package nwsync

import (
	"crypto/sha1"
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
)

// AssembleOptions describes one merged manifest.
type AssembleOptions struct {
	Order       []string // artifact names, highest priority first
	EntriesDir  string   // directory holding <name>.nsym and <name>.nsym.json
	OutDir      string   // repository root; the manifest lands in <out>/manifests
	GroupID     int      // 1 = current, 2 = testing; 0 means absent
	ModuleName  string
	Description string
}

// AssembleResult reports what one assemble run produced.
type AssembleResult struct {
	SHA1         string
	ManifestPath string
	Entries      int
}

// Assemble merges the per-artifact NSYM manifests named by Order into one
// manifest. It reads no bulk data at all — only the small index files.
//
// Merge rule is resref shadowing, not concatenation: a resref present in more
// than one artifact resolves to the earliest artifact in Order, which is how
// the game resolves it (upstream's resman adds haks in reverse and lets the
// last one win). Get this backwards and the wrong texture ships silently.
func Assemble(options AssembleOptions) (AssembleResult, error) {
	if len(options.Order) == 0 {
		return AssembleResult{}, fmt.Errorf("assemble: --order names no artifacts")
	}

	type key struct {
		resref  string
		restype uint16
	}
	merged := make([]Entry, 0, 1024)
	winner := make(map[key]bool, 1024)
	var onDiskBytes int64
	emitterVersion := ""
	emitterSource := ""

	for _, name := range options.Order {
		manifestPath := filepath.Join(options.EntriesDir, name+".nsym")
		data, err := os.ReadFile(manifestPath)
		if err != nil {
			return AssembleResult{}, fmt.Errorf("assemble: no index for %q: %w", name, err)
		}
		entries, err := readManifest(data)
		if err != nil {
			return AssembleResult{}, fmt.Errorf("%s: %w", manifestPath, err)
		}
		sidecar, err := readSidecar(manifestPath + ".json")
		if err != nil {
			return AssembleResult{}, err
		}
		// Two producers of blobs means a skewed emitter can write blobs the
		// merged manifest quietly disagrees with. Refuse to merge across
		// mismatched emitter versions.
		if emitterVersion == "" {
			emitterVersion, emitterSource = sidecar.CreatedWith, name
		} else if sidecar.CreatedWith != emitterVersion {
			return AssembleResult{}, fmt.Errorf(
				"assemble: emitter version mismatch: %s was emitted with %q, %s with %q",
				emitterSource, emitterVersion, name, sidecar.CreatedWith)
		}
		// on_disk_bytes overcounts by the handful of cross-artifact
		// duplicates. It is a display statistic; no dedupe pass for it.
		onDiskBytes += sidecar.OnDiskBytes

		for _, entry := range entries {
			identity := key{resref: entry.ResRef, restype: entry.ResType}
			if winner[identity] {
				continue
			}
			winner[identity] = true
			merged = append(merged, entry)
		}
	}

	if len(merged) == 0 {
		return AssembleResult{}, fmt.Errorf("assemble: merged manifest is empty")
	}

	data, err := writeManifest(merged)
	if err != nil {
		return AssembleResult{}, err
	}
	sha1Hex := fmt.Sprintf("%x", sha1.Sum(data))
	manifestPath := filepath.Join(options.OutDir, "manifests", sha1Hex)
	sidecar := Sidecar{
		ModuleName:  options.ModuleName,
		Description: options.Description,
		GroupID:     options.GroupID,
	}
	if err := writeManifestPair(manifestPath, data, merged, onDiskBytes, sidecar); err != nil {
		return AssembleResult{}, err
	}
	return AssembleResult{SHA1: sha1Hex, ManifestPath: manifestPath, Entries: len(merged)}, nil
}

func readSidecar(path string) (Sidecar, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return Sidecar{}, fmt.Errorf("assemble: missing sidecar: %w", err)
	}
	var sidecar Sidecar
	if err := json.Unmarshal(data, &sidecar); err != nil {
		return Sidecar{}, fmt.Errorf("%s: %w", path, err)
	}
	return sidecar, nil
}