package kiosk

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"net/url"
	"strings"
	"time"

	"git.golem15.com/golem15/summercms/modules/compass"
	"git.golem15.com/golem15/summercms/modules/fetchguard"
)

// DefaultRegistryURL is the registry an application uses when its config
// has no plugins.registry_url.
const DefaultRegistryURL = "https://summercms.io"

// registryURLKey is the config key naming the registry origin: the file
// config/plugins.yaml, key registry_url, or SUMMER_PLUGINS__REGISTRY_URL.
const registryURLKey = "plugins.registry_url"

// Limits of every registry call: a registry answer is small JSON, so a
// larger body or a slow server is an error, not something to wait for.
const (
	registryMaxBytes = 4 << 20
	registryTimeout  = 10 * time.Second
)

var (
	// ErrRegistryDisabled is returned by NewClient for an empty base URL:
	// plugins.registry_url is set to "" and registry calls are off.
	ErrRegistryDisabled = errors.New("the plugin registry is disabled (plugins.registry_url is empty)")
	// ErrNotFound is wrapped by the errors of a Client call the registry
	// answered with 404: no plugin has that ID.
	ErrNotFound = errors.New("not in the registry")
)

// RegistryURL returns the registry origin configured in cfg: the
// DefaultRegistryURL when plugins.registry_url is absent (or cfg is nil),
// the configured value without a trailing slash otherwise. An empty
// result means registry calls are disabled.
func RegistryURL(cfg *compass.Config) string {
	if cfg == nil || !cfg.Has(registryURLKey) {
		return DefaultRegistryURL
	}
	return strings.TrimRight(strings.TrimSpace(cfg.String(registryURLKey)), "/")
}

// Client reads the registry API v1 of one registry origin. Every request
// goes through a fetchguard client in TrustedMode (the origin is operator
// configuration) with a 4 MiB body cap, a 10 second timeout and no
// redirects, so the base URL must be the final origin.
type Client struct {
	base string
	http *fetchguard.Client
}

// NewClient builds a Client for the registry at baseURL, an http or https
// origin without user info, query or fragment, for example
// https://summercms.io. An empty baseURL returns ErrRegistryDisabled. cfg
// may be nil.
func NewClient(baseURL string, cfg *compass.Config) (*Client, error) {
	baseURL = strings.TrimRight(strings.TrimSpace(baseURL), "/")
	if baseURL == "" {
		return nil, ErrRegistryDisabled
	}
	u, err := url.Parse(baseURL)
	if err != nil {
		return nil, fmt.Errorf("kiosk: registry URL %q: %w", baseURL, err)
	}
	switch {
	case u.Scheme != "http" && u.Scheme != "https":
		return nil, fmt.Errorf("kiosk: registry URL %q must start with https:// or http://", baseURL)
	case u.Host == "":
		return nil, fmt.Errorf("kiosk: registry URL %q has no host", baseURL)
	case u.User != nil:
		return nil, fmt.Errorf("kiosk: registry URL must not carry user info")
	case u.RawQuery != "" || u.Fragment != "" || u.ForceQuery:
		return nil, fmt.Errorf("kiosk: registry URL %q must not have a query or fragment", baseURL)
	}
	hc, err := fetchguard.NewClient(fetchguard.Policy{
		Mode:     fetchguard.TrustedMode,
		MaxBytes: registryMaxBytes,
		Timeout:  registryTimeout,
	}, cfg)
	if err != nil {
		return nil, fmt.Errorf("kiosk: registry client: %w", err)
	}
	return &Client{base: baseURL, http: hc}, nil
}

// BaseURL returns the registry origin the client calls.
func (c *Client) BaseURL() string {
	return c.base
}

// List returns the registry's plugins matching the search q and the
// category (both optional).
func (c *Client) List(ctx context.Context, q, category string) (ListResponse, error) {
	query := url.Values{}
	if q != "" {
		query.Set("q", q)
	}
	if category != "" {
		query.Set("category", category)
	}
	path := "/plugins"
	if len(query) > 0 {
		path += "?" + query.Encode()
	}
	var resp ListResponse
	err := c.get(ctx, path, "", &resp)
	return resp, err
}

// Plugin returns one plugin with its README and the requirements of its
// latest release. An unknown ID gives an error wrapping ErrNotFound.
func (c *Client) Plugin(ctx context.Context, id string) (RegistryPluginDetail, error) {
	var resp DetailResponse
	err := c.get(ctx, "/plugins/"+url.PathEscape(id), id, &resp)
	return resp.Data, err
}

// Versions returns every release of a plugin, newest first. An unknown ID
// gives an error wrapping ErrNotFound.
func (c *Client) Versions(ctx context.Context, id string) ([]RegistryVersion, error) {
	var resp VersionsResponse
	err := c.get(ctx, "/plugins/"+url.PathEscape(id)+"/versions", id, &resp)
	return resp.Data, err
}

func (c *Client) get(ctx context.Context, path, id string, out any) error {
	header := http.Header{}
	header.Set("Accept", "application/json")
	res, err := c.http.Get(ctx, c.base+RegistryAPIPath+path, header)
	if err != nil {
		return fmt.Errorf("registry %s: %w", c.base, err)
	}
	switch {
	case res.StatusCode == http.StatusNotFound:
		if id != "" {
			return fmt.Errorf("%s is %w at %s", id, ErrNotFound, c.base)
		}
		return fmt.Errorf("registry %s: %w", c.base, ErrNotFound)
	case res.StatusCode >= 300 && res.StatusCode < 400:
		return fmt.Errorf("registry %s answered with a redirect to %q; set plugins.registry_url to the final origin", c.base, res.Header.Get("Location"))
	case res.StatusCode < 200 || res.StatusCode >= 300:
		var e ErrorResponse
		if json.Unmarshal(res.Body, &e) == nil && e.Error.Code != "" {
			return fmt.Errorf("registry %s: HTTP %d %s: %s", c.base, res.StatusCode, e.Error.Code, e.Error.Message)
		}
		return fmt.Errorf("registry %s: HTTP %d", c.base, res.StatusCode)
	}
	if err := json.Unmarshal(res.Body, out); err != nil {
		return fmt.Errorf("registry %s: decode %s: %w", c.base, path, err)
	}
	return nil
}