package main

import (
	"bufio"
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
)

// Policy describes coverage threshold configuration.
type Policy struct {
	MinimumStatementCoverage float64         `json:"minimum_statement_coverage"`
	CriticalPackages         []PackagePolicy `json:"critical_packages"`
}

// PackagePolicy overrides defaults for a specific package.
type PackagePolicy struct {
	Package                  string   `json:"package"`
	MinimumStatementCoverage float64  `json:"minimum_statement_coverage"`
	Include                  bool     `json:"include"`
	Exclusions               []string `json:"exclusions"`
}

// Coverage aggregates covered and total statements for a package.
type Coverage struct {
	Covered int64
	Total   int64
}

// PackageResult is the policy-evaluated coverage result for one package.
type PackageResult struct {
	Package   string
	Covered   int64
	Total     int64
	Percent   float64
	Threshold float64
	Pass      bool
}

// LoadPolicy reads policy JSON from disk.
func LoadPolicy(path string) (Policy, error) {
	f, err := openValidatedReadOnlyFile(path, ".json", "policy")
	if err != nil {
		return Policy{}, err
	}
	defer f.Close()

	var p Policy
	if err := json.NewDecoder(f).Decode(&p); err != nil {
		return Policy{}, fmt.Errorf("decode policy: %w", err)
	}
	if p.MinimumStatementCoverage <= 0 {
		p.MinimumStatementCoverage = 80.0
	}
	return p, nil
}

// ParseCoverProfile parses a Go coverprofile and aggregates package coverage.
func ParseCoverProfile(profilePath string, policy Policy) (map[string]Coverage, error) {
	f, err := openValidatedReadOnlyFile(profilePath, "", "coverage profile")
	if err != nil {
		return nil, err
	}
	defer f.Close()

	coverage := make(map[string]Coverage)
	s := bufio.NewScanner(f)
	lineNo := 0
	for s.Scan() {
		lineNo++
		line := strings.TrimSpace(s.Text())
		if lineNo == 1 {
			if !strings.HasPrefix(line, "mode:") {
				return nil, fmt.Errorf("invalid coverage profile header")
			}
			continue
		}
		if line == "" {
			continue
		}

		parts := strings.Fields(line)
		if len(parts) != 3 {
			return nil, fmt.Errorf("invalid coverage line %d", lineNo)
		}
		fileAndRange := parts[0]
		numStmts, err := strconv.ParseInt(parts[1], 10, 64)
		if err != nil {
			return nil, fmt.Errorf("invalid statements count at line %d: %w", lineNo, err)
		}
		execCount, err := strconv.ParseInt(parts[2], 10, 64)
		if err != nil {
			return nil, fmt.Errorf("invalid execution count at line %d: %w", lineNo, err)
		}

		idx := strings.Index(fileAndRange, ":")
		if idx < 0 {
			return nil, fmt.Errorf("invalid file segment at line %d", lineNo)
		}
		filePath := fileAndRange[:idx]
		pkg := filepath.ToSlash(filepath.Dir(filePath))
		if isExcludedFile(pkg, filePath, policy) {
			continue
		}

		agg := coverage[pkg]
		agg.Total += numStmts
		if execCount > 0 {
			agg.Covered += numStmts
		}
		coverage[pkg] = agg
	}
	if err := s.Err(); err != nil {
		return nil, fmt.Errorf("scan coverage profile: %w", err)
	}

	return coverage, nil
}

func openValidatedReadOnlyFile(path string, requiredExt string, label string) (*os.File, error) {
	cleaned := filepath.Clean(strings.TrimSpace(path))
	if cleaned == "" || cleaned == "." {
		return nil, fmt.Errorf("invalid %s path", label)
	}

	if requiredExt != "" {
		ext := strings.ToLower(filepath.Ext(cleaned))
		if ext != strings.ToLower(requiredExt) {
			return nil, fmt.Errorf("invalid %s file extension: got %q, want %q", label, ext, requiredExt)
		}
	}

	absPath, err := filepath.Abs(cleaned)
	if err != nil {
		return nil, fmt.Errorf("resolve %s path: %w", label, err)
	}

	info, err := os.Stat(absPath)
	if err != nil {
		return nil, fmt.Errorf("stat %s: %w", label, err)
	}
	if info.IsDir() {
		return nil, fmt.Errorf("%s path must be a file, got directory", label)
	}

	// #nosec G304 -- path is explicitly cleaned, normalized, and pre-validated as an existing file.
	f, err := os.Open(absPath)
	if err != nil {
		return nil, fmt.Errorf("open %s: %w", label, err)
	}

	return f, nil
}

// EvaluateCoverage evaluates package coverage against policy thresholds.
func EvaluateCoverage(packages []string, byPackage map[string]Coverage, policy Policy) []PackageResult {
	results := make([]PackageResult, 0, len(packages))
	for _, pkg := range packages {
		if !isPackageIncluded(pkg, policy) {
			continue
		}
		agg := byPackage[pkg]
		percent := 100.0
		if agg.Total > 0 {
			percent = float64(agg.Covered) * 100.0 / float64(agg.Total)
		}
		threshold := thresholdForPackage(pkg, policy)
		pass := agg.Total == 0 || percent >= threshold
		results = append(results, PackageResult{
			Package:   pkg,
			Covered:   agg.Covered,
			Total:     agg.Total,
			Percent:   percent,
			Threshold: threshold,
			Pass:      pass,
		})
	}
	sort.Slice(results, func(i, j int) bool {
		return results[i].Package < results[j].Package
	})
	return results
}

func thresholdForPackage(pkg string, policy Policy) float64 {
	for _, entry := range policy.CriticalPackages {
		if entry.Package == pkg && entry.MinimumStatementCoverage > 0 {
			return entry.MinimumStatementCoverage
		}
	}
	if policy.MinimumStatementCoverage > 0 {
		return policy.MinimumStatementCoverage
	}
	return 80.0
}

func isPackageIncluded(pkg string, policy Policy) bool {
	for _, entry := range policy.CriticalPackages {
		if entry.Package == pkg {
			return entry.Include
		}
	}
	return true
}

func isExcludedFile(pkg string, filePath string, policy Policy) bool {
	base := filepath.Base(filePath)

	// Exclude known generated artifacts and thin composition wiring.
	if strings.HasSuffix(base, "_gen.go") ||
		base == "generated.go" ||
		base == "models_gen.go" ||
		base == "schema.resolvers.go" ||
		base == "main.go" {
		return true
	}

	for _, entry := range policy.CriticalPackages {
		if entry.Package != pkg {
			continue
		}
		for _, ex := range entry.Exclusions {
			if ex == "" {
				continue
			}
			if strings.HasSuffix(filePath, ex) || strings.Contains(filePath, "/"+ex) {
				return true
			}
		}
	}
	return false
}