/*
 * @(#)Interpreter.java                        2.1 2003/10/07
 *
 * Copyright (C) 1999, 2003 D.A. Watt and D.F. Brown
 * Dept. of Computing Science, University of Glasgow, Glasgow G12 8QQ Scotland
 * and School of Computer and Math Sciences, The Robert Gordon University,
 * St. Andrew Street, Aberdeen AB25 1HG, Scotland.
 * All rights reserved.
 *
 * This software is provided free for educational use only. It may
 * not be used for commercial purposes without the prior written permission
 * of the authors.
 */

package triangle.abstractMachine;

import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

public class Interpreter {

	static String objectName;

	// DATA STORE

	static int[] data = new int[1024];

	// DATA STORE REGISTERS AND OTHER REGISTERS

	final static int CB = 0, SB = 0, HB = 1024; // = upper bound of data array + 1

	static int CT, CP, ST, HT, LB, status;

	// status values
	final static int running = 0, halted = 1, failedDataStoreFull = 2, failedInvalidCodeAddress = 3,
			failedInvalidInstruction = 4, failedOverflow = 5, failedZeroDivide = 6, failedIOError = 7;

	static long accumulator;

	static int content(int r) {
		var register = Register.values()[r];
		return content(register);
	}

	static int content(Register r) {
		// Returns the current content of register r,
		// even if r is one of the pseudo-registers L1..L6.

		switch (r) {
		case CB:
			return CB;
		case CT:
			return CT;
		case PB:
			return Machine.PB;
		case PT:
			return Machine.PT;
		case SB:
			return SB;
		case ST:
			return ST;
		case HB:
			return HB;
		case HT:
			return HT;
		case LB:
			return LB;
		case L1:
			return data[LB];
		case L2:
			return data[data[LB]];
		case L3:
			return data[data[data[LB]]];
		case L4:
			return data[data[data[data[LB]]]];
		case L5:
			return data[data[data[data[data[LB]]]]];
		case L6:
			return data[data[data[data[data[data[LB]]]]]];
		case CP:
			return CP;
		default:
			return 0;
		}
	}

	// PROGRAM STATUS

	static void dump() {
		// Writes a summary of the machine state.

		System.out.println("");
		System.out.println("State of data store and registers:");
		System.out.println("");
		if (HT == HB) {
			System.out.println("            |--------|          (heap is empty)");
		} else {
			System.out.println("       HB-->");
			System.out.println("            |--------|");
			for (var addr = HB - 1; addr >= HT; addr--) {
				System.out.print(addr + ":");
				if (addr == HT) {
					System.out.print(" HT-->");
				} else {
					System.out.print("      ");
				}
				System.out.println("|" + data[addr] + "|");
			}
			System.out.println("            |--------|");
		}
		System.out.println("            |////////|");
		System.out.println("            |////////|");
		if (ST == SB) {
			System.out.println("            |--------|          (stack is empty)");
		} else {
			var dynamicLink = LB;
			var staticLink = LB;
			var localRegNum = Register.LB;
			System.out.println("      ST--> |////////|");
			System.out.println("            |--------|");
			for (var addr = ST - 1; addr >= SB; addr--) {
				System.out.print(addr + ":");
				if (addr == SB) {
					System.out.print(" SB-->");
				} else if (addr == staticLink) {
					switch (localRegNum) {
					case LB:
						System.out.print(" LB-->");
						break;
					case L1:
						System.out.print(" L1-->");
						break;
					case L2:
						System.out.print(" L2-->");
						break;
					case L3:
						System.out.print(" L3-->");
						break;
					case L4:
						System.out.print(" L4-->");
						break;
					case L5:
						System.out.print(" L5-->");
						break;
					case L6:
						System.out.print(" L6-->");
						break;
					default:
						break;
					}
					staticLink = data[addr];
					localRegNum = Register.values()[localRegNum.ordinal() + 1];
				} else {
					System.out.print("      ");
				}
				if (addr == dynamicLink && dynamicLink != SB) {
					System.out.print("|SL=" + data[addr] + "|");
				} else if (addr == dynamicLink + 1 && dynamicLink != SB) {
					System.out.print("|DL=" + data[addr] + "|");
				} else if (addr == dynamicLink + 2 && dynamicLink != SB) {
					System.out.print("|RA=" + data[addr] + "|");
				} else {
					System.out.print("|" + data[addr] + "|");
				}
				System.out.println("");
				if (addr == dynamicLink) {
					System.out.println("            |--------|");
					dynamicLink = data[addr + 1];
				}
			}
		}
		System.out.println("");
	}

	static void showStatus() {
		// Writes an indication of whether and why the program has terminated.
		System.out.println("");
		switch (status) {
		case running:
			System.out.println("Program is running.");
			break;
		case halted:
			System.out.println("Program has halted normally.");
			break;
		case failedDataStoreFull:
			System.out.println("Program has failed due to exhaustion of Data Store.");
			break;
		case failedInvalidCodeAddress:
			System.out.println("Program has failed due to an invalid code address.");
			break;
		case failedInvalidInstruction:
			System.out.println("Program has failed due to an invalid instruction.");
			break;
		case failedOverflow:
			System.out.println("Program has failed due to overflow.");
			break;
		case failedZeroDivide:
			System.out.println("Program has failed due to division by zero.");
			break;
		case failedIOError:
			System.out.println("Program has failed due to an IO error.");
			break;
		}
		if (status != halted) {
			dump();
		}
	}

	// INTERPRETATION

	static void checkSpace(int spaceNeeded) {
		// Signals failure if there is not enough space to expand the stack or
		// heap by spaceNeeded.

		if (HT - ST < spaceNeeded) {
			status = failedDataStoreFull;
		}
	}

	static boolean isTrue(int datum) {
		// Tests whether the given datum represents true.
		return (datum == Machine.trueRep);
	}

	static boolean equal(int size, int addr1, int addr2) {
		// Tests whether two multi-word objects are equal, given their common
		// size and their base addresses.

		boolean eq;
		int index;

		eq = true;
		index = 0;
		while (eq && (index < size)) {
			if (data[addr1 + index] == data[addr2 + index]) {
				index = index + 1;
			} else {
				eq = false;
			}
		}

		return eq;
	}

	static int overflowChecked(long datum) {
		// Signals failure if the datum is too large to fit into a single word,
		// otherwise returns the datum as a single word.

		if ((-Machine.maxintRep <= datum) && (datum <= Machine.maxintRep)) {
			return (int) datum;
		} else {
			status = failedOverflow;
			return 0;
		}
	}

	static int toInt(boolean b) {
		return b ? Machine.trueRep : Machine.falseRep;
	}

	static int currentChar;

	static int readInt() throws java.io.IOException {
		int temp = 0;
		int sign = 1;

		do {
			currentChar = System.in.read();
		} while (Character.isWhitespace((char) currentChar));

		if ((currentChar == '-') || (currentChar == '+')) {
			do {
				sign = (currentChar == '-') ? -1 : 1;
				currentChar = System.in.read();
			} while ((currentChar == '-') || currentChar == '+');
		}

		if (Character.isDigit((char) currentChar)) {
			do {
				temp = temp * 10 + (currentChar - '0');
				currentChar = System.in.read();
			} while (Character.isDigit((char) currentChar));
		}

		return sign * temp;
	}

	static void callPrimitive(int primitiveDisplacement) {
		// Invokes the given primitive routine.

		int addr, size;
		char ch;

		var primitive = Primitive.values()[primitiveDisplacement];
		switch (primitive) {
		case ID:
			break; // nothing to be done
		case NOT:
			data[ST - 1] = toInt(!isTrue(data[ST - 1]));
			break;
		case AND:
			ST = ST - 1;
			data[ST - 1] = toInt(isTrue(data[ST - 1]) & isTrue(data[ST]));
			break;
		case OR:
			ST = ST - 1;
			data[ST - 1] = toInt(isTrue(data[ST - 1]) | isTrue(data[ST]));
			break;
		case SUCC:
			data[ST - 1] = overflowChecked(data[ST - 1] + 1);
			break;
		case PRED:
			data[ST - 1] = overflowChecked(data[ST - 1] - 1);
			break;
		case NEG:
			data[ST - 1] = -data[ST - 1];
			break;
		case ADD:
			ST = ST - 1;
			accumulator = data[ST - 1];
			data[ST - 1] = overflowChecked(accumulator + data[ST]);
			break;
		case SUB:
			ST = ST - 1;
			accumulator = data[ST - 1];
			data[ST - 1] = overflowChecked(accumulator - data[ST]);
			break;
		case MULT:
			ST = ST - 1;
			accumulator = data[ST - 1];
			data[ST - 1] = overflowChecked(accumulator * data[ST]);
			break;
		case DIV:
			ST = ST - 1;
			accumulator = data[ST - 1];
			if (data[ST] != 0) {
				data[ST - 1] = (int) (accumulator / data[ST]);
			} else {
				status = failedZeroDivide;
			}
			break;
		case MOD:
			ST = ST - 1;
			accumulator = data[ST - 1];
			if (data[ST] != 0) {
				data[ST - 1] = (int) (accumulator % data[ST]);
			} else {
				status = failedZeroDivide;
			}
			break;
		case LT:
			ST = ST - 1;
			data[ST - 1] = toInt(data[ST - 1] < data[ST]);
			break;
		case LE:
			ST = ST - 1;
			data[ST - 1] = toInt(data[ST - 1] <= data[ST]);
			break;
		case GE:
			ST = ST - 1;
			data[ST - 1] = toInt(data[ST - 1] >= data[ST]);
			break;
		case GT:
			ST = ST - 1;
			data[ST - 1] = toInt(data[ST - 1] > data[ST]);
			break;
		case EQ:
			size = data[ST - 1]; // size of each comparand
			ST = ST - 2 * size;
			data[ST - 1] = toInt(equal(size, ST - 1, ST - 1 + size));
			break;
		case NE:
			size = data[ST - 1]; // size of each comparand
			ST = ST - 2 * size;
			data[ST - 1] = toInt(!equal(size, ST - 1, ST - 1 + size));
			break;
		case EOL:
			data[ST] = toInt(currentChar == '\n');
			ST = ST + 1;
			break;
		case EOF:
			data[ST] = toInt(currentChar == -1);
			ST = ST + 1;
			break;
		case GET:
			ST = ST - 1;
			addr = data[ST];
			try {
				currentChar = System.in.read();
			} catch (java.io.IOException s) {
				status = failedIOError;
			}
			data[addr] = currentChar;
			break;
		case PUT:
			ST = ST - 1;
			ch = (char) data[ST];
			System.out.print(ch);
			break;
		case GETEOL:
			try {
				while ((currentChar = System.in.read()) != '\n')
					;
			} catch (java.io.IOException s) {
				status = failedIOError;
			}
			break;
		case PUTEOL:
			System.out.println("");
			break;
		case GETINT:
			ST = ST - 1;
			addr = data[ST];
			try {
				accumulator = readInt();
			} catch (java.io.IOException s) {
				status = failedIOError;
			}
			data[addr] = (int) accumulator;
			break;
		case PUTINT:
			ST = ST - 1;
			accumulator = data[ST];
			System.out.print(accumulator);
			break;
		case NEW:
			size = data[ST - 1];
			checkSpace(size);
			HT = HT - size;
			data[ST - 1] = HT;
			break;
		case DISPOSE:
			ST = ST - 1; // no action taken at present
			break;
		}
	}

	static void interpretProgram() {
		// Runs the program in code store.

		Instruction currentInstr;

		// Initialize registers ...
		ST = SB;
		HT = HB;
		LB = SB;
		CP = CB;
		status = running;
		do {
			// Fetch instruction ...
			currentInstr = Machine.code[CP];
			// Decode instruction ...
			var op = currentInstr.opCode;
			var r = currentInstr.register;
			var n = currentInstr.length;
			var d = currentInstr.operand;
			int addr;

			// Execute instruction ...
			switch (op) {
			case LOAD:
				addr = d + content(r);
				checkSpace(n);
				for (var index = 0; index < n; index++) {
					data[ST + index] = data[addr + index];
				}
				ST = ST + n;
				CP = CP + 1;
				break;
			case LOADA:
				addr = d + content(r);
				checkSpace(1);
				data[ST] = addr;
				ST = ST + 1;
				CP = CP + 1;
				break;
			case LOADI:
				ST = ST - 1;
				addr = data[ST];
				checkSpace(n);
				for (var index = 0; index < n; index++) {
					data[ST + index] = data[addr + index];
				}
				ST = ST + n;
				CP = CP + 1;
				break;
			case LOADL:
				checkSpace(1);
				data[ST] = d;
				ST = ST + 1;
				CP = CP + 1;
				break;
			case STORE:
				addr = d + content(r);
				ST = ST - n;
				for (var index = 0; index < n; index++) {
					data[addr + index] = data[ST + index];
				}
				CP = CP + 1;
				break;
			case STOREI:
				ST = ST - 1;
				addr = data[ST];
				ST = ST - n;
				for (var index = 0; index < n; index++) {
					data[addr + index] = data[ST + index];
				}
				CP = CP + 1;
				break;
			case CALL:
				addr = d + content(r);
				if (addr >= Machine.PB) {
					callPrimitive(addr - Machine.PB);
					CP = CP + 1;
				} else {
					checkSpace(3);
					if (0 <= n && n <= 15) {
						data[ST] = content(n); // static link
					} else {
						status = failedInvalidInstruction;
					}
					data[ST + 1] = LB; // dynamic link
					data[ST + 2] = CP + 1; // return address
					LB = ST;
					ST = ST + 3;
					CP = addr;
				}
				break;
			case CALLI:
				ST = ST - 2;
				addr = data[ST + 1];
				if (addr >= Machine.PB) {
					callPrimitive(addr - Machine.PB);
					CP = CP + 1;
				} else {
					// data[ST] = static link already
					data[ST + 1] = LB; // dynamic link
					data[ST + 2] = CP + 1; // return address
					LB = ST;
					ST = ST + 3;
					CP = addr;
				}
				break;
			case RETURN:
				addr = LB - d;
				CP = data[LB + 2];
				LB = data[LB + 1];
				ST = ST - n;
				for (var index = 0; index < n; index++) {
					data[addr + index] = data[ST + index];
				}
				ST = addr + n;
				break;
			case PUSH:
				checkSpace(d);
				ST = ST + d;
				CP = CP + 1;
				break;
			case POP:
				addr = ST - n - d;
				ST = ST - n;
				for (var index = 0; index < n; index++) {
					data[addr + index] = data[ST + index];
				}
				ST = addr + n;
				CP = CP + 1;
				break;
			case JUMP:
				CP = d + content(r);
				break;
			case JUMPI:
				ST = ST - 1;
				CP = data[ST];
				break;
			case JUMPIF:
				ST = ST - 1;
				if (data[ST] == n) {
					CP = d + content(r);
				} else {
					CP = CP + 1;
				}
				break;
			case HALT:
				status = halted;
				break;
			}
			if (CP < CB || CP >= CT) {
				status = failedInvalidCodeAddress;
			}
		} while (status == running);
	}

	// LOADING

	static void loadObjectProgram(String objectName) {
		// Loads the TAM object program into code store from the named file.

		boolean finished = false;

		try (var objectFile = new FileInputStream(objectName)) {
			var objectStream = new DataInputStream(objectFile);

			var addr = Machine.CB;
			while (!finished) {
				Machine.code[addr] = Instruction.read(objectStream);
				if (Machine.code[addr] == null) {
					finished = true;
				} else {
					addr = addr + 1;
				}
			}
			CT = addr;
		} catch (FileNotFoundException s) {
			CT = CB;
			System.err.println("Error opening object file: " + s);
		} catch (IOException s) {
			CT = CB;
			System.err.println("Error reading object file: " + s);
		}
	}

	// RUNNING

	public static void main(String[] args) {
		System.out.println("********** TAM Interpreter (Java Version 2.1) **********");

		if (args.length == 1) {
			objectName = args[0];
		} else {
			objectName = "obj.tam";
		}

		loadObjectProgram(objectName);
		if (CT != CB) {
			interpretProgram();
			showStatus();
		}
	}
}