import type { Applied, Availability, Capability, Change, Command, Commit, CoreSnapshot, Document, ElementRecord, Geometry, HistoryEntry, HistoryState, Id, OperationIntent, Origin, Registry, Result, Snapshot } from './types.ts';
import { applyChanges, createDocument, invert, targetElement, validateDocument } from './document.ts';
import { clone, equal, fault, freeze, readMap, reject, validJson } from './values.ts';

import {createDocumentQueries,advanceDocumentQueries,type QueryBudget} from './queries.ts';
import { canvasTransform, convertGeometry } from './coordinates.ts';
import { unitScale, withUnitScale } from './units.ts';
import { removalChanges, repairConnectionOwners } from './structure.ts';
import { planHistoryChanges } from './history.ts';
import { describeHistoryTransition } from './history-transition.ts';

export type EditorOptions<Runtime = undefined> = {
  registry: Registry; document: Document; queryBudget?:QueryBudget; createId?: () => Id; historyLimit?: number;
  policy?: (command: Command, document: Document) => Availability;
  traversalPolicy?: (entry: HistoryEntry, direction: 'undo' | 'redo') => Availability;
  onListenerError?: (error: unknown) => void;
  allowRawChanges?: boolean;
  recovery?: CoreSnapshot & { readonly rootRevision: number };
  runtime?: Runtime;
  /** Installed by the engine. Pure preparation: an error rejects the entire commit. */
  reduceRuntime?: (previous: Runtime, next: CoreSnapshot, commit: Commit) => Runtime;
  /** Engine may attach transport semantics without changing identity, order or document changes. */
  prepareIntent?: (intent: OperationIntent, runtime: Runtime) => OperationIntent;
  /** Pure coordinator hook for all publication paths; may replace runtime only or reject. */
  prepareRuntime?: (previous: Snapshot<Runtime>, next: Snapshot<Runtime>) => Runtime;
  nextOperationSequence?: (runtime: Runtime, fallback: number) => number;
};
export type Transaction = { dispatch(command: Command): Availability; getDocument(): Document };
export type Editor = ReturnType<typeof createEditor>;
const isThenable = (value: unknown) => !!value && (typeof value === 'object' || typeof value === 'function') && typeof (value as { then?: unknown }).then === 'function';

export function createEditor<Runtime = undefined>(options: EditorOptions<Runtime>) {
  const source = options.recovery?.document ?? options.document;
  const document = createDocument(source.projectId, [...source.canvases.values()], [...source.elements.values()], source.tombstones);
  validateDocument(document, options.registry);
  let state: Snapshot<Runtime> = Object.freeze({ revision: options.recovery?.revision ?? 0, rootRevision: options.recovery?.rootRevision ?? 0, document, history: options.recovery?.history ?? Object.freeze({ undo: Object.freeze([]), redo: Object.freeze([]), entries: readMap(new Map<Id, HistoryEntry>()) }), operations: options.recovery?.operations ?? readMap(new Map<Id, OperationIntent>()), runtime: options.runtime as Runtime });
  let queries=createDocumentQueries(document,options.registry,state.revision,options.queryBudget);
  const queriesByDocument=new WeakMap([[document,queries]]);
  let entered = false, disposed = false, sequence = 0;
  for (const intent of state.operations.values()) sequence = Math.max(sequence, intent.sequence);
  const listeners = new Set<(commit: Commit, snapshot: Snapshot<Runtime>) => void>();
  const createId = options.createId || (() => globalThis.crypto.randomUUID());
  const limit = options.historyLimit ?? 100;
  if (!Number.isSafeInteger(limit) || limit < 1) throw fault('invalid_history_limit');

  function plan(document: Document, command: Command): { document: Document; changes: readonly Change[] } {
    const permission = options.policy?.(command, document);
    if (permission && !permission.enabled) throw fault(permission.code, permission.targets);
    let changes: readonly Change[];
    if (command.type === 'canvas.create') {
      if (document.canvases.has(command.canvas.id)) throw fault('duplicate_identity', [command.canvas.id]);
      changes = [{ kind: 'canvas', id: command.canvas.id, before: null, after: command.canvas }];
    } else if (command.type === 'canvas.reparent') {
      const canvas = document.canvases.get(command.canvasId);
      if (!canvas) throw fault('canvas_not_loaded', [command.canvasId]);
      changes = equal(canvas.parent, command.parent) ? [] : [{ kind: 'canvas', id: canvas.id, before: canvas, after: { ...canvas, parent: command.parent } }];
      if(changes.length)changes=[...changes,...repairConnectionOwners(document,applyChanges(document,changes))];
    } else if (command.type === 'element.create') {
      const element = command.element;
      if (document.elements.has(element.id) || document.tombstones.has(element.id)) throw fault('duplicate_identity', [element.id]);
      if (options.registry.resolve(element) !== 'known') throw fault('unsupported_component', [element.id]);
      changes = [{ kind: 'element', id: element.id, before: null, after: element }];
    } else if (command.type === 'changes.apply') {
      if (!options.allowRawChanges) throw fault('raw_changes_not_allowed');
      changes = command.changes;
    } else {
      let element = targetElement(document, command.target);
      if (options.registry.resolve(element) !== 'known') throw fault('unsupported_component', [element.id]);
      if (command.type === 'connection.path') {
        if (element.structure !== 'connection' || !options.registry.supports(element, 'connection.edit')) throw fault('unsupported_capability', [element.id]);
        if (!validJson(command.path)) throw fault('invalid_connection_path', [element.id]);
        changes = options.registry.handlers.get(element.componentId)!.get('connection.edit')!({ element, input: freeze({ patch: { path: clone(command.path) } }) });
        for (const change of changes) if (change.kind !== 'field' || change.field !== 'path' || change.target.id !== element.id || change.target.incarnation !== element.incarnation) throw fault('invalid_handler_change', [element.id]);
      } else if(command.type==='connection.endpoints'){
        if(element.structure!=='connection'||!options.registry.supports(element,'connection.edit'))throw fault('unsupported_capability',[element.id]);
        changes=[];
        for(const [field,endpoint]of [['source',command.source],['target',command.destination]] as const)if(endpoint&&!equal(element[field],endpoint))changes=[...changes,{kind:'field',target:command.target,field,before:element[field],after:clone(endpoint)}];
        if(changes.length)changes=[...changes,...repairConnectionOwners(document,applyChanges(document,changes))];
      } else if (command.type === 'element.remove') {
        changes = removalChanges(document,command.target,queriesByDocument.get(document));
      } else if (command.type === 'element.move') {
        if (!options.registry.supports(element, 'geometry.move')) throw fault('unsupported_capability', [element.id]);
        changes = [{ kind: 'field', target: command.target, field: 'ownerCanvasId', before: element.ownerCanvasId, after: command.canvasId }];
        if(element.structure==='node'){
          const source=canvasTransform(document,element.ownerCanvasId),destination=canvasTransform(document,command.canvasId),presentation=withUnitScale(element.data.presentation,unitScale(element.data.presentation)*source.scale/destination.scale);
          if(!equal(presentation,element.data.presentation))changes=[...changes,{kind:'field',target:command.target,field:'data.presentation',before:element.data.presentation??null,beforePresent:Object.hasOwn(element.data,'presentation'),after:presentation??null,afterPresent:presentation!==undefined}];
          const geometry=command.geometry??(element.ownerCanvasId===command.canvasId?element.geometry:convertGeometry(element.geometry,canvasTransform(document,element.ownerCanvasId),canvasTransform(document,command.canvasId)));
          if(!equal(geometry,element.geometry))changes=[...changes,{kind:'field',target:command.target,field:'geometry',before:element.geometry,after:geometry}];
        }
        for (const canvas of document.canvases.values()) if (canvas.parent?.entryElementId === element.id) changes = [...changes, { kind: 'canvas', id: canvas.id, before: canvas, after: { ...canvas, parent: { ...canvas.parent, canvasId: command.canvasId } } }];
        changes=[...changes,...repairConnectionOwners(document,applyChanges(document,changes))];
      } else {
        const output: Change[] = [];
        const run = (capability: Capability, patch: unknown) => {
          const handler = options.registry.handlers.get(element.componentId)?.get(capability);
          if (!handler) throw fault('unsupported_capability', [element.id, capability]);
          const generated = handler({ element, input: freeze({ patch: clone(patch) }) });
          // A handler is scoped to this target; it cannot write another object or domain.
          for (const change of generated) if (change.target.id !== element.id || change.target.incarnation !== element.incarnation || (capability === 'content.edit' ? !change.field.startsWith('data.') : change.field !== 'geometry')) throw fault('invalid_handler_change', [element.id]);
          output.push(...generated);
          element = targetElement(applyChanges(document, output), command.target);
        };
        if (command.type === 'element.data') run('content.edit', command.patch);
        else {
          if (element.structure !== 'node' || Object.keys(command.patch).some(key => !['x', 'y', 'width', 'height', 'rotation'].includes(key))) throw fault('invalid_geometry_patch', [element.id]);
          const parts: [Capability, Partial<Geometry>][] = [
            ['geometry.move', Object.fromEntries(Object.entries(command.patch).filter(([key]) => key === 'x' || key === 'y'))],
            ['geometry.resize', Object.fromEntries(Object.entries(command.patch).filter(([key]) => key === 'width' || key === 'height'))],
            ['geometry.rotate', Object.fromEntries(Object.entries(command.patch).filter(([key]) => key === 'rotation'))],
          ];
          for (const [capability, patch] of parts) if (Object.keys(patch).length) run(capability, patch);
        }
        changes = output;
      }
    }
    const next = applyChanges(document, changes);
    return { document: next, changes: freeze(clone(changes)) };
  }

  function assertOpen() {
    if (disposed) throw fault('editor_disposed');
    if (entered) throw fault('reentrant_dispatch');
  }
  function prepareState(next: Snapshot<Runtime>): Snapshot<Runtime> {
    if(!options.prepareRuntime)return next;
    const runtime=options.prepareRuntime(state,next);
    if(isThenable(runtime))throw fault('async_transaction');
    return runtime===next.runtime?next:Object.freeze({...next,runtime});
  }
  function emit(commit: Commit) {
    for (const listener of [...listeners]) try { listener(commit, state); } catch (error) { try { options.onListenerError?.(error); } catch { /* Observers cannot roll back a committed state. */ } }
  }
  function uniqueId(used: Set<Id>): Id {
    const id = createId();
    if (!id || used.has(id) || state.operations.has(id) || state.history.entries.has(id)) throw fault('duplicate_operation_id');
    used.add(id); return id;
  }
  function publish(document: Document, changes: readonly Change[], origin: Origin, history: HistoryState, historyEntryId?: Id): Applied {
    const used = new Set<Id>();
    for (const id of history.entries.keys()) used.add(id);
    // Canonical remote/ACK/replay updates must never feed back into the outbox.
    const outbound = !['remote', 'ack', 'replay'].includes(origin);
    const operationIds = Object.freeze(outbound ? [uniqueId(used)] : []);
    const operations = new Map(state.operations);
    const nextSequence = outbound ? options.nextOperationSequence?.(state.runtime, sequence + 1) ?? sequence + 1 : sequence;
    if (!Number.isSafeInteger(nextSequence) || outbound && nextSequence <= sequence) throw fault('invalid_operation_sequence');
    if (historyEntryId) {
      const entries = new Map(history.entries), entry = entries.get(historyEntryId)!;
      entries.set(entry.id, freeze({ ...entry, operationIds: [...entry.operationIds, ...operationIds] }));
      history = Object.freeze({ ...history, entries: readMap(entries) });
    }
    if (outbound) {
      const canvasIds = new Set<Id>();
      for (const change of changes) {
        if (change.kind === 'canvas') {
          canvasIds.add(change.id);
          if (change.before?.parent) canvasIds.add(change.before.parent.canvasId);
          if (change.after?.parent) canvasIds.add(change.after.parent.canvasId);
        } else if (change.kind === 'element') {
          if (change.before) canvasIds.add(change.before.ownerCanvasId);
          if (change.after) canvasIds.add(change.after.ownerCanvasId);
          if (!change.before && change.after?.structure === 'connection') {
            for (const endpoint of [change.after.source, change.after.target]) {
              const element = document.elements.get(endpoint.elementId) ?? state.document.elements.get(endpoint.elementId);
              if (element) canvasIds.add(element.ownerCanvasId);
            }
          }
        } else {
          const before = state.document.elements.get(change.target.id), after = document.elements.get(change.target.id);
          if (before) canvasIds.add(before.ownerCanvasId);
          if (after) canvasIds.add(after.ownerCanvasId);
          if (change.field === 'ownerCanvasId') { canvasIds.add(change.before as Id); canvasIds.add(change.after as Id); }
          if (change.field === 'source' || change.field === 'target') {
            for (const endpoint of [change.before, change.after]) {
              const id = (endpoint as { elementId?: Id })?.elementId;
              const element = id ? document.elements.get(id) ?? state.document.elements.get(id) : undefined;
              if (element) canvasIds.add(element.ownerCanvasId);
            }
          }
        }
      }
      const historyTransition=describeHistoryTransition(state.history,history,state.rootRevision+1,historyEntryId,true);
      const intent: OperationIntent = freeze({ id: operationIds[0], operationType: 'document.change', operationSchemaVersion: 1, sequence: nextSequence, origin, canvasIds: [...canvasIds].sort(), changes, dependencies: [],...(historyTransition?{historyTransition}:{}) });
      const prepared=options.prepareIntent?.(intent,state.runtime) ?? intent;
      if(prepared.operationType==='run.apply'&&!validJson(prepared.action)||!['document.change','run.apply'].includes(prepared.operationType)||['id','operationSchemaVersion','sequence','origin','canvasIds','changes','dependencies','historyTransition'].some(key=>!equal((prepared as unknown as Record<string,unknown>)[key],(intent as unknown as Record<string,unknown>)[key])))throw fault('invalid_prepared_intent');
      operations.set(intent.id, freeze(clone(prepared)));
    }
    const next: CoreSnapshot = Object.freeze({ revision: state.revision + 1, document, history, operations: readMap(operations) });
    const commit = freeze({ revision: next.revision, origin, changes, operationIds });
    const runtime = options.reduceRuntime ? options.reduceRuntime(state.runtime, next, commit) : state.runtime;
    if (isThenable(runtime)) throw fault('async_transaction');
    const nextState=prepareState(Object.freeze({ ...next, rootRevision: state.rootRevision + 1, runtime })),nextQueries=advanceDocumentQueries(queries,document,options.registry,next.revision,changes);
    state=nextState;queries=nextQueries;queriesByDocument.set(document,queries);
    if (outbound) sequence = nextSequence;
    emit(commit);
    return Object.freeze({ status: 'applied', revision: state.revision, operationIds, ...(historyEntryId ? { historyEntryId } : {}) });
  }

  function transaction(callback: (transaction: Transaction) => unknown, settings: { label?: string; groupId?: Id; history?: boolean; origin?: Origin } = {}): Result {
    try { assertOpen(); } catch (error) { return reject(error); }
    entered = true;
    let active = true, document = state.document, failed: unknown;
    const changes: Change[] = [];
    const tx: Transaction = Object.freeze({
      dispatch(command: Command): Availability {
        if (!active) throw fault('transaction_closed');
        if (failed) return { enabled: false, ...reject(failed) };
        try {
          const result = plan(document, command); document = result.document; changes.push(...result.changes);
          return { enabled: true };
        } catch (error) { failed = error; const result = reject(error); return { enabled: false, code: result.code, targets: result.targets }; }
      },
      getDocument() { if (!active) throw fault('transaction_closed'); return document; },
    });
    try {
      const result = callback(tx);
      active = false;
      if (isThenable(result)) { Promise.resolve(result).catch(() => {}); throw fault('async_transaction'); }
      if (failed) throw failed;
      validateDocument(document, options.registry);
      if (!changes.length || documentsEqual(document, state.document)) return Object.freeze({ status: 'applied', revision: state.revision, operationIds: Object.freeze([]) });
      let history = state.history, historyEntryId: Id | undefined;
      if (settings.history !== false && (!settings.origin || settings.origin === 'user')) {
        const entries = new Map(history.entries), undo = [...history.undo];
        for (const id of history.redo) entries.delete(id);
        const prior = undo.length ? entries.get(undo[undo.length - 1]) : undefined;
        if (settings.groupId && prior?.groupId === settings.groupId) {
          historyEntryId = prior.id;
          entries.set(prior.id, freeze({ ...prior, changes: [...prior.changes, ...changes] }));
        } else {
          historyEntryId = uniqueId(new Set());
          entries.set(historyEntryId, freeze({ id: historyEntryId, label: settings.label || 'Edit', changes: [...changes], operationIds: [], ...(settings.groupId ? { groupId: settings.groupId } : {}) }));
          undo.push(historyEntryId);
        }
        while (undo.length > limit) entries.delete(undo.shift()!);
        history = Object.freeze({ undo: Object.freeze(undo), redo: Object.freeze([]), entries: readMap(entries) });
      }
      return publish(document, freeze([...changes]), settings.origin || 'user', history, historyEntryId);
    } catch (error) { active = false; return reject(error); }
    finally { entered = false; }
  }
  function dispatch(command: Command, settings?: Parameters<typeof transaction>[1]): Result {
    return transaction(tx => { tx.dispatch(command); }, settings);
  }
  function can(command: Command): Availability {
    try { if (disposed) throw fault('editor_disposed'); const result = plan(state.document, command); validateDocument(result.document, options.registry); return { enabled: true }; }
    catch (error) { const result = reject(error); return { enabled: false, code: result.code, targets: result.targets }; }
  }
  function traverse(direction: 'undo' | 'redo'): Result {
    try { assertOpen(); } catch (error) { return reject(error); }
    entered = true;
    try {
      const source = state.history[direction], id = source[source.length - 1];
      if (!id) throw fault('history_empty');
      const entry = state.history.entries.get(id)!;
      const allowed = options.traversalPolicy?.(entry, direction);
      if (allowed && !allowed.enabled) throw fault(allowed.code, allowed.targets);
      const planned=direction==='undo'?invert(entry.changes):entry.changes;
      const {document,changes,remap,restored}=planHistoryChanges(state.document,planned,options.registry);
      const entries=new Map(state.history.entries);
      // Later redo entries belong to the lifecycle restored by this explicit history action.
      // Frozen operations retain their original identities and incarnations.
      if(restored)for(const [otherId,other]of entries)if(otherId!==id)entries.set(otherId,freeze({...other,changes:other.changes.map(remap)}));
      entries.set(id,freeze({...entry,changes:direction==='undo'?invert(changes):changes}));
      const history: HistoryState = Object.freeze({ undo: Object.freeze(direction === 'undo' ? state.history.undo.slice(0, -1) : [...state.history.undo, id]), redo: Object.freeze(direction === 'redo' ? state.history.redo.slice(0, -1) : [...state.history.redo, id]), entries: readMap(entries) });
      return publish(document, changes, direction, history, id);
    } catch (error) { return reject(error); }
    finally { entered = false; }
  }
  return Object.freeze({ getSnapshot: () => state,getQueries:(document=state.document)=>{const value=queriesByDocument.get(document);if(!value)throw fault('query_snapshot_unavailable');return value;}, registry: options.registry, dispatch, transaction, can,
    subscribe(listener: (commit: Commit, snapshot: Snapshot<Runtime>) => void) { if (disposed) throw fault('editor_disposed'); listeners.add(listener); return () => { listeners.delete(listener); }; },
    /** Engine-only metadata commit, sharing the document/history publication boundary. */
    updateRuntime(reduce: (runtime: Runtime) => Runtime, expectedRootRevision = state.rootRevision): Result {
      try { assertOpen(); } catch (error) { return reject(error); }
      entered = true;
      try {
        if (expectedRootRevision !== state.rootRevision) throw fault('stale_plan');
        const runtime = reduce(state.runtime);
        if (isThenable(runtime)) throw fault('async_transaction');
        if (runtime !== state.runtime) {
          state = prepareState(Object.freeze({ ...state, rootRevision: state.rootRevision + 1, runtime }));
          emit(freeze({ revision: state.revision, origin: 'ack', changes: [], operationIds: [] }));
        }
        return Object.freeze({ status: 'applied', revision: state.revision, operationIds: Object.freeze([]) });
      } catch (error) { return reject(error); }
      finally { entered = false; }
    },
    /** Engine-only canonical proposal: validation and runtime state publish as one root. */
    reconcile(document: Document, runtime: Runtime, expectedRootRevision: number, replacement?: { readonly history: HistoryState; readonly operations: ReadonlyMap<Id,OperationIntent> }): Result {
      try { assertOpen(); } catch (error) { return reject(error); }
      entered = true;
      try {
        if (expectedRootRevision !== state.rootRevision) throw fault('stale_plan');
        if (document.projectId !== state.document.projectId) throw fault('project_mismatch');
        const next = createDocument(document.projectId, [...document.canvases.values()], [...document.elements.values()], document.tombstones);
        validateDocument(next, options.registry);
        let nextSequence=sequence;
        if(replacement){
          const {history,operations}=replacement,ids=[...history.undo,...history.redo];
          if(new Set(ids).size!==ids.length||ids.length!==history.entries.size||ids.some(id=>!history.entries.has(id)))throw fault('invalid_history');
          for(const [id,intent]of state.operations)if(!equal(intent,operations.get(id)))throw fault('operation_identity_conflict',[id]);
          for(const [id,intent]of operations){if(id!==intent.id||!Number.isSafeInteger(intent.sequence)||intent.sequence<1)throw fault('invalid_operation_sequence');nextSequence=Math.max(nextSequence,intent.sequence);}
          for(const [id,entry]of history.entries)if(entry.id!==id||entry.operationIds.some(operationId=>!operations.has(operationId)))throw fault('invalid_history');
        }
        const changed = !documentsEqual(next, state.document);
        const nextState=prepareState(Object.freeze({ ...state, ...(replacement?{history:replacement.history,operations:replacement.operations}:{}), document: changed ? next : state.document, runtime, revision: state.revision + Number(changed), rootRevision: state.rootRevision + 1 })),nextQueries=changed?advanceDocumentQueries(queries,next,options.registry,state.revision+1):queries;
        state=nextState;queries=nextQueries;if(changed)queriesByDocument.set(next,queries);
        sequence=nextSequence;
        emit(freeze({ revision: state.revision, origin: 'ack', changes: [], operationIds: [] }));
        return Object.freeze({ status: 'applied', revision: state.revision, operationIds: Object.freeze([]) });
      } catch (error) { return reject(error); }
      finally { entered = false; }
    },
    history: Object.freeze({ undo: () => traverse('undo'), redo: () => traverse('redo'), canUndo: () => !!state.history.undo.length, canRedo: () => !!state.history.redo.length }),
    dispose() { disposed = true; listeners.clear(); },
  });
}
function documentsEqual(a: Document, b: Document): boolean {
  return equal([...a.canvases], [...b.canvases]) && equal([...a.elements], [...b.elements]) && equal([...a.tombstones], [...b.tombstones]);
}