package history

import (
	"bufio"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"time"
)

type CapacityDiskPoint struct {
	Mount      string `json:"mount"`
	UsedBytes  uint64 `json:"used_bytes"`
	TotalBytes uint64 `json:"total_bytes"`
}

type CapacitySnapshot struct {
	Timestamp time.Time           `json:"timestamp"`
	Disks     []CapacityDiskPoint `json:"disks,omitempty"`
}

type CapacityStore struct {
	dir string
}

func NewCapacityStore(baseDir string) *CapacityStore {
	if strings.TrimSpace(baseDir) == "" {
		baseDir = "."
	}
	return &CapacityStore{dir: filepath.Join(baseDir, "history", "capacity")}
}

func (s *CapacityStore) Path(clusterID string) string {
	return filepath.Join(s.dir, sanitizeClusterID(clusterID)+".jsonl")
}

func (s *CapacityStore) Append(clusterID string, snap CapacitySnapshot) error {
	if strings.TrimSpace(clusterID) == "" {
		return errors.New("empty cluster id")
	}
	if snap.Timestamp.IsZero() {
		snap.Timestamp = time.Now().UTC()
	}
	if len(snap.Disks) == 0 {
		return nil
	}
	if err := os.MkdirAll(s.dir, 0o700); err != nil {
		return err
	}
	f, err := os.OpenFile(s.Path(clusterID), os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o600)
	if err != nil {
		return err
	}
	defer f.Close()
	b, err := json.Marshal(snap)
	if err != nil {
		return err
	}
	_, err = f.Write(append(b, '\n'))
	return err
}

func (s *CapacityStore) Load(clusterID string, since time.Time) ([]CapacitySnapshot, error) {
	if strings.TrimSpace(clusterID) == "" {
		return nil, errors.New("empty cluster id")
	}
	f, err := os.Open(s.Path(clusterID))
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return []CapacitySnapshot{}, nil
		}
		return nil, err
	}
	defer f.Close()
	sc := bufio.NewScanner(f)
	sc.Buffer(make([]byte, 0, 64*1024), 8*1024*1024)
	out := make([]CapacitySnapshot, 0, 512)
	for sc.Scan() {
		line := strings.TrimSpace(sc.Text())
		if line == "" {
			continue
		}
		var snap CapacitySnapshot
		if err := json.Unmarshal([]byte(line), &snap); err != nil {
			continue
		}
		if !since.IsZero() && snap.Timestamp.Before(since) {
			continue
		}
		if len(snap.Disks) == 0 {
			continue
		}
		out = append(out, snap)
	}
	if err := sc.Err(); err != nil {
		return nil, fmt.Errorf("scan capacity: %w", err)
	}
	return out, nil
}