import type { Task, WorkflowStepResult } from "./types.js";

const BLOCKING_TASK_STATUSES = new Set([
  "failed",
  "awaiting-inspection",
]);

const NON_TERMINAL_STEP_STATUSES = new Set([
  "pending",
  "in-progress",
]);

const NON_TERMINAL_WORKFLOW_STATUSES = new Set<WorkflowStepResult["status"]>([
  "pending",
]);

/**
 * Returns a human-readable reason when a task in review is not safe to finalize.
 * Undefined means the task is eligible to move from `in-review` to `done`.
 */
export function getTaskMergeBlocker(
  task: Pick<Task, "column" | "paused" | "status" | "error" | "steps" | "workflowStepResults">,
): string | undefined {
  if (task.column !== "in-review") {
    return `task is in '${task.column}', must be in 'in-review'`;
  }

  if (task.paused) {
    return "task is paused";
  }

  if (task.status && BLOCKING_TASK_STATUSES.has(task.status)) {
    return task.error
      ? `task is marked '${task.status}': ${task.error}`
      : `task is marked '${task.status}'`;
  }

  if (task.steps.length > 0 && task.steps.some((step) => NON_TERMINAL_STEP_STATUSES.has(step.status))) {
    return "task has incomplete steps";
  }

  // Only pre-merge workflow step failures block merge.
  // Post-merge failures run after merge and do not block it.
  if (
    task.workflowStepResults?.some((result) => {
      const phase = result.phase || "pre-merge";
      return phase === "pre-merge" && NON_TERMINAL_WORKFLOW_STATUSES.has(result.status);
    })
  ) {
    return "task has incomplete or failed pre-merge workflow steps";
  }

  if (
    task.workflowStepResults?.some((result) => {
      const phase = result.phase || "pre-merge";
      return phase === "pre-merge" && result.status === "failed";
    })
  ) {
    return "task has failed pre-merge workflow steps";
  }

  return undefined;
}

export function isTaskReadyForMerge(
  task: Pick<Task, "column" | "paused" | "status" | "error" | "steps" | "workflowStepResults">,
): boolean {
  return getTaskMergeBlocker(task) === undefined;
}