const shift = (number, shift) => {
    return number * Math.pow(2, shift)
}

const getUint24 = (dataview, pos) => {
  return shift(dataview.getUint16(pos+1,true),8) + dataview.getUint8(pos,true)
}

const getUint48 = (dataview, pos) => {
    return shift(dataview.getUint32(pos+2,true),16) + dataview.getUint16(pos,true)
}

const parseHeader = dataview => {
    var magic = dataview.getUint16(0,true)
    // assert that the magic number (2 bytes) matches 19792
    var version = dataview.getUint16(2,true)
    var json_size = dataview.getUint32(4,true)
    var root_entries = dataview.getUint16(8,true)
    return {version:version,json_size:json_size,root_entries:root_entries}
}

const bytesToMap = dataview => {
    let m = new Map() 
    for (var i = 0; i < dataview.byteLength; i+=17) {
        var z_raw = dataview.getUint8(i,true)
        var z = z_raw & 127
        var is_dir = z_raw >> 7
        var x = getUint24(dataview,i+1)
        var y = getUint24(dataview,i+4)
        var offset = getUint48(dataview,i+7)
        var length = dataview.getUint32(i+13,true)
        m.set(z + '_' + x + '_' + y,[offset,length,is_dir])
    }
    return m
}

export class PMTiles {
    constructor(url, options = {}) {
        this.url = url
        const controller = new AbortController()
        const signal = controller.signal
        this.root = fetch(this.url,{signal:signal, headers:{Range:'bytes=0-511999'}}).then(resp => {
            if (resp.headers.get('Content-Length') != 512000) {
                console.error("Content-Length mismatch indicates byte serving not supported; aborting.")
                controller.abort()
            }
            return resp.arrayBuffer()
        }).then(buf => {
            const header = parseHeader(new DataView(buf,0,10))
            var dec = new TextDecoder("utf-8")
            return {
                metadata: JSON.parse(dec.decode(new DataView(buf,10,header.json_size))),
                dir:bytesToMap(new DataView(buf,10+header.json_size,17*header.root_entries))
            }
        })

        this.step = 0
        this.leaves = new Map()
        this.outstanding_requests = new Map()
    }

    metadata = func => {
        this.root.then(root => {
            func(root.metadata)
        })
    }

    getLeaf = (offset, len) => {
        return new Promise((resolve,reject) => {
            if (this.leaves.has(offset)) {
                this.leaves.get(offset)[0]++
                resolve(this.leaves.get(offset)[1])
            } else if (this.outstanding_requests.has(offset)) {
                this.outstanding_requests.get(offset).push(resolve)
            } else {
                this.outstanding_requests.set(offset,[])
                fetch(this.url, {headers:{Range:'bytes=' + offset + '-' + (offset + len-1)}}).then(resp => {
                    return resp.arrayBuffer()
                }).then(buf => {
                    var map = bytesToMap(new DataView(buf),len/17)
                    if (this.leaves.size > 32) {
                        var minStep = Infinity
                        var minKey = undefined
                        this.leaves.forEach((val,key) => {
                            if (val[0] < minStep) {
                                minStep = val[0]
                                minKey = key
                            }
                        })
                        this.leaves.delete(minKey)
                    }

                    this.leaves.set(offset,[this.step++,map])
                    resolve(map)
                    this.outstanding_requests.get(offset).forEach(f => f(map))
                    this.outstanding_requests.delete(offset)
                })
            }
        })
    }

    getZxy = (z,x,y) => {
        var strid = z + '_' + x + '_' + y
        return this.root.then(root => {
            if (root.dir.has(strid) && root.dir.get(strid)[2] == 0) {
                return root.dir.get(strid)
            } else {
               if (z >= 7) {
                    var z7_tile_diff = (z - 7)
                    var z7_tile = [7,Math.trunc(x / (1 << z7_tile_diff)), Math.trunc(y / (1 << z7_tile_diff))]
                    var z7_tile_str = z7_tile[0] + "_" + z7_tile[1] + "_" + z7_tile[2]
                    if (root.dir.has(z7_tile_str) && root.dir.get(z7_tile_str)[2] == 1) {
                        const val = root.dir.get(z7_tile_str)
                        return this.getLeaf(val[0],val[1]).then(leafdir => {
                            if (leafdir.has(strid)) {
                                return leafdir.get(strid)
                            }
                            return null
                        })
                    }
               } 
            }
            return null
        }) 
    }

    transformRequest = (u,t,tile,done) => {
        if (u.endsWith('.pmtiles') && done) {
            var tid = tile.tileID.canonical
            var strid = tid.z + '_' + tid.x + '_' + tid.y
            this.getZxy(tid.z,tid.x,tid.y).then(val => {
                if (val) {
                    done({url: this.url, headers:{'Range':'bytes=' + val[0] + '-' + (val[0]+val[1]-1)}})
                }
            })
        }
        return {url: u}
    }

    // take URL here
    leafletLayer = options => {
        const self = this
        var cls = L.GridLayer.extend({
            createTile: function(coord, done){
                var tile = document.createElement('img')
                var error

                self.getZxy(coord.z,coord.x,coord.y).then(result => {
                    if (result === null) return
                    fetch(self.url,{headers:{Range:'bytes=' + result[0] + '-' + (result[0]+result[1]-1)}}).then(resp => {
                        return resp.arrayBuffer()
                    }).then(buf => {
                        var blob = new Blob( [buf], { type: "image/png" } )
                        var imageUrl = window.URL.createObjectURL(blob)
                        tile.src = imageUrl
                        done(error,tile)
                    })
                })
                return tile
            },

            _removeTile: function (key) {
                var tile = this._tiles[key]
                if (!tile) { return }
                tile.el.width = 0
                tile.el.height = 0
                tile.el.deleted = true
                L.DomUtil.remove(tile.el)
                delete this._tiles[key]
                this.fire('tileunload', {
                    tile: tile.el,
                    coords: this._keyToTileCoords(key)
                })
            },
        })
        return new cls(options)
    }
}