use std::sync::Once;
use std::time::Instant;

use metrics::{Unit, counter, describe_counter, describe_histogram, histogram};

pub const OUTCOME_SUCCESS: &str = "success";
pub const OUTCOME_ERROR: &str = "error";
pub const OUTCOME_ACQUIRED: &str = "acquired";
pub const OUTCOME_REJECTED: &str = "rejected";

static DESCRIBE_ONCE: Once = Once::new();

pub fn ensure_described() {
    DESCRIBE_ONCE.call_once(describe_all);
}

fn describe_all() {
    describe_counter!(
        "gitssh_sessions_total",
        "SSH client sessions partitioned by outcome (acquired, rejected) when the session semaphore is granted or full."
    );
    describe_counter!(
        "gitssh_exec_total",
        "SSH exec requests partitioned by git service and outcome (success, error)."
    );
    describe_counter!(
        "gitssh_subprocess_total",
        "Git subprocess runs partitioned by git service and status (success, error)."
    );
    describe_histogram!(
        "gitssh_subprocess_duration_seconds",
        Unit::Seconds,
        "Duration of git subprocess runs."
    );
}

pub(crate) fn outcome(ok: bool) -> &'static str {
    if ok { OUTCOME_SUCCESS } else { OUTCOME_ERROR }
}

pub(crate) fn record_session(acquired: bool) {
    ensure_described();
    counter!(
        "gitssh_sessions_total",
        "outcome" => if acquired { OUTCOME_ACQUIRED } else { OUTCOME_REJECTED }
    )
    .increment(1);
}

pub(crate) fn record_exec(service: &'static str, ok: bool) {
    ensure_described();
    counter!(
        "gitssh_exec_total",
        "service" => service,
        "outcome" => outcome(ok)
    )
    .increment(1);
}

pub(crate) fn record_subprocess(service: &'static str, ok: bool) {
    ensure_described();
    counter!(
        "gitssh_subprocess_total",
        "service" => service,
        "status" => outcome(ok)
    )
    .increment(1);
}

pub(crate) struct SubprocessTimer {
    start: Instant,
}

impl SubprocessTimer {
    pub(crate) fn start() -> Self {
        ensure_described();
        Self {
            start: Instant::now(),
        }
    }
}

impl Drop for SubprocessTimer {
    fn drop(&mut self) {
        histogram!("gitssh_subprocess_duration_seconds").record(self.start.elapsed());
    }
}