import type { TSchema } from "@alkdev/typebox";
import { KindGuard } from "@alkdev/typebox";
import type { UNode } from "@alkdev/ujsx";
import { createHostRoot } from "@alkdev/ujsx";
import { hasCycle } from "graphology-dag";
import { DirectedGraph } from "graphology";
import type { FlowGraph } from "../graph/construction.js";
import type { OperationNodeAttrs } from "../schema/node.js";
import type { OperationEdgeAttrs } from "../schema/edge.js";
import type { ValidationError, AnyValidationError } from "../error/index.js";
import { GraphologyHostConfig } from "../host/graphology.js";
import { reachableFrom } from "../graph/queries.js";

function getRequiredTopLevelFields(schema: unknown): Set<string> {
  const fields = new Set<string>();
  if (schema === null || schema === undefined || typeof schema !== "object") return fields;
  const s = schema as TSchema;
  if (!KindGuard.IsObject(s)) return fields;
  const props = s.properties as Record<string, TSchema> | undefined;
  const required = s.required as string[] | undefined;
  if (props && required) {
    for (const key of required) {
      fields.add(key);
    }
  }
  return fields;
}

function getProvidedFields(schema: unknown): Set<string> {
  const fields = new Set<string>();
  if (schema === null || schema === undefined || typeof schema !== "object") return fields;
  const s = schema as TSchema;
  if (!KindGuard.IsObject(s)) return fields;
  const props = s.properties as Record<string, TSchema> | undefined;
  if (props) {
    for (const key of Object.keys(props)) {
      fields.add(key);
    }
  }
  return fields;
}

export function validatePreconditions(
  graph: FlowGraph<typeof import("../schema/node.js").OperationNodeAttrs, typeof import("../schema/edge.js").OperationEdgeAttrs>,
): ValidationError[] {
  const errors: ValidationError[] = [];
  const nodeKeys = graph.nodes();

  for (const nodeKey of nodeKeys) {
    const attrs = graph.getNodeAttributes(nodeKey) as unknown as OperationNodeAttrs;
    const inputSchema = attrs.inputSchema;
    const requiredFields = getRequiredTopLevelFields(inputSchema);

    if (requiredFields.size === 0) continue;

    const predecessors = graph.predecessors(nodeKey);
    if (predecessors.length === 0) {
      for (const field of requiredFields) {
        errors.push({
          type: "schema",
          nodeKey,
          field,
          message: `Required input field "${field}" has no predecessor providing it`,
        });
      }
      continue;
    }

    const providedFields = new Set<string>();
    for (const predKey of predecessors) {
      const predAttrs = graph.getNodeAttributes(predKey) as unknown as OperationNodeAttrs;
      const predProvided = getProvidedFields(predAttrs.outputSchema);
      for (const field of predProvided) {
        providedFields.add(field);
      }
    }

    for (const field of requiredFields) {
      if (!providedFields.has(field)) {
        errors.push({
          type: "schema",
          nodeKey,
          field,
          message: `Required input field "${field}" is not provided by any predecessor`,
        });
      }
    }
  }

  return errors;
}

function collectOperationNodeKeys(dag: DirectedGraph): string[] {
  const names: string[] = [];
  dag.forEachNode((key) => {
    if (!key.startsWith("__")) {
      names.push(key);
    }
  });
  return names;
}

export function validateTemplate(
  template: UNode,
  operationGraph: FlowGraph<typeof import("../schema/node.js").OperationNodeAttrs, typeof import("../schema/edge.js").OperationEdgeAttrs>,
): AnyValidationError[] {
  const errors: AnyValidationError[] = [];

  let renderedDag: DirectedGraph;
  try {
    const root = createHostRoot(GraphologyHostConfig, null);
    root.render(template);
    renderedDag = root.ctx.graph as DirectedGraph;
  } catch {
    renderedDag = new DirectedGraph();
  }

  const templateNodeKeys = collectOperationNodeKeys(renderedDag);
  const graphNodeKeys = new Set(operationGraph.nodes());

  for (const opKey of templateNodeKeys) {
    if (!graphNodeKeys.has(opKey)) {
      errors.push({
        type: "graph",
        category: "orphan-node",
        details: { operation: opKey, message: `Operation "${opKey}" not found in operation graph` },
      });
    }
  }

  if (hasCycle(renderedDag)) {
    errors.push({
      type: "graph",
      category: "cycle",
      details: { message: "Rendered template DAG contains a cycle" },
    });
  }

  for (const opKey of templateNodeKeys) {
    if (!graphNodeKeys.has(opKey)) continue;
    const outEdges = renderedDag.outEdges(opKey) ?? [];
    for (const edge of outEdges) {
      const target = renderedDag.target(edge);
      if (target.startsWith("__")) continue;
      if (!graphNodeKeys.has(target)) continue;
      if (operationGraph.hasEdge(opKey, target)) {
        const edgeAttrs = operationGraph.getEdgeAttributes(opKey, target) as unknown as OperationEdgeAttrs;
        if (!edgeAttrs.compatible) {
          errors.push({
            type: "type-compat",
            sourceKey: opKey,
            targetKey: target,
            compatible: false,
            mismatches: edgeAttrs.mismatches ?? [],
          });
        }
      }
    }
  }

  if (templateNodeKeys.length > 1) {
    const roots: string[] = [];
    for (const key of templateNodeKeys) {
      const inDegree = renderedDag.inDegree(key);
      if (inDegree === 0) {
        roots.push(key);
      }
    }

    if (roots.length > 0) {
      const reachable = reachableFrom(renderedDag, roots);
      for (const nodeKey of templateNodeKeys) {
        if (!reachable.has(nodeKey)) {
          errors.push({
            type: "graph",
            category: "orphan-node",
            details: { nodeKey, message: `Operation "${nodeKey}" is not reachable from start` },
          });
        }
      }
    }
  }

  for (const nodeKey of templateNodeKeys) {
    const inDegree = renderedDag.inDegree(nodeKey);
    const outDegree = renderedDag.outDegree(nodeKey);
    if (inDegree === 0 && outDegree === 0 && templateNodeKeys.length > 1) {
      errors.push({
        type: "graph",
        category: "orphan-node",
        details: { nodeKey, message: `Operation "${nodeKey}" has no edges (orphan node)` },
      });
    }
  }

  return errors;
}