<template>
    <DocSectionText v-bind="$attrs">
        <p>
            Lazy mode is handy to deal with large datasets, instead of loading the entire data, small chunks of data is loaded by invoking corresponding callbacks everytime <i>paging</i>, <i>sorting</i> and <i>filtering</i> occurs. Sample below
            imitates lazy loading data from a remote datasource using an in-memory list and timeouts to mimic network connection.
        </p>
        <p>
            Enabling the <i>lazy</i> property and assigning the logical number of rows to <i>totalRecords</i> by doing a projection query are the key elements of the implementation so that paginator displays the UI assuming there are actually records
            of totalRecords size although in reality they are not present on page, only the records that are displayed on the current page exist.
        </p>
        <p>In addition, only the root elements should be loaded, children can be loaded on demand using <i>nodeExpand</i> callback.</p>
    </DocSectionText>
    <div class="card">
        <TreeTable :value="nodes" :lazy="true" :paginator="true" :rows="rows" :loading="loading" @nodeExpand="onExpand" @page="onPage" :totalRecords="totalRecords">
            <Column field="name" header="Name" expander></Column>
            <Column field="size" header="Size"></Column>
            <Column field="type" header="Type"></Column>
        </TreeTable>
    </div>
    <DocSectionCode :code="code" />
</template>

<script>
export default {
    data() {
        return {
            nodes: null,
            rows: 10,
            loading: false,
            totalRecords: 0,
            code: {
                basic: `
<TreeTable :value="nodes" :lazy="true" :paginator="true" :rows="rows" :loading="loading"
    @nodeExpand="onExpand" @page="onPage" :totalRecords="totalRecords">
    <Column field="name" header="Name" expander></Column>
    <Column field="size" header="Size"></Column>
    <Column field="type" header="Type"></Column>
</TreeTable>
`,
                options: `
<template>
    <div class="card">
        <TreeTable :value="nodes" :lazy="true" :paginator="true" :rows="rows" :loading="loading"
            @nodeExpand="onExpand" @page="onPage" :totalRecords="totalRecords">
            <Column field="name" header="Name" expander></Column>
            <Column field="size" header="Size"></Column>
            <Column field="type" header="Type"></Column>
        </TreeTable>
    </div>
</template>

<script>
export default {
    data() {
        return {
            nodes: null,
            rows: 10,
            loading: false,
            totalRecords: 0
        };
    },
    mounted() {
        this.loading = true;

        setTimeout(() => {
            this.loading = false;
            this.nodes = this.loadNodes(0, this.rows);
            this.totalRecords = 1000;
        }, 1000);
    },
    methods: {
        onExpand(node) {
            if (!node.children) {
                this.loading = true;

                setTimeout(() => {
                    let lazyNode = { ...node };

                    lazyNode.children = [
                        {
                            data: {
                                name: lazyNode.data.name + ' - 0',
                                size: Math.floor(Math.random() * 1000) + 1 + 'kb',
                                type: 'File'
                            }
                        },
                        {
                            data: {
                                name: lazyNode.data.name + ' - 1',
                                size: Math.floor(Math.random() * 1000) + 1 + 'kb',
                                type: 'File'
                            }
                        }
                    ];

                    let nodes = this.nodes.map((n) => {
                        if (n.key === node.key) {
                            n = lazyNode;
                        }

                        return n;
                    });

                    this.loading = false;
                    this.nodes = nodes;
                }, 250);
            }
        },
        onPage(event) {
            this.loading = true;

            //imitate delay of a backend call
            setTimeout(() => {
                this.loading = false;
                this.nodes = this.loadNodes(event.first, this.rows);
            }, 1000);
        },
        loadNodes(first, rows) {
            let nodes = [];

            for (let i = 0; i < rows; i++) {
                let node = {
                    key: first + i,
                    data: {
                        name: 'Item ' + (first + i),
                        size: Math.floor(Math.random() * 1000) + 1 + 'kb',
                        type: 'Type ' + (first + i)
                    },
                    leaf: false
                };

                nodes.push(node);
            }

            return nodes;
        }
    }
};
<\/script>
`,
                composition: `
<template>
    <div>
        <TreeTable :value="nodes" :lazy="true" :paginator="true" :rows="rows" :loading="loading"
            @nodeExpand="onExpand" @page="onPage" :totalRecords="totalRecords">
            <Column field="name" header="Name" :expander="true"></Column>
            <Column field="size" header="Size"></Column>
            <Column field="type" header="Type"></Column>
        </TreeTable>
    </div>                   
</template>

<script setup>
import { ref, onMounted } from 'vue';

onMounted(() => {
    loading.value = true;

    setTimeout(() => {
        loading.value = false;
        nodes.value = loadNodes(0, rows.value);
        totalRecords.value = 1000;
    }, 1000);
});

const nodes = ref();
const rows = ref(10);
const loading = ref(false);
const totalRecords = ref(0);
const onExpand = (node) => {
    if (!node.children) {
        loading.value = true;

        setTimeout(() => {
            let lazyNode = {...node};

            lazyNode.children = [
                {
                    data: {
                        name: lazyNode.data.name + ' - 0',
                        size: Math.floor(Math.random() * 1000) + 1 + 'kb',
                        type: 'File'
                    },
                },
                {
                    data: {
                        name: lazyNode.data.name + ' - 1',
                        size: Math.floor(Math.random() * 1000) + 1 + 'kb',
                        type: 'File'
                    }
                }
            ];

            let newNodes = nodes.value.map(n => {
                if (n.key === node.key) {
                    n = lazyNode;
                }

                return n;
            });

            loading.value = false;
            nodes.value = newNodes;
        }, 250);
    }
};
const onPage = (event) => {
    loading.value = true;

    //imitate delay of a backend call
    setTimeout(() => {
        loading.value = false;
        nodes.value = loadNodes(event.first, rows.value);
    }, 1000);
};
const loadNodes = (first, rows) => {
    let nodes = [];

    for(let i = 0; i < rows; i++) {
        let node = {
            key: (first + i),
            data: {
                name: 'Item ' + (first + i),
                size: Math.floor(Math.random() * 1000) + 1 + 'kb',
                type: 'Type ' + (first + i)
            },
            leaf: false
        };

        nodes.push(node);
    }

    return nodes;
};
<\/script>
`
            }
        };
    },
    mounted() {
        this.loading = true;

        setTimeout(() => {
            this.loading = false;
            this.nodes = this.loadNodes(0, this.rows);
            this.totalRecords = 1000;
        }, 1000);
    },
    methods: {
        onExpand(node) {
            if (!node.children) {
                this.loading = true;

                setTimeout(() => {
                    let lazyNode = { ...node };

                    lazyNode.children = [
                        {
                            data: {
                                name: lazyNode.data.name + ' - 0',
                                size: Math.floor(Math.random() * 1000) + 1 + 'kb',
                                type: 'File'
                            }
                        },
                        {
                            data: {
                                name: lazyNode.data.name + ' - 1',
                                size: Math.floor(Math.random() * 1000) + 1 + 'kb',
                                type: 'File'
                            }
                        }
                    ];

                    let nodes = this.nodes.map((n) => {
                        if (n.key === node.key) {
                            n = lazyNode;
                        }

                        return n;
                    });

                    this.loading = false;
                    this.nodes = nodes;
                }, 250);
            }
        },
        onPage(event) {
            this.loading = true;

            //imitate delay of a backend call
            setTimeout(() => {
                this.loading = false;
                this.nodes = this.loadNodes(event.first, this.rows);
            }, 1000);
        },
        loadNodes(first, rows) {
            let nodes = [];

            for (let i = 0; i < rows; i++) {
                let node = {
                    key: first + i,
                    data: {
                        name: 'Item ' + (first + i),
                        size: Math.floor(Math.random() * 1000) + 1 + 'kb',
                        type: 'Type ' + (first + i)
                    },
                    leaf: false
                };

                nodes.push(node);
            }

            return nodes;
        }
    }
};
</script>
