//! Implementation of instructions for MOS 6502.

/// List of all instructions for MOS 6502.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum Instruction {
	/// Load accumulator.
	Lda,
}

/// Addressing modes for MOS 6502.
#[derive(Clone, Copy, Debug)]
pub enum AddressingMode {
	/// Immediate mode
	Immediate,

	/// Zero Page mode
	ZeroPage,

	/// ZeroPage.X mode
	ZeroPageX,
}

/// Operation retrieved from decoding an opcode.
pub struct Operation {
	/// [`AddressingMode`]
	pub addressing_mode: AddressingMode,

	/// [`Instruction`]
	pub instruction: Instruction,
}

impl Operation {
	/// Creates a new operation from the `instruction` and `addressing_mode`.
	pub const fn new(instruction: Instruction, addressing_mode: AddressingMode) -> Self {
		Self {
			addressing_mode,
			instruction,
		}
	}
}

/// Gets the operation from the passed in opcode. Returns [`None`] if no
/// operation exists.
pub const fn get_operation(opcode: u8) -> Option<Operation> {
	match opcode {
		0xA5 => Some(Operation::new(Instruction::Lda, AddressingMode::ZeroPage)),
		0xA9 => Some(Operation::new(Instruction::Lda, AddressingMode::Immediate)),
		0xB5 => Some(Operation::new(Instruction::Lda, AddressingMode::ZeroPageX)),
		_ => None,
	}
}