/**
 * Outcome-Driven Action Queue State Machine for autonomous agent execution.
 * Manages compound instruction synthesis, state transitions, outcome verification,
 * and dynamic execution steering.
 */

export type ActionStepStatus = "pending" | "running" | "completed" | "cancelled" | "failed";

export interface ActionQueueStep {
  id: string;
  intent: string;
  outcomeCriteria: string;
  status: ActionStepStatus;
  startedAt?: number;
  completedAt?: number;
}

export interface DynamicActionQueue {
  steps: ActionQueueStep[];
  activeStepId: string | null;
  synthesizeInput(
    rawText: string,
    options?: { criteriaTemplate?: (intent: string) => string },
  ): ActionQueueStep[];
  cancelActive(reason?: string): ActionQueueStep | null;
  advance(): ActionQueueStep | null;
}

export interface ActionQueueSnapshot {
  steps: ActionQueueStep[];
  activeStepId: string | null;
}

export type StepVerificationGate = (
  step: ActionQueueStep,
  output?: unknown,
) => boolean | Promise<boolean>;

export const ALLOWED_STEP_TRANSITIONS: Record<ActionStepStatus, readonly ActionStepStatus[]> = {
  pending: ["running", "cancelled"],
  running: ["completed", "failed", "cancelled"],
  completed: [],
  failed: ["running", "cancelled"],
  cancelled: [],
};

export function canTransitionStep(from: ActionStepStatus, to: ActionStepStatus): boolean {
  return (ALLOWED_STEP_TRANSITIONS[from] as readonly ActionStepStatus[])?.includes(to) ?? false;
}

export function assertStepTransition(from: ActionStepStatus, to: ActionStepStatus): void {
  if (!canTransitionStep(from, to)) {
    throw new Error(`Illegal step transition from ${from} to ${to}`);
  }
}

export function isTerminalStepStatus(status: ActionStepStatus): boolean {
  return status === "completed" || status === "cancelled";
}

export function isActiveStepStatus(status: ActionStepStatus): boolean {
  return status === "running";
}

const STEP_SPLIT_REGEX = /(?:;|\.|\n+|\r+|\bthen\b|\band then\b|\bnext\b|,\s*and\b|,)/i;

export class DynamicActionQueueImpl implements DynamicActionQueue {
  public steps: ActionQueueStep[] = [];
  public activeStepId: string | null = null;
  private verificationGate?: StepVerificationGate;

  constructor(initialSteps: ActionQueueStep[] = [], activeStepId: string | null = null) {
    this.steps = initialSteps.map((s) => ({ ...s }));
    this.activeStepId = activeStepId;
  }

  setVerificationGate(gate: StepVerificationGate | undefined): void {
    this.verificationGate = gate;
  }

  getVerificationGate(): StepVerificationGate | undefined {
    return this.verificationGate;
  }

  async verifyStep(stepId: string, output?: unknown): Promise<boolean> {
    const step = this.steps.find((s) => s.id === stepId);
    if (!step) return false;
    if (!this.verificationGate) return true;
    return Boolean(await this.verificationGate(step, output));
  }

  synthesizeInput(
    rawText: string,
    options?: { criteriaTemplate?: (intent: string) => string },
  ): ActionQueueStep[] {
    const trimmed = rawText.trim();
    if (!trimmed) return [];

    const criteriaFn =
      options?.criteriaTemplate ?? ((intent: string) => `Verify ${intent} completed successfully`);

    const parts = trimmed
      .split(STEP_SPLIT_REGEX)
      .map((s) => s.trim())
      .filter((s) => s.length > 0);

    const created: ActionQueueStep[] = [];
    for (const part of parts) {
      const step: ActionQueueStep = {
        id: `step-${this.steps.length + 1}`,
        intent: part,
        outcomeCriteria: criteriaFn(part),
        status: "pending",
      };
      this.steps.push(step);
      created.push(step);
    }
    return created;
  }

  cancelActive(_reason?: string): ActionQueueStep | null {
    if (!this.activeStepId) return null;
    const step = this.steps.find((s) => s.id === this.activeStepId);
    if (!step) {
      this.activeStepId = null;
      return null;
    }

    if (step.status === "running" || step.status === "pending") {
      step.status = "cancelled";
      step.completedAt = Date.now();
    }
    this.activeStepId = null;
    return step;
  }

  advance(): ActionQueueStep | null {
    // If a step is currently running, complete it
    if (this.activeStepId) {
      const active = this.steps.find((s) => s.id === this.activeStepId);
      if (active && active.status === "running") {
        active.status = "completed";
        active.completedAt = Date.now();
      }
    }

    // Do not auto-advance past a failed step
    const hasFailed = this.steps.some((s) => s.status === "failed");
    if (hasFailed) {
      this.activeStepId = null;
      return null;
    }

    // Advance to next pending step
    const next = this.steps.find((s) => s.status === "pending");
    if (next) {
      next.status = "running";
      next.startedAt = Date.now();
      this.activeStepId = next.id;
      return next;
    }

    this.activeStepId = null;
    return null;
  }

  updateStepStatus(stepId: string, status: ActionStepStatus, _reason?: string): ActionQueueStep {
    const step = this.steps.find((s) => s.id === stepId);
    if (!step) {
      throw new Error(`Step not found: ${stepId}`);
    }

    assertStepTransition(step.status, status);

    step.status = status;
    const now = Date.now();

    if (status === "running") {
      step.startedAt = step.startedAt ?? now;
      this.activeStepId = step.id;
    } else {
      if (status === "completed" || status === "cancelled" || status === "failed") {
        step.completedAt = now;
      }
      if (this.activeStepId === step.id) {
        this.activeStepId = null;
      }
    }

    return step;
  }

  reorderSteps(fromIndex: number, toIndex: number): void {
    if (
      fromIndex < 0 ||
      fromIndex >= this.steps.length ||
      toIndex < 0 ||
      toIndex >= this.steps.length
    ) {
      throw new RangeError(
        `Invalid step reorder indices: ${fromIndex} -> ${toIndex} (queue length: ${this.steps.length})`,
      );
    }
    if (fromIndex === toIndex) return;

    const [moved] = this.steps.splice(fromIndex, 1);
    if (moved) {
      this.steps.splice(toIndex, 0, moved);
    }
  }

  insertStep(
    stepData: {
      id?: string;
      intent: string;
      outcomeCriteria?: string;
      status?: ActionStepStatus;
      startedAt?: number;
      completedAt?: number;
    },
    atIndex?: number,
  ): ActionQueueStep {
    const id = stepData.id ?? `step-${this.steps.length + 1}`;
    const step: ActionQueueStep = {
      id,
      intent: stepData.intent,
      outcomeCriteria:
        stepData.outcomeCriteria ?? `Verify ${stepData.intent} completed successfully`,
      status: stepData.status ?? "pending",
      startedAt: stepData.startedAt,
      completedAt: stepData.completedAt,
    };

    if (typeof atIndex === "number" && atIndex >= 0 && atIndex <= this.steps.length) {
      this.steps.splice(atIndex, 0, step);
    } else {
      this.steps.push(step);
    }

    return step;
  }

  removeStep(stepId: string): boolean {
    const index = this.steps.findIndex((s) => s.id === stepId);
    if (index === -1) return false;

    if (this.activeStepId === stepId) {
      this.activeStepId = null;
    }
    this.steps.splice(index, 1);
    return true;
  }

  retryStep(stepId: string): ActionQueueStep {
    const step = this.steps.find((s) => s.id === stepId);
    if (!step) {
      throw new Error(`Step not found: ${stepId}`);
    }
    if (step.status !== "failed") {
      throw new Error(
        `Cannot retry step with status "${step.status}"; only failed steps can be retried`,
      );
    }

    step.status = "pending";
    step.completedAt = undefined;
    return step;
  }

  getStep(stepId: string): ActionQueueStep | undefined {
    return this.steps.find((s) => s.id === stepId);
  }

  getActiveStep(): ActionQueueStep | null {
    if (!this.activeStepId) return null;
    return this.steps.find((s) => s.id === this.activeStepId) ?? null;
  }

  getPendingSteps(): ActionQueueStep[] {
    return this.steps.filter((s) => s.status === "pending");
  }

  isComplete(): boolean {
    return (
      this.steps.length > 0 &&
      this.steps.every(
        (s) => s.status === "completed" || s.status === "cancelled" || s.status === "failed",
      )
    );
  }

  hasFailed(): boolean {
    return this.steps.some((s) => s.status === "failed");
  }

  clear(): void {
    this.steps = [];
    this.activeStepId = null;
  }

  toJSON(): ActionQueueSnapshot {
    return {
      steps: this.steps.map((s) => ({ ...s })),
      activeStepId: this.activeStepId,
    };
  }

  static fromJSON(snapshot: ActionQueueSnapshot): DynamicActionQueueImpl {
    return new DynamicActionQueueImpl(snapshot.steps, snapshot.activeStepId);
  }
}

/** Convenient alias */
export const ActionQueue = DynamicActionQueueImpl;