// Copyright 2016-2018, Pulumi Corporation.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package main

import (
	"context"
	"encoding/json"
	"flag"
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"syscall"

	pbempty "github.com/golang/protobuf/ptypes/empty"
	"github.com/pkg/errors"
	"google.golang.org/grpc"

	"github.com/pulumi/pulumi/pkg/util/cmdutil"
	"github.com/pulumi/pulumi/pkg/util/logging"
	"github.com/pulumi/pulumi/pkg/util/rpcutil"
	"github.com/pulumi/pulumi/pkg/version"
	"github.com/pulumi/pulumi/sdk/go/pulumi"
	pulumirpc "github.com/pulumi/pulumi/sdk/proto/go"
)

// Launches the language host, which in turn fires up an RPC server implementing the LanguageRuntimeServer endpoint.
func main() {
	var tracing string
	flag.StringVar(&tracing, "tracing", "", "Emit tracing to a Zipkin-compatible tracing endpoint")

	flag.Parse()
	args := flag.Args()
	logging.InitLogging(false, 0, false)
	cmdutil.InitTracing("pulumi-language-go", "pulumi-language-go", tracing)

	// Pluck out the engine so we can do logging, etc.
	if len(args) == 0 {
		cmdutil.Exit(errors.New("missing required engine RPC address argument"))
	}
	engineAddress := args[0]

	// Fire up a gRPC server, letting the kernel choose a free port.
	port, done, err := rpcutil.Serve(0, nil, []func(*grpc.Server) error{
		func(srv *grpc.Server) error {
			host := newLanguageHost(engineAddress, tracing)
			pulumirpc.RegisterLanguageRuntimeServer(srv, host)
			return nil
		},
	}, nil)
	if err != nil {
		cmdutil.Exit(errors.Wrapf(err, "could not start language host RPC server"))
	}

	// Otherwise, print out the port so that the spawner knows how to reach us.
	fmt.Printf("%d\n", port)

	// And finally wait for the server to stop serving.
	if err := <-done; err != nil {
		cmdutil.Exit(errors.Wrapf(err, "language host RPC stopped serving"))
	}
}

// goLanguageHost implements the LanguageRuntimeServer interface for use as an API endpoint.
type goLanguageHost struct {
	engineAddress string
	tracing       string
}

func newLanguageHost(engineAddress, tracing string) pulumirpc.LanguageRuntimeServer {
	return &goLanguageHost{
		engineAddress: engineAddress,
		tracing:       tracing,
	}
}

// GetRequiredPlugins computes the complete set of anticipated plugins required by a program.
func (host *goLanguageHost) GetRequiredPlugins(ctx context.Context,
	req *pulumirpc.GetRequiredPluginsRequest) (*pulumirpc.GetRequiredPluginsResponse, error) {
	return &pulumirpc.GetRequiredPluginsResponse{}, nil
}

const unableToFindProgramTemplate = "unable to find program: %s"

// findProgram attempts to find the needed program in various locations on the
// filesystem, eventually resorting to searching in $PATH.
func findProgram(program string) (string, error) {

	// look in the same directory
	cwd, err := os.Getwd()
	if err != nil {
		return "", errors.Wrap(err, "unable to get current working directory")
	}

	cwdProgram := filepath.Join(cwd, program)
	if fileInfo, err := os.Stat(cwdProgram); !os.IsNotExist(err) && !fileInfo.Mode().IsDir() {
		logging.V(5).Infof("program %s found in CWD", program)
		return cwdProgram, nil
	}

	// look in $GOPATH/bin
	if goPath := os.Getenv("GOPATH"); len(goPath) > 0 {
		goPathProgram := filepath.Join(goPath, "bin", program)
		if fileInfo, err := os.Stat(goPathProgram); !os.IsNotExist(err) && !fileInfo.Mode().IsDir() {
			logging.V(5).Infof("program %s found in $GOPATH/bin", program)
			return goPathProgram, nil
		}
	}

	// look in the $PATH somewhere
	if fullPath, err := exec.LookPath(program); err == nil {
		logging.V(5).Infof("program %s found in $PATH", program)
		return fullPath, nil
	}

	return "", errors.Errorf(unableToFindProgramTemplate, program)
}

// RPC endpoint for LanguageRuntimeServer::Run
func (host *goLanguageHost) Run(ctx context.Context, req *pulumirpc.RunRequest) (*pulumirpc.RunResponse, error) {
	// Create the environment we'll use to run the process.  This is how we pass the RunInfo to the actual
	// Go program runtime, to avoid needing any sort of program interface other than just a main entrypoint.
	env, err := host.constructEnv(req)
	if err != nil {
		return nil, errors.Wrap(err, "failed to prepare environment")
	}

	// by default we try to run a named executable on the path, but we will fallback to 'go run' style execution
	goRunInvoke := false

	// The program to execute is simply the name of the project.  This ensures good Go toolability, whereby
	// you can simply run `go install .` to build a Pulumi program prior to running it, among other benefits.
	// For ease of use, if we don't find a pre-built program, we attempt to invoke via 'go run' on behalf of the user.
	program, err := findProgram(req.GetProject())
	if err != nil {
		const message = "problem executing program (could not run language executor)"
		if err.Error() == fmt.Sprintf(unableToFindProgramTemplate, req.GetProject()) {
			logging.V(5).Infof("Unable to find program %s in $PATH, attempting invocation via 'go run'", program)
			program, err = findProgram("go")
			if err != nil {
				return nil, errors.Wrap(err, message)
			}
			goRunInvoke = true
		} else {
			return nil, errors.Wrap(err, message)
		}
	}

	logging.V(5).Infof("language host launching process: %s", program)

	// Now simply spawn a process to execute the requested program, wiring up stdout/stderr directly.
	var errResult string
	var cmd *exec.Cmd

	if goRunInvoke {
		cwd, err := os.Getwd()
		if err != nil {
			return nil, errors.Wrap(err, "unable to get current working directory")
		}

		goFileSearchPattern := filepath.Join(cwd, "*.go")
		if matches, err := filepath.Glob(goFileSearchPattern); err != nil || len(matches) == 0 {
			return nil, errors.Errorf("Failed to find go files for 'go run' matching %s", goFileSearchPattern)
		}

		args := []string{"run", cwd}
		// go run $cwd
		cmd = exec.Command(program, args...)
	} else {
		cmd = exec.Command(program)
	}

	cmd.Env = env
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	if err := cmd.Run(); err != nil {
		if exiterr, ok := err.(*exec.ExitError); ok {
			// If the program ran, but exited with a non-zero error code.  This will happen often, since user
			// errors will trigger this.  So, the error message should look as nice as possible.
			if status, stok := exiterr.Sys().(syscall.WaitStatus); stok {
				err = errors.Errorf("program exited with non-zero exit code: %d", status.ExitStatus())
			} else {
				err = errors.Wrapf(exiterr, "program exited unexpectedly")
			}
		} else {
			// Otherwise, we didn't even get to run the program.  This ought to never happen unless there's
			// a bug or system condition that prevented us from running the language exec.  Issue a scarier error.
			err = errors.Wrapf(err, "problem executing program (could not run language executor)")
		}

		errResult = err.Error()
	}

	return &pulumirpc.RunResponse{Error: errResult}, nil
}

// constructEnv constructs an environment for a Go progam by enumerating all of the optional and non-optional
// arguments present in a RunRequest.
func (host *goLanguageHost) constructEnv(req *pulumirpc.RunRequest) ([]string, error) {
	config, err := host.constructConfig(req)
	if err != nil {
		return nil, err
	}

	env := os.Environ()
	maybeAppendEnv := func(k, v string) {
		if v != "" {
			env = append(env, fmt.Sprintf("%s=%s", k, v))
		}
	}

	maybeAppendEnv(pulumi.EnvProject, req.GetProject())
	maybeAppendEnv(pulumi.EnvStack, req.GetStack())
	maybeAppendEnv(pulumi.EnvConfig, config)
	maybeAppendEnv(pulumi.EnvDryRun, fmt.Sprintf("%v", req.GetDryRun()))
	maybeAppendEnv(pulumi.EnvParallel, fmt.Sprint(req.GetParallel()))
	maybeAppendEnv(pulumi.EnvMonitor, req.GetMonitorAddress())
	maybeAppendEnv(pulumi.EnvEngine, host.engineAddress)

	return env, nil
}

// constructConfig JSON-serializes the configuration data given as part of a RunRequest.
func (host *goLanguageHost) constructConfig(req *pulumirpc.RunRequest) (string, error) {
	configMap := req.GetConfig()
	if configMap == nil {
		return "", nil
	}

	configJSON, err := json.Marshal(configMap)
	if err != nil {
		return "", err
	}

	return string(configJSON), nil
}

func (host *goLanguageHost) GetPluginInfo(ctx context.Context, req *pbempty.Empty) (*pulumirpc.PluginInfo, error) {
	return &pulumirpc.PluginInfo{
		Version: version.Version,
	}, nil
}
