code/scripts/build_selector_v4_pairwise.py

"""
Selector v4 — PAIRWISE selector SFT data builder (Chase-SQL style).

Chase-SQL (Pourreza et al.) frames the selector as a head-to-head judge:
given (question, schema, candidate_A, candidate_B, exec_a, exec_b), the
model outputs which one is more likely correct. At inference, K=8 candidates
are compared in a round-robin tournament (28 calls) or single-elimination
bracket (7 calls); the candidate with the most pairwise wins is picked.

Pros vs pointwise YES/NO:
  - Direct preference signal (no calibration of independent probabilities).
  - Captures fine-grained discrimination between near-duplicate SQLs.

Data construction:
  For each BIRD-train question with at least one YES and one NO trajectory:
    - For each (yes_sql, no_sql) pair, emit TWO records:
        A = yes, B = no, label = "A"
        A = no,  B = yes, label = "B"
      → 50/50 label balance, twice the data.
  Hard negatives: prefer NO SQLs with high lexical overlap to a YES SQL
  (Jaccard on word tokens). Cap at HARDNEG_PER_POS per YES per question.

Output:
  data/sft_selector_v4_pairwise/{train,test}
  Each row: {"prompt", "completion", "messages", "question", "db_id"}
"""
import json, os, re, sys, random
from concurrent.futures import ThreadPoolExecutor, as_completed

ROOT = "/weka/s225250685/mats-tist"
os.chdir(ROOT); sys.path.insert(0, ROOT)
os.environ.setdefault("DB_EXEC_API_DISABLE", "1")
os.environ.setdefault("PYTHONNOUSERSITE", "1")

from validator_data.validator import _execute_sql
from datasets import Dataset, DatasetDict
from scripts.rich_schema import render_rich_schema

PAIRWISE_PROMPT = (
    "You are a SQL correctness judge. Compare two candidate SQL queries that "
    "attempt to answer the same question. Pick the one MORE LIKELY to be correct.\n\n"
    "Database schema (with column descriptions, value descriptions, and example values):\n"
    "{schema}\n\n"
    "Question: {question}\n"
    "External knowledge: {evidence}\n\n"
    "Candidate A:\n{sql_a}\n\n"
    "Execution result of A:\n{exec_a}\n\n"
    "Candidate B:\n{sql_b}\n\n"
    "Execution result of B:\n{exec_b}\n\n"
    "Which candidate is more likely to correctly answer the question? "
    "Answer with a single letter: A or B."
)

SRC_PATHS = [
    "data/rollouts/bird_train_3stage_K4.jsonl",
    "data/rollouts/scaleup_bird_train_2stage_K4.jsonl",
    "data/rollouts/scaleup_bird_train_3stage_K4.jsonl",
    "data/rollouts/iter2_bird_train_3stage_K8.jsonl",
]
OUT_DIR = "data/sft_selector_v4_pairwise"

HARDNEG_PER_POS = 3        # hardest NO partners per YES SQL
MAX_PAIRS_PER_Q = 6        # cap raw (YES, NO) pairs per question (→ 12 records after 2× swap)
MAX_SCHEMA_CHARS = 3000    # smaller than v3 since two SQLs share prompt
EXEC_TIMEOUT = 5           # reduced from 8 to avoid login-node OOM


def safe_truncate(s, n=400):
    s = str(s) if s is not None else ""
    return s if len(s) <= n else s[:n] + "..."

def tokens(sql):
    return set(re.findall(r"[a-zA-Z_][a-zA-Z0-9_]+|[<>=!]+", (sql or "").lower()))

def jaccard(a, b):
    if not a or not b: return 0.0
    return len(a & b) / max(len(a | b), 1)

def exec_str(db_path, sql):
    try:
        r, err = _execute_sql("./" + db_path, sql, timeout=EXEC_TIMEOUT)
    except Exception as e:
        return f"Error: {str(e)[:140]}"
    if err:
        return f"Error: {str(r)[:140]}"
    rows = str(r)[:220]
    if rows.strip() and rows.strip() != "[]":
        return f"OK. Rows preview: {rows}"
    return "OK. (no rows returned)"


def collect_question_groups():
    by_q = {}
    for src in SRC_PATHS:
        if not os.path.exists(src):
            print(f"skip missing: {src}", flush=True)
            continue
        print(f"loading {src}...", flush=True)
        with open(src) as f:
            for line in f:
                line = line.strip()
                if not line: continue
                s = json.loads(line)
                key = (s.get("question",""), s.get("db_id",""))
                if key not in by_q:
                    by_q[key] = {"sample": s, "cands": [], "seen": set()}
                for t in s.get("trajectories", []):
                    sql = (t.get("fixed_sql") or t.get("planner_sql") or "").strip()
                    if not sql: continue
                    norm = re.sub(r"\s+", " ", sql.lower())
                    if norm in by_q[key]["seen"]: continue
                    by_q[key]["seen"].add(norm)
                    correct = bool(t.get("is_fixed_correct") if t.get("fixed_sql") else t.get("is_planner_correct"))
                    by_q[key]["cands"].append((sql, correct))
    print(f"unique questions: {len(by_q)}", flush=True)
    out = []
    for k, v in by_q.items():
        yes = [c[0] for c in v["cands"] if c[1]]
        no  = [c[0] for c in v["cands"] if not c[1]]
        if not yes or not no:
            continue
        out.append((v["sample"], yes, no))
    print(f"questions with BOTH YES and NO: {len(out)}", flush=True)
    return out


def build_pair_records(rng, qgroups):
    """For each question, emit at most MAX_PAIRS_PER_Q (yes, no) pairs with hard-neg ranking.
    Each pair becomes 2 records (A=YES,B=NO; A=NO,B=YES)."""
    raw = []
    for sample, yes_list, no_list in qgroups:
        # Score every NO by best Jaccard against any YES
        no_scored = []
        yes_toks = [tokens(y) for y in yes_list]
        for ns in no_list:
            t_no = tokens(ns)
            best = max((jaccard(t_no, ty) for ty in yes_toks), default=0.0)
            no_scored.append((best, ns))
        no_scored.sort(reverse=True)

        pairs = []
        for ys in yes_list:
            for _, ns in no_scored[:HARDNEG_PER_POS]:
                pairs.append((ys, ns))
                if len(pairs) >= MAX_PAIRS_PER_Q:
                    break
            if len(pairs) >= MAX_PAIRS_PER_Q:
                break
        for ys, ns in pairs:
            raw.append((sample, ys, ns))
    return raw


def render_pair(rng_seed, item):
    """Produce TWO records (swapped A/B) so labels are balanced."""
    sample, sql_yes, sql_no = item
    rng = random.Random(rng_seed)
    db_path = sample["db_path"]
    schema = safe_truncate(render_rich_schema(sample, split="train"), MAX_SCHEMA_CHARS)
    question = sample.get("question", "")
    evidence = sample.get("evidence", "") or "None"

    exec_yes = safe_truncate(exec_str(db_path, sql_yes), 220)
    exec_no  = safe_truncate(exec_str(db_path, sql_no), 220)

    out = []
    for swap in (False, True):
        if not swap:
            a, b, ea, eb, label = sql_yes, sql_no, exec_yes, exec_no, "A"
        else:
            a, b, ea, eb, label = sql_no, sql_yes, exec_no, exec_yes, "B"
        prompt = PAIRWISE_PROMPT.format(
            schema=schema, question=question, evidence=evidence,
            sql_a=safe_truncate(a, 600), exec_a=ea,
            sql_b=safe_truncate(b, 600), exec_b=eb,
        )
        out.append({
            "prompt": prompt,
            "completion": label,
            "messages": [
                {"role": "user", "content": prompt},
                {"role": "assistant", "content": label},
            ],
            "question": question,
            "db_id": sample.get("db_id", ""),
        })
    return out


def main():
    rng = random.Random(42)
    qg = collect_question_groups()
    raw = build_pair_records(rng, qg)
    print(f"raw (yes, no) pairs: {len(raw)} → records: {2*len(raw)}", flush=True)

    out = []
    with ThreadPoolExecutor(max_workers=8) as exe:
        futs = [exe.submit(render_pair, i, it) for i, it in enumerate(raw)]
        n_done = 0
        for fut in as_completed(futs):
            try:
                out.extend(fut.result())
            except Exception as e:
                print(f"render err: {e}", flush=True)
            n_done += 1
            if n_done % 1000 == 0:
                print(f"  rendered {n_done}/{len(raw)} pairs", flush=True)

    rng.shuffle(out)
    n_test = max(500, len(out) // 25)
    test = out[:n_test]; train = out[n_test:]
    n_a = sum(1 for r in train if r["completion"] == "A")
    print(f"\n=== v4 PAIRWISE selector data ===")
    print(f"  train: {len(train)} ({100*n_a/max(len(train),1):.1f}% A-label)")
    print(f"  test:  {len(test)}")
    avg = sum(len(r["prompt"]) for r in train) / max(len(train),1)
    print(f"  avg prompt chars: {avg:.0f}")
    DatasetDict({
        "train": Dataset.from_list(train),
        "test": Dataset.from_list(test),
    }).save_to_disk(OUT_DIR)
    print(f"  saved {OUT_DIR}", flush=True)


if __name__ == "__main__":
    main()