// Fenrir console screen reader.
// Copyright (c) 2026 Storm Dragon
// SPDX-License-Identifier: GPL-3.0-or-later
//
// This program is free software: you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by the Free
// Software Foundation, either version 3 of the License, or (at your option)
// any later version.
//
// This program is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
// more details.
//
// You should have received a copy of the GNU General Public License along with
// this program. If not, see <https://www.gnu.org/licenses/gpl-3.0.html>.

// Package sound plays preloaded cues through one persistent in-process stream.
package sound

import (
	"context"
	"errors"
	"fmt"
	"math"
	"os"
	"path/filepath"
	"strconv"
	"sync"
	"sync/atomic"
	"time"

	"github.com/jfreymuth/pulse"

	"git.stormux.org/storm/fenrir/internal/presentation"
)

type Service struct {
	clips            map[presentation.Cue]*clip
	pending          atomic.Pointer[clip]
	notification     atomic.Pointer[clip]
	draining         *notificationPlayback // audio callback owns this boundary
	tones            [101]*clip
	indentationTones [101]*clip
	progress         atomic.Pointer[clip]
	cancelProgress   atomic.Bool
	progressing      bool // audio callback owns this flag
	startup          atomic.Pointer[clip]
	closed           atomic.Bool
	finishing        atomic.Bool
	volume           atomic.Uint32 // float32 bits shared with the audio callback
	current          *clip         // audio callback owns current and offset
	offset           int
	starting         bool // audio callback keeps the startup cue through its last sample
	closeBackend     func()
	drainBackend     func(context.Context) error
	errors           chan error
	done             chan struct{}
	workers          sync.WaitGroup
}

// Open may return a usable service plus warnings for missing individual cues.
// Availability failures are nonfatal to speech and keyboard operation.
func Open(roots []string, options Options) (*Service, error) {
	if err := Validate_selection(options.Driver, options.Device); err != nil {
		return nil, err
	}
	volume := options.Volume
	if math.IsNaN(volume) || math.IsInf(volume, 0) || volume < 0 || volume > 1 {
		return nil, fmt.Errorf("sound volume must be between 0.0 and 1.0")
	}
	clips, warning := load_theme(roots)
	// Generated tones remain available even without an installed sound pack.
	s := &Service{clips: clips, tones: progress_clips(), indentationTones: indentation_clips(), errors: make(chan error, 1), done: make(chan struct{})}
	s.Set_volume(volume)
	driver, _ := Find_driver(options.Driver)
	if err := driver.open(s, options.Device); err != nil {
		return nil, errors.Join(warning, err)
	}
	return s, warning
}

func (s *Service) Errors() <-chan error { return s.errors }

// Set_volume applies a validated 0..1 gain to the next audio buffer, including
// any cue or progress tone already playing. Cached samples remain unchanged.
func (s *Service) Set_volume(volume float64) {
	s.volume.Store(math.Float32bits(float32(volume)))
}

// Server returns PulseAudio protocol addresses in connection order. The bundled
// PipeWire helper exposes /tmp/pulse.sock for console clients; system-wide
// PulseAudio services can expose /run/pulse/native.
// The client library tries each address, including after authentication errors.
func Server(explicit, sudoUID string) string {
	if explicit != "" {
		return explicit
	}
	runtimeDir := os.Getenv("XDG_RUNTIME_DIR")
	if uid, err := strconv.ParseUint(sudoUID, 10, 32); err == nil {
		runtimeDir = fmt.Sprintf("/run/user/%d", uid)
	} else if runtimeDir == "" {
		runtimeDir = fmt.Sprintf("/run/user/%d", os.Getuid())
	}
	return "unix:" + filepath.Join(runtimeDir, "pulse/native") + " unix:/tmp/pulse.sock unix:/run/pulse/native"
}

// Play only replaces a mailbox pointer. Startup has its own slot so initial
// screen feedback cannot replace it. Other cues retain only the latest request.
// Admission never waits for audio or touches the filesystem.
func (s *Service) Play(cue presentation.Cue) bool {
	if s == nil || s.closed.Load() || s.finishing.Load() {
		return false
	}
	if item := s.clips[cue]; item != nil {
		if cue == presentation.Ready {
			s.startup.Store(item)
		} else {
			s.pending.Store(item)
		}
		return true
	}
	return false
}

func (s *Service) read_samples(samples []float32) (int, error) {
	clear(samples)
	if s.closed.Load() {
		return len(samples), nil
	}
	// Notification cues retain their tail despite ordinary cue updates. Their
	// boundary drains the device before speech is released by Play_wait.
	if s.current != nil && s.current.notification != nil {
		request := s.current.notification
		if request.ctx.Err() != nil || s.finishing.Load() {
			s.offset = len(s.current.samples)
		}
		if s.offset == len(s.current.samples) {
			s.draining, s.current = request, nil
			return 0, errNotificationDrain
		}
		return s.copy_samples(samples)
	}
	if s.cancelProgress.Swap(false) && s.progressing {
		s.current, s.progressing = nil, false
	}
	if s.finishing.Load() {
		s.progress.Store(nil)
		s.startup.Store(nil)
		s.starting = false
	} else if next := s.startup.Swap(nil); next != nil {
		s.current, s.offset, s.starting, s.progressing = next, 0, true, false
	}
	if !s.starting {
		if next := s.notification.Swap(nil); next != nil && next.notification.ctx.Err() == nil && !s.finishing.Load() {
			s.current, s.offset, s.progressing = next, 0, false
		} else if next := s.pending.Swap(nil); next != nil {
			s.current, s.offset, s.progressing = next, 0, false
		}
	}
	if s.current == nil && !s.finishing.Load() {
		if next := s.progress.Swap(nil); next != nil {
			s.current, s.offset, s.progressing = next, 0, true
		}
	}
	if s.current != nil && s.offset == len(s.current.samples) && s.current.finished != nil {
		close(s.current.finished)
		s.current = nil
		return 0, pulse.EndOfData
	}
	return s.copy_samples(samples)
}

func (s *Service) copy_samples(samples []float32) (int, error) {
	if s.current != nil {
		count := copy(samples, s.current.samples[s.offset:])
		volume := math.Float32frombits(s.volume.Load())
		if s.progressing {
			volume *= progressGain
		}
		for index := range count {
			samples[index] *= volume
		}
		s.offset += count
		if s.offset == len(s.current.samples) && s.current.finished == nil && s.current.notification == nil {
			s.current = nil
			s.starting, s.progressing = false, false
		}
	}
	return len(samples), nil
}

// Finish is called after input/review admission stops and keyboards are
// released. Wait for the final cue's samples to be submitted, then drain the
// server before Close destroys the stream. Waiting is bounded by the clip's
// duration plus one second even when callbacks stop arriving.
func (s *Service) Finish(ctx context.Context) error {
	if s == nil || s.closed.Load() || s.finishing.Swap(true) {
		return nil
	}
	s.Clear_progress()
	item := s.clips[presentation.Stopped]
	if item == nil || math.Float32frombits(s.volume.Load()) == 0 {
		return nil
	}
	ctx, cancel := context.WithTimeout(ctx, time.Second+time.Duration(len(item.samples))*time.Second/(sampleRate*2))
	defer cancel()
	final := &clip{samples: item.samples, finished: make(chan struct{})}
	s.pending.Store(final)
	select {
	case <-final.finished:
		if s.drainBackend != nil {
			return s.drainBackend(ctx)
		}
		return nil
	case <-s.done:
		return nil
	case err := <-s.errors:
		return err
	case <-ctx.Done():
		return ctx.Err()
	}
}

func (s *Service) Close() {
	if s == nil || s.closed.Swap(true) {
		return
	}
	s.pending.Store(nil)
	s.notification.Store(nil)
	s.Clear_progress()
	s.startup.Store(nil)
	if s.done != nil {
		close(s.done)
	}
	s.workers.Wait()
	if s.closeBackend != nil {
		s.closeBackend()
	}
}