from __future__ import annotations

from pathlib import Path
from typing import Any

import yaml

from engine.models import (
    ArtifactSpec,
    BudgetSpec,
    ConstraintSpec,
    LoggingSpec,
    MutationSpec,
    ObjectiveSpec,
    PolicySpec,
    RunnerSpec,
    ScorerParseSpec,
    ScorerSpec,
    TaskSpec,
)


class TaskValidationError(ValueError):
    pass


def _require_mapping(value: Any, path: str) -> dict[str, Any]:
    if not isinstance(value, dict):
        raise TaskValidationError(f"{path} must be a mapping")
    return value


def _require_list(value: Any, path: str) -> list[Any]:
    if not isinstance(value, list):
        raise TaskValidationError(f"{path} must be a list")
    return value


def _require_value(mapping: dict[str, Any], key: str) -> Any:
    if key not in mapping:
        raise TaskValidationError(f"missing required field: {key}")
    return mapping[key]


def load_task(task_path: Path) -> TaskSpec:
    def _require_str(mapping: dict[str, Any], key: str, path: str) -> str:
        value = _require_value(mapping, key)
        if not isinstance(value, str):
            raise TaskValidationError(f"{path}.{key} must be a string")
        return value

    def _require_int(mapping: dict[str, Any], key: str, path: str) -> int:
        value = _require_value(mapping, key)
        if not isinstance(value, int) or isinstance(value, bool):
            raise TaskValidationError(f"{path}.{key} must be an integer")
        return value

    def _require_str_list(mapping: dict[str, Any], key: str, path: str) -> list[str]:
        items = _require_list(_require_value(mapping, key), f"{path}.{key}")
        result: list[str] = []
        for index, item in enumerate(items):
            if not isinstance(item, str):
                raise TaskValidationError(f"{path}.{key}[{index}] must be a string")
            result.append(item)
        return result

    def _require_tie_breakers(mapping: dict[str, Any], key: str, path: str) -> list[dict[str, str]]:
        items = _require_list(_require_value(mapping, key), f"{path}.{key}")
        result: list[dict[str, str]] = []
        for index, item in enumerate(items):
            entry = _require_mapping(item, f"{path}.{key}[{index}]")
            result.append({str(k): str(v) for k, v in entry.items()})
        return result

    task_data = yaml.safe_load(task_path.read_text(encoding="utf-8"))
    root = _require_mapping(task_data, "task")

    task_id = _require_str(root, "id", "task")
    description = _require_str(root, "description", "task")

    artifacts_data = _require_mapping(_require_value(root, "artifacts"), "task.artifacts")
    artifacts = ArtifactSpec(
        include=_require_str_list(artifacts_data, "include", "task.artifacts"),
        exclude=_require_str_list(artifacts_data, "exclude", "task.artifacts"),
        max_files_per_iteration=_require_int(artifacts_data, "max_files_per_iteration", "task.artifacts"),
    )

    mutation_data = _require_mapping(_require_value(root, "mutation"), "task.mutation")
    mutation = MutationSpec(
        mode=_require_str(mutation_data, "mode", "task.mutation"),
        allowed_file_types=_require_str_list(mutation_data, "allowed_file_types", "task.mutation"),
        max_changed_lines=_require_int(mutation_data, "max_changed_lines", "task.mutation"),
    )

    runner_data = _require_mapping(_require_value(root, "runner"), "task.runner")
    runner = RunnerSpec(
        command=_require_str(runner_data, "command", "task.runner"),
        cwd=_require_str(runner_data, "cwd", "task.runner"),
        timeout_seconds=_require_int(runner_data, "timeout_seconds", "task.runner"),
    )

    scorer_data = _require_mapping(_require_value(root, "scorer"), "task.scorer")
    scorer_parse_data = _require_mapping(_require_value(scorer_data, "parse"), "task.scorer.parse")
    scorer = ScorerSpec(
        type=_require_str(scorer_data, "type", "task.scorer"),
        command=_require_str(scorer_data, "command", "task.scorer"),
        parse=ScorerParseSpec(
            format=_require_str(scorer_parse_data, "format", "task.scorer.parse"),
            score_field=_require_str(scorer_parse_data, "score_field", "task.scorer.parse"),
            metrics_field=_require_str(scorer_parse_data, "metrics_field", "task.scorer.parse"),
        ),
    )

    objective_data = _require_mapping(_require_value(root, "objective"), "task.objective")
    direction = _require_str(objective_data, "direction", "task.objective")
    if direction not in {"maximize", "minimize"}:
        raise TaskValidationError("task.objective.direction must be maximize or minimize")
    objective = ObjectiveSpec(
        primary_metric=_require_str(objective_data, "primary_metric", "task.objective"),
        direction=direction,
    )

    constraints_data = _require_list(_require_value(root, "constraints"), "task.constraints")
    constraints = []
    for index, item in enumerate(constraints_data):
        constraint_data = _require_mapping(item, f"task.constraints[{index}]")
        constraints.append(
            ConstraintSpec(
                metric=_require_str(constraint_data, "metric", f"task.constraints[{index}]"),
                op=_require_str(constraint_data, "op", f"task.constraints[{index}]"),
                value=_require_value(constraint_data, "value"),
            )
        )

    policy_data = _require_mapping(_require_value(root, "policy"), "task.policy")
    policy = PolicySpec(
        keep_if=_require_str(policy_data, "keep_if", "task.policy"),
        tie_breakers=_require_tie_breakers(policy_data, "tie_breakers", "task.policy"),
        on_failure=_require_str(policy_data, "on_failure", "task.policy"),
    )

    budget_data = _require_mapping(_require_value(root, "budget"), "task.budget")
    budget = BudgetSpec(
        max_iterations=_require_int(budget_data, "max_iterations", "task.budget"),
        max_failures=_require_int(budget_data, "max_failures", "task.budget"),
    )

    logging_data = _require_mapping(_require_value(root, "logging"), "task.logging")
    logging = LoggingSpec(
        results_file=_require_str(logging_data, "results_file", "task.logging"),
        candidate_dir=_require_str(logging_data, "candidate_dir", "task.logging"),
    )

    return TaskSpec(
        id=task_id,
        description=description,
        artifacts=artifacts,
        mutation=mutation,
        runner=runner,
        scorer=scorer,
        objective=objective,
        constraints=constraints,
        policy=policy,
        budget=budget,
        logging=logging,
        root_dir=task_path.parent,
    )