// Copyright 2019 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

package fxicfg

import (
	"context"
	"io/ioutil"
	"os"
	"path/filepath"

	"fuchsia.googlesource.com/infra/infra/fxicfg/builtins"
	"fuchsia.googlesource.com/infra/infra/fxicfg/loaders"
	"fuchsia.googlesource.com/infra/infra/fxicfg/state"
	"go.chromium.org/luci/starlark/starlarkproto"

	luci "go.chromium.org/luci/starlark/interpreter"
	"go.starlark.net/starlark"
)

const (
	// The default output directory, if one is not supplied.
	defaultOutputDir = "generated"
)

// Generate executes LUCI's starlark interpreter with Fuchsia packages and globals.
//
// `loader` is the root luci.Loader that knows how to load all client starlark
// files. `main` is the file to execute first.
//
// The interpreter maintains a state.State object that client code modifies. The resulting
// state is returned iff execution completed without error. Otherwise, an empty State is
// returned.
func Generate(loader luci.Loader, main string) (state.State, starlark.StringDict, error) {
	// load("@stdlib//..."): loads packages compiled into this go binary from starlark
	// sources in fxicfg/starlark/stdlib/...
	pkgs := loaders.EmbeddedLoader()

	// load("@proto//..."): loads fuchsia-specific protobuf modules.
	pkgs["proto"] = loaders.ProtoLoader()

	// load("//..."): loads client starlark modules.
	pkgs[luci.MainPkg] = loader

	// Proto predeclared provides builtin LUCI textproto functionality. These are included
	// in the global namespace of all starlark programs.
	predecl := make(starlark.StringDict)
	predecl["proto"] = starlarkproto.ProtoLib()["proto"]
	for k, v := range builtins.All() {
		predecl[k] = v
	}

	tm := state.ThreadModifier(*state.NewState())
	interp := luci.Interpreter{
		Predeclared: predecl,
		Packages:    pkgs,
		PreExec: func(th *starlark.Thread, pkg, path string) {
			tm.WriteTo(th)
		},
		PostExec: func(th *starlark.Thread, pkg, path string) {
			tm.ReadFrom(th)
		},
	}

	ctx := context.Background()
	if err := interp.Init(ctx); err != nil {
		return state.State{}, nil, err
	}
	globals, err := interp.ExecModule(ctx, luci.MainPkg, main)
	if err != nil {
		return state.State{}, nil, err
	}

	return tm.State(), globals, nil
}

func CommitState(s state.State) error {
	dir := s.OutputDir
	if dir == "" {
		dir = defaultOutputDir
	}
	if err := os.MkdirAll(dir, 0755); err != nil {
		return err
	}
	for k, v := range s.OutputFiles {
		path := filepath.Join(dir, k)
		if err := ioutil.WriteFile(path, v, 0644); err != nil {
			return err
		}
	}
	return nil
}