'use strict';

let opcodes = {
  0x01: { mnemonic: 'ADD', evaluate: (vm) => {
    let v1 = vm.stack.pop();
    let v2 = vm.stack.pop();
    vm.stack.push(v1+v2);
  }},
  0x02: { mnemonic: 'MUL', evaluate: (vm) => {
    // Pop the top two arguments off of the stack,
    // and then push the result on to the stack.
    let v1 = vm.stack.pop();
    let v2 = vm.stack.pop();
    vm.stack.push(v1*v2);
  }},
  0x03: { mnemonic: 'SUB', evaluate: (vm) => {
    let v1 = vm.stack.pop();
    let v2 = vm.stack.pop();
    vm.stack.push(v1-v2);
  }},
  0x52: { mnemonic: 'MLOAD', evaluate: (vm) => {
    let offset = vm.stack.pop();
    vm.stack.push(vm.memory[offset]);
  }},
  0x53: { mnemonic: 'MSTORE', evaluate: (vm) => {
    let offset = vm.stack.pop();
    let value = vm.stack.pop();
    vm.memory[offset] = value;
  }},
  0x56: { mnemonic: 'JUMP', evaluate: (vm) => {
    let offset = vm.stack.pop();
    vm.pc = offset;
  }},
  0x57: { mnemonic: 'JUMPI', evaluate: (vm) => {
    let offset = vm.stack.pop();
    let condition = vm.stack.pop();
    if (condition) {
      vm.pc = offset;
    }
  }},
  0x5B: { mnemonic: 'JUMPDEST', evaluate: (vm) => {
    // Does nothing.  We could check to make sure that jumps
    // always land at JUMPDEST opcodes, but it is not totally
    // clear that it is worth the bother.
  }},
  0x60: { mnemonic: 'PUSH1', evaluate: (vm) => {
    // The next byte is data, not another instruction
    vm.pc++;
    let v = vm.bytecode.readUInt8(vm.pc);
    vm.stack.push(v);
  }},
  0x90: { mnemonic: 'SWAP1', evaluate: (vm) => {
    let v1 = vm.stack.pop();
    let v2 = vm.stack.pop();
    vm.stack.push(v1);
    vm.stack.push(v2);
  }},
  0x0c: { mnemonic: 'PRINT', evaluate: (vm) => {
    // **NOTE**: This is not a real EVM opcode.
    console.log(vm.stack.pop());
  }},
};

exports.opcodes = opcodes;