//! JamJum JP-Mini wire protocol, reverse-engineered from KuSuite 5.3 (see jpmini.py).
//!
//! Packet: 78 59 <cmd> <len: 3 bytes LE> <payload> <checksum = !sum(payload)>
//! SysEx:  F0 <packet as LSB-first 7-bit bitstream> F7

pub const SLOTS: usize = 16;
const PAYLOAD_SLOTS: usize = 18;
const CMD_PAD_RGB: u8 = 0x51;

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct Rgb(pub u8, pub u8, pub u8);

impl Rgb {
    pub const OFF: Rgb = Rgb(0, 0, 0);
}

pub type Grid = [Rgb; SLOTS];

fn packet(cmd: u8, payload: &[u8]) -> Vec<u8> {
    let n = payload.len() as u32;
    let mut p = vec![0x78, 0x59, cmd, n as u8, (n >> 8) as u8, (n >> 16) as u8];
    p.extend_from_slice(payload);
    p.push(!payload.iter().fold(0u8, |a, &b| a.wrapping_add(b)));
    p
}

fn pack7(data: &[u8]) -> Vec<u8> {
    let mut out = Vec::with_capacity(data.len() * 8 / 7 + 1);
    let (mut acc, mut bits) = (0u32, 0u32);
    for &b in data {
        acc |= u32::from(b) << bits;
        bits += 8;
        while bits >= 7 {
            out.push((acc & 0x7F) as u8);
            acc >>= 7;
            bits -= 7;
        }
    }
    if bits > 0 {
        out.push((acc & 0x7F) as u8);
    }
    out
}

/// Complete SysEx message setting all 16 pads of the bank currently displayed.
pub fn pad_colors_sysex(grid: &Grid) -> Vec<u8> {
    let mut payload = Vec::with_capacity(1 + 3 * PAYLOAD_SLOTS);
    payload.push(0xFF);
    for &Rgb(r, g, b) in grid {
        payload.extend_from_slice(&[g, r, b]); // the device expects G, R, B
    }
    payload.resize(1 + 3 * PAYLOAD_SLOTS, 0);
    let mut msg = vec![0xF0];
    msg.extend(pack7(&packet(CMD_PAD_RGB, &payload)));
    msg.push(0xF7);
    msg
}

#[cfg(test)]
mod tests {
    use super::*;

    fn hex(s: &str) -> Vec<u8> {
        s.split_whitespace()
            .map(|b| u8::from_str_radix(b, 16).unwrap())
            .collect()
    }

    #[test]
    fn pack7_matches_reference() {
        assert_eq!(
            pack7(&[0x78, 0x59, 0xFF, 0x00, 0x80]),
            vec![0x78, 0x32, 0x7D, 0x07, 0x00, 0x10]
        );
    }

    #[test]
    fn all_off_matches_reference() {
        let expected = hex(
            "F0 78 32 45 3A 03 00 40 7F 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 \
             00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 \
             00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 F7",
        );
        assert_eq!(pad_colors_sysex(&[Rgb::OFF; SLOTS]), expected);
    }

    #[test]
    fn mixed_grid_matches_reference() {
        let mut grid = [Rgb::OFF; SLOTS];
        grid[0] = Rgb(0, 0, 255);
        grid[1] = Rgb(40, 40, 40);
        grid[15] = Rgb(255, 100, 0);
        let expected = hex(
            "F0 78 32 45 3A 03 00 40 7F 00 00 7C 47 02 05 0A 00 00 00 00 00 00 00 00 00 00 00 00 \
             00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 \
             00 00 00 00 20 76 1F 00 00 00 00 00 00 00 40 09 F7",
        );
        assert_eq!(pad_colors_sysex(&grid), expected);
    }
}