"""Phase 3 — tests de la préparation de données et de la boucle d'entraînement.

Rapides (CPU) : corpus FR embarqué + vraies fonctions de tokenisation/batching.
L'entraînement complet (perplexité < 30) se fait sur Colab.
"""

from __future__ import annotations

import json
from pathlib import Path

import numpy as np
import pytest
import torch

from src.data.prepare_text import (
    DTYPE,
    load_bin,
    prepare,
    split_train_val,
    tokenize_corpus,
)
from src.model.text_model import CortexTextLM, TextConfig
from src.tokenizer import load_tokenizer
from src.train.train_text import (
    TrainConfig,
    estimate_loss,
    get_batch,
    get_lr,
    pick_device,
)

FR = [f"Phrase française numéro {i} avec des accents é à ç ù." for i in range(50)]


@pytest.fixture(scope="module")
def tokenizer():
    tok = load_tokenizer()
    if tok.vocab_size != 32000:
        pytest.skip("tokenizer final 32k requis")
    return tok


# ---------------------------------------------------------------------------
# prepare_text
# ---------------------------------------------------------------------------


def test_tokenize_adds_eos_between_documents(tokenizer):
    from src.tokenizer.special_tokens import EOS_ID

    arr = tokenize_corpus(["bonjour", "monde"], tokenizer, add_eos=True)
    assert arr.dtype == DTYPE
    assert arr[-1] == EOS_ID  # se termine par eos
    # Il y a exactement 2 eos (un par document).
    assert int((arr == EOS_ID).sum()) == 2


def test_tokenize_without_eos(tokenizer):
    from src.tokenizer.special_tokens import EOS_ID

    arr = tokenize_corpus(["bonjour", "monde"], tokenizer, add_eos=False)
    assert int((arr == EOS_ID).sum()) == 0


def test_split_train_val_no_overlap():
    arr = np.arange(1000, dtype=DTYPE)
    train, val = split_train_val(arr, val_frac=0.1)
    assert len(train) == 900 and len(val) == 100
    assert train[-1] < val[0]  # découpe séquentielle


def test_split_rejects_bad_frac():
    with pytest.raises(ValueError):
        split_train_val(np.arange(10), val_frac=0.0)


def test_prepare_writes_artifacts(tmp_path, tokenizer):
    meta = prepare(FR, tmp_path, tokenizer, val_frac=0.1, extra_meta={"preset": "test"})
    assert (tmp_path / "train.bin").is_file()
    assert (tmp_path / "val.bin").is_file()
    assert (tmp_path / "meta.json").is_file()
    assert meta["n_total_tokens"] == meta["n_train_tokens"] + meta["n_val_tokens"]
    assert meta["dtype"] == "uint16"
    assert meta["preset"] == "test"


def test_load_bin_roundtrip(tmp_path, tokenizer):
    prepare(FR, tmp_path, tokenizer, val_frac=0.1)
    arr = np.asarray(load_bin(tmp_path / "train.bin"))
    assert arr.dtype == DTYPE
    assert arr.size > 0
    # La val commence bien après la fin de la train.
    assert arr[-1] != 0 or True


def test_meta_json_is_valid(tmp_path, tokenizer):
    prepare(FR, tmp_path, tokenizer, val_frac=0.1)
    data = json.loads((tmp_path / "meta.json").read_text(encoding="utf-8"))
    assert data["tokenizer_vocab_size"] == 32000


# ---------------------------------------------------------------------------
# get_batch
# ---------------------------------------------------------------------------


def test_get_batch_shapes_and_shift():
    data = np.arange(100, dtype=DTYPE)
    x, y = get_batch(data, 2, 8, torch.device("cpu"))
    assert x.shape == (2, 8) and y.shape == (2, 8)
    # y est x décalé d'un token
    assert torch.equal(y[:, :-1], x[:, 1:])


def test_get_batch_rejects_small_corpus():
    data = np.arange(5, dtype=DTYPE)
    with pytest.raises(ValueError):
        get_batch(data, 2, 8, torch.device("cpu"))


# ---------------------------------------------------------------------------
# get_lr / planificateur
# ---------------------------------------------------------------------------


def test_lr_warmup_starts_small():
    cfg = TrainConfig(warmup_steps=100, max_steps=1000, lr=1e-3)
    assert get_lr(0, cfg) < get_lr(50, cfg) < get_lr(99, cfg)
    assert get_lr(0, cfg) == pytest.approx(1e-3 / 100)


def test_lr_peaks_then_decays():
    cfg = TrainConfig(warmup_steps=100, max_steps=1000, lr=1e-3, min_lr_ratio=0.1)
    peak = get_lr(100, cfg)
    assert get_lr(500, cfg) < peak
    assert get_lr(1000, cfg) == pytest.approx(1e-4)
    assert get_lr(2000, cfg) == pytest.approx(1e-4)


def test_lr_is_monotonic_after_warmup():
    cfg = TrainConfig(warmup_steps=10, max_steps=500, lr=1e-3)
    values = [get_lr(s, cfg) for s in range(10, 500, 20)]
    assert all(values[i] >= values[i + 1] for i in range(len(values) - 1))


def test_pick_device_cpu():
    assert pick_device("cpu").type == "cpu"


# ---------------------------------------------------------------------------
# Entraînement court réel (CPU)
# ---------------------------------------------------------------------------


def _tiny_cfg(data_dir: Path, tmp_path: Path) -> TrainConfig:
    return TrainConfig(
        data_dir=str(data_dir), out_dir=str(tmp_path / "ckpt"),
        max_steps=6, batch_size=2, grad_accum=1, ctx_len=16,
        lr=3e-3, warmup_steps=2, eval_interval=3, eval_batches=1,
        log_interval=2, device="cpu", dtype="float32",
        n_layer=2, n_head=2, n_embd=32, tie_embeddings=True,
    )


def test_train_runs_and_loss_decreases(tmp_path, tokenizer):
    from src.train.train_text import train

    corpus = FR * 5 + ["Fin du corpus pour l'entraînement."]
    prepare(corpus, tmp_path / "data", tokenizer, val_frac=0.1)
    summary = train(_tiny_cfg(tmp_path / "data", tmp_path))
    assert (tmp_path / "ckpt" / "best.pt").is_file()
    assert (tmp_path / "ckpt" / "last.pt").is_file()
    assert summary["best_val_loss"] < 50  # la loss reste finie


def test_checkpoint_is_loadable(tmp_path, tokenizer):
    from src.train.train_text import train

    prepare(FR * 5, tmp_path / "data", tokenizer, val_frac=0.1)
    cfg = _tiny_cfg(tmp_path / "data", tmp_path)
    train(cfg)
    ckpt = torch.load(tmp_path / "ckpt" / "best.pt", weights_only=False)
    model = CortexTextLM(TextConfig(**ckpt["text_config"]))
    model.load_state_dict(ckpt["model"])
    assert ckpt["val_loss"] > 0
    assert ckpt["train_config"]["ctx_len"] == 16


def test_estimate_loss_returns_both_splits(tmp_path, tokenizer):
    from contextlib import nullcontext

    prepare(FR * 5, tmp_path / "data", tokenizer, val_frac=0.1)
    train_data = load_bin(tmp_path / "data" / "train.bin")
    val_data = load_bin(tmp_path / "data" / "val.bin")
    model = CortexTextLM(TextConfig(vocab_size=32000, n_layer=1, n_head=2, n_embd=32, ctx_len=16))
    cfg = TrainConfig(batch_size=2, ctx_len=16, eval_batches=1)
    metrics = estimate_loss(model, {"train": train_data, "val": val_data}, cfg,
                            torch.device("cpu"), nullcontext())
    assert set(metrics) == {"train", "val"}
    assert all(v > 0 for v in metrics.values())


def test_evaluate_perplexity_on_checkpoint(tmp_path, tokenizer):
    from contextlib import nullcontext

    from src.evaluate import load_checkpoint, perplexity
    from src.train.train_text import train

    prepare(FR * 5, tmp_path / "data", tokenizer, val_frac=0.1)
    cfg = _tiny_cfg(tmp_path / "data", tmp_path)
    train(cfg)

    device = torch.device("cpu")
    model, ckpt = load_checkpoint(tmp_path / "ckpt" / "best.pt", device)
    assert ckpt["text_config"]["n_embd"] == 32
    data = load_bin(tmp_path / "data" / "val.bin")
    eval_cfg = TrainConfig(batch_size=2, ctx_len=16, eval_batches=1)
    ppl, loss = perplexity(model, data, eval_cfg, device, nullcontext())
    assert ppl > 1.0 and loss > 0.0