//! Per-query eval runner. See [`run_eval`] / [`run_eval_with_config`].

use std::fs::File;
use std::io::{BufWriter, Write};
use std::path::PathBuf;
use std::time::Instant;

use anyhow::{Context, Result};
use kebab_app::App;
use kebab_config::expand_path;
use kebab_core::{SearchFilters, SearchQuery};
use kebab_store_sqlite::{EvalRunRow, SqliteStore};
use time::OffsetDateTime;

use crate::loader::{load_golden_set, validate_against_db};
use crate::metrics::{DEFAULT_GOLDEN_PATH, KEBAB_EVAL_GOLDEN};
use crate::types::{EvalRun, EvalRunOpts, GoldenQuery, QueryResult};

/// Convert a wall-clock duration since `start` into milliseconds clamped
/// to `u32::MAX`. The `QueryResult.elapsed_ms` and `eval_runs.duration_ms`
/// fields are `u32`; saturate (rather than wrap) so a stuck run never
/// reports a misleading sub-second duration.
fn elapsed_ms_u32(start: Instant) -> u32 {
    start.elapsed().as_millis().min(u128::from(u32::MAX)) as u32
}

/// Run the golden suite end-to-end against the active XDG-loaded
/// [`kebab_config::Config`]. Wraps [`run_eval_with_config`] with
/// `Config::load(None)`.
pub fn run_eval(opts: &EvalRunOpts) -> Result<EvalRun> {
    let cfg = kebab_config::Config::load(None).context("load Config for run_eval")?;
    run_eval_with_config(&cfg, opts)
}

/// Run the golden suite end-to-end against an explicit
/// [`kebab_config::Config`]. Used by integration tests (TempDir-backed
/// data_dir) and any future caller that wants to drive the runner
/// against a non-default config.
pub fn run_eval_with_config(cfg: &kebab_config::Config, opts: &EvalRunOpts) -> Result<EvalRun> {
    let started = Instant::now();

    // ── 1. Load golden set ────────────────────────────────────────────────
    //
    // `with_context` already names the path on error, so a separate
    // `tracing::debug!` here would just be noise.
    let golden_path = resolve_golden_path();
    let queries = load_golden_set(&golden_path).with_context(|| {
        format!(
            "load golden set from {} (override via KEBAB_EVAL_GOLDEN)",
            golden_path.display()
        )
    })?;
    validate_against_db(&queries, cfg)?;

    // ── 2. Mint identifiers + open store ──────────────────────────────────
    let run_id = mint_run_id();
    let created_at = OffsetDateTime::now_utc();
    let commit_hash = std::env::var("KEBAB_COMMIT_HASH")
        .ok()
        .filter(|s| !s.is_empty());

    // Open the store once so every per-query write reuses the same
    // connection-mutex lifetime.
    let store = SqliteStore::open(cfg).context("open SqliteStore for run_eval")?;
    store
        .run_migrations()
        .context("run migrations for run_eval")?;

    // ── 3. Build config_snapshot_json ─────────────────────────────────────
    let config_snapshot_json = build_config_snapshot(cfg, opts.k)?;
    let config_snapshot_text =
        serde_json::to_string(&config_snapshot_json).context("serialize config_snapshot_json")?;

    // ── 4. Per-query execution ────────────────────────────────────────────
    //
    // Open one `App` for the whole suite. The embedder / vector store /
    // LLM are memoized on the App, so a 50-query run pays the ~470 MB
    // ONNX init + Lance reopen + Ollama handshake exactly once.
    let app = App::open_with_config(cfg.clone()).context("open App for run_eval")?;

    let mut per_query: Vec<QueryResult> = Vec::with_capacity(queries.len());
    for gq in &queries {
        let qr = execute_query(&app, gq, opts);
        per_query.push(qr);
    }

    // ── 5. Persist eval_runs + eval_query_results ────────────────────────
    // Serialize per-query JSON up front so the SQLite transaction below
    // never holds the connection mutex through serde failures.
    let mut results: Vec<(String, String)> = Vec::with_capacity(per_query.len());
    for qr in &per_query {
        let json = serde_json::to_string(qr)
            .with_context(|| format!("serialize QueryResult for {}", qr.query_id))?;
        results.push((qr.query_id.clone(), json));
    }
    let row = EvalRunRow {
        run_id: &run_id,
        suite: opts.suite.as_str(),
        config_snapshot_json: &config_snapshot_text,
        aggregate_json: "{}",
        commit_hash: commit_hash.as_deref(),
        created_at,
    };
    store
        .record_eval_run_with_results(&row, &results)
        .context("record eval_runs + eval_query_results (transactional)")?;

    // ── 6. Mirror to runs_dir/<run_id>/per_query.jsonl ────────────────────
    write_per_query_jsonl(cfg, &run_id, &per_query)?;

    let duration_ms = elapsed_ms_u32(started);
    tracing::info!(
        target: "kebab-eval",
        run_id = %run_id,
        suite = %opts.suite,
        queries = per_query.len(),
        duration_ms,
        "kb-eval: run complete"
    );

    Ok(EvalRun {
        run_id,
        created_at,
        commit_hash,
        config_snapshot_json,
        per_query,
    })
}

/// Mint a `run_<lower>` identifier. UUIDv7 stands in for ULID — same
/// timestamp-ordered monotonicity, already in workspace deps. Lower-
/// case simple form to match the `ulid_lower()` shape the spec asks
/// for.
fn mint_run_id() -> String {
    let id = uuid::Uuid::now_v7().simple().to_string();
    format!("run_{id}")
}

/// Resolve the golden YAML path. Honors the `KEBAB_EVAL_GOLDEN` env
/// override; otherwise relative to CWD. The path is NOT expanded for
/// `~` / `${...}` placeholders — direct file paths only.
fn resolve_golden_path() -> PathBuf {
    match std::env::var(KEBAB_EVAL_GOLDEN) {
        Ok(s) if !s.is_empty() => PathBuf::from(s),
        _ => PathBuf::from(DEFAULT_GOLDEN_PATH),
    }
}

/// Run one [`GoldenQuery`] through the kb-app facade. Errors are
/// captured into `QueryResult.error` so the run continues.
fn execute_query(app: &App, gq: &GoldenQuery, opts: &EvalRunOpts) -> QueryResult {
    let started = Instant::now();

    let search_query = SearchQuery {
        text: gq.query.clone(),
        mode: opts.mode,
        k: opts.k,
        filters: SearchFilters::default(),
    };

    let (hits_top_k, mut error) = match app.search(search_query) {
        Ok(hits) => (hits, None),
        Err(e) => (Vec::new(), Some(format!("{e:#}"))),
    };

    // Optional RAG path: only attempted when `with_rag` and the search
    // call did not already error out (we want one error per query, not
    // a duplicated one).
    let answer = if opts.with_rag && error.is_none() {
        let ask_opts = kebab_app::AskOpts {
            k: opts.k,
            explain: true,
            mode: opts.mode,
            temperature: opts.temperature,
            seed: opts.seed,
            stream_sink: None,
            // p9-fb-15: golden eval is single-shot per query; no
            // conversational history.
            history: Vec::new(),
            conversation_id: None,
            turn_index: None,
            // p9-fb-41: golden eval baseline runs are single-pass; the
            // multi-hop path is opted into per query via a future
            // fixture flag (PR-4+) once the runner learns to dispatch.
            multi_hop: false,
        };
        match app.ask(&gq.query, ask_opts) {
            Ok(ans) => Some(ans),
            Err(e) => {
                error = Some(format!("{e:#}"));
                None
            }
        }
    } else {
        None
    };

    QueryResult {
        query_id: gq.id.clone(),
        query: gq.query.clone(),
        mode: opts.mode,
        hits_top_k,
        answer,
        elapsed_ms: elapsed_ms_u32(started),
        error,
    }
}

/// Build the `config_snapshot_json` value: full Config as `config` plus
/// the auxiliary version fields the spec calls out.
///
/// `index_version` is intentionally `None` here — it is composed
/// dynamically by `kb-app` on a per-call basis from the configured
/// embedder (e.g., `vec:<model>@<version>:<dim>`), so it is not a
/// stable run-time property of the config alone. P5-2 may compose it
/// from `embedding.{model,version,dimensions}` if it needs the field
/// for compare reports.
fn build_config_snapshot(cfg: &kebab_config::Config, eval_k: usize) -> Result<serde_json::Value> {
    let cfg_value = serde_json::to_value(cfg).context("serialize Config")?;
    Ok(serde_json::json!({
        "config": cfg_value,
        "eval_k": eval_k,
        "chunker_version": cfg.ingest.chunking.chunker_version,
        "embedding": {
            "model": cfg.models.embedding.model,
            "version": cfg.models.embedding.version,
            "dimensions": cfg.models.embedding.dimensions,
            "provider": cfg.models.embedding.provider,
        },
        "llm": {
            "model_id": cfg.models.llm.model,
            "provider": cfg.models.llm.provider,
        },
        "prompt_template_version": cfg.rag.prompt_template_version,
        "score_gate": cfg.rag.score_gate,
        "rrf_k": cfg.search.rrf_k,
        "index_version": serde_json::Value::Null,
    }))
}

/// Write the `runs_dir/<run_id>/per_query.jsonl` mirror (design §6.3).
/// Each `QueryResult` is one line, separator `\n`. The directory is
/// created if it doesn't exist; an existing file is overwritten (a
/// `run_id` collision would already have failed the `eval_runs`
/// PRIMARY KEY upstream).
fn write_per_query_jsonl(
    cfg: &kebab_config::Config,
    run_id: &str,
    per_query: &[QueryResult],
) -> Result<()> {
    // `data_dir` may itself contain `${XDG_DATA_HOME:-…}` / `~` (the
    // workspace-default does); resolve it before threading it into the
    // `{data_dir}` substitution of `runs_dir`.
    let resolved_data_dir = expand_path(&cfg.storage.data_dir, "");
    let runs_dir = expand_path(&cfg.storage.runs_dir, &resolved_data_dir.to_string_lossy());
    let run_dir = runs_dir.join(run_id);
    std::fs::create_dir_all(&run_dir)
        .with_context(|| format!("create run dir {}", run_dir.display()))?;
    let path = run_dir.join("per_query.jsonl");
    let file = File::create(&path)
        .with_context(|| format!("create per_query.jsonl at {}", path.display()))?;
    let mut w = BufWriter::new(file);
    for qr in per_query {
        serde_json::to_writer(&mut w, qr)
            .with_context(|| format!("serialize QueryResult for {}", qr.query_id))?;
        w.write_all(b"\n")
            .context("write newline separator in per_query.jsonl")?;
    }
    w.flush().context("flush per_query.jsonl")?;
    Ok(())
}