from __future__ import annotations

from dataclasses import dataclass
from typing import Literal

from core_dsl import WorkflowDefinition, parse_workflow_definition
from core_shared import JSONValue
from pydantic import ValidationError

DiagnosticSeverity = Literal["error", "warning", "info"]


@dataclass(frozen=True)
class WorkflowDiagnostic:
    severity: DiagnosticSeverity
    code: str
    message: str
    node_id: str | None = None
    edge_index: int | None = None


@dataclass(frozen=True)
class WorkflowNodeInspection:
    id: str
    type: str
    name: str | None
    incoming_count: int
    outgoing_count: int
    reachable: bool


@dataclass(frozen=True)
class WorkflowEdgeInspection:
    source: str
    target: str
    condition: str | None
    valid_source: bool
    valid_target: bool


@dataclass(frozen=True)
class WorkflowDebugStep:
    step_index: int
    node_id: str
    node_type: str
    name: str | None
    next_node_ids: list[str]


@dataclass(frozen=True)
class WorkflowInspection:
    valid: bool
    diagnostics: list[WorkflowDiagnostic]
    workflow: WorkflowDefinition | None
    nodes: list[WorkflowNodeInspection]
    edges: list[WorkflowEdgeInspection]
    entry_node_ids: list[str]
    terminal_node_ids: list[str]
    isolated_node_ids: list[str]
    unreachable_node_ids: list[str]
    cycle_detected: bool


@dataclass(frozen=True)
class WorkflowDebugPlan:
    inspection: WorkflowInspection
    execution_preview: list[WorkflowDebugStep]
    max_preview_steps: int
    truncated: bool


def inspect_workflow_dsl(payload: dict[str, JSONValue] | None) -> WorkflowInspection:
    if payload is None:
        return WorkflowInspection(
            valid=False,
            diagnostics=[
                WorkflowDiagnostic(
                    severity="error",
                    code="dsl.required",
                    message="workflow dsl_json is required")
            ],
            workflow=None,
            nodes=[],
            edges=[],
            entry_node_ids=[],
            terminal_node_ids=[],
            isolated_node_ids=[],
            unreachable_node_ids=[],
            cycle_detected=False)

    try:
        workflow = parse_workflow_definition(payload)
    except ValidationError as exc:
        return WorkflowInspection(
            valid=False,
            diagnostics=[
                WorkflowDiagnostic(
                    severity="error",
                    code="dsl.schema_invalid",
                    message=str(exc))
            ],
            workflow=None,
            nodes=[],
            edges=[],
            entry_node_ids=[],
            terminal_node_ids=[],
            isolated_node_ids=[],
            unreachable_node_ids=[],
            cycle_detected=False)

    if workflow is None:
        return WorkflowInspection(
            valid=False,
            diagnostics=[
                WorkflowDiagnostic(
                    severity="error",
                    code="dsl.required",
                    message="workflow dsl_json is required")
            ],
            workflow=None,
            nodes=[],
            edges=[],
            entry_node_ids=[],
            terminal_node_ids=[],
            isolated_node_ids=[],
            unreachable_node_ids=[],
            cycle_detected=False)

    diagnostics: list[WorkflowDiagnostic] = []
    node_ids = [node.id for node in workflow.nodes]
    node_id_set = set(node_ids)
    duplicate_node_ids = sorted({node_id for node_id in node_ids if node_ids.count(node_id) > 1})
    for node_id in duplicate_node_ids:
        diagnostics.append(
            WorkflowDiagnostic(
                severity="error",
                code="node.duplicate_id",
                message=f"duplicate node id: {node_id}",
                node_id=node_id)
        )

    incoming_counts = {node_id: 0 for node_id in node_ids}
    outgoing_counts = {node_id: 0 for node_id in node_ids}
    adjacency: dict[str, list[str]] = {node_id: [] for node_id in node_ids}
    edge_inspections: list[WorkflowEdgeInspection] = []

    for edge_index, edge in enumerate(workflow.edges):
        valid_source = edge.source in node_id_set
        valid_target = edge.target in node_id_set
        edge_inspections.append(
            WorkflowEdgeInspection(
                source=edge.source,
                target=edge.target,
                condition=edge.condition,
                valid_source=valid_source,
                valid_target=valid_target)
        )
        if not valid_source:
            diagnostics.append(
                WorkflowDiagnostic(
                    severity="error",
                    code="edge.source_missing",
                    message=f"edge source node does not exist: {edge.source}",
                    node_id=edge.source,
                    edge_index=edge_index)
            )
        if not valid_target:
            diagnostics.append(
                WorkflowDiagnostic(
                    severity="error",
                    code="edge.target_missing",
                    message=f"edge target node does not exist: {edge.target}",
                    node_id=edge.target,
                    edge_index=edge_index)
            )
        if valid_source and valid_target:
            outgoing_counts[edge.source] = outgoing_counts.get(edge.source, 0) + 1
            incoming_counts[edge.target] = incoming_counts.get(edge.target, 0) + 1
            adjacency.setdefault(edge.source, []).append(edge.target)

    if not workflow.nodes:
        diagnostics.append(
            WorkflowDiagnostic(
                severity="error",
                code="workflow.nodes_required",
                message="workflow must contain at least one node")
        )

    entry_node_ids = [node_id for node_id in node_ids if incoming_counts.get(node_id, 0) == 0]
    terminal_node_ids = [node_id for node_id in node_ids if outgoing_counts.get(node_id, 0) == 0]
    isolated_node_ids = [
        node_id
        for node_id in node_ids
        if incoming_counts.get(node_id, 0) == 0 and outgoing_counts.get(node_id, 0) == 0
    ]

    if len(entry_node_ids) > 1:
        diagnostics.append(
            WorkflowDiagnostic(
                severity="warning",
                code="workflow.multiple_entry_nodes",
                message=f"workflow has multiple entry nodes: {', '.join(entry_node_ids)}")
        )
    if not terminal_node_ids and workflow.nodes:
        diagnostics.append(
            WorkflowDiagnostic(
                severity="warning",
                code="workflow.no_terminal_node",
                message="workflow has no terminal node")
        )

    reachable_node_ids = _find_reachable_nodes(entry_node_ids, adjacency)
    unreachable_node_ids = [node_id for node_id in node_ids if node_id not in reachable_node_ids]
    for node_id in unreachable_node_ids:
        diagnostics.append(
            WorkflowDiagnostic(
                severity="warning",
                code="node.unreachable",
                message=f"node is not reachable from an entry node: {node_id}",
                node_id=node_id)
        )

    cycle_detected = _detect_cycle(node_ids, adjacency)
    if cycle_detected:
        diagnostics.append(
            WorkflowDiagnostic(
                severity="warning",
                code="workflow.cycle_detected",
                message="workflow graph contains a cycle; debugger preview may be truncated")
        )

    node_inspections = [
        WorkflowNodeInspection(
            id=node.id,
            type=node.type,
            name=node.name,
            incoming_count=incoming_counts.get(node.id, 0),
            outgoing_count=outgoing_counts.get(node.id, 0),
            reachable=node.id in reachable_node_ids)
        for node in workflow.nodes
    ]
    valid = not any(item.severity == "error" for item in diagnostics)
    return WorkflowInspection(
        valid=valid,
        diagnostics=diagnostics,
        workflow=workflow,
        nodes=node_inspections,
        edges=edge_inspections,
        entry_node_ids=entry_node_ids,
        terminal_node_ids=terminal_node_ids,
        isolated_node_ids=isolated_node_ids,
        unreachable_node_ids=unreachable_node_ids,
        cycle_detected=cycle_detected)


def build_debug_plan(
    payload: dict[str, JSONValue] | None,
    *,
    max_preview_steps: int = 50) -> WorkflowDebugPlan:
    inspection = inspect_workflow_dsl(payload)
    workflow = inspection.workflow
    if workflow is None or not inspection.valid:
        return WorkflowDebugPlan(
            inspection=inspection,
            execution_preview=[],
            max_preview_steps=max_preview_steps,
            truncated=False)

    node_map = {node.id: node for node in workflow.nodes}
    adjacency: dict[str, list[str]] = {node.id: [] for node in workflow.nodes}
    for edge in workflow.edges:
        if edge.source in node_map and edge.target in node_map:
            adjacency.setdefault(edge.source, []).append(edge.target)

    preview: list[WorkflowDebugStep] = []
    queue = list(inspection.entry_node_ids)
    seen_visits: dict[str, int] = {}
    truncated = False

    while queue and len(preview) < max_preview_steps:
        node_id = queue.pop(0)
        node = node_map.get(node_id)
        if node is None:
            continue
        seen_visits[node_id] = seen_visits.get(node_id, 0) + 1
        if seen_visits[node_id] > 1:
            continue
        next_node_ids = adjacency.get(node_id, [])
        preview.append(
            WorkflowDebugStep(
                step_index=len(preview),
                node_id=node.id,
                node_type=node.type,
                name=node.name,
                next_node_ids=next_node_ids)
        )
        queue.extend(next_node_ids)

    if queue:
        truncated = True

    return WorkflowDebugPlan(
        inspection=inspection,
        execution_preview=preview,
        max_preview_steps=max_preview_steps,
        truncated=truncated)


def _find_reachable_nodes(entry_node_ids: list[str], adjacency: dict[str, list[str]]) -> set[str]:
    reachable: set[str] = set()
    stack = list(entry_node_ids)
    while stack:
        node_id = stack.pop()
        if node_id in reachable:
            continue
        reachable.add(node_id)
        stack.extend(adjacency.get(node_id, []))
    return reachable


def _detect_cycle(node_ids: list[str], adjacency: dict[str, list[str]]) -> bool:
    visiting: set[str] = set()
    visited: set[str] = set()

    def visit(node_id: str) -> bool:
        if node_id in visiting:
            return True
        if node_id in visited:
            return False
        visiting.add(node_id)
        for next_node_id in adjacency.get(node_id, []):
            if visit(next_node_id):
                return True
        visiting.remove(node_id)
        visited.add(node_id)
        return False

    return any(visit(node_id) for node_id in node_ids)