package handlers

import (
	"context"
	"crypto/x509"
	"encoding/pem"
	"errors"
	"io"
	"net/http"
	"net/url"
	"reflect"
	"strings"
	"time"

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

	"smoop-api/internal/models"
	"smoop-api/internal/vault"
)

type CertsHandler struct {
	db  *gorm.DB
	pki *vault.PKIClient
	ttl string // e.g. "720h"
}

func NewCertsHandler(db *gorm.DB, pki *vault.PKIClient, ttl string) *CertsHandler {
	return &CertsHandler{db: db, pki: pki, ttl: ttl}
}

// ---- helpers ----------------------------------------------------------------

func readCSRFromRequest(c *gin.Context) (string, error) {
	// Accept: multipart/form with file "csr", or JSON {"csr":"PEM..."} or text/plain body
	// 1) multipart file
	if f, err := c.FormFile("csr"); err == nil && f != nil {
		ff, err := f.Open()
		if err != nil {
			return "", err
		}
		defer ff.Close()
		b, err := io.ReadAll(ff)
		return string(b), err
	}
	// 2) JSON
	var body struct {
		CSR string `json:"csr"`
	}
	if err := c.ShouldBindJSON(&body); err == nil && body.CSR != "" {
		return body.CSR, nil
	}
	// 3) raw text
	b, _ := io.ReadAll(c.Request.Body)
	if len(b) > 0 {
		return string(b), nil
	}
	return "", errors.New("csr required")
}

func parseLeafPEM(pemStr string) (*x509.Certificate, error) {
	block, _ := pem.Decode([]byte(pemStr))
	if block == nil {
		return nil, errors.New("pem decode failed")
	}
	return x509.ParseCertificate(block.Bytes)
}

func parseClientCertFromHeader(escaped string) (*x509.Certificate, error) {
	if escaped == "" {
		return nil, errors.New("empty client cert header")
	}
	raw, err := url.QueryUnescape(escaped)
	if err != nil {
		// Some Nginx builds already space-escape; still try raw
		raw = escaped
	}
	block, _ := pem.Decode([]byte(raw))
	if block == nil {
		return nil, errors.New("failed to decode PEM in client cert header")
	}
	return x509.ParseCertificate(block.Bytes)
}

// ---- enroll (no mTLS, just device exists) -----------------------------------
// POST /enroll/:guid
func (h *CertsHandler) Enroll(c *gin.Context) {
	guid := c.Param("guid")
	// ensure device exists
	var dev models.Device
	if err := h.db.First(&dev, "guid = ?", guid).Error; err != nil {
		if errors.Is(err, gorm.ErrRecordNotFound) {
			c.JSON(http.StatusNotFound, gin.H{"error": "device not found"})
			return
		}
		c.JSON(http.StatusInternalServerError, gin.H{"error": "lookup failed"})
		return
	}

	csr, err := readCSRFromRequest(c)
	if err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
		return
	}

	// sign in Vault
	ctx, cancel := context.WithTimeout(c, 30*time.Second)
	defer cancel()
	sign, err := h.pki.SignCSR(ctx, csr, "urn:device:"+guid, h.ttl)
	if err != nil {
		c.JSON(http.StatusBadGateway, gin.H{"error": "vault sign failed"})
		return
	}

	// persist cert metadata
	leaf, err := parseLeafPEM(sign.Certificate)
	if err == nil {
		_ = h.db.Create(&models.DeviceCertificate{
			DeviceGUID: guid,
			SerialHex:  strings.ToUpper(leaf.SerialNumber.Text(16)),
			IssuerCN:   leaf.Issuer.CommonName,
			SubjectDN:  leaf.Subject.String(),
			NotBefore:  leaf.NotBefore,
			NotAfter:   leaf.NotAfter,
			PemCert:    sign.Certificate,
		}).Error
	}

	// response bundle
	c.JSON(http.StatusOK, gin.H{
		"certificate": sign.Certificate,
		"issuing_ca":  sign.IssuingCA,
		"ca_chain":    sign.CAChain,
	})
}

// ---- renew (mTLS; cert must not be revoked; CSR pubkey must match current) --
// POST /renew/:guid
func (h *CertsHandler) Renew(c *gin.Context) {
	guidAny, _ := c.Get("mtlsDeviceGUID")
	serialAny, _ := c.Get("mtlsSerialHex")
	guid := guidAny.(string)
	currentSerial := serialAny.(string)

	csr, err := readCSRFromRequest(c)
	if err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
		return
	}

	// Check CSR pubkey == current client cert pubkey (strong binding)
	clientCert, err := parseClientCertFromHeader(c.GetHeader("X-SSL-Client-Cert"))
	if err != nil {
		c.JSON(http.StatusUnauthorized, gin.H{"error": "invalid client cert"})
		return
	}
	csrBlock, _ := pem.Decode([]byte(csr))
	if csrBlock == nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "csr decode failed"})
		return
	}
	parsedCSR, err := x509.ParseCertificateRequest(csrBlock.Bytes)
	if err != nil || parsedCSR.PublicKey == nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": "csr parse failed"})
		return
	}
	if !reflect.DeepEqual(parsedCSR.PublicKey, clientCert.PublicKey) {
		c.JSON(http.StatusForbidden, gin.H{"error": "csr key does not match current certificate key"})
		return
	}

	// sign
	ctx, cancel := context.WithTimeout(c, 30*time.Second)
	defer cancel()
	sign, err := h.pki.SignCSR(ctx, csr, "urn:device:"+guid, h.ttl)
	if err != nil {
		c.JSON(http.StatusBadGateway, gin.H{"error": "vault sign failed"})
		return
	}

	leaf, _ := parseLeafPEM(sign.Certificate)
	if leaf != nil {
		_ = h.db.Create(&models.DeviceCertificate{
			DeviceGUID: guid,
			SerialHex:  strings.ToUpper(leaf.SerialNumber.Text(16)),
			IssuerCN:   leaf.Issuer.CommonName,
			SubjectDN:  leaf.Subject.String(),
			NotBefore:  leaf.NotBefore,
			NotAfter:   leaf.NotAfter,
			PemCert:    sign.Certificate,
		}).Error
	}

	c.JSON(http.StatusOK, gin.H{
		"certificate": sign.Certificate,
		"issuing_ca":  sign.IssuingCA,
		"ca_chain":    sign.CAChain,
		"old_serial":  currentSerial,
	})
}