// Copyright 2024 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package path

import (
	"slices"
	"strings"

	"github.com/blevesearch/bleve/v2/analysis"
	"github.com/blevesearch/bleve/v2/registry"
)

const (
	Name = "gitea/path"
)

type TokenFilter struct{}

func NewTokenFilter() *TokenFilter {
	return &TokenFilter{}
}

func TokenFilterConstructor(config map[string]any, cache *registry.Cache) (analysis.TokenFilter, error) {
	return NewTokenFilter(), nil
}

func (s *TokenFilter) Filter(input analysis.TokenStream) analysis.TokenStream {
	if len(input) == 1 {
		// if there is only one token, we dont need to generate the reversed chain
		return generatePathTokens(input, false)
	}

	normal := generatePathTokens(input, false)
	reversed := generatePathTokens(input, true)

	return append(normal, reversed...)
}

// Generates path tokens from the input tokens.
// This mimics the behavior of the path hierarchy tokenizer in ES. It takes the input tokens and combine them, generating a term for each component
// in tree (e.g., foo/bar/baz.md will generate foo, foo/bar, and foo/bar/baz.md).
//
// If the reverse flag is set, the order of the tokens is reversed (the same input will generate baz.md, baz.md/bar, baz.md/bar/foo). This is useful
// to efficiently search for filenames without supplying the fullpath.
func generatePathTokens(input analysis.TokenStream, reversed bool) analysis.TokenStream {
	terms := make([]string, 0, len(input))
	longestTerm := 0

	if reversed {
		slices.Reverse(input)
	}

	for i := 0; i < len(input); i++ {
		var sb strings.Builder
		sb.WriteString(string(input[0].Term))

		for j := 1; j < i; j++ {
			sb.WriteString("/")
			sb.WriteString(string(input[j].Term))
		}

		term := sb.String()

		if longestTerm < len(term) {
			longestTerm = len(term)
		}

		terms = append(terms, term)
	}

	output := make(analysis.TokenStream, 0, len(terms))

	for _, term := range terms {
		var start, end int

		if reversed {
			start = 0
			end = len(term)
		} else {
			start = longestTerm - len(term)
			end = longestTerm
		}

		token := analysis.Token{
			Position: 1,
			Start:    start,
			End:      end,
			Type:     analysis.AlphaNumeric,
			Term:     []byte(term),
		}

		output = append(output, &token)
	}

	return output
}

func init() {
	registry.RegisterTokenFilter(Name, TokenFilterConstructor)
}