/// Step 6: Local IMAP server.
///
/// Implements the nine commands skim uses (LOGIN, NOOP, SELECT, FETCH ×2,
/// SEARCH, STORE, EXPUNGE, LOGOUT) on a plain-TCP listener on localhost.
/// Each accepted connection is handled in its own tokio task.
use std::sync::Arc;

use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader};
use tokio::net::{TcpListener, TcpStream};

use crate::api::{ApiClient, LABEL_INBOX};
use crate::{crypto, SharedState};

// ── Public entry point ────────────────────────────────────────────────────────

pub async fn run(state: SharedState, port: u16) -> Result<(), Box<dyn std::error::Error>> {
    let listener = TcpListener::bind(format!("0.0.0.0:{port}")).await?;
    println!("IMAP listening on port {port}");
    run_with_listener(state, listener).await
}

/// Accept connections on an already-bound listener. Used by the embedded bridge
/// so ports are guaranteed to be occupied before `start()` returns.
pub async fn run_with_listener(
    state: SharedState,
    listener: TcpListener,
) -> Result<(), Box<dyn std::error::Error>> {
    loop {
        let (socket, _addr) = listener.accept().await?;
        let state = Arc::clone(&state);
        tokio::spawn(async move {
            if let Err(e) = handle_connection(socket, state).await {
                eprintln!("IMAP connection error: {e}");
            }
        });
    }
}

// ── Per-connection handler ────────────────────────────────────────────────────

async fn handle_connection(
    socket: TcpStream,
    state: SharedState,
) -> Result<(), Box<dyn std::error::Error>> {
    let (reader, mut writer) = socket.into_split();
    let mut lines = BufReader::new(reader).lines();
    let mut authenticated = false;

    writer
        .write_all(b"* OK IMAP4rev1 ProtonBridge ready\r\n")
        .await?;

    while let Some(raw) = lines.next_line().await? {
        let line = raw.trim_end();
        if line.is_empty() {
            continue;
        }

        // Every IMAP command is "TAG COMMAND [rest…]"
        let mut parts = line.splitn(3, ' ');
        let tag = parts.next().unwrap_or("*").to_string();
        let cmd = parts.next().unwrap_or("").to_ascii_uppercase();
        let rest = parts.next().unwrap_or("").trim().to_string();

        let logout = cmd == "LOGOUT";
        let response =
            dispatch(&tag, &cmd, &rest, &state, &mut authenticated).await;

        // for log_line in response.lines() {
        //     eprintln!("IMAP > {log_line}");
        // }
        writer.write_all(response.as_bytes()).await?;
        if logout {
            break;
        }
    }
    Ok(())
}

// ── Command dispatcher ────────────────────────────────────────────────────────

async fn dispatch(
    tag: &str,
    cmd: &str,
    rest: &str,
    state: &SharedState,
    authenticated: &mut bool,
) -> String {
    match cmd {
        "CAPABILITY" => {
            format!(
                "* CAPABILITY IMAP4rev1 AUTH=PLAIN\r\n\
                 {tag} OK CAPABILITY completed\r\n"
            )
        }
        "LOGIN" => {
            let mut p = rest.splitn(2, ' ');
            let _user = unquote(p.next().unwrap_or(""));
            let pass = unquote(p.next().unwrap_or(""));
            let local_pw = state.lock().await.config.bridge.local_password.clone();
            if pass == local_pw {
                *authenticated = true;
                format!("{tag} OK LOGIN completed\r\n")
            } else {
                format!("{tag} NO [AUTHENTICATIONFAILED] Invalid credentials\r\n")
            }
        }
        "NOOP" => format!("{tag} OK NOOP completed\r\n"),
        "LOGOUT" => format!("* BYE Logging out\r\n{tag} OK LOGOUT completed\r\n"),

        // All remaining commands require authentication.
        _ if !*authenticated => {
            format!("{tag} NO Not authenticated\r\n")
        }

        "SELECT" => cmd_select(tag, state).await,
        "EXAMINE" => cmd_select(tag, state).await, // read-only alias
        "FETCH" => cmd_fetch(tag, rest, state).await,
        "SEARCH" => cmd_search(tag, rest, state).await,
        "STORE" => cmd_store(tag, rest, state).await,
        "EXPUNGE" => cmd_expunge(tag, state).await,

        _ => format!("{tag} BAD Unknown or unimplemented command\r\n"),
    }
}

// ── SELECT ────────────────────────────────────────────────────────────────────

async fn cmd_select(tag: &str, state: &SharedState) -> String {
    let (http_client, session) = {
        let st = state.lock().await;
        (st.http_client.clone(), st.session.clone())
    };
    let api = ApiClient::new(&http_client, &session);
    let messages = match api.list_messages(LABEL_INBOX, 0, 50).await {
        Ok((msgs, _)) => msgs,
        Err(e) => {
            eprintln!("SELECT list_messages failed: {e}");
            return format!("{tag} NO SELECT failed\r\n");
        }
    };
    let count = {
        let mut st = state.lock().await;
        st.store.load_all(messages);
        st.store.count()
    };
    format!(
        "* {count} EXISTS\r\n\
         * 0 RECENT\r\n\
         * FLAGS (\\Answered \\Flagged \\Deleted \\Seen \\Draft)\r\n\
         * OK [PERMANENTFLAGS (\\Deleted \\Seen \\*)] Limited\r\n\
         * OK [UIDVALIDITY 1] UIDs valid\r\n\
         * OK [UIDNEXT {next}] Predicted next UID\r\n\
         {tag} OK [READ-WRITE] SELECT completed\r\n",
        next = count + 1,
    )
}

// ── FETCH ─────────────────────────────────────────────────────────────────────

async fn cmd_fetch(tag: &str, rest: &str, state: &SharedState) -> String {
    // rest = "seq_set ITEMS" or "seq_set (ITEMS)"
    let mut parts = rest.splitn(2, ' ');
    let seq_set = parts.next().unwrap_or("").to_string();
    let items = parts
        .next()
        .unwrap_or("")
        .trim()
        .trim_matches(|c| c == '(' || c == ')')
        .to_ascii_uppercase();

    if items.contains("HEADER.FIELDS") {
        fetch_headers(tag, &seq_set, state).await
    } else {
        fetch_body(tag, &seq_set, state).await
    }
}

async fn fetch_headers(tag: &str, seq_set: &str, state: &SharedState) -> String {
    // Collect all metadata under a single short lock — no I/O while locked.
    let rows: Vec<(u32, String, String, String, i64)> = {
        let st = state.lock().await;
        let count = st.store.count();
        parse_seq_set(seq_set, count)
            .into_iter()
            .filter_map(|seq| {
                st.store.get_meta(seq).map(|m| {
                    (
                        seq,
                        m.subject.clone(),
                        m.sender.name.clone(),
                        m.sender.address.clone(),
                        m.time,
                    )
                })
            })
            .collect()
    };

    let mut out = Vec::new();
    for (seq, subject, name, addr, time) in &rows {
        let block = format!(
            "Subject: {subject}\r\nFrom: {name} <{addr}>\r\nDate: {date}\r\n\r\n",
            date = rfc2822(*time),
        );
        let n = block.as_bytes().len();
        out.extend_from_slice(
            format!(
                "* {seq} FETCH (BODY[HEADER.FIELDS (SUBJECT FROM DATE)] {{{n}}}\r\n"
            )
            .as_bytes(),
        );
        out.extend_from_slice(block.as_bytes());
        out.extend_from_slice(b")\r\n");
    }
    out.extend_from_slice(format!("{tag} OK FETCH completed\r\n").as_bytes());
    String::from_utf8_lossy(&out).into_owned()
}

async fn fetch_body(tag: &str, seq_set: &str, state: &SharedState) -> String {
    let count = state.lock().await.store.count();
    let seqs = parse_seq_set(seq_set, count);
    let seq = match seqs.first() {
        Some(&s) => s,
        None => return format!("{tag} NO invalid sequence\r\n"),
    };

    // Grab proton_id + connection details under a brief lock.
    let (proton_id, meta_snapshot, http_client, session) = {
        let st = state.lock().await;
        let m = match st.store.get_meta(seq) {
            Some(m) => (
                m.subject.clone(),
                m.sender.name.clone(),
                m.sender.address.clone(),
                m.time,
            ),
            None => return format!("{tag} NO no such message\r\n"),
        };
        let id = st.store.proton_id(seq).unwrap_or("").to_string();
        (id, m, st.http_client.clone(), st.session.clone())
    };

    // API call — lock is released.
    let api = ApiClient::new(&http_client, &session);
    let full_msg = match api.get_message(&proton_id).await {
        Ok(m) => m,
        Err(e) => {
            eprintln!("FETCH get_message failed: {e}");
            return format!("{tag} NO fetch failed\r\n");
        }
    };

    // Decrypt — re-acquire lock only for the synchronous crypto step.
    let plaintext = {
        let st = state.lock().await;
        let keys: Vec<&crypto::PrivateKey> = st.key_pool.iter().collect();
        match crypto::decrypt_body(&full_msg.body, &keys) {
            Ok(p) => p,
            Err(e) => {
                eprintln!("FETCH decrypt_body failed: {e}");
                return format!("{tag} NO decrypt failed\r\n");
            }
        }
    };

    let (subject, sender_name, sender_addr, time) = meta_snapshot;
    let message = format!(
        "From: {sender_name} <{sender_addr}>\r\n\
         Subject: {subject}\r\n\
         Date: {date}\r\n\
         Content-Type: {mime}; charset=utf-8\r\n\
         MIME-Version: 1.0\r\n\
         \r\n\
         {plaintext}",
        date = rfc2822(time),
        mime = full_msg.mime_type,
    );
    let n = message.as_bytes().len();
    let mut out = Vec::new();
    out.extend_from_slice(
        format!("* {seq} FETCH (BODY[] {{{n}}}\r\n").as_bytes(),
    );
    out.extend_from_slice(message.as_bytes());
    out.extend_from_slice(b")\r\n");
    out.extend_from_slice(format!("{tag} OK FETCH completed\r\n").as_bytes());
    String::from_utf8_lossy(&out).into_owned()
}

// ── SEARCH ────────────────────────────────────────────────────────────────────

async fn cmd_search(tag: &str, criteria: &str, state: &SharedState) -> String {
    // skim sends: OR SUBJECT "query" FROM "query"
    let query = extract_quoted(criteria).unwrap_or("");
    let seqs = state
        .lock()
        .await
        .store
        .search_subject_or_from(query);
    let nums: Vec<String> = seqs.iter().map(|n| n.to_string()).collect();
    format!(
        "* SEARCH {}\r\n{tag} OK SEARCH completed\r\n",
        nums.join(" ")
    )
}

// ── STORE ─────────────────────────────────────────────────────────────────────

async fn cmd_store(tag: &str, rest: &str, state: &SharedState) -> String {
    // rest = "seq_set +FLAGS (\Deleted)" (or similar)
    let mut parts = rest.splitn(2, ' ');
    let seq_set = parts.next().unwrap_or("").to_string();
    let flags = parts.next().unwrap_or("").to_ascii_uppercase();

    if !flags.contains("DELETED") {
        return format!("{tag} OK STORE completed\r\n");
    }

    let mut st = state.lock().await;
    let count = st.store.count();
    let seqs = parse_seq_set(&seq_set, count);
    let mut out = String::new();
    for seq in seqs {
        st.store.mark_deleted(seq);
        out.push_str(&format!("* {seq} FETCH (FLAGS (\\Deleted))\r\n"));
    }
    out.push_str(&format!("{tag} OK STORE completed\r\n"));
    out
}

// ── EXPUNGE ───────────────────────────────────────────────────────────────────

async fn cmd_expunge(tag: &str, state: &SharedState) -> String {
    let (proton_ids, removed_seqs, http_client, session) = {
        let mut st = state.lock().await;
        let (ids, seqs) = st.store.expunge();
        (ids, seqs, st.http_client.clone(), st.session.clone())
    };

    if !proton_ids.is_empty() {
        let api = ApiClient::new(&http_client, &session);
        if let Err(e) = api.delete_messages(&proton_ids).await {
            eprintln!("EXPUNGE delete_messages failed: {e}");
        }
    }

    let mut out = String::new();
    for seq in &removed_seqs {
        out.push_str(&format!("* {seq} EXPUNGE\r\n"));
    }
    out.push_str(&format!("{tag} OK EXPUNGE completed\r\n"));
    out
}

// ── Helpers ───────────────────────────────────────────────────────────────────

fn unquote(s: &str) -> &str {
    s.strip_prefix('"')
        .and_then(|s| s.strip_suffix('"'))
        .unwrap_or(s)
}

/// Extract the first double-quoted string from `s`.
fn extract_quoted(s: &str) -> Option<&str> {
    let start = s.find('"')? + 1;
    let end = s[start..].find('"')? + start;
    Some(&s[start..end])
}

/// Parse an IMAP sequence set (e.g. "1:50", "3,5,7", "42", "*") into a Vec of
/// seq numbers, clamped to [1, max].
fn parse_seq_set(set: &str, max: u32) -> Vec<u32> {
    if max == 0 {
        return vec![];
    }
    let mut result = Vec::new();
    for part in set.split(',') {
        let part = part.trim();
        if let Some((a, b)) = part.split_once(':') {
            let start: u32 = if a == "*" { max } else { a.parse().unwrap_or(1) };
            let end: u32 = if b == "*" { max } else { b.parse().unwrap_or(max) };
            let (lo, hi) = (start.min(end), start.max(end));
            for seq in lo..=hi.min(max) {
                result.push(seq);
            }
        } else if part == "*" {
            result.push(max);
        } else {
            let seq: u32 = part.parse().unwrap_or(0);
            if seq >= 1 && seq <= max {
                result.push(seq);
            }
        }
    }
    result
}

/// Format a Unix timestamp as an RFC 2822 date string.
fn rfc2822(unix: i64) -> String {
    use chrono::{DateTime, Utc};
    DateTime::<Utc>::from_timestamp(unix, 0)
        .unwrap_or_default()
        .format("%a, %d %b %Y %H:%M:%S +0000")
        .to_string()
}