// Package bls is a typed client for the Bureau of Labor Statistics public API v2, used to pull the
// OEWS regional wage baseline for the Galapagos occupations. It has no database dependency: it fetches
// the latest annual wage per series; the rates sync (cmd/rates-sync) writes the cache. The
// registrationKey is read from env on the server and sent only in the request body, never logged.
package bls

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

// BaseV2 is the BLS public API v2 timeseries endpoint.
const BaseV2 = "https://api.bls.gov/publicAPI/v2/timeseries/data/"

const maxBatch = 50 // BLS allows up to 50 series per request with a registered key

// ErrThrottled is returned when the BLS daily request threshold is reached.
var ErrThrottled = errors.New("bls: daily request threshold reached")

// Client calls the BLS API.
type Client struct {
	key  string
	base string
	http *http.Client
}

// New builds a client. An empty base uses the v2 endpoint.
func New(key, base string) *Client {
	if strings.TrimSpace(base) == "" {
		base = BaseV2
	}
	return &Client{key: key, base: base, http: &http.Client{Timeout: 45 * time.Second}}
}

// Series is one returned series with its latest data point.
type Series struct {
	ID    string
	Year  string
	Value string
}

// FetchLatest pulls the latest data point for each series id, batching to respect the API limit.
func (c *Client) FetchLatest(ctx context.Context, seriesIDs []string) ([]Series, error) {
	var out []Series
	for start := 0; start < len(seriesIDs); start += maxBatch {
		end := start + maxBatch
		if end > len(seriesIDs) {
			end = len(seriesIDs)
		}
		batch, err := c.fetchBatch(ctx, seriesIDs[start:end])
		if err != nil {
			return out, err
		}
		out = append(out, batch...)
	}
	return out, nil
}

func (c *Client) fetchBatch(ctx context.Context, ids []string) ([]Series, error) {
	payload, err := json.Marshal(map[string]any{
		"seriesid":        ids,
		"latest":          true,
		"registrationKey": c.key,
	})
	if err != nil {
		return nil, fmt.Errorf("bls: marshal request: %w", err)
	}
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.base, bytes.NewReader(payload))
	if err != nil {
		return nil, errors.New("bls: failed to build request")
	}
	req.Header.Set("Content-Type", "application/json")

	resp, err := c.http.Do(req)
	if err != nil {
		return nil, errors.New("bls: request failed")
	}
	defer func() { _ = resp.Body.Close() }()

	if resp.StatusCode == http.StatusTooManyRequests {
		return nil, ErrThrottled
	}
	if resp.StatusCode != http.StatusOK {
		snippet, _ := io.ReadAll(io.LimitReader(resp.Body, 512))
		return nil, fmt.Errorf("bls: status %d: %s", resp.StatusCode, strings.TrimSpace(string(snippet)))
	}

	var r blsResponse
	if err := json.NewDecoder(resp.Body).Decode(&r); err != nil {
		return nil, fmt.Errorf("bls: decode response: %w", err)
	}
	if r.Status != "REQUEST_SUCCEEDED" {
		msg := strings.ToLower(strings.Join(r.Message, " "))
		if strings.Contains(msg, "threshold") || strings.Contains(msg, "daily") || strings.Contains(msg, "limit") {
			return nil, ErrThrottled
		}
		return nil, fmt.Errorf("bls: request not processed: %s", strings.Join(r.Message, "; "))
	}

	out := make([]Series, 0, len(r.Results.Series))
	for _, s := range r.Results.Series {
		if len(s.Data) == 0 {
			continue // no data published for this series
		}
		d := s.Data[0] // latest=true puts the most recent point first
		out = append(out, Series{ID: s.SeriesID, Year: d.Year, Value: d.Value})
	}
	return out, nil
}

type blsResponse struct {
	Status  string   `json:"status"`
	Message []string `json:"message"`
	Results struct {
		Series []struct {
			SeriesID string `json:"seriesID"`
			Data     []struct {
				Year   string `json:"year"`
				Period string `json:"period"`
				Value  string `json:"value"`
			} `json:"data"`
		} `json:"series"`
	} `json:"Results"`
}