// Copyright 2019 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 frontend

import (
	"context"
	"fmt"
	"strconv"
	"strings"

	"golang.org/x/pkgsite/internal"
	"golang.org/x/pkgsite/internal/postgres"
	"golang.org/x/pkgsite/internal/stdlib"
)

// ImportsDetails contains information for a package's imports.
type ImportsDetails struct {
	ModulePath string

	// ExternalImports is the collection of package imports that are not in
	// the Go standard library and are not part of the same module
	ExternalImports []string

	// InternalImports is an array of packages representing the package's
	// imports that are part of the same module.
	InternalImports []string

	// StdLib is an array of packages representing the package's imports
	// that are in the Go standard library.
	StdLib []string
}

// fetchImportsDetails fetches imports for the package version specified by
// pkgPath, modulePath and version from the database and returns a ImportsDetails.
func fetchImportsDetails(ctx context.Context, ds internal.DataSource, pkgPath, modulePath, resolvedVersion string) (_ *ImportsDetails, err error) {
	u, err := ds.GetUnit(ctx, &internal.UnitMeta{
		Path: pkgPath,
		ModuleInfo: internal.ModuleInfo{
			ModulePath: modulePath,
			Version:    resolvedVersion,
		},
	}, internal.WithImports)
	if err != nil {
		return nil, err
	}

	var externalImports, moduleImports, std []string
	for _, p := range u.Imports {
		if stdlib.Contains(p) {
			std = append(std, p)
		} else if strings.HasPrefix(p+"/", modulePath+"/") {
			moduleImports = append(moduleImports, p)
		} else {
			externalImports = append(externalImports, p)
		}
	}

	return &ImportsDetails{
		ModulePath:      modulePath,
		ExternalImports: externalImports,
		InternalImports: moduleImports,
		StdLib:          std,
	}, nil
}

// ImportedByDetails contains information for the collection of packages that
// import a given package.
type ImportedByDetails struct {
	// ModulePath is the module path for the package referenced on this page.
	ModulePath string

	// ImportedBy is the collection of packages that import the
	// given package and are not part of the same module.
	// They are organized into a tree of sections by prefix.
	ImportedBy []*Section

	// NumImportedByDisplay is the display text at the top of the imported by
	// tab section, which shows the imported by count and package limit.
	NumImportedByDisplay string

	// Total is the total number of importers.
	Total int
}

var (
	// tabImportedByLimit is the maximum number of importers displayed on the imported
	// by page.
	tabImportedByLimit = 20001
)

// fetchImportedByDetails fetches importers for the package version specified by
// path and version from the database and returns a ImportedByDetails.
func fetchImportedByDetails(ctx context.Context, ds internal.DataSource, pkgPath, modulePath string) (*ImportedByDetails, error) {
	db, ok := ds.(*postgres.DB)
	if !ok {
		// The proxydatasource does not support the imported by page.
		return nil, proxydatasourceNotSupportedErr()
	}

	importedBy, err := db.GetImportedBy(ctx, pkgPath, modulePath, tabImportedByLimit)
	if err != nil {
		return nil, err
	}
	numImportedBy, err := db.GetImportedByCount(ctx, pkgPath, modulePath)
	if err != nil {
		return nil, err
	}
	sections := Sections(importedBy, nextPrefixAccount)

	display := strconv.Itoa(numImportedBy)
	if numImportedBy >= tabImportedByLimit {
		display += fmt.Sprintf(" (displaying %d packages)", tabImportedByLimit-1)
	}
	return &ImportedByDetails{
		ModulePath:           modulePath,
		ImportedBy:           sections,
		NumImportedByDisplay: display,
		Total:                numImportedBy,
	}, nil
}