// Global Three.js variables
let scene, camera, renderer, terrainMesh, controls;
let terrainSize = 64;
let isAnimating = false;
let animationId = null;

// Initialize the 3D scene
function initScene() {
    const canvas = document.getElementById('terrain-canvas');
    
    // Scene setup
    scene = new THREE.Scene();
    scene.background = new THREE.Color(0x1a202c);
    
    // Camera setup
    camera = new THREE.PerspectiveCamera(75, canvas.clientWidth / canvas.clientHeight, 0.1, 1000);
    camera.position.set(terrainSize * 0.7, terrainSize * 0.7, terrainSize * 0.7);
    camera.lookAt(0, 0, 0);
    
    // Renderer setup
    renderer = new THREE.WebGLRenderer({ canvas, antialias: true });
    renderer.setSize(canvas.clientWidth, canvas.clientHeight);
    
    // Lighting
    const ambientLight = new THREE.AmbientLight(0x404040);
    scene.add(ambientLight);
    
    const directionalLight = new THREE.DirectionalLight(0xffffff, 0.8);
    directionalLight.position.set(1, 1, 1);
    scene.add(directionalLight);
    
    // Orbit controls
    controls = new THREE.OrbitControls(camera, renderer.domElement);
    controls.enableDamping = true;
    controls.dampingFactor = 0.25;
    
    // Handle window resize
    window.addEventListener('resize', onWindowResize);
}

// Generate terrain using specified algorithm
function generateTerrain(algorithm) {
    // Remove existing terrain if any
    if (terrainMesh) {
        scene.remove(terrainMesh);
        terrainMesh.geometry.dispose();
        terrainMesh.material.dispose();
    }
    
    // Get parameters from sliders
    terrainSize = parseInt(document.getElementById('size-slider').value);
    const roughness = parseFloat(document.getElementById('roughness-slider').value);
    const heightScale = parseInt(document.getElementById('height-slider').value);
    const waterLevel = parseInt(document.getElementById('water-slider').value) / 100;
    
    // Generate heightmap
    let heightmap = generateHeightmap(algorithm, terrainSize, roughness, heightScale);
    
    // Create geometry from heightmap
    const geometry = createGeometryFromHeightmap(heightmap, terrainSize, heightScale);
    
    // Create material with water effect
    const material = createTerrainMaterial(heightmap, terrainSize, heightScale, waterLevel);
    
    // Create mesh
    terrainMesh = new THREE.Mesh(geometry, material);
    scene.add(terrainMesh);
    
    // Update camera position based on terrain size
    camera.position.set(terrainSize * 0.7, terrainSize * 0.7, terrainSize * 0.7);
    camera.lookAt(0, 0, 0);
    controls.update();
    
    // Start animation if not already running
    if (!isAnimating) {
        animate();
    }
    
    // Update 2D previews
    updatePreviews(heightmap, algorithm);
}

// Generate heightmap using specified algorithm
function generateHeightmap(algorithm, size, roughness, heightScale) {
    const heightmap = new Array(size * size).fill(0);
    
    // Simplified implementations for demo purposes
    switch(algorithm) {
        case 'diamond-square':
            // Implement diamond-square algorithm
            diamondSquare(heightmap, size, roughness);
            break;
            
        case 'perlin':
            // Implement Perlin noise
            for (let y = 0; y < size; y++) {
                for (let x = 0; x < size; x++) {
                    const value = noise.perlin2(x * roughness / 10, y * roughness / 10);
                    heightmap[y * size + x] = (value + 1) * 0.5 * heightScale;
                }
            }
            break;
            
        case 'simplex':
            // Implement Simplex noise
            for (let y = 0; y < size; y++) {
                for (let x = 0; x < size; x++) {
                    const value = noise.simplex2(x * roughness / 10, y * roughness / 10);
                    heightmap[y * size + x] = (value + 1) * 0.5 * heightScale;
                }
            }
            break;
            
        default:
            console.error('Unknown algorithm:', algorithm);
    }
    
    return heightmap;
}

// Simplified Diamond-Square implementation
function diamondSquare(heightmap, size, roughness) {
    // Initialize corners
    heightmap[0] = Math.random() * roughness;
    heightmap[size - 1] = Math.random() * roughness;
    heightmap[size * (size - 1)] = Math.random() * roughness;
    heightmap[size * size - 1] = Math.random() * roughness;
    
    let step = size - 1;
    let scale = roughness;
    
    while (step > 1) {
        // Diamond step
        for (let y = 0; y < size - 1; y += step) {
            for (let x = 0; x < size - 1; x += step) {
                const avg = (
                    heightmap[y * size + x] +
                    heightmap[y * size + (x + step)] +
                    heightmap[(y + step) * size + x] +
                    heightmap[(y + step) * size + (x + step)]
                ) / 4;
                
                const centerX = x + step / 2;
                const centerY = y + step / 2;
                const centerIndex = centerY * size + centerX;
                heightmap[centerIndex] = avg + (Math.random() * 2 - 1) * scale;
            }
        }
        
        // Square step
        for (let y = 0; y < size; y += step / 2) {
            for (let x = (y + step / 2) % step; x < size; x += step) {
                let sum = 0;
                let count = 0;
                
                // Top neighbor
                if (y - step / 2 >= 0) {
                    sum += heightmap[(y - step / 2) * size + x];
                    count++;
                }
                
                // Bottom neighbor
                if (y + step / 2 < size) {
                    sum += heightmap[(y + step / 2) * size + x];
                    count++;
                }
                
                // Left neighbor
                if (x - step / 2 >= 0) {
                    sum += heightmap[y * size + (x - step / 2)];
                    count++;
                }
                
                // Right neighbor
                if (x + step / 2 < size) {
                    sum += heightmap[y * size + (x + step / 2)];
                    count++;
                }
                
                if (count > 0) {
                    heightmap[y * size + x] = sum / count + (Math.random() * 2 - 1) * scale;
                }
            }
        }
        
        step = Math.floor(step / 2);
        scale *= roughness;
    }
}

// Create Three.js geometry from heightmap
function createGeometryFromHeightmap(heightmap, size, heightScale) {
    const geometry = new THREE.PlaneGeometry(size, size, size - 1, size - 1);
    
    // Apply heightmap to vertices
    for (let i = 0; i < geometry.attributes.position.count; i++) {
        const x = i % size;
        const y = Math.floor(i / size);
        geometry.attributes.position.setZ(i, heightmap[y * size + x]);
    }
    
    geometry.rotateX(-Math.PI / 2);
    geometry.computeVertexNormals();
    
    return geometry;
}

// Create terrain material with water effect
function createTerrainMaterial(heightmap, size, heightScale, waterLevel) {
    // Find min and max heights
    let minHeight = Infinity;
    let maxHeight = -Infinity;
    
    for (const height of heightmap) {
        if (height < minHeight) minHeight = height;
        if (height > maxHeight) maxHeight = height;
    }
    
    const waterHeight = minHeight + (maxHeight - minHeight) * waterLevel;
    
    // Create color gradient
    const texture = new THREE.CanvasTexture(createTerrainTexture(size, minHeight, maxHeight, waterHeight));
    
    return new THREE.MeshStandardMaterial({
        map: texture,
        metalness: 0.1,
        roughness: 0.7,
        flatShading: false
    });
}

// Create terrain texture with elevation colors
function createTerrainTexture(size, minHeight, maxHeight, waterHeight) {
    const canvas = document.createElement('canvas');
    canvas.width = size;
    canvas.height = size;
    const ctx = canvas.getContext('2d');
    
    // Draw gradient based on height
    const imageData = ctx.createImageData(size, size);
    
    for (let y = 0; y < size; y++) {
        for (let x = 0; x < size; x++) {
            const idx = (y * size + x) * 4;
            const height = heightmap[y * size + x];
            
            // Water
            if (height <= waterHeight) {
                const depth = (waterHeight - height) / (waterHeight - minHeight);
                imageData.data[idx] = 30 + 50 * depth; // R
                imageData.data[idx + 1] = 80 + 100 * depth; // G
                imageData.data[idx + 2] = 150 + 100 * depth; // B
            }
            // Beach/Sand
            else if (height <= waterHeight + (maxHeight - waterHeight) * 0.05) {
                imageData.data[idx] = 210; // R
                imageData.data[idx + 1] = 190; // G
                imageData.data[idx + 2] = 140; // B
            }
            // Grass
            else if (height <= waterHeight + (maxHeight - waterHeight) * 0.3) {
                const t = (height - waterHeight) / ((maxHeight - waterHeight) * 0.3);
                imageData.data[idx] = 50 + 80 * t; // R
                imageData.data[idx + 1] = 100 + 80 * t; // G
                imageData.data[idx + 2] = 50 + 30 * t; // B
            }
            // Rock
            else if (height <= waterHeight + (maxHeight - waterHeight) * 0.7) {
                const t = (height - waterHeight - (maxHeight - waterHeight) * 0.3) / ((maxHeight - waterHeight) * 0.4);
                imageData.data[idx] = 100 + 50 * t; // R
                imageData.data[idx + 1] = 80 + 20 * t; // G
                imageData.data[idx + 2] = 60 + 20 * t; // B
            }
            // Snow
            else {
                const t = (height - waterHeight - (maxHeight - waterHeight) * 0.7) / ((maxHeight - waterHeight) * 0.3);
                imageData.data[idx] = 180 + 75 * t; // R
                imageData.data[idx + 1] = 190 + 65 * t; // G
                imageData.data[idx + 2] = 200 + 55 * t; // B
            }
            
            imageData.data[idx + 3] = 255; // Alpha
        }
    }
    
    ctx.putImageData(imageData, 0, 0);
    return canvas;
}

// Update 2D preview canvases
function updatePreviews(heightmap, algorithm) {
    const size = Math.min(128, terrainSize);
    const previewCanvas = document.getElementById(`${algorithm}-canvas`);
    const ctx = previewCanvas.getContext('2d');
    
    // Scale heightmap to fit preview
    const step = Math.floor(terrainSize / size);
    const imageData = ctx.createImageData(size, size);
    
    for (let y = 0; y < size; y++) {
        for (let x = 0; x < size; x++) {
            const idx = (y * size + x) * 4;
            const height = heightmap[y * step * terrainSize + x * step];
            const normalizedHeight = Math.floor((height / Math.max(...heightmap)) * 255);
            
            imageData.data[idx] = normalizedHeight; // R
            imageData.data[idx + 1] = normalizedHeight; // G
            imageData.data[idx + 2] = normalizedHeight; // B
            imageData.data[idx + 3] = 255; // Alpha
        }
    }
    
    ctx.putImageData(imageData, 0, 0);
}

// Animation loop
function animate() {
    isAnimating = true;
    animationId = requestAnimationFrame(animate);
    controls.update();
    renderer.render(scene, camera);
}

// Handle window resize
function onWindowResize() {
    const canvas = document.getElementById('terrain-canvas');
    camera.aspect = canvas.clientWidth / canvas.clientHeight;
    camera.updateProjectionMatrix();
    renderer.setSize(canvas.clientWidth, canvas.clientHeight);
}

// Camera controls
function rotateCamera(direction) {
    const angle = direction === 'left' ? -Math.PI / 8 : Math.PI / 8;
    camera.position.applyAxisAngle(new THREE.Vector3(0, 1, 0), angle);
    camera.lookAt(0, 0, 0);
}

function resetCamera() {
    camera.position.set(terrainSize * 0.7, terrainSize * 0.7, terrainSize * 0.7);
    camera.lookAt(0, 0, 0);
    controls.update();
}

// Initialize when DOM is loaded
document.addEventListener('DOMContentLoaded', function() {
    initScene();
    generateTerrain('diamond-square');
});