"""Text prompt / completion adapter for the merchant policy.

Serialize an observation into a compact prompt the model can condition
on, and parse a JSON completion back into a typed
``ChargebackOpsAction``. Both helpers are pure — no provider calls, no
side effects — so they are cheap to unit-test.
"""

from __future__ import annotations

import json
import re
from typing import Any

try:
    from ..core.models import ChargebackOpsAction
except ImportError:  # pragma: no cover
    from core.models import ChargebackOpsAction


_SYSTEM_INSTRUCTION = (
    "You play the merchant-side agent in a chargeback dispute. "
    "Look at the observation and choose the single best next action. "
    "Return JSON only: "
    '{"action_type": "...", "case_id": "...", "strategy": "...", '
    '"evidence_ids": [...], "note": "..."} '
    "Use only action_types listed in available_actions. Omit fields you "
    "do not need."
)


_ALLOWED_ACTION_FIELDS: frozenset[str] = frozenset(
    {
        "action_type",
        "case_id",
        "system_name",
        "evidence_ids",
        "compelling_evidence_ids",
        "strategy",
        "note",
    }
)


def _compact_observation(observation: dict[str, Any]) -> dict[str, Any]:
    """Drop fields that add tokens without signal for the merchant policy."""

    visible_case = observation.get("visible_case")
    compact_case: dict[str, Any] | None = None
    if visible_case is not None:
        compact_case = {
            "case_id": visible_case["case_id"],
            "status": visible_case["status"],
            "reason_code": visible_case["reason_code"],
            "amount": visible_case["amount"],
            "currency": visible_case["currency"],
            "current_strategy": visible_case.get("current_strategy"),
            "systems_revealed": visible_case.get("systems_revealed", []),
            "retrieved_evidence": [
                {
                    "evidence_id": item["evidence_id"],
                    "source_system": item["source_system"],
                    "title": item["title"],
                }
                for item in visible_case.get("retrieved_evidence", [])
            ],
            "attached_evidence": [
                item["evidence_id"]
                for item in visible_case.get("attached_evidence", [])
            ],
            "policy": visible_case.get("policy"),
        }

    return {
        "objective": observation.get("objective", ""),
        "selected_case_id": observation.get("selected_case_id"),
        "available_actions": observation.get("available_actions", []),
        "steps_remaining": observation.get("steps_remaining", 0),
        "queue": [
            {
                "case_id": item["case_id"],
                "status": item["status"],
                "reason_code": item["reason_code"],
                "amount": item["amount"],
                "steps_until_deadline": item["steps_until_deadline"],
            }
            for item in observation.get("queue", [])
        ],
        "visible_case": compact_case,
        "last_action_result": observation.get("last_action_result", ""),
    }


def build_prompt(observation: dict[str, Any]) -> str:
    """Return a deterministic prompt for the merchant policy."""

    compact = _compact_observation(observation)
    body = json.dumps(compact, separators=(",", ":"), sort_keys=True)
    return f"{_SYSTEM_INSTRUCTION}\nOBSERVATION:\n{body}\nACTION:"


def parse_completion(text: str) -> dict[str, Any] | None:
    """Parse a model completion into a raw action dict, or return None.

    Tolerates: code fences, leading prose / `<think>` blocks, prefix words
    naming the action_type before the JSON, and JSON truncated mid-string
    (auto-closes at the last balanced field). Required because untrained
    Qwen-style chat models often emit valid JSON head + truncated tail —
    a strict parser would zero out the entire training signal.
    """

    if not text:
        return None
    cleaned = text.strip()
    cleaned = re.sub(r"<think>.*?</think>", "", cleaned, flags=re.DOTALL).strip()
    cleaned = re.sub(r"^```(?:json)?\s*", "", cleaned)
    cleaned = re.sub(r"```\s*$", "", cleaned).strip()

    start = cleaned.find("{")
    if start == -1:
        return None
    prefix = cleaned[:start].strip()
    body = cleaned[start:]

    data: dict[str, Any] | None = None
    try:
        candidate = json.loads(body)
        if isinstance(candidate, dict):
            data = candidate
    except json.JSONDecodeError:
        pass

    if data is None:
        depth = 0
        in_str = False
        esc = False
        last_safe = -1
        for i, ch in enumerate(body):
            if esc:
                esc = False
                continue
            if ch == "\\":
                esc = True
                continue
            if ch == '"':
                in_str = not in_str
                continue
            if in_str:
                continue
            if ch == "{":
                depth += 1
            elif ch == "}":
                depth -= 1
                if depth == 0:
                    try:
                        candidate = json.loads(body[: i + 1])
                        if isinstance(candidate, dict):
                            data = candidate
                            break
                    except json.JSONDecodeError:
                        pass
            elif ch == "," and depth == 1:
                last_safe = i
        if data is None and last_safe != -1:
            try:
                candidate = json.loads(body[:last_safe] + "}")
                if isinstance(candidate, dict):
                    data = candidate
            except json.JSONDecodeError:
                pass

    if data is None:
        return None

    if "action_type" not in data and prefix:
        m = re.match(r"[a-z_][a-z0-9_]*", prefix.lower())
        if m:
            data["action_type"] = m.group(0)

    return {k: v for k, v in data.items() if k in _ALLOWED_ACTION_FIELDS}


def action_from_completion(text: str) -> ChargebackOpsAction | None:
    """Parse a completion and build a validated :class:`ChargebackOpsAction`."""

    parsed = parse_completion(text)
    if parsed is None or "action_type" not in parsed:
        return None
    try:
        return ChargebackOpsAction(**parsed)
    except Exception:
        return None


__all__ = [
    "action_from_completion",
    "build_prompt",
    "parse_completion",
]