package forecast

import (
	"context"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"os"
)

// Fetcher returns the CSV bytes for a forecast source. The HTTP fetcher pulls a public export URL; the
// file fetcher reads an operator provided export, because the GSA tool export is a download from a gated
// dashboard rather than a clean API. The caller closes the reader.
type Fetcher func(ctx context.Context) (io.ReadCloser, error)

// HTTPFetcher fetches a CSV export from a URL. Error messages name only the host, never the full URL, so
// a credential embedded in the configured URL (https://[credentials removed]@host/forecast.csv) cannot leak into
// a log on a fetch failure.
func HTTPFetcher(client *http.Client, rawURL string) Fetcher {
	return func(ctx context.Context) (io.ReadCloser, error) {
		host := "unknown host"
		if u, err := url.Parse(rawURL); err == nil && u.Host != "" {
			host = u.Host
		}
		req, err := http.NewRequestWithContext(ctx, http.MethodGet, rawURL, nil)
		if err != nil {
			// The underlying error can echo the full URL, so report only the host.
			return nil, fmt.Errorf("forecast: build request for %s failed", host)
		}
		req.Header.Set("Accept", "text/csv")
		resp, err := client.Do(req)
		if err != nil {
			return nil, fmt.Errorf("forecast: fetch %s: %w", host, err)
		}
		if resp.StatusCode != http.StatusOK {
			resp.Body.Close()
			return nil, fmt.Errorf("forecast: fetch %s: status %d", host, resp.StatusCode)
		}
		return resp.Body, nil
	}
}

// FileFetcher reads a CSV export from a local path, the path an operator points at after downloading the
// export from the gated dashboard.
func FileFetcher(path string) Fetcher {
	return func(_ context.Context) (io.ReadCloser, error) {
		f, err := os.Open(path)
		if err != nil {
			return nil, fmt.Errorf("forecast: open %s: %w", path, err)
		}
		return f, nil
	}
}

// Source is a named forecast feed: a Fetcher plus a Mapping. It is the generic base every agency
// forecast reuses, so adding a new agency is a Source value (its export location and its column mapping),
// not new parsing code.
type Source struct {
	name    string
	fetch   Fetcher
	mapping Mapping
}

// NewSource builds a forecast source.
func NewSource(name string, fetch Fetcher, mapping Mapping) *Source {
	return &Source{name: name, fetch: fetch, mapping: mapping}
}

// Name is the provenance label for this forecast feed.
func (s *Source) Name() string { return s.name }

// Records fetches the export and parses it, returning the normalized records and the count of rows it
// skipped as unparseable.
func (s *Source) Records(ctx context.Context) ([]Record, int, error) {
	body, err := s.fetch(ctx)
	if err != nil {
		return nil, 0, err
	}
	defer body.Close()
	return Parse(body, s.mapping)
}