package k2v

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

	"github.com/aws/aws-sdk-go-v2/aws"
	v4 "github.com/aws/aws-sdk-go-v2/aws/signer/v4"
)

const CausalityTokenHeader = "X-Garage-Causality-Token"

var TombstoneItemErr = errors.New("item is a tombstone")
var NoSuchItemErr = errors.New("item does not exist")
var ConcurrentItemsErr = errors.New("item has multiple concurrent values")

var awsSigner = v4.NewSigner()

type Bucket string

type CausalityToken string

type Item []byte

func (i Item) GoString() string {
	return string(i)
}

type Key struct {
	ID     string
	Secret string
}

type Client struct {
	key        Key
	endpoint   string
	httpClient *http.Client
	middleware []RequestMiddleware
}

type ClientOption func(*Client)

type RequestMiddleware func(*http.Request) error

func WithHTTPClient(httpClient *http.Client) ClientOption {
	return func(c *Client) {
		c.httpClient = httpClient
	}
}

func WithRequestMiddleware(middleware ...RequestMiddleware) ClientOption {
	return func(c *Client) {
		c.middleware = append(c.middleware, middleware...)
	}
}

func NewClient(endpoint string, key Key, opts ...ClientOption) *Client {
	cli := &Client{
		endpoint:   endpoint,
		key:        key,
		httpClient: http.DefaultClient,
	}

	for _, opt := range opts {
		opt(cli)
	}

	return cli
}

func (c *Client) Clone(opts ...ClientOption) *Client {
	cli := *c
	for _, opt := range opts {
		opt(&cli)
	}
	return &cli
}

func (c *Client) Close() {
	c.httpClient.CloseIdleConnections()
}

func (c *Client) executeRequest(req *http.Request) (*http.Response, error) {
	if err := c.signRequest(req); err != nil {
		return nil, err
	}

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return nil, err
	}
	// caller is responsible for closing body
	return resp, nil
}

func (c *Client) signRequest(req *http.Request) error {
	creds := aws.Credentials{
		AccessKeyID:     c.key.ID,
		SecretAccessKey: c.key.Secret,
	}
	const noBody = "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
	req.Header.Set("X-Amz-Content-Sha256", noBody)

	err := awsSigner.SignHTTP(req.Context(), creds, req, noBody, "k2v", "garage", time.Now())
	if err != nil {
		return err
	}
	return nil
}

type ReadIndexQuery struct {
	// Prefix restricts listing to partition keys that start with this value.
	Prefix string

	// Start is the first partition key to list, in lexicographical order.
	Start string

	// End is the last partition key to list (excluded).
	End string

	// Limit for maximum number of partition keys to list.
	Limit int

	// Reverse iterates in reverse lexicographical order.
	Reverse bool
}

type ReadIndexResponsePartitionKey struct {
	PK        string `json:"pk"`
	Entries   int    `json:"entries"`
	Conflicts int    `json:"conflicts"`
	Values    int    `json:"values"`
	Bytes     int    `json:"bytes"`
}

type ReadIndexResponse struct {
	Prefix        *string                         `json:"prefix"`
	Start         *string                         `json:"start"`
	End           *string                         `json:"end"`
	Limit         *int                            `json:"limit"`
	Reverse       bool                            `json:"reverse"`
	PartitionKeys []ReadIndexResponsePartitionKey `json:"partitionKeys"`
	More          bool                            `json:"more"`
	NextStart     *string                         `json:"nextStart"`
}

func (c *Client) ReadIndex(ctx context.Context, b Bucket, q ReadIndexQuery) (*ReadIndexResponse, error) {
	u, err := url.Parse(c.endpoint)
	if err != nil {
		return nil, err
	}
	u.Path = string(b)

	query := make(url.Values)
	if q.Prefix != "" {
		query.Set("prefix", q.Prefix)
	}
	if q.Start != "" {
		query.Set("start", q.Start)
	}
	if q.End != "" {
		query.Set("end", q.End)
	}
	if q.Limit > 0 {
		query.Set("limit", strconv.Itoa(q.Limit))
	}
	if q.Reverse {
		query.Set("reverse", "true")
	}
	u.RawQuery = query.Encode()

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
	if err != nil {
		return nil, err
	}

	resp, err := c.executeRequest(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, err
	}

	var ret ReadIndexResponse
	if err := json.Unmarshal(body, &ret); err != nil {
		return nil, err
	}
	return &ret, nil
}

func (c *Client) ReadItemMulti(ctx context.Context, b Bucket, pk string, sk string) ([]Item, CausalityToken, error) {
	u, err := url.Parse(c.endpoint)
	if err != nil {
		return nil, "", err
	}
	u.Path = string(b) + "/" + pk
	query := make(url.Values)
	query.Set("sort_key", sk)
	u.RawQuery = query.Encode()

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
	if err != nil {
		return nil, "", err
	}
	req.Header.Set("Accept", strings.Join([]string{"application/octet-stream", "application/json"}, ","))

	resp, err := c.executeRequest(req)
	if err != nil {
		return nil, "", err
	}
	defer resp.Body.Close()

	ct := CausalityToken(resp.Header.Get("X-Garage-Causality-Token"))

	switch resp.StatusCode {
	case http.StatusOK:
		break
	case http.StatusNoContent:
		return nil, ct, TombstoneItemErr
	case http.StatusNotFound:
		return nil, "", NoSuchItemErr
	default:
		return nil, "", fmt.Errorf("http status code %d", resp.StatusCode)
	}

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, "", err
	}

	switch resp.Header.Get("Content-Type") {
	case "application/octet-stream":
		// single item, return as-is
		return []Item{body}, ct, nil
	case "application/json":
		var items []Item
		if err != nil {
			return nil, "", err
		}
		if err := json.Unmarshal(body, &items); err != nil {
			return nil, "", err
		}
		return items, ct, nil
	default:
		return nil, "", fmt.Errorf("unsupported content-type: %s", resp.Header.Get("Content-Type"))
	}
}

func (c *Client) ReadItemSingle(ctx context.Context, b Bucket, pk string, sk string) (Item, CausalityToken, error) {
	return c.readItemSingle(ctx, b, pk, sk, "", 0)
}

func (c *Client) readItemSingle(ctx context.Context, b Bucket, pk string, sk string, ct CausalityToken, timeout time.Duration) (Item, CausalityToken, error) {
	u, err := url.Parse(c.endpoint)
	if err != nil {
		return nil, "", err
	}
	u.Path = string(b) + "/" + pk
	query := make(url.Values)
	query.Set("sort_key", sk)
	if ct != "" && timeout > 0 {
		query.Set("causality_token", string(ct))
		query.Set("timeout", strconv.Itoa(int(timeout.Seconds())))
	}
	u.RawQuery = query.Encode()

	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
	if err != nil {
		return nil, "", err
	}
	req.Header.Set("Accept", "application/octet-stream")

	resp, err := c.executeRequest(req)
	if err != nil {
		return nil, "", err
	}
	defer resp.Body.Close()

	ct = CausalityToken(resp.Header.Get("X-Garage-Causality-Token"))

	switch resp.StatusCode {
	case http.StatusOK:
		break
	case http.StatusNoContent:
		return nil, ct, TombstoneItemErr
	case http.StatusNotFound:
		return nil, "", NoSuchItemErr
	case http.StatusConflict:
		return nil, ct, ConcurrentItemsErr
	default:
		return nil, "", fmt.Errorf("http status code %d", resp.StatusCode)
	}

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, "", err
	}
	return body, ct, nil
}

func (c *Client) DeleteItem(ctx context.Context, b Bucket, pk string, sk string, ct CausalityToken) error {
	if ct == "" {
		return errors.New("continuity token is required for delete")
	}

	u, err := url.Parse(c.endpoint)
	if err != nil {
		return err
	}
	u.Path = string(b) + "/" + pk
	query := make(url.Values)
	query.Set("sort_key", sk)
	u.RawQuery = query.Encode()

	req, err := http.NewRequestWithContext(ctx, http.MethodDelete, u.String(), nil)
	if err != nil {
		return err
	}
	req.Header.Set(CausalityTokenHeader, string(ct))

	resp, err := c.executeRequest(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusNoContent {
		body, err := io.ReadAll(resp.Body)
		if err != nil {
			return err
		}
		return fmt.Errorf("http status code %d: %s", resp.StatusCode, string(body))
	}

	return nil
}

func (c *Client) InsertItem(ctx context.Context, b Bucket, pk string, sk string, ct CausalityToken, item []byte) error {
	u, err := url.Parse(c.endpoint)
	if err != nil {
		return err
	}
	u.Path = string(b) + "/" + pk
	query := make(url.Values)
	query.Set("sort_key", sk)
	u.RawQuery = query.Encode()

	req, err := http.NewRequestWithContext(ctx, http.MethodPut, u.String(), bytes.NewReader(item))
	if err != nil {
		return err
	}
	if ct != "" {
		req.Header.Set("X-Garage-Causality-Token", string(ct))
	}

	resp, err := c.executeRequest(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusNoContent {
		body, err := io.ReadAll(resp.Body)
		if err != nil {
			return err
		}
		return fmt.Errorf("http status code %d: %s", resp.StatusCode, string(body))
	}

	return nil
}