package buildstep

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

	"git.novox.be/novox/mesh-sdk/go/catalogue"
	"git.novox.be/novox/mesh-sdk/go/delivery"
	"git.novox.be/novox/mesh-sdk/go/forgekey"
)

// ModuleTree is what a merge holds of one module directory: its tree id, the sha256 of its module.json and the sha256
// of each lock file it has (go.sum, package-lock.json), from which the checker and the indexer take the module's inputs
// (novox/hq ADR 0484 clause 3).
type ModuleTree struct {
	Tree     string            `json:"tree"`
	Manifest string            `json:"manifest"`
	Locks    map[string]string `json:"locks,omitempty"`
	// Paths are, of a module whose every artifact names its paths, each named path's git object id at the commit; Tree
	// is then their delivery.NamedTree with Manifest (novox/hq ADR 0499 clause 2). Absent otherwise.
	Paths map[string]string `json:"paths,omitempty"`
}

var lockFiles = []string{"go.sum", "package-lock.json"}

// ModuleTrees are the trees, in commit, of every directory of the workspace dir that holds a module.json, by directory
// (the repository's root is "."); for a module whose every artifact names its paths, the named tree of those paths and
// their objects (novox/hq ADR 0499 clause 2). The workspace is at commit, so the manifests and the lock files are read from it. env is
// the environment git runs with (nil for none). Both build modules' fetch steps answer it for a merge.
func ModuleTrees(ctx context.Context, run forgekey.Runner, env []string, dir, commit string) (map[string]ModuleTree, error) {
	r := run(ctx, env, "git", "-C", dir, "ls-files", "--", "module.json", "*/module.json")
	if r.Status != 0 || r.Err != "" {
		return nil, fmt.Errorf("git ls-files: %s", firstLine(r.Err+" "+r.Stderr))
	}
	trees := map[string]ModuleTree{}
	for _, l := range strings.Split(r.Stdout, "\n") {
		if l = strings.TrimSpace(l); l == "" {
			continue
		}
		mdir := filepath.ToSlash(filepath.Dir(l))
		spec := commit + ":" + mdir
		if mdir == "." {
			spec = commit + "^{tree}"
		}
		t := run(ctx, env, "git", "-C", dir, "rev-parse", spec)
		if t.Status != 0 || t.Err != "" {
			return nil, fmt.Errorf("git rev-parse %s: %s", spec, firstLine(t.Err+" "+t.Stderr))
		}
		mt := ModuleTree{Tree: strings.TrimSpace(t.Stdout)}
		raw, err := os.ReadFile(filepath.Join(dir, filepath.FromSlash(l)))
		if err != nil {
			return nil, err
		}
		mt.Manifest = sha256Hex(raw)
		if err := narrow(ctx, run, env, dir, commit, mdir, raw, &mt); err != nil {
			return nil, err
		}
		for _, lock := range lockFiles {
			if raw, err := os.ReadFile(filepath.Join(dir, filepath.FromSlash(mdir), lock)); err == nil {
				if mt.Locks == nil {
					mt.Locks = map[string]string{}
				}
				mt.Locks[lock] = sha256Hex(raw)
			}
		}
		trees[mdir] = mt
	}
	return trees, nil
}

// narrow sets mt's Paths and its named Tree when the module's manifest names paths on every artifact (novox/hq ADR 0499
// clause 2): one `git ls-tree -z` gives each named path's object at commit. The merge preview reads the manifest here, as
// the indexer does, and no other build step reads paths from one (ADR 0495 clause 1). A manifest that does not parse
// is not narrowed: the indexer gives it none. A named path absent at commit fails, naming the module and the path.
func narrow(ctx context.Context, run forgekey.Runner, env []string, dir, commit, mdir string, raw []byte, mt *ModuleTree) error {
	m, err := catalogue.ParseManifest(raw)
	if err != nil {
		return nil
	}
	paths, every := m.NamedPaths()
	if !every {
		return nil
	}
	full := make([]string, len(paths))
	for i, p := range paths {
		full[i] = path.Join(mdir, p)
	}
	r := run(ctx, env, "git", append([]string{"-C", dir, "ls-tree", "-z", commit, "--"}, full...)...)
	if r.Status != 0 || r.Err != "" {
		return fmt.Errorf("git ls-tree %s of the module %s: %s", commit, mdir, firstLine(r.Err+" "+r.Stderr))
	}
	objects := map[string]string{}
	for _, l := range strings.Split(r.Stdout, "\x00") {
		meta, name, ok := strings.Cut(l, "\t")
		fields := strings.Fields(meta)
		if !ok || len(fields) != 3 {
			continue
		}
		objects[name] = fields[2]
	}
	mt.Paths = map[string]string{}
	for i, p := range paths {
		object := objects[full[i]]
		if object == "" {
			return fmt.Errorf("the module %s names the path %q, which is not in %s", mdir, p, commit)
		}
		mt.Paths[p] = object
	}
	named, err := delivery.NamedTree(mt.Manifest, mt.Paths)
	if err != nil {
		return fmt.Errorf("the module %s: %w", mdir, err)
	}
	mt.Tree = named
	return nil
}

func sha256Hex(b []byte) string { h := sha256.Sum256(b); return hex.EncodeToString(h[:]) }