package web

import (
	"net/http"
	"sort"
	"sync"
	"time"

	"golang.org/x/sync/errgroup"
)

func init() {
	http.DefaultClient.Timeout = 5 * time.Second
}

// Result represents a search result
type Result struct {
	Title   string
	Link    string
	Desc    string
	Engines []string
	Rank    int
}

// Engine represents a search engine for web results (not images, shopping, erc.)
type Engine interface {
	// Set search keyword for engine
	SetKeyword(string)

	// Set User Agent. If string is empty,
	// an acceptable will should be used.
	SetUserAgent(string)

	// Set page number to search
	SetPage(int)

	// Initialize engine (make requests, set variables, etc.)
	Init() error

	// Run function for each search result,
	// inputting index
	Each(func(int) error) error

	// Get title from index given by Each()
	Title(int) (string, error)
	// Get link from index given by Each()
	Link(int) (string, error)
	// Get description from index given by Each()
	Desc(int) (string, error)

	// Return shortened name of search engine.
	// Should be lowercase (e.g. google, ddg, bing)
	Name() string
}

// Options represents search options
type Options struct {
	Keyword   string
	UserAgent string
	Page      int
}

// Search searches the given engines concurrently and returns the results
func Search(opts Options, engines ...Engine) ([]*Result, error) {
	var outMtx sync.Mutex
	var out []*Result

	// Create new error group
	wg := errgroup.Group{}
	// For every engine
	for index, engine := range engines {
		// Copy index and engine (for goroutine)
		curIndex, curEngine := index, engine
		wg.Go(func() error {
			// Set options
			curEngine.SetKeyword(opts.Keyword)
			curEngine.SetUserAgent(opts.UserAgent)
			curEngine.SetPage(opts.Page)

			// Attempt to init engine
			if err := curEngine.Init(); err != nil {
				return err
			}

			// For each result
			err := curEngine.Each(func(i int) error {
				// Get result link
				link, err := curEngine.Link(i)
				if err != nil {
					return err
				}

				// Calculate result rank
				rank := (curIndex * 100) + i

				// Check if result exists
				index, exists := linkExists(out, link)
				// If result already exists
				if exists {
					// Add engine to the existing result
					out[index].Engines = append(out[index].Engines, curEngine.Name())
					// If the rank is higher than the old one, update it
					if rank < out[index].Rank {
						out[index].Rank = rank
					}
					return nil
				}

				// Get result title
				title, err := curEngine.Title(i)
				if err != nil {
					return err
				}

				// Get result description
				desc, err := curEngine.Desc(i)
				if err != nil {
					return err
				}

				// If title, link, or description empty, ignore
				if title == "" || link == "" || desc == "" {
					return nil
				}

				// If length of description, truncate
				if len(desc) > 500 {
					desc = desc[:500] + "..."
				}

				// Create result struct
				result := &Result{
					Title:   title,
					Link:    link,
					Desc:    desc,
					Rank:    rank,
					Engines: []string{curEngine.Name()},
				}

				// Lock out mutex
				outMtx.Lock()
				// Add result to slice
				out = append(out, result)
				// Unlock out mutex
				outMtx.Unlock()

				return nil
			})
			if err != nil {
				return err
			}

			// Sort slice by rank
			sort.Slice(out, func(i, j int) bool {
				return out[i].Rank < out[j].Rank
			})
			return nil
		})
	}

	// Wait for error group
	if err := wg.Wait(); err != nil {
		return out, err
	}

	return out, nil
}

// linkExists checks if a link exists in the results
func linkExists(results []*Result, link string) (int, bool) {
	// For every result
	for index, result := range results {
		// If link is the same as provided
		if result.Link == link {
			// Return index with true
			return index, true
		}
	}
	return -1, false
}