package ted

import (
	"bytes"
	"context"
	"encoding/csv"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strings"
	"time"
)

const (
	calendarURL  = "%s/en/release-calendar/-/download/file/CSV/%d"
	searchAPIURL = "https://api.ted.europa.eu/v3/notices/search"
)

type searchAPIRequest struct {
	Query  string   `json:"query"`
	Fields []string `json:"fields"`
	Limit  int      `json:"limit"`
}

type searchAPIResponse struct {
	Notices []struct {
		OJSNumber string `json:"ojs-number"`
	} `json:"notices"`
}

// GetOJS resolves the OJS package id for a publication date.
// It tries the TED release calendar CSV first, then falls back to the TED Search API
// when the calendar download is blocked (e.g. AWS WAF HTTP 202).
func GetOJS(ctx context.Context, baseURL string, year int, date, userAgent string, client *http.Client) (string, error) {
	if ojs, err := getOJSFromCalendarCSV(ctx, baseURL, year, date, userAgent, client); err == nil {
		return ojs, nil
	} else if !isCalendarUnavailable(err) {
		return "", err
	}

	return getOJSFromSearchAPIAt(ctx, date, userAgent, client, searchAPIURL)
}

func getOJSFromCalendarCSV(ctx context.Context, baseURL string, year int, date, userAgent string, client *http.Client) (string, error) {
	url := fmt.Sprintf(calendarURL, baseURL, year)

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return "", fmt.Errorf("create calendar request: %w", err)
	}
	if strings.TrimSpace(userAgent) != "" {
		req.Header.Set("User-Agent", userAgent)
	}

	resp, err := client.Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return "", err
	}

	if resp.StatusCode != http.StatusOK {
		return "", fmt.Errorf("calendar HTTP error: %d %s (body: %s)", resp.StatusCode, resp.Status, previewBody(body))
	}

	reader := csv.NewReader(bytes.NewReader(body))
	records, err := reader.ReadAll()
	if err != nil {
		return "", fmt.Errorf("parse calendar CSV: %w", err)
	}

	if len(records) < 2 {
		return "", fmt.Errorf("ojs calendar is empty (rows=%d, body=%s)", len(records), previewBody(body))
	}

	targetDate := strings.TrimSpace(date)
	for _, row := range records[1:] {
		if len(row) < 2 {
			continue
		}
		rowDate := strings.TrimSpace(row[1])
		if rowDate == targetDate {
			return fmt.Sprintf("%d%05s", year, strings.TrimSpace(row[0])), nil
		}
	}

	return "", fmt.Errorf("can not find ojs number for date %s", date)
}

func getOJSFromSearchAPIAt(ctx context.Context, date, userAgent string, client *http.Client, apiURL string) (string, error) {
	parsed, err := time.Parse("02/01/2006", strings.TrimSpace(date))
	if err != nil {
		return "", fmt.Errorf("parse publication date %s: %w", date, err)
	}

	payload, err := json.Marshal(searchAPIRequest{
		Query:  fmt.Sprintf("publication-date=%s", parsed.Format("20060102")),
		Fields: []string{"ojs-number"},
		Limit:  1,
	})
	if err != nil {
		return "", fmt.Errorf("marshal search request: %w", err)
	}

	req, err := http.NewRequestWithContext(ctx, http.MethodPost, apiURL, bytes.NewReader(payload))
	if err != nil {
		return "", fmt.Errorf("create search request: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Accept", "application/json")
	if strings.TrimSpace(userAgent) != "" {
		req.Header.Set("User-Agent", userAgent)
	}

	resp, err := client.Do(req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return "", err
	}

	if resp.StatusCode != http.StatusOK {
		return "", fmt.Errorf("search API HTTP error: %d %s (body: %s)", resp.StatusCode, resp.Status, previewBody(body))
	}

	var result searchAPIResponse
	if err := json.Unmarshal(body, &result); err != nil {
		return "", fmt.Errorf("decode search API response: %w", err)
	}
	if len(result.Notices) == 0 || strings.TrimSpace(result.Notices[0].OJSNumber) == "" {
		return "", fmt.Errorf("can not find ojs number for date %s", date)
	}

	return formatOJSPackageID(parsed.Year(), result.Notices[0].OJSNumber)
}

func formatOJSPackageID(fallbackYear int, ojsNumber string) (string, error) {
	parts := strings.Split(strings.TrimSpace(ojsNumber), "/")
	if len(parts) != 2 {
		return "", fmt.Errorf("unexpected ojs-number format %q", ojsNumber)
	}

	seq := strings.TrimSpace(parts[0])
	yearStr := strings.TrimSpace(parts[1])
	if seq == "" || yearStr == "" {
		return "", fmt.Errorf("unexpected ojs-number format %q", ojsNumber)
	}

	year := fallbackYear
	if parsedYear, err := time.Parse("2006", yearStr); err == nil {
		year = parsedYear.Year()
	}

	return fmt.Sprintf("%d%05s", year, seq), nil
}

func isCalendarUnavailable(err error) bool {
	if err == nil {
		return false
	}
	msg := err.Error()
	return strings.Contains(msg, "calendar HTTP error: 202") ||
		strings.Contains(msg, "ojs calendar is empty")
}

func previewBody(body []byte) string {
	const maxLen = 160
	s := strings.TrimSpace(string(body))
	s = strings.ReplaceAll(s, "\n", " ")
	s = strings.ReplaceAll(s, "\r", " ")
	if len(s) <= maxLen {
		return s
	}
	return s[:maxLen] + "..."
}