/*

# Adapter Interface

The search adapter needs to provide the following functions that are called from search.js

## init()

Initialize the search engine and the search index

### Parameters

none

### Returns

none

### Remarks

Once successfully completed, needs to call

	````
    window.relearn.isSearchEngineReady = true;
    window.relearn.executeInitialSearch();
	````

## search()

Performs the search and returs found results.

### Parameters

term: string // the search term that was typed in by the user

### Returns

Must return an array of found pages, sorted with the most relevant page first.

Each array item needs the following layout:

````
{
    index: string, // optional, id of the page in the search index
    matches: string[], // optional, TODO: have to find out what it does
    page: {
        breadcrumb: string,
        title: string,
        uri: string,
        content: string,
        tags: string[]
    }
}
````
*/

let lunrIndex, pagesIndex;

function init() {
    function initLunrIndex( index ){
        pagesIndex = index;
        // Set up Lunr by declaring the fields we use
        // Also provide their boost level for the ranking
        lunrIndex = lunr(function() {
            this.use(lunr.multiLanguage.apply(null, contentLangs));
            this.ref('index');
            this.field('title', {
                boost: 15
            });
            this.field('tags', {
                boost: 10
            });
            this.field('content', {
                boost: 5
            });

            this.pipeline.remove(lunr.stemmer);
            this.searchPipeline.remove(lunr.stemmer);

            // Feed Lunr with each file and let index them
            pagesIndex.forEach(function(page, idx) {
                page.index = idx;
                this.add(page);
            }, this);
        });

        window.relearn.isSearchEngineReady = true;
        window.relearn.executeInitialSearch();
    }

    if( window.index_js_url ){
        var js = document.createElement("script");
        js.src = index_js_url;
        js.setAttribute("async", "");
        js.onload = function(){
            initLunrIndex(relearn_searchindex);
        };
        js.onerror = function(e){
            console.error('Error getting Hugo index file');
        };
        document.head.appendChild(js);
    }
}

function search(term) {
    function searchPatterns(word) {
        // for short words high amounts of typos doesn't make sense
        // for long words we allow less typos because this largly increases search time
        var typos = [
            { len:  -1, typos: 1 },
            { len:  60, typos: 2 },
            { len:  40, typos: 3 },
            { len:  20, typos: 4 },
            { len:  16, typos: 3 },
            { len:  12, typos: 2 },
            { len:   8, typos: 1 },
            { len:   4, typos: 0 },
        ];
        return [
            word + '^100',
            word + '*^10',
            '*' + word + '^10',
            word + '~' + typos.reduce( function( a, c, i ){ return word.length < c.len ? c : a; } ).typos + '^1'
        ];
    }

    // Find the item in our index corresponding to the Lunr one to have more info
    // Remove Lunr special search characters: https://lunrjs.com/guides/searching.html
    term = term.replace( /[*:^~+-]/g, ' ' );
    var searchTerm = lunr.tokenizer( term ).reduce( function(a,token){return a.concat(searchPatterns(token.str))}, []).join(' ');
    return !searchTerm || !lunrIndex ? [] : lunrIndex.search(searchTerm).map(function(result) {
        return { index: result.ref, matches: Object.keys(result.matchData.metadata), page: pagesIndex[ result.ref ] };
    });
}

export { init, search };