package repository

import (
	"context"
	"strings"

	"go.mongodb.org/mongo-driver/v2/bson"
	"go.mongodb.org/mongo-driver/v2/mongo"
	"go.mongodb.org/mongo-driver/v2/mongo/options"
)

type GlossaryRepo struct {
	col *mongo.Collection
}

func NewGlossaryRepo(db *MongoDB) *GlossaryRepo {
	return &GlossaryRepo{col: db.Collection("glossary")}
}

// GlossaryEntryDoc is the full glossary entry with definition.
type GlossaryEntryDoc struct {
	ID             bson.ObjectID `bson:"_id" json:"id"`
	Term           string        `bson:"term" json:"term"`
	Definition     string        `bson:"definition" json:"definition"`
	DefinitionHTML string        `bson:"definitionHtml" json:"definition_html"`
}

// GlossaryTermSummary is a lightweight entry for sidebar listing (no definition).
type GlossaryTermSummary struct {
	ID   bson.ObjectID `bson:"_id" json:"id"`
	Term string        `bson:"term" json:"term"`
}

// GlossaryLetterCount holds the count of entries per base letter.
type GlossaryLetterCount struct {
	Letter string `json:"letter"`
	Count  int    `json:"count"`
}

// diacriticToBase maps diacritical first characters to ASCII base letters.
// Must match the frontend mapping in the glossary page.
var diacriticToBase = map[rune]rune{
	'Ā': 'A', 'Ä': 'A',
	'Ī': 'I', 'É': 'I',
	'Ū': 'U', 'Ü': 'U',
	'Ṛ': 'R', 'Ṝ': 'R',
	'Ś': 'S', 'Ç': 'S', 'Ṣ': 'S',
	'Ñ': 'N', 'Ṇ': 'N', 'Ṅ': 'N',
	'Ṭ': 'T',
	'Ḍ': 'D',
	'Ḥ': 'H',
	// Lowercase equivalents
	'ā': 'A', 'ä': 'A',
	'ī': 'I', 'é': 'I',
	'ū': 'U', 'ü': 'U',
	'ṛ': 'R', 'ṝ': 'R',
	'ś': 'S', 'ç': 'S', 'ṣ': 'S',
	'ñ': 'N', 'ṇ': 'N', 'ṅ': 'N',
	'ṭ': 'T',
	'ḍ': 'D',
	'ḥ': 'H',
}

// baseLetter returns the ASCII base letter for the first character of a term.
func baseLetter(term string) string {
	if term == "" {
		return "?"
	}
	first := []rune(term)[0]
	if base, ok := diacriticToBase[first]; ok {
		return string(base)
	}
	return strings.ToUpper(string(first))
}

// regexPrefixes returns the set of first characters (including diacritical variants)
// that map to the given base letter, for use in a MongoDB $regex query.
func regexPrefixes(letter string) string {
	upper := strings.ToUpper(letter)
	if len(upper) == 0 {
		return ""
	}
	base := rune(upper[0])

	// Collect all characters that map to this base letter
	chars := []rune{base, rune(strings.ToLower(upper)[0])}
	for k, v := range diacriticToBase {
		if v == base {
			chars = append(chars, k)
		}
	}

	// Build regex character class: ^[AĀÄāä]
	return "^[" + string(chars) + "]"
}

// ---------------------------------------------------------------------------
// Queries
// ---------------------------------------------------------------------------

// GetAll returns all glossary entries sorted by term.
func (r *GlossaryRepo) GetAll(ctx context.Context) ([]GlossaryEntryDoc, error) {
	opts := options.Find().SetSort(bson.M{"term": 1})
	cursor, err := r.col.Find(ctx, bson.M{}, opts)
	if err != nil {
		return nil, err
	}
	defer cursor.Close(ctx)
	var results []GlossaryEntryDoc
	if err := cursor.All(ctx, &results); err != nil {
		return nil, err
	}
	return results, nil
}

// GetByTerm returns a single glossary entry by exact term match.
func (r *GlossaryRepo) GetByTerm(ctx context.Context, term string) (*GlossaryEntryDoc, error) {
	var doc GlossaryEntryDoc
	err := r.col.FindOne(ctx, bson.M{"term": term}).Decode(&doc)
	if err != nil {
		if err == mongo.ErrNoDocuments {
			return nil, nil
		}
		return nil, err
	}
	return &doc, nil
}

// GetByLetter returns all glossary entries whose term starts with the given
// base letter (including diacritical variants). Sorted by term.
func (r *GlossaryRepo) GetByLetter(ctx context.Context, letter string) ([]GlossaryEntryDoc, error) {
	regex := regexPrefixes(letter)
	if regex == "" {
		return nil, nil
	}

	filter := bson.M{"term": bson.M{"$regex": regex}}
	opts := options.Find().SetSort(bson.M{"term": 1})

	cursor, err := r.col.Find(ctx, filter, opts)
	if err != nil {
		return nil, err
	}
	defer cursor.Close(ctx)

	var results []GlossaryEntryDoc
	if err := cursor.All(ctx, &results); err != nil {
		return nil, err
	}
	return results, nil
}

// GetTermsByLetter returns lightweight term summaries (no definitions) for a
// given base letter. Used for sidebar listing.
func (r *GlossaryRepo) GetTermsByLetter(ctx context.Context, letter string) ([]GlossaryTermSummary, error) {
	regex := regexPrefixes(letter)
	if regex == "" {
		return nil, nil
	}

	filter := bson.M{"term": bson.M{"$regex": regex}}
	opts := options.Find().
		SetSort(bson.M{"term": 1}).
		SetProjection(bson.M{"term": 1})

	cursor, err := r.col.Find(ctx, filter, opts)
	if err != nil {
		return nil, err
	}
	defer cursor.Close(ctx)

	var results []GlossaryTermSummary
	if err := cursor.All(ctx, &results); err != nil {
		return nil, err
	}
	return results, nil
}

// GetLetterCounts returns the count of entries per base letter.
// This is computed in Go since MongoDB can't easily map diacritical first
// characters to base letters in an aggregation pipeline.
func (r *GlossaryRepo) GetLetterCounts(ctx context.Context) ([]GlossaryLetterCount, error) {
	// Fetch only the term field
	opts := options.Find().SetProjection(bson.M{"term": 1})
	cursor, err := r.col.Find(ctx, bson.M{}, opts)
	if err != nil {
		return nil, err
	}
	defer cursor.Close(ctx)

	var docs []struct {
		Term string `bson:"term"`
	}
	if err := cursor.All(ctx, &docs); err != nil {
		return nil, err
	}

	counts := make(map[string]int)
	for _, doc := range docs {
		letter := baseLetter(doc.Term)
		counts[letter]++
	}

	// Convert to sorted slice
	result := make([]GlossaryLetterCount, 0, len(counts))
	for letter, count := range counts {
		result = append(result, GlossaryLetterCount{Letter: letter, Count: count})
	}

	// Sort alphabetically
	for i := 0; i < len(result); i++ {
		for j := i + 1; j < len(result); j++ {
			if result[j].Letter < result[i].Letter {
				result[i], result[j] = result[j], result[i]
			}
		}
	}

	return result, nil
}