// ASN.1 JavaScript decoder
// Copyright (c) 2008-2018 Lapo Luchini <lapo@lapo.it>
// Copyright (c) 2019-2019 Markus Hadenfeldt <git@teaspeak.de>

// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

declare class Int10 {
    constructor(value?: any);

    sub(sub: number);
    mulAdd(mul: number, add: number);
    simplify();
}

const ellipsis = "\u2026";

function string_cut(str, len) {
    if (str.length > len)
        str = str.substring(0, len) + ellipsis;
    return str;
}

export class Stream {
    private static HEX_DIGITS = "0123456789ABCDEF";
    private static reTimeS = /^(\d\d)(0[1-9]|1[0-2])(0[1-9]|[12]\d|3[01])([01]\d|2[0-3])(?:([0-5]\d)(?:([0-5]\d)(?:[.,](\d{1,3}))?)?)?(Z|[-+](?:[0]\d|1[0-2])([0-5]\d)?)?$/;
    private static reTimeL = /^(\d\d\d\d)(0[1-9]|1[0-2])(0[1-9]|[12]\d|3[01])([01]\d|2[0-3])(?:([0-5]\d)(?:([0-5]\d)(?:[.,](\d{1,3}))?)?)?(Z|[-+](?:[0]\d|1[0-2])([0-5]\d)?)?$/;

    position: number;
    data: string | ArrayBuffer;

    constructor(data: string | Stream | ArrayBuffer, position: number) {
        if (data instanceof Stream)
            this.data = data.data;
        else
            this.data = data;

        this.position = position;
    }

    length() : number {
        if (this.data instanceof ArrayBuffer)
            return this.data.byteLength;
        return this.data.length;
    }

    get(position?: number) {
        if (position === undefined)
            position = this.position++;

        if (position >= this.length())
            throw 'Requesting byte offset ' + this.position + ' on a stream of length ' + this.length();

        return (typeof(this.data) === "string") ? this.data.charCodeAt(position) : this.data[position];
    }

    hexByte(byte: number) {
        return Stream.HEX_DIGITS.charAt((byte >> 4) & 0xF) + Stream.HEX_DIGITS.charAt(byte & 0xF);
    }

    parseStringISO(start, end) {
        let s = "";
        for (let i = start; i < end; ++i)
            s += String.fromCharCode(this.get(i));
        return s;
    }

    parseStringUTF(start, end) {
        let s = "";
        for (let i = start; i < end;) {
            let c = this.get(i++);
            if (c < 128)
                s += String.fromCharCode(c);
            else if ((c > 191) && (c < 224))
                s += String.fromCharCode(((c & 0x1F) << 6) | (this.get(i++) & 0x3F));
            else
                s += String.fromCharCode(((c & 0x0F) << 12) | ((this.get(i++) & 0x3F) << 6) | (this.get(i++) & 0x3F));
        }
        return s;
    }

    parseStringBMP(start, end) {
        let str = "", hi, lo;
        for (let i = start; i < end;) {
            hi = this.get(i++);
            lo = this.get(i++);
            str += String.fromCharCode((hi << 8) | lo);
        }
        return str;
    }

    parseTime(start, end, shortYear) {
        let s = this.parseStringISO(start, end),
            m = (shortYear ? Stream.reTimeS : Stream.reTimeL).exec(s);
        if (!m)
            return "Unrecognized time: " + s;
        if (shortYear) {
            // to avoid querying the timer, use the fixed range [1970, 2069]
            // it will conform with ITU X.400 [-10, +40] sliding window until 2030
            //m[1] = +m[1];
            //m[1] += (parseInt(m[1]) < 70) ? 2000 : 1900;
            throw "fixme!";
        }
        s = m[1] + "-" + m[2] + "-" + m[3] + " " + m[4];
        if (m[5]) {
            s += ":" + m[5];
            if (m[6]) {
                s += ":" + m[6];
                if (m[7])
                    s += "." + m[7];
            }
        }
        if (m[8]) {
            s += " UTC";
            if (m[8] != 'Z') {
                s += m[8];
                if (m[9])
                    s += ":" + m[9];
            }
        }
        return s;
    };

    parseInteger(start, end) {
        let current: number = this.get(start);

        let negative = (current > 127);
        let padding = negative ? 255 : 0;
        let length;
        let descriptor: number | string;

        // skip unuseful bits (not allowed in DER)
        while (current == padding && ++start < end)
            current = this.get(start);

        length = end - start;
        if (length === 0)
            return negative ? '-1' : '0';

        // show bit length of huge integers
        if (length > 4) {
            descriptor = current;
            length <<= 3; /* calculate bit length */

            while (((descriptor ^ padding) & 0x80) == 0) {
                descriptor <<= 1;
                --length;
            }
            descriptor = "(" + length + " bit)\n";
        }
        // decode the integer
        if (negative) current = current - 256;

        let number = "";
        if(typeof(Int10) !== "undefined") {
            let n = new Int10(current);
            for (let i = start + 1; i < end; ++i)
                n.mulAdd(256, this.get(i));
            number = n.toString();
        } else {
            let n = 0;
            for (let i = start + 1; i < end; ++i) {
                n <<= 8;
                n += this.get(i);
            }
            number = n.toString();
        }
        return descriptor + number;
    };

    isASCII(start: number, end: number) {
        for (let i = start; i < end; ++i) {
            const c = this.get(i);
            if (c < 32 || c > 176)
                return false;
        }
        return true;
    };

    parseBitString(start, end, maxLength) {
        let unusedBit = this.get(start),
            lenBit = ((end - start - 1) << 3) - unusedBit,
            intro = "(" + lenBit + " bit)\n",
            s = "";
        for (let i = start + 1; i < end; ++i) {
            let b = this.get(i),
                skip = (i == end - 1) ? unusedBit : 0;
            for (let j = 7; j >= skip; --j)
                s += (b >> j) & 1 ? "1" : "0";
            if (s.length > maxLength)
                return intro + string_cut(s, maxLength);
        }
        return intro + s;
    };

    parseOctetString(start, end, maxLength) {
        if (this.isASCII(start, end))
            return string_cut(this.parseStringISO(start, end), maxLength);
        let len = end - start,
            s = "(" + len + " byte)\n";
        maxLength /= 2; // we work in bytes
        if (len > maxLength)
            end = start + maxLength;
        for (let i = start; i < end; ++i)
            s += this.hexByte(this.get(i));
        if (len > maxLength)
            s += ellipsis;
        return s;
    };

    parseOID(start, end, maxLength) {
        let s = '',
            n = new Int10(),
            bits = 0;
        for (let i = start; i < end; ++i) {
            let v = this.get(i);
            n.mulAdd(128, v & 0x7F);
            bits += 7;
            if (!(v & 0x80)) { // finished
                if (s === '') {
                    n = n.simplify();
                    if (n instanceof Int10) {
                        n.sub(80);
                        s = "2." + n.toString();
                    } else {
                        let m = n < 80 ? n < 40 ? 0 : 1 : 2;
                        s = m + "." + (n - m * 40);
                    }
                } else
                    s += "." + n.toString();
                if (s.length > maxLength)
                    return string_cut(s, maxLength);
                n = new Int10();
                bits = 0;
            }
        }
        if (bits > 0)
            s += ".incomplete";
        /* FIXME
        if (typeof oids === 'object') {
            let oid = oids[s];
            if (oid) {
                if (oid.d) s += "\n" + oid.d;
                if (oid.c) s += "\n" + oid.c;
                if (oid.w) s += "\n(warning!)";
            }
        }
        */
        return s;
    };
}

export enum TagClass {
    UNIVERSAL = 0x00,
    APPLICATION = 0x01,
    CONTEXT = 0x02,
    PRIVATE = 0x03
}

export enum TagType {
    EOC = 0x00,
    BOOLEAN = 0x01,
    INTEGER = 0x02,
    BIT_STRING = 0x03,
    OCTET_STRING = 0x04,
    NULL = 0x05,
    OBJECT_IDENTIFIER = 0x06,
    ObjectDescriptor = 0x07,
    EXTERNAL = 0x08,
    REAL = 0x09,
    ENUMERATED = 0x0A,
    EMBEDDED_PDV = 0x0B,
    UTF8String = 0x0C,
    SEQUENCE = 0x10,
    SET = 0x11,
    NumericString = 0x12,
    PrintableString = 0x13, // ASCII subset
    TeletextString = 0x14, // aka T61String
    VideotexString = 0x15,
    IA5String = 0x16, // ASCII
    UTCTime = 0x17,
    GeneralizedTime = 0x18,
    GraphicString = 0x19,
    VisibleString = 0x1A, // ASCII subset
    GeneralString = 0x1B,
    UniversalString = 0x1C,
    BMPString = 0x1E
}

class ASN1Tag {
    tagClass: TagClass;
    type: TagType;
    tagConstructed: boolean;
    tagNumber: number;

    constructor(stream: Stream) {
        let buf = stream.get();
        this.tagClass = buf >> 6;
        this.tagConstructed = ((buf & 0x20) !== 0);
        this.tagNumber = buf & 0x1F;
        if (this.tagNumber == 0x1F) { // long tag
            let n = new Int10();
            do {
                buf = stream.get();
                n.mulAdd(128, buf & 0x7F);
            } while (buf & 0x80);
            this.tagNumber = n.simplify();
        }
    }

    isUniversal() {
        return this.tagClass === 0x00;
    };

    isEOC() {
        return this.tagClass === 0x00 && this.tagNumber === 0x00;
    };
}

export class ASN1 {
    stream: Stream;
    header: number;
    length: number;
    tag: ASN1Tag;
    children: ASN1[];

    constructor(stream: Stream, header: number, length: number, tag: ASN1Tag, children: ASN1[]) {
        this.stream = stream;
        this.header = header;
        this.length = length;
        this.tag = tag;
        this.children = children;
    }

    content(max_length?: number, type?: TagType) { // a preview of the content (intended for humans)
        if (this.tag === undefined) return null;
        if (max_length === undefined)
            max_length = Infinity;

        let content = this.posContent(),
            len = Math.abs(this.length);

        if (!this.tag.isUniversal()) {
            if (this.children !== null)
                return "(" + this.children.length + " elem)";
            return this.stream.parseOctetString(content, content + len, max_length);
        }
        switch (type || this.tag.tagNumber) {
            case 0x01: // BOOLEAN
                return (this.stream.get(content) === 0) ? "false" : "true";
            case 0x02: // INTEGER
                return this.stream.parseInteger(content, content + len);
            case 0x03: // BIT_STRING
                return this.children ? "(" + this.children.length + " elem)" :
                    this.stream.parseBitString(content, content + len, max_length);
            case 0x04: // OCTET_STRING
                return this.children ? "(" + this.children.length + " elem)" :
                    this.stream.parseOctetString(content, content + len, max_length);
            //case 0x05: // NULL
            case 0x06: // OBJECT_IDENTIFIER
                return this.stream.parseOID(content, content + len, max_length);
            //case 0x07: // ObjectDescriptor
            //case 0x08: // EXTERNAL
            //case 0x09: // REAL
            //case 0x0A: // ENUMERATED
            //case 0x0B: // EMBEDDED_PDV
            case 0x10: // SEQUENCE
            case 0x11: // SET
                if (this.children !== null)
                    return "(" + this.children.length + " elem)";
                else
                    return "(no elem)";
            case 0x0C: // UTF8String
                return string_cut(this.stream.parseStringUTF(content, content + len), max_length);
            case 0x12: // NumericString
            case 0x13: // PrintableString
            case 0x14: // TeletexString
            case 0x15: // VideotexString
            case 0x16: // IA5String
            //case 0x19: // GraphicString
            case 0x1A: // VisibleString
                //case 0x1B: // GeneralString
                //case 0x1C: // UniversalString
                return string_cut(this.stream.parseStringISO(content, content + len), max_length);
            case 0x1E: // BMPString
                return string_cut(this.stream.parseStringBMP(content, content + len), max_length);
            case 0x17: // UTCTime
            case 0x18: // GeneralizedTime
                return this.stream.parseTime(content, content + len, (this.tag.tagNumber == 0x17));
        }
        return null;
    };

    typeName(): string {
        switch (this.tag.tagClass) {
            case 0: // universal
                return TagType[this.tag.tagNumber] || ("Universal_" + this.tag.tagNumber.toString());
            case 1:
                return "Application_" + this.tag.tagNumber.toString();
            case 2:
                return "[" + this.tag.tagNumber.toString() + "]"; // Context
            case 3:
                return "Private_" + this.tag.tagNumber.toString();
        }
    };

    toString() {
        return this.typeName() + "@" + this.stream.position + "[header:" + this.header + ",length:" + this.length + ",sub:" + ((this.children === null) ? 'null' : this.children.length) + "]";
    }

    toPrettyString(indent) {
        if (indent === undefined) indent = '';
        let s = indent + this.typeName() + " @" + this.stream.position;
        if (this.length >= 0)
            s += "+";
        s += this.length;
        if (this.tag.tagConstructed)
            s += " (constructed)";
        else if ((this.tag.isUniversal() && ((this.tag.tagNumber == 0x03) || (this.tag.tagNumber == 0x04))) && (this.children !== null))
            s += " (encapsulates)";
        let content = this.content();
        if (content)
            s += ": " + content.replace(/\n/g, '|');
        s += "\n";
        if (this.children !== null) {
            indent += '  ';
            for (let i = 0, max = this.children.length; i < max; ++i)
                s += this.children[i].toPrettyString(indent);
        }
        return s;
    };

    posStart() {
        return this.stream.position;
    };

    posContent() {
        return this.stream.position + this.header;
    };

    posEnd() {
        return this.stream.position + this.header + Math.abs(this.length);
    };

    static decodeLength(stream: Stream) {
        let buf = stream.get();
        const len = buf & 0x7F;
        if (len == buf)
            return len;
        if (len > 6) // no reason to use Int10, as it would be a huge buffer anyways
            throw "Length over 48 bits not supported at position " + (stream.position - 1);
        if (len === 0)
            return null; // undefined

        buf = 0;
        for (let i = 0; i < len; ++i)
            buf = (buf << 8) + stream.get();
        return buf;
    };

    static encodeLength(buffer: Uint8Array, offset: number, length: number) {
        if(length < 0x7F) {
            buffer[offset] = length;
        } else {
            buffer[offset] = 0x80;
            let index = 1;
            while(length > 0) {
                buffer[offset + index++] = length & 0xFF;
                length >>= 8;
                buffer[offset] += 1;
            }
        }
    }
}

function decode0(stream: Stream) {
    const streamStart = new Stream(stream, 0); /* copy */
    const tag = new ASN1Tag(stream);
    let len = ASN1.decodeLength(stream);
    const start = stream.position;
    const length_header = start - streamStart.position;
    let children = null;
    const query_children = () => {
        children = [];
        if (len !== null) {
            const end = start + len;
            if (end > stream.length())
                throw 'Container at offset ' + start + ' has a length of ' + len + ', which is past the end of the stream';
            while (stream.position < end)
                children[children.length] = decode0(stream);
            if (stream.position != end)
                throw 'Content size is not correct for container at offset ' + start;
        } else {
            // undefined length
            try {
                while (true) {
                    const s = decode0(stream);
                    if (s.tag.isEOC()) break;
                    children[children.length] = s;
                }
                len = start - stream.position; // undefined lengths are represented as negative values
            } catch (e) {
                throw 'Exception while decoding undefined length content at offset ' + start + ': ' + e;
            }
        }
    };
    if (tag.tagConstructed) {
        // must have valid content
        query_children();
    } else if (tag.isUniversal() && ((tag.tagNumber == 0x03) || (tag.tagNumber == 0x04))) {
        // sometimes BitString and OctetString are used to encapsulate ASN.1
        try {
            if (tag.tagNumber == 0x03)
                if (stream.get() != 0)
                    throw "BIT STRINGs with unused bits cannot encapsulate.";
            query_children();
            for (let i = 0; i < children.length; ++i)
                if (children[i].tag.isEOC())
                    throw 'EOC is not supposed to be actual content.';
        } catch (e) {
            // but silently ignore when they don't
            children = null;
            //DEBUG console.log('Could not decode structure at ' + start + ':', e);
        }
    }
    if (children === null) {
        if (len === null)
            throw "We can't skip over an invalid tag with undefined length at offset " + start;
        stream.position = start + Math.abs(len);
    }
    return new ASN1(streamStart, length_header, len, tag, children);
}

export function decode(stream: string | ArrayBuffer) {
    return decode0(new Stream(stream, 0));
}