package state

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"sync"
	"time"
)

// State is the full persisted state of the daemon.
type State struct {
	Feeds []FeedState `json:"feeds"`
	Jobs  []Job       `json:"jobs"`
}

// FeedState holds per-feed metadata from HTTP responses.
type FeedState struct {
	URL          string `json:"url"`
	LastModified string `json:"last_modified,omitempty"`
	ETag         string `json:"etag,omitempty"`
}

// Job represents a download job with retry state.
type Job struct {
	FeedURL       string     `json:"feed_url"`
	EnclosureURL  string     `json:"enclosure_url"`
	DestPath      string     `json:"dest_path"`
	Status        string     `json:"status"`
	AttemptCount  int        `json:"attempt_count"`
	MaxRetries    int        `json:"max_retries"`
	NextAttemptAt *time.Time `json:"next_attempt_at,omitempty"` // nil means ready now
	Error         string     `json:"error,omitempty"`
	Duration      float64    `json:"duration,omitempty"` // expected media duration in seconds (YouTube)
}

// JobStatus values.
const (
	StatusPending     = "pending"
	StatusDownloading = "downloading"
	StatusRetrying    = "retrying"
	StatusDownloaded  = "downloaded"
	StatusFailed      = "failed"
	StatusSkipped     = "skipped" // resolved but excluded by start_date; never downloaded
)

// Manager provides thread-safe access to persisted state.
type Manager struct {
	mu    sync.Mutex
	path  string
	state *State
}

// NewManager creates a new state manager pointing at the given file path.
func NewManager(path string) (*Manager, error) {
	dir := filepath.Dir(path)
	if err := os.MkdirAll(dir, 0755); err != nil {
		return nil, fmt.Errorf("create state directory: %w", err)
	}
	return &Manager{path: path, state: &State{}}, nil
}

// Load reads the state file from disk. If it doesn't exist or is empty, returns an empty state.
func (m *Manager) Load() error {
	m.mu.Lock()
	defer m.mu.Unlock()

	data, err := os.ReadFile(m.path)
	if err != nil {
		if os.IsNotExist(err) {
			m.state = &State{}
			return nil
		}
		return fmt.Errorf("read state: %w", err)
	}

	if len(data) == 0 {
		m.state = &State{}
		return nil
	}

	var s State
	if err := json.Unmarshal(data, &s); err != nil {
		return fmt.Errorf("parse state: %w", err)
	}

	m.state = &s
	return nil
}

// Save atomically writes the current state to disk with pretty-printed JSON.
func (m *Manager) Save() error {
	m.mu.Lock()
	defer m.mu.Unlock()

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

	dir := filepath.Dir(m.path)
	tmpFile, err := os.CreateTemp(dir, ".rssd-state-*.tmp")
	if err != nil {
		return fmt.Errorf("create temp file: %w", err)
	}
	tmpName := tmpFile.Name()

	if _, err := tmpFile.Write(data); err != nil {
		tmpFile.Close()
		os.Remove(tmpName)
		return fmt.Errorf("write temp state: %w", err)
	}
	if err := tmpFile.Close(); err != nil {
		os.Remove(tmpName)
		return fmt.Errorf("close temp state: %w", err)
	}

	if err := os.Rename(tmpName, m.path); err != nil {
		os.Remove(tmpName)
		return fmt.Errorf("rename state file: %w", err)
	}

	return nil
}

// JobSnapshot is a copy of a Job suitable for read-only inspection.
type JobSnapshot struct {
	FeedURL       string
	EnclosureURL  string
	DestPath      string
	Status        string
	AttemptCount  int
	MaxRetries    int
	NextAttemptAt *time.Time // nil means ready now
	Error         string
	Duration      float64
}

// ForEachJob iterates over all jobs and calls fn for each one.
// The callback receives a pointer to a copy of the job (not the live state),
// so it must not modify fields. Use UpdateJob or AddJob for mutations.
// fn may perform I/O without risk of deadlock — the lock is released before
// any callback invocation.
func (m *Manager) ForEachJob(fn func(*JobSnapshot)) {
	m.mu.Lock()
	jobsCopy := make([]JobSnapshot, len(m.state.Jobs))
	for i := range m.state.Jobs {
		j := &m.state.Jobs[i]
		jobsCopy[i] = JobSnapshot{
			FeedURL:       j.FeedURL,
			EnclosureURL:  j.EnclosureURL,
			DestPath:      j.DestPath,
			Status:        j.Status,
			AttemptCount:  j.AttemptCount,
			MaxRetries:    j.MaxRetries,
			NextAttemptAt: j.NextAttemptAt,
			Error:         j.Error,
			Duration:      j.Duration,
		}
	}
	m.mu.Unlock()

	for i := range jobsCopy {
		fn(&jobsCopy[i])
	}
}

// State returns a copy of the current in-memory state for iteration.
func (m *Manager) State() *State {
	m.mu.Lock()
	defer m.mu.Unlock()
	return m.state
}

// AddJob adds a new download job if one with this enclosure URL doesn't already exist.
// duration is the expected media duration in seconds (0 = unknown, used for
// YouTube duration sanity checks). Returns true if the job was added.
func (m *Manager) AddJob(feedURL, enclosureURL, destPath string, maxRetries int, duration float64) bool {
	return m.addJob(feedURL, enclosureURL, destPath, StatusPending, maxRetries, duration)
}

// AddJobWithStatus adds a new job with an explicit initial status (used to
// record videos resolved but excluded by the start_date filter, so they are
// not re-resolved on every poll). Returns true if the job was added.
func (m *Manager) AddJobWithStatus(feedURL, enclosureURL, destPath, status string, duration float64) bool {
	return m.addJob(feedURL, enclosureURL, destPath, status, 0, duration)
}

func (m *Manager) addJob(feedURL, enclosureURL, destPath, status string, maxRetries int, duration float64) bool {
	m.mu.Lock()
	defer m.mu.Unlock()

	// Check if this enclosure URL already has a job.
	for _, j := range m.state.Jobs {
		if j.EnclosureURL == enclosureURL {
			return false // already exists
		}
	}

	job := Job{
		FeedURL:       feedURL,
		EnclosureURL:  enclosureURL,
		DestPath:      destPath,
		Status:        status,
		AttemptCount:  0,
		MaxRetries:    maxRetries,
		NextAttemptAt: nil,
		Error:         "",
		Duration:      duration,
	}

	m.state.Jobs = append(m.state.Jobs, job)
	return true
}

// UpdateJob finds a job by enclosure URL and applies the update function.
// Returns true if the job was found and updated.
func (m *Manager) UpdateJob(enclosureURL string, fn func(*Job)) bool {
	m.mu.Lock()
	defer m.mu.Unlock()

	for i := range m.state.Jobs {
		if m.state.Jobs[i].EnclosureURL == enclosureURL {
			fn(&m.state.Jobs[i])
			return true
		}
	}
	return false
}

// FindJobByURL returns a pointer to the job for the given enclosure URL, or nil.
func (m *Manager) FindJobByURL(enclosureURL string) *Job {
	m.mu.Lock()
	defer m.mu.Unlock()

	for i := range m.state.Jobs {
		if m.state.Jobs[i].EnclosureURL == enclosureURL {
			return &m.state.Jobs[i]
		}
	}
	return nil
}

// HasJob returns true if a job with the given enclosure URL exists.
func (m *Manager) HasJob(enclosureURL string) bool {
	m.mu.Lock()
	defer m.mu.Unlock()

	for _, j := range m.state.Jobs {
		if j.EnclosureURL == enclosureURL {
			return true
		}
	}
	return false
}

// FindFeedByURL returns the FeedState for a given feed URL, or nil.
func (m *Manager) FindFeedByURL(feedURL string) *FeedState {
	m.mu.Lock()
	defer m.mu.Unlock()

	for i := range m.state.Feeds {
		if m.state.Feeds[i].URL == feedURL {
			return &m.state.Feeds[i]
		}
	}
	return nil
}

// UpsertFeed adds or updates a feed's metadata (ETag, Last-Modified).
func (m *Manager) UpsertFeed(feedURL, lastModified, etag string) {
	m.mu.Lock()
	defer m.mu.Unlock()

	for i := range m.state.Feeds {
		if m.state.Feeds[i].URL == feedURL {
			m.state.Feeds[i].LastModified = lastModified
			m.state.Feeds[i].ETag = etag
			return
		}
	}

	m.state.Feeds = append(m.state.Feeds, FeedState{
		URL:          feedURL,
		LastModified: lastModified,
		ETag:         etag,
	})
}