"""Pure helpers shared across API handlers.

Ported from miru-tracer's ``ui/helpers.py`` and ``ui/lens_common.py`` minus
everything Gradio-specific. The frontend sends internal keys directly
("completion"/"chat"/"raw", "auto"/"off"/"prefill", "logit"/"jacobian"/"diff",
"adjusted"/"raw", "text"/"id") so no label mapping happens server-side.
"""

from __future__ import annotations

import json

from miru_tracer.core.interventions import Intervention
from miru_tracer.core.sampling import SamplingParams

LENS_MODES = ("logit", "jacobian", "diff")
GENERATION_MODES = ("completion", "chat", "raw")
THINKING_MODES = ("auto", "off", "prefill")


def ui_sampling_params(strategy, temperature, top_k, top_p) -> SamplingParams:
    """Build SamplingParams from raw widget values (clamped, not raising)."""
    return SamplingParams(
        strategy=strategy,
        temperature=float(temperature),
        top_k=int(top_k or 0),
        top_p=min(max(float(top_p), 1e-3), 1.0),
    )


class ChatValidationError(ValueError):
    """The chat JSON the user entered is not a valid message list."""


def parse_chat_messages(text: str) -> list[dict[str, str]]:
    """Parse and validate the chat-messages JSON from the UI.

    Raises:
        ChatValidationError: with a user-presentable message.
    """
    try:
        messages = json.loads(text)
    except json.JSONDecodeError as e:
        raise ChatValidationError(f"Invalid JSON: {e}") from e
    if not isinstance(messages, list) or not messages:
        raise ChatValidationError("Chat messages must be a non-empty JSON array")
    for message in messages:
        if (
            not isinstance(message, dict)
            or "role" not in message
            or "content" not in message
        ):
            raise ChatValidationError(
                "Each message must have 'role' and 'content' fields"
            )
    return messages


def token_ref_to_id(ref: str, tokenizer, mode: str) -> int:
    """Resolve a user token reference under an explicit interpretation mode.

    ``mode == "id"``: parse a numeric token id; surrounding whitespace is
    tolerated and non-numeric input is rejected. ``mode == "text"``: encode
    the text verbatim — leading/trailing whitespace is significant (" Paris"
    and "Paris" are different BPE tokens) and digits are NEVER treated as an
    id — returning the first token id.

    Raises:
        ValueError: empty ref, unencodable text, non-numeric id, or an
        out-of-range id.
    """
    if mode == "id":
        stripped = ref.strip()
        if not stripped:
            raise ValueError("Empty token reference")
        if not stripped.lstrip("-").isdigit():
            raise ValueError(f"Not a numeric token id: {ref!r}")
        token_id = int(stripped)
        if not 0 <= token_id < len(tokenizer):
            raise ValueError(
                f"Token id {token_id} out of range (vocab size {len(tokenizer)})"
            )
        return token_id
    if not ref.strip():
        raise ValueError("Empty token reference")
    encoded = tokenizer.encode(ref, add_special_tokens=False)
    if not encoded:
        raise ValueError(f"Could not tokenize {ref!r}")
    return int(encoded[0])


def parse_layer_refs(text: str) -> list[int]:
    """Comma-separated layers and inclusive ranges -> unique sorted layer list.

    E.g. ``"11, 12-15, 18"`` -> ``[11, 12, 13, 14, 15, 18]``.

    Raises:
        ValueError: empty input, malformed entry, or a descending range.
    """
    layers: list[int] = []
    for part in (str(text) if text is not None else "").split(","):
        part = part.strip()
        if not part:
            continue
        lo, sep, hi = part.partition("-")
        lo, hi = lo.strip(), hi.strip()
        if not lo.isdigit() or (sep and not hi.isdigit()):
            raise ValueError(
                f"Bad layer reference {part!r}: use a number or range like 12-15"
            )
        start, end = int(lo), int(hi) if sep else int(lo)
        if end < start:
            raise ValueError(f"Descending layer range {part!r}")
        layers.extend(range(start, end + 1))
    if not layers:
        raise ValueError("Empty layer reference")
    return sorted(set(layers))


def layer_selection(n_layers: int, start, end, stride) -> list[int]:
    """Resolve UI layer-range inputs into a concrete layer list.

    ``end`` is inclusive; -1 (or blank) means the final layer. The final
    selected layer is always included even if the stride skips it.
    """
    start = int(start) if start is not None else 0
    end = int(end) if end is not None else -1
    stride = max(int(stride) if stride else 1, 1)
    if end < 0:
        end = n_layers - 1
    start = max(0, min(start, n_layers - 1))
    end = max(start, min(end, n_layers - 1))
    layers = list(range(start, end + 1, stride))
    if layers[-1] != end:
        layers.append(end)
    return layers


# ------------------------------------------------------------- interventions


def intervention_signature(iv: Intervention) -> tuple:
    """Stable key for deciding whether two UI interventions are duplicates."""
    if iv.kind == "steer":
        return (iv.kind, iv.layer, iv.token_id, float(iv.strength), iv.basis)
    if iv.kind == "swap":
        return (iv.kind, iv.layer, iv.token_id, iv.token_id_to, iv.basis)
    return (iv.kind, iv.layer, iv.token_id, iv.basis)


def add_unique_intervention_rows(rows: list, candidates: list) -> tuple[list, list, int]:
    """Append candidates whose effective intervention parameters are new."""
    updated = list(rows or [])
    seen = {intervention_signature(row["intervention"]) for row in updated}
    added = []
    skipped = 0
    for row in candidates:
        signature = intervention_signature(row["intervention"])
        if signature in seen:
            skipped += 1
            continue
        updated.append(row)
        added.append(row)
        seen.add(signature)
    return updated, added, skipped


def enabled_interventions(rows: list) -> list[Intervention]:
    return [row["intervention"] for row in rows or [] if row.get("enabled", True)]


def describe_with_basis(iv: Intervention, tokenizer=None) -> str:
    """Human description of an intervention with its basis appended."""
    return f"{iv.describe(tokenizer)} ({iv.basis})"


def intervened_layer_titles(
    interventions: list[Intervention], tokenizer=None
) -> dict[int, str]:
    """Map each edited layer to a ``'; '``-joined description of its edits."""
    titles: dict[int, str] = {}
    for iv in interventions:
        desc = describe_with_basis(iv, tokenizer)
        titles[iv.layer] = f"{titles[iv.layer]}; {desc}" if iv.layer in titles else desc
    return titles


def interventions_summary(
    interventions: list[Intervention], tokenizer=None, *, limit: int = 4
) -> str:
    """One-line summary of the active interventions for the status area."""
    parts = [describe_with_basis(iv, tokenizer) for iv in interventions[:limit]]
    if len(interventions) > limit:
        parts.append(f"+{len(interventions) - limit} more")
    return "; ".join(parts)


def intervention_visibility_warning(
    interventions: list[Intervention], mode: str, n_layers: int, tokenizer=None
) -> str | None:
    """Warn when an edit's basis differs from the current lens view mode.

    A jacobian-basis edit moves the residual along pre-transport directions
    (``J_ℓ v = û_t``), visible under the Jacobian lens but nearly invisible
    under the Logit lens — and vice versa. The final layer is basis-independent
    (both bases use ``û_t`` directly), and Diff renders both readouts, so
    neither triggers a warning. For a fixed ``mode`` at most one basis can
    mismatch, so this returns a single line (or None).
    """
    if mode == "diff":
        return None
    final = n_layers - 1
    mismatched = [iv for iv in interventions if iv.layer != final and iv.basis != mode]
    if not mismatched:
        return None
    basis = mismatched[0].basis  # only one basis can mismatch a given mode
    shown = "; ".join(iv.describe(tokenizer) for iv in mismatched[:3])
    if len(mismatched) > 3:
        shown += f" (+{len(mismatched) - 3} more)"
    verb = "uses" if len(mismatched) == 1 else "use"
    pronoun = "its" if len(mismatched) == 1 else "their"
    want = "Jacobian" if basis == "jacobian" else "Logit"
    return (
        f"⚠ {shown} {verb} {basis} basis — switch Lens to {want} (or Diff) "
        f"to see {pronoun} effect in the readouts."
    )