }
}

private let base = 36
private let tMin = 1
private let tMax = 26
private let initialBias = 72
private let initialN: Int = 128 // 0x80
private let delimiter: Character = "-"; // '\x2D'
private let prefixPunycode = "xn--"
private let asciiPunycode = Array("abcdefghijklmnopqrstuvwxyz0123456789")

private extension String {
    func toValue(_ index: Int) -> Character {
        return asciiPunycode[index]
    }

    func adapt(_ delta: Int, numPoints: Int, firstTime: Bool) -> Int {
        let skew = 38
        let damp = firstTime ? 700 : 2
        var delta = delta
        delta = delta / damp
        delta += delta / numPoints
        var k = 0
        while delta > ((base - tMin) * tMax) / 2 {
            delta /= (base - tMin)
            k += base
        }
        return k + ((base - tMin + 1) * delta) / (delta + skew)
    }

    func encode(_ input: String) -> String {
        var output = ""
        var d: Int = 0
        var extendedChars = [Int]()
        for c in input.unicodeScalars {
            if Int(c.value) < initialN {
                d += 1
                output.append(String(c))
            } else {
                extendedChars.append(Int(c.value))
            }
        }
        if extendedChars.count == 0 {
            return output
        }
        if d > 0 {
            output.append(delimiter)
        }

        var n = initialN
        var delta = 0
        var bias = initialBias
        var h: Int = 0
        var b: Int = 0

        if d > 0 {
            h = output.unicodeScalars.count - 1
            b = output.unicodeScalars.count - 1
        } else {
            h = output.unicodeScalars.count
            b = output.unicodeScalars.count
        }

        while h < input.unicodeScalars.count {
            var char = Int(0x7fffffff)
            for c in input.unicodeScalars {
                let ci = Int(c.value)
                if char > ci && ci >= n {
                    char = ci
                }
            }
            delta = delta + (char - n) * (h + 1)
            if delta < 0 {
                print("error: invalid char:")
                output = ""
                return output
            }
            n = char
            for c in input.unicodeScalars {
                let ci = Int(c.value)
                if ci < n || ci < initialN {
                    delta += 1
                    continue
                }
                if ci > n {
                    continue
                }
                var q = delta
                var k = base
                while true {
                    let t = max(min(k - bias, tMax), tMin)
                    if q < t {
                        break
                    }
                    let code = t + ((q - t) % (base - t))
                    output.append(toValue(code))
                    q = (q - t) / (base - t)
                    k += base
                }
                output.append(toValue(q))
                bias = self.adapt(delta, numPoints: h + 1, firstTime: h == b)
                delta = 0
                h += 1
            }
            delta += 1
            n += 1
        }
        return output
    }

    func isValidUnicodeScala(_ s: String) -> Bool {
        for c in s.unicodeScalars {
            let ci = Int(c.value)
            if ci >= initialN {
                return false
            }
        }
        return true
    }

    func utf8HostToAscii() -> String {
        if isValidUnicodeScala(self) {
            return self
        }
        var labels = self.components(separatedBy: ".")
        for (i, part) in labels.enumerated() {
            if !isValidUnicodeScala(part) {
                let a = encode(part)
                labels[i] = prefixPunycode + a
            }
        }
        let resultString = labels.joined(separator: ".")
        return resultString
    }
}