import type { Task, TaskStatus } from "../tool/types.js";
import type { TaskState } from "./state.js";

/** Tasks excluding deleted tombstones — the canonical "what's visible". */
export function selectVisibleTasks(state: TaskState): readonly Task[] {
	return state.tasks.filter((t) => t.status !== "deleted");
}

/** Total counts for the overlay heading (`Todos (n/m)`). */
export interface TodoCounts {
	total: number;
	pending: number;
	inProgress: number;
	completed: number;
}
export function selectTodoCounts(state: TaskState): TodoCounts {
	const visible = selectVisibleTasks(state);
	return {
		total: visible.length,
		pending: visible.filter((task) => task.status === "pending").length,
		inProgress: visible.filter((task) => task.status === "in_progress").length,
		completed: visible.filter((task) => task.status === "completed").length,
	};
}

/**
 * Resolve a task's subject by id from the live state for renderCall's
 * accent label. `undefined` when the id is unknown — caller falls back to
 * `#id` plain rendering.
 */
export function selectTaskSubjectById(state: TaskState, id: number): string | undefined {
	return state.tasks.find((t) => t.id === id)?.subject;
}

/**
 * Select task rows for the widget body. `budget` covers task rows plus an
 * overflow summary when needed; the caller separately reserves the heading
 * and trailing spacer. Overflow admission is status-prioritized
 * (`in_progress`, `pending`, `completed`), while the returned rows retain the
 * store's natural order so status transitions do not reorder the whole list.
 */
export interface OverlayLayout {
	visible: readonly Task[];
	hiddenPending: number;
	hiddenCompleted: number;
}
export function selectOverlayLayout(state: TaskState, budget: number): OverlayLayout {
	const all = selectVisibleTasks(state);
	if (all.length <= budget) {
		return { visible: all, hiddenPending: 0, hiddenCompleted: 0 };
	}

	const taskBudget = Math.max(0, budget - 1);
	const prioritized = [
		...all.filter((task) => task.status === "in_progress"),
		...all.filter((task) => task.status === "pending"),
		...all.filter((task) => task.status === "completed"),
	];
	const selected = new Set(prioritized.slice(0, taskBudget));
	const visible = all.filter((task) => selected.has(task));

	return {
		visible,
		hiddenPending:
			all.filter((task) => task.status === "pending").length -
			visible.filter((task) => task.status === "pending").length,
		hiddenCompleted:
			all.filter((task) => task.status === "completed").length -
			visible.filter((task) => task.status === "completed").length,
	};
}

/**
 * Helper: whether any visible task is `pending` or `in_progress`. The overlay
 * uses this to pick the heading emphasis from the active icon preset.
 */
export function selectHasActive(state: TaskState): boolean {
	return selectVisibleTasks(state).some((t) => t.status === "in_progress" || t.status === "pending");
}

export const ACTIVE_STATUSES: ReadonlySet<TaskStatus> = new Set(["pending", "in_progress"]);

function compactSubject(subject: string): string {
	return subject.replace(/\s+/g, " ").trim();
}

/** Build the short per-run system-prompt suffix from canonical live state. */
export function formatCurrentTodoState(state: TaskState): string | undefined {
	const active = state.tasks.filter((task) => ACTIVE_STATUSES.has(task.status));
	if (active.length === 0) return undefined;

	const lines = [
		"Current Todo state:",
		...active.map((task) => `- #${task.id} ${task.status}: ${compactSubject(task.subject)}`),
	];
	const completedCount = state.tasks.filter((task) => task.status === "completed").length;
	if (completedCount > 0) {
		lines.push(`- ${completedCount} completed ${completedCount === 1 ? "task" : "tasks"} hidden`);
	}
	return lines.join("\n");
}

/** Ephemeral context fallback when live state changes after run-start injection. */
export function formatCurrentTodoStateUpdate(state: TaskState): string {
	const current = formatCurrentTodoState(state);
	if (current) return current.replace("Current Todo state:", "Current Todo state update:");

	const lines = ["Current Todo state update:", "- No pending or in_progress tasks"];
	const completedCount = state.tasks.filter((task) => task.status === "completed").length;
	if (completedCount > 0) {
		lines.push(`- ${completedCount} completed ${completedCount === 1 ? "task" : "tasks"} hidden`);
	}
	return lines.join("\n");
}