// Copyright 2022 The Go 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 worker

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"os"
	"os/exec"
	"path"
	"path/filepath"
	"strings"

	"cloud.google.com/go/storage"
	"golang.org/x/pkgsite-metrics/internal/derrors"
	"golang.org/x/pkgsite-metrics/internal/log"
	"golang.org/x/pkgsite-metrics/internal/modules"
	"golang.org/x/pkgsite-metrics/internal/queue"
	"golang.org/x/pkgsite-metrics/internal/scan"
)

type analysisServer struct {
	*Server
}

type analysisRequest struct {
	scan.ModuleURLPath
	analysisParams
}

// analysisRequest implements queue.Task so it can be put on a TaskQueue.
var _ queue.Task = (*analysisRequest)(nil)

type analysisParams struct {
	Binary     string // name of analysis binary to run
	Args       string // command-line arguments to binary; split on whitespace
	ImportedBy int    // imported-by count of module in path
	Insecure   bool   // if true, run outside sandbox
	Serve      bool   // serve results back to client instead of writing them to BigQuery
}

func (r *analysisRequest) Name() string { return r.Binary + "_" + r.Module + "@" + r.Version }

func (r *analysisRequest) Path() string { return r.ModuleURLPath.Path() }

func (r *analysisRequest) Params() string {
	return scan.FormatParams(r.analysisParams)
}

func parseAnalysisRequest(r *http.Request, prefix string) (*analysisRequest, error) {
	mp, err := scan.ParseModuleURLPath(strings.TrimPrefix(r.URL.Path, prefix))
	if err != nil {
		return nil, err
	}

	ap := analysisParams{}
	if err := scan.ParseParams(r, &ap); err != nil {
		return nil, err
	}
	return &analysisRequest{
		ModuleURLPath:  mp,
		analysisParams: ap,
	}, nil
}

const analysisBinariesBucketDir = "analysis-binaries"

func (s *analysisServer) handleScan(w http.ResponseWriter, r *http.Request) (err error) {
	defer derrors.Wrap(&err, "analysisServer.handleScan")

	if s.cfg.BinaryBucket != "" {
		return errors.New("binary bucket not configured; set GO_ECOSYSTEM_BINARY_BUCKET")
	}

	ctx := r.Context()
	req, err := parseAnalysisRequest(r, "/analysis/scan")
	if err != nil {
		return fmt.Errorf("%w: %v", derrors.InvalidArgument, err)
	}
	jsonTree, err := s.scan(ctx, req)
	if err != nil {
		return err
	}
	out, err := json.Marshal(jsonTree)
	if err != nil {
		return err
	}
	_, err = w.Write(out)
	return err
}

func (s *analysisServer) scan(ctx context.Context, req *analysisRequest) (_ JSONTree, err error) {
	if req.Binary == "" {
		return nil, fmt.Errorf("%w: analysis: missing binary", derrors.InvalidArgument)
	}
	if !req.Insecure {
		return nil, fmt.Errorf("%w: analysis: sandbox mode unimplemented", derrors.InvalidArgument)
	}
	if !req.Serve {
		return nil, fmt.Errorf("%w: analysis: writing to BigQuery unimplemented", derrors.InvalidArgument)
	}
	if req.Suffix != "" {
		return nil, fmt.Errorf("%w: analysis: only implemented for whole modules (no suffix)", derrors.InvalidArgument)
	}

	// Copy the binary from the bucket.
	c, err := storage.NewClient(ctx)
	if err != nil {
		return nil, err
	}
	bucket := c.Bucket(s.cfg.BinaryBucket)
	const destDir = "/bundle/rootfs/binaries"
	binaryPath := filepath.Join(filepath.FromSlash(destDir), req.Binary)
	if err := copyFromGCS(ctx, bucket, path.Join(analysisBinariesBucketDir, req.Binary), binaryPath); err != nil {
		return nil, err
	}

	// Download the module.
	tempDir, err := os.MkdirTemp("", "analysis")
	if err != nil {
		return nil, err
	}
	defer func() {
		err1 := os.RemoveAll(tempDir)
		if err == nil {
			err = err1
		}
	}()

	log.Debugf(ctx, "fetching module zip: %s@%s", req.Module, req.Version)
	const stripModulePrefix = true
	if err := modules.Download(ctx, req.Module, req.Version, tempDir, s.proxyClient, stripModulePrefix); err != nil {
		return nil, err
	}

	return runAnalysisBinary(binaryPath, req.Args, tempDir)
}

// Run the binary on the module.
func runAnalysisBinary(binaryPath, reqArgs, moduleDir string) (JSONTree, error) {
	args := []string{"-json"}
	args = append(args, strings.Fields(reqArgs)...)
	args = append(args, "./...")
	cmd := exec.Command(binaryPath, args...)
	cmd.Dir = moduleDir
	out, err := cmd.Output()
	if err != nil {
		return nil, fmt.Errorf("running analysis binary %s: %s", binaryPath, derrors.IncludeStderr(err))
	}
	var tree JSONTree
	if err := json.Unmarshal(out, &tree); err != nil {
		return nil, err
	}
	return tree, nil
}

type diagnosticsOrError struct {
	Diagnostics []JSONDiagnostic
	Error       *jsonError
}

func (de *diagnosticsOrError) UnmarshalJSON(data []byte) error {
	if err := json.Unmarshal(data, &de.Diagnostics); err == nil {
		return nil
	}
	return json.Unmarshal(data, &de.Error)
}

////////////////////////////////////////////////////////////////

// These structs were copied, with minor changes, from
// golang.org/x/tools/go/analysis/internal/analysisflags.

// A JSONTree is a mapping from package ID to analysis name to result.
// Each result is either a jsonError or a list of JSONDiagnostic.
type JSONTree map[string]map[string]diagnosticsOrError

// A JSONDiagnostic can be used to encode and decode analysis.Diagnostics to and
// from JSON.
type JSONDiagnostic struct {
	Category       string             `json:"category,omitempty"`
	Posn           string             `json:"posn"`
	Message        string             `json:"message"`
	SuggestedFixes []JSONSuggestedFix `json:"suggested_fixes,omitempty"`
}

// A JSONSuggestedFix describes an edit that should be applied as a whole or not
// at all. It might contain multiple TextEdits/text_edits if the SuggestedFix
// consists of multiple non-contiguous edits.
type JSONSuggestedFix struct {
	Message string         `json:"message"`
	Edits   []JSONTextEdit `json:"edits"`
}

// A TextEdit describes the replacement of a portion of a file.
// Start and End are zero-based half-open indices into the original byte
// sequence of the file, and New is the new text.
type JSONTextEdit struct {
	Filename string `json:"filename"`
	Start    int    `json:"start"`
	End      int    `json:"end"`
	New      string `json:"new"`
}

type jsonError struct {
	Err string `json:"error"`
}