//! Tests for a candidate version, before the broker installs it.
//!
//! A test is a JSON file in `source/tests/*.json`, one scenario per file:
//!
//! ```json
//! {
//!   "description": "add, then list",
//!   "steps": [
//!     {"send": {"type": "add", "text": "milk"}, "expect": {"type": "added"}},
//!     {"send": {"type": "list"}, "from": "someone", "expect": [{"type": "notes"}], "to": "someone"}
//!   ]
//! }
//! ```
//!
//! Each step sends `send` (optional, from `from` or "test"), then reads one
//! message for each entry of `expect` (an object or a list). An expected body
//! matches if it is a subset of the actual body. With `to`, each message must
//! also go to that recipient.
//!
//! Each file runs in a fresh instance on a copy of the actor's `/data` and
//! `/public` (empty folders for a new actor), without network. A version
//! without test files passes.

use std::path::Path;
use std::time::Duration;

use anyhow::{Result, anyhow, bail};
use serde_json::{Value, json};
use wasmtime::component::Component;

use crate::broker::{Broker, SHUTDOWN_DEADLINE, shutdown_line, truncate};
use crate::runtime::Instance;
use crate::world;

const EXPECT_TIMEOUT: Duration = Duration::from_secs(10);

/// `expected` matches `actual` if every key of an expected object exists in
/// the actual object with a matching value. Other values must be equal.
pub fn subset_match(expected: &Value, actual: &Value) -> bool {
    match (expected, actual) {
        (Value::Object(e), Value::Object(a)) => e.iter().all(|(k, v)| a.get(k).is_some_and(|av| subset_match(v, av))),
        (Value::Array(e), Value::Array(a)) => e.len() == a.len() && e.iter().zip(a).all(|(x, y)| subset_match(x, y)),
        _ => expected == actual,
    }
}

struct Scratch {
    dir: std::path::PathBuf,
}

impl Drop for Scratch {
    fn drop(&mut self) {
        let _ = std::fs::remove_dir_all(&self.dir);
    }
}

fn stderr_tail(path: &Path) -> String {
    let text = std::fs::read_to_string(path).unwrap_or_default();
    let start = text.len().saturating_sub(2000);
    let mut s = start;
    while !text.is_char_boundary(s) {
        s += 1;
    }
    text[s..].to_string()
}

/// The version under test, which starts from a copy of the actor's state.
struct Candidate<'a> {
    broker: &'a Broker,
    id: &'a str,
    version: u64,
    component: &'a Component,
}

/// Run every test file of `<source>/tests/`.
pub async fn test(broker: &Broker, id: &str, version: u64, component: &Component, source: Option<&Path>) -> Result<Value> {
    let candidate = Candidate { broker, id, version, component };
    let Some(source) = source else { return Ok(json!({"passed": []})) };
    let mut files: Vec<_> = std::fs::read_dir(source.join("tests"))
        .map(|rd| rd.filter_map(|e| Some(e.ok()?.path())).filter(|p| p.extension().is_some_and(|x| x == "json")).collect())
        .unwrap_or_default();
    files.sort();
    let mut passed = Vec::new();
    for file in &files {
        let name = file.file_name().unwrap().to_string_lossy().to_string();
        candidate.run_file(file).await.map_err(|e| anyhow!("test {name} failed: {e:#}"))?;
        passed.push(name);
    }
    Ok(json!({"passed": passed}))
}

impl Candidate<'_> {
    /// Start an instance on a fresh copy of the state, without network.
    fn start(&self) -> Result<(Instance, Scratch)> {
        static N: std::sync::atomic::AtomicU64 = std::sync::atomic::AtomicU64::new(0);
        let n = N.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
        let dir = self.broker.world.scratch_dir().join(format!("{}-{}-{n}", self.id, std::process::id()));
        let scratch = Scratch { dir: dir.clone() };
        let world = &self.broker.world;
        for (from, name) in [(world.data_dir(self.id), "data"), (world.public_dir(self.id), "public")] {
            std::fs::create_dir_all(dir.join(name))?;
            if from.is_dir() {
                world::copy_tree(&from, &dir.join(name))?;
            }
        }
        let cfg = self.broker.instance_config(self.id, self.version, Some(&dir));
        Ok((self.broker.runtime.start(self.component, cfg)?, scratch))
    }

    async fn run_file(&self, file: &Path) -> Result<()> {
        let test: Value = serde_json::from_str(&std::fs::read_to_string(file)?).map_err(|e| anyhow!("invalid JSON: {e}"))?;
        let steps = test["steps"].as_array().ok_or_else(|| anyhow!("missing \"steps\" list"))?;
        let (mut inst, scratch) = self.start()?;
        let stderr = scratch.dir.join("stderr.log");
        // Lines that the candidate wrote while a step was sent.
        let mut early = std::collections::VecDeque::new();
        for (n, step) in steps.iter().enumerate() {
            let n = n + 1;
            if let Some(body) = step.get("send") {
                let from = step["from"].as_str().unwrap_or("test");
                let env = json!({"id": format!("test/{n}"), "from": from, "body": body});
                inst.send_line(&env.to_string(), |line| early.push_back(line))
                    .await
                    .map_err(|e| anyhow!("step {n}: candidate does not read stdin: {e}"))?;
            }
            let expected = match step.get("expect") {
                None => vec![],
                Some(Value::Array(list)) => list.clone(),
                Some(one) => vec![one.clone()],
            };
            for expected in expected {
                let next = async { if early.is_empty() { inst.stdout.recv().await } else { early.pop_front() } };
                let line = match tokio::time::timeout(EXPECT_TIMEOUT, next).await {
                    Err(_) => bail!("step {n}: no message within {EXPECT_TIMEOUT:?}; expected {expected}"),
                    Ok(None) => {
                        let exit = inst.wait().await;
                        bail!("step {n}: candidate ended ({exit}); expected {expected}. stderr:\n{}", stderr_tail(&stderr))
                    }
                    Ok(Some(l)) => l,
                };
                let msg: Value = serde_json::from_str(&line)
                    .map_err(|_| anyhow!("step {n}: candidate wrote a non-JSON line: {}", truncate(&line, 300)))?;
                if !subset_match(&expected, &msg["body"]) {
                    bail!("step {n}: expected body {expected}, got {}", truncate(&msg["body"].to_string(), 1000));
                }
                if let Some(to) = step.get("to")
                    && msg.get("to") != Some(to)
                {
                    bail!("step {n}: expected recipient {to}, got {}", msg.get("to").unwrap_or(&Value::Null));
                }
            }
        }
        inst.stop(&shutdown_line(), SHUTDOWN_DEADLINE, |_| {}).await;
        Ok(())
    }
}