"""spec_builder — derive a ToolSpec from a tool's pydantic InputModel (analytical tools round).

The shipped analytics tools are pure compute functions (`src/tools/analytics/*.py`)
registered as hand-written `ToolSpec` entries (`src/tools/registry.py`). As the new
analytical tools land, each one declares a pydantic **InputModel** whose fields ARE
its call arguments; this module turns that model — plus the three-part description
the Planner reads — into the exact `ToolSpec` shape the registry already uses, so the
model and the registry entry can never drift.

Why not a base class (decided with the agent team): the tools STAY pure functions —
the repo's deliberate "compute-only, easy to unit-test" design (see the STATUS note
in `analytics/temporal.py`). This helper is the entire "framework": one function to
build the registry spec from a model, one to compose the description string. A tool
inherits from nothing.

Contract kept byte-compatible with the hand-written specs (`src/tools/contracts.py`):

    input_schema = {"required": [...], "properties": {arg: {"type": ...}}}

The planner validator (Check 8a) reads `required` (presence-only) and treats
`properties` as prompt DOCUMENTATION, not a runtime type check (see the ToolSpec
docstring). pydantic's `model_json_schema()` emits a richer schema (nested `$defs`,
`anyOf` for optionals, per-field `title`); `input_schema_from_model` SIMPLIFIES it to
the shape above — one primary JSON type per field, plus any `Field(description=...)`
carried through so the per-input descriptions the tool team asked for reach the
planner prompt.
"""

from __future__ import annotations

from typing import Any

from pydantic import BaseModel

from src.tools.contracts import ToolSpec

_NULL = "null"


def _primary_type(prop: dict[str, Any]) -> str | None:
    """The single JSON type to advertise for one field.

    Handles the three shapes pydantic emits: a direct ``{"type": ...}``; an
    optional/union ``anyOf``/``oneOf`` (take the first non-null member); and a
    ``$ref`` to a nested model or enum (no primitive type — return None so the
    caller omits ``type`` rather than inventing one).
    """
    t = prop.get("type")
    if isinstance(t, str):
        return t
    for union_key in ("anyOf", "oneOf"):
        for sub in prop.get(union_key, []):
            sub_t = sub.get("type")
            if isinstance(sub_t, str) and sub_t != _NULL:
                return sub_t
    return None


def _simplify(prop: dict[str, Any]) -> dict[str, Any]:
    """One pydantic property schema -> the lightweight registry property dict."""
    simplified: dict[str, Any] = {}
    primary = _primary_type(prop)
    if primary is not None:
        simplified["type"] = primary
    description = prop.get("description")
    if description:
        simplified["description"] = description
    return simplified


def input_schema_from_model(model: type[BaseModel]) -> dict[str, Any]:
    """Build the registry ``input_schema`` ({required, properties}) from a model.

    ``required`` mirrors the model's no-default fields; ``properties`` is one
    simplified entry per field (see `_simplify`). Property ORDER follows the
    model's field declaration order, so keep ``data`` (the Pattern A placeholder)
    first in every InputModel for readable planner prompts.
    """
    schema = model.model_json_schema()
    properties = schema.get("properties", {})
    return {
        "required": list(schema.get("required", [])),
        "properties": {name: _simplify(prop) for name, prop in properties.items()},
    }


def spec_from_model(
    *,
    name: str,
    category: str,
    output_kind: str,
    description: str,
    input_model: type[BaseModel],
    phase: str = "P0",
) -> ToolSpec:
    """A `ToolSpec` for a functional analytics tool, with `input_schema` from `input_model`.

    Args:
        name: the `analyze_*` tool name (matches the invoker dispatch key).
        category: dotted registry category, e.g. ``"analytics.timeseries"``.
        output_kind: the `ToolOutput.kind` the compute fn produces.
        description: the prompt-style string the Planner reads — build it with
            `build_description` so every tool follows the same when/when-not/output
            shape.
        input_model: the tool's pydantic InputModel; its fields are the tool args.
        phase: rollout phase (P0/P1/P2), default "P0" to match existing specs.
    """
    return ToolSpec(
        name=name,
        category=category,
        input_schema=input_schema_from_model(input_model),
        output_kind=output_kind,
        description=description,
        phase=phase,
    )


def build_description(
    *,
    summary: str,
    use_when: str,
    dont_use_when: list[str],
    output: str,
    examples: list[str] | None = None,
) -> str:
    """Compose a Planner-facing description in the house format (see visualization.py).

    Encodes the tool team's three required parts — WHEN to use, when NOT to use,
    and what the OUTPUT is — around a one-line summary, matching the existing
    `DESCRIPTION` constants so the planner prompt reads uniformly across old and
    new tools.
    """
    lines = [f"Summary: {summary}", "", f"USE WHEN {use_when}", "", "DON'T USE WHEN:"]
    lines += [f"  - {reason}" for reason in dont_use_when]
    lines += ["", f"OUTPUT: {output}"]
    if examples:  # None or [] -> omit the section
        lines += ["", "Example questions:"]
        lines += [f"  - {q}" for q in examples]
    return "\n".join(lines)