package main

import (
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"strings"
	"time"

	"github.com/gin-gonic/gin"
	"gorm.io/gorm"
)

func hashRedeemCode(code string) string {
	s := sha256.Sum256([]byte(strings.ToUpper(strings.TrimSpace(code))))
	return hex.EncodeToString(s[:])
}

func generateRedeemCode() (string, error) {
	b := make([]byte, 9)
	if _, err := rand.Read(b); err != nil {
		return "", err
	}
	const alphabet = "ABCDEFGHJKLMNPQRSTUVWXYZ23456789"
	out := make([]byte, 12)
	for i := range out {
		out[i] = alphabet[int(b[i%len(b)])%len(alphabet)]
	}
	return string(out[:4]) + "-" + string(out[4:8]) + "-" + string(out[8:]), nil
}

func (a *App) adminCreateRedeemBatch(c *gin.Context) {
	var in struct {
		Credits   int64      `json:"credits"`
		Count     int        `json:"count"`
		ExpiresAt *time.Time `json:"expiresAt"`
		Note      string     `json:"note"`
	}
	if c.BindJSON(&in) != nil || in.Credits <= 0 || in.Count < 1 || in.Count > 10000 {
		c.JSON(400, gin.H{"error": "credits/count invalid"})
		return
	}
	admin := c.MustGet("user").(*User)
	batch := RedeemBatch{Code: fmt.Sprintf("B-%d", time.Now().UnixNano()), Credits: in.Credits, Count: in.Count, ExpiresAt: in.ExpiresAt, Note: in.Note, CreatedBy: admin.ID}
	codes := make([]string, 0, in.Count)
	err := a.db.Transaction(func(tx *gorm.DB) error {
		if err := tx.Create(&batch).Error; err != nil {
			return err
		}
		for i := 0; i < in.Count; i++ {
			code, err := generateRedeemCode()
			if err != nil {
				return err
			}
			row := RedeemCode{BatchID: batch.ID, CodeHash: hashRedeemCode(code), Prefix: code[:4], Credits: in.Credits, Status: "unused", ExpiresAt: in.ExpiresAt}
			if err := tx.Create(&row).Error; err != nil {
				return err
			}
			codes = append(codes, code)
		}
		return nil
	})
	if err != nil {
		c.JSON(500, gin.H{"error": err.Error()})
		return
	}
	a.audit(admin.ID, "redeem.batch.create", "redeem_batch", fmt.Sprint(batch.ID), fmt.Sprintf("credits=%d,count=%d", batch.Credits, batch.Count))
	c.JSON(201, gin.H{"batch": batch, "codes": codes})
}

func (a *App) redeem(c *gin.Context) {
	user := c.MustGet("user").(*User)
	var in struct {
		Code string `json:"code"`
	}
	if c.BindJSON(&in) != nil || strings.TrimSpace(in.Code) == "" {
		c.JSON(400, gin.H{"error": "code required"})
		return
	}
	now := time.Now()
	var amount int64
	err := a.db.Transaction(func(tx *gorm.DB) error {
		var code RedeemCode
		if err := tx.Where("code_hash = ?", hashRedeemCode(in.Code)).First(&code).Error; err != nil {
			return err
		}
		if code.Status != "unused" {
			return errors.New("code already used or unavailable")
		}
		if code.ExpiresAt != nil && code.ExpiresAt.Before(now) {
			return errors.New("code expired")
		}
		var account CreditAccount
		if err := tx.Where("user_id = ?", user.ID).First(&account).Error; err != nil {
			if !errors.Is(err, gorm.ErrRecordNotFound) {
				return err
			}
			account = CreditAccount{UserID: user.ID}
			if err := tx.Create(&account).Error; err != nil {
				return err
			}
		}
		account.Balance += code.Credits
		if err := tx.Save(&account).Error; err != nil {
			return err
		}
		code.Status, code.RedeemedBy, code.RedeemedAt = "used", &user.ID, &now
		if err := tx.Save(&code).Error; err != nil {
			return err
		}
		if err := tx.Create(&RedeemRecord{CodeID: code.ID, BatchID: code.BatchID, UserID: user.ID, Credits: code.Credits}).Error; err != nil {
			return err
		}
		if err := tx.Create(&CreditTransaction{UserID: user.ID, Type: "redeem", Amount: code.Credits, BalanceAfter: account.Balance, ReferenceType: "redeem_code", ReferenceID: fmt.Sprint(code.ID), Reason: "redeem code"}).Error; err != nil {
			return err
		}
		amount = code.Credits
		return nil
	})
	if err != nil {
		status := 500
		if errors.Is(err, gorm.ErrRecordNotFound) {
			status = 404
		}
		c.JSON(status, gin.H{"error": err.Error()})
		return
	}
	a.audit(user.ID, "redeem.use", "redeem_code", "hash:"+hashRedeemCode(in.Code)[:12], fmt.Sprintf("credits=%d", amount))
	c.JSON(200, gin.H{"credits": amount})
}

func (a *App) adminRevokeRedeemBatch(c *gin.Context) {
	id := c.Param("id")
	if err := a.db.Model(&RedeemCode{}).Where("batch_id = ? AND status = ?", id, "unused").Update("status", "revoked").Error; err != nil {
		c.JSON(500, gin.H{"error": err.Error()})
		return
	}
	admin := c.MustGet("user").(*User)
	a.audit(admin.ID, "redeem.batch.revoke", "redeem_batch", id, "unused codes revoked")
	c.JSON(200, gin.H{"ok": true})
}

func (a *App) adminListRedeemBatches(c *gin.Context) {
	var batches []RedeemBatch
	if err := a.db.Order("id desc").Limit(100).Find(&batches).Error; err != nil {
		c.JSON(500, gin.H{"error": err.Error()})
		return
	}
	c.JSON(200, gin.H{"data": batches})
}