// Copyright 2026 Moko Consulting <hello@mokoconsulting.tech>
// SPDX-License-Identifier: GPL-3.0-or-later

package security

import (
	"bytes"
	"crypto/sha256"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strings"
	"time"

	security_model "code.mokoconsulting.tech/MokoConsulting/MokoGitea/models/security"
	"code.mokoconsulting.tech/MokoConsulting/MokoGitea/modules/git"
	"code.mokoconsulting.tech/MokoConsulting/MokoGitea/modules/log"
)

// ──────────────────────────────────────────────────────────────────────
// Dependency manifest parsers
// ──────────────────────────────────────────────────────────────────────

// dependency represents a single package with version.
type dependency struct {
	Name      string
	Version   string
	Ecosystem string // "Go", "npm", "PyPI", "Packagist"
	FilePath  string // which manifest file it came from
}

// manifestParser extracts dependencies from a file's contents.
type manifestParser struct {
	FileName  string
	Ecosystem string
	Parse     func(content string, filePath string) []dependency
}

var manifestParsers = []manifestParser{
	{"go.mod", "Go", parseGoMod},
	{"package.json", "npm", parsePackageJSON},
	{"composer.json", "Packagist", parseComposerJSON},
	{"requirements.txt", "PyPI", parseRequirementsTxt},
}

// parseGoMod extracts dependencies from go.mod.
func parseGoMod(content, filePath string) []dependency {
	var deps []dependency
	inRequire := false

	for _, line := range strings.Split(content, "\n") {
		line = strings.TrimSpace(line)

		if line == ")" {
			inRequire = false
			continue
		}
		if strings.HasPrefix(line, "require (") || strings.HasPrefix(line, "require(") {
			inRequire = true
			continue
		}

		if inRequire {
			// Lines like: github.com/foo/bar v1.2.3
			parts := strings.Fields(line)
			if len(parts) >= 2 && !strings.HasPrefix(parts[0], "//") {
				deps = append(deps, dependency{
					Name:      parts[0],
					Version:   parts[1],
					Ecosystem: "Go",
					FilePath:  filePath,
				})
			}
			continue
		}

		// Single-line require: require github.com/foo/bar v1.2.3
		if strings.HasPrefix(line, "require ") && !strings.Contains(line, "(") {
			parts := strings.Fields(line)
			if len(parts) >= 3 {
				deps = append(deps, dependency{
					Name:      parts[1],
					Version:   parts[2],
					Ecosystem: "Go",
					FilePath:  filePath,
				})
			}
		}
	}
	return deps
}

// parsePackageJSON extracts dependencies from package.json.
func parsePackageJSON(content, filePath string) []dependency {
	var pkg struct {
		Dependencies    map[string]string `json:"dependencies"`
		DevDependencies map[string]string `json:"devDependencies"`
	}
	if err := json.Unmarshal([]byte(content), &pkg); err != nil {
		return nil
	}

	var deps []dependency
	for name, version := range pkg.Dependencies {
		deps = append(deps, dependency{
			Name:      name,
			Version:   cleanSemver(version),
			Ecosystem: "npm",
			FilePath:  filePath,
		})
	}
	for name, version := range pkg.DevDependencies {
		deps = append(deps, dependency{
			Name:      name,
			Version:   cleanSemver(version),
			Ecosystem: "npm",
			FilePath:  filePath,
		})
	}
	return deps
}

// parseComposerJSON extracts dependencies from composer.json.
func parseComposerJSON(content, filePath string) []dependency {
	var pkg struct {
		Require    map[string]string `json:"require"`
		RequireDev map[string]string `json:"require-dev"`
	}
	if err := json.Unmarshal([]byte(content), &pkg); err != nil {
		return nil
	}

	var deps []dependency
	for name, version := range pkg.Require {
		if name == "php" || strings.HasPrefix(name, "ext-") {
			continue // skip platform requirements
		}
		deps = append(deps, dependency{
			Name:      name,
			Version:   cleanSemver(version),
			Ecosystem: "Packagist",
			FilePath:  filePath,
		})
	}
	for name, version := range pkg.RequireDev {
		if name == "php" || strings.HasPrefix(name, "ext-") {
			continue
		}
		deps = append(deps, dependency{
			Name:      name,
			Version:   cleanSemver(version),
			Ecosystem: "Packagist",
			FilePath:  filePath,
		})
	}
	return deps
}

// parseRequirementsTxt extracts dependencies from requirements.txt.
func parseRequirementsTxt(content, filePath string) []dependency {
	var deps []dependency
	for _, line := range strings.Split(content, "\n") {
		line = strings.TrimSpace(line)
		if line == "" || strings.HasPrefix(line, "#") || strings.HasPrefix(line, "-") {
			continue
		}

		// Handle: package==1.0.0, package>=1.0.0, package~=1.0.0
		for _, sep := range []string{"==", ">=", "~=", "<=", "!="} {
			if idx := strings.Index(line, sep); idx > 0 {
				name := strings.TrimSpace(line[:idx])
				version := strings.TrimSpace(line[idx+len(sep):])
				// Strip any trailing constraints like ",<2.0"
				if ci := strings.Index(version, ","); ci > 0 {
					version = version[:ci]
				}
				deps = append(deps, dependency{
					Name:      name,
					Version:   version,
					Ecosystem: "PyPI",
					FilePath:  filePath,
				})
				break
			}
		}
	}
	return deps
}

// cleanSemver strips npm/composer range prefixes (^, ~, >=) to get a plain version.
func cleanSemver(v string) string {
	v = strings.TrimSpace(v)
	v = strings.TrimLeft(v, "^~>=<!")
	v = strings.TrimSpace(v)
	// If it has " || " or " - " (ranges), take the first version
	if idx := strings.Index(v, " "); idx > 0 {
		v = v[:idx]
	}
	return v
}

// ──────────────────────────────────────────────────────────────────────
// OSV.dev API client
// ──────────────────────────────────────────────────────────────────────

const osvBatchURL = "https://api.osv.dev/v1/querybatch"
const osvMaxBatch = 1000 // OSV batch limit

var osvClient = &http.Client{Timeout: 30 * time.Second}

// osvQuery is a single query in a batch request.
type osvQuery struct {
	Package *osvPackage `json:"package"`
	Version string      `json:"version"`
}

type osvPackage struct {
	Name      string `json:"name"`
	Ecosystem string `json:"ecosystem"`
}

// osvBatchRequest is the batch query body.
type osvBatchRequest struct {
	Queries []osvQuery `json:"queries"`
}

// osvBatchResponse is the batch response.
type osvBatchResponse struct {
	Results []osvResult `json:"results"`
}

type osvResult struct {
	Vulns []osvVuln `json:"vulns"`
}

type osvVuln struct {
	ID       string        `json:"id"`
	Summary  string        `json:"summary"`
	Details  string        `json:"details"`
	Severity []osvSeverity `json:"severity"`
	Aliases  []string      `json:"aliases"`
}

type osvSeverity struct {
	Type  string `json:"type"`  // "CVSS_V3", "CVSS_V2"
	Score string `json:"score"` // CVSS vector string
}

// queryOSV sends a batch of dependencies to OSV.dev and returns vulnerabilities.
func queryOSV(deps []dependency) (*osvBatchResponse, error) {
	queries := make([]osvQuery, 0, len(deps))
	for _, d := range deps {
		if d.Version == "" || d.Version == "*" || d.Version == "latest" {
			continue // can't query without a concrete version
		}
		queries = append(queries, osvQuery{
			Package: &osvPackage{Name: d.Name, Ecosystem: d.Ecosystem},
			Version: d.Version,
		})
	}

	if len(queries) == 0 {
		return &osvBatchResponse{}, nil
	}

	body, err := json.Marshal(osvBatchRequest{Queries: queries})
	if err != nil {
		return nil, fmt.Errorf("marshal OSV request: %w", err)
	}

	resp, err := osvClient.Post(osvBatchURL, "application/json", bytes.NewReader(body))
	if err != nil {
		return nil, fmt.Errorf("OSV API request: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		respBody, _ := io.ReadAll(io.LimitReader(resp.Body, 1024))
		return nil, fmt.Errorf("OSV API returned %d: %s", resp.StatusCode, string(respBody))
	}

	var result osvBatchResponse
	if err := json.NewDecoder(resp.Body).Decode(&result); err != nil {
		return nil, fmt.Errorf("decode OSV response: %w", err)
	}
	return &result, nil
}

// ──────────────────────────────────────────────────────────────────────
// Severity mapping
// ──────────────────────────────────────────────────────────────────────

// mapCVSSSeverity converts a CVSS v3 base score to an AlertSeverity.
func mapCVSSSeverity(vulnSeverities []osvSeverity) security_model.AlertSeverity {
	for _, s := range vulnSeverities {
		if s.Type == "CVSS_V3" {
			score := extractCVSSBaseScore(s.Score)
			switch {
			case score >= 9.0:
				return security_model.SeverityCritical
			case score >= 7.0:
				return security_model.SeverityHigh
			case score >= 4.0:
				return security_model.SeverityMedium
			case score > 0:
				return security_model.SeverityLow
			}
		}
	}

	// No CVSS score available - default to medium
	return security_model.SeverityMedium
}

// extractCVSSBaseScore parses the base score from a CVSS v3 vector string.
// Vector format: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
// We compute a simplified score from the vector metrics.
func extractCVSSBaseScore(vector string) float64 {
	if vector == "" {
		return 0
	}

	// CVSS v3 vectors encode severity in metrics. Use a simplified
	// lookup based on the most impactful metrics.
	parts := make(map[string]string)
	for _, segment := range strings.Split(vector, "/") {
		kv := strings.SplitN(segment, ":", 2)
		if len(kv) == 2 {
			parts[kv[0]] = kv[1]
		}
	}

	// Simplified scoring based on key CVSS v3 metrics
	var score float64

	// Attack Vector (AV)
	switch parts["AV"] {
	case "N": // Network
		score += 3.0
	case "A": // Adjacent
		score += 2.0
	case "L": // Local
		score += 1.0
	case "P": // Physical
		score += 0.5
	}

	// Attack Complexity (AC)
	switch parts["AC"] {
	case "L": // Low
		score += 1.5
	case "H": // High
		score += 0.5
	}

	// Privileges Required (PR)
	switch parts["PR"] {
	case "N": // None
		score += 1.5
	case "L": // Low
		score += 1.0
	case "H": // High
		score += 0.5
	}

	// Impact metrics (C/I/A)
	for _, metric := range []string{"C", "I", "A"} {
		switch parts[metric] {
		case "H":
			score += 1.2
		case "L":
			score += 0.5
		}
	}

	// Cap at 10.0
	if score > 10.0 {
		score = 10.0
	}
	return score
}

// ──────────────────────────────────────────────────────────────────────
// DependencyScanner
// ──────────────────────────────────────────────────────────────────────

// DependencyScanner checks project dependencies against known vulnerabilities.
type DependencyScanner struct{}

// NewDependencyScanner creates a new dependency vulnerability scanner.
func NewDependencyScanner() *DependencyScanner {
	return &DependencyScanner{}
}

func (s *DependencyScanner) Type() security_model.ScannerType {
	return security_model.ScannerDependency
}

func (s *DependencyScanner) ScanCommit(commit *git.Commit) ([]Finding, error) {
	return s.ScanTree(commit)
}

func (s *DependencyScanner) ScanTree(commit *git.Commit) ([]Finding, error) {
	if commit == nil {
		return nil, nil
	}

	// Step 1: Find and parse manifest files
	entries, err := commit.ListEntriesRecursiveFast()
	if err != nil {
		return nil, fmt.Errorf("ListEntriesRecursiveFast: %w", err)
	}

	var allDeps []dependency
	for _, entry := range entries {
		if !entry.IsRegular() {
			continue
		}

		path := entry.Name()
		baseName := path
		if idx := strings.LastIndex(path, "/"); idx >= 0 {
			baseName = path[idx+1:]
		}

		// Skip vendored/nested files
		lower := strings.ToLower(path)
		if strings.Contains(lower, "vendor/") || strings.Contains(lower, "node_modules/") ||
			strings.Contains(lower, "testdata/") {
			continue
		}

		for _, parser := range manifestParsers {
			if baseName == parser.FileName {
				reader, err := entry.Blob().DataAsync()
				if err != nil {
					log.Trace("DependencyScanner: skip %s: %v", path, err)
					continue
				}
				content, err := io.ReadAll(io.LimitReader(reader, 5*1024*1024)) // 5MB limit
				reader.Close()
				if err != nil {
					continue
				}

				deps := parser.Parse(string(content), path)
				allDeps = append(allDeps, deps...)
				break
			}
		}
	}

	if len(allDeps) == 0 {
		return nil, nil
	}

	log.Info("DependencyScanner: found %d dependencies across manifest files", len(allDeps))

	// Step 2: Query OSV in batches
	var findings []Finding
	for i := 0; i < len(allDeps); i += osvMaxBatch {
		end := i + osvMaxBatch
		if end > len(allDeps) {
			end = len(allDeps)
		}
		batch := allDeps[i:end]

		resp, err := queryOSV(batch)
		if err != nil {
			log.Error("DependencyScanner: OSV query failed: %v", err)
			continue
		}

		// Step 3: Map results to findings
		// OSV batch response indices correspond 1:1 with the query indices.
		// But we may have skipped deps with empty versions, so build the
		// queryable subset to align indices.
		queryable := make([]dependency, 0, len(batch))
		for _, d := range batch {
			if d.Version != "" && d.Version != "*" && d.Version != "latest" {
				queryable = append(queryable, d)
			}
		}

		for j, result := range resp.Results {
			if j >= len(queryable) {
				break
			}
			dep := queryable[j]

			for _, vuln := range result.Vulns {
				severity := mapCVSSSeverity(vuln.Severity)

				// Build CVE alias for rule ID (prefer CVE over GHSA)
				ruleID := vuln.ID
				for _, alias := range vuln.Aliases {
					if strings.HasPrefix(alias, "CVE-") {
						ruleID = alias
						break
					}
				}

				title := fmt.Sprintf("%s in %s@%s", ruleID, dep.Name, dep.Version)

				description := vuln.Summary
				if description == "" {
					description = vuln.Details
				}
				// Truncate long descriptions
				if len(description) > 500 {
					description = description[:497] + "..."
				}

				// Metadata JSON
				meta, _ := json.Marshal(map[string]string{
					"vuln_id":   vuln.ID,
					"ecosystem": dep.Ecosystem,
					"package":   dep.Name,
					"version":   dep.Version,
				})

				fingerprint := fmt.Sprintf("%x", sha256.Sum256([]byte(vuln.ID+":"+dep.Name+":"+dep.Version)))

				findings = append(findings, Finding{
					Scanner:     security_model.ScannerDependency,
					Severity:    severity,
					RuleID:      ruleID,
					Title:       title,
					Description: description,
					FilePath:    dep.FilePath,
					CommitSHA:   commit.ID.String(),
					Fingerprint: fingerprint[:32],
					Metadata:    string(meta),
				})
			}
		}
	}

	return findings, nil
}