import * as yaml from "js-yaml";
import { MAX_TASK_TITLE_LENGTH } from "@/model/taskFile";
import { isTaskPriority, TASK_PRIORITY_ORDER } from "@/model/taskPriority";
import { isTaskStatus, TASK_STATUS_ORDER } from "@/model/taskStatus";
import {
	extractFrontmatterBlock,
	findFieldRange,
	type TextRange,
} from "./frontmatterBlock";

export type FrontmatterIssueSeverity = "error" | "warning";

export type FrontmatterIssue = {
	field?: string;
	message: string;
	severity: FrontmatterIssueSeverity;
	range: TextRange;
};

const KNOWN_KEYS = new Set([
	"id",
	"title",
	"status",
	"priority",
	"tags",
	"assignee",
	"created",
	"updated",
]);

function isParseableDate(value: unknown): boolean {
	if (value instanceof Date) {
		return !Number.isNaN(value.getTime());
	}
	if (typeof value !== "string" || value.trim() === "") {
		return false;
	}
	const ms = Date.parse(value);
	return !Number.isNaN(ms);
}

function fieldRangeOrBlock(
	content: string,
	key: string,
	blockRange: TextRange,
): TextRange {
	return findFieldRange(content, key) ?? blockRange;
}

/**
 * Validate task file frontmatter. Pure — no vscode.
 * Ranges are 0-based line/column.
 */
export function validateFrontmatter(content: string): FrontmatterIssue[] {
	const issues: FrontmatterIssue[] = [];
	const block = extractFrontmatterBlock(content);

	if (!block) {
		issues.push({
			message: "Task file must start with YAML frontmatter (---)",
			severity: "error",
			range: { startLine: 0, startCol: 0, endLine: 0, endCol: 0 },
		});
		return issues;
	}

	if (block.closeLine < 0) {
		issues.push({
			message: "Frontmatter is not closed (missing closing ---)",
			severity: "error",
			range: block.range,
		});
		return issues;
	}

	let data: unknown;
	try {
		data = yaml.load(block.yaml);
	} catch (error) {
		const detail = error instanceof Error ? error.message : "invalid YAML";
		issues.push({
			message: `Invalid YAML: ${detail}`,
			severity: "error",
			range: block.range,
		});
		return issues;
	}

	if (data === null || data === undefined) {
		issues.push({
			message: "Frontmatter is empty",
			severity: "error",
			range: block.range,
		});
		return issues;
	}

	if (typeof data !== "object" || Array.isArray(data)) {
		issues.push({
			message: "Frontmatter must be a YAML mapping",
			severity: "error",
			range: block.range,
		});
		return issues;
	}

	const record = data as Record<string, unknown>;
	const blockRange = block.range;

	for (const key of Object.keys(record)) {
		if (!KNOWN_KEYS.has(key)) {
			issues.push({
				field: key,
				message: `Unknown field "${key}"`,
				severity: "warning",
				range: fieldRangeOrBlock(content, key, blockRange),
			});
		}
	}

	// id
	if (record.id === undefined) {
		issues.push({
			field: "id",
			message: 'Missing required field "id"',
			severity: "error",
			range: blockRange,
		});
	} else if (typeof record.id !== "string" || record.id.trim() === "") {
		issues.push({
			field: "id",
			message: '"id" must be a non-empty string',
			severity: "error",
			range: fieldRangeOrBlock(content, "id", blockRange),
		});
	}

	// title
	if (record.title === undefined) {
		issues.push({
			field: "title",
			message: 'Missing required field "title"',
			severity: "error",
			range: blockRange,
		});
	} else if (typeof record.title !== "string" || record.title.trim() === "") {
		issues.push({
			field: "title",
			message: '"title" must be a non-empty string',
			severity: "error",
			range: fieldRangeOrBlock(content, "title", blockRange),
		});
	} else if (record.title.length > MAX_TASK_TITLE_LENGTH) {
		issues.push({
			field: "title",
			message: `"title" must be at most ${MAX_TASK_TITLE_LENGTH} characters (now ${record.title.length})`,
			severity: "error",
			range: fieldRangeOrBlock(content, "title", blockRange),
		});
	}

	// status
	if (record.status === undefined) {
		issues.push({
			field: "status",
			message: 'Missing required field "status"',
			severity: "error",
			range: blockRange,
		});
	} else if (!isTaskStatus(record.status)) {
		issues.push({
			field: "status",
			message: `"status" must be one of: ${TASK_STATUS_ORDER.join(", ")}`,
			severity: "error",
			range: fieldRangeOrBlock(content, "status", blockRange),
		});
	}

	// priority
	if (record.priority === undefined) {
		issues.push({
			field: "priority",
			message: 'Missing required field "priority"',
			severity: "error",
			range: blockRange,
		});
	} else if (!isTaskPriority(record.priority)) {
		issues.push({
			field: "priority",
			message: `"priority" must be one of: ${TASK_PRIORITY_ORDER.join(", ")}`,
			severity: "error",
			range: fieldRangeOrBlock(content, "priority", blockRange),
		});
	}

	// tags (optional)
	if (record.tags !== undefined) {
		if (!Array.isArray(record.tags)) {
			issues.push({
				field: "tags",
				message: '"tags" must be an array of strings',
				severity: "error",
				range: fieldRangeOrBlock(content, "tags", blockRange),
			});
		} else if (record.tags.some((t) => typeof t !== "string")) {
			issues.push({
				field: "tags",
				message: '"tags" must be an array of strings',
				severity: "error",
				range: fieldRangeOrBlock(content, "tags", blockRange),
			});
		}
	}

	// assignee (optional)
	if (record.assignee !== undefined && typeof record.assignee !== "string") {
		issues.push({
			field: "assignee",
			message: '"assignee" must be a string',
			severity: "error",
			range: fieldRangeOrBlock(content, "assignee", blockRange),
		});
	}

	// created
	if (record.created === undefined) {
		issues.push({
			field: "created",
			message: 'Missing required field "created"',
			severity: "error",
			range: blockRange,
		});
	} else if (!isParseableDate(record.created)) {
		issues.push({
			field: "created",
			message: '"created" must be a parseable date (ISO 8601 recommended)',
			severity: "error",
			range: fieldRangeOrBlock(content, "created", blockRange),
		});
	}

	// updated
	if (record.updated === undefined) {
		issues.push({
			field: "updated",
			message: 'Missing required field "updated"',
			severity: "error",
			range: blockRange,
		});
	} else if (!isParseableDate(record.updated)) {
		issues.push({
			field: "updated",
			message: '"updated" must be a parseable date (ISO 8601 recommended)',
			severity: "error",
			range: fieldRangeOrBlock(content, "updated", blockRange),
		});
	}

	return issues;
}