package main

import (
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"os"
	"path/filepath"
	"sort"
)

type httpCacheEntry struct {
	Body string
	Err  error
}

var httpCache = map[string]httpCacheEntry{}

type httpStatusError struct {
	StatusCode int
	Status     string
}

// Is implements the interface for [errors.Is].
func (e *httpStatusError) Is(target error) bool {
	switch target {
	case os.ErrNotExist:
		return e.StatusCode == http.StatusNotFound
	default:
		return false
	}
}

// Error implements [error].
func (e *httpStatusError) Error() string {
	return fmt.Sprintf("unexpected HTTP status: %v", e.Status)
}

func httpGet(u string, hdr map[string]string) (string, error) {
	cacheKey := url.QueryEscape(u)
	hdrKeys := make([]string, 0, len(hdr))
	for k := range hdr {
		hdrKeys = append(hdrKeys, http.CanonicalHeaderKey(k))
	}
	sort.Strings(hdrKeys)
	for _, k := range hdrKeys {
		cacheKey += "|" + url.QueryEscape(k) + ":" + url.QueryEscape(hdr[k])
	}

	if cache, ok := httpCache[cacheKey]; ok {
		fmt.Printf("CACHE-GET %q\n", u)
		return cache.Body, cache.Err
	}
	if err := os.Mkdir(".http-cache", 0777); err != nil && !os.IsExist(err) {
		return "", err
	}
	cacheFile := filepath.Join(".http-cache", cacheKey)
	if bs, err := os.ReadFile(cacheFile); err == nil {
		fmt.Printf("CACHE-GET %q\n", u)
		httpCache[cacheKey] = httpCacheEntry{Body: string(bs)}
		return httpCache[cacheKey].Body, nil
	} else if !os.IsNotExist(err) {
		httpCache[cacheKey] = httpCacheEntry{Err: err}
		return "", err
	}

	fmt.Printf("GET %q...", u)
	req, err := http.NewRequest(http.MethodGet, u, nil)
	if err != nil {
		httpCache[cacheKey] = httpCacheEntry{Err: err}
		return "", err
	}
	for k, v := range hdr {
		req.Header.Add(k, v)
	}
	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		fmt.Printf(" err\n")
		httpCache[cacheKey] = httpCacheEntry{Err: err}
		return "", err
	}
	if resp.StatusCode != http.StatusOK {
		fmt.Printf(" err\n")
		httpCache[cacheKey] = httpCacheEntry{Err: err}
		return "", &httpStatusError{StatusCode: resp.StatusCode, Status: resp.Status}
	}
	bs, err := io.ReadAll(resp.Body)
	if err != nil {
		fmt.Printf(" err\n")
		httpCache[cacheKey] = httpCacheEntry{Err: err}
		httpCache[cacheKey] = httpCacheEntry{Err: err}
		return "", err
	}
	fmt.Printf(" ok\n")
	if err := os.WriteFile(cacheFile, bs, 0666); err != nil {
		return "", err
	}
	httpCache[cacheKey] = httpCacheEntry{Body: string(bs)}
	return httpCache[cacheKey].Body, nil
}

func httpGetJSON(u string, hdr map[string]string, out any) error {
	str, err := httpGet(u, hdr)
	if err != nil {
		return err
	}
	return json.Unmarshal([]byte(str), out)
}

func httpGetPaginatedJSON[T any](uStr string, hdr map[string]string, out *[]T, pageFn func(i int) url.Values) error {
	u, err := url.Parse(uStr)
	if err != nil {
		return err
	}
	query := u.Query()

	for i := 0; true; i++ {
		pageParams := pageFn(i)
		for k, v := range pageParams {
			query[k] = v
		}

		u.RawQuery = query.Encode()
		var resp []T
		if err := httpGetJSON(u.String(), hdr, &resp); err != nil {
			return err
		}
		fmt.Printf(" -> %d records\n", len(resp))
		if len(resp) == 0 {
			break
		}
		*out = append(*out, resp...)
	}

	return nil
}