// Package apiutil contains utilities which are useful for implementing api
// endpoints.
package apiutil

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"strconv"
	"strings"

	"dev.mediocregopher.com/mediocre-go-lib.git/mlog"
)

// JSONResult writes the JSON encoding of the given value as the response body.
func JSONResult(
	ctx context.Context, logger *mlog.Logger, rw http.ResponseWriter, v any,
) {
	b, err := json.Marshal(v)
	if err != nil {
		InternalServerError(ctx, logger, rw, "%w", err)
		return
	}
	b = append(b, '\n')

	rw.Header().Set("Content-Type", "application/json")
	rw.Write(b)
}

// BadRequest writes a 400 status and a JSON encoded error struct containing the
// given error (created using `fmt.Errorf(fmtStr, args...)`) as the response
// body.
func BadRequest(
	ctx context.Context,
	logger *mlog.Logger,
	rw http.ResponseWriter,
	fmtStr string,
	args ...any,
) {
	err := fmt.Errorf(fmtStr, args...)
	logger.Warn(ctx, "bad request", err)

	rw.WriteHeader(400)
	JSONResult(ctx, logger, rw, struct {
		Error string `json:"error"`
	}{
		Error: err.Error(),
	})
}

// InternalServerError writes a 500 status and a JSON encoded error struct
// containing a generic error as the response body (though it will log the given
// one).
func InternalServerError(
	ctx context.Context,
	logger *mlog.Logger,
	rw http.ResponseWriter,
	fmtStr string,
	args ...any,
) {
	err := fmt.Errorf(fmtStr, args...)
	logger.Error(ctx, "internal server error", err)

	rw.WriteHeader(500)
	JSONResult(ctx, logger, rw, struct {
		Error string `json:"error"`
	}{
		Error: "internal server error",
	})
}

// StrToInt parses the given string as an integer, or returns the given default
// integer if the string is empty.
func StrToInt(str string, defaultVal int) (int, error) {
	if str == "" {
		return defaultVal, nil
	}
	return strconv.Atoi(str)
}

// GetCookie returns the namd cookie's value, or the given default value if the
// cookie is not set.
//
// This will only return an error if there was an unexpected error parsing the
// Request's cookies.
func GetCookie(r *http.Request, cookieName, defaultVal string) (string, error) {
	c, err := r.Cookie(cookieName)
	if errors.Is(err, http.ErrNoCookie) {
		return defaultVal, nil
	} else if err != nil {
		return "", fmt.Errorf("reading cookie %q: %w", cookieName, err)
	}

	return c.Value, nil
}

// RandStr returns a human-readable random string with the given number of bytes
// of randomness.
func RandStr(numBytes int) string {
	b := make([]byte, numBytes)
	if _, err := rand.Read(b); err != nil {
		panic(err)
	}
	return hex.EncodeToString(b)
}

// MethodMux will take the request method (GET, POST, etc...) and handle the
// request using the corresponding Handler in the given map.
//
// If no Handler is defined for a method then a 405 Method Not Allowed error is
// returned.
//
// If the method "*" is defined then all methods not defined will be directed to
// that handler, and 405 Method Not Allowed is never returned.
//
// If the GET argument 'method' is present then the ToUpper of that is taken to
// be the name of the method.
func MethodMux(handlers map[string]http.Handler) http.Handler {

	return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {

		method := strings.ToUpper(r.Method)
		formMethod := strings.ToUpper(r.FormValue("method"))

		if formMethod != "" {
			method = formMethod
		}

		if handler, ok := handlers[method]; ok {
			handler.ServeHTTP(rw, r)
			return
		}

		if handler, ok := handlers["*"]; ok {
			handler.ServeHTTP(rw, r)
			return
		}

		http.Error(rw, "Method not allowed", http.StatusMethodNotAllowed)
	})
}