/*
   GoToSocial
   Copyright (C) 2021-2023 GoToSocial Authors admin@gotosocial.org

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU Affero General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU Affero General Public License for more details.

   You should have received a copy of the GNU Affero General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

package middleware

import (
	"bufio"
	"context"
	"crypto/rand"
	"encoding/base32"
	"encoding/binary"
	"io"
	"sync"
	"time"

	"codeberg.org/gruf/go-kv"
	"github.com/gin-gonic/gin"
	"github.com/superseriousbusiness/gotosocial/internal/log"
)

type ctxType string

var (
	// ridCtxKey is the key underwhich we store request IDs in a context.
	ridCtxKey ctxType = "id"

	// crand provides buffered reads of random input.
	crand = bufio.NewReader(rand.Reader)
	mrand sync.Mutex

	// base32enc is a base 32 encoding based on a human-readable character set (no padding).
	base32enc = base32.NewEncoding("0123456789abcdefghjkmnpqrstvwxyz").WithPadding(-1)
)

// generateID generates a new ID string.
func generateID() string {
	// 0:8  = timestamp
	// 8:12 = entropy
	//
	// inspired by ULID.
	b := make([]byte, 12)

	// Get current time in milliseconds.
	ms := uint64(time.Now().UnixMilli())

	// Store binary time data in byte buffer.
	binary.LittleEndian.PutUint64(b[0:8], ms)

	mrand.Lock()
	// Read random bits into buffer end.
	_, _ = io.ReadFull(crand, b[8:12])
	mrand.Unlock()

	// Encode the binary time+entropy ID.
	return base32enc.EncodeToString(b)
}

// RequestID fetches the stored request ID from context.
func RequestID(ctx context.Context) string {
	id, _ := ctx.Value(ridCtxKey).(string)
	return id
}

// AddRequestID returns a gin middleware which adds a unique ID to each request (both response header and context).
func AddRequestID(header string) gin.HandlerFunc {
	log.Hook(func(ctx context.Context, kvs []kv.Field) []kv.Field {
		if id, _ := ctx.Value(ridCtxKey).(string); id != "" {
			// Add stored request ID to log entry fields.
			return append(kvs, kv.Field{K: "requestID", V: id})
		}
		return kvs
	})

	return func(c *gin.Context) {
		// Look for existing ID.
		id := c.GetHeader(header)

		if id == "" {
			// Generate new ID.
			//
			// 0:8  = timestamp
			// 8:12 = entropy
			id = generateID()
			// Set the request ID in the req header in case we pass the request along
			// to another service
			c.Request.Header.Set(header, id)
		}

		// Store request ID in new request ctx and set new gin request obj.
		ctx := context.WithValue(c.Request.Context(), ridCtxKey, id)
		c.Request = c.Request.WithContext(ctx)

		// Set the request ID in the rsp header.
		c.Writer.Header().Set(header, id)
	}
}