// Copyright 2020 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 postgres

import (
	"context"
	"database/sql"
	"fmt"
	"path"
	"reflect"
	"sort"
	"strings"

	"github.com/lib/pq"
	"golang.org/x/pkgsite/internal/derrors"
	"golang.org/x/pkgsite/internal/licenses"
	"golang.org/x/pkgsite/internal/stdlib"
)

// GetLicenses returns the licenses that applies to the fullPath for the given module version.
// It returns an InvalidArgument error if the module path or version is invalid.
func (db *DB) GetLicenses(ctx context.Context, fullPath, modulePath, resolvedVersion string) (_ []*licenses.License, err error) {
	defer derrors.Wrap(&err, "GetLicenses(ctx, %q, %q, %q)", fullPath, modulePath, resolvedVersion)

	if fullPath == "" || resolvedVersion == "" {
		return nil, fmt.Errorf("neither fullpath nor resolvedVersion can be empty: %w", derrors.InvalidArgument)
	}
	query := `
		SELECT
			l.types,
			l.file_path,
			l.contents,
			l.coverage
		FROM
			licenses l
		INNER JOIN
			paths p
		ON
			p.module_id=l.module_id
		INNER JOIN
			modules m
		ON
			p.module_id=m.id
		WHERE
			p.path = $1
			AND m.module_path = $2
			AND m.version = $3;`

	rows, err := db.db.Query(ctx, query, fullPath, modulePath, resolvedVersion)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	moduleLicenses, err := collectLicenses(rows)
	if err != nil {
		return nil, err
	}

	// The `query` returns all licenses for the module version. We need to
	// filter the licenses that applies to the specified fullPath, i.e.
	// A license in the current or any parent directory of the specified
	// fullPath applies to it.
	var lics []*licenses.License
	for _, l := range moduleLicenses {
		if modulePath == stdlib.ModulePath {
			lics = append(lics, l)
		} else {
			licensePath := path.Join(modulePath, path.Dir(l.FilePath))
			if strings.HasPrefix(fullPath, licensePath) {
				lics = append(lics, l)
			}
		}
	}
	return lics, nil
}

// LegacyGetModuleLicenses returns all licenses associated with the given module path and
// version. These are the top-level licenses in the module zip file.
// It returns an InvalidArgument error if the module path or version is invalid.
func (db *DB) LegacyGetModuleLicenses(ctx context.Context, modulePath, version string) (_ []*licenses.License, err error) {
	defer derrors.Wrap(&err, "LegacyGetModuleLicenses(ctx, %q, %q)", modulePath, version)

	if modulePath == "" || version == "" {
		return nil, fmt.Errorf("neither modulePath nor version can be empty: %w", derrors.InvalidArgument)
	}
	query := `
	SELECT
		types, file_path, contents, coverage
	FROM
		licenses
	WHERE
		module_path = $1 AND version = $2 AND position('/' in file_path) = 0
    `
	rows, err := db.db.Query(ctx, query, modulePath, version)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	return collectLicenses(rows)
}

// LegacyGetPackageLicenses returns all licenses associated with the given package path and
// version.
// It returns an InvalidArgument error if the module path or version is invalid.
func (db *DB) LegacyGetPackageLicenses(ctx context.Context, pkgPath, modulePath, version string) (_ []*licenses.License, err error) {
	defer derrors.Wrap(&err, "LegacyGetPackageLicenses(ctx, %q, %q, %q)", pkgPath, modulePath, version)

	if pkgPath == "" || version == "" {
		return nil, fmt.Errorf("neither pkgPath nor version can be empty: %w", derrors.InvalidArgument)
	}
	query := `
		SELECT
			l.types,
			l.file_path,
			l.contents,
			l.coverage
		FROM
			licenses l
		INNER JOIN (
			SELECT DISTINCT ON (license_file_path)
				module_path,
				version,
				unnest(license_paths) AS license_file_path
			FROM
				packages
			WHERE
				path = $1
				AND module_path = $2
				AND version = $3
		) p
		ON
			p.module_path = l.module_path
			AND p.version = l.version
			AND p.license_file_path = l.file_path;`

	rows, err := db.db.Query(ctx, query, pkgPath, modulePath, version)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	return collectLicenses(rows)
}

// collectLicenses converts the sql rows to a list of licenses. The columns
// must be types, file_path and contents, in that order.
func collectLicenses(rows *sql.Rows) ([]*licenses.License, error) {
	mustHaveColumns(rows, "types", "file_path", "contents", "coverage")
	var lics []*licenses.License
	for rows.Next() {
		var (
			lic          = &licenses.License{Metadata: &licenses.Metadata{}}
			licenseTypes []string
		)
		if err := rows.Scan(pq.Array(&licenseTypes), &lic.FilePath, &lic.Contents, jsonbScanner{&lic.Coverage}); err != nil {
			return nil, fmt.Errorf("row.Scan(): %v", err)
		}
		lic.Types = licenseTypes
		lics = append(lics, lic)
	}
	sort.Slice(lics, func(i, j int) bool {
		return compareLicenses(lics[i].Metadata, lics[j].Metadata)
	})
	if err := rows.Err(); err != nil {
		return nil, err
	}
	return lics, nil
}

// mustHaveColumns panics if the columns of rows does not match wantColumns.
func mustHaveColumns(rows *sql.Rows, wantColumns ...string) {
	gotColumns, err := rows.Columns()
	if err != nil {
		panic(err)
	}
	if !reflect.DeepEqual(gotColumns, wantColumns) {
		panic(fmt.Sprintf("got columns %v, want $%v", gotColumns, wantColumns))
	}
}

// zipLicenseMetadata constructs licenses.Metadata from the given license types
// and paths, by zipping and then sorting.
func zipLicenseMetadata(licenseTypes []string, licensePaths []string) (_ []*licenses.Metadata, err error) {
	defer derrors.Wrap(&err, "zipLicenseMetadata(%v, %v)", licenseTypes, licensePaths)

	if len(licenseTypes) != len(licensePaths) {
		return nil, fmt.Errorf("BUG: got %d license types and %d license paths", len(licenseTypes), len(licensePaths))
	}
	byPath := make(map[string]*licenses.Metadata)
	var mds []*licenses.Metadata
	for i, p := range licensePaths {
		md, ok := byPath[p]
		if !ok {
			md = &licenses.Metadata{FilePath: p}
			mds = append(mds, md)
		}
		// By convention, we insert a license path with empty corresponding license
		// type if we are unable to detect *any* licenses in the file. This ensures
		// that we mark this package as non-redistributable.
		if licenseTypes[i] != "" {
			md.Types = append(md.Types, licenseTypes[i])
		}
	}
	sort.Slice(mds, func(i, j int) bool {
		return compareLicenses(mds[i], mds[j])
	})
	return mds, nil
}

// compareLicenses reports whether i < j according to our license sorting
// semantics.
func compareLicenses(i, j *licenses.Metadata) bool {
	if len(strings.Split(i.FilePath, "/")) > len(strings.Split(j.FilePath, "/")) {
		return true
	}
	return i.FilePath < j.FilePath
}