const std = @import("std");
const chunk = @import("chunk.zig");
const value = @import("value.zig");

const Chunk = chunk.Chunk;
const StdOut = *std.io.OutStream(std.fs.File.WriteError);

pub const InterpretResult = enum {
    Ok,
    CompileError,
    RuntimeError,
};

pub const VM = struct {
    chk: *Chunk,
    ip: usize,
    stdout: StdOut,

    pub fn init(stdout: StdOut, chk: *Chunk) VM {
        return VM{
            .stdout = stdout,
            .chk = chk,
            .ip = 0,
        };
    }

    fn readByte(self: *VM) u8 {
        var byte: u8 = self.chk.code[self.ip];
        self.ip += 1;
        return byte;
    }

    fn readConst(self: *VM) value.Value {
        return self.chk.constants.values[self.readByte()];
    }

    fn readConstLong(self: *VM) value.Value {
        const v3 = self.readByte();
        const v2 = self.readByte();
        const v1 = self.readByte();
        const const_idx = (@intCast(u24, v3) << 16) |
            (@intCast(u24, v2) << 8) |
            v1;

        return self.chk.constants.values[const_idx];
    }

    fn run(self: *VM) !InterpretResult {
        while (true) {
            var instruction = self.readByte();

            switch (instruction) {
                chunk.OpCode.Constant => blk: {
                    var constant = self.readConst();
                    try value.printValue(self.stdout, constant);
                    break :blk;
                },
                chunk.OpCode.ConstantLong => blk: {
                    var constant = self.readConstLong();
                    try value.printValue(self.stdout, constant);
                    break :blk;
                },
                chunk.OpCode.Return => blk: {
                    return InterpretResult.Ok;
                },
                else => blk: {
                    std.debug.warn("Unknown instruction: {x}\n", instruction);
                    return InterpretResult.RuntimeError;
                },
            }
        }
    }

    pub fn interpret(self: *VM) !InterpretResult {
        self.ip = 0;
        return try self.run();
    }
};