package httpx

import (
	"context"
	"fmt"
	"io"
	"net/http"
	"strings"

	"git.codelab.vc/pkg/httpx/balancer"
	"git.codelab.vc/pkg/httpx/circuitbreaker"
	"git.codelab.vc/pkg/httpx/middleware"
	"git.codelab.vc/pkg/httpx/retry"
)

// Client is a high-level HTTP client that composes middleware for retry,
// circuit breaking, load balancing, logging, and more.
type Client struct {
	httpClient      *http.Client
	baseURL         string
	errorMapper     ErrorMapper
	balancerCloser  *balancer.Closer
}

// New creates a new Client with the given options.
//
// The middleware chain is assembled as (outermost → innermost):
//
//	Logging → User Middlewares → Retry → Circuit Breaker → Balancer → Base Transport
func New(opts ...Option) *Client {
	o := &clientOptions{
		transport: http.DefaultTransport,
	}
	for _, opt := range opts {
		opt(o)
	}

	// Build the middleware chain from inside out.
	var chain []middleware.Middleware

	// Balancer (innermost, wraps base transport).
	var balancerCloser *balancer.Closer
	if len(o.endpoints) > 0 {
		var mw middleware.Middleware
		mw, balancerCloser = balancer.Transport(o.endpoints, o.balancerOpts...)
		chain = append(chain, mw)
	}

	// Circuit breaker wraps balancer.
	if o.enableCB {
		chain = append(chain, circuitbreaker.Transport(o.cbOpts...))
	}

	// Retry wraps circuit breaker + balancer.
	if o.enableRetry {
		chain = append(chain, retry.Transport(o.retryOpts...))
	}

	// User middlewares.
	for i := len(o.middlewares) - 1; i >= 0; i-- {
		chain = append(chain, o.middlewares[i])
	}

	// Logging (outermost).
	if o.logger != nil {
		chain = append(chain, middleware.Logging(o.logger))
	}

	// Assemble: chain[last] is outermost.
	rt := o.transport
	for _, mw := range chain {
		rt = mw(rt)
	}

	return &Client{
		httpClient: &http.Client{
			Transport: rt,
			Timeout:   o.timeout,
		},
		baseURL:        o.baseURL,
		errorMapper:    o.errorMapper,
		balancerCloser: balancerCloser,
	}
}

// Do executes an HTTP request.
func (c *Client) Do(ctx context.Context, req *http.Request) (*Response, error) {
	req = req.WithContext(ctx)
	if err := c.resolveURL(req); err != nil {
		return nil, err
	}

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return nil, &Error{
			Op:  req.Method,
			URL: req.URL.String(),
			Err: err,
		}
	}

	r := newResponse(resp)

	if c.errorMapper != nil {
		if mapErr := c.errorMapper(resp); mapErr != nil {
			return r, &Error{
				Op:         req.Method,
				URL:        req.URL.String(),
				StatusCode: resp.StatusCode,
				Err:        mapErr,
			}
		}
	}

	return r, nil
}

// Get performs a GET request to the given URL.
func (c *Client) Get(ctx context.Context, url string) (*Response, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return nil, err
	}
	return c.Do(ctx, req)
}

// Post performs a POST request to the given URL with the given body.
func (c *Client) Post(ctx context.Context, url string, body io.Reader) (*Response, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, body)
	if err != nil {
		return nil, err
	}
	return c.Do(ctx, req)
}

// Put performs a PUT request to the given URL with the given body.
func (c *Client) Put(ctx context.Context, url string, body io.Reader) (*Response, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodPut, url, body)
	if err != nil {
		return nil, err
	}
	return c.Do(ctx, req)
}

// Delete performs a DELETE request to the given URL.
func (c *Client) Delete(ctx context.Context, url string) (*Response, error) {
	req, err := http.NewRequestWithContext(ctx, http.MethodDelete, url, nil)
	if err != nil {
		return nil, err
	}
	return c.Do(ctx, req)
}

// Close releases resources associated with the Client, such as background
// health checker goroutines. It is safe to call multiple times.
func (c *Client) Close() {
	if c.balancerCloser != nil {
		c.balancerCloser.Close()
	}
}

// HTTPClient returns the underlying *http.Client for advanced use cases.
// Mutating the returned client may bypass the configured middleware chain.
func (c *Client) HTTPClient() *http.Client {
	return c.httpClient
}

func (c *Client) resolveURL(req *http.Request) error {
	if c.baseURL == "" {
		return nil
	}
	// Only resolve relative URLs (no scheme).
	if req.URL.Scheme == "" && req.URL.Host == "" {
		path := req.URL.String()
		if !strings.HasPrefix(path, "/") {
			path = "/" + path
		}
		base := strings.TrimRight(c.baseURL, "/")
		u, err := req.URL.Parse(base + path)
		if err != nil {
			return fmt.Errorf("httpx: resolving URL %q with base %q: %w", path, c.baseURL, err)
		}
		req.URL = u
	}
	return nil
}