const fs = require('fs');

const align = (t, b) => t % b == 0 ? t : t + b - t % b;

const getSerial = (buffer: Buffer, offset: number, base1: number, base2: number) => {
    if( offset >= base2 ){
        let n = Math.floor( (offset-base2) / 8 );
        let c = (base1-8) / 3;
        for(let i=0; i < c; ++i ){
            let a = buffer.readUInt16LE(base1 + i*2);
            let b = buffer.readUInt16LE(base1 + i*2 + 2);
            if( a <= n && n < b ){
                let start = 8 + i * 3;
                let str = String.fromCharCode( buffer[start], buffer[start+1], buffer[start+2] );
                return [str, i];
            }
        }
        return ["????", -1];
    } else if( offset >= base1 && offset < base2 - 2 ) {
        let n = offset - base1;
        n = Math.floor( n/2 );
        let start = 8 + n * 3;
        let str = String.fromCharCode( buffer[start], buffer[start+1], buffer[start+2] );
        return [str, n];
    }
    else return ["????", -1];
}

const describe = (buffer: Buffer, offset: number) => {
    console.info(`error at ${offset}`);
    let n = buffer.readUInt16LE(4);
    let serialbase = 8;
    let offsetbase = serialbase + 3*n;
    let cheatbase = offsetbase + 2 * (n+1);
    let cheatcnt = buffer.readUInt16LE(cheatbase-2);
    let expandbase = align( cheatbase + 8 * cheatcnt, 32 );
    let serial = "????", entry = -1;
    if( offset >= offsetbase ) [serial, entry] = getSerial(buffer, offset, offsetbase, cheatbase);

    console.debug("is it right? %d - %d - %d - %d", serialbase, offsetbase, cheatbase, align(expandbase, 32));
    if( offset < serialbase ){  // 属于HEAD数据
        if( offset < 4){
            console.log("INSIDE MAGIC NUMBER");
            console.log("ACL?");
            console.log(new Array(offset).fill(" ").join("")+"^");
        }
        else if( offset < 6 ){
            console.log("INSIDE SERIAL LENGTH");
            console.log(n.toString(16).padStart(4, '0'));
            console.log(new Array(5 - offset).fill("  ").join("")+" ^");
        }
        else {
            console.log("INSIDE MAX CHEAT PARAGRAPH");
            n = buffer.readUInt16LE(6);
            console.log(n.toString(16).padStart(4, '0'));
            console.log(new Array(7 - offset).fill("  ").join("")+" ^");
        }
    }
    else if( offset < offsetbase ){
        let start = serialbase + Math.floor( (offset-serialbase)/3  ) * 3;
        console.log("INSITDE SERIAL COLLECTIONS", "index =", Math.floor(  (offset-serialbase)/3  ));
        console.log( String.fromCharCode( buffer[start], buffer[start+1], buffer[start+2] ) );
        console.log( new Array(offset-start).fill(" ").join("")+"^" );
    }
    else if( offset < cheatbase ){
        let start = offsetbase + Math.floor( (offset-offsetbase)/2  ) * 2;
        console.log("INSITDE SERIAL EXTENSIONS", "index =", Math.floor(  (offset-offsetbase)/2  ), "serial(3) =", serial);
        if( offset > offsetbase+1 ){
            n = buffer.readUInt16LE(start-2);
            console.log(n.toString(16).padStart(4, "0"), "   <<<  ", getSerial(buffer, offset-2, offsetbase, cheatbase)[0]);
        }
        n = buffer.readUInt16LE(start);
        console.log(n.toString(16).padStart(4, '0') );
        console.log(new Array(offset - start).fill("  ").join("")+" ^");
    }
    else if( offset < expandbase ){
        if( offset < cheatbase + cheatcnt * 8 ){
            let start = cheatbase + Math.floor( (offset-cheatbase) / 8 ) * 8;
            let entstart = buffer.readUInt16LE( offsetbase + entry*2 ), h, l;
            entstart = cheatbase + entstart * 8;
            console.log("INSITDE CHEAT SEGMENTS", "index =", Math.floor(  (offset-cheatbase)/8  ), "serial(3) =", serial);
            while( entstart < start ){
                h = buffer.readUInt32LE(entstart);
                l = buffer.readUInt32LE(entstart+4);
                console.log(h.toString(16).padStart(8, '0') + "  " + l.toString(16).padStart(8, '0'));
                entstart += 8;
            }
            h = buffer.readUInt32LE(start);
            l = buffer.readUInt32LE(start+4);
            console.log(h.toString(16).padStart(8, '0') + "  " + l.toString(16).padStart(8, '0'));
            if( offset - start < 4 ){
                console.log(new Array(3 - (offset - start)).fill("  ").join("")+" ^");
            }
            else console.log(new Array(12 - (offset - start)).fill("  ").join("")+" ^");
        }
        else {
            console.log("INSITDE CHEAT SEGMENTS PADDING" );
        }
    }
    else if( offset < buffer.length ){
        console.log("INSIDE CHEAT BINARY");
        // 1 index from cheatbase
        // 2 index from offsetbase
        // 3 get offset for cheat bin
        // 4 show for entry size/entry record/string table/index table/code table
    }
    else {
        console.error("INVALID POSITION AT %d", offset);
    }
}

const main = (argv: string[]) => {
    if( argv.length < 2 ) {
        console.info("Usage: explain <file1> <file2>");
        return;
    }
    const first: Buffer = fs.readFileSync(argv[0]);
    const second: Buffer = fs.readFileSync(argv[1]);

    let diff = 0;
    for(; first[diff] === second[diff]; diff++);
    describe(first,diff);
    console.log("------------------");
    describe(second,diff);
}

main( process.argv.slice(2) );