package experiment

import (
	"encoding/binary"
	"fmt"
	"math"
	"os"
	"path/filepath"
	"time"
)

// Metadata represents experiment metadata stored in meta.bin
type Metadata struct {
	CommitID  string
	Timestamp int64
	JobName   string
	User      string
}

// Manager handles experiment storage and metadata
type Manager struct {
	basePath string
}

func NewManager(basePath string) *Manager {
	return &Manager{
		basePath: basePath,
	}
}

// Initialize ensures the experiment directory exists
func (m *Manager) Initialize() error {
	if err := os.MkdirAll(m.basePath, 0755); err != nil {
		return fmt.Errorf("failed to create experiment base directory: %w", err)
	}
	return nil
}

// GetExperimentPath returns the path for a given commit ID
func (m *Manager) GetExperimentPath(commitID string) string {
	return filepath.Join(m.basePath, commitID)
}

// GetFilesPath returns the path to the files directory for an experiment
func (m *Manager) GetFilesPath(commitID string) string {
	return filepath.Join(m.GetExperimentPath(commitID), "files")
}

// GetMetadataPath returns the path to meta.bin for an experiment
func (m *Manager) GetMetadataPath(commitID string) string {
	return filepath.Join(m.GetExperimentPath(commitID), "meta.bin")
}

// ExperimentExists checks if an experiment with the given commit ID exists
func (m *Manager) ExperimentExists(commitID string) bool {
	path := m.GetExperimentPath(commitID)
	info, err := os.Stat(path)
	return err == nil && info.IsDir()
}

// CreateExperiment creates the directory structure for a new experiment
func (m *Manager) CreateExperiment(commitID string) error {
	filesPath := m.GetFilesPath(commitID)

	if err := os.MkdirAll(filesPath, 0755); err != nil {
		return fmt.Errorf("failed to create experiment directory: %w", err)
	}

	return nil
}

// WriteMetadata writes experiment metadata to meta.bin
func (m *Manager) WriteMetadata(meta *Metadata) error {
	path := m.GetMetadataPath(meta.CommitID)

	// Binary format:
	// [version:1][timestamp:8][commit_id_len:1][commit_id:var][job_name_len:1][job_name:var][user_len:1][user:var]

	buf := make([]byte, 0, 256)

	// Version
	buf = append(buf, 0x01)

	// Timestamp
	ts := make([]byte, 8)
	binary.BigEndian.PutUint64(ts, uint64(meta.Timestamp))
	buf = append(buf, ts...)

	// Commit ID
	buf = append(buf, byte(len(meta.CommitID)))
	buf = append(buf, []byte(meta.CommitID)...)

	// Job Name
	buf = append(buf, byte(len(meta.JobName)))
	buf = append(buf, []byte(meta.JobName)...)

	// User
	buf = append(buf, byte(len(meta.User)))
	buf = append(buf, []byte(meta.User)...)

	return os.WriteFile(path, buf, 0644)
}

// ReadMetadata reads experiment metadata from meta.bin
func (m *Manager) ReadMetadata(commitID string) (*Metadata, error) {
	path := m.GetMetadataPath(commitID)

	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("failed to read metadata: %w", err)
	}

	if len(data) < 10 {
		return nil, fmt.Errorf("metadata file too short")
	}

	meta := &Metadata{}
	offset := 0

	// Version
	version := data[offset]
	offset++
	if version != 0x01 {
		return nil, fmt.Errorf("unsupported metadata version: %d", version)
	}

	// Timestamp
	meta.Timestamp = int64(binary.BigEndian.Uint64(data[offset : offset+8]))
	offset += 8

	// Commit ID
	commitIDLen := int(data[offset])
	offset++
	meta.CommitID = string(data[offset : offset+commitIDLen])
	offset += commitIDLen

	// Job Name
	if offset >= len(data) {
		return meta, nil
	}
	jobNameLen := int(data[offset])
	offset++
	meta.JobName = string(data[offset : offset+jobNameLen])
	offset += jobNameLen

	// User
	if offset >= len(data) {
		return meta, nil
	}
	userLen := int(data[offset])
	offset++
	meta.User = string(data[offset : offset+userLen])

	return meta, nil
}

// ListExperiments returns all experiment commit IDs
func (m *Manager) ListExperiments() ([]string, error) {
	entries, err := os.ReadDir(m.basePath)
	if err != nil {
		return nil, fmt.Errorf("failed to read experiments directory: %w", err)
	}

	var commitIDs []string
	for _, entry := range entries {
		if entry.IsDir() {
			commitIDs = append(commitIDs, entry.Name())
		}
	}

	return commitIDs, nil
}

// PruneExperiments removes old experiments based on retention policy
func (m *Manager) PruneExperiments(keepCount int, olderThanDays int) ([]string, error) {
	commitIDs, err := m.ListExperiments()
	if err != nil {
		return nil, err
	}

	type experiment struct {
		commitID  string
		timestamp int64
	}

	var experiments []experiment
	for _, commitID := range commitIDs {
		meta, err := m.ReadMetadata(commitID)
		if err != nil {
			continue // Skip experiments with invalid metadata
		}
		experiments = append(experiments, experiment{
			commitID:  commitID,
			timestamp: meta.Timestamp,
		})
	}

	// Sort by timestamp (newest first)
	for i := 0; i < len(experiments); i++ {
		for j := i + 1; j < len(experiments); j++ {
			if experiments[j].timestamp > experiments[i].timestamp {
				experiments[i], experiments[j] = experiments[j], experiments[i]
			}
		}
	}

	var pruned []string
	cutoffTime := time.Now().AddDate(0, 0, -olderThanDays).Unix()

	for i, exp := range experiments {
		shouldPrune := false

		// Keep the newest N experiments
		if i >= keepCount {
			shouldPrune = true
		}

		// Also prune if older than threshold
		if olderThanDays > 0 && exp.timestamp < cutoffTime {
			shouldPrune = true
		}

		if shouldPrune {
			expPath := m.GetExperimentPath(exp.commitID)
			if err := os.RemoveAll(expPath); err != nil {
				// Log but continue
				continue
			}
			pruned = append(pruned, exp.commitID)
		}
	}

	return pruned, nil
}

// Metric represents a single data point in an experiment
type Metric struct {
	Name      string  `json:"name"`
	Value     float64 `json:"value"`
	Step      int     `json:"step"`
	Timestamp int64   `json:"timestamp"`
}

// GetMetricsPath returns the path to metrics.bin for an experiment
func (m *Manager) GetMetricsPath(commitID string) string {
	return filepath.Join(m.GetExperimentPath(commitID), "metrics.bin")
}

// LogMetric appends a metric to the experiment's metrics file
func (m *Manager) LogMetric(commitID string, name string, value float64, step int) error {
	path := m.GetMetricsPath(commitID)

	// Binary format for each metric:
	// [timestamp:8][step:4][value:8][name_len:1][name:var]

	buf := make([]byte, 0, 64)

	// Timestamp
	ts := make([]byte, 8)
	binary.BigEndian.PutUint64(ts, uint64(time.Now().Unix()))
	buf = append(buf, ts...)

	// Step
	st := make([]byte, 4)
	binary.BigEndian.PutUint32(st, uint32(step))
	buf = append(buf, st...)

	// Value (float64)
	val := make([]byte, 8)
	binary.BigEndian.PutUint64(val, math.Float64bits(value))
	buf = append(buf, val...)

	// Name
	if len(name) > 255 {
		name = name[:255]
	}
	buf = append(buf, byte(len(name)))
	buf = append(buf, []byte(name)...)

	// Append to file
	f, err := os.OpenFile(path, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
	if err != nil {
		return fmt.Errorf("failed to open metrics file: %w", err)
	}
	defer f.Close()

	if _, err := f.Write(buf); err != nil {
		return fmt.Errorf("failed to write metric: %w", err)
	}

	return nil
}

// GetMetrics reads all metrics for an experiment
func (m *Manager) GetMetrics(commitID string) ([]Metric, error) {
	path := m.GetMetricsPath(commitID)

	data, err := os.ReadFile(path)
	if err != nil {
		if os.IsNotExist(err) {
			return []Metric{}, nil
		}
		return nil, fmt.Errorf("failed to read metrics file: %w", err)
	}

	var metrics []Metric
	offset := 0

	for offset < len(data) {
		if offset+21 > len(data) { // Min size check
			break
		}

		m := Metric{}

		// Timestamp
		m.Timestamp = int64(binary.BigEndian.Uint64(data[offset : offset+8]))
		offset += 8

		// Step
		m.Step = int(binary.BigEndian.Uint32(data[offset : offset+4]))
		offset += 4

		// Value
		bits := binary.BigEndian.Uint64(data[offset : offset+8])
		m.Value = math.Float64frombits(bits)
		offset += 8

		// Name
		nameLen := int(data[offset])
		offset++

		if offset+nameLen > len(data) {
			break
		}
		m.Name = string(data[offset : offset+nameLen])
		offset += nameLen

		metrics = append(metrics, m)
	}

	return metrics, nil
}