//! Bounded observation of this process's local HTTP API, never external traffic.
use std::{
    collections::VecDeque,
    sync::{Arc, Mutex},
    time::{Instant, SystemTime, UNIX_EPOCH},
};

pub type Activity = Arc<Mutex<ActivityLog>>;
pub const BODY_PREVIEW: usize = 32 * 1024;
const MAX_RECORDS: usize = 80;

#[derive(Clone, Debug)]
pub struct Exchange {
    pub id: u64,
    pub method: String,
    pub path: String,
    pub origin: String,
    pub timestamp: String,
    pub request: String,
    pub response: String,
    pub status: Option<u16>,
    pub elapsed_ms: u128,
    pub request_headers: String,
    pub response_headers: String,
    started: Instant,
}

#[derive(Debug, Default)]
pub struct ActivityLog {
    pub records: VecDeque<Exchange>,
    next_id: u64,
}
impl ActivityLog {
    pub fn begin(&mut self, method: String, path: String, origin: String, headers: String) -> u64 {
        self.next_id += 1;
        let id = self.next_id;
        let seconds = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap_or_default()
            .as_secs()
            % 86400;
        self.records.push_back(Exchange {
            id,
            method,
            path: preview(&path),
            origin,
            timestamp: format!(
                "{:02}:{:02}:{:02} UTC",
                seconds / 3600,
                seconds / 60 % 60,
                seconds % 60
            ),
            request: String::new(),
            response: String::new(),
            status: None,
            elapsed_ms: 0,
            request_headers: preview(&headers),
            response_headers: String::new(),
            started: Instant::now(),
        });
        while self.records.len() > MAX_RECORDS {
            self.records.pop_front();
        }
        id
    }
    pub fn body(&mut self, id: u64, body: &str) {
        if let Some(record) = self.records.iter_mut().find(|r| r.id == id) {
            record.request = preview(body);
        }
    }
    pub fn finish(&mut self, id: u64, status: u16, body: &str, headers: String) {
        if let Some(record) = self.records.iter_mut().find(|r| r.id == id) {
            record.status = Some(status);
            record.response = preview(body);
            record.elapsed_ms = record.started.elapsed().as_millis();
            record.response_headers = preview(&headers);
        }
    }
}

pub fn preview(value: &str) -> String {
    if value.len() <= BODY_PREVIEW {
        return value.to_owned();
    }
    let mut end = BODY_PREVIEW;
    while !value.is_char_boundary(end) {
        end -= 1;
    }
    format!("{}\n[preview truncated at 32 KiB]", &value[..end])
}