"""Greedy translation eval on line-aligned src/ref files.

    python -m kda.training.eval_mt \\
        --ckpt ckpts/k3_wiki.pt --src /data/eval/zh2en.src.txt \\
        --ref /data/eval/zh2en.ref.txt --target-lang en
"""

from __future__ import annotations

import argparse
import json
from pathlib import Path

import torch

from kda.training.data import eos_id, load_tokenizer
from kda.training.prompts import instruction_prompt
from kda.training.success import _chrf, _detect_lang, translation_success
from kda.training.toy import load_ckpt


def _read_lines(path: str) -> list[str]:
    return [ln.strip() for ln in Path(path).read_text(encoding="utf-8").splitlines() if ln.strip()]


def _instruction(src: str, target_lang: str) -> str:
    return instruction_prompt(src, target_lang)


@torch.inference_mode()
def decode_one(model, tok, prompt: str, device: str, max_new: int) -> str:
    ids = tok.encode(prompt)
    if not ids:
        return ""
    inp = torch.tensor([ids], dtype=torch.long, device=device)
    out = model.generate(inp, max_new, eos_token_id=eos_id(tok))
    gen = out[0, inp.size(1) :].tolist()
    return tok.decode(gen).strip()


def evaluate_pairs(
    model,
    tok,
    srcs: list[str],
    refs: list[str],
    *,
    target_lang: str,
    device: str,
    max_new: int,
    limit: int | None,
) -> dict:
    n = len(srcs)
    if limit is not None:
        n = min(n, limit)
    hyps: list[str] = []
    wins = 0
    copies = 0
    lang_ok = 0
    chrf_sum = 0.0
    for i in range(n):
        src, ref = srcs[i], refs[i]
        hyp = decode_one(model, tok, _instruction(src, target_lang), device, max_new)
        hyps.append(hyp)
        ok = translation_success(src, hyp, ref, target_lang=target_lang)
        wins += int(ok)
        copies += int(_chrf(hyp, src) >= 80.0 or hyp == src)
        want = "zh" if target_lang.startswith("zh") else "en"
        lang_ok += int(_detect_lang(hyp) == want)
        chrf_sum += _chrf(hyp, ref)
    corpus = {}
    try:
        from sacrebleu.metrics import BLEU, CHRF

        corpus["chrf"] = float(CHRF(word_order=2).corpus_score(hyps, [refs[:n]]).score)
        corpus["bleu"] = float(BLEU().corpus_score(hyps, [refs[:n]]).score)
    except Exception:
        corpus["chrf"] = chrf_sum / max(n, 1)
        corpus["bleu"] = None
    return {
        "n": n,
        "success_rate": wins / max(n, 1),
        "copy_rate": copies / max(n, 1),
        "lang_ok": lang_ok / max(n, 1),
        "chrf": corpus["chrf"],
        "bleu": corpus["bleu"],
        "hyps": hyps,
    }


def main() -> None:
    p = argparse.ArgumentParser(description=__doc__)
    p.add_argument("--ckpt", required=True)
    p.add_argument("--tokenizer", default=None, help="override ckpt tokenizer field")
    p.add_argument("--src", default=None, help="one source sentence per line")
    p.add_argument("--ref", default=None, help="one reference sentence per line")
    p.add_argument("--target-lang", default="en", choices=["en", "zh"])
    p.add_argument("--max-new", type=int, default=64)
    p.add_argument("--limit", type=int, default=None)
    p.add_argument("--prefix", default=None, help="single-prompt smoke decode")
    p.add_argument("--device", default="auto")
    args = p.parse_args()

    device = args.device
    if device == "auto":
        device = "cuda" if torch.cuda.is_available() else "cpu"

    model, _config = load_ckpt(args.ckpt)
    model.to(device).eval()
    payload = torch.load(args.ckpt, map_location="cpu", weights_only=False)
    tok_src = args.tokenizer or payload.get("tokenizer")
    if not tok_src:
        raise SystemExit("need --tokenizer or a 'tokenizer' field in the checkpoint")
    tok = load_tokenizer(tok_src)

    if args.prefix:
        print(decode_one(model, tok, args.prefix, device, args.max_new))

    if args.src and args.ref:
        srcs, refs = _read_lines(args.src), _read_lines(args.ref)
        if len(srcs) != len(refs):
            raise SystemExit(f"src/ref length mismatch: {len(srcs)} vs {len(refs)}")
        out = evaluate_pairs(
            model,
            tok,
            srcs,
            refs,
            target_lang=args.target_lang,
            device=device,
            max_new=args.max_new,
            limit=args.limit,
        )
        printable = {k: v for k, v in out.items() if k != "hyps"}
        print(json.dumps(printable, ensure_ascii=False, indent=2))
    elif not args.prefix:
        raise SystemExit("pass --prefix and/or --src + --ref")


if __name__ == "__main__":
    main()