// https://dev.to/ndesmic/building-a-minimal-wasi-polyfill-for-browsers-4nel
// http://www.wasmtutor.com/webassembly-barebones-wasi
// https://github.com/emscripten-core/emscripten/blob/c017fc2d6961962ee87ae387462a099242dfbbd2/src/library_wasi.js#L451
// https://github.com/emscripten-core/emscripten/blob/c017fc2d6961962ee87ae387462a099242dfbbd2/src/library_fs.js
// https://github.com/WebAssembly/wasi-libc/blob/main/libc-bottom-half/sources/preopens.c
// https://fossies.org/linux/wasm3/source/extra/wasi_core.h
// https://wasix.org/docs/api-reference/wasi/fd_read

const use_debug = true;
const debug = use_debug ? console.log : () => { };

export enum FDType {
    UNKNOWN = 0,
    BLOCK_DEVICE = 1,
    CHARACTER_DEVICE = 2,
    DIRECTORY = 3,
    REGULAR_FILE = 4,
    SOCKET_DGRAM = 5,
    SOCKET_STREAM = 6,
    SYMBOLIC_LINK = 7,
}

export enum FDRights {
    FD_DATASYNC = 1,
    FD_READ = 2,
    FD_SEEK = 4,
    FD_FDSTAT_SET_FLAGS = 8,
    FD_SYNC = 16,
    FD_TELL = 32,
    FD_WRITE = 64,
    FD_ADVISE = 128,
    FD_ALLOCATE = 256,
    PATH_CREATE_DIRECTORY = 512,
    PATH_CREATE_FILE = 1024,
    PATH_LINK_SOURCE = 2048,
    PATH_LINK_TARGET = 4096,
    PATH_OPEN = 8192,
    FD_READDIR = 16384,
    PATH_READLINK = 32768,
    PATH_RENAME_SOURCE = 65536,
    PATH_RENAME_TARGET = 131072,
    PATH_FILESTAT_GET = 262144,
    PATH_FILESTAT_SET_SIZE = 524288,
    PATH_FILESTAT_SET_TIMES = 1048576,
    FD_FILESTAT_GET = 2097152,
    FD_FILESTAT_SET_SIZE = 4194304,
    FD_FILESTAT_SET_TIMES = 8388608,
    PATH_SYMLINK = 16777216,
    PATH_REMOVE_DIRECTORY = 33554432,
    PATH_UNLINK_FILE = 67108864,
    POLL_FD_READWRITE = 134217728,
    SOCK_SHUTDOWN = 268435456,
    FD_ALL = 536870911, // TODO?
}

export enum FDFlags {
    APPEND = 1,
    DSYNC = 2,
    NONBLOCK = 4,
    RSYNC = 8,
    SYNC = 16,
}

export enum FDOpenFlags {
    CREAT = 1,
    DIRECTORY = 2,
    EXCL = 4,
    TRUNC = 8,
}

export enum WASIErrors {
    SUCCESS = 0,
    TOOBIG = 1,
    ACCES = 2,
    ADDRINUSE = 3,
    ADDRNOTAVAIL = 4,
    AFNOSUPPORT = 5,
    AGAIN = 6,
    ALREADY = 7,
    BADF = 8,
    BADMSG = 9,
    BUSY = 10,
    CANCELED = 11,
    CHILD = 12,
    CONNABORTED = 13,
    CONNREFUSED = 14,
    CONNRESET = 15,
    DEADLK = 16,
    DESTADDRREQ = 17,
    DOM = 18,
    DQUOT = 19,
    EXIST = 20,
    FAULT = 21,
    FBIG = 22,
    HOSTUNREACH = 23,
    IDRM = 24,
    ILSEQ = 25,
    INPROGRESS = 26,
    INTR = 27,
    INVAL = 28,
    IO = 29,
    ISCONN = 30,
    ISDIR = 31,
    LOOP = 32,
    MFILE = 33,
    MLINK = 34,
    MSGSIZE = 35,
    MULTIHOP = 36,
    NAMETOOLONG = 37,
    NETDOWN = 38,
    NETRESET = 39,
    NETUNREACH = 40,
    NFILE = 41,
    NOBUFS = 42,
    NODEV = 43,
    NOENT = 44,
    NOEXEC = 45,
    NOLCK = 46,
    NOLINK = 47,
    NOMEM = 48,
    NOMSG = 49,
    NOPROTOOPT = 50,
    NOSPC = 51,
    NOSYS = 52,
    NOTCONN = 53,
    NOTDIR = 54,
    NOTEMPTY = 55,
    NOTRECOVERABLE = 56,
    NOTSOCK = 57,
    NOTSUP = 58,
    NOTTY = 59,
    NXIO = 60,
    OVERFLOW = 61,
    OWNERDEAD = 62,
    PERM = 63,
    PIPE = 64,
    PROTO = 65,
    PROTONOSUPPORT = 66,
    PROTOTYPE = 67,
    RANGE = 68,
    ROFS = 69,
    SPIPE = 70,
    SRCH = 71,
    STALE = 72,
    TIMEDOUT = 73,
    TXTBSY = 74,
    XDEV = 75,
    NOTCAPABLE = 76,
}



export class WASIFileDescriptor {
    fdindex: number = -1;
    data: Uint8Array = new Uint8Array(16);
    flags: number = 0;
    size: number = 0;
    offset: number = 0;

    constructor(public name: string, public type: FDType, public rights: number) {
        this.rights = -1; // TODO?
    }
    ensureCapacity(size: number) {
        if (this.data.byteLength < size) {
            const newdata = new Uint8Array(size * 2); // TODO?
            newdata.set(this.data);
            this.data = newdata;
        }
    }
    write(chunk: Uint8Array) {
        this.ensureCapacity(this.offset + chunk.byteLength);
        this.data.set(chunk, this.offset);
        this.offset += chunk.byteLength;
        this.size = Math.max(this.size, this.offset);
    }
    read(chunk: Uint8Array) {
        const len = Math.min(chunk.byteLength, this.size - this.offset);
        chunk.set(this.data.subarray(this.offset, this.offset + len));
        this.offset += len;
        return len;
    }
    truncate() {
        this.size = 0;
        this.offset = 0;
    }
    llseek(offset: number, whence: number) {
        switch (whence) {
            case 0: // SEEK_SET
                this.offset = offset;
                break;
            case 1: // SEEK_CUR
                this.offset += offset;
                break;
            case 2: // SEEK_END
                this.offset = this.size + offset;
                break;
        }
        if (this.offset < 0) this.offset = 0;
        if (this.offset > this.size) this.offset = this.size;
    }
    getBytes() {
        return this.data.subarray(0, this.size);
    }
    toString() {
        return `FD(${this.fdindex} "${this.name}" 0x${this.type.toString(16)} 0x${this.rights.toString(16)} ${this.offset}/${this.size}/${this.data.byteLength})`;
    }
}

class WASIStreamingFileDescriptor extends WASIFileDescriptor {
    constructor(fdindex: number, name: string, type: FDType, rights: number,
        private stream: NodeJS.WritableStream) {
        super(name, type, rights);
        this.fdindex = fdindex;
    }
    write(chunk: Uint8Array) {
        this.stream.write(chunk);
    }
}

export class WASIFilesystem {
    private files: Map<string, WASIFileDescriptor> = new Map();
    private dirs: Map<string, WASIFileDescriptor> = new Map();

    constructor() {
        this.putDirectory("/");
    }
    putDirectory(name: string, rights?: number) {
        if (!rights) rights = FDRights.PATH_OPEN | FDRights.PATH_CREATE_DIRECTORY | FDRights.PATH_CREATE_FILE;
        const dir = new WASIFileDescriptor(name, FDType.DIRECTORY, rights);
        this.dirs.set(name, dir);
        return dir;
    }
    putFile(name: string, data: string | Uint8Array, rights?: number) {
        if (typeof data === 'string') {
            data = new TextEncoder().encode(data);
        }
        if (!rights) rights = FDRights.FD_READ | FDRights.FD_WRITE;
        const file = new WASIFileDescriptor(name, FDType.REGULAR_FILE, rights);
        file.write(data);
        file.offset = 0;
        this.files.set(name, file);
        return file;
    }
    getFile(name: string) {
        return this.files.get(name);
    }
}

export class WASIRunner {
    #compiled: WebAssembly.Module;
    #instance; // TODO
    #memarr8: Uint8Array;
    #memarr32: Int32Array;
    #args: Uint8Array[] = [];

    stdin = new WASIStreamingFileDescriptor(0, '<stdin>', FDType.CHARACTER_DEVICE, FDRights.FD_READ, process.stdin);
    stdout = new WASIStreamingFileDescriptor(1, '<stdout>', FDType.CHARACTER_DEVICE, FDRights.FD_WRITE, process.stdout);
    stderr = new WASIStreamingFileDescriptor(2, '<stderr>', FDType.CHARACTER_DEVICE, FDRights.FD_WRITE, process.stderr);

    fds: WASIFileDescriptor[] = [this.stdin, this.stdout, this.stderr];
    exited = false;
    errno = -1;
    fs = new WASIFilesystem();

    async loadAsync(wasmSource: Uint8Array) {
        this.#compiled = await WebAssembly.compile(wasmSource);
        this.#instance = await WebAssembly.instantiate(this.#compiled, this.getImportObject());
    }
    setArgs(args: string[]) {
        this.#args = args.map(arg => new TextEncoder().encode(arg + '\0'));
    }
    addPreopenDirectory(name: string) {
        return this.openFile(name, FDOpenFlags.DIRECTORY | FDOpenFlags.CREAT);
    }
    openFile(path: string, o_flags: number, mode?: number): WASIFileDescriptor | number {
        let file = this.fs.getFile(path);
        mode = typeof mode == 'undefined' ? 438 /* 0666 */ : mode;
        if (o_flags & FDOpenFlags.CREAT) {
            if (file == null) {
                if (o_flags & FDOpenFlags.DIRECTORY) {
                    file = this.fs.putDirectory(path);
                } else {
                    file = this.fs.putFile(path, new Uint8Array(), FDRights.FD_ALL);
                }
            } else {
                if (o_flags & FDOpenFlags.TRUNC) { // truncate
                    file.truncate();
                } else return WASIErrors.INVAL;
            }
        } else {
            if (file == null) return WASIErrors.NOSYS;
            if (o_flags & FDOpenFlags.DIRECTORY) { // check type
                if (file.type !== FDType.DIRECTORY) return WASIErrors.NOSYS;
            }
            if (o_flags & FDOpenFlags.EXCL) return WASIErrors.INVAL; // already exists
            if (o_flags & FDOpenFlags.TRUNC) { // truncate
                file.truncate();
            }
        }
        file.fdindex = this.fds.length;
        this.fds.push(file);
        return file;
    }
    mem8() {
        if (!this.#memarr8?.byteLength) {
            this.#memarr8 = new Uint8Array(this.#instance.exports.memory.buffer);
        }
        return this.#memarr8;
    }
    mem32() {
        if (!this.#memarr32?.byteLength) {
            this.#memarr32 = new Int32Array(this.#instance.exports.memory.buffer);
        }
        return this.#memarr32;
    }
    run() {
        try {
            this.#instance.exports._start();
            if (!this.exited) {
                this.exited = true;
                this.errno = 0;
            }
        } catch (err) {
            if (!this.exited) throw err;
        }
        return this.getErrno();
    }
    getImportObject() {
        return {
            "wasi_snapshot_preview1": this.getWASISnapshotPreview1(),
            "env": this.getEnv(),
        }
    }
    peek8(ptr: number) {
        return this.mem8()[ptr];
    }
    peek16(ptr: number) {
        return this.mem8()[ptr] | (this.mem8()[ptr + 1] << 8);
    }
    peek32(ptr: number) {
        return this.mem32()[ptr >>> 2];
    }
    poke8(ptr: number, val: number) {
        this.mem8()[ptr] = val;
    }
    poke16(ptr: number, val: number) {
        this.mem8()[ptr] = val;
        this.mem8()[ptr + 1] = val >> 8;
    }
    poke32(ptr: number, val: number) {
        this.mem32()[ptr >>> 2] = val;
    }
    poke64(ptr: number, val: number) {
        this.mem32()[ptr >>> 2] = val;
        this.mem32()[(ptr >>> 2) + 1] = 0;
    }
    pokeUTF8(str: string, ptr: number, maxlen: number) {
        const enc = new TextEncoder();
        const bytes = enc.encode(str);
        const len = Math.min(bytes.length, maxlen);
        this.mem8().set(bytes.subarray(0, len), ptr);
    }
    peekUTF8(ptr: number, maxlen: number) {
        const bytes = this.mem8().subarray(ptr, ptr + maxlen);
        const dec = new TextDecoder();
        return dec.decode(bytes);
    }
    getErrno() {
        return this.errno;
        //let errno_ptr = this.#instance.exports.__errno_location();
        //return this.peek32(errno_ptr);
    }
    args_sizes_get(argcount_ptr: number, argv_buf_size_ptr: number) {
        debug("args_sizes_get", argcount_ptr, argv_buf_size_ptr);
        this.poke32(argcount_ptr, this.#args.length);
        this.poke32(argv_buf_size_ptr, this.#args.reduce((acc, arg) => acc + arg.length, 0));
        return 0;
    }
    args_get(argv_ptr: number, argv_buf_ptr: number) {
        debug("args_get", argv_ptr, argv_buf_ptr);
        let argv = argv_ptr;
        let argv_buf = argv_buf_ptr;
        for (let arg of this.#args) {
            this.poke32(argv, argv_buf);
            argv += 4;
            for (let i = 0; i < arg.length; i++) {
                this.poke8(argv_buf, arg[i]);
                argv_buf++;
            }
        }
        return 0;
    }
    fd_write(fd, iovs, iovs_len) {
        debug("fd_write", fd, iovs, iovs_len);
        const stream = this.fds[fd];
        const iovecs = this.mem32().subarray(iovs >>> 2, (iovs + iovs_len * 8) >>> 2);
        let total = 0;
        for (let i = 0; i < iovs_len; i++) {
            const ptr = iovecs[i * 2];
            const len = iovecs[i * 2 + 1];
            const chunk = this.mem8().subarray(ptr, ptr + len);
            total += len;
            stream.write(chunk);
        }
        return total;
    }
    fd_read(fd, iovs, iovs_len, nread_ptr) {
        const stream = this.fds[fd];
        const iovecs = this.mem32().subarray(iovs >>> 2, (iovs + iovs_len * 8) >>> 2);
        let total = 0;
        for (let i = 0; i < iovs_len; i++) {
            const ptr = iovecs[i * 2];
            const len = iovecs[i * 2 + 1];
            const chunk = this.mem8().subarray(ptr, ptr + len);
            total += stream.read(chunk);
        }
        this.poke32(nread_ptr, total);
        debug("fd_read", fd, iovs, iovs_len, '->', total);
        return WASIErrors.SUCCESS;
    }
    fd_seek(fd: number, offset: number, whence: number, newoffset_ptr: number) {
        const file = this.fds[fd];
        debug("fd_seek", fd, offset, whence, file);
        if (file != null) {
            file.llseek(offset, whence);
            this.poke64(newoffset_ptr, file.offset);
            return WASIErrors.SUCCESS;
        }
        return WASIErrors.BADF;
    }
    fd_close(fd: number) {
        debug("fd_close", fd);
        const file = this.fds[fd];
        if (file != null) {
            this.fds[fd] = null;
            return 0;
        }
        return WASIErrors.BADF;
    }
    proc_exit(errno: number) {
        debug("proc_exit", errno);
        this.errno = errno;
        this.exited = true;
    }
    fd_prestat_get(fd: number, prestat_ptr: number) {
        const file = this.fds[fd];
        debug("fd_prestat_get", fd, prestat_ptr, file?.name);
        if (file && file.type === FDType.DIRECTORY) {
            const enc_name = new TextEncoder().encode(file.name);
            this.poke8(prestat_ptr + 0, 0); // __WASI_PREOPENTYPE_DIR
            this.poke64(prestat_ptr + 8, enc_name.length);
            return WASIErrors.SUCCESS;
        }
        return WASIErrors.BADF;
    }
    fd_fdstat_get(fd: number, fdstat_ptr: number) {
        const file = this.fds[fd];
        debug("fd_fdstat_get", fd, fdstat_ptr, file + "");
        if (file != null) {
            this.poke16(fdstat_ptr + 0, file.type); // fs_filetype
            this.poke16(fdstat_ptr + 2, file.flags); // fs_flags
            this.poke64(fdstat_ptr + 8, file.rights); // fs_rights_base
            this.poke64(fdstat_ptr + 16, file.rights);  // fs_rights_inheriting
            return WASIErrors.SUCCESS;
        }
        return WASIErrors.BADF;
    }
    fd_prestat_dir_name(fd: number, path_ptr: number, path_len: number) {
        const file = this.fds[fd];
        debug("fd_prestat_dir_name", fd, path_ptr, path_len);
        if (file != null) {
            this.pokeUTF8(file.name, path_ptr, path_len);
            return WASIErrors.SUCCESS;
        }
        return WASIErrors.INVAL;
    }
    path_open(dirfd: number, dirflags: number, path_ptr: number, path_len: number,
        o_flags: number, fs_rights_base: number, fs_rights_inheriting: number,
        fd_flags: number, fd_ptr: number)
    {
        const dir = this.fds[dirfd];
        if (dir == null) return WASIErrors.BADF;
        if (dir.type !== FDType.DIRECTORY) return WASIErrors.NOTDIR;
        const filename = this.peekUTF8(path_ptr, path_len);
        const path = dir.name + '/' + filename;
        const fd = this.openFile(path, o_flags, fd_flags);
        debug("path_open", path, dirfd, dirflags, 
            o_flags, //fs_rights_base, fs_rights_inheriting,
            fd_flags, fd_ptr, '->', fd + "");
        if (typeof fd === 'number') return fd; // error msg
        this.poke32(fd_ptr, fd.fdindex);
        return WASIErrors.SUCCESS;
    }
    random_get(ptr: number, len: number) {
        debug("random_get", ptr, len);
        for (let i=0; i<len; i++) {
            // TODO: don't use for crypto
            this.poke8(ptr + i, Math.floor(Math.random() * 256));
        }
        return WASIErrors.SUCCESS;
    }
    getWASISnapshotPreview1() {
        return {
            args_sizes_get: this.args_sizes_get.bind(this),
            args_get: this.args_get.bind(this),
            proc_exit: this.proc_exit.bind(this),
            path_open: this.path_open.bind(this),
            fd_prestat_get: this.fd_prestat_get.bind(this),
            fd_prestat_dir_name: this.fd_prestat_dir_name.bind(this),
            fd_fdstat_get: this.fd_fdstat_get.bind(this),
            fd_fdstat_set_flags() { debug("fd_fdstat_set_flags"); return 0; },
            fd_read: this.fd_read.bind(this),
            fd_write: this.fd_write.bind(this),
            fd_seek: this.fd_seek.bind(this),
            fd_close: this.fd_close.bind(this),
            fd_readdir() { debug("fd_readdir"); return 0; },
            path_unlink_file() { debug("path_unlink_file"); return 0; },
            environ_sizes_get() { debug("environ_sizes_get"); return 0; },
            environ_get() { debug("environ_get"); return 0; },
            clock_time_get() { debug("clock_time_get"); return 0; },
            path_filestat_get() { debug("path_filestat_get"); return 0; },
            random_get: this.random_get.bind(this),
        }
    }
    getEnv() {
        return {
            __syscall_unlinkat() { debug('unlink'); return 0; },
        }
    }
}