/**
 * image-utils.ts — Browser-side image validation, reading, resizing, and processing.
 *
 * Pure utilities shared by chat mode (drag/paste → base64 inline) and terminal mode
 * (drag/paste → upload). All functions are side-effect-free except for Canvas usage
 * in resizeImageInBrowser.
 *
 * Observability:
 * - console.warn on validation failure (wrong MIME type, oversized file)
 * - Errors thrown with descriptive messages for upstream catch handlers
 */

// ─── Constants ────────────────────────────────────────────────────────────────

const ALLOWED_MIME_TYPES = new Set([
	"image/jpeg",
	"image/png",
	"image/gif",
	"image/webp",
]);

/** Raw file size limit before base64 encoding (20 MB) */
const MAX_RAW_FILE_SIZE = 20 * 1024 * 1024;

/** Maximum base64 payload size after encoding/resize (4.5 MB) */
const MAX_BASE64_PAYLOAD_SIZE = 4.5 * 1024 * 1024;

/** Maximum image dimension (width or height) before resize triggers */
const MAX_DIMENSION = 2000;

/** Maximum number of pending images per message */
export const MAX_PENDING_IMAGES = 5;

// ─── Types ────────────────────────────────────────────────────────────────────

export interface PendingImage {
	/** Unique identifier for removal */
	id: string;
	/** Base64-encoded image data (no data URI prefix) */
	data: string;
	/** MIME type of the image */
	mimeType: string;
	/** Blob URL for efficient thumbnail rendering — must be revoked on cleanup */
	previewUrl: string;
}

// ─── Validation ───────────────────────────────────────────────────────────────

export function validateImageFile(file: File): {
	valid: boolean;
	error?: string;
} {
	if (!ALLOWED_MIME_TYPES.has(file.type)) {
		const error = `Unsupported image type: ${file.type || "unknown"}. Accepted: JPEG, PNG, GIF, WebP.`;
		console.warn("[image-utils] validation failed:", error);
		return { valid: false, error };
	}

	if (file.size > MAX_RAW_FILE_SIZE) {
		const sizeMB = (file.size / (1024 * 1024)).toFixed(1);
		const error = `Image too large (${sizeMB} MB). Maximum: 20 MB.`;
		console.warn("[image-utils] validation failed:", error);
		return { valid: false, error };
	}

	return { valid: true };
}

// ─── File Reading ─────────────────────────────────────────────────────────────

export function readFileAsBase64(file: File): Promise<string> {
	return new Promise((resolve, reject) => {
		const reader = new FileReader();
		reader.onload = () => {
			const arrayBuffer = reader.result as ArrayBuffer;
			const bytes = new Uint8Array(arrayBuffer);
			let binary = "";
			for (let i = 0; i < bytes.length; i++) {
				binary += String.fromCharCode(bytes[i]);
			}
			resolve(btoa(binary));
		};
		reader.onerror = () => reject(new Error("Failed to read image file"));
		reader.readAsArrayBuffer(file);
	});
}

// ─── Resize ───────────────────────────────────────────────────────────────────

/**
 * Resize an image if its dimensions exceed MAX_DIMENSION or its payload exceeds
 * MAX_BASE64_PAYLOAD_SIZE.
 *
 * For GIF/WebP: skip resize if the base64 payload is already under the byte limit
 * (canvas strips animation frames). If over limit, convert to JPEG.
 *
 * Re-checks final payload size after resize; rejects if still over limit.
 */
export async function resizeImageInBrowser(
	base64: string,
	mimeType: string,
): Promise<{ data: string; mimeType: string }> {
	const payloadBytes = base64.length * 0.75; // approximate decoded size

	// For animated formats (GIF/WebP), preserve if under limit
	if (
		(mimeType === "image/gif" || mimeType === "image/webp") &&
		payloadBytes <= MAX_BASE64_PAYLOAD_SIZE
	) {
		return { data: base64, mimeType };
	}

	// Load image to check dimensions
	const img = await loadImage(base64, mimeType);
	const needsDimensionResize =
		img.width > MAX_DIMENSION || img.height > MAX_DIMENSION;
	const needsPayloadResize = payloadBytes > MAX_BASE64_PAYLOAD_SIZE;

	if (!needsDimensionResize && !needsPayloadResize) {
		return { data: base64, mimeType };
	}

	// Determine output format — animated formats convert to JPEG when resized
	const outputMime =
		mimeType === "image/gif" || mimeType === "image/webp"
			? "image/jpeg"
			: mimeType;

	// Calculate target dimensions
	let targetWidth = img.width;
	let targetHeight = img.height;

	if (needsDimensionResize) {
		const scale = Math.min(
			MAX_DIMENSION / img.width,
			MAX_DIMENSION / img.height,
		);
		targetWidth = Math.round(img.width * scale);
		targetHeight = Math.round(img.height * scale);
	}

	// Canvas resize
	const canvas = document.createElement("canvas");
	canvas.width = targetWidth;
	canvas.height = targetHeight;
	const ctx = canvas.getContext("2d");
	if (!ctx) throw new Error("Canvas 2D context not available");

	ctx.drawImage(img, 0, 0, targetWidth, targetHeight);

	// Encode — JPEG gets quality 0.85, PNG is lossless
	const quality = outputMime === "image/jpeg" ? 0.85 : undefined;
	const dataUrl = canvas.toDataURL(outputMime, quality);
	const resizedBase64 = dataUrl.split(",")[1];

	// Re-check payload size
	const finalBytes = resizedBase64.length * 0.75;
	if (finalBytes > MAX_BASE64_PAYLOAD_SIZE) {
		throw new Error(
			`Image still exceeds 4.5 MB after resize (${(finalBytes / (1024 * 1024)).toFixed(1)} MB). Try a smaller image.`,
		);
	}

	return { data: resizedBase64, mimeType: outputMime };
}

// ─── Orchestrator ─────────────────────────────────────────────────────────────

/**
 * Single entry point: validate → read → resize.
 * Used by both chat mode and terminal mode.
 */
export async function processImageFile(
	file: File,
): Promise<{ data: string; mimeType: string }> {
	const validation = validateImageFile(file);
	if (!validation.valid) {
		throw new Error(validation.error);
	}

	const base64 = await readFileAsBase64(file);
	return resizeImageInBrowser(base64, file.type);
}

// ─── Helpers ──────────────────────────────────────────────────────────────────

function loadImage(
	base64: string,
	mimeType: string,
): Promise<HTMLImageElement> {
	return new Promise((resolve, reject) => {
		const img = new Image();
		img.onload = () => resolve(img);
		img.onerror = () => reject(new Error("Failed to decode image"));
		img.src = `data:${mimeType};base64,${base64}`;
	});
}

/** Generate a short unique ID for pending image tracking */
export function generateImageId(): string {
	return `img-${Date.now()}-${Math.random().toString(36).slice(2, 8)}`;
}