//椭球相关参数计算
const a = 6378137; //长半轴 a
const f = 1 / 298.257223563; //扁率 (a-b)/a
const b = a * (1 - f); //短半轴 b
const e = Math.sqrt(a * a - b * b) / a; //椭球第一偏心率

function degToRad(deg) {
    return deg / 180 * Math.PI;
}

function radToDeg(rad) {
    return rad / Math.PI * 180;
}

function wgs84ToWebMercator(lat, lon) {
    let x = a * lon;
    let y = a * Math.log(Math.tan(Math.PI / 4 + lat / 2));
    return { x: x, y: y };
}

function webMercatorToWgs84(x, y) {
    let lon = x / a;
    let lat = 2 * Math.atan(Math.pow(Math.E, y / a)) - Math.PI / 2;
    return { lon: lon, lat: lat }
}

function lon2tile(lon, z) {
    return (Math.floor((lon + 180) / 360 * Math.pow(2, z)));
}

function lat2tile(lat, z) {
    return (Math.floor((1 - Math.log(Math.tan(lat * Math.PI / 180) +
            1 / Math.cos(lat * Math.PI / 180)) / Math.PI) /
        2 * Math.pow(2, z)));
}

function lon2x(lon, z) {
    return ((lon + 180) / 360 * Math.pow(2, z));
}

function lat2y(lat, z) {
    return ((1 - Math.log(Math.tan(lat * Math.PI / 180) +
            1 / Math.cos(lat * Math.PI / 180)) / Math.PI) /
        2 * Math.pow(2, z));
}

function tile2long(x, z) {
    return (x / Math.pow(2, z) * 360 - 180);
}

function tile2lat(y, z) {
    var n = Math.PI - 2 * Math.PI * y / Math.pow(2, z);
    return (180 / Math.PI * Math.atan(0.5 * (Math.exp(n) - Math.exp(-n))));
}

//https://tile.openstreetmap.org/z/x/y.png
//https://tile.openstreetmap.org/15/26794/14256.png

let cache = new Array();

function downloadimg(z, x, y) {
    const src = 'https://tile.openstreetmap.org/' + z + '/' + x + '/' + y + '.png';
    let img = new Image();
    img.src = src;
    img.onload = () => {
        console.log('downloaded' + z + '/' + x + '/' + y + '.png');
        cache.push({ img: img, z: z, x: x, y: y });
    }
}

function getIndex(z, x, y) {
    for (let i = 0; i < cache.length; i++) {
        const e = cache[i];
        if (e.z == z && e.x == x && e.y == y) {
            return i;
        } else {
            continue;
        }
    }
    //last
    downloadimg(z, x, y);
    return cache.length;
}

//已知条件 lat long zoom_level 显示范围的宽高
let zoom_level = 15;
let lat = 22.7490073;
let long = 114.3781213;
let width = 1600;
let height = 900;

function calBasetile(lat, long, zoom_level) {
    let basetile = {};
    basetile.x = lon2x(long, zoom_level); //对应zoomlevel下long的x坐标
    basetile.y = lat2y(lat, zoom_level); //对应zoomlevel下lat的y坐标
    basetile.tilex = lon2tile(long, zoom_level); //对应zoomlevel下long的x tile编号
    basetile.tiley = lat2tile(lat, zoom_level); //对应zoomlevel下lat的y tile编号
    basetile.offsetx = Math.floor((basetile.x - basetile.tilex) * 256); //相对于左上角，其点的x偏移值
    basetile.offsety = Math.floor((basetile.y - basetile.tiley) * 256); //相对于左上角，其点的y偏移值

    basetile.minx = width / 2 - basetile.offsetx;
    basetile.maxx = basetile.minx + 256;
    basetile.miny = height / 2 - basetile.offsety;
    basetile.maxy = basetile.miny + 256;

    basetile.p1 = Math.floor(basetile.maxy / 256 + 0.5);
    basetile.p2 = Math.floor((height - basetile.miny) / 256 + 0.5);
    basetile.p3 = Math.floor(basetile.maxx / 256 + 0.5);
    basetile.p4 = Math.floor((width - basetile.minx) / 256 + 0.5);
    console.log(basetile);
    return basetile;
}

//基于已知条件计算需要的各个tile
function needtiles(basetile, p1, p2, p3, p4) {
    let tiles = new Array();
    let tilex = basetile.tilex;
    let tiley = basetile.tiley;
    tiles.push({ x: tilex, y: tiley });
    for (let i = 0; i < p4; i++) {
        tiles.push({ x: tilex + i + 1, y: tiley });
    }
    for (let i = 0; i < p3; i++) {
        tiles.push({ x: tilex - i - 1, y: tiley });
    }
    for (let i = 0; i < p1; i++) {
        for (let j = 0; j < p3 + p4 + 1; j++) {
            tiles.push({ x: tilex - p3 + j, y: tiley - i - 1 });
        }
    }
    for (let i = 0; i < p2; i++) {
        for (let j = 0; j < p3 + p4 + 1; j++) {
            tiles.push({ x: tilex - p3 + j, y: tiley + i + 1 });
        }
    }
    //console.log(tiles);
    //console.log(tiles.length);
    return tilesfilter(tiles, zoom_level);
}

//过滤超过限制的tiles
function tilesfilter(tiles, zoom_level) {
    const maxrange = Math.pow(2, zoom_level) - 1;
    let newtiles = new Array();
    for (let i = 0; i < tiles.length; i++) {
        if (tiles[i].x < 0 || tiles[i].x > maxrange) {
            continue;
        }
        if (tiles[i].y < 0 || tiles[i].y > maxrange) {
            continue;
        }
        newtiles.push(tiles[i]);
    }
    return newtiles;
}

let basetile = calBasetile(lat, long, zoom_level);
let tiles = needtiles(basetile, basetile.p1, basetile.p2, basetile.p3, basetile.p4);


//渲染问题
//通过与基准之间的位置关系计算渲染的坐标
//minx miny 即为基准tile当前渲染位置

// for (let i = 0; i < tiles.length; i++) {
//     const element = tiles[i];
//     let renderx = (element.x - tilex) * 256 + minx;
//     let rendery = (element.y - tiley) * 256 + miny;
//     console.log({ x: renderx, y: rendery });
// }

let canvas = document.getElementById('map');
canvas.width = map.clientWidth;
canvas.height = map.clientHeight;
let ctx = canvas.getContext('2d');

function clearcanvas() {
    ctx.clearRect(0, 0, canvas.width, canvas.height);
}

function drawPoint(x, y) {
    ctx.fillStyle = "white"
    ctx.strokeStyle = "#a35312"
    ctx.beginPath();
    ctx.arc(x, y, 3, 0, Math.PI * 2, true);
    ctx.closePath();
    ctx.fill();
    ctx.stroke();
}

function drawRect(x, y) {
    ctx.strokeStyle = "white"
    ctx.strokeRect(x, y, 256, 256);
}

function drawImg(z, tilex, tiley, x, y, ) {
    const index = getIndex(z, tilex, tiley);
    if (cache[index]) {
        ctx.drawImage(cache[index].img, x, y);
    }
}

function drawtext(text, x, y) {
    ctx.fillStyle = "white"
    ctx.font = "18px serif";
    ctx.textAlign = "center";
    ctx.textBaseline = "middle";
    ctx.fillText(text, x, y);
}

function drawgrid(basetile, tiles) {
    let minx = basetile.minx;
    let miny = basetile.miny;
    let offsetx = basetile.offsetx;
    let offsety = basetile.offsety;
    let tilex = basetile.tilex;
    let tiley = basetile.tiley;
    clearcanvas();
    drawPoint(minx + offsetx, miny + offsety);
    for (let i = 0; i < tiles.length; i++) {
        const element = tiles[i];
        let renderx = (element.x - tilex) * 256 + minx;
        let rendery = (element.y - tiley) * 256 + miny;
        //console.log({ x: renderx, y: rendery });
        drawPoint(renderx, rendery);
        drawRect(renderx, rendery);
        drawImg(zoom_level, tiles[i].x, tiles[i].y, renderx, rendery);
        const showtext = 'x:' + element.x + ' ' + 'y:' + element.y;
        drawtext(zoom_level, renderx + 256 / 2, rendery + 256 / 2);
        drawtext(showtext, renderx + showtext.length / 4 * 18 + 4, rendery + 9);
    }
}

drawgrid(basetile, tiles);

// drawPoint(width / 2, height / 2);

// const element = tiles[0];
// let renderx = (element.x - tilex) * 256 + minx;
// let rendery = (element.y - tiley) * 256 + miny;
// drawPoint(renderx, rendery);
// drawPoint(renderx + 256 / 2, rendery + 256 / 2);
// drawRect(renderx, rendery);

// drawtext(showtext, renderx + 256 / 2, rendery + 256 / 2);
// console.log({ x: renderx, y: rendery });

//实现移动缩放方法
//缩放
map.onwheel = (e) => {
    //console.log(e);
    const zoomleveloffset = (e.deltaY > 0) ? 1 : -1;
    zoom_level -= zoomleveloffset;
    if (zoom_level < 0) {
        zoom_level = 0;
        return;
    }

    if (zoom_level > 19) {
        zoom_level = 19;
        return;
    }
    console.log(zoom_level);
    //clearcanvas();
    //重新计算basetile
    basetile = calBasetile(lat, long, zoom_level);
    tiles = needtiles(basetile, basetile.p1, basetile.p2, basetile.p3, basetile.p4);
    drawgrid(basetile, tiles);
}

let moveflag = false;
let downpoing = { x: 0, y: 0 };

map.onmousedown = (e) => {
    console.log('鼠标按下');
    moveflag = true;
    downpoing.x = e.offsetX;
    downpoing.y = e.offsetY;
}

map.onmouseup = (e) => {
    console.log('鼠标松开');
    moveflag = false;
}

map.onmousemove = (e) => {
    if (moveflag) {
        //console.log('有效位移');
        const movex = downpoing.x - e.offsetX;
        const movey = downpoing.y - e.offsetY;
        //实现移动逻辑
        let xp = basetile.x + movex / 256; //注意像素移动要除以256
        let yp = basetile.y + movey / 256;
        long = tile2long(xp, zoom_level);
        let latp = tile2lat(yp, zoom_level);
        //需要在y方向限制移动范围
        //(2*Math.atan(Math.pow(Math.E,Math.PI))-Math.PI/2)/Math.PI*180
        //85.0511287798066
        if (Math.abs(latp) > 89.99999) return;
        // if (lat2y(latp, zoom_level) == Infinity || lat2y(latp, zoom_level) == NaN) {
        //     console.log('outrange');
        //     return;
        // }
        lat = latp;
        console.log(long + ' ' + lat);
        basetile = calBasetile(lat, long, zoom_level);
        tiles = needtiles(basetile, basetile.p1, basetile.p2, basetile.p3, basetile.p4);
        drawgrid(basetile, tiles);

        downpoing.x = e.offsetX;
        downpoing.y = e.offsetY;
    }
}

//