package stage

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strings"

	"gitea.maximumdirect.net/eric/narratio/internal/artifacts"
	"gitea.maximumdirect.net/eric/narratio/internal/config"
	"gitea.maximumdirect.net/eric/narratio/internal/manifest"
	"gopkg.in/yaml.v3"
)

type prepareStage struct{}

func (prepareStage) Name() string { return "prepare" }

func (prepareStage) Declares() IODecl {
	return IODecl{
		Inputs: []artifacts.Ref{
			{Kind: "config", Category: "inputs", RelativePath: "session.yml"},
			{Kind: "config", Category: "inputs", RelativePath: "pipeline.resolved.yml"},
			{Kind: "config", Category: "inputs", RelativePath: "speakers.yml"},
			{Kind: "config", Category: "inputs", RelativePath: "autocorrect.yml"},
			{Kind: "config", Category: "inputs", RelativePath: "glossary.yml"},
			{Kind: "audio", Category: "audio", RelativePath: "*.flac"},
		},
	}
}

func (prepareStage) Run(_ context.Context, env *Env, m *manifest.Manifest) (*StageResult, error) {
	if env == nil || env.Config == nil {
		return nil, fmt.Errorf("prepare: stage environment config is required")
	}
	if env.ArtifactStore == nil {
		return nil, fmt.Errorf("prepare: artifact store is required")
	}
	if env.Config.Session == nil || env.Config.Pipeline == nil {
		return nil, fmt.Errorf("prepare: resolved config must include pipeline and session")
	}

	sessionID := strings.TrimSpace(m.SessionID)
	if sessionID == "" {
		sessionID = strings.TrimSpace(env.Config.Session.SessionID)
	}
	if sessionID == "" {
		return nil, fmt.Errorf("prepare: session id is required")
	}

	paths, err := env.ArtifactStore.EnsureLayout(sessionID)
	if err != nil {
		return nil, fmt.Errorf("prepare: ensure workdir layout: %w", err)
	}

	sessionSrc := env.Config.SessionPath
	if err := requireFile(sessionSrc, "session.yml"); err != nil {
		return nil, fmt.Errorf("prepare: %w", err)
	}
	sessionDir := filepath.Dir(sessionSrc)

	speakersSrc, err := resolvePath(sessionDir, env.Config.Session.Inputs.SpeakersFile)
	if err != nil {
		return nil, fmt.Errorf("prepare: speakers path: %w", err)
	}
	autocorrectSrc, err := resolvePath(sessionDir, env.Config.Session.Inputs.AutocorrectFile)
	if err != nil {
		return nil, fmt.Errorf("prepare: autocorrect path: %w", err)
	}
	glossarySrc, err := resolvePath(sessionDir, env.Config.Session.Inputs.GlossaryFile)
	if err != nil {
		return nil, fmt.Errorf("prepare: glossary path: %w", err)
	}

	for _, required := range []struct {
		path string
		name string
	}{
		{path: speakersSrc, name: "speakers.yml"},
		{path: autocorrectSrc, name: "autocorrect.yml"},
		{path: glossarySrc, name: "glossary.yml"},
	} {
		if err := requireFile(required.path, required.name); err != nil {
			return nil, fmt.Errorf("prepare: %w", err)
		}
	}

	resolvedAudio, err := resolveAudioFiles(sessionDir, env.Config.Session.Inputs)
	if err != nil {
		return nil, fmt.Errorf("prepare: resolve audio inputs: %w", err)
	}

	copiedByDest := map[string]string{}
	inputs := make([]manifest.InputRecord, 0, 5+len(resolvedAudio))
	registerInput := func(kind, path, checksum string) {
		inputs = append(inputs, manifest.InputRecord{Kind: kind, Path: path, Checksum: checksum})
	}

	sessionDst := filepath.Join(paths.InputsDir, "session.yml")
	sessionChecksum, err := copyFileIfChanged(env.ArtifactStore, sessionSrc, sessionDst)
	if err != nil {
		return nil, fmt.Errorf("prepare: materialize session.yml: %w", err)
	}
	registerInput("session_config", sessionDst, sessionChecksum)

	pipelineResolvedBytes, err := renderResolvedPipeline(env.Config.Pipeline)
	if err != nil {
		return nil, fmt.Errorf("prepare: render pipeline.resolved.yml: %w", err)
	}
	pipelineDst := filepath.Join(paths.InputsDir, "pipeline.resolved.yml")
	pipelineChecksum, err := writeBytesIfChanged(env.ArtifactStore, pipelineDst, pipelineResolvedBytes)
	if err != nil {
		return nil, fmt.Errorf("prepare: materialize pipeline.resolved.yml: %w", err)
	}
	registerInput("pipeline_resolved", pipelineDst, pipelineChecksum)

	for _, cfgFile := range []struct {
		kind string
		src  string
		dst  string
	}{
		{kind: "speakers", src: speakersSrc, dst: filepath.Join(paths.InputsDir, "speakers.yml")},
		{kind: "autocorrect", src: autocorrectSrc, dst: filepath.Join(paths.InputsDir, "autocorrect.yml")},
		{kind: "glossary", src: glossarySrc, dst: filepath.Join(paths.InputsDir, "glossary.yml")},
	} {
		checksum, err := copyFileIfChanged(env.ArtifactStore, cfgFile.src, cfgFile.dst)
		if err != nil {
			return nil, fmt.Errorf("prepare: materialize %s: %w", cfgFile.kind, err)
		}
		registerInput(cfgFile.kind, cfgFile.dst, checksum)
	}

	for _, src := range resolvedAudio {
		base := filepath.Base(src)
		if prev, exists := copiedByDest[base]; exists && prev != src {
			return nil, fmt.Errorf("prepare: duplicate audio basename %q from %q and %q", base, prev, src)
		}
		copiedByDest[base] = src

		dst := filepath.Join(paths.AudioDir, base)
		checksum, err := copyFileIfChanged(env.ArtifactStore, src, dst)
		if err != nil {
			return nil, fmt.Errorf("prepare: materialize audio %q: %w", base, err)
		}
		registerInput("audio", dst, checksum)
	}

	sort.Slice(inputs, func(i, j int) bool {
		if inputs[i].Kind != inputs[j].Kind {
			return inputs[i].Kind < inputs[j].Kind
		}
		return inputs[i].Path < inputs[j].Path
	})
	m.Inputs = inputs

	return &StageResult{
		Metadata: map[string]any{
			"prepared":             true,
			"stage":                "prepare",
			"inputs_count":         len(inputs),
			"audio_files_resolved": len(resolvedAudio),
		},
	}, nil
}

func renderResolvedPipeline(cfg *config.PipelineConfig) ([]byte, error) {
	return yaml.Marshal(cfg)
}

func resolveAudioFiles(sessionDir string, inputs config.SessionInputsConfig) ([]string, error) {
	if len(inputs.AudioFiles) > 0 {
		out := make([]string, 0, len(inputs.AudioFiles))
		for _, p := range inputs.AudioFiles {
			resolved, err := resolvePath(sessionDir, p)
			if err != nil {
				return nil, err
			}
			if !isFlac(resolved) {
				return nil, fmt.Errorf("audio file %q must have .flac extension", resolved)
			}
			if err := requireFile(resolved, "audio file"); err != nil {
				return nil, err
			}
			out = append(out, resolved)
		}
		sort.Strings(out)
		return out, nil
	}

	audioDir, err := resolvePath(sessionDir, inputs.AudioDir)
	if err != nil {
		return nil, err
	}
	entries, err := os.ReadDir(audioDir)
	if err != nil {
		return nil, fmt.Errorf("read audio directory %q: %w", audioDir, err)
	}

	out := make([]string, 0)
	for _, entry := range entries {
		if entry.IsDir() {
			continue
		}
		name := entry.Name()
		full := filepath.Join(audioDir, name)
		if !isFlac(full) {
			continue
		}
		if err := requireFile(full, "audio file"); err != nil {
			return nil, err
		}
		out = append(out, full)
	}

	if len(out) == 0 {
		return nil, fmt.Errorf("no .flac files found in audio directory %q", audioDir)
	}
	sort.Strings(out)
	return out, nil
}

func resolvePath(baseDir, p string) (string, error) {
	trimmed := strings.TrimSpace(p)
	if trimmed == "" {
		return "", fmt.Errorf("path is required")
	}
	if filepath.IsAbs(trimmed) {
		return filepath.Clean(trimmed), nil
	}
	return filepath.Clean(filepath.Join(baseDir, trimmed)), nil
}

func requireFile(path string, label string) error {
	if strings.TrimSpace(path) == "" {
		return fmt.Errorf("%s path is required", label)
	}
	info, err := os.Stat(path)
	if err != nil {
		return fmt.Errorf("%s %q not found: %w", label, path, err)
	}
	if info.IsDir() {
		return fmt.Errorf("%s %q is a directory", label, path)
	}
	return nil
}

func isFlac(path string) bool {
	return strings.EqualFold(filepath.Ext(path), ".flac")
}

func copyFileIfChanged(store artifacts.Store, src, dst string) (string, error) {
	srcChecksum, err := store.Checksum(src)
	if err != nil {
		return "", err
	}

	exists, err := store.Exists(dst)
	if err != nil {
		return "", err
	}
	if exists {
		dstChecksum, err := store.Checksum(dst)
		if err != nil {
			return "", err
		}
		if dstChecksum == srcChecksum {
			return srcChecksum, nil
		}
	}

	data, err := os.ReadFile(src)
	if err != nil {
		return "", err
	}
	if err := store.WriteFileAtomic(dst, data, 0o644); err != nil {
		return "", err
	}
	return srcChecksum, nil
}

func writeBytesIfChanged(store artifacts.Store, dst string, data []byte) (string, error) {
	digest := sha256.Sum256(data)
	targetChecksum := hex.EncodeToString(digest[:])

	exists, err := store.Exists(dst)
	if err != nil {
		return "", err
	}
	if exists {
		dstChecksum, err := store.Checksum(dst)
		if err != nil {
			return "", err
		}
		if dstChecksum == targetChecksum {
			return targetChecksum, nil
		}
	}

	if err := store.WriteFileAtomic(dst, data, 0o644); err != nil {
		return "", err
	}
	return targetChecksum, nil
}