import {inspect} from "util"; // NodeJS library
import {createHash} from "crypto";
import {Buffer} from "buffer";
import * as _ from "lodash";

import {UUID, PrimitiveValue} from "./types";
import {bufferXOR} from "./buffer_xor";
import {Delta} from "./delta";

export interface PrimitiveDelta extends Delta {
}

export class NodeCreation implements PrimitiveDelta {
  readonly id: UUID;
  readonly hash: Buffer;
  readonly description: string;

  // Inverse dependency: Deletions of this node.
  deletions: Array<NodeDeletion> = []; // append-only

  // Inverse dependency: Creation outgoing edges.
  outgoingEdges: Array<EdgeCreation> = []; // append-only

  // Inverse dependency: All the times this node was the target of an edge update.
  incomingEdges: Array<EdgeCreation | EdgeUpdate> = []; // append-only

  constructor(hash: Buffer, id: UUID) {
    this.hash = hash;
    this.id = id;
    this.description = "NEW("+this.id.value.toString().slice(0,8)+")";
  }

  getDependencies(): [] {
    return [];
  }

  getTypedDependencies(): [] {
    return [];
  }

  getConflicts(): [] {
    return [];
  }

  getHash(): Buffer {
    return this.hash;
  }

  getDescription(): string {
    return this.description;
  }

  // pretty print to console under NodeJS
  [inspect.custom](depth: number, options: object) {
    return "NodeCreation{" + inspect(this.id, options) + "}";
  }

  toString(): string {
    return this[inspect.custom](0, {});
  }

  serialize(): any {
    return {
      type: "NodeCreation",
      id: this.id.value,
    }
  }

  *iterPrimitiveDeltas(): Iterable<Delta> {
    yield this;
  }
}

export class NodeDeletion implements PrimitiveDelta {
  readonly hash: Buffer;
  readonly description: string;

  // Dependency: The node being deleted.
  readonly creation: NodeCreation;

  // Dependency: All outgoing edges of the deleted node must be deleted also.
  readonly deletedOutgoingEdges: Array<EdgeCreation | EdgeUpdate>;

  // Dependency: For every time the deleted node was target of an edge, the deletion depends on the EdgeUpdate that sets this edge to have a different target.
  readonly afterIncomingEdges: Array<EdgeUpdate | NodeDeletion>;

  // Conflicts: Concurrent deletion of the same node.
  deleteConflicts: Array<NodeDeletion> = [];

  // Conflicts: Concurrent creation of an edge with as source the deleted node.
  edgeSourceConflicts: Array<EdgeCreation> = [];

  // Conflicts: Concurrent update and deletion of an edge (because its source node is deleted).
  updateConflicts: Array<EdgeUpdate | NodeDeletion> = [];

  // Conflicts: Concurrent creation/update of an edge with as target the deleted node.
  edgeTargetConflicts: Array<EdgeCreation | EdgeUpdate> = [];

  // Parameters:
  //   deletedOutgoingEdges: For every outgoing edge of this node being deleted, must explicitly specify the most recent EdgeCreation/EdgeUpdate on this edge, to make it explicit that this deletion happens AFTER the EdgeCreation/EdgeUpdate (instead of concurrently, which is a conflict).
  //   afterIncomingEdges: For every edge that is or was (once) incoming to this node, must explicitly specify an EdgeUpdate/NodeDeletion that makes this edge point somewhere else (no longer to this node).
  constructor(hash: Buffer, creation: NodeCreation, deletedOutgoingEdges: Array<EdgeCreation|EdgeUpdate>, afterIncomingEdges: Array<EdgeUpdate|NodeDeletion>) {
    this.hash = hash;
    this.creation = creation;
    this.deletedOutgoingEdges = deletedOutgoingEdges;
    this.afterIncomingEdges = afterIncomingEdges;

    // Check some assertions
    if (_.uniq(deletedOutgoingEdges).length !== deletedOutgoingEdges.length) {
      throw new Error("Assertion failed: deletedOutgoingEdges contains duplicates.");
    }
    if (_.uniq(afterIncomingEdges).length !== afterIncomingEdges.length) {
      throw new Error("Assertion failed: deletedOutgoingEdges contains duplicates.");
    }
    for (const supposedlyOutgoingEdge of this.deletedOutgoingEdges) {
      if (supposedlyOutgoingEdge.getCreation().source !== this.creation) {
        throw new Error("Assertion failed: Every element of delOutgoings must be an EdgeCreation or EdgeUpdate of an outgoing edge of the deleted node.")
      }
    }
    for (const supposedlyIncomingEdge of this.afterIncomingEdges) {
      if (supposedlyIncomingEdge instanceof NodeDeletion) {
        // should check if the NodeDeletion deletes an edge that was *once* 
        let isReallyIncomingEdge = false;
        for (const deletedEdge of supposedlyIncomingEdge.deletedOutgoingEdges) {
          let current: EdgeCreation|EdgeUpdate|undefined = deletedEdge;
          while (current !== undefined) {
            if (current.target.getTarget() === this.creation) {
              isReallyIncomingEdge = true;
              break;
            }
            if (current instanceof EdgeUpdate) current = current.overwrites
            else break;
          }
          if (isReallyIncomingEdge) break;
        }
        if (!isReallyIncomingEdge) {
          throw new Error("Assertion failed: NodeDeletion in afterIncomingEdges does not delete an incoming edge.");
        }
      }
      else {      
        if (supposedlyIncomingEdge.target.getTarget() === this.creation) {
          throw new Error("Assertion failed: Every element in afterIncomingEdges MUST set the target of the edge to SOME PLACE ELSE.");
        }
        if (![...supposedlyIncomingEdge.iterUpdates()].some(e => e.target.getTarget() === this.creation)) {
          throw new Error("Assertion failed: None of the EdgeUpdates of supposedlyIncomingEdge set the target to the node being deleted.");
        }
      }
    }

    this.description = "DEL("+this.creation.id.value.toString().slice(0,8)+")"

    // Detect conflicts

    // Delete/delete
    for (const concurrentDeletion of this.creation.deletions) {
      // Symmetric:
      this.deleteConflicts.push(concurrentDeletion);
      concurrentDeletion.deleteConflicts.push(this);
    }

    // Concurrently created outgoing edges of this node
    for (const outgoingEdgeCreation of this.creation.outgoingEdges) {
      if (!this.deletedOutgoingEdges.some(edge => edge.getCreation() === outgoingEdgeCreation)) {
        // Conflict: The deleted node has an outgoing edge that this deletion does not depend on.
        // Symmetric
        this.edgeSourceConflicts.push(outgoingEdgeCreation);
        outgoingEdgeCreation.deleteSourceConflicts.push(this);
      }
    }

    // Related to previous conflict type: Concurrent edge updates
    for (const deletedEdge of this.deletedOutgoingEdges) {
      for (const concurrentEdgeUpdate of deletedEdge.overwrittenBy) {
        if (this.afterIncomingEdges.includes(concurrentEdgeUpdate)) {
          // This is a special case that can occur when a node with a self-edge is deleted.
          // Not a conflict.
        }
        else {
          // Conflict: Edge concurrently updated and deleted.
          // Symmetric
          this.updateConflicts.push(concurrentEdgeUpdate);
          concurrentEdgeUpdate.updateConflicts.push(this);
        }
      }
    }

    function overwritesEdge(op: EdgeCreation | EdgeUpdate | NodeDeletion, edge: EdgeUpdate | EdgeCreation) {
      if (op === edge) {
        return true;
      }
      if (op instanceof EdgeUpdate) {
        return overwritesEdge(op.overwrites, edge);
      }
      if (op instanceof NodeDeletion) {
        return op.deletedOutgoingEdges.some(deletedEdge => overwritesEdge(deletedEdge, edge));
      }
      return false;
    }

    // Concurrently updated incoming edges of this node
    for (const incomingEdge of this.creation.incomingEdges) {
      // every incoming edge of deleted node must have been overwritten by an EdgeUpdate that is an explicit dependency:
      if (!this.afterIncomingEdges.some(edge => overwritesEdge(edge, incomingEdge))) {
        // Symmetric
        this.edgeTargetConflicts.push(incomingEdge);
        incomingEdge.target.addDeleteTargetConflict(this);
      }
    }


    // Create inverse dependencies

    this.creation.deletions.push(this);

    for (const deletedEdge of this.deletedOutgoingEdges) {
      // NodeDeletion acts a bit as an EdgeUpdate here
      deletedEdge.overwrittenBy.push(this);
    }
  }

  getDependencies(): Array<Delta> {
    return Array<Delta>().concat(
      [this.creation],
      this.deletedOutgoingEdges,
      this.afterIncomingEdges,
    );
  }

  getTypedDependencies(): Array<[Delta, string]> {
    return Array<[Delta, string]>().concat(
      [[this.creation, "DEL"]],
      this.deletedOutgoingEdges.map(edge => ([edge, "D"])),
      this.afterIncomingEdges.map(edge => ([edge, "A"])),
    );
  }

  getConflicts(): Array<Delta> {
    return Array<Delta>().concat(
      this.deleteConflicts,
      this.edgeSourceConflicts,
      this.edgeTargetConflicts,
      this.updateConflicts,
    );
  }

  getHash(): Buffer {
    return this.hash;
  }

  getDescription(): string {
    return this.description;
  }

  // pretty print to console under NodeJS
  [inspect.custom](depth: number, options: object) {
    return "NodeDeletion{" + inspect(this.creation.id, options) + ",delEdges=" + this.deletedOutgoingEdges.map(e => inspect(e, options)).join(",") + ",after=" + this.afterIncomingEdges.map(e => inspect(e, options)).join(",") + "}";
  }

  toString(): string {
    return this[inspect.custom](0, {});
  }

  serialize(): any {
    return {
      type: "NodeDeletion",
      creation: this.creation.hash.toString('base64'),
      deletedOutgoingEdges: this.deletedOutgoingEdges.map(d => d.hash.toString('base64')),
      afterIncomingEdges: this.afterIncomingEdges.map(d => d.hash.toString('base64')),
    };
  }

  *iterPrimitiveDeltas(): Iterable<Delta> {
    yield this;
  }
}

// Target of an edge can be: another node, nothing (edge doesn't exist) or a value (i.e., string, number or boolean)
export type EdgeTargetType = NodeCreation | null | PrimitiveValue;

// Target of an edge can be either: (1) another node, (2) a value or (3) null (hides the edge - initially all edges are assumed to be null).
export interface SetsTarget {
  getTarget(): EdgeTargetType;
  addDeleteTargetConflict(nodeDeletion: NodeDeletion);
  getDeleteTargetConflicts(): ReadonlyArray<NodeDeletion>;
  getDependencies(): ReadonlyArray<NodeCreation>;
  getTypedDependencies(): ReadonlyArray<[NodeCreation, string]>;
  getHash(): Buffer;
  serialize(): any;
}

// Common functionality in EdgeCreation and EdgeUpdate: both set the target of an edge, and this can conflict with the deletion of the target.
class SetsTargetToNode implements SetsTarget {
  // Dependency
  private readonly targetNode: NodeCreation;

  // Conflict: Concurrent deletion of target node.
  private deleteTargetConflicts: Array<NodeDeletion> = []; // append-only

  constructor(targetNode: NodeCreation, edgeOperation: EdgeCreation|EdgeUpdate) {
    this.targetNode = targetNode;

    // Concurrent deletion of target node
    if (this.targetNode instanceof NodeCreation) {
      for (const targetDeletion of this.targetNode.deletions) {
        if (targetDeletion.afterIncomingEdges.some(edge => {
          while (true) {
            if (edge === edgeOperation) return true;
            if (edge instanceof EdgeUpdate && edge.overwrites instanceof EdgeUpdate) edge = edge.overwrites;
            else return false;
          }
        })) {
          // this can never happen - something is very wrong if you get this error:
          throw new Error("Assertion failed - did not expect existing deletion to be aware of a new edge update");
        }
        // Symmetric
        this.deleteTargetConflicts.push(targetDeletion);
        targetDeletion.edgeTargetConflicts.push(edgeOperation);
      }

      // Create inverse dependency
      this.targetNode.incomingEdges.push(edgeOperation);
    }
  }

  getTarget(): EdgeTargetType {
    return this.targetNode;
  }
  addDeleteTargetConflict(nodeDeletion: NodeDeletion) {
    this.deleteTargetConflicts.push(nodeDeletion);
  }
  getDeleteTargetConflicts(): ReadonlyArray<NodeDeletion> {
    return this.deleteTargetConflicts;
  }
  getDependencies(): ReadonlyArray<NodeCreation> {
    return [this.targetNode];
  }
  getTypedDependencies(): ReadonlyArray<[NodeCreation, string]> {
    return [[this.targetNode, "TGT"]];
  }
  getHash(): Buffer {
    return this.targetNode.hash;
  }
  [inspect.custom](depth: number, options: object) {
    return inspect(this.targetNode.id, options);
  }
  serialize(): any {
    return {
      type: "node",
      creation: this.targetNode.hash.toString('base64'),
    }
  }
}
class SetsTargetToValue implements SetsTarget {
  readonly value: PrimitiveValue | null;

  constructor(value: PrimitiveValue | null) {
    this.value = value;
  }

  getTarget(): EdgeTargetType {
    return this.value;
  }
  addDeleteTargetConflict(nodeDeletion: NodeDeletion) {
    throw new Error("Assertion error: SetsTargetToValue cannot be involved in conflict with NodeDeletion");
  }
  getDeleteTargetConflicts(): ReadonlyArray<NodeDeletion> {
    return [];
  }
  getDependencies(): ReadonlyArray<NodeCreation> {
    return [];
  }
  getTypedDependencies(): ReadonlyArray<[NodeCreation, string]> {
    return [];
  }
  getHash(): Buffer {
    return Buffer.from(JSON.stringify(this.value));
  }
  [inspect.custom](depth: number, options: object) {
    return inspect(this.value, options);
  }
  serialize(): any {
    return {
      type: "value",
      value: this.value,
    }
  }
}

function makeSetsTarget(target: EdgeTargetType, edgeOperation: EdgeCreation|EdgeUpdate) {
  if (target instanceof NodeCreation) {
    return new SetsTargetToNode(target, edgeOperation);
  } else {
    return new SetsTargetToValue(target);
  }
}

export class EdgeCreation implements PrimitiveDelta {
  // Dependencies
  readonly source: NodeCreation;
  readonly label: string;
  readonly target: SetsTarget;

  readonly hash: Buffer;
  readonly description: string;

  // Inverse dependency
  // NodeDeletion if source of edge is deleted.
  overwrittenBy: Array<EdgeUpdate | NodeDeletion> = []; // append-only

  // Conflicts: Concurrent creations of the same edge.
  createConflicts: Array<EdgeCreation> = []; // append-only

  // Conflicts: Concurrent deletions of source node.
  deleteSourceConflicts: Array<NodeDeletion> = []; // append-only

  constructor(hash: Buffer, source: NodeCreation, label: string, target: EdgeTargetType) {
    this.hash = hash;
    this.source = source;
    this.label = label;
    this.target = makeSetsTarget(target, this);

    this.description = "EDG("+this.label+")";

    // Detect conflicts

    // Create/create
    for (const outgoingEdge of this.source.outgoingEdges) {
      if (outgoingEdge.label === this.label) {
        // Symmetric:
        this.createConflicts.push(outgoingEdge);
        outgoingEdge.createConflicts.push(this);
      }
    }

    // Concurrent deletions of source node
    for (const sourceDeletion of this.source.deletions) {
      if (sourceDeletion.deletedOutgoingEdges.some(edge => edge.getCreation() === this)) {
        // this can never happen - something is very wrong if you get this error:
        throw new Error("Assertion failed - did not expect existing deletion to be aware of a new edge creation");
      }
      // Symmetric
      this.deleteSourceConflicts.push(sourceDeletion);
      sourceDeletion.edgeSourceConflicts.push(this);
    }

    // Create inverse dependency
    this.source.outgoingEdges.push(this);
  }

  // Helper
  getCreation(): EdgeCreation {
    return this;
  }

  getDependencies(): Array<NodeCreation> {
    return [this.source, ...this.target.getDependencies()];
  }

  getTypedDependencies(): Array<[NodeCreation, string]> {
    return [[this.source, "SRC"], ...this.target.getTypedDependencies()];
  }

  getConflicts(): Array<Delta> {
    return Array<Delta>().concat(
      this.createConflicts,
      this.deleteSourceConflicts,
      this.target.getDeleteTargetConflicts(),
    );
  }

  getHash(): Buffer {
    return this.hash;
  }

  getDescription(): string {
    return this.description;
  }

  // pretty print to console under NodeJS
  [inspect.custom](depth: number, options: object) {
    return "EdgeCreation{src=" + inspect(this.source.id, options) + ",tgt=" + inspect(this.target, options) + ",label=" + this.label + "}";
  }

  toString(): string {
    return this[inspect.custom](0, {});
  }

  serialize(): any {
    return {
      type: "EdgeCreation",
      source: this.source.hash.toString('base64'),
      label: this.label,
      target: this.target.serialize(),
    };
  }

  *iterPrimitiveDeltas(): Iterable<Delta> {
    yield this;
  }
}

export class EdgeUpdate implements PrimitiveDelta {
  // Dependencies
  readonly overwrites: EdgeCreation | EdgeUpdate;
  readonly target: SetsTarget;

  readonly hash: Buffer;
  readonly description: string;

  // Inverse dependency
  // NodeDeletion if source of edge is deleted.
  overwrittenBy: Array<EdgeUpdate | NodeDeletion> = []; // append-only

  // Conflicts: Concurrent updates
  updateConflicts: Array<EdgeUpdate | NodeDeletion> = []; // append-only

  constructor(hash: Buffer, overwrites: EdgeCreation | EdgeUpdate, newTarget: EdgeTargetType) {
    this.hash = hash;
    this.overwrites = overwrites;
    this.target = makeSetsTarget(newTarget, this);

    this.description = "EDG";

    // Detect conflicts

    // Concurrent updates (by EdgeUpdate or NodeDeletion)
    for (const concurrentUpdate of this.overwrites.overwrittenBy) {
      // Symmetric
      this.updateConflicts.push(concurrentUpdate);
      concurrentUpdate.updateConflicts.push(this);
    }

    // Create inverse dependency
    this.overwrites.overwrittenBy.push(this);
  }

  // Helper
  getCreation(): EdgeCreation {
    return this.overwrites.getCreation();
  }

  getDependencies(): Array<Delta> {
    return [this.overwrites, ...this.target.getDependencies()];
  }

  getTypedDependencies(): Array<[Delta, string]> {
    return [[this.overwrites, "UPD"], ...this.target.getTypedDependencies()];
  }

  getConflicts(): Array<Delta> {
    return Array<Delta>().concat(
      this.updateConflicts,
      this.target.getDeleteTargetConflicts(),
    );
  }

  getHash(): Buffer {
    return this.hash;
  }

  getDescription(): string {
    return this.description;
  }

  // pretty print to console under NodeJS
  [inspect.custom](depth: number, options: object) {
    return "EdgeUpdate{upd=" + inspect(this.overwrites, options) + ",tgt=" + inspect(this.target, options) + "}";
  }

  toString(): string {
    return this[inspect.custom](0, {});
  }

  serialize(): any {
    return {
      type: "EdgeUpdate",
      overwrites: this.overwrites.hash.toString('base64'),
      target: this.target.serialize(),
    };
  }

  *iterUpdates() {
    let current: EdgeUpdate | EdgeCreation = this;
    while (true) {
      yield current;
      if (current instanceof EdgeUpdate) {
        current = current.overwrites;
      } else {
        return;
      }
    }
  }

  *iterPrimitiveDeltas(): Iterable<Delta> {
    yield this;
  }
}

function targetToHash(target: EdgeTargetType): any {
  // just needs to return something "unique" to feed into the hash function
  if (target instanceof NodeCreation) {
    return target.hash;
  }
  else {
    return "value" + JSON.stringify(target);
  }
}

// Ensures that deltas with the same hash are only created once.
export class PrimitiveRegistry {
  deltas: Map<string, PrimitiveDelta> = new Map();

  private createIdempotent(hash: Buffer, callback) {
    const base64 = hash.toString('base64');
    return this.deltas.get(base64) || (() => {
      const delta = callback();
      this.deltas.set(base64, delta);
      return delta;
    })();
  }

  newNodeCreation(id: UUID): NodeCreation {
    const hash = createHash('sha256')
      .update(JSON.stringify(id.value)) // prevent collisions between 'true' (actual boolean) and '"true"' (string "true"), or 42 (number) and "42" (string)
      .digest();
    return this.createIdempotent(hash, () => new NodeCreation(hash, id));
  }

  newNodeDeletion(creation: NodeCreation, deletedOutgoingEdges: Array<EdgeCreation|EdgeUpdate>, afterIncomingEdges: Array<EdgeUpdate|NodeDeletion>): NodeDeletion {
    // hash will be calculated based on all EdgeCreations/EdgeUpdates/NodeDeletions that we depend on, by XOR (insensitive to array order).
    let hash = createHash('sha256').update(creation.hash);
    let union = Buffer.alloc(32); // all zeroes - neutral element for XOR
    for (const deletedOutgoing of deletedOutgoingEdges) {
      union = bufferXOR(union, deletedOutgoing.getHash());
    }
    for (const afterIncoming of afterIncomingEdges) {
      union = bufferXOR(union, afterIncoming.getHash());
    }
    const buf = hash.update(union).digest();
    return this.createIdempotent(buf, () => new NodeDeletion(buf, creation, deletedOutgoingEdges, afterIncomingEdges));
  }

  newEdgeCreation(source: NodeCreation, label: string, target: EdgeTargetType): EdgeCreation {
    const hash = createHash('sha256')
      .update(source.hash)
      .update('create').update(label)
      .update('target=').update(targetToHash(target))
      .digest();
    return this.createIdempotent(hash, () => new EdgeCreation(hash, source, label, target));
  }

  newEdgeUpdate(overwrites: EdgeCreation | EdgeUpdate, target: EdgeTargetType): EdgeUpdate {
    const hash = createHash('sha256')
      .update(overwrites.hash)
      .update('target=').update(targetToHash(target))
      .digest();
    return this.createIdempotent(hash, () => new EdgeUpdate(hash, overwrites, target));
  }
}