package research

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"

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

var ErrHTTPSourceRejected = errors.New("http research source rejected")

type HTTPConnector struct {
	Client       *http.Client
	AllowedHosts map[string]struct{}
	MaxBytes     int64
}

func (c HTTPConnector) Collect(ctx context.Context, request epistemics.WebResearchRequest, nowUnixMillis int64) (epistemics.ResearchCandidate, error) {
	if request.Plan.Validate() != nil || request.SourceID == "" || strings.TrimSpace(request.Statement) == "" || nowUnixMillis < 1 {
		return epistemics.ResearchCandidate{}, ErrHTTPSourceRejected
	}
	u, err := url.Parse(request.URL)
	if err != nil || u.Scheme != "https" || u.User != nil || u.Host == "" || !c.allowedHost(strings.ToLower(u.Hostname())) {
		return epistemics.ResearchCandidate{}, ErrHTTPSourceRejected
	}
	client := c.Client
	if client == nil {
		client = &http.Client{}
	}
	maxBytes := c.MaxBytes
	if maxBytes <= 0 || maxBytes > 4<<20 {
		maxBytes = 256 << 10
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
	if err != nil {
		return epistemics.ResearchCandidate{}, ErrHTTPSourceRejected
	}
	response, err := client.Do(req)
	if err != nil {
		return epistemics.ResearchCandidate{}, fmt.Errorf("read web source: %w", err)
	}
	defer response.Body.Close()
	if response.StatusCode < 200 || response.StatusCode >= 300 {
		return epistemics.ResearchCandidate{}, fmt.Errorf("web source status: %s", response.Status)
	}
	body, err := io.ReadAll(io.LimitReader(response.Body, maxBytes+1))
	if err != nil || int64(len(body)) > maxBytes || len(body) == 0 {
		return epistemics.ResearchCandidate{}, ErrHTTPSourceRejected
	}
	digest := sha256.Sum256(body)
	digestText := "sha256:" + hex.EncodeToString(digest[:])
	key := sha256.Sum256([]byte(u.String() + "\x00" + digestText))
	keyText := hex.EncodeToString(key[:])
	snapshotID := epistemics.SourceSnapshotID("snapshot:" + keyText)
	return epistemics.ResearchCandidate{
		PropositionKey: request.PropositionKey, Statement: request.Statement,
		Source:   epistemics.Source{ID: request.SourceID, Kind: "web", Locator: u.String(), Title: request.Title, Publisher: u.Hostname()},
		Snapshot: epistemics.SourceSnapshot{ID: snapshotID, SourceID: request.SourceID, ContentDigest: digestText, CapturedAtUnixMillis: nowUnixMillis, Freshness: epistemics.FreshnessCurrent},
		Excerpt:  epistemics.SourceExcerpt{ID: epistemics.SourceExcerptID("excerpt:" + keyText), SnapshotID: snapshotID, Text: string(body), Start: 0, End: int64(len(body))},
		Evidence: epistemics.EvidenceObserved, Coverage: epistemics.CoverageComplete, Conflict: epistemics.ConflictNone,
	}, nil
}

func (c HTTPConnector) allowedHost(host string) bool {
	_, ok := c.AllowedHosts[host]
	return ok
}