// Package statusfile mirrors the controller's runtime status into a single-line
// file (~/.antidrift_status) so an external consumer — a window-manager status
// bar — can display it with a plain file read.
package statusfile

import (
	"context"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"time"

	"antidrift/internal/domain"
	"antidrift/internal/session"
)

// statusFileName is the file written under the user's home directory.
const statusFileName = ".antidrift_status"

// interval is how often the writer re-renders. Minute granularity is enough for
// a status bar, so a coarse tick keeps the write rate (and disk churn) low.
const interval = time.Minute

// DefaultPath resolves ~/.antidrift_status.
func DefaultPath() (string, error) {
	home, err := os.UserHomeDir()
	if err != nil {
		return "", err
	}
	return filepath.Join(home, statusFileName), nil
}

// Render produces the single status line for the given state. It is empty for
// Locked/idle so a bar module can hide itself. Drift status strings ("drifting")
// match the JSON contract the web UI already consumes.
func Render(st session.State, now time.Time) string {
	switch st.RuntimeState {
	case domain.RuntimeActive:
		timer := remaining(st, now)
		switch {
		case st.Drift != nil && st.Drift.Status == "drifting":
			return "⚠ DRIFT " + timer
		case st.Drift != nil && st.Drift.Nudge != "":
			return "● " + timer + " ·?"
		default:
			return "● " + timer
		}
	case domain.RuntimePlanning:
		return "◔ planning"
	case domain.RuntimeReview:
		return "✓ review"
	default:
		return ""
	}
}

// remaining formats the minutes left until the commitment deadline, rounded up
// so a partial minute still reads as a minute and the count hits 0m only at the
// end. It returns 0m when no deadline is known.
func remaining(st session.State, now time.Time) string {
	if st.Commitment == nil || st.Commitment.DeadlineUnixSecs == 0 {
		return "0m"
	}
	left := time.Unix(st.Commitment.DeadlineUnixSecs, 0).Sub(now)
	if left < 0 {
		left = 0
	}
	mins := int((left + time.Minute - 1) / time.Minute) // ceil
	return fmt.Sprintf("%dm", mins)
}

// Writer periodically renders the controller state and writes it to a file,
// rewriting only when the line changes.
type Writer struct {
	path  string
	state func() session.State
	now   func() time.Time

	last  string
	wrote bool
}

// NewWriter builds a Writer for path, reading state via the given accessor.
func NewWriter(path string, state func() session.State) *Writer {
	return &Writer{path: path, state: state, now: time.Now}
}

// Run writes the status file immediately, then on every tick when the rendered
// line has changed. It removes the file on ctx cancellation so a stale status
// does not linger after shutdown.
func (w *Writer) Run(ctx context.Context) {
	t := time.NewTicker(interval)
	defer t.Stop()
	w.write()
	for {
		select {
		case <-ctx.Done():
			_ = os.Remove(w.path)
			return
		case <-t.C:
			w.write()
		}
	}
}

func (w *Writer) write() {
	line := Render(w.state(), w.now())
	if w.wrote && line == w.last {
		return
	}
	if err := os.WriteFile(w.path, []byte(line), 0o644); err != nil {
		log.Printf("statusfile: write %s: %v", w.path, err)
		return
	}
	w.last = line
	w.wrote = true
}