//go:build linux || freebsd
// +build linux freebsd

package output

import (
	"encoding/json"
	"fmt"
	"os"
	"time"

	"codeberg.org/petrbalvin/goget/internal/core"
)

// ResumeMetaFileSuffix is the file suffix used for resume metadata files.
const ResumeMetaFileSuffix = ".goget.meta"

// ResumeMetadata holds metadata for resuming interrupted downloads.
type ResumeMetadata struct {
	URL          string        `json:"url"`
	ETag         string        `json:"etag,omitempty"`
	LastModified string        `json:"last_modified,omitempty"`
	Downloaded   int64         `json:"downloaded"`
	Total        int64         `json:"total,omitempty"`
	LastWrite    time.Time     `json:"last_write"`
	Version      string        `json:"version"`
	Chunks       map[int]int64 `json:"chunks,omitempty"` // per-chunk progress for parallel downloads
}

// NewResumeMetadata creates a new ResumeMetadata instance with the given parameters.
func NewResumeMetadata(url, etag, lastModified string, downloaded, total int64) *ResumeMetadata {
	return &ResumeMetadata{
		URL:          url,
		ETag:         etag,
		LastModified: lastModified,
		Downloaded:   downloaded,
		Total:        total,
		LastWrite:    time.Now(),
		Version:      "1.0",
	}
}

// Save writes the metadata to a JSON file alongside the downloaded file.
func (rm *ResumeMetadata) Save(outputPath string) error {
	metaPath := outputPath + ResumeMetaFileSuffix
	data, err := json.MarshalIndent(rm, "", "  ")
	if err != nil {
		return fmt.Errorf("failed to marshal meta: %w", err)
	}
	return os.WriteFile(metaPath, data, 0600)
}

// LoadResumeMetadata reads resume metadata from the associated JSON file.
func LoadResumeMetadata(outputPath string) (*ResumeMetadata, error) {
	metaPath := outputPath + ResumeMetaFileSuffix
	data, err := os.ReadFile(metaPath)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}
		return nil, fmt.Errorf("failed to read meta: %w", err)
	}

	var rm ResumeMetadata
	if err := json.Unmarshal(data, &rm); err != nil {
		return nil, fmt.Errorf("failed to parse metadata: %w", err)
	}

	return &rm, nil
}

// DeleteResumeMetadata removes the metadata file associated with the given output path.
func DeleteResumeMetadata(outputPath string) error {
	metaPath := outputPath + ResumeMetaFileSuffix
	if err := os.Remove(metaPath); err != nil && !os.IsNotExist(err) {
		return err
	}
	return nil
}

// CanResume checks whether a download can be resumed by validating the metadata file.
// It returns true only if valid metadata exists and matches the requested URL.
func CanResume(outputPath string, reqURL string) (bool, *ResumeMetadata, error) {
	// Check if output file exists
	info, err := os.Stat(outputPath)
	if err != nil {
		if os.IsNotExist(err) {
			return false, nil, nil
		}
		return false, nil, err
	}

	// Load metadata
	meta, err := LoadResumeMetadata(outputPath)
	if err != nil {
		return false, nil, err
	}

	// Without valid metadata, resume is not safe (file may be from another download or corrupted)
	if meta == nil {
		return false, nil, nil
	}

	// Verify URL matches
	if meta.URL != reqURL {
		return false, nil, fmt.Errorf("url mismatch: metadata for %s, requested %s", meta.URL, reqURL)
	}

	// Verify file size matches
	if info.Size() != meta.Downloaded {
		return false, nil, fmt.Errorf("size mismatch: file has %d bytes, metadata expects %d", info.Size(), meta.Downloaded)
	}

	return true, meta, nil
}

// GetResumeInfo creates a ResumeInfo from the metadata for use in download resumption.
func GetResumeInfo(meta *ResumeMetadata, outputPath string) (*core.ResumeInfo, error) {
	info, err := os.Stat(outputPath)
	if err != nil {
		return nil, err
	}

	return &core.ResumeInfo{
		DownloadedBytes: meta.Downloaded,
		ETag:            meta.ETag,
		LastModified:    meta.LastModified,
		URL:             meta.URL,
		LastWrite:       info.ModTime(),
	}, nil
}

// FileExists checks whether a file exists at the given path.
func FileExists(path string) bool {
	_, err := os.Stat(path)
	return err == nil
}

// GetFileSize returns the size of the file at the given path.
func GetFileSize(path string) (int64, error) {
	info, err := os.Stat(path)
	if err != nil {
		return 0, err
	}
	return info.Size(), nil
}

// CleanupResumeFiles removes the downloaded file and its associated metadata file.
func CleanupResumeFiles(outputPath string) error {
	if err := os.Remove(outputPath); err != nil && !os.IsNotExist(err) {
		return err
	}
	return DeleteResumeMetadata(outputPath)
}