//! PC/SC access to the reader (ACR1252U PICC slot) and Type 2 tag memory.

use crate::ndef::{self, Record, RecordView};
use pcsc::{
    Attribute, Card, Context, Error as PcscError, MAX_BUFFER_SIZE, Protocols, Scope, ShareMode,
};
use serde::Serialize;

const GET_UID: [u8; 5] = [0xFF, 0xCA, 0x00, 0x00, 0x00];

/// Last inspected tag, so the status poll does not re-read the whole tag every second.
#[derive(Default)]
pub struct Cache {
    tag: Option<TagInfo>,
}

#[derive(Clone, Serialize)]
pub struct TagInfo {
    pub uid: String,
    pub kind: String,
    pub formatted: bool,
    pub capacity: Option<usize>,
    pub used: Option<usize>,
    pub writable: bool,
    pub records: Vec<RecordView>,
    /// Why the tag cannot be programmed, or a read error.
    pub note: Option<String>,
}

#[derive(Serialize)]
#[serde(tag = "state", rename_all = "snake_case")]
pub enum Status {
    NoReader { message: String },
    NoCard { reader: String },
    Card { reader: String, tag: Box<TagInfo> },
    Error { message: String },
}

#[derive(Serialize)]
pub struct Programmed {
    pub uid: String,
    pub record: RecordView,
    pub bytes: usize,
    pub capacity: usize,
}

enum Kind {
    Type2,
    Unsupported(String),
}

struct Cc {
    formatted: bool,
    capacity: usize,
    writable: bool,
}

fn open() -> Result<(String, Option<Card>), Status> {
    let no_reader = || Status::NoReader {
        message: "No NFC reader found. Is the ACR1252U plugged in?".into(),
    };
    let ctx = Context::establish(Scope::User).map_err(|e| match e {
        PcscError::NoService | PcscError::ServiceStopped | PcscError::NoReadersAvailable => {
            no_reader()
        }
        e => Status::Error {
            message: format!("PC/SC: {e}"),
        },
    })?;
    let readers = ctx.list_readers_owned().map_err(|e| match e {
        PcscError::NoReadersAvailable | PcscError::NoService | PcscError::ServiceStopped => {
            no_reader()
        }
        e => Status::Error {
            message: format!("PC/SC: {e}"),
        },
    })?;
    // The ACR1252U shows up as two readers: "... PICC 0" (contactless) and "... SAM 0".
    let reader = readers
        .iter()
        .find(|r| r.to_string_lossy().contains("PICC"))
        .or_else(|| readers.first())
        .ok_or_else(no_reader)?;
    let name = reader.to_string_lossy().into_owned();
    match ctx.connect(reader, ShareMode::Shared, Protocols::ANY) {
        Ok(card) => Ok((name, Some(card))),
        Err(
            PcscError::NoSmartcard
            | PcscError::RemovedCard
            | PcscError::UnpoweredCard
            | PcscError::UnresponsiveCard
            | PcscError::ResetCard,
        ) => Ok((name, None)),
        Err(PcscError::ReaderUnavailable | PcscError::UnknownReader) => Err(no_reader()),
        Err(e) => Err(Status::Error {
            message: format!("Connecting to the tag failed: {e}"),
        }),
    }
}

fn apdu(card: &Card, cmd: &[u8]) -> Result<Vec<u8>, String> {
    let mut buf = [0u8; MAX_BUFFER_SIZE];
    let r = card.transmit(cmd, &mut buf).map_err(|e| {
        format!("Tag communication failed ({e}). Keep the tag still on the reader.")
    })?;
    if r.len() < 2 {
        return Err("Reader returned a short response.".into());
    }
    let (data, sw) = r.split_at(r.len() - 2);
    if sw != [0x90, 0x00] {
        return Err(format!(
            "Tag rejected the command (status {:02X}{:02X}).",
            sw[0], sw[1]
        ));
    }
    Ok(data.to_vec())
}

fn hex(b: &[u8]) -> String {
    b.iter()
        .map(|x| format!("{x:02X}"))
        .collect::<Vec<_>>()
        .join(":")
}

/// Card type from the PC/SC Part 3 storage-card ATR (3B 8F 80 01 80 4F 0C A0 00 00 03 06 SS NN NN ...).
fn kind(atr: &[u8]) -> Kind {
    let storage = atr.len() >= 15
        && atr[..7] == [0x3B, 0x8F, 0x80, 0x01, 0x80, 0x4F, 0x0C]
        && atr[7..12] == [0xA0, 0x00, 0x00, 0x03, 0x06];
    if !storage {
        return Kind::Unsupported("ISO 14443-4 card (e.g. DESFire, bank card or phone)".into());
    }
    match (atr[13], atr[14]) {
        (0x00, 0x03) | (0x00, 0x3A) => Kind::Type2,
        (0x00, 0x01) => Kind::Unsupported("MIFARE Classic 1K".into()),
        (0x00, 0x02) => Kind::Unsupported("MIFARE Classic 4K".into()),
        (0x00, 0x26) => Kind::Unsupported("MIFARE Mini".into()),
        (a, b) => Kind::Unsupported(format!("storage card type {a:02X}{b:02X}")),
    }
}

fn type2_name(cc: &Cc) -> String {
    let chip = match cc.capacity {
        48 => " (MIFARE Ultralight)",
        128 => " (Ultralight EV1)",
        144 => " (NTAG213)",
        496 => " (NTAG215)",
        872 => " (NTAG216)",
        _ => "",
    };
    format!("NFC Type 2{chip}")
}

fn read_cc(card: &Card) -> Result<Cc, String> {
    let d = apdu(card, &[0xFF, 0xB0, 0x00, 0x03, 0x10])?; // pages 3..6
    let cc = d
        .get(..4)
        .ok_or("Could not read the capability container.")?;
    Ok(Cc {
        formatted: cc[0] == 0xE1,
        capacity: cc[2] as usize * 8,
        // lower nibble of byte 3 = write access (0 = granted)
        writable: cc[3] & 0x0F == 0,
    })
}

/// Read `len` bytes starting at page 4, 16 bytes (4 pages) per command.
fn read_data(card: &Card, len: usize) -> Result<Vec<u8>, String> {
    let mut out = Vec::with_capacity(len + 16);
    let mut page = 4u8;
    while out.len() < len {
        out.extend(apdu(card, &[0xFF, 0xB0, 0x00, page, 0x10])?);
        page = page.checked_add(4).ok_or("Tag memory too large.")?;
    }
    out.truncate(len);
    Ok(out)
}

fn write_page(card: &Card, page: usize, data: &[u8]) -> Result<(), String> {
    let page = u8::try_from(page).map_err(|_| "Page number out of range.")?;
    let mut cmd = vec![0xFF, 0xD6, 0x00, page, 0x04];
    cmd.extend_from_slice(data);
    apdu(card, &cmd).map(|_| ())
}

fn inspect(card: &Card, uid: String) -> TagInfo {
    let mut info = TagInfo {
        uid,
        kind: String::new(),
        formatted: false,
        capacity: None,
        used: None,
        writable: false,
        records: vec![],
        note: None,
    };
    let atr = card
        .get_attribute_owned(Attribute::AtrString)
        .unwrap_or_default();
    if let Kind::Unsupported(name) = kind(&atr) {
        info.kind = name;
        info.note =
            Some("Only NTAG21x / MIFARE Ultralight (NFC Type 2) tags can be programmed.".into());
        return info;
    }
    let result = (|| -> Result<(), String> {
        let cc = read_cc(card)?;
        info.kind = type2_name(&cc);
        info.formatted = cc.formatted;
        info.writable = cc.writable;
        if !cc.formatted {
            info.note = Some("Tag is not NDEF formatted.".into());
            return Ok(());
        }
        info.capacity = Some(cc.capacity);
        if !cc.writable {
            info.note = Some("Tag is locked (read-only).".into());
        }
        let area = read_data(card, cc.capacity)?;
        match ndef::find_message(&area)? {
            Some((msg, used)) => {
                info.used = Some(used);
                info.records = ndef::decode(msg)?;
            }
            None => info.used = Some(0),
        }
        Ok(())
    })();
    if let Err(e) = result {
        if info.kind.is_empty() {
            info.kind = "NFC Type 2".into();
        }
        info.note = Some(e);
    }
    info
}

pub fn status(cache: &mut Cache) -> Status {
    let (reader, card) = match open() {
        Ok(x) => x,
        Err(s) => {
            cache.tag = None;
            return s;
        }
    };
    let Some(card) = card else {
        cache.tag = None;
        return Status::NoCard { reader };
    };
    let uid = match apdu(&card, &GET_UID) {
        Ok(u) => hex(&u),
        Err(_) => return Status::NoCard { reader },
    };
    if let Some(tag) = cache.tag.as_ref().filter(|t| t.uid == uid) {
        return Status::Card {
            reader,
            tag: Box::new(tag.clone()),
        };
    }
    let tag = inspect(&card, uid);
    // Don't cache a failed read (tag moved away mid-read): retry on the next poll.
    let failed = tag
        .note
        .as_deref()
        .is_some_and(|n| n.contains("communication") || n.contains("rejected"));
    cache.tag = (!failed).then(|| tag.clone());
    Status::Card {
        reader,
        tag: Box::new(tag),
    }
}

fn status_message(s: Status) -> String {
    match s {
        Status::NoReader { message } | Status::Error { message } => message,
        Status::NoCard { .. } => "No tag on the reader.".into(),
        Status::Card { .. } => "Unexpected reader state.".into(),
    }
}

pub fn program(cache: &mut Cache, input: &str) -> Result<Programmed, String> {
    let input = input.trim();
    if input.is_empty() {
        return Err("Enter a URL or some text first.".into());
    }
    let record = Record::auto(input);
    let tlv = ndef::tlv(&ndef::encode(&record));

    let (_, card) = open().map_err(status_message)?;
    let card =
        card.ok_or("No tag on the reader. Place a tag on the reader and press Program again.")?;
    let uid = hex(&apdu(&card, &GET_UID)?);
    let atr = card
        .get_attribute_owned(Attribute::AtrString)
        .unwrap_or_default();
    if let Kind::Unsupported(name) = kind(&atr) {
        return Err(format!(
            "{name} is not supported. Use an NTAG21x / MIFARE Ultralight tag."
        ));
    }
    let cc = read_cc(&card)?;
    if !cc.formatted {
        return Err("Tag is not NDEF formatted (no capability container).".into());
    }
    if !cc.writable {
        return Err("Tag is locked (read-only).".into());
    }
    if tlv.len() > cc.capacity {
        return Err(format!(
            "Too long: needs {} bytes, this tag holds {}.",
            tlv.len(),
            cc.capacity
        ));
    }

    let mut data = tlv;
    data.resize(data.len().div_ceil(4) * 4, 0);
    // Empty the NDEF TLV first and write its header last, so an interrupted
    // write leaves an empty tag instead of a corrupt message.
    write_page(&card, 4, &[0x03, 0x00, 0xFE, 0x00])?;
    for (i, chunk) in data.chunks(4).enumerate().skip(1) {
        write_page(&card, 4 + i, chunk)?;
    }
    write_page(&card, 4, &data[..4])?;

    let back = read_data(&card, data.len())?;
    if back != data {
        return Err("Verification failed: the tag content does not match what was written.".into());
    }
    cache.tag = None; // re-read on the next status poll
    Ok(Programmed {
        uid,
        record: record.view(),
        bytes: data.len(),
        capacity: cc.capacity,
    })
}