/**
 * zcatgui WASM Glue Code
 *
 * Provides the JavaScript side of the WASM backend:
 * - Canvas management
 * - Event handling (keyboard, mouse)
 * - Framebuffer presentation
 */

class ZcatguiRuntime {
    constructor(canvasId) {
        this.canvas = document.getElementById(canvasId);
        if (!this.canvas) {
            throw new Error(`Canvas with id '${canvasId}' not found`);
        }
        this.ctx = this.canvas.getContext('2d');
        this.imageData = null;
        this.wasm = null;
        this.memory = null;

        // Event queue
        this.eventQueue = [];
        this.maxEvents = 256;

        // Setup event listeners
        this.setupEventListeners();
    }

    /**
     * Load and initialize the WASM module
     */
    async load(wasmPath) {
        const importObject = {
            env: {
                js_canvas_init: (width, height) => this.canvasInit(width, height),
                js_canvas_present: (pixelsPtr, width, height) => this.canvasPresent(pixelsPtr, width, height),
                js_get_canvas_width: () => this.canvas.width,
                js_get_canvas_height: () => this.canvas.height,
                js_console_log: (ptr, len) => this.consoleLog(ptr, len),
                js_get_time_ms: () => BigInt(performance.now() | 0),
                js_poll_event: (bufferPtr) => this.pollEvent(bufferPtr),
            },
        };

        const response = await fetch(wasmPath);
        const bytes = await response.arrayBuffer();
        const result = await WebAssembly.instantiate(bytes, importObject);

        this.wasm = result.instance;
        this.memory = this.wasm.exports.memory;

        return this.wasm;
    }

    /**
     * Initialize canvas
     */
    canvasInit(width, height) {
        this.canvas.width = width;
        this.canvas.height = height;
        this.imageData = this.ctx.createImageData(width, height);
        console.log(`zcatgui: Canvas initialized ${width}x${height}`);
    }

    /**
     * Present framebuffer to canvas
     */
    canvasPresent(pixelsPtr, width, height) {
        if (!this.imageData || this.imageData.width !== width || this.imageData.height !== height) {
            this.imageData = this.ctx.createImageData(width, height);
        }

        // Copy RGBA pixels from WASM memory to ImageData
        // Pixels are stored as u32 (RGBA packed), need to read as Uint32Array then convert
        const pixels32 = new Uint32Array(this.memory.buffer, pixelsPtr, width * height);
        const pixels8 = this.imageData.data;

        // Convert from RGBA u32 to separate R, G, B, A bytes
        for (let i = 0; i < pixels32.length; i++) {
            const pixel = pixels32[i];
            const offset = i * 4;
            // RGBA format (assuming little-endian)
            pixels8[offset + 0] = pixel & 0xFF;         // R
            pixels8[offset + 1] = (pixel >> 8) & 0xFF;  // G
            pixels8[offset + 2] = (pixel >> 16) & 0xFF; // B
            pixels8[offset + 3] = (pixel >> 24) & 0xFF; // A
        }

        this.ctx.putImageData(this.imageData, 0, 0);
    }

    /**
     * Log to console from WASM
     */
    consoleLog(ptr, len) {
        const bytes = new Uint8Array(this.memory.buffer, ptr, len);
        const text = new TextDecoder().decode(bytes);
        console.log(`[zcatgui] ${text}`);
    }

    /**
     * Poll event from queue
     * Returns event type and writes data to buffer
     */
    pollEvent(bufferPtr) {
        if (this.eventQueue.length === 0) {
            return 0; // No event
        }

        const event = this.eventQueue.shift();
        const buffer = new Uint8Array(this.memory.buffer, bufferPtr, 64);

        switch (event.type) {
            case 'keydown':
                buffer[0] = event.keyCode;
                buffer[1] = this.getModifiers(event);
                return 1;

            case 'keyup':
                buffer[0] = event.keyCode;
                buffer[1] = this.getModifiers(event);
                return 2;

            case 'mousemove':
                this.writeI32(buffer, 0, event.x);
                this.writeI32(buffer, 4, event.y);
                return 3;

            case 'mousedown':
                this.writeI32(buffer, 0, event.x);
                this.writeI32(buffer, 4, event.y);
                buffer[8] = event.button;
                return 4;

            case 'mouseup':
                this.writeI32(buffer, 0, event.x);
                this.writeI32(buffer, 4, event.y);
                buffer[8] = event.button;
                return 5;

            case 'wheel':
                this.writeI32(buffer, 0, event.x);
                this.writeI32(buffer, 4, event.y);
                this.writeI32(buffer, 8, event.deltaX);
                this.writeI32(buffer, 12, event.deltaY);
                return 6;

            case 'resize':
                this.writeU32(buffer, 0, event.width);
                this.writeU32(buffer, 4, event.height);
                return 7;

            case 'quit':
                return 8;

            case 'textinput':
                const encoded = new TextEncoder().encode(event.text);
                buffer[0] = Math.min(encoded.length, 31);
                buffer.set(encoded.slice(0, 31), 1);
                return 9;

            default:
                return 0;
        }
    }

    /**
     * Setup DOM event listeners
     */
    setupEventListeners() {
        // Keyboard events
        document.addEventListener('keydown', (e) => {
            if (this.shouldCaptureKey(e)) {
                e.preventDefault();
                this.queueEvent({
                    type: 'keydown',
                    keyCode: e.keyCode,
                    ctrlKey: e.ctrlKey,
                    shiftKey: e.shiftKey,
                    altKey: e.altKey,
                });

                // Also queue text input for printable characters
                if (e.key.length === 1 && !e.ctrlKey && !e.altKey) {
                    this.queueEvent({
                        type: 'textinput',
                        text: e.key,
                    });
                }
            }
        });

        document.addEventListener('keyup', (e) => {
            if (this.shouldCaptureKey(e)) {
                e.preventDefault();
                this.queueEvent({
                    type: 'keyup',
                    keyCode: e.keyCode,
                    ctrlKey: e.ctrlKey,
                    shiftKey: e.shiftKey,
                    altKey: e.altKey,
                });
            }
        });

        // Mouse events
        this.canvas.addEventListener('mousemove', (e) => {
            const rect = this.canvas.getBoundingClientRect();
            this.queueEvent({
                type: 'mousemove',
                x: Math.floor(e.clientX - rect.left),
                y: Math.floor(e.clientY - rect.top),
            });
        });

        this.canvas.addEventListener('mousedown', (e) => {
            const rect = this.canvas.getBoundingClientRect();
            this.queueEvent({
                type: 'mousedown',
                x: Math.floor(e.clientX - rect.left),
                y: Math.floor(e.clientY - rect.top),
                button: e.button,
            });
        });

        this.canvas.addEventListener('mouseup', (e) => {
            const rect = this.canvas.getBoundingClientRect();
            this.queueEvent({
                type: 'mouseup',
                x: Math.floor(e.clientX - rect.left),
                y: Math.floor(e.clientY - rect.top),
                button: e.button,
            });
        });

        this.canvas.addEventListener('wheel', (e) => {
            e.preventDefault();
            const rect = this.canvas.getBoundingClientRect();
            this.queueEvent({
                type: 'wheel',
                x: Math.floor(e.clientX - rect.left),
                y: Math.floor(e.clientY - rect.top),
                deltaX: Math.sign(e.deltaX) * 3,
                deltaY: Math.sign(e.deltaY) * 3,
            });
        }, { passive: false });

        // Resize observer
        const resizeObserver = new ResizeObserver((entries) => {
            for (const entry of entries) {
                if (entry.target === this.canvas) {
                    this.queueEvent({
                        type: 'resize',
                        width: entry.contentRect.width,
                        height: entry.contentRect.height,
                    });
                }
            }
        });
        resizeObserver.observe(this.canvas);

        // Prevent context menu
        this.canvas.addEventListener('contextmenu', (e) => e.preventDefault());

        // Focus canvas for keyboard input
        this.canvas.tabIndex = 0;
        this.canvas.focus();
    }

    /**
     * Check if we should capture this key event
     */
    shouldCaptureKey(e) {
        // Always capture when canvas is focused
        if (document.activeElement === this.canvas) {
            return true;
        }
        // Capture arrow keys, space, etc. even if not focused
        const captureKeys = [37, 38, 39, 40, 32, 9, 27]; // arrows, space, tab, escape
        return captureKeys.includes(e.keyCode);
    }

    /**
     * Get modifier flags
     */
    getModifiers(e) {
        let mods = 0;
        if (e.ctrlKey) mods |= 1;
        if (e.shiftKey) mods |= 2;
        if (e.altKey) mods |= 4;
        return mods;
    }

    /**
     * Queue an event
     */
    queueEvent(event) {
        if (this.eventQueue.length < this.maxEvents) {
            this.eventQueue.push(event);
        }
    }

    /**
     * Write i32 to buffer (little-endian)
     */
    writeI32(buffer, offset, value) {
        const view = new DataView(buffer.buffer, buffer.byteOffset + offset, 4);
        view.setInt32(0, value, true);
    }

    /**
     * Write u32 to buffer (little-endian)
     */
    writeU32(buffer, offset, value) {
        const view = new DataView(buffer.buffer, buffer.byteOffset + offset, 4);
        view.setUint32(0, value, true);
    }
}

// Export for use
if (typeof module !== 'undefined' && module.exports) {
    module.exports = { ZcatguiRuntime };
} else {
    window.ZcatguiRuntime = ZcatguiRuntime;
}