//! Drive `claude /usage` via a pseudo-TTY and parse the rendered output
//! into structured percentages.
//!
//! This is the only way to get the *real* subscription-side numbers (the
//! same ones the user sees when typing `/usage` interactively). Anthropic
//! doesn't expose `/usage` via `claude --print`, and the percentages aren't
//! cached anywhere on disk between invocations.
//!
//! Output we parse (whitespace-collapsed, ANSI stripped):
//!
//!   Current session
//!   ████████████▌                       67% used
//!   Resets 2:50am (Europe/London)
//!
//!   Current week (all models)
//!   ████                                 8% used
//!   Resets May 9, 12pm (Europe/London)
//!
//!   Current week (Sonnet only)
//!   ██▌                                  5% used
//!   Resets May 9, 12pm (Europe/London)
//!
//! The "Sonnet only" section is not always present (depends on plan tier
//! and recent usage). We treat it as optional.

use anyhow::{Context, Result};
use chrono::{DateTime, Utc};
use portable_pty::{native_pty_system, CommandBuilder, PtySize};
use serde::Serialize;
use std::io::{Read, Write};
use std::time::{Duration, Instant};

#[derive(Debug, Clone, Serialize)]
pub struct UsageBar {
    /// e.g. "Current session", "Current week (all models)"
    pub label: String,
    /// 0..=100
    pub percent: u8,
    /// Free text describing reset, e.g. "2:50am (Europe/London)" or
    /// "May 9, 12pm (Europe/London)". Anthropic's renderer is the source
    /// of truth here; we don't try to re-format.
    pub resets_at_text: String,
}

#[derive(Debug, Clone, Serialize)]
pub struct CliUsage {
    pub session: Option<UsageBar>,
    pub week_all: Option<UsageBar>,
    pub week_sonnet: Option<UsageBar>,
    pub fetched_at: DateTime<Utc>,
    /// True if at least one bar parsed. False on parse failure / timeout
    /// (UI can fall back to JSONL-derived numbers).
    pub ok: bool,
    /// Raw stripped text, kept for diagnostics in Settings.
    pub raw_text: String,
}

/// Spawn `claude`, send `/usage`, capture output, kill, parse.
///
/// `command_override` lets the caller supply an alternate program (e.g.
/// `wsl.exe` with args) for the Windows-host case. None means just `claude`.
pub fn fetch_blocking(command_override: Option<&str>) -> Result<CliUsage> {
    let raw = drive_claude_usage(command_override, Duration::from_secs(20))?;
    let stripped = strip_ansi_collapse(&raw);
    parse_usage_text(&stripped, raw)
}

/// Pick a sensible default command line for invoking `claude`.
///
/// Order:
///   1. Native `claude` (Windows: `claude.exe` on PATH; Unix: `claude`).
///   2. On Windows: enumerate WSL distros via `wsl.exe -l -q` and probe
///      each by running `bash -lc 'command -v claude'`. First hit wins.
///   3. Fallback: bare `claude` (will fail, but at least with a clear error).
///
/// This is called fresh on every `/usage` fetch, but each probe is cheap
/// (<200ms typical) and only runs when no override is set.
fn default_command() -> CommandBuilder {
    if let Some(parts) = autodetect_command() {
        let mut c = CommandBuilder::new(&parts[0]);
        for a in &parts[1..] {
            c.arg(a);
        }
        return c;
    }
    CommandBuilder::new("claude")
}

/// Returns the auto-detected argv (program + args) for invoking claude, or
/// None if nothing reachable was found.
pub fn autodetect_command() -> Option<Vec<String>> {
    // 1. Native claude.
    if which_exists("claude") {
        return Some(vec!["claude".to_string()]);
    }

    // 2. WSL distros (Windows only).
    if cfg!(windows) && which_exists("wsl.exe") {
        for distro in list_wsl_distros() {
            if probe_claude_in_wsl(&distro) {
                return Some(vec![
                    "wsl.exe".to_string(),
                    "-d".to_string(),
                    distro,
                    "bash".to_string(),
                    "-lc".to_string(),
                    "claude".to_string(),
                ]);
            }
        }
    }

    None
}

fn which_exists(name: &str) -> bool {
    let probe = if cfg!(windows) { "where" } else { "which" };
    crate::paths::quiet_command(probe)
        .arg(name)
        .output()
        .map(|o| o.status.success() && !o.stdout.is_empty())
        .unwrap_or(false)
}

fn list_wsl_distros() -> Vec<String> {
    let Ok(out) = crate::paths::quiet_command("wsl.exe").args(["-l", "-q"]).output() else {
        return Vec::new();
    };
    if !out.status.success() {
        return Vec::new();
    }
    // wsl.exe outputs UTF-16LE.
    let raw_u16: Vec<u16> = out
        .stdout
        .chunks_exact(2)
        .map(|b| u16::from_le_bytes([b[0], b[1]]))
        .collect();
    String::from_utf16_lossy(&raw_u16)
        .lines()
        .map(|l| l.trim_matches(|c: char| c == '\u{FEFF}' || c.is_whitespace()).to_string())
        .filter(|l| !l.is_empty())
        .collect()
}

fn probe_claude_in_wsl(distro: &str) -> bool {
    crate::paths::quiet_command("wsl.exe")
        .args(["-d", distro, "bash", "-lc", "command -v claude"])
        .output()
        .map(|o| o.status.success() && !o.stdout.is_empty())
        .unwrap_or(false)
}

/// Spawn the CLI in a PTY, send `/usage`, capture stdout for `total_timeout`,
/// then send `/exit` and return raw bytes (still containing ANSI escapes).
fn drive_claude_usage(command_override: Option<&str>, total_timeout: Duration) -> Result<Vec<u8>> {
    let pty_system = native_pty_system();
    let pair = pty_system
        .openpty(PtySize {
            rows: 50,
            cols: 200, // wide so /usage doesn't wrap awkwardly
            pixel_width: 0,
            pixel_height: 0,
        })
        .context("openpty")?;

    let mut cmd = match command_override {
        Some(s) if !s.trim().is_empty() => {
            // Allow simple "wsl.exe -d Ubuntu bash -lc claude" style strings.
            let parts: Vec<&str> = s.split_whitespace().collect();
            let mut c = CommandBuilder::new(parts[0]);
            for arg in &parts[1..] {
                c.arg(arg);
            }
            c
        }
        _ => default_command(),
    };
    // claude inspects $TERM; give it something reasonable.
    cmd.env("TERM", "xterm-256color");

    let mut child = pair.slave.spawn_command(cmd).context("spawn claude")?;
    drop(pair.slave); // close our copy of the slave

    let mut writer = pair.master.take_writer().context("take_writer")?;
    let mut reader = pair.master.try_clone_reader().context("clone_reader")?;

    // Read in a background thread; communicate via a channel.
    let (tx, rx) = std::sync::mpsc::channel::<Vec<u8>>();
    let reader_handle = std::thread::spawn(move || {
        let mut buf = [0u8; 8192];
        loop {
            match reader.read(&mut buf) {
                Ok(0) | Err(_) => break,
                Ok(n) => {
                    if tx.send(buf[..n].to_vec()).is_err() {
                        break;
                    }
                }
            }
        }
    });

    let mut output: Vec<u8> = Vec::with_capacity(64 * 1024);

    // 1. Wait ~3.5s for the TUI to initialize (welcome banner, prompt, etc).
    drain(&rx, &mut output, Duration::from_millis(3500));

    // 2. Send /usage.
    writer.write_all(b"/usage\r").context("write /usage")?;
    writer.flush().ok();

    // 3. Drain output until quiet period or total deadline.
    let deadline = Instant::now() + total_timeout;
    let mut last_growth = Instant::now();
    let prev_len = output.len();
    let _ = prev_len;
    loop {
        let pre = output.len();
        drain(&rx, &mut output, Duration::from_millis(700));
        if output.len() > pre {
            last_growth = Instant::now();
        }
        // Quiet for >1.2s → assume render finished.
        if last_growth.elapsed() > Duration::from_millis(1200) {
            break;
        }
        if Instant::now() > deadline {
            break;
        }
    }

    // 4. Best-effort exit. If it doesn't shut down, we'll kill the child.
    let _ = writer.write_all(b"/exit\r");
    let _ = writer.flush();
    drain(&rx, &mut output, Duration::from_millis(500));

    drop(writer);
    let _ = child.kill();
    let _ = child.wait();
    drop(pair.master);
    let _ = reader_handle.join();

    Ok(output)
}

fn drain(
    rx: &std::sync::mpsc::Receiver<Vec<u8>>,
    out: &mut Vec<u8>,
    timeout: Duration,
) {
    let deadline = Instant::now() + timeout;
    while let Some(remaining) = deadline.checked_duration_since(Instant::now()) {
        match rx.recv_timeout(remaining) {
            Ok(chunk) => out.extend_from_slice(&chunk),
            Err(_) => break,
        }
    }
}

/// Strip CSI / OSC / DCS escape sequences and collapse runs of identical
/// re-rendered lines (TUIs paint the same content many times during scan).
pub fn strip_ansi_collapse(raw: &[u8]) -> String {
    // CSI: ESC [ ... <terminator>
    // OSC: ESC ] ... BEL
    // DCS / SOS / PM / APC: ESC P / X / ^ / _ ... ESC \
    static CSI_RE: once_cell::sync::Lazy<regex::bytes::Regex> =
        once_cell::sync::Lazy::new(|| {
            regex::bytes::Regex::new(
                r"\x1b\[[0-9;?]*[ -/]*[@-~]|\x1b\][^\x07]*\x07|\x1b[PX^_].*?\x1b\\",
            )
            .unwrap()
        });
    let cleaned = CSI_RE.replace_all(raw, &b""[..]);
    // Drop stray BEL / lone ESC.
    let cleaned: Vec<u8> = cleaned
        .iter()
        .copied()
        .filter(|&b| b != 0x07 && b != 0x1b)
        .collect();
    let text = String::from_utf8_lossy(&cleaned).to_string();

    // Collapse repeated lines (TUI redraws same line hundreds of times).
    let mut out: Vec<&str> = Vec::new();
    for line in text.lines() {
        let trimmed = line.trim_end();
        if out.last().map(|p| *p == trimmed).unwrap_or(false) {
            continue;
        }
        out.push(trimmed);
    }
    // Keep blank lines for parser hints, but collapse runs of >1 blank.
    let mut compressed: Vec<&str> = Vec::with_capacity(out.len());
    let mut prev_blank = false;
    for line in out {
        let blank = line.is_empty();
        if blank && prev_blank {
            continue;
        }
        compressed.push(line);
        prev_blank = blank;
    }
    compressed.join("\n")
}

/// Parse the cleaned text into a [`CliUsage`].
///
/// Strategy: scan for the headings ("Current session", "Current week (all models)",
/// "Current week (Sonnet only)") then look for `NN% used` and `Resets …` on the
/// next few lines after each heading.
pub fn parse_usage_text(stripped: &str, raw_for_diag: Vec<u8>) -> Result<CliUsage> {
    let lines: Vec<&str> = stripped.lines().collect();

    let find_section = |label: &str| -> Option<UsageBar> {
        let idx = lines.iter().position(|l| {
            let t = l.trim();
            // Some renderings squash spaces ("Currentsession"). Match both.
            t == label || t.replace(' ', "") == label.replace(' ', "")
        })?;
        // Look at the next 6 lines for "X% used" and "Resets ...".
        let mut percent: Option<u8> = None;
        let mut resets: Option<String> = None;
        for line in &lines[idx + 1..(idx + 7).min(lines.len())] {
            if percent.is_none() {
                if let Some(cap) = PCT_RE.captures(line) {
                    if let Ok(n) = cap[1].parse::<u8>() {
                        percent = Some(n);
                    }
                }
            }
            if resets.is_none() {
                if let Some(cap) = RESET_RE.captures(line) {
                    resets = Some(cap[1].trim().to_string());
                }
            }
            if percent.is_some() && resets.is_some() {
                break;
            }
        }
        Some(UsageBar {
            label: label.to_string(),
            percent: percent?,
            resets_at_text: resets.unwrap_or_default(),
        })
    };

    let session = find_section("Current session");
    let week_all = find_section("Current week (all models)");
    let week_sonnet = find_section("Current week (Sonnet only)");

    let ok = session.is_some() || week_all.is_some();
    let _ = raw_for_diag; // accepted for API compat; we surface the cleaned form

    Ok(CliUsage {
        session,
        week_all,
        week_sonnet,
        fetched_at: Utc::now(),
        ok,
        raw_text: stripped.to_string(),
    })
}

static PCT_RE: once_cell::sync::Lazy<regex::Regex> =
    once_cell::sync::Lazy::new(|| regex::Regex::new(r"(\d{1,3})\s*%\s*used").unwrap());

static RESET_RE: once_cell::sync::Lazy<regex::Regex> =
    once_cell::sync::Lazy::new(|| regex::Regex::new(r"Resets?\s+(.+)$").unwrap());

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

    const SAMPLE: &str = r"Settings  Status   Config   Usage   Stats

Session

Total cost:            $0.0000
Total duration (API):  0s
Total duration (wall): 4s

Current session
█████████████████████████████████▌                 67% used
Resets 2:50am (Europe/London)

Current week (all models)
████                                               8% used
Resets May 9, 12pm (Europe/London)

Current week (Sonnet only)
██▌                                                5% used
Resets May 9, 12pm (Europe/London)

What's contributing to your limits usage?
";

    #[test]
    fn parses_three_bars() {
        let u = parse_usage_text(SAMPLE, Vec::new()).unwrap();
        assert!(u.ok);
        let s = u.session.expect("session");
        assert_eq!(s.percent, 67);
        assert!(s.resets_at_text.contains("2:50am"));
        let w = u.week_all.expect("week_all");
        assert_eq!(w.percent, 8);
        assert!(w.resets_at_text.contains("May 9"));
        let so = u.week_sonnet.expect("week_sonnet");
        assert_eq!(so.percent, 5);
    }

    #[test]
    fn parser_tolerates_missing_sonnet_section() {
        let s = SAMPLE
            .split("Current week (Sonnet only)")
            .next()
            .unwrap();
        let u = parse_usage_text(s, Vec::new()).unwrap();
        assert!(u.session.is_some());
        assert!(u.week_all.is_some());
        assert!(u.week_sonnet.is_none());
    }
}