package cache

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

	"golang.org/x/sync/errgroup"
)

var UploadConcurrency = 4
var UploadChunkSize = 32 * 1024 * 1024

type Client struct {
	base string
	http *http.Client
}

type auth struct {
	transport http.RoundTripper
	token     string
}

func (t *auth) RoundTrip(req *http.Request) (*http.Response, error) {
	req.Header.Add("Authorization", fmt.Sprintf("Bearer %s", t.token))
	return t.transport.RoundTrip(req)
}

func New(token, url string) *Client {
	t := &auth{transport: &retry{transport: &http.Transport{}}, token: token}
	return &Client{
		base: url,
		http: &http.Client{Transport: t},
	}
}

func (c *Client) url(p string) string {
	return path.Join(c.base, "_apis/artifactcache", p)
}

func (c *Client) version(k string) string {
	h := sha256.New()
	h.Write([]byte("|go-actionscache-1.0"))
	return hex.EncodeToString(h.Sum(nil))
}

type ApiError struct {
	Message   string `json:"message"`
	TypeName  string `json:"typeName"`
	TypeKey   string `json:"typeKey"`
	ErrorCode int    `json:"errorCode"`
}

func (e ApiError) Error() string {
	return e.Message
}

func (e ApiError) Is(err error) bool {
	if err == os.ErrExist {
		if strings.Contains(e.TypeKey, "AlreadyExists") {
			return true
		}
	}
	return false
}

func checkApiError(res *http.Response) error {
	if res.StatusCode >= 200 && res.StatusCode < 300 {
		return nil
	}
	dec := json.NewDecoder(io.LimitReader(res.Body, 32*1024))

	var details ApiError
	if err := dec.Decode(&details); err != nil {
		return err
	}

	if details.Message != "" {
		return details
	} else {
		return fmt.Errorf("unknown error %s", res.Status)
	}
}

func (c *Client) Load(ctx context.Context, keys ...string) (*Entry, error) {
	u, err := url.Parse(c.url("cache"))
	if err != nil {
		return nil, err
	}
	q := u.Query()
	q.Set("keys", strings.Join(keys, ","))
	q.Set("version", c.version(keys[0]))
	u.RawQuery = q.Encode()

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
	if err != nil {
		return nil, err
	}
	req.Header.Add("Accept", "application/json;api-version=6.0-preview.1")

	res, err := c.http.Do(req)
	if err != nil {
		return nil, err
	}
	defer res.Body.Close()

	err = checkApiError(res)
	if err != nil {
		return nil, err
	}

	dec := json.NewDecoder(io.LimitReader(res.Body, 32*1024))

	var ce Entry
	if err = dec.Decode(&ce); err != nil {
		return nil, err
	}

	ce.http = c.http
	return &ce, nil
}

func (c *Client) Save(ctx context.Context, key string, b Blob) error {
	id, err := c.reserve(ctx, key)
	if err != nil {
		return err
	}
	err = c.upload(ctx, id, b)
	if err != nil {
		return err
	}
	return c.commit(ctx, id, b.Size())
}

type ReserveCacheReq struct {
	Key     string `json:"key"`
	Version string `json:"version"`
}

type ReserveCacheRes struct {
	CacheID int `json:"cacheID"`
}

func (c *Client) reserve(ctx context.Context, key string) (int, error) {
	payload := ReserveCacheReq{Key: key, Version: c.version(key)}

	buf := new(bytes.Buffer)
	if err := json.NewEncoder(buf).Encode(payload); err != nil {
		return 0, err
	}

	url := c.url("caches")
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, buf)
	if err != nil {
		return 0, err
	}
	req.Header.Add("Content-Type", "application/json")

	res, err := c.http.Do(req)
	if err != nil {
		return 0, err
	}
	defer res.Body.Close()

	err = checkApiError(res)
	if err != nil {
		return 0, err
	}

	dec := json.NewDecoder(io.LimitReader(res.Body, 32*1024))

	var cr ReserveCacheRes
	if err = dec.Decode(&cr); err != nil {
		return 0, err
	}

	if cr.CacheID == 0 {
		return 0, fmt.Errorf("invalid response (cache id is 0)")
	}
	return cr.CacheID, nil
}

type CommitCacheReq struct {
	Size int64 `json:"size"`
}

func (c *Client) commit(ctx context.Context, id int, size int64) error {
	payload := CommitCacheReq{Size: size}

	buf := new(bytes.Buffer)
	if err := json.NewEncoder(buf).Encode(payload); err != nil {
		return err
	}

	url := c.url(fmt.Sprintf("caches/%d", id))
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, buf)
	if err != nil {
		return err
	}
	req.Header.Add("Content-Type", "application/json")

	res, err := c.http.Do(req)
	if err != nil {
		return err
	}
	defer res.Body.Close()

	err = checkApiError(res)
	if err != nil {
		return err
	}

	return nil
}

func (c *Client) upload(ctx context.Context, id int, b Blob) error {
	var mu sync.Mutex
	grp, ctx := errgroup.WithContext(ctx)
	offset := int64(0)
	for i := 0; i < UploadConcurrency; i++ {
		grp.Go(func() error {
			for {
				mu.Lock()
				start := offset
				if start >= b.Size() {
					mu.Unlock()
					return nil
				}
				end := start + int64(UploadChunkSize)
				if end > b.Size() {
					end = b.Size()
				}
				offset = end
				mu.Unlock()

				if err := c.create(ctx, id, b, start, end-start); err != nil {
					return err
				}
			}
		})
	}
	return grp.Wait()
}

func (c *Client) create(ctx context.Context, id int, ra io.ReaderAt, off, n int64) error {
	url := c.url(fmt.Sprintf("caches/%d", id))
	req, err := http.NewRequestWithContext(ctx, http.MethodPatch, url, io.NewSectionReader(ra, off, n))
	if err != nil {
		return err
	}
	req.Header.Add("Content-Type", "application/octet-stream")
	req.Header.Add("Content-Range", fmt.Sprintf("bytes %d-%d/*", off, off+n-1))

	res, err := c.http.Do(req)
	if err != nil {
		return err
	}
	defer res.Body.Close()

	err = checkApiError(res)
	if err != nil {
		return err
	}

	return nil
}

type Entry struct {
	Key   string `json:"cacheKey"`
	Scope string `json:"scope"`
	URL   string `json:"archiveLocation"`

	http *http.Client
}

// Download returns a ReaderAtCloser for pulling the data. Concurrent reads are not allowed
func (ce *Entry) Download(ctx context.Context) ReaderAtCloser {
	return NewReaderAtCloser(func(offset int64) (io.ReadCloser, error) {
		req, err := http.NewRequestWithContext(ctx, "GET", ce.URL, nil)
		if err != nil {
			return nil, err
		}
		if offset != 0 {
			req.Header.Set("Range", fmt.Sprintf("bytes=%d-", offset))
		}
		client := ce.http
		if client == nil {
			client = http.DefaultClient
		}

		res, err := client.Do(req)
		if err != nil {
			return nil, err
		}

		if res.StatusCode < 200 || res.StatusCode >= 300 {
			if res.StatusCode == http.StatusRequestedRangeNotSatisfiable {
				return nil, fmt.Errorf("invalid status response %v for %s, range: %v", res.Status, ce.URL, req.Header.Get("Range"))
			}
			return nil, fmt.Errorf("invalid status response %v for %s", res.Status, ce.URL)
		}
		if offset != 0 {
			cr := res.Header.Get("content-range")
			if !strings.HasPrefix(cr, fmt.Sprintf("bytes %d-", offset)) {
				res.Body.Close()
				return nil, fmt.Errorf("unhandled content range in response: %v", cr)
			}
		}
		return res.Body, nil
	})
}

func (ce *Entry) WriteTo(ctx context.Context, w io.Writer) error {
	rac := ce.Download(ctx)
	if _, err := io.Copy(w, &rc{ReaderAt: rac}); err != nil {
		return err
	}
	return rac.Close()
}