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use std::io::{Read, Write};

use state::State;
use common::BfResult;
use traits::Interpretable;
use super::*;

impl Interpretable for Program {
    fn interpret_state<R: Read, W: Write>(
        &self, mut state: State, mut input: R, mut output: W) -> BfResult<()>
    {
        interpret(self, &mut state, &mut input, &mut output)
    }
}

fn interpret<R, W>(instructions: &Program, state: &mut State,
                   input: &mut R, output: &mut W)
                   -> BfResult<()>
    where R: Read, W: Write
{
    for instruction in instructions {
        interpret_instruction(instruction, state, input, output)?;
    }

    Ok(())
}

#[inline]
fn interpret_instruction<R, W>(instruction: &Statement, state: &mut State,
                               input: &mut R, output: &mut W)
                               -> BfResult<()>
    where R: Read, W: Write
{
    use super::Statement::*;
    use super::Command::*;

    match *instruction {
        Cmd(Left) => state.left(1usize)?,
        Cmd(Right) => state.right(1usize)?,
        Cmd(Up) => state.up(1),
        Cmd(Down) => state.down(1),
        Cmd(In) => state.read(input),
        Cmd(Out) => state.write(output),
        Cmd(Begin) | Cmd(End) =>
            panic!("Invalid instruction: Begin or End"),
        Loop(ref program) => {
            while state.load() != 0  {
                interpret(program, state, input, output)?;
            }
        }
    }

    Ok(())
}

#[cfg(test)]
mod tests {
    use test_helpers::*;
    use super::*;
    use common::Command::*;
    use super::Statement::*;

    #[test]
    fn assert_no_output() {
        assert_interpret(&[Cmd(Right)] as &Program, &[], &[]);
    }

    #[test]
    fn assert_output_0() {
        assert_interpret(&[Cmd(Right), Cmd(Out)] as &Program, &[], &[0]);
    }

    #[test]
    fn assert_output_1() {
        assert_interpret(&[Cmd(Up), Cmd(Out)] as &Program, &[], &[1]);
    }

    #[test]
    fn assert_increment_input() {
        let prog: &Program = &[Cmd(In), Cmd(Up), Cmd(Out)];
        assert_interpret(prog, &[0], &[1]);
        assert_interpret(prog, &[5], &[6]);
        assert_interpret(prog, &[255], &[0]);
    }

    #[test]
    fn assert_increment_loop() {
        let prog: &Program = &[Cmd(In), mk_loop(vec![Cmd(Up), Cmd(Out), Cmd(In)])];
        assert_interpret(prog, &[0], &[]);
        assert_interpret(prog, &[1, 0], &[2]);
        assert_interpret(prog, &[1, 4, 0], &[2, 5]);
        assert_interpret(prog, &[8, 255, 18, 0], &[9, 0, 19]);
    }

    #[test]
    fn hello_world() {
        assert_parse_interpret(HELLO_WORLD_SRC, "", "Hello, World!");
    }

    #[test]
    fn factoring() {
        assert_parse_interpret(FACTOR_SRC, "2\n", "2: 2\n");
        assert_parse_interpret(FACTOR_SRC, "3\n", "3: 3\n");
        assert_parse_interpret(FACTOR_SRC, "6\n", "6: 2 3\n");
        assert_parse_interpret(FACTOR_SRC, "100\n", "100: 2 2 5 5\n");
    }

    fn assert_parse_interpret(program: &[u8], input: &str, output: &str) {
        use super::super::parser::parse_program;

        let program = parse_program(program).unwrap();
        assert_interpret(&*program, input.as_bytes(), output.as_bytes());
    }

    fn mk_loop(instructions: Vec<Statement>) -> Statement {
        Statement::Loop(instructions.into_boxed_slice())
    }
}