package main

import (
	"io/fs"
	"log"
	"net/http"
	"path/filepath"
	"sort"
	"strings"
	"unicode"
)

type searchResult struct {
	Name  string
	URL   string
	Path  string
	Score int
}

type searchPageData struct {
	Title    string
	Crumbs   []crumb
	EditMode bool
	Query    string
	Results  []searchResult
	RenderMS int64
}

// handleSearch walks the wiki root and renders a search results page for the
// query in r.URL.Query().Get("q"). Only invoked when path is "/" and "q" is
// present.
func (h *handler) handleSearch(w http.ResponseWriter, r *http.Request) {
	query := strings.TrimSpace(r.URL.Query().Get("q"))
	results := searchWiki(h.root, query)

	title := "Search"
	if query != "" {
		title = "Search: " + query
	}
	data := searchPageData{
		Title:   title,
		Crumbs:  []crumb{{Name: "search", URL: "/?q=" + query}},
		Query:   query,
		Results: results,
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	data.RenderMS = elapsedMS(r)
	if err := searchTmpl.ExecuteTemplate(w, "layout", data); err != nil {
		log.Printf("search template error: %v", err)
	}
}

// searchWiki walks root and scores each directory by how well the folder name
// matches the query. Page contents are not searched. Higher score = more
// relevant; exact matches rank first.
func searchWiki(root, query string) []searchResult {
	if query == "" {
		return nil
	}
	qLower := strings.ToLower(query)
	qTokens := tokenize(qLower)
	if len(qTokens) == 0 {
		return nil
	}

	walkRoot := resolveWalkRoot(root)
	var results []searchResult
	_ = filepath.WalkDir(walkRoot, func(fsPath string, d fs.DirEntry, err error) error {
		if err != nil {
			return nil
		}
		if skip, walkErr := hiddenSkip(fsPath, walkRoot, d); skip {
			return walkErr
		}
		if !d.IsDir() || fsPath == walkRoot {
			return nil
		}
		name := d.Name()
		score := scoreName(strings.ToLower(name), qLower, qTokens)
		if score == 0 {
			return nil
		}
		rel, relErr := filepath.Rel(walkRoot, fsPath)
		if relErr != nil {
			return nil
		}
		results = append(results, searchResult{
			Name:  name,
			URL:   "/" + filepath.ToSlash(rel) + "/",
			Path:  filepath.ToSlash(rel),
			Score: score,
		})
		return nil
	})

	sort.SliceStable(results, func(i, j int) bool {
		if results[i].Score != results[j].Score {
			return results[i].Score > results[j].Score
		}
		di, dj := strings.Count(results[i].Path, "/"), strings.Count(results[j].Path, "/")
		if di != dj {
			return di < dj
		}
		return strings.ToLower(results[i].Name) < strings.ToLower(results[j].Name)
	})
	return results
}

// scoreName ranks how well nameLower matches the query. Whole-name exact
// match dominates; otherwise score is the sum of each token's best match
// against the words in the name. Position within the name does not matter —
// nesting depth is the tiebreaker, applied by the caller.
func scoreName(nameLower, qLower string, qTokens []string) int {
	if nameLower == qLower {
		return 1000
	}
	score := 0
	nameWords := tokenize(nameLower)
	for _, qt := range qTokens {
		best := 0
		for _, w := range nameWords {
			switch {
			case w == qt:
				if best < 100 {
					best = 100
				}
			case strings.HasPrefix(w, qt):
				if best < 50 {
					best = 50
				}
			case strings.Contains(w, qt):
				if best < 20 {
					best = 20
				}
			case levenshtein(w, qt) <= 2:
				if best < 5 {
					best = 5
				}
			}
		}
		score += best
	}
	return score
}

// resolveWalkRoot resolves symlinks so WalkDir descends into the real tree
// even when the configured wiki root is itself a symlink (as on the NAS).
func resolveWalkRoot(root string) string {
	if r, err := filepath.EvalSymlinks(root); err == nil {
		return r
	}
	return root
}

// hiddenSkip handles dotfile/dot-dir entries during a WalkDir. It returns
// (skipped, walkErr): skipped=true means the caller should `return walkErr`
// to either prune the subtree (hidden dir) or move past the entry (hidden
// file). When skipped=false the entry should be processed normally.
func hiddenSkip(fsPath, walkRoot string, d fs.DirEntry) (bool, error) {
	if !strings.HasPrefix(d.Name(), ".") {
		return false, nil
	}
	if d.IsDir() && fsPath != walkRoot {
		return true, filepath.SkipDir
	}
	return true, nil
}

// tokenize splits s into lowercase word tokens, breaking on any rune that is
// not a letter or digit. Unicode-aware so umlauts etc. survive intact.
func tokenize(s string) []string {
	var tokens []string
	var b strings.Builder
	for _, r := range s {
		if unicode.IsLetter(r) || unicode.IsDigit(r) {
			b.WriteRune(unicode.ToLower(r))
			continue
		}
		if b.Len() > 0 {
			tokens = append(tokens, b.String())
			b.Reset()
		}
	}
	if b.Len() > 0 {
		tokens = append(tokens, b.String())
	}
	return tokens
}

// levenshtein returns the edit distance between a and b. Operates on runes so
// multi-byte characters count as one edit.
func levenshtein(a, b string) int {
	ar, br := []rune(a), []rune(b)
	if len(ar) == 0 {
		return len(br)
	}
	if len(br) == 0 {
		return len(ar)
	}
	prev := make([]int, len(br)+1)
	curr := make([]int, len(br)+1)
	for j := range prev {
		prev[j] = j
	}
	for i := 1; i <= len(ar); i++ {
		curr[0] = i
		for j := 1; j <= len(br); j++ {
			cost := 1
			if ar[i-1] == br[j-1] {
				cost = 0
			}
			del := prev[j] + 1
			ins := curr[j-1] + 1
			sub := prev[j-1] + cost
			curr[j] = min3(del, ins, sub)
		}
		prev, curr = curr, prev
	}
	return prev[len(br)]
}

func min3(a, b, c int) int {
	m := a
	if b < m {
		m = b
	}
	if c < m {
		m = c
	}
	return m
}