package parser

import (
	"bufio"
	"compress/gzip"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"sort"
	"strings"
)

// ScanDirectory scans dir for nginx access and error log files.
// It matches filenames like access*.log* and error*.log*.
// If includeGzip is false, .gz files are skipped.
// Returns (accessFiles, errorFiles, error) sorted newest-first.
func ScanDirectory(dir string, includeGzip bool) ([]string, []string, error) {
	entries, err := os.ReadDir(dir)
	if err != nil {
		return nil, nil, fmt.Errorf("scandir %q: %w", dir, err)
	}

	var accessFiles, errorFiles []string
	for _, e := range entries {
		if e.IsDir() {
			continue
		}
		name := e.Name()
		if !includeGzip && strings.HasSuffix(name, ".gz") {
			continue
		}
		if matchesLogPattern(name, "access") {
			accessFiles = append(accessFiles, filepath.Join(dir, name))
		} else if matchesLogPattern(name, "error") {
			errorFiles = append(errorFiles, filepath.Join(dir, name))
		}
	}

	sortLogFiles(accessFiles)
	sortLogFiles(errorFiles)
	return accessFiles, errorFiles, nil
}

// matchesLogPattern returns true if filename starts with prefix and contains ".log".
func matchesLogPattern(name, prefix string) bool {
	if !strings.HasPrefix(name, prefix) {
		return false
	}
	return strings.Contains(name, ".log")
}

// logSortKey returns a sort key such that:
//   - "access.log"      → (0, 0)   — most recent
//   - "access.log.1"    → (1, 0)
//   - "access.log.1.gz" → (1, 1)
//   - "access.log.2.gz" → (2, 1)
func logSortKey(path string) (int, int) {
	name := filepath.Base(path)
	// strip prefix up to and including ".log"
	idx := strings.Index(name, ".log")
	if idx < 0 {
		return 999, 0
	}
	suffix := name[idx+4:] // e.g. "", ".1", ".1.gz", ".2.gz"

	isGz := 0
	if strings.HasSuffix(suffix, ".gz") {
		isGz = 1
		suffix = strings.TrimSuffix(suffix, ".gz")
	}
	suffix = strings.TrimPrefix(suffix, ".")

	num := 0
	if suffix != "" {
		fmt.Sscanf(suffix, "%d", &num)
	}
	return num, isGz
}

func sortLogFiles(files []string) {
	sort.SliceStable(files, func(i, j int) bool {
		ni, gi := logSortKey(files[i])
		nj, gj := logSortKey(files[j])
		if ni != nj {
			return ni < nj
		}
		return gi < gj
	})
}

// openLogFile opens a log file for reading.
// If the path ends in ".gz", it transparently decompresses.
func openLogFile(path string) (io.ReadCloser, error) {
	f, err := os.Open(path)
	if err != nil {
		return nil, fmt.Errorf("open %q: %w", path, err)
	}
	if strings.HasSuffix(path, ".gz") {
		gz, err := gzip.NewReader(f)
		if err != nil {
			f.Close()
			return nil, fmt.Errorf("gzip %q: %w", path, err)
		}
		return &gzipReadCloser{gz: gz, f: f}, nil
	}
	return f, nil
}

// gzipReadCloser closes both the gzip reader and underlying file.
type gzipReadCloser struct {
	gz *gzip.Reader
	f  *os.File
}

func (g *gzipReadCloser) Read(p []byte) (int, error) { return g.gz.Read(p) }
func (g *gzipReadCloser) Close() error {
	err := g.gz.Close()
	g.f.Close()
	return err
}

// ReadAccessEntries reads all access log entries from the given files.
// Malformed lines are silently skipped.
func ReadAccessEntries(files []string) ([]AccessEntry, error) {
	var entries []AccessEntry
	for _, path := range files {
		rc, err := openLogFile(path)
		if err != nil {
			return nil, err
		}
		scanner := bufio.NewScanner(rc)
		for scanner.Scan() {
			if e, err := ParseAccessLine(scanner.Text()); err == nil {
				entries = append(entries, e)
			}
		}
		rc.Close()
		if err := scanner.Err(); err != nil {
			return nil, fmt.Errorf("scan %q: %w", path, err)
		}
	}
	return entries, nil
}

// ReadErrorEntries reads all error log entries from the given files.
// Malformed lines are silently skipped.
func ReadErrorEntries(files []string) ([]ErrorEntry, error) {
	var entries []ErrorEntry
	for _, path := range files {
		rc, err := openLogFile(path)
		if err != nil {
			return nil, err
		}
		scanner := bufio.NewScanner(rc)
		for scanner.Scan() {
			if e, err := ParseErrorLine(scanner.Text()); err == nil {
				entries = append(entries, e)
			}
		}
		rc.Close()
		if err := scanner.Err(); err != nil {
			return nil, fmt.Errorf("scan %q: %w", path, err)
		}
	}
	return entries, nil
}