"""Task template library for seeded variant generation (D-029, REQ-3-005).

A `TaskTemplate` binds a competency (D-021-aligned corpus ID), a statement
skeleton with `{slot}` placeholders, typed `ParameterSlot`s, difficulty-
normalization rubric anchors (the expected feature envelope that bounds
variant fairness in the a-5 envelope test — grader-prompt shipment is the
tracked P4 follow-up; grading is variant-blind today), and starter-file
scaffolds served into the sandbox workdir (wired in P6).

Slot sampling is PURE CODE: `random.Random(seed)` over typed slots — fully
reproducible for a given seed, independent of the LLM. The LLM only renders
the seeded slot values into the statement skeleton (D-020 defense).
"""

from __future__ import annotations

import random
import re
from typing import Literal

from pydantic import BaseModel, ConfigDict, Field, field_validator

SlotType = Literal["enum", "int_range", "string_set"]


class ParameterSlot(BaseModel):
    """One typed fill-in for a statement skeleton."""

    model_config = ConfigDict(frozen=True)

    name: str = Field(min_length=1)
    type: SlotType
    values: list[str] = Field(default_factory=list)  # enum/string_set options
    lo: int | None = None  # int_range bounds
    hi: int | None = None

    @field_validator("values")
    @classmethod
    def _values_nonempty_for_enums(cls, v: list[str], info) -> list[str]:
        if info.data.get("type") in ("enum", "string_set") and not v:
            raise ValueError(f"slot {info.data.get('name')!r} needs values")
        return v

    def sample(self, rng: random.Random) -> str | int:
        """Deterministic sample from the seeded RNG. Validated after sampling."""
        if self.type == "enum" or self.type == "string_set":
            return rng.choice(self.values)
        if self.type == "int_range":
            lo = self.lo if self.lo is not None else 0
            hi = self.hi if self.hi is not None else lo
            if hi < lo:
                raise ValueError(f"slot {self.name!r}: hi < lo")
            return rng.randint(lo, hi)
        raise ValueError(f"unsupported slot type: {self.type!r}")

    def validate_value(self, value: str | int) -> bool:
        """Is `value` schema-valid for this slot? (params JSON gate, a-5.)"""
        if self.type in ("enum", "string_set"):
            return isinstance(value, str) and value in self.values
        if self.type == "int_range":
            lo = self.lo if self.lo is not None else 0
            hi = self.hi if self.hi is not None else lo
            return isinstance(value, int) and lo <= value <= hi
        return False


class RubricAnchors(BaseModel):
    """Difficulty-normalization anchors for the grader (a-5).

    Expected FEATURE ENVELOPE (digest-space): the expected effort band
    for this template, so two variants of one template are held to the
    same bar regardless of which slot values a learner drew. The a-5
    envelope test (tests/variants/test_generator.py) binds variants to
    these bands in code. Shipping them into the grader prompt context is
    the P4 must-have follow-up tracked for final review: grading is
    variant-blind in the current wiring (engine.py stamps
    variant_seed=None), so today the anchors gate variant fairness in
    tests only — not yet in the LLM prompt.
    """

    model_config = ConfigDict(frozen=True)

    expected_edit_count_band: tuple[int, int]
    expected_min_test_runs: int
    expected_error_fix_cycles_band: tuple[int, int]
    notes: str = ""


class TaskTemplate(BaseModel):
    """A reusable task shape; variants instantiate it per learner."""

    model_config = ConfigDict(frozen=True)

    id: str = Field(min_length=1)
    competency_id: str = Field(min_length=1)  # D-021 corpus alignment
    title: str
    statement_skeleton: str = Field(min_length=1)  # {slot} placeholders
    slots: list[ParameterSlot] = Field(min_length=1)
    rubric_anchors: RubricAnchors
    starter_files: dict[str, str] = Field(default_factory=dict)  # path -> content
    test_command: str

    @field_validator("statement_skeleton")
    @classmethod
    def _skeleton_placeholders(cls, v: str) -> str:
        if "{" not in v or "}" not in v:
            raise ValueError("statement_skeleton needs at least one {slot}")
        return v

    def render(self, params: dict[str, str | int]) -> str:
        """Fill the skeleton with validated params."""
        for slot in self.slots:
            if slot.name not in params:
                raise ValueError(f"missing param for slot {slot.name!r}")
            if not slot.validate_value(params[slot.name]):
                raise ValueError(f"invalid value for slot {slot.name!r}: {params[slot.name]!r}")
        return self.statement_skeleton.format(**params)

    def sample_params(self, seed: int) -> dict[str, str | int]:
        """Seeded, reproducible, schema-valid slot values (pure code)."""
        rng = random.Random(seed)
        return {slot.name: slot.sample(rng) for slot in self.slots}


# --- Template library (v0.3 initial set) --------------------------------------
# Competency IDs are D-021-aligned with the Python corpus
# (ai_service/corpus/learner_context.py) and the TS mock-data layer
# (packages/mock-data/competency-stacks.ts: deterministic cid() scheme).

TEMPLATES: dict[str, TaskTemplate] = {
    "tpl-llm-judge": TaskTemplate(
        id="tpl-llm-judge",
        competency_id="stack-orchestration-c007",
        title="Build an LLM-as-Judge Evaluator",
        statement_skeleton=(
            "Build a small LLM-as-judge evaluator for {domain} answers. "
            "The judge must score each answer on {criterion} using a 0-4 scale, "
            "return structured JSON, and handle at least {edge_cases} edge-case "
            "answer classes (empty, off-topic, adversarial). Include a tiny "
            "repro test set of at least {test_size} examples and print a summary "
            "table of scores."
        ),
        slots=[
            ParameterSlot(
                name="domain",
                type="enum",
                values=["customer-support", "code-review", "summarization", "tutoring"],
            ),
            ParameterSlot(
                name="criterion",
                type="enum",
                values=["factual-accuracy", "helpfulness", "safety", "completeness"],
            ),
            ParameterSlot(name="edge_cases", type="int_range", lo=2, hi=4),
            ParameterSlot(name="test_size", type="int_range", lo=3, hi=8),
        ],
        rubric_anchors=RubricAnchors(
            expected_edit_count_band=(3, 25),
            expected_min_test_runs=2,
            expected_error_fix_cycles_band=(0, 4),
            notes="Slot draw changes the SCENARIO, not the engineering depth.",
        ),
        starter_files={
            "README.md": (
                "# LLM-as-Judge Evaluator\n\n"
                "Implement `judge.py`:\n"
                "- `score(answer: str) -> dict` — 0-4 on the named criterion\n"
                "- structured JSON output (schema below)\n"
                "- edge-case classes handled explicitly\n"
                "- `pytest` must pass\n"
            ),
            "judge.py": "def score(answer: str) -> dict:\n    raise NotImplementedError\n",
            "test_judge.py": "def test_placeholder():\n    assert True\n",
        },
        test_command="pytest -q",
    ),
    "tpl-guardrail-schema": TaskTemplate(
        id="tpl-guardrail-schema",
        competency_id="stack-orchestration-c008",
        title="Schema Guardrail Pipeline",
        statement_skeleton=(
            "Implement an output-validation guardrail for a model returning "
            "{entity} records. Validate against a typed schema with {field_count} "
            "required fields, coerce or reject {failure_mode} failures, and emit "
            "a fallback response for invalid payloads. Cover with at least "
            "{test_size} unit tests including malformed JSON."
        ),
        slots=[
            ParameterSlot(
                name="entity",
                type="enum",
                values=["user-profile", "job-posting", "candidate", "invoice"],
            ),
            ParameterSlot(
                name="failure_mode",
                type="enum",
                values=["strict-reject", "coerce-when-safe"],
            ),
            ParameterSlot(name="field_count", type="int_range", lo=4, hi=8),
            ParameterSlot(name="test_size", type="int_range", lo=4, hi=10),
        ],
        rubric_anchors=RubricAnchors(
            expected_edit_count_band=(3, 30),
            expected_min_test_runs=2,
            expected_error_fix_cycles_band=(0, 5),
            notes="All slot draws land in the same engineering band.",
        ),
        starter_files={
            "README.md": (
                "# Schema Guardrail\n\nImplement `guardrail.py`:\n"
                "- `validate(payload: dict) -> dict | Fallback`\n"
                "- required-field checks, failure policy, fallback emission\n"
            ),
            "guardrail.py": "def validate(payload: dict):\n    raise NotImplementedError\n",
            "test_guardrail.py": "def test_placeholder():\n    assert True\n",
        },
        test_command="pytest -q",
    ),
    "tpl-rag-chunker": TaskTemplate(
        id="tpl-rag-chunker",
        competency_id="stack-orchestration-c005",
        title="RAG Chunking Strategy",
        statement_skeleton=(
            "Implement a document chunker for {doc_type} retrieval. Support "
            "{strategy} chunking with a target size of ~{chunk_size} tokens, "
            "preserve {invariant} across chunk boundaries, and evaluate overlap "
            "quality with at least {test_size} fixture documents."
        ),
        slots=[
            ParameterSlot(
                name="doc_type",
                type="enum",
                values=["technical-docs", "legal-contracts", "transcripts"],
            ),
            ParameterSlot(
                name="strategy",
                type="enum",
                values=["fixed-window", "semantic-boundary", "hybrid"],
            ),
            ParameterSlot(
                name="invariant",
                type="enum",
                values=["code-block-integrity", "section-headers", "sentence-completeness"],
            ),
            ParameterSlot(name="chunk_size", type="int_range", lo=200, hi=800),
            ParameterSlot(name="test_size", type="int_range", lo=3, hi=6),
        ],
        rubric_anchors=RubricAnchors(
            expected_edit_count_band=(4, 35),
            expected_min_test_runs=2,
            expected_error_fix_cycles_band=(0, 6),
            notes="Strategy draw changes implementation shape, not depth.",
        ),
        starter_files={
            "README.md": (
                "# RAG Chunker\n\nImplement `chunker.py`:\n"
                "- `chunk(text: str) -> list[str]`\n- invariant preserved\n- tests green\n"
            ),
            "chunker.py": "def chunk(text: str) -> list[str]:\n    raise NotImplementedError\n",
            "test_chunker.py": "def test_placeholder():\n    assert True\n",
        },
        test_command="pytest -q",
    ),
}


_KNOWN_COMPETENCY_IDS: set[str] = {
    # D-021: mirrored from ai_service/corpus/learner_context.py — the Python
    # source of truth for stack-orchestration competencies used by v0.2 agents.
    "stack-orchestration-c001",
    "stack-orchestration-c002",
    "stack-orchestration-c003",
    "stack-orchestration-c004",
    "stack-orchestration-c005",
    "stack-orchestration-c007",
    "stack-orchestration-c008",
    "stack-orchestration-c011",
    "stack-designer-c001",
    "stack-designer-c002",
    "stack-safety-c021",
}


def get_template(template_id: str) -> TaskTemplate | None:
    return TEMPLATES.get(template_id)


def template_for_competency(competency_id: str) -> list[TaskTemplate]:
    return [t for t in TEMPLATES.values() if t.competency_id == competency_id]


def validate_competency_binding() -> None:
    """All templates must bind to known D-021 corpus competency IDs."""
    for t in TEMPLATES.values():
        if t.competency_id not in _KNOWN_COMPETENCY_IDS:
            raise ValueError(
                f"template {t.id!r} binds unknown competency {t.competency_id!r}"
            )


def slots_pattern_ok(skeleton: str, slots: list[ParameterSlot]) -> bool:
    """Every {placeholder} in the skeleton has a matching slot and vice versa."""
    placeholders = set(re.findall(r"\{([a-z_][a-z0-9_]*)\}", skeleton))
    slot_names = {s.name for s in slots}
    return placeholders == slot_names