//! Walk the ladder, once, by building real sessions (docs/dev/inference.md §4).
//!
//! A rung is taken when a session builds on it, runs, and is faster than
//! the floor. Both halves matter: a provider can register and then fail at
//! partition time, and a provider can take a graph — or quietly hand most
//! of it back to the CPU — and run it slower than the CPU would have. The outcome is cached against a fingerprint of the
//! runtime, the driver, the hardware and the models, and trusted until any
//! of those changes.

use std::path::{Path, PathBuf};
use std::time::Instant;

use crate::{api::Runtime, state, Cache, Config, Form, Role, Rung};

/// The rungs to try on this platform, best first, under the user's ceiling.
fn ladder(ceiling: Option<Rung>) -> Vec<Rung> {
    #[cfg(target_os = "android")]
    let all = [Rung::Hexagon];
    // A desktop has one vendor's GPU; the other vendor's providers are
    // "not enabled in this build" or a library that fails to load, and
    // either answer arrives in milliseconds.
    #[cfg(not(target_os = "android"))]
    let all = [Rung::TensorRt, Rung::Cuda, Rung::MiGraphX];
    all.into_iter()
        .filter(|r| ceiling.is_none_or(|c| *r <= c))
        .collect()
}

/// The probe body. Sets the cache and clears `probing` when done; never
/// panics out, because a failed probe is a result (the floor) and not an
/// error.
pub fn run(runtime: Runtime) {
    let cfg = state().lock().unwrap().config.clone();
    let fingerprint = fingerprint(&runtime, &cfg);

    if let Some(cached) = read_cache(&cfg) {
        if cached.fingerprint == fingerprint && cached.rung.is_some() {
            log::info!(
                "inference: cached selection {} ({})",
                cached.rung.unwrap().label(),
                cached.reason
            );
            finish(cached);
            return;
        }
    }

    let mut cache = Cache {
        fingerprint,
        ..Cache::default()
    };

    if !runtime.is_native() {
        cache.rung = Some(Rung::Cpu);
        cache.reason = "no ONNX Runtime found; tract on one core".into();
        write_cache(&cfg, &cache);
        finish(cache);
        return;
    }

    let Some((role, canonical)) = probe_model(&cfg) else {
        cache.rung = Some(Rung::Cpu);
        cache.reason = "no model to probe with".into();
        write_cache(&cfg, &cache);
        finish(cache);
        return;
    };

    let floor = match time_rung(Rung::Cpu, role, &canonical, &cfg) {
        Ok((ms, _)) => ms,
        Err(e) => {
            // The CPU provider failing is the runtime failing; there is
            // nothing below it to try, and the reason is worth reading.
            cache.rung = Some(Rung::Cpu);
            cache.reason = format!("CPU provider failed: {e}");
            write_cache(&cfg, &cache);
            finish(cache);
            return;
        }
    };
    log::info!("inference: floor {floor:.1} ms on the CPU provider");

    for rung in ladder(cfg.ceiling) {
        match time_rung(rung, role, &canonical, &cfg) {
            Ok((ms, key)) if ms < floor => {
                cache.rung = Some(rung);
                cache.reason = format!("{ms:.1} ms against {floor:.1} ms on the CPU");
                if let Some(key) = key {
                    cache.compiled.insert(key);
                }
                break;
            }
            Ok((ms, _)) => {
                let why = format!("{ms:.1} ms, slower than the CPU's {floor:.1} ms");
                log::info!("inference: {} rejected: {why}", rung.label());
                cache.failed.push((rung, why));
            }
            Err(e) => {
                log::info!("inference: {} failed: {e}", rung.label());
                cache.failed.push((rung, e));
            }
        }
    }
    if cache.rung.is_none() {
        cache.rung = Some(Rung::Cpu);
        cache.reason = match cache.failed.first() {
            Some((r, why)) => format!("{} {}", r.label(), first_line(why)),
            None => "the only rung on this platform".into(),
        };
    }
    write_cache(&cfg, &cache);
    finish(cache);
}

fn finish(cache: Cache) {
    let mut s = state().lock().unwrap();
    s.cache = cache;
    s.probing = false;
}

/// The smallest detector, or the smallest model of any role if there is
/// none. A ~2 MB detector is the cheapest real test of a provider, and the
/// detector is the role the int8 forms exist for — the eye classifiers are
/// smaller still, and a Hexagon probed with one would fail for want of a
/// form nobody ships.
fn probe_model(cfg: &Config) -> Option<(Role, PathBuf)> {
    let smallest = |want: Option<Role>| {
        cfg.models
            .iter()
            .filter(|(role, _)| want.is_none_or(|w| *role == w))
            .filter_map(|(role, path)| {
                let size = std::fs::metadata(path).ok()?.len();
                Some((size, *role, path.clone()))
            })
            .min_by_key(|(size, _, _)| *size)
            .map(|(_, role, path)| (role, path))
    };
    smallest(Some(Role::Detector)).or_else(|| smallest(None))
}

/// Build, run once for the engine, then time three runs; the median in
/// milliseconds and, for a compiling rung, the cache key of the engine this
/// just built.
fn time_rung(
    rung: Rung,
    role: Role,
    canonical: &Path,
    cfg: &Config,
) -> Result<(f64, Option<String>), String> {
    let want = rung.form(role);
    let path = match want {
        Form::Int8 => {
            let p = crate::int8_sibling(canonical);
            if !p.is_file() {
                return Err(format!("no int8 form of {}", canonical.display()));
            }
            p
        }
        Form::F32 => canonical.to_path_buf(),
    };
    let bytes = std::fs::read(&path).map_err(|e| e.to_string())?;
    let started = Instant::now();
    let mut session =
        crate::session::build(rung, role, &bytes, cfg).map_err(|e| first_line(&e.to_string()))?;
    log::info!(
        "inference: {} session built in {:.1} s",
        rung.label(),
        started.elapsed().as_secs_f64()
    );

    let shape: Vec<usize> = session.inputs()[0]
        .dtype()
        .tensor_shape()
        .ok_or("model input is not a tensor")?
        .iter()
        .map(|&d| if d > 0 { d as usize } else { 1 })
        .collect();
    let zeros = vec![0f32; shape.iter().product()];
    let run = |session: &mut ort::session::Session| -> Result<f64, String> {
        let input = ort::value::Tensor::from_array((shape.clone(), zeros.clone()))
            .map_err(|e| e.to_string())?;
        let t = Instant::now();
        let out = session
            .run(ort::inputs![input])
            .map_err(|e| e.to_string())?;
        let _ = out[0]
            .try_extract_tensor::<f32>()
            .map_err(|e| e.to_string())?;
        Ok(t.elapsed().as_secs_f64() * 1e3)
    };
    run(&mut session)?;
    let mut times = [run(&mut session)?, run(&mut session)?, run(&mut session)?];
    times.sort_by(|a, b| a.partial_cmp(b).unwrap());
    let key = rung.compiles().then(|| crate::engines::key(rung, &bytes));
    Ok((times[1], key))
}

/// The part of a provider's error a person can act on. ONNX Runtime's
/// begin with a source path and a C++ template signature; the words —
/// "CUDA failure 999: unknown error", "FAIL : Failed to load library" —
/// come after, and the settings row has room for one line of them.
fn first_line(s: &str) -> String {
    let line = s.lines().next().unwrap_or("");
    let start = ["failure", "FAIL :", "Error:", "error:"]
        .iter()
        .filter_map(|m| line.find(m))
        .min()
        .unwrap_or(0);
    line[start..].chars().take(200).collect()
}

/// Everything a change of which should re-probe: the runtime, where it
/// came from and which providers sit beside it, this crate, the platform,
/// the driver or SoC, and the models.
fn fingerprint(runtime: &Runtime, cfg: &Config) -> String {
    let mut parts = vec![
        format!("engine {}", env!("CARGO_PKG_VERSION")),
        format!("{} {}", std::env::consts::OS, std::env::consts::ARCH),
        match runtime {
            Runtime::Tract => "tract".to_string(),
            Runtime::OnnxRuntime { path, version } => {
                format!(
                    "ort {version} {} [{}]",
                    path.display(),
                    providers_beside(path)
                )
            }
        },
        device_identity(),
    ];
    for (role, bytes) in &cfg.embedded {
        parts.push(format!(
            "{role:?} embedded {:016x}",
            crate::engines::hash(bytes)
        ));
    }
    for (role, path) in &cfg.models {
        let hash = std::fs::read(path)
            .map(|b| crate::engines::hash(&b))
            .unwrap_or(0);
        parts.push(format!("{role:?} {hash:016x}"));
        let int8 = crate::int8_sibling(path);
        if let Ok(b) = std::fs::read(&int8) {
            parts.push(format!("{role:?} int8 {:016x}", crate::engines::hash(&b)));
        }
    }
    parts.join("\n")
}

/// The `libonnxruntime_providers_*.so` files in the runtime's directory.
/// A distribution's CPU-only and ROCm builds are the same version at the
/// same path; the provider libraries beside them are what differs.
fn providers_beside(runtime: &Path) -> String {
    let Some(dir) = runtime.parent() else {
        return String::new();
    };
    let mut names: Vec<String> = std::fs::read_dir(dir)
        .into_iter()
        .flatten()
        .filter_map(|e| e.ok())
        .filter_map(|e| e.file_name().into_string().ok())
        .filter(|n| {
            n.starts_with("libonnxruntime_providers_") || n.starts_with("onnxruntime_providers_")
        })
        .collect();
    names.sort();
    names.join(" ")
}

#[cfg(target_os = "linux")]
fn device_identity() -> String {
    // The NVIDIA driver's version line, or the ROCm release the AMD stack
    // came from (`rocm-core` writes it; the kernel driver has no version
    // of its own). Absent means neither.
    if let Some(line) = std::fs::read_to_string("/proc/driver/nvidia/version")
        .ok()
        .and_then(|s| s.lines().next().map(str::to_string))
    {
        return line;
    }
    if let Ok(rocm) = std::fs::read_to_string("/opt/rocm/.info/version") {
        return format!("rocm {}", rocm.trim());
    }
    "no nvidia driver, no rocm".into()
}

#[cfg(target_os = "android")]
fn device_identity() -> String {
    // The SoC and the vendor's build: a Hexagon appears or disappears with
    // either.
    format!(
        "{} {}",
        system_property("ro.soc.model"),
        system_property("ro.build.version.incremental")
    )
}

#[cfg(target_os = "android")]
fn system_property(name: &str) -> String {
    extern "C" {
        fn __system_property_get(
            name: *const std::ffi::c_char,
            value: *mut std::ffi::c_char,
        ) -> i32;
    }
    let name = std::ffi::CString::new(name).unwrap();
    let mut buf = [0u8; 92]; // PROP_VALUE_MAX
                             // SAFETY: bionic's documented call; the buffer is PROP_VALUE_MAX bytes.
    let n = unsafe { __system_property_get(name.as_ptr(), buf.as_mut_ptr().cast()) };
    String::from_utf8_lossy(&buf[..n.max(0) as usize]).into_owned()
}

#[cfg(not(any(target_os = "linux", target_os = "android")))]
fn device_identity() -> String {
    String::new()
}

fn cache_path(cfg: &Config) -> PathBuf {
    cfg.cache_dir.join("backend.json")
}

fn read_cache(cfg: &Config) -> Option<Cache> {
    let text = std::fs::read_to_string(cache_path(cfg)).ok()?;
    serde_json::from_str(&text).ok()
}

/// Written whole and renamed into place, so a reader never sees half.
pub fn write_cache(cfg: &Config, cache: &Cache) {
    if cfg.cache_dir.as_os_str().is_empty() {
        return;
    }
    let path = cache_path(cfg);
    let tmp = path.with_extension("json.tmp");
    let _ = std::fs::create_dir_all(&cfg.cache_dir);
    if let Ok(text) = serde_json::to_string_pretty(cache) {
        if std::fs::write(&tmp, text).is_ok() {
            let _ = std::fs::rename(&tmp, &path);
        }
    }
}