"""Pure functions for guessing how a raw HF dataset row maps onto a
(system, user, assistant) triplet, based on a handful of sample rows.

Nothing here touches the network - callers fetch sample rows separately
(see hf_inspect.py) and hand them in. That split is deliberate:
this logic is the part worth unit-testing on its own, against fixed
sample data, without spinning up HTTP calls every time.
"""
from __future__ import annotations

from typing import Optional

from models import FieldMapping

# Known flat-column name pairs, checked case-insensitively against the
# dataset's actual column names. Ordered roughly by how common they are
# across instruction-tuning datasets on the Hub.
_KNOWN_FLAT_PAIRS = [
    ("instruction", "output"),
    ("instruction", "response"),
    ("prompt", "chosen"),
    ("prompt", "completion"),
    ("query", "answer"),
    ("query", "answers"),
    ("question", "solution"),
    ("question", "answer"),
    ("input", "output"),
]

# Known (human_tag, assistant_tag) pairs for the role key inside a
# conversation-list column (e.g. ShareGPT's "from", OpenAI's "role").
_KNOWN_TAG_PAIRS = [
    ("human", "gpt"),
    ("user", "assistant"),
    ("user", "model"),
]


def _is_list_of_dicts_column(values: list) -> bool:
    for v in values:
        if not isinstance(v, list) or not v:
            return False
        if not all(isinstance(item, dict) for item in v):
            return False
    return True


def detect_flat_pair(columns: list) -> Optional[FieldMapping]:
    """Match the dataset's column names against known flat pairs."""
    lower_to_actual = {c.lower(): c for c in columns}
    for user_name, asst_name in _KNOWN_FLAT_PAIRS:
        if user_name in lower_to_actual and asst_name in lower_to_actual:
            return FieldMapping(
                kind="flat_pair",
                config={
                    "user_field": lower_to_actual[user_name],
                    "assistant_field": lower_to_actual[asst_name],
                },
            )
    return None


def _guess_role_and_content_key(values: list, keys: set):
    """Pick which key behaves like a role tag (short, low-cardinality
    strings) and which behaves like free-text content (longer, varied).
    Returns (role_key, content_key), or (None, None) if it can't tell.
    """
    candidates = list(keys)
    if len(candidates) < 2:
        return None, None

    avg_lengths = {}
    distinct_counts = {}
    for key in candidates:
        all_values = [item.get(key) for value_list in values for item in value_list if key in item]
        string_values = [v for v in all_values if isinstance(v, str)]
        if not string_values:
            avg_lengths[key] = float("inf")
            distinct_counts[key] = len(set(map(str, all_values)))
            continue
        avg_lengths[key] = sum(len(v) for v in string_values) / len(string_values)
        distinct_counts[key] = len(set(string_values))

    role_key = min(candidates, key=lambda k: (distinct_counts[k], avg_lengths[k]))
    remaining = [k for k in candidates if k != role_key]
    content_key = max(remaining, key=lambda k: avg_lengths[k])
    return role_key, content_key


def detect_list_column(sample_rows: list) -> Optional[dict]:
    """Find a column whose values look like a conversation list (ShareGPT's
    `conversations`, OpenAI's `messages`, or anything shaped like them) and
    figure out which sub-key is the role and which is the content.

    Returns a dict describing what was found - used both to try full
    auto-detection and to pre-fill the manual-mapping UI when auto-detect
    isn't confident. Returns None if nothing list-shaped turned up.
    """
    if not sample_rows:
        return None

    columns = list(sample_rows[0].keys())
    for col in columns:
        values = [row.get(col) for row in sample_rows]
        if not _is_list_of_dicts_column(values):
            continue

        common_keys = None
        for value_list in values:
            for item in value_list:
                keys = set(item.keys())
                common_keys = keys if common_keys is None else (common_keys & keys)
        if not common_keys or len(common_keys) < 2:
            continue

        role_key, content_key = _guess_role_and_content_key(values, common_keys)
        if role_key is None:
            continue

        tag_values = sorted(
            {
                item.get(role_key)
                for value_list in values
                for item in value_list
                if role_key in item and item.get(role_key) is not None
            }
        )

        return {
            "list_field": col,
            "role_key": role_key,
            "content_key": content_key,
            "tag_values": tag_values,
        }

    return None


def detect_conversation_list(sample_rows: list) -> Optional[FieldMapping]:
    """Full auto-detect for conversation-list columns. Only returns a
    mapping when both the human and assistant tags are recognized -
    anything less certain falls through to manual mapping on purpose.
    """
    found = detect_list_column(sample_rows)
    if not found:
        return None

    tags_lower = {str(t).lower(): t for t in found["tag_values"] if t is not None}
    for human_tag, gpt_tag in _KNOWN_TAG_PAIRS:
        if human_tag in tags_lower and gpt_tag in tags_lower:
            return FieldMapping(
                kind="conversation_list",
                config={
                    "list_field": found["list_field"],
                    "role_key": found["role_key"],
                    "content_key": found["content_key"],
                    "human_tag": tags_lower[human_tag],
                    "gpt_tag": tags_lower[gpt_tag],
                },
            )
    return None


def auto_detect(sample_rows: list) -> Optional[FieldMapping]:
    """Try every detector in order of confidence. Returns None if nothing
    lands cleanly - caller should fall back to manual mapping.
    """
    if not sample_rows:
        return None
    mapping = detect_conversation_list(sample_rows)
    if mapping:
        return mapping
    columns = list(sample_rows[0].keys())
    return detect_flat_pair(columns)