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from __future__ import annotations

import copy
import re
from collections.abc import Mapping
from pathlib import Path
from typing import Any

from pydantic import ValidationError

from app.core.exceptions import TemplateValidationError
from app.templates.models import PreparedTemplate, ResolvedPipelineStep
from app.templates.schema import (
    OutputDefinition,
    ParameterDefinition,
    ParameterType,
    TemplateDefinition,
)

VARIABLE_PATTERN = re.compile(r"{{\s*([a-z][a-z0-9_]*)\s*}}")
EXACT_VARIABLE_PATTERN = re.compile(r"^\s*{{\s*([a-z][a-z0-9_]*)\s*}}\s*$")
INPUT_SELECTOR_PATTERN = re.compile(
    r"^(?:current|original|originals|original:[0-9]+|artifact:[a-z][a-z0-9_]*)$"
)


class TemplateValidator:
    """Validates template definitions, parameters, variables, and operation names."""

    def __init__(self, supported_operations: set[str]) -> None:
        self.supported_operations = frozenset(supported_operations)

    def validate_definition(self, template: TemplateDefinition) -> None:
        """Fail if a parsed YAML definition is unsafe or internally inconsistent."""
        for name, definition in template.parameters.items():
            if definition.has_default:
                self._validate_value(name, definition.default, definition)
        known_parameters = set(template.parameters)
        saved_artifacts: set[str] = set()
        for index, step in enumerate(template.pipeline):
            if step.operation not in self.supported_operations:
                raise TemplateValidationError(
                    f"Template '{template.id}' uses unsupported operation '{step.operation}'",
                    details={"step": index, "operation": step.operation},
                )
            referenced = self._variables(step.when) | self._variables(step.operation_parameters())
            self._validate_variables(referenced, known_parameters, template.id, index)
            for parameter in referenced:
                definition = template.parameters.get(parameter)
                if definition and not definition.required and not definition.has_default:
                    raise TemplateValidationError(
                        f"Template '{template.id}' references optional parameter '{parameter}' without a default",
                        details={"step": index},
                    )
            for selector in step.inputs or []:
                if not INPUT_SELECTOR_PATTERN.fullmatch(selector):
                    raise TemplateValidationError(
                        f"Template '{template.id}' has invalid input selector '{selector}'",
                        details={"step": index},
                    )
                if selector.startswith("artifact:"):
                    artifact = selector.split(":", 1)[1]
                    if artifact not in saved_artifacts:
                        raise TemplateValidationError(
                            f"Template '{template.id}' references artifact '{artifact}' before it is saved",
                            details={"step": index},
                        )
            if step.save_as:
                if step.save_as in saved_artifacts:
                    raise TemplateValidationError(
                        f"Template '{template.id}' saves duplicate artifact '{step.save_as}'"
                    )
                saved_artifacts.add(step.save_as)
        output_variables = self._variables(template.output.model_dump())
        self._validate_variables(output_variables, known_parameters, template.id, -1)
        for parameter in output_variables:
            definition = template.parameters.get(parameter)
            if definition and not definition.required and not definition.has_default:
                raise TemplateValidationError(
                    f"Template '{template.id}' output references optional parameter '{parameter}' without a default"
                )
        if "{{" not in template.output.format:
            output_format = template.output.format.lower().lstrip(".")
            if output_format not in template.supported_outputs:
                raise TemplateValidationError(
                    f"Template '{template.id}' output format is not declared in supported_outputs"
                )

    def prepare(
        self, template: TemplateDefinition, supplied: Mapping[str, Any] | None
    ) -> PreparedTemplate:
        """Resolve validated runtime parameters and render a safe pipeline."""
        parameters = self.resolve_parameters(template, supplied)
        steps: list[ResolvedPipelineStep] = []
        for step in template.pipeline:
            rendered_when = self._substitute(step.when, parameters)
            if not isinstance(rendered_when, bool):
                raise TemplateValidationError(
                    f"Template '{template.id}' step condition must resolve to a boolean"
                )
            rendered_parameters = self._substitute(step.operation_parameters(), parameters)
            steps.append(
                ResolvedPipelineStep(
                    operation=step.operation,
                    parameters=rendered_parameters,
                    enabled=rendered_when,
                    inputs=step.inputs,
                    save_as=step.save_as,
                )
            )
        output_data = self._substitute(template.output.model_dump(), parameters)
        try:
            output = OutputDefinition.model_validate(output_data)
        except ValidationError as exc:
            raise TemplateValidationError(
                f"Template '{template.id}' output did not resolve to a valid contract"
            ) from exc
        output_format = output.format.strip().lower().lstrip(".")
        if not re.fullmatch(r"[a-z0-9][a-z0-9_+-]*", output_format):
            raise TemplateValidationError(f"Template '{template.id}' output format is invalid")
        if output_format not in template.supported_outputs:
            raise TemplateValidationError(
                f"Template '{template.id}' output format is not declared in supported_outputs"
            )
        if output.filename:
            filename = output.filename
            if Path(filename).name != filename or len(filename) > 255:
                raise TemplateValidationError(
                    f"Template '{template.id}' output filename must be a safe basename"
                )
        return PreparedTemplate(
            definition=template,
            parameters=parameters,
            pipeline=tuple(steps),
            output=output,
        )

    def resolve_parameters(
        self, template: TemplateDefinition, supplied: Mapping[str, Any] | None
    ) -> dict[str, Any]:
        """Apply defaults and enforce declared parameter names and strict types."""
        provided = dict(supplied or {})
        unknown = sorted(set(provided) - set(template.parameters))
        if unknown:
            raise TemplateValidationError(
                "Unknown template parameter(s)", details={"parameters": unknown}
            )
        resolved: dict[str, Any] = {}
        for name, definition in template.parameters.items():
            if name in provided:
                value = provided[name]
            elif definition.has_default:
                value = copy.deepcopy(definition.default)
            elif definition.required:
                raise TemplateValidationError(f"Required template parameter '{name}' is missing")
            else:
                continue
            self._validate_value(name, value, definition)
            resolved[name] = value
        return resolved

    def _validate_value(self, name: str, value: Any, definition: ParameterDefinition) -> None:
        expected = definition.type
        valid = {
            ParameterType.STRING: isinstance(value, str),
            ParameterType.INTEGER: isinstance(value, int) and not isinstance(value, bool),
            ParameterType.NUMBER: isinstance(value, (int, float)) and not isinstance(value, bool),
            ParameterType.BOOLEAN: isinstance(value, bool),
            ParameterType.ARRAY: isinstance(value, list),
            ParameterType.OBJECT: isinstance(value, dict),
        }[expected]
        if not valid:
            raise TemplateValidationError(f"Template parameter '{name}' must be {expected.value}")
        if definition.enum is not None and value not in definition.enum:
            raise TemplateValidationError(
                f"Template parameter '{name}' must be one of the declared enum values"
            )
        if isinstance(value, (int, float)) and not isinstance(value, bool):
            if definition.minimum is not None and value < definition.minimum:
                raise TemplateValidationError(f"Template parameter '{name}' is below its minimum")
            if definition.maximum is not None and value > definition.maximum:
                raise TemplateValidationError(f"Template parameter '{name}' exceeds its maximum")
        if isinstance(value, (str, list, dict)):
            if definition.min_length is not None and len(value) < definition.min_length:
                raise TemplateValidationError(
                    f"Template parameter '{name}' is shorter than allowed"
                )
            if definition.max_length is not None and len(value) > definition.max_length:
                raise TemplateValidationError(f"Template parameter '{name}' is longer than allowed")

    def _validate_variables(
        self,
        variables: set[str],
        known_parameters: set[str],
        template_id: str,
        step: int,
    ) -> None:
        for variable in variables:
            if variable not in known_parameters:
                raise TemplateValidationError(
                    f"Template '{template_id}' references unknown parameter '{variable}'",
                    details={"step": step},
                )

    def _variables(self, value: Any) -> set[str]:
        if isinstance(value, str):
            remainder = VARIABLE_PATTERN.sub("", value)
            if "{{" in remainder or "}}" in remainder:
                raise TemplateValidationError(
                    "Template variables must use the exact '{{ parameter }}' syntax"
                )
            return set(VARIABLE_PATTERN.findall(value))
        if isinstance(value, dict):
            return (
                set().union(*(self._variables(item) for item in value.values())) if value else set()
            )
        if isinstance(value, list):
            return set().union(*(self._variables(item) for item in value)) if value else set()
        return set()

    def _substitute(self, value: Any, parameters: Mapping[str, Any]) -> Any:
        if isinstance(value, str):
            exact = EXACT_VARIABLE_PATTERN.fullmatch(value)
            if exact:
                name = exact.group(1)
                if name not in parameters:
                    raise TemplateValidationError(
                        f"Template parameter '{name}' has no resolved value"
                    )
                return copy.deepcopy(parameters[name])

            def replace(match: re.Match[str]) -> str:
                name = match.group(1)
                if name not in parameters:
                    raise TemplateValidationError(
                        f"Template parameter '{name}' has no resolved value"
                    )
                replacement = parameters[name]
                if isinstance(replacement, (dict, list)):
                    raise TemplateValidationError(
                        f"Structured parameter '{name}' cannot be embedded in a string"
                    )
                return str(replacement)

            return VARIABLE_PATTERN.sub(replace, value)
        if isinstance(value, dict):
            return {key: self._substitute(item, parameters) for key, item in value.items()}
        if isinstance(value, list):
            return [self._substitute(item, parameters) for item in value]
        return copy.deepcopy(value)