// Package devkit provides a developer toolkit for common automation commands.
// LEK-1 | lthn.ai | EUPL-1.2
package devkit

import (
	"bufio"
	"encoding/json"
	"fmt"
	"math"
	"os"
	"regexp"
	"strconv"
	"strings"
	"time"
)

// CoverageSnapshot represents a point-in-time coverage measurement.
type CoverageSnapshot struct {
	Timestamp time.Time              `json:"timestamp"`
	Packages  map[string]float64     `json:"packages"`  // package → coverage %
	Total     float64                `json:"total"`      // overall coverage %
	Meta      map[string]string      `json:"meta,omitempty"` // optional metadata (commit, branch, etc.)
}

// CoverageRegression flags a package whose coverage dropped between runs.
type CoverageRegression struct {
	Package  string
	Previous float64
	Current  float64
	Delta    float64 // Negative means regression
}

// CoverageComparison holds the result of comparing two snapshots.
type CoverageComparison struct {
	Regressions  []CoverageRegression
	Improvements []CoverageRegression
	NewPackages  []string  // Packages present in current but not previous
	Removed      []string  // Packages present in previous but not current
	TotalDelta   float64   // Change in overall coverage
}

// CoverageStore persists coverage snapshots to a JSON file.
type CoverageStore struct {
	Path string // File path for JSON storage
}

// NewCoverageStore creates a store backed by the given file path.
func NewCoverageStore(path string) *CoverageStore {
	return &CoverageStore{Path: path}
}

// Append adds a snapshot to the store.
func (s *CoverageStore) Append(snap CoverageSnapshot) error {
	snapshots, err := s.Load()
	if err != nil && !os.IsNotExist(err) {
		return fmt.Errorf("load snapshots: %w", err)
	}

	snapshots = append(snapshots, snap)

	data, err := json.MarshalIndent(snapshots, "", "  ")
	if err != nil {
		return fmt.Errorf("marshal snapshots: %w", err)
	}

	if err := os.WriteFile(s.Path, data, 0644); err != nil {
		return fmt.Errorf("write %s: %w", s.Path, err)
	}
	return nil
}

// Load reads all snapshots from the store.
func (s *CoverageStore) Load() ([]CoverageSnapshot, error) {
	data, err := os.ReadFile(s.Path)
	if err != nil {
		return nil, err
	}

	var snapshots []CoverageSnapshot
	if err := json.Unmarshal(data, &snapshots); err != nil {
		return nil, fmt.Errorf("parse %s: %w", s.Path, err)
	}
	return snapshots, nil
}

// Latest returns the most recent snapshot, or nil if the store is empty.
func (s *CoverageStore) Latest() (*CoverageSnapshot, error) {
	snapshots, err := s.Load()
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}
		return nil, err
	}
	if len(snapshots) == 0 {
		return nil, nil
	}

	latest := &snapshots[0]
	for i := range snapshots {
		if snapshots[i].Timestamp.After(latest.Timestamp) {
			latest = &snapshots[i]
		}
	}
	return latest, nil
}

// ParseCoverProfile parses output from `go test -coverprofile=cover.out` format.
// Each line is: mode: set/count/atomic (first line) or
// package/file.go:startLine.startCol,endLine.endCol stmts count
func ParseCoverProfile(data string) (CoverageSnapshot, error) {
	snap := CoverageSnapshot{
		Timestamp: time.Now(),
		Packages:  make(map[string]float64),
	}

	type pkgStats struct {
		covered int
		total   int
	}
	packages := make(map[string]*pkgStats)

	scanner := bufio.NewScanner(strings.NewReader(data))
	for scanner.Scan() {
		line := scanner.Text()
		if strings.HasPrefix(line, "mode:") {
			continue
		}

		// Format: pkg/file.go:line.col,line.col numStmt count
		parts := strings.Fields(line)
		if len(parts) != 3 {
			continue
		}

		// Extract package from file path
		filePath := parts[0]
		colonIdx := strings.Index(filePath, ":")
		if colonIdx < 0 {
			continue
		}
		file := filePath[:colonIdx]

		// Package is everything up to the last /
		pkg := file
		if lastSlash := strings.LastIndex(file, "/"); lastSlash >= 0 {
			pkg = file[:lastSlash]
		}

		stmts, err := strconv.Atoi(parts[1])
		if err != nil {
			continue
		}
		count, err := strconv.Atoi(parts[2])
		if err != nil {
			continue
		}

		if _, ok := packages[pkg]; !ok {
			packages[pkg] = &pkgStats{}
		}
		packages[pkg].total += stmts
		if count > 0 {
			packages[pkg].covered += stmts
		}
	}

	totalCovered := 0
	totalStmts := 0

	for pkg, stats := range packages {
		if stats.total > 0 {
			snap.Packages[pkg] = math.Round(float64(stats.covered)/float64(stats.total)*1000) / 10
		} else {
			snap.Packages[pkg] = 0
		}
		totalCovered += stats.covered
		totalStmts += stats.total
	}

	if totalStmts > 0 {
		snap.Total = math.Round(float64(totalCovered)/float64(totalStmts)*1000) / 10
	}

	return snap, nil
}

// ParseCoverOutput parses the human-readable `go test -cover ./...` output.
// Extracts lines like: ok  example.com/pkg  0.5s  coverage: 85.0% of statements
func ParseCoverOutput(output string) (CoverageSnapshot, error) {
	snap := CoverageSnapshot{
		Timestamp: time.Now(),
		Packages:  make(map[string]float64),
	}

	re := regexp.MustCompile(`ok\s+(\S+)\s+.*coverage:\s+([\d.]+)%`)
	scanner := bufio.NewScanner(strings.NewReader(output))

	totalPct := 0.0
	count := 0

	for scanner.Scan() {
		matches := re.FindStringSubmatch(scanner.Text())
		if len(matches) == 3 {
			pct, _ := strconv.ParseFloat(matches[2], 64)
			snap.Packages[matches[1]] = pct
			totalPct += pct
			count++
		}
	}

	if count > 0 {
		snap.Total = math.Round(totalPct/float64(count)*10) / 10
	}

	return snap, nil
}

// CompareCoverage computes the difference between two snapshots.
func CompareCoverage(previous, current CoverageSnapshot) CoverageComparison {
	comp := CoverageComparison{
		TotalDelta: math.Round((current.Total-previous.Total)*10) / 10,
	}

	// Check each current package against previous
	for pkg, curPct := range current.Packages {
		prevPct, existed := previous.Packages[pkg]
		if !existed {
			comp.NewPackages = append(comp.NewPackages, pkg)
			continue
		}

		delta := math.Round((curPct-prevPct)*10) / 10
		if delta < 0 {
			comp.Regressions = append(comp.Regressions, CoverageRegression{
				Package:  pkg,
				Previous: prevPct,
				Current:  curPct,
				Delta:    delta,
			})
		} else if delta > 0 {
			comp.Improvements = append(comp.Improvements, CoverageRegression{
				Package:  pkg,
				Previous: prevPct,
				Current:  curPct,
				Delta:    delta,
			})
		}
	}

	// Check for removed packages
	for pkg := range previous.Packages {
		if _, exists := current.Packages[pkg]; !exists {
			comp.Removed = append(comp.Removed, pkg)
		}
	}

	return comp
}

// LEK-1 | lthn.ai | EUPL-1.2