import { describeGraph } from "./builder.js";
import { graphUpdateSchema, situationGraphSchema } from "./schema.js";
import {
  applyGraphUpdate,
  detectDuplicateNodeIds,
  findAffectedNodes,
  selectActiveUnknownCandidate,
  validateGraphReferences,
  validateGraphUpdate,
} from "./utils.js";

function cloneJsonSafe(value) {
  return JSON.parse(JSON.stringify(value));
}

function zodIssuesToErrors(error) {
  return (
    error?.issues?.map((issue) => {
      const path = issue.path?.length ? `${issue.path.join(".")}: ` : "";
      return `${path}${issue.message}`;
    }) ?? ["Validation failed"]
  );
}

function collectDuplicateEdgeIds(edges) {
  const counts = new Map();

  for (const edge of edges) {
    counts.set(edge.id, (counts.get(edge.id) ?? 0) + 1);
  }

  return [...counts.entries()]
    .filter(([, count]) => count > 1)
    .map(([edgeId, count]) => ({ edgeId, count }));
}

function buildAffectedNodeIds(graph, proposal) {
  const affected = new Set(proposal.affectedNodeIds ?? []);

  for (const update of proposal.updatedNodes ?? []) {
    affected.add(update.nodeId);
    for (const nodeId of findAffectedNodes(graph, update.nodeId)) {
      affected.add(nodeId);
    }
  }

  for (const nodeId of proposal.resolvedUnknownNodeIds ?? []) {
    affected.add(nodeId);
    for (const affectedNodeId of findAffectedNodes(graph, nodeId)) {
      affected.add(affectedNodeId);
    }
  }

  return [...affected];
}

function buildChangesApplied(proposal, affectedNodeIds) {
  return {
    addedNodeCount: proposal.addedNodes.length,
    updatedNodeCount: proposal.updatedNodes.length,
    addedEdgeCount: proposal.addedEdges.length,
    removedEdgeCount: proposal.removedEdgeIds.length,
    resolvedUnknownCount: proposal.resolvedUnknownNodeIds.length,
    affectedNodeCount: affectedNodeIds.length,
  };
}

export function applyValidatedProposal({ situationGraph, proposal }) {
  const graphValidation = situationGraphSchema.safeParse(situationGraph);
  const proposalValidation = graphUpdateSchema.safeParse(proposal);

  const existingGraphReferenceValidation = graphValidation.success
    ? validateGraphReferences(situationGraph)
    : null;

  const existingDuplicateNodeIds = graphValidation.success
    ? detectDuplicateNodeIds(situationGraph.nodes)
    : [];
  const existingDuplicateEdgeIds = graphValidation.success
    ? collectDuplicateEdgeIds(situationGraph.edges)
    : [];

  if (
    !graphValidation.success ||
    !existingGraphReferenceValidation?.valid ||
    existingDuplicateNodeIds.length > 0 ||
    existingDuplicateEdgeIds.length > 0
  ) {
    return {
      success: false,
      stage: "graph_validation",
      errors: [
        ...(!graphValidation.success
          ? zodIssuesToErrors(graphValidation.error)
          : []),
        ...(!existingGraphReferenceValidation?.valid
          ? existingGraphReferenceValidation.errors
          : []),
        ...existingDuplicateNodeIds.map(
          ({ nodeId, count }) =>
            `Graph contains duplicate node ID: "${nodeId}" (${count} occurrences)`,
        ),
        ...existingDuplicateEdgeIds.map(
          ({ edgeId, count }) =>
            `Graph contains duplicate edge ID: "${edgeId}" (${count} occurrences)`,
        ),
      ],
    };
  }

  if (!proposalValidation.success) {
    return {
      success: false,
      stage: "proposal_compatibility",
      errors: zodIssuesToErrors(proposalValidation.error),
    };
  }

  const validatedProposal = proposalValidation.data;
  const proposalCompatibilityErrors = [];
  const proposalGraphValidation = validateGraphUpdate(
    situationGraph,
    validatedProposal,
  );

  if (!proposalGraphValidation.valid) {
    proposalCompatibilityErrors.push(...proposalGraphValidation.errors);
  }

  const existingEdgeIds = new Set(situationGraph.edges.map((edge) => edge.id));
  const reachableNodeIds = new Set([
    ...situationGraph.nodes.map((node) => node.id),
    ...validatedProposal.addedNodes.map((node) => node.id),
  ]);
  const addedEdgeDuplicateIds = collectDuplicateEdgeIds(
    validatedProposal.addedEdges,
  );
  proposalCompatibilityErrors.push(
    ...addedEdgeDuplicateIds.map(
      ({ edgeId, count }) =>
        `Proposal contains duplicate added edge ID: "${edgeId}" (${count} occurrences)`,
    ),
  );

  for (const edge of validatedProposal.addedEdges) {
    if (existingEdgeIds.has(edge.id)) {
      proposalCompatibilityErrors.push(
        `Cannot add edge with duplicate ID: "${edge.id}"`,
      );
    }
    if (!reachableNodeIds.has(edge.fromNodeId)) {
      proposalCompatibilityErrors.push(
        `Added edge references non-existent fromNodeId: "${edge.fromNodeId}"`,
      );
    }
    if (!reachableNodeIds.has(edge.toNodeId)) {
      proposalCompatibilityErrors.push(
        `Added edge references non-existent toNodeId: "${edge.toNodeId}"`,
      );
    }
  }

  const removedEdgeIds = new Set(validatedProposal.removedEdgeIds);
  for (const edgeId of removedEdgeIds) {
    if (!existingEdgeIds.has(edgeId)) {
      proposalCompatibilityErrors.push(
        `Cannot remove non-existent edge: "${edgeId}"`,
      );
    }
  }

  const combinedNodeDuplicates = detectDuplicateNodeIds([
    ...situationGraph.nodes,
    ...validatedProposal.addedNodes,
  ]);
  proposalCompatibilityErrors.push(
    ...combinedNodeDuplicates.map(
      ({ nodeId, count }) =>
        `Proposal would produce duplicate node ID: "${nodeId}" (${count} occurrences)`,
    ),
  );

  if (proposalCompatibilityErrors.length > 0) {
    return {
      success: false,
      stage: "proposal_compatibility",
      errors: proposalCompatibilityErrors,
    };
  }

  const graphSnapshot = cloneJsonSafe(situationGraph);
  const proposalSnapshot = cloneJsonSafe(validatedProposal);
  const previousActiveUnknownNodeId = graphSnapshot.activeUnknownNodeId ?? null;
  const affectedNodeIds = buildAffectedNodeIds(graphSnapshot, proposalSnapshot);

  const applied = applyGraphUpdate(graphSnapshot, proposalSnapshot);
  if (!applied.success) {
    return {
      success: false,
      stage: "application",
      errors: applied.errors,
    };
  }

  const updatedSituationGraph = {
    ...graphSnapshot,
    nodes: applied.nodes,
    edges: applied.edges,
    resolvedNodeIds: applied.resolvedNodeIds,
  };

  const activeUnknownWasResolved =
    previousActiveUnknownNodeId != null &&
    updatedSituationGraph.resolvedNodeIds.includes(previousActiveUnknownNodeId);

  let newActiveUnknownNodeId = previousActiveUnknownNodeId;
  if (activeUnknownWasResolved) {
    newActiveUnknownNodeId = null;
  }

  const remainingUnknownExists =
    newActiveUnknownNodeId != null &&
    updatedSituationGraph.nodes.some(
      (node) =>
        node.id === newActiveUnknownNodeId &&
        node.kind === "unknown" &&
        !updatedSituationGraph.resolvedNodeIds.includes(node.id),
    );

  if (!remainingUnknownExists) {
    newActiveUnknownNodeId =
      selectActiveUnknownCandidate(
        updatedSituationGraph,
        updatedSituationGraph.resolvedNodeIds,
      )?.nodeId ?? null;
  }

  updatedSituationGraph.activeUnknownNodeId = newActiveUnknownNodeId;
  updatedSituationGraph.currentSummary = describeGraph(updatedSituationGraph);

  const resultGraphValidation = situationGraphSchema.safeParse(
    updatedSituationGraph,
  );
  const resultReferenceValidation = resultGraphValidation.success
    ? validateGraphReferences(updatedSituationGraph)
    : null;
  const resultDuplicateNodeIds = resultGraphValidation.success
    ? detectDuplicateNodeIds(updatedSituationGraph.nodes)
    : [];
  const resultDuplicateEdgeIds = resultGraphValidation.success
    ? collectDuplicateEdgeIds(updatedSituationGraph.edges)
    : [];

  if (
    !resultGraphValidation.success ||
    !resultReferenceValidation?.valid ||
    resultDuplicateNodeIds.length > 0 ||
    resultDuplicateEdgeIds.length > 0
  ) {
    return {
      success: false,
      stage: "result_validation",
      errors: [
        ...(!resultGraphValidation.success
          ? zodIssuesToErrors(resultGraphValidation.error)
          : []),
        ...(!resultReferenceValidation?.valid
          ? resultReferenceValidation.errors
          : []),
        ...resultDuplicateNodeIds.map(
          ({ nodeId, count }) =>
            `Updated graph contains duplicate node ID: "${nodeId}" (${count} occurrences)`,
        ),
        ...resultDuplicateEdgeIds.map(
          ({ edgeId, count }) =>
            `Updated graph contains duplicate edge ID: "${edgeId}" (${count} occurrences)`,
        ),
      ],
    };
  }

  return {
    success: true,
    updatedSituationGraph,
    graphUpdate: validatedProposal,
    affectedNodeIds,
    resolvedUnknownNodeIds: validatedProposal.resolvedUnknownNodeIds,
    previousActiveUnknownNodeId,
    newActiveUnknownNodeId,
    changesApplied: buildChangesApplied(validatedProposal, affectedNodeIds),
  };
}