package api

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"mime/multipart"
	"net/http"
	"os"
	"strconv"
	"strings"

	"github.com/kb-search/kb/internal/config"
)

// FileUpload describes a file to include in a multipart request.
type FileUpload struct {
	FieldName string
	FileName  string
	Reader    io.Reader
}

// Package-level version info, set once by cmd.init via SetVersionInfo.
var (
	clientVersion    string
	minEngineVersion string
)

// SetVersionInfo configures the client and minimum engine version for compatibility checking.
// Called once from cmd package initialization.
func SetVersionInfo(cv, minEV string) {
	clientVersion = cv
	minEngineVersion = minEV
}

// Client is an HTTP client for the kb-search engine API.
type Client struct {
	baseURL        string
	apiKey         string
	httpClient     *http.Client
	versionChecked bool
}

// NewClient creates a Client from the current configuration.
func NewClient() *Client {
	cfg := config.Get()
	return &Client{
		baseURL:    cfg.EngineURL,
		apiKey:     cfg.APIKey,
		httpClient: &http.Client{},
	}
}

func (c *Client) newRequest(method, path string, body io.Reader) (*http.Request, error) {
	url := c.baseURL + path
	req, err := http.NewRequest(method, url, body)
	if err != nil {
		return nil, err
	}
	if c.apiKey != "" {
		req.Header.Set("Authorization", "Bearer "+c.apiKey)
	}
	return req, nil
}

func (c *Client) do(req *http.Request) (*http.Response, error) {
	c.checkEngineVersion()
	resp, err := c.httpClient.Do(req)
	if err != nil {
		return nil, fmt.Errorf("Cannot reach engine at %s: %v", c.baseURL, err)
	}
	return resp, nil
}

func (c *Client) checkEngineVersion() {
	if c.versionChecked {
		return
	}
	c.versionChecked = true

	minVer := minEngineVersion
	if minVer == "" || minVer == "dev" {
		return
	}

	statusReq, err := c.newRequest(http.MethodGet, "/api/v1/status", nil)
	if err != nil {
		return
	}
	resp, err := c.httpClient.Do(statusReq)
	if err != nil {
		return // unreachable — let the actual request surface the error
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return // auth error or other issue — let the actual request surface it
	}

	var status struct {
		Version string `json:"version"`
	}
	if err := json.NewDecoder(resp.Body).Decode(&status); err != nil {
		return
	}

	if !semverAtLeast(status.Version, minVer) {
		fmt.Fprintf(os.Stderr, "Error: kb client v%s requires engine v%s+ (connected engine is v%s)\nUpdate your engine image to engine-v%s or later.\n",
			clientVersion, minVer, status.Version, minVer)
		os.Exit(1)
	}
}

// semverAtLeast returns true if version >= minimum, comparing major.minor.patch.
func semverAtLeast(version, minimum string) bool {
	parse := func(s string) (int, int, int) {
		s = strings.TrimPrefix(s, "v")
		parts := strings.SplitN(s, ".", 3)
		var major, minor, patch int
		if len(parts) >= 1 {
			major, _ = strconv.Atoi(parts[0])
		}
		if len(parts) >= 2 {
			minor, _ = strconv.Atoi(parts[1])
		}
		if len(parts) >= 3 {
			patch, _ = strconv.Atoi(parts[2])
		}
		return major, minor, patch
	}

	vMaj, vMin, vPat := parse(version)
	mMaj, mMin, mPat := parse(minimum)

	if vMaj != mMaj {
		return vMaj > mMaj
	}
	if vMin != mMin {
		return vMin > mMin
	}
	return vPat >= mPat
}

// Get performs a GET request to the given path.
func (c *Client) Get(path string) (*http.Response, error) {
	req, err := c.newRequest(http.MethodGet, path, nil)
	if err != nil {
		return nil, err
	}
	return c.do(req)
}

// Post performs a POST request with a JSON body.
func (c *Client) Post(path string, body interface{}) (*http.Response, error) {
	data, err := json.Marshal(body)
	if err != nil {
		return nil, fmt.Errorf("failed to marshal request body: %w", err)
	}
	req, err := c.newRequest(http.MethodPost, path, bytes.NewReader(data))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Content-Type", "application/json")
	return c.do(req)
}

// PostMultipart performs a POST request with multipart/form-data encoding.
func (c *Client) PostMultipart(path string, fields map[string]string, file *FileUpload) (*http.Response, error) {
	var buf bytes.Buffer
	w := multipart.NewWriter(&buf)

	for k, v := range fields {
		if err := w.WriteField(k, v); err != nil {
			return nil, fmt.Errorf("failed to write field %s: %w", k, err)
		}
	}

	if file != nil {
		part, err := w.CreateFormFile(file.FieldName, file.FileName)
		if err != nil {
			return nil, fmt.Errorf("failed to create form file: %w", err)
		}
		if _, err := io.Copy(part, file.Reader); err != nil {
			return nil, fmt.Errorf("failed to copy file data: %w", err)
		}
	}

	if err := w.Close(); err != nil {
		return nil, fmt.Errorf("failed to close multipart writer: %w", err)
	}

	req, err := c.newRequest(http.MethodPost, path, &buf)
	if err != nil {
		return nil, err
	}
	req.Header.Set("Content-Type", w.FormDataContentType())
	return c.do(req)
}

// Delete performs a DELETE request to the given path.
func (c *Client) Delete(path string) (*http.Response, error) {
	req, err := c.newRequest(http.MethodDelete, path, nil)
	if err != nil {
		return nil, err
	}
	return c.do(req)
}

// Put performs a PUT request with a JSON body.
func (c *Client) Put(path string, body interface{}) (*http.Response, error) {
	data, err := json.Marshal(body)
	if err != nil {
		return nil, fmt.Errorf("failed to marshal request body: %w", err)
	}
	req, err := c.newRequest(http.MethodPut, path, bytes.NewReader(data))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Content-Type", "application/json")
	return c.do(req)
}

// Patch performs a PATCH request with a JSON body.
func (c *Client) Patch(path string, body interface{}) (*http.Response, error) {
	data, err := json.Marshal(body)
	if err != nil {
		return nil, fmt.Errorf("failed to marshal request body: %w", err)
	}
	req, err := c.newRequest(http.MethodPatch, path, bytes.NewReader(data))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Content-Type", "application/json")
	return c.do(req)
}

// DecodeJSON reads the response body and decodes it into target.
func DecodeJSON(resp *http.Response, target interface{}) error {
	defer resp.Body.Close()
	return json.NewDecoder(resp.Body).Decode(target)
}

// CheckError returns a formatted error for non-2xx responses, or nil on success.
func CheckError(resp *http.Response) error {
	if resp.StatusCode >= 200 && resp.StatusCode < 300 {
		return nil
	}
	defer resp.Body.Close()
	body, _ := io.ReadAll(resp.Body)

	var errResp struct {
		Detail string `json:"detail"`
	}
	if json.Unmarshal(body, &errResp) == nil && errResp.Detail != "" {
		return fmt.Errorf("API error (%d): %s", resp.StatusCode, errResp.Detail)
	}
	return fmt.Errorf("API error (%d): %s", resp.StatusCode, string(body))
}