use alloc::string::ToString;

/// Strips Radiotap, IEEE 802.11p and LLC headers from a binary message buffer
///
/// Convenience function combining [`remove_radiotap_hdr`], [`remove_80211_hdr`] and [`remove_llc_hdr`].
///
/// # Errors
/// Returns a human-readable error when parsing failed
pub fn remove_pcap_headers(data: &[u8]) -> Result<&[u8], alloc::string::String> {
    remove_radiotap_hdr(data).and_then(remove_wlan_headers)
}

/// Strips IEEE 802.11p and LLC headers from a binary message buffer
///
/// Convenience function combining [`remove_80211_hdr`] and [`remove_llc_hdr`].
///
/// IEEE 802.11 data frames always have an LLC header.
/// Since `remove_80211_hdr` only allows data frames, we usually need to remove them, too.
///
/// # Errors
/// Returns a human-readable error when parsing failed
pub fn remove_wlan_headers(data: &[u8]) -> Result<&[u8], alloc::string::String> {
    remove_80211_hdr(data).and_then(remove_llc_hdr)
}

#[allow(clippy::missing_errors_doc, reason = "no documentation present")]
fn remove_radiotap_hdr(data: &[u8]) -> Result<&[u8], alloc::string::String> {
    /*
     * Radiotap Header has the following format
     * - u_int8_t   header version (currently always zero)
     * - u_int8_t   (padding for byte alignment);
     * - u_int16_t  entire header length;
     * - u_int32_t  bitmask which subsequent data is present
     */

    let radiotap_version: u8 = data[0];
    if radiotap_version != 0 {
        return Err(alloc::format!(
            "Unknown header version {radiotap_version:#x}"
        ));
    }

    let hdr_len: usize = u16::from_le_bytes([data[2], data[3]]).into();
    let (_, remaining) = data.split_at(hdr_len);

    Ok(remaining)
}

#[allow(clippy::missing_errors_doc, reason = "no documentation present")]
fn remove_80211_hdr(data: &[u8]) -> Result<&[u8], alloc::string::String> {
    /*
     * IEEE 802.11 Header has the following format (26-32 bytes)
     * - 2 bytes frame control
     *      byte 0: .... ..00: Version 0
     *      byte 0: .... 10..: Type data frame
     *      byte 0: 1000 ....: QoS Data
     * - 2 bytes duration
     * - 6 bytes addr 1 (receiver)
     * - 6 bytes addr 2 (transmitter)
     * - 6 bytes addr 3 (BSSID)
     * - 2 bytes sequence control
     * - 0 or 6 bytes addr 4
     * - 0 or 2 bytes QOS control
     * - 0 or 4 bytes HT control
     */

    let ieee80211_framecontrol: u8 = data[0];

    let ieee80211_fc_version: u8 = ieee80211_framecontrol & 0x03; // 0000.00xx
    if ieee80211_fc_version != 0 {
        return Err(
            alloc::format!("Unknown 802.11 header version {ieee80211_fc_version}").to_string(),
        );
    }

    let ieee80211_fc_type: u8 = (ieee80211_framecontrol & 0x0c) >> 2; // 0000.xx00
    if ieee80211_fc_type != 0b10 {
        // only select data frames
        return Err(
            alloc::format!("Unsupported 802.11 frame type {ieee80211_fc_type}").to_string(),
        );
    }

    let ieee80211_fc_subtype: u8 = (ieee80211_framecontrol & 0xf0) >> 4; // xxxx.0000
    if !(ieee80211_fc_subtype == 0b1000 || ieee80211_fc_subtype == 0b0000) {
        // only select QoS or "normal" data frames
        return Err(
            alloc::format!("Unsupported 802.11 frame subtype {ieee80211_fc_subtype:#04x}")
                .to_string(),
        );
    }

    let hdr_len: usize = 26; // QoS data frame is usually 26 bytes (sequence control, no addr 4, QoS, no HT)
    let (_, remaining) = data.split_at(hdr_len);

    Ok(remaining)
}

#[allow(clippy::missing_errors_doc, reason = "no documentation present")]
fn remove_llc_hdr(data: &[u8]) -> Result<&[u8], alloc::string::String> {
    /*
     * LLC Header has the following format (8 bytes)
     * - 1 bytes DSAP
     * - 1 bytes SSAP
     * - 1 bytes control field
     * - 3 bytes organization code
     * - 2 bytes Type (0x8947 BE is GeoNetworking)
     */

    let llc_type: u16 = (u16::from(data[6]) << 8) | u16::from(data[7]);

    if llc_type != 0x8947 {
        return Err(alloc::format!("Unknown LLC payload type {llc_type:#x}").to_string());
    }

    let hdr_len: usize = 8; // TODO: Is this the right size?
    let (_, remaining) = data.split_at(hdr_len);

    Ok(remaining)
}
