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package org.jruby.util;

import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.Channel;
import java.nio.channels.ReadableByteChannel;
import java.nio.channels.WritableByteChannel;

import org.jruby.Ruby;
import org.jruby.RubyFixnum;
import org.jruby.RubyString;
import org.jruby.exceptions.ReadPartialBufferOverflowException;
import org.jruby.runtime.CallSite;
import org.jruby.runtime.ThreadContext;
import org.jruby.runtime.builtin.IRubyObject;
import org.jruby.runtime.MethodIndex;
import org.jruby.runtime.callsite.CacheEntry;
import org.jruby.runtime.callsite.FunctionalCachingCallSite;
import org.jruby.runtime.callsite.RespondToCallSite;

import static org.jruby.api.Convert.asFixnum;
import static org.jruby.api.Convert.toInt;

/**
 * Wrap an IO object in a Channel.
 *
 * @see IOReadableByteChannel
 * @see IOWritableByteChannel
 * @see IOReadableWritableByteChannel
 */
public abstract class IOChannel implements Channel {
    protected final IRubyObject io;
    private final CallSite closeAdapter = MethodIndex.getFunctionalCallSite("close");
    private final RespondToCallSite respondToClosed = new RespondToCallSite("closed?");
    private final CallSite isClosedAdapter = MethodIndex.getFunctionalCallSite("closed?");
    protected final Ruby runtime;

    protected IOChannel(final IRubyObject io) {
        this.io = io;
        this.runtime = io.getRuntime();
    }
    
    public void close() throws IOException {
        ThreadContext context = runtime.getCurrentContext();

        // no call site use here since this will likely only be called once
        if (io.respondsTo("close")) {
            closeAdapter.call(context, io, io);
        }

        // can't close, assume it doesn't need to be
    }

    public boolean isOpen() {
        ThreadContext context = runtime.getCurrentContext();

        if (respondToClosed.respondsTo(context, io, io)) {
            return !isClosedAdapter.call(context, io, io).isTrue();
        }

        // can't determine, assume it's open
        return true;
    }

    protected static int read(Ruby runtime, IRubyObject io, FunctionalCachingCallSite read, ByteBuffer dst) throws IOException {
        ThreadContext context = runtime.getCurrentContext();
        int remaining = dst.remaining();

        CacheEntry readMethodEntry = read.retrieveCache(io);
        RubyFixnum remainingFixnum = asFixnum(context, remaining);
        IRubyObject readValue, retValue;
        if (readMethodEntry.method.getSignature().isTwoArguments()) {
            if (dst.hasArray()) {
                readValue = RubyString.newStringNoCopy(runtime, dst.array(), dst.position(), remaining);
            } else {
                readValue = RubyString.newStringLight(runtime, remaining);
            }
            retValue = read.call(context, io, io, remainingFixnum, readValue);
        } else {
            retValue = readValue = read.call(context, io, io, remainingFixnum);
        }

        int returnValue = -1;
        RubyString readString;
        if (!retValue.isNil()
                && (readString = readValue.convertToString()).size() > 0) {
            ByteList str = readString.getByteList();
            int realSize = str.getRealSize();

            if (realSize > remaining) {
                throw new ReadPartialBufferOverflowException(
                        "error calling " + io.getType() + "#readpartial: requested " + remaining + " bytes but received " + realSize);
            }

            dst.put(str.getUnsafeBytes(), str.getBegin(), realSize);
            returnValue = realSize;
        }
        return returnValue;
    }

    /**
     * Perform a write to the given IO-like object, using the given call site, and passing the contents of the given
     * buffer.
     *
     * The buffer and its contents should not be referenced beyond the method's return.
     *
     * @param runtime the current runtime
     * @param io the target IO-like object
     * @param write the call site for making dynamic `write` calls
     * @param src the data to write
     * @return the amount of data reported written by the dynamic `write` call
     */
    protected static int write(Ruby runtime, IRubyObject io, FunctionalCachingCallSite write, ByteBuffer src) {
        ByteList buffer;
        int position = src.position();
        int remaining = src.remaining();

        // copy buffer contents to a ByteList
        if (src.hasArray()) {
            buffer = new ByteList(src.array(), src.position(), remaining, true);
        } else {
            buffer = new ByteList(remaining);
            buffer.append(src, remaining);
        }

        var context = runtime.getCurrentContext();
        // call write with new String based on this ByteList
        IRubyObject written = write.call(context, io, io, RubyString.newStringLight(runtime, buffer));
        int wrote = toInt(context, written);

        // set source position to match bytes written
        if (wrote > 0) src.position(position + wrote);

        return wrote;
    }

    protected FunctionalCachingCallSite initReadSite(String readMethod) {
        // no call site use here since this will only be called once
        if(io.respondsTo(readMethod)) {
            return new FunctionalCachingCallSite(readMethod);
        } else {
            throw new IllegalArgumentException(io.getMetaClass() + "not coercible to " + getClass().getSimpleName() + ": no '" + readMethod + "' method");
        }
    }

    protected FunctionalCachingCallSite initWriteSite() {
        // no call site use here since this will only be called once
        if(io.respondsTo("write")) {
            return new FunctionalCachingCallSite("write");
        } else if (io.respondsTo("<<")) {
            return new FunctionalCachingCallSite("<<");
        } else {
            throw new IllegalArgumentException(io.getMetaClass() + "not coercible to " + getClass().getSimpleName() + ": no 'write' method");
        }
    }

    /**
     * A {@link ReadableByteChannel} wrapper around an IO-like Ruby object.
     */
    public static class IOReadableByteChannel extends IOChannel implements ReadableByteChannel {
        private final FunctionalCachingCallSite read;

        public IOReadableByteChannel(final IRubyObject io) {
            this(io, "read");
        }

        public IOReadableByteChannel(final IRubyObject io, final String readMethod) {
            super(io);
            read = initReadSite(readMethod);
        }
        
        public int read(ByteBuffer dst) throws IOException {
            return read(runtime, io, read, dst);
        }
    }


    /**
     * A {@link WritableByteChannel} wrapper around an IO-like Ruby object.
     */
    public static class IOWritableByteChannel extends IOChannel implements WritableByteChannel {
        private final FunctionalCachingCallSite write;
        public IOWritableByteChannel(final IRubyObject io) {
            super(io);
            write = initWriteSite();
        }

        public int write(ByteBuffer src) throws IOException {
            return write(runtime, io, write, src);
        }
    }


    /**
     * A {@link ReadableByteChannel} and {@link WritableByteChannel} wrapper around an IO-like Ruby object.
     */
    public static class IOReadableWritableByteChannel extends IOChannel implements ReadableByteChannel, WritableByteChannel {
        private final FunctionalCachingCallSite write;
        private final FunctionalCachingCallSite read;
        public IOReadableWritableByteChannel(final IRubyObject io) {
            super(io);
            read = initReadSite("read");
            write = initWriteSite();
        }

        public int read(ByteBuffer dst) throws IOException {
            return read(runtime, io, read, dst);
        }

        public int write(ByteBuffer src) throws IOException {
            return write(runtime, io, write, src);
        }
    }

}
