// Package weatherapi adapts the internal weather API to forecast bundles.
package weatherapi

import (
	"bytes"
	"context"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"os"
	"path"
	"path/filepath"
	"strconv"
	"strings"
	"time"

	"gitea.maximumdirect.net/eric/weatherreporter/internal/config"
	"gitea.maximumdirect.net/eric/weatherreporter/internal/forecast"
)

type Client struct {
	baseURL       *url.URL
	httpClient    *http.Client
	units         string
	format        string
	timezone      string
	precision     int
	missingSource config.MissingSourceConfig
	now           func() time.Time
}

type Option func(*Client)

func WithHTTPClient(httpClient *http.Client) Option {
	return func(c *Client) {
		if httpClient != nil {
			c.httpClient = httpClient
		}
	}
}

func WithClock(now func() time.Time) Option {
	return func(c *Client) {
		if now != nil {
			c.now = now
		}
	}
}

func New(cfg config.Config, opts ...Option) (*Client, error) {
	if strings.TrimSpace(cfg.WeatherAPI.BaseURL) == "" {
		return nil, fmt.Errorf("weather_api.base_url is required")
	}
	baseURL, err := url.Parse(cfg.WeatherAPI.BaseURL)
	if err != nil || baseURL.Scheme == "" || baseURL.Host == "" {
		return nil, fmt.Errorf("weather_api.base_url must be an absolute URL")
	}

	timeout := cfg.WeatherAPI.Timeout
	if timeout <= 0 {
		timeout = 10 * time.Second
	}

	client := &Client{
		baseURL:    baseURL,
		httpClient: &http.Client{Timeout: timeout},
		units:      cfg.WeatherAPI.Units,
		format:     cfg.WeatherAPI.Format,
		timezone:   cfg.WeatherAPI.Timezone,
		precision:  cfg.WeatherAPI.Precision,
		missingSource: config.MissingSourceConfig{
			Default: cfg.MissingSource.Default,
			Sources: cfg.MissingSource.Sources,
		},
		now: time.Now,
	}
	for _, opt := range opts {
		opt(client)
	}
	return client, nil
}

func (c *Client) FetchBundle(ctx context.Context) (*forecast.Bundle, error) {
	fetchedAt := c.now()
	builder := bundleBuilder{
		client:    c,
		bundle:    &forecast.Bundle{FetchedAt: fetchedAt},
		fetchedAt: fetchedAt,
	}

	if err := builder.fetchObservation(ctx); err != nil {
		return nil, err
	}
	if err := builder.fetchCurrent(ctx); err != nil {
		return nil, err
	}
	if err := builder.fetchHourly(ctx); err != nil {
		return nil, err
	}
	if err := builder.fetchNarrative(ctx); err != nil {
		return nil, err
	}
	if err := builder.fetchAlerts(ctx); err != nil {
		return nil, err
	}
	if err := builder.fetchDiscussion(ctx); err != nil {
		return nil, err
	}
	if err := builder.addStub("daily", "daily forecast data is not available from the weather API yet"); err != nil {
		return nil, err
	}
	if err := builder.addStub("weather_story", "NWS weather story is not available from the weather API yet"); err != nil {
		return nil, err
	}

	return builder.bundle, nil
}

type bundleBuilder struct {
	client    *Client
	bundle    *forecast.Bundle
	fetchedAt time.Time
}

func (b *bundleBuilder) fetchObservation(ctx context.Context) error {
	raw, source, err := b.client.fetch(ctx, "observations", "/observations", queryOptions{precision: true})
	if err != nil {
		return err
	}
	if raw == nil {
		return b.handleMissing(&source, "observation data is missing", false)
	}
	var observation forecast.Observation
	if err := decodeSource(raw, &observation); err != nil {
		return b.handleMalformed(&source, err, false)
	}
	source.IssuedAt = &observation.Timestamp
	b.bundle.Observation = &observation
	b.addSource(source)
	return nil
}

func (b *bundleBuilder) fetchCurrent(ctx context.Context) error {
	raw, source, err := b.client.fetch(ctx, "current", "/conditions/current", queryOptions{precision: true})
	if err != nil {
		return err
	}
	if raw == nil {
		return b.handleMissing(&source, "current conditions data is missing", false)
	}
	var current forecast.Current
	if err := decodeSource(raw, &current); err != nil {
		return b.handleMalformed(&source, err, false)
	}
	b.bundle.Current = &current
	b.addSource(source)
	return nil
}

func (b *bundleBuilder) fetchHourly(ctx context.Context) error {
	raw, source, err := b.client.fetch(ctx, "hourly", "/forecast/hourly", queryOptions{precision: true, timezone: true})
	if err != nil {
		return err
	}
	if raw == nil {
		return b.handleMissing(&source, "hourly forecast data is missing", true)
	}
	var hourly forecast.ForecastRun
	if err := decodeSource(raw, &hourly); err != nil {
		return fmt.Errorf("decode hourly forecast from %s: %w", source.Endpoint, err)
	}
	if len(hourly.Periods) == 0 {
		return fmt.Errorf("hourly forecast from %s contains no periods", source.Endpoint)
	}
	source.IssuedAt = &hourly.IssuedAt
	source.UpdatedAt = hourly.UpdatedAt
	b.bundle.Hourly = &hourly
	b.addSource(source)
	return nil
}

func (b *bundleBuilder) fetchNarrative(ctx context.Context) error {
	raw, source, err := b.client.fetch(ctx, "narrative", "/forecast/narrative", queryOptions{precision: true, timezone: true})
	if err != nil {
		return err
	}
	if raw == nil {
		return b.handleMissing(&source, "narrative forecast data is missing", false)
	}
	var narrative forecast.ForecastRun
	if err := decodeSource(raw, &narrative); err != nil {
		return b.handleMalformed(&source, err, false)
	}
	source.IssuedAt = &narrative.IssuedAt
	source.UpdatedAt = narrative.UpdatedAt
	b.bundle.Narrative = &narrative
	b.addSource(source)
	return nil
}

func (b *bundleBuilder) fetchAlerts(ctx context.Context) error {
	raw, source, err := b.client.fetch(ctx, "alerts", "/alerts/active", queryOptions{})
	if err != nil {
		return err
	}
	if raw == nil {
		return b.handleMissing(&source, "active alerts data is missing", false)
	}
	var alerts forecast.AlertRun
	if err := decodeSource(raw, &alerts); err != nil {
		return b.handleMalformed(&source, err, false)
	}
	alerts.Raw = append(json.RawMessage(nil), raw...)
	if alerts.AsOf != nil {
		source.IssuedAt = alerts.AsOf
	}
	b.bundle.Alerts = &alerts
	b.addSource(source)
	return nil
}

func (b *bundleBuilder) fetchDiscussion(ctx context.Context) error {
	raw, source, err := b.client.fetch(ctx, "discussion", "/discussion", queryOptions{timezone: true})
	if err != nil {
		return err
	}
	if raw == nil {
		return b.handleMissing(&source, "forecast discussion data is missing", false)
	}
	var discussion forecast.Discussion
	if err := decodeSource(raw, &discussion); err != nil {
		return b.handleMalformed(&source, err, false)
	}
	source.IssuedAt = &discussion.IssuedAt
	source.UpdatedAt = discussion.UpdatedAt
	b.bundle.Discussion = &discussion
	b.addSource(source)
	return nil
}

func (b *bundleBuilder) addStub(sourceName string, message string) error {
	source := forecast.Source{
		Name:      sourceName,
		FetchedAt: b.fetchedAt,
		Missing:   true,
	}
	return b.applyMissingPolicy(&source, "missing_source", message)
}

func (b *bundleBuilder) handleMissing(source *forecast.Source, message string, required bool) error {
	source.Missing = true
	if required {
		return fmt.Errorf("%s from %s is required", message, source.Endpoint)
	}
	return b.applyMissingPolicy(source, "missing_source", message)
}

func (b *bundleBuilder) handleMalformed(source *forecast.Source, err error, required bool) error {
	if required {
		return fmt.Errorf("decode %s from %s: %w", source.Name, source.Endpoint, err)
	}
	source.Missing = true
	return b.applyMissingPolicy(source, "malformed_source", fmt.Sprintf("malformed %s data: %v", source.Name, err))
}

func (b *bundleBuilder) applyMissingPolicy(source *forecast.Source, code string, message string) error {
	policy := b.client.policyFor(source.Name)
	if policy == config.MissingSourceError {
		return fmt.Errorf("%s: %s", source.Name, message)
	}
	if policy == config.MissingSourceWarn {
		warning := forecast.SourceWarning{
			Source:             source.Name,
			Code:               code,
			Severity:           "warning",
			Message:            message,
			Endpoint:           source.Endpoint,
			CompletenessImpact: "source omitted from bundle",
		}
		source.Warnings = append(source.Warnings, warning)
		b.bundle.Warnings = append(b.bundle.Warnings, warning)
	}
	b.addSource(*source)
	return nil
}

func (b *bundleBuilder) addSource(source forecast.Source) {
	b.bundle.Sources = append(b.bundle.Sources, source)
}

func (c *Client) policyFor(source string) config.MissingSourcePolicy {
	if policy, ok := c.missingSource.Sources[source]; ok {
		return policy
	}
	return c.missingSource.Default
}

type queryOptions struct {
	precision bool
	timezone  bool
}

type envelope struct {
	Data json.RawMessage `json:"data"`
}

func (c *Client) fetch(ctx context.Context, sourceName string, endpoint string, opts queryOptions) (json.RawMessage, forecast.Source, error) {
	reqURL := c.endpointURL(endpoint, opts)
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, reqURL.String(), nil)
	if err != nil {
		return nil, forecast.Source{}, fmt.Errorf("create request for %s: %w", endpoint, err)
	}

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return nil, forecast.Source{}, fmt.Errorf("fetch %s: %w", endpoint, err)
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(io.LimitReader(resp.Body, 10<<20))
	if err != nil {
		return nil, forecast.Source{}, fmt.Errorf("read %s response: %w", endpoint, err)
	}
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return nil, forecast.Source{}, fmt.Errorf("fetch %s: unexpected HTTP status %d: %s", endpoint, resp.StatusCode, strings.TrimSpace(string(body)))
	}

	var env envelope
	if err := json.Unmarshal(body, &env); err != nil {
		return nil, forecast.Source{}, fmt.Errorf("decode %s envelope: %w", endpoint, err)
	}

	source := forecast.Source{
		Name:      sourceName,
		Endpoint:  endpoint,
		Query:     queryMap(reqURL.Query()),
		FetchedAt: c.now(),
	}
	if len(env.Data) == 0 || bytes.Equal(bytes.TrimSpace(env.Data), []byte("null")) {
		source.Missing = true
		return nil, source, nil
	}
	hash, err := sourceHash(env.Data)
	if err != nil {
		return env.Data, source, nil
	}
	source.DataSHA256 = hash
	return env.Data, source, nil
}

func (c *Client) endpointURL(endpoint string, opts queryOptions) *url.URL {
	reqURL := *c.baseURL
	reqURL.Path = path.Join(c.baseURL.Path, endpoint)
	query := reqURL.Query()
	query.Set("format", c.format)
	query.Set("units", c.units)
	if opts.precision {
		query.Set("precision", strconv.Itoa(c.precision))
	}
	if opts.timezone {
		query.Set("tz", c.timezone)
	}
	reqURL.RawQuery = query.Encode()
	return &reqURL
}

func queryMap(values url.Values) map[string]string {
	if len(values) == 0 {
		return nil
	}
	out := make(map[string]string, len(values))
	for key, value := range values {
		if len(value) > 0 {
			out[key] = value[0]
		}
	}
	return out
}

func decodeSource(raw json.RawMessage, target any) error {
	if err := json.Unmarshal(raw, target); err != nil {
		return err
	}
	return nil
}

func sourceHash(raw json.RawMessage) (string, error) {
	var compact bytes.Buffer
	if err := json.Compact(&compact, raw); err != nil {
		return "", err
	}
	sum := sha256.Sum256(compact.Bytes())
	return hex.EncodeToString(sum[:]), nil
}

func SaveBundle(path string, bundle *forecast.Bundle) error {
	data, err := json.MarshalIndent(bundle, "", "  ")
	if err != nil {
		return fmt.Errorf("marshal forecast bundle: %w", err)
	}
	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
		return fmt.Errorf("create bundle directory %q: %w", filepath.Dir(path), err)
	}
	tmp, err := os.CreateTemp(filepath.Dir(path), "."+filepath.Base(path)+".*.tmp")
	if err != nil {
		return fmt.Errorf("create temporary bundle file: %w", err)
	}
	tmpName := tmp.Name()
	defer os.Remove(tmpName)

	if _, err := tmp.Write(data); err != nil {
		tmp.Close()
		return fmt.Errorf("write temporary bundle file: %w", err)
	}
	if err := tmp.Close(); err != nil {
		return fmt.Errorf("close temporary bundle file: %w", err)
	}
	if err := os.Rename(tmpName, path); err != nil {
		return fmt.Errorf("save bundle %q: %w", path, err)
	}
	return nil
}