package cors_fasthttp

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

	"github.com/valyala/fasthttp"
	"go.uber.org/zap"

	"git.loafle.net/commons_go/logging"
)

// Cors http handler
type Cors interface {
	Handler(h fasthttp.RequestHandler) fasthttp.RequestHandler
}

// Cors http handler
type cors struct {
	ctx    context.Context
	logger *zap.Logger
	co     CorsOptions
	// Set to true when allowed origins contains a "*"
	allowedOriginsAll bool
	// Normalized list of plain allowed origins
	allowedOrigins []string
	// List of allowed origins containing wildcards
	allowedWOrigins []wildcard
	// Set to true when allowed headers contains a "*"
	allowedHeadersAll bool
	// Normalized list of allowed headers
	allowedHeaders []string
	// Normalized list of allowed methods
	allowedMethods []string
	// Normalized list of exposed headers
	exposedHeaders []string
}

// New creates a new Cors handler with the provided options.
func New(ctx context.Context, co CorsOptions) Cors {
	c := &cors{
		ctx:            ctx,
		logger:         logging.WithContext(ctx),
		co:             co,
		exposedHeaders: convert(co.ExposedHeaders, http.CanonicalHeaderKey),
	}

	// Normalize options
	// Note: for origins and methods matching, the spec requires a case-sensitive matching.
	// As it may error prone, we chose to ignore the spec here.

	// Allowed Origins
	// Allowed Origins
	if len(co.AllowedOrigins) == 0 {
		if co.AllowOriginFunc == nil {
			// Default is all origins
			c.allowedOriginsAll = true
		}
	} else {
		c.allowedOrigins = []string{}
		c.allowedWOrigins = []wildcard{}
		for _, origin := range co.AllowedOrigins {
			// Normalize
			origin = strings.ToLower(origin)
			if origin == "*" {
				// If "*" is present in the list, turn the whole list into a match all
				c.allowedOriginsAll = true
				c.allowedOrigins = nil
				c.allowedWOrigins = nil
				break
			} else if i := strings.IndexByte(origin, '*'); i >= 0 {
				// Split the origin in two: start and end string without the *
				w := wildcard{origin[0:i], origin[i+1 : len(origin)]}
				c.allowedWOrigins = append(c.allowedWOrigins, w)
			} else {
				c.allowedOrigins = append(c.allowedOrigins, origin)
			}
		}
	}

	// Allowed Headers
	if len(co.AllowedHeaders) == 0 {
		// Use sensible defaults
		c.allowedHeaders = []string{"Origin", "Accept", "Content-Type"}
	} else {
		// Origin is always appended as some browsers will always request for this header at preflight
		c.allowedHeaders = convert(append(co.AllowedHeaders, "Origin"), http.CanonicalHeaderKey)
		for _, h := range co.AllowedHeaders {
			if h == "*" {
				c.allowedHeadersAll = true
				c.allowedHeaders = nil
				break
			}
		}
	}

	// Allowed Methods
	if len(co.AllowedMethods) == 0 {
		// Default is spec's "simple" methods
		c.allowedMethods = []string{"GET", "POST", "HEAD"}
	} else {
		c.allowedMethods = convert(co.AllowedMethods, strings.ToUpper)
	}

	return c
}

// Default creates a new Cors handler with default options.
func Default(ctx context.Context) Cors {
	return New(ctx, CorsOptions{})
}

// AllowAll create a new Cors handler with permissive configuration allowing all
// origins with all standard methods with any header and credentials.
func AllowAll(ctx context.Context) Cors {
	return New(ctx, CorsOptions{
		AllowedOrigins:   []string{"*"},
		AllowedMethods:   []string{"HEAD", "GET", "POST", "PUT", "PATCH", "DELETE"},
		AllowedHeaders:   []string{"*"},
		AllowCredentials: true,
	})
}

// Handler apply the CORS specification on the request, and add relevant CORS headers
// as necessary.
func (c *cors) Handler(h fasthttp.RequestHandler) fasthttp.RequestHandler {
	return fasthttp.RequestHandler(func(ctx *fasthttp.RequestCtx) {
		if string(ctx.Method()) == "OPTIONS" && ctx.Request.Header.Peek("Access-Control-Request-Method") != nil {
			c.logger.Info("Handler: Preflight request")
			c.handlePreflight(ctx)
			// Preflight requests are standalone and should stop the chain as some other
			// middleware may not handle OPTIONS requests correctly. One typical example
			// is authentication middleware ; OPTIONS requests won't carry authentication
			// headers (see #1)
			if c.co.OptionsPassthrough {
				h(ctx)
			} else {
				ctx.SetStatusCode(fasthttp.StatusOK)
			}
		} else {
			c.logger.Info("Handler: Actual request")
			c.handleActualRequest(ctx)
			h(ctx)
		}
	})
}

// handlePreflight handles pre-flight CORS requests
func (c *cors) handlePreflight(ctx *fasthttp.RequestCtx) {
	origin := string(ctx.Request.Header.Peek("Origin"))

	if string(ctx.Method()) != "OPTIONS" {
		c.logger.Info(fmt.Sprintf("  Preflight aborted: %s!=OPTIONS", string(ctx.Method())))
		return
	}
	// Always set Vary headers
	// see https://github.com/rs/cors/issues/10,
	//     https://github.com/rs/cors/commit/dbdca4d95feaa7511a46e6f1efb3b3aa505bc43f#commitcomment-12352001
	ctx.Response.Header.Add("Vary", "Origin")
	ctx.Response.Header.Add("Vary", "Access-Control-Request-Method")
	ctx.Response.Header.Add("Vary", "Access-Control-Request-Headers")

	if origin == "" {
		c.logger.Info("  Preflight aborted: empty origin")
		return
	}
	if !c.isOriginAllowed(origin) {
		c.logger.Info(fmt.Sprintf("  Preflight aborted: origin '%s' not allowed", origin))
		return
	}

	reqMethod := string(ctx.Request.Header.Peek("Access-Control-Request-Method"))
	if !c.isMethodAllowed(reqMethod) {
		c.logger.Info(fmt.Sprintf("  Preflight aborted: method '%s' not allowed", reqMethod))
		return
	}
	reqHeaders := parseHeaderList(string(ctx.Request.Header.Peek("Access-Control-Request-Headers")))
	if !c.areHeadersAllowed(reqHeaders) {
		c.logger.Info(fmt.Sprintf("  Preflight aborted: headers '%v' not allowed", reqHeaders))
		return
	}
	if c.allowedOriginsAll && !c.co.AllowCredentials {
		ctx.Response.Header.Set("Access-Control-Allow-Origin", "*")
	} else {
		ctx.Response.Header.Set("Access-Control-Allow-Origin", origin)
	}
	// Spec says: Since the list of methods can be unbounded, simply returning the method indicated
	// by Access-Control-Request-Method (if supported) can be enough
	ctx.Response.Header.Set("Access-Control-Allow-Methods", strings.ToUpper(reqMethod))
	if len(reqHeaders) > 0 {
		// Spec says: Since the list of headers can be unbounded, simply returning supported headers
		// from Access-Control-Request-Headers can be enough
		ctx.Response.Header.Set("Access-Control-Allow-Headers", strings.Join(reqHeaders, ", "))
	}
	if c.co.AllowCredentials {
		ctx.Response.Header.Set("Access-Control-Allow-Credentials", "true")
	}
	if c.co.MaxAge > 0 {
		ctx.Response.Header.Set("Access-Control-Max-Age", strconv.Itoa(c.co.MaxAge))
	}
	// c.logger.Info(fmt.Sprintf("  Preflight response headers: %v", ctx.Response.Header.))
}

// handleActualRequest handles simple cross-origin requests, actual request or redirects
func (c *cors) handleActualRequest(ctx *fasthttp.RequestCtx) {
	origin := string(ctx.Request.Header.Peek("Origin"))
	method := string(ctx.Method())

	if method == "OPTIONS" {
		c.logger.Info(fmt.Sprintf("  Actual request no headers added: method == %s", method))
		return
	}
	// Always set Vary, see https://github.com/rs/cors/issues/10
	ctx.Response.Header.Add("Vary", "Origin")
	if origin == "" {
		c.logger.Info("  Actual request no headers added: missing origin")
		return
	}
	if !c.isOriginAllowed(origin) {
		c.logger.Info(fmt.Sprintf("  Actual request no headers added: origin '%s' not allowed", origin))
		return
	}

	// Note that spec does define a way to specifically disallow a simple method like GET or
	// POST. Access-Control-Allow-Methods is only used for pre-flight requests and the
	// spec doesn't instruct to check the allowed methods for simple cross-origin requests.
	// We think it's a nice feature to be able to have control on those methods though.
	if !c.isMethodAllowed(method) {
		c.logger.Info(fmt.Sprintf("  Actual request no headers added: method '%s' not allowed", method))

		return
	}
	if c.allowedOriginsAll && !c.co.AllowCredentials {
		ctx.Response.Header.Set("Access-Control-Allow-Origin", "*")
	} else {
		ctx.Response.Header.Set("Access-Control-Allow-Origin", origin)
	}
	if len(c.exposedHeaders) > 0 {
		ctx.Response.Header.Set("Access-Control-Expose-Headers", strings.Join(c.exposedHeaders, ", "))
	}
	if c.co.AllowCredentials {
		ctx.Response.Header.Set("Access-Control-Allow-Credentials", "true")
	}
	// c.logf("  Actual response added headers: %v", headers)
}

// isOriginAllowed checks if a given origin is allowed to perform cross-domain requests
// on the endpoint
func (c *cors) isOriginAllowed(origin string) bool {
	if c.co.AllowOriginFunc != nil {
		return c.co.AllowOriginFunc(origin)
	}
	if c.allowedOriginsAll {
		return true
	}
	origin = strings.ToLower(origin)
	for _, o := range c.allowedOrigins {
		if o == origin {
			return true
		}
	}
	for _, w := range c.allowedWOrigins {
		if w.match(origin) {
			return true
		}
	}
	return false
}

// isMethodAllowed checks if a given method can be used as part of a cross-domain request
// on the endpoing
func (c *cors) isMethodAllowed(method string) bool {
	if len(c.allowedMethods) == 0 {
		// If no method allowed, always return false, even for preflight request
		return false
	}
	method = strings.ToUpper(method)
	if method == "OPTIONS" {
		// Always allow preflight requests
		return true
	}
	for _, m := range c.allowedMethods {
		if m == method {
			return true
		}
	}
	return false
}

// areHeadersAllowed checks if a given list of headers are allowed to used within
// a cross-domain request.
func (c *cors) areHeadersAllowed(requestedHeaders []string) bool {
	if c.allowedHeadersAll || len(requestedHeaders) == 0 {
		return true
	}
	for _, header := range requestedHeaders {
		header = http.CanonicalHeaderKey(header)
		found := false
		for _, h := range c.allowedHeaders {
			if h == header {
				found = true
			}
		}
		if !found {
			return false
		}
	}
	return true
}