use std::fs::{File, OpenOptions};
use std::io::Write;
use std::path::PathBuf;
use std::sync::{Mutex, OnceLock};
use std::time::{SystemTime, UNIX_EPOCH};

static TRACE_FILE: OnceLock<Option<Mutex<File>>> = OnceLock::new();
static TRACE_BYTES: OnceLock<bool> = OnceLock::new();

pub fn enabled() -> bool {
    TRACE_FILE.get_or_init(open_trace_file).is_some()
}

pub fn bytes_enabled() -> bool {
    *TRACE_BYTES.get_or_init(|| truthy_env("DOSH_TRACE_BYTES"))
}

pub fn event(name: &str, fields: &[(&str, String)]) {
    let Some(file) = TRACE_FILE.get_or_init(open_trace_file) else {
        return;
    };
    let now = SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .map(|duration| duration.as_millis())
        .unwrap_or(0);
    let mut line = format!(
        "ts_ms={} pid={} event={}",
        now,
        std::process::id(),
        shell_escape(name)
    );
    for (key, value) in fields {
        line.push(' ');
        line.push_str(key);
        line.push('=');
        line.push_str(&shell_escape(value));
    }
    line.push('\n');
    if let Ok(mut file) = file.lock() {
        let _ = file.write_all(line.as_bytes());
        let _ = file.flush();
    }
}

pub fn bytes_summary(bytes: &[u8]) -> String {
    let mut parts = vec![
        format!("len={}", bytes.len()),
        format!(
            "esc={}",
            contains_byte(bytes, 0x1b) || contains_byte(bytes, 0x9b)
        ),
        format!("focus={}", has_focus_report(bytes)),
        format!("mouseish={}", looks_mouseish(bytes)),
        format!("printable={}", printable_count(bytes)),
    ];
    if bytes_enabled() {
        parts.push(format!("hex={}", hex_prefix(bytes, 160)));
    }
    parts.join(",")
}

fn open_trace_file() -> Option<Mutex<File>> {
    let raw = std::env::var_os("DOSH_TRACE")?;
    let normalized = raw.to_string_lossy().to_ascii_lowercase();
    if normalized.is_empty() || matches!(normalized.as_str(), "0" | "false" | "off") {
        return None;
    }
    let path = if matches!(normalized.as_str(), "1" | "true" | "on") {
        default_trace_path()
    } else {
        PathBuf::from(raw)
    };
    if let Some(parent) = path.parent() {
        let _ = std::fs::create_dir_all(parent);
    }
    OpenOptions::new()
        .create(true)
        .append(true)
        .open(&path)
        .ok()
        .map(Mutex::new)
}

fn default_trace_path() -> PathBuf {
    let root = dirs::cache_dir()
        .unwrap_or_else(std::env::temp_dir)
        .join("dosh")
        .join("trace");
    let exe = std::env::current_exe()
        .ok()
        .and_then(|path| {
            path.file_stem()
                .map(|stem| stem.to_string_lossy().to_string())
        })
        .unwrap_or_else(|| "dosh".to_string());
    root.join(format!("{}-{}.log", exe, std::process::id()))
}

fn truthy_env(name: &str) -> bool {
    std::env::var_os(name).is_some_and(|value| {
        let normalized = value.to_string_lossy().to_ascii_lowercase();
        !normalized.is_empty() && !matches!(normalized.as_str(), "0" | "false" | "off")
    })
}

fn shell_escape(value: &str) -> String {
    if value.bytes().all(|byte| {
        byte.is_ascii_alphanumeric()
            || matches!(byte, b'.' | b'-' | b'_' | b':' | b'/' | b',' | b'=')
    }) {
        return value.to_string();
    }
    let mut out = String::from("'");
    for ch in value.chars() {
        if ch == '\'' {
            out.push_str("'\\''");
        } else {
            out.push(ch);
        }
    }
    out.push('\'');
    out
}

fn contains_byte(bytes: &[u8], needle: u8) -> bool {
    bytes.contains(&needle)
}

fn has_focus_report(bytes: &[u8]) -> bool {
    bytes
        .windows(3)
        .any(|window| matches!(window, b"\x1b[I" | b"\x1b[O"))
        || bytes
            .windows(2)
            .any(|window| matches!(window, b"\x9bI" | b"\x9bO"))
}

fn looks_mouseish(bytes: &[u8]) -> bool {
    bytes.windows(3).any(|window| window == b"\x1b[<")
        || bytes.windows(2).any(|window| window == b"\x9b<")
        || bytes.iter().filter(|byte| **byte == b';').take(3).count() >= 2
}

fn printable_count(bytes: &[u8]) -> usize {
    bytes
        .iter()
        .filter(|byte| byte.is_ascii_graphic() || **byte == b' ')
        .count()
}

fn hex_prefix(bytes: &[u8], max: usize) -> String {
    let mut out = String::with_capacity(bytes.len().min(max) * 2);
    for byte in bytes.iter().take(max) {
        use std::fmt::Write as _;
        let _ = write!(&mut out, "{byte:02x}");
    }
    if bytes.len() > max {
        out.push_str("...");
    }
    out
}