package research

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"strings"

	"git.cin.su/m/Assistant/contracts/epistemics"
)

var ErrRepositoryPathRejected = errors.New("repository source path rejected")

type RepositoryConnector struct{ Root string }

func (c RepositoryConnector) Collect(ctx context.Context, request epistemics.RepositoryResearchRequest, nowUnixMillis int64) (epistemics.ResearchCandidate, error) {
	if err := request.Plan.Validate(); err != nil {
		return epistemics.ResearchCandidate{}, err
	}
	if request.SourceID == "" || strings.TrimSpace(request.Statement) == "" || nowUnixMillis < 1 {
		return epistemics.ResearchCandidate{}, ErrRepositoryPathRejected
	}
	root, err := filepath.Abs(c.Root)
	if err != nil || root == "" {
		return epistemics.ResearchCandidate{}, ErrRepositoryPathRejected
	}
	path, err := filepath.Abs(filepath.Join(root, filepath.FromSlash(request.Path)))
	if err != nil || !withinRoot(root, path) {
		return epistemics.ResearchCandidate{}, ErrRepositoryPathRejected
	}
	select {
	case <-ctx.Done():
		return epistemics.ResearchCandidate{}, ctx.Err()
	default:
	}
	content, err := os.ReadFile(path)
	if err != nil || len(content) == 0 {
		return epistemics.ResearchCandidate{}, fmt.Errorf("read repository source: %w", err)
	}
	digest := sha256.Sum256(content)
	digestText := "sha256:" + hex.EncodeToString(digest[:])
	key := sha256.Sum256([]byte(filepath.ToSlash(path) + "\x00" + digestText))
	keyText := hex.EncodeToString(key[:])
	return epistemics.ResearchCandidate{
		PropositionKey: request.PropositionKey,
		Statement:      request.Statement,
		Source:         epistemics.Source{ID: request.SourceID, Kind: "repository", Locator: "file://" + filepath.ToSlash(path), Title: filepath.Base(path), Publisher: "local-repository"},
		Snapshot:       epistemics.SourceSnapshot{ID: epistemics.SourceSnapshotID("snapshot:" + keyText), SourceID: request.SourceID, ContentDigest: digestText, CapturedAtUnixMillis: nowUnixMillis, Freshness: epistemics.FreshnessCurrent},
		Excerpt:        epistemics.SourceExcerpt{ID: epistemics.SourceExcerptID("excerpt:" + keyText), SnapshotID: epistemics.SourceSnapshotID("snapshot:" + keyText), Text: string(content), Start: 0, End: int64(len(content))},
		Evidence:       epistemics.EvidenceObserved,
		Coverage:       epistemics.CoverageComplete,
		Conflict:       epistemics.ConflictNone,
	}, nil
}

func withinRoot(root, path string) bool {
	rel, err := filepath.Rel(root, path)
	return err == nil && rel != ".." && !strings.HasPrefix(rel, ".."+string(filepath.Separator)) && !filepath.IsAbs(rel)
}