package handler

import (
	"context"
	"fmt"
	"math"
	"net/http"
	"sort"
	"strconv"
	"strings"

	"github.com/prabhupadasays/spsays-bff/internal/repository"
	"github.com/prabhupadasays/spsays-bff/pkg/response"
	"github.com/typesense/typesense-go/v2/typesense/api"
)

// SearchHandler handles search requests via Typesense.
type SearchHandler struct {
	ts *repository.TypesenseClient
}

// NewSearchHandler creates a new SearchHandler.
func NewSearchHandler(ts *repository.TypesenseClient) *SearchHandler {
	return &SearchHandler{ts: ts}
}

// validSearchTypes lists the valid values for the "type" query parameter.
var validSearchTypes = map[string]bool{
	"all":             true,
	"verses":          true,
	"prose":           true,
	"letters":         true,
	"transcriptions":  true,
	"glossary":        true,
	"essays":          true,
	"journals":        true,
	"magazines":       true,
	"other_documents": true,
}

// collectionQueryByFields maps each Typesense collection to the fields to search.
// Field order matters: most relevant fields first. Used with query_by_weights
// to control ranking — identifiers and primary text rank higher than secondary
// text like purport/content where references/citations may appear.
var collectionQueryByFields = map[string]string{
	// Note: purport intentionally excluded from default verse search — matches there
	// (where verses are quoted in commentary) drown out actual verse-text matches.
	"verses":          "reference,transliteration,transliteration_ascii,translation,translation_ascii",
	"prose":           "title,title_ascii,content,content_ascii",
	"letters":         "recipient_display,recipient_display_ascii,content,content_ascii",
	"transcriptions":  "reference,name,name_ascii,content,content_ascii",
	"glossary":        "term,term_ascii,definition,definition_ascii",
	"essays":          "title,title_ascii,content,content_ascii",
	"journals":        "title,title_ascii,content,content_ascii",
	"magazines":       "title,title_ascii,content,content_ascii",
	"other_documents": "title,title_ascii,content,content_ascii",
}

// collectionQueryByWeights assigns weights matching the order of fields above.
// Higher weight = stronger ranking signal. Identifiers/primary text dominate.
var collectionQueryByWeights = map[string]string{
	"verses":          "10,8,8,4,4", // reference, transliteration, transliteration_ascii, translation, translation_ascii
	"prose":           "10,10,2,2",
	"letters":         "10,10,2,2",
	"transcriptions":  "10,8,8,2,2",
	"glossary":        "10,10,4,4",
	"essays":          "10,10,2,2",
	"journals":        "10,10,2,2",
	"magazines":       "10,10,2,2",
	"other_documents": "10,10,2,2",
}

// searchStopwordsSet is the name of the Typesense stopwords set applied to
// every search. The set is configured server-side (`PUT /stopwords/common`)
// and contains conversational words like "letter", "to", "of", "essay", etc.
//
// Without this, a query like "letter to tusta krsna" ranks letters that merely
// contain "letter" and "to" in their body above letters whose recipient is
// actually "Tusta Krsna", because those common tokens contribute heavily to
// the multi-field score.
const searchStopwordsSet = "common"

// searchResultItem represents a single search result in the API response.
type searchResultItem struct {
	Collection string                 `json:"collection"`
	Slug       string                 `json:"slug,omitempty"`
	Title      string                 `json:"title"`
	Snippet    string                 `json:"snippet"`
	URL        string                 `json:"url"`
	Meta       map[string]interface{} `json:"meta,omitempty"`
	score      int64                  // internal, not serialized
}

// searchResponse is the shape of the data field in the API response.
type searchResponse struct {
	Query      string             `json:"query"`
	Type       string             `json:"type"`
	Results    []searchResultItem `json:"results"`
	Total      int                `json:"total"`
	Page       int                `json:"page"`
	Limit      int                `json:"limit"`
	TotalPages int                `json:"total_pages"`
}

// Search handles GET /api/v1/search?q=...&type=all&page=1&limit=20
func (h *SearchHandler) Search(w http.ResponseWriter, r *http.Request) {
	query := strings.TrimSpace(r.URL.Query().Get("q"))
	if query == "" {
		response.Error(w, http.StatusBadRequest, "query parameter 'q' is required")
		return
	}

	searchType := r.URL.Query().Get("type")
	if searchType == "" {
		searchType = "all"
	}

	// Parse comma-separated types (e.g., "verses,letters,transcriptions")
	var requestedTypes []string
	if searchType != "all" {
		for _, t := range strings.Split(searchType, ",") {
			t = strings.TrimSpace(t)
			if t == "" || t == "all" {
				continue
			}
			if !validSearchTypes[t] {
				response.Error(w, http.StatusBadRequest, fmt.Sprintf("invalid type '%s'", t))
				return
			}
			requestedTypes = append(requestedTypes, t)
		}
		if len(requestedTypes) == 0 {
			searchType = "all"
		}
	}

	page := parseIntParam(r.URL.Query().Get("page"), 1)
	if page < 1 {
		page = 1
	}

	limit := parseIntParam(r.URL.Query().Get("limit"), 20)
	if limit < 1 {
		limit = 1
	}
	if limit > 100 {
		limit = 100
	}

	ctx := r.Context()

	var results []searchResultItem
	var totalFound int

	if searchType == "all" {
		// Search all 9 collections
		results, totalFound = h.multiSearch(ctx, nil, query, page, limit)
	} else if len(requestedTypes) == 1 {
		// Single collection — use singleSearch for efficiency
		results, totalFound = h.singleSearch(ctx, requestedTypes[0], query, page, limit)
	} else {
		// Multiple collections — use multiSearch with a subset
		results, totalFound = h.multiSearch(ctx, requestedTypes, query, page, limit)
	}

	totalPages := int(math.Ceil(float64(totalFound) / float64(limit)))

	resp := searchResponse{
		Query:      query,
		Type:       searchType,
		Results:    results,
		Total:      totalFound,
		Page:       page,
		Limit:      limit,
		TotalPages: totalPages,
	}

	response.JSON(w, http.StatusOK, resp)
}

// multiSearch searches across all 9 collections using Typesense multi_search,
// merges results by text_match score, and returns a single paginated list.
// multiSearch searches across multiple collections using Typesense multi_search.
// If collections is nil, searches all 9 collections.
func (h *SearchHandler) multiSearch(ctx context.Context, collections []string, query string, page, limit int) ([]searchResultItem, int) {
	if collections == nil {
		collections = []string{
			"verses", "prose", "letters", "transcriptions", "glossary",
			"essays", "journals", "magazines", "other_documents",
		}
	}

	exhaustive := true
	prioritizeExact := true
	prioritizeTokenPos := true
	searches := make([]api.MultiSearchCollectionParameters, 0, len(collections))
	for _, col := range collections {
		queryBy := collectionQueryByFields[col]
		weights := collectionQueryByWeights[col]
		perPage := limit
		pg := page
		params := api.MultiSearchCollectionParameters{
			Collection:       col,
			Q:                stringPtr(query),
			QueryBy:          stringPtr(queryBy),
			PerPage:          &perPage,
			Page:             &pg,
			Prefix:           stringPtr("true"),
			NumTypos:         stringPtr("2"),
			ExhaustiveSearch: &exhaustive,
			Stopwords:        stringPtr(searchStopwordsSet),
			// Boost docs whose tokens are exact matches and appear early in the field
			// so "karma" outranks "karmic" and frequent matches outrank single ones.
			PrioritizeExactMatch:    &prioritizeExact,
			PrioritizeTokenPosition: &prioritizeTokenPos,
		}
		if weights != "" {
			params.QueryByWeights = stringPtr(weights)
		}
		searches = append(searches, params)
	}

	searchParams := api.MultiSearchSearchesParameter{
		Searches: searches,
	}

	commonParams := &api.MultiSearchParams{}

	msResult, err := h.ts.Client.MultiSearch.Perform(ctx, commonParams, searchParams)
	if err != nil {
		return []searchResultItem{}, 0
	}

	allItems := []searchResultItem{}
	totalFound := 0

	for i, sr := range msResult.Results {
		collectionName := collections[i]
		if sr.Found != nil {
			totalFound += *sr.Found
		}
		if sr.Hits == nil {
			continue
		}
		for _, hit := range *sr.Hits {
			item := hitToResultItem(collectionName, &hit)
			allItems = append(allItems, item)
		}
	}

	// Sort by text_match score descending
	sort.Slice(allItems, func(i, j int) bool {
		return allItems[i].score > allItems[j].score
	})

	// Paginate the merged results: since each sub-search already returned `limit`
	// results for the given page, the merged set has at most 9*limit items.
	// We take the top `limit` after sorting.
	if len(allItems) > limit {
		allItems = allItems[:limit]
	}

	return allItems, totalFound
}

// singleSearch searches a single collection.
func (h *SearchHandler) singleSearch(ctx context.Context, collection, query string, page, limit int) ([]searchResultItem, int) {
	queryBy, ok := collectionQueryByFields[collection]
	if !ok {
		return []searchResultItem{}, 0
	}

	exhaustive := true
	prioritizeExact := true
	prioritizeTokenPos := true
	params := &api.SearchCollectionParams{
		Q:                stringPtr(query),
		QueryBy:          stringPtr(queryBy),
		Page:             &page,
		PerPage:          &limit,
		Prefix:           stringPtr("true"),
		NumTypos:         stringPtr("2"),
		ExhaustiveSearch: &exhaustive,
		Stopwords:        stringPtr(searchStopwordsSet),
		// Boost docs whose tokens are exact matches and appear early in the field
		// so "karma" outranks "karmic" and frequent matches outrank single ones.
		PrioritizeExactMatch:    &prioritizeExact,
		PrioritizeTokenPosition: &prioritizeTokenPos,
	}
	if weights := collectionQueryByWeights[collection]; weights != "" {
		params.QueryByWeights = stringPtr(weights)
	}

	sr, err := h.ts.Client.Collection(collection).Documents().Search(ctx, params)
	if err != nil {
		return []searchResultItem{}, 0
	}

	totalFound := 0
	if sr.Found != nil {
		totalFound = *sr.Found
	}

	items := []searchResultItem{}
	if sr.Hits != nil {
		for _, hit := range *sr.Hits {
			item := hitToResultItem(collection, &hit)
			items = append(items, item)
		}
	}

	return items, totalFound
}

// hitToResultItem converts a Typesense SearchResultHit into our API result shape.
func hitToResultItem(collection string, hit *api.SearchResultHit) searchResultItem {
	doc := make(map[string]interface{})
	if hit.Document != nil {
		doc = *hit.Document
	}

	var score int64
	if hit.TextMatch != nil {
		score = *hit.TextMatch
	}

	item := searchResultItem{
		Collection: collection,
		URL:        getStringField(doc, "url"),
		score:      score,
	}

	// Extract title based on collection type
	switch collection {
	case "verses":
		item.Title = getStringField(doc, "reference")
		item.Slug = slugFromURL(item.URL)
		item.Meta = map[string]interface{}{
			"book":      getStringField(doc, "book"),
			"reference": getStringField(doc, "reference"),
		}
	case "prose":
		item.Title = getStringField(doc, "title")
		item.Slug = slugFromURL(item.URL)
		item.Meta = map[string]interface{}{
			"book": getStringField(doc, "book"),
			"type": getStringField(doc, "type"),
		}
	case "letters":
		recipient := getStringField(doc, "recipient_display")
		if recipient != "" {
			item.Title = "Letter to " + recipient
		} else {
			item.Title = "Letter"
		}
		item.Slug = slugFromURL(item.URL)
		item.Meta = map[string]interface{}{
			"recipient_display": recipient,
		}
		if date, ok := doc["date"]; ok {
			item.Meta["date"] = date
		}
		if location, ok := doc["location"]; ok {
			item.Meta["location"] = location
		}
	case "transcriptions":
		item.Title = getStringField(doc, "name")
		item.Slug = slugFromURL(item.URL)
		item.Meta = map[string]interface{}{
			"type": getStringField(doc, "type"),
		}
		if place, ok := doc["place"]; ok {
			item.Meta["place"] = place
		}
		if date, ok := doc["date"]; ok {
			item.Meta["date"] = date
		}
		if ref, ok := doc["reference"]; ok {
			item.Meta["reference"] = ref
		}
	case "glossary":
		item.Title = getStringField(doc, "term")
		item.Slug = getStringField(doc, "term")
		item.Meta = map[string]interface{}{
			"first_letter": getStringField(doc, "first_letter"),
		}
	case "essays":
		item.Title = getStringField(doc, "title")
		item.Slug = slugFromURL(item.URL)
		item.Meta = map[string]interface{}{
			"author": getStringField(doc, "author"),
		}
		if year, ok := doc["year"]; ok {
			item.Meta["year"] = year
		}
	case "journals":
		item.Title = getStringField(doc, "title")
		item.Slug = slugFromURL(item.URL)
		item.Meta = map[string]interface{}{
			"book": getStringField(doc, "book"),
		}
	case "magazines":
		item.Title = getStringField(doc, "title")
		item.Slug = slugFromURL(item.URL)
		item.Meta = map[string]interface{}{
			"book": getStringField(doc, "book"),
		}
	case "other_documents":
		item.Title = getStringField(doc, "title")
		item.Slug = slugFromURL(item.URL)
		item.Meta = map[string]interface{}{
			"book": getStringField(doc, "book"),
		}
	}

	// Extract snippet from highlights
	item.Snippet = extractSnippet(hit, collection)

	return item
}

// extractSnippet builds a snippet string from Typesense highlight data.
// It prefers the newer highlight map, falling back to the deprecated highlights array.
func extractSnippet(hit *api.SearchResultHit, collection string) string {
	// Try the highlights array (deprecated but widely available)
	if hit.Highlights != nil && len(*hit.Highlights) > 0 {
		for _, hl := range *hit.Highlights {
			if hl.Snippet != nil && *hl.Snippet != "" {
				return *hl.Snippet
			}
			if hl.Snippets != nil && len(*hl.Snippets) > 0 {
				return (*hl.Snippets)[0]
			}
		}
	}

	// Try the highlight map (v2 style)
	if hit.Highlight != nil {
		hlMap := *hit.Highlight
		// Prioritize content/text fields for snippet
		priorityFields := snippetPriorityFields(collection)
		for _, field := range priorityFields {
			if val, ok := hlMap[field]; ok {
				if s := extractHighlightValue(val); s != "" {
					return s
				}
			}
		}
		// Fallback: return any highlighted field
		for _, val := range hlMap {
			if s := extractHighlightValue(val); s != "" {
				return s
			}
		}
	}

	return ""
}

// snippetPriorityFields returns the fields to check first for snippets, per collection.
func snippetPriorityFields(collection string) []string {
	switch collection {
	case "verses":
		return []string{"translation", "purport", "transliteration", "reference"}
	case "prose":
		return []string{"content", "title"}
	case "letters":
		return []string{"content", "recipient_display"}
	case "transcriptions":
		return []string{"content", "name", "reference"}
	case "glossary":
		return []string{"definition", "term"}
	case "essays":
		return []string{"content", "title"}
	case "journals", "magazines", "other_documents":
		return []string{"content", "title"}
	default:
		return []string{"content", "title"}
	}
}

// extractHighlightValue tries to pull a string snippet from a highlight value,
// which may be a string, a map with "snippet" or "matched_tokens", etc.
func extractHighlightValue(val interface{}) string {
	switch v := val.(type) {
	case string:
		if v != "" {
			return v
		}
	case map[string]interface{}:
		if snippet, ok := v["snippet"].(string); ok && snippet != "" {
			return snippet
		}
		if value, ok := v["value"].(string); ok && value != "" {
			return value
		}
	}
	return ""
}

// getStringField safely extracts a string value from a map.
func getStringField(doc map[string]interface{}, key string) string {
	if val, ok := doc[key]; ok {
		if s, ok := val.(string); ok {
			return s
		}
	}
	return ""
}

// slugFromURL extracts the last path segment from a URL as a slug.
func slugFromURL(u string) string {
	u = strings.TrimRight(u, "/")
	parts := strings.Split(u, "/")
	if len(parts) > 0 {
		return parts[len(parts)-1]
	}
	return ""
}

// parseIntParam parses an integer from a query param string with a default fallback.
func parseIntParam(s string, defaultVal int) int {
	if s == "" {
		return defaultVal
	}
	v, err := strconv.Atoi(s)
	if err != nil {
		return defaultVal
	}
	return v
}

// stringPtr returns a pointer to a string value.
func stringPtr(s string) *string {
	return &s
}