// Package gomoddirectives a linter that handle `replace`, `retract`, `exclude` directives into `go.mod`.
package gomoddirectives

import (
	"fmt"
	"go/token"
	"strings"

	"golang.org/x/mod/modfile"
)

const (
	reasonRetract          = "a comment is mandatory to explain why the version has been retracted"
	reasonExclude          = "exclude directive is not allowed"
	reasonReplaceLocal     = "local replacement are not allowed"
	reasonReplace          = "replacement are not allowed"
	reasonReplaceIdentical = "the original module and the replacement are identical"
	reasonReplaceDuplicate = "multiple replacement of the same module"
)

// Result the analysis result.
type Result struct {
	Reason string
	Start  token.Position
	End    token.Position
}

// NewResult creates a new Result.
func NewResult(file *modfile.File, line *modfile.Line, reason string) Result {
	return Result{
		Start:  token.Position{Filename: file.Syntax.Name, Line: line.Start.Line, Column: line.Start.LineRune},
		End:    token.Position{Filename: file.Syntax.Name, Line: line.End.Line, Column: line.End.LineRune},
		Reason: reason,
	}
}

func (r Result) String() string {
	return fmt.Sprintf("%s: %s", r.Start, r.Reason)
}

// Options the analyzer options.
type Options struct {
	ReplaceAllowList          []string
	ReplaceAllowLocal         bool
	ExcludeForbidden          bool
	RetractAllowNoExplanation bool
}

// Analyze analyzes a project.
func Analyze(opts Options) ([]Result, error) {
	f, err := GetModuleFile()
	if err != nil {
		return nil, fmt.Errorf("failed to get module file: %w", err)
	}

	return AnalyzeFile(f, opts), nil
}

// AnalyzeFile analyzes a mod file.
func AnalyzeFile(file *modfile.File, opts Options) []Result {
	var results []Result

	if !opts.RetractAllowNoExplanation {
		for _, r := range file.Retract {
			if r.Rationale != "" {
				continue
			}

			results = append(results, NewResult(file, r.Syntax, reasonRetract))
		}
	}

	if opts.ExcludeForbidden {
		for _, e := range file.Exclude {
			results = append(results, NewResult(file, e.Syntax, reasonExclude))
		}
	}

	uniqReplace := map[string]struct{}{}

	for _, r := range file.Replace {
		reason := check(opts, r)
		if reason != "" {
			results = append(results, NewResult(file, r.Syntax, reason))
			continue
		}

		if r.Old.Path == r.New.Path && r.Old.Version == r.New.Version {
			results = append(results, NewResult(file, r.Syntax, reasonReplaceIdentical))
			continue
		}

		if _, ok := uniqReplace[r.Old.Path+r.Old.Version]; ok {
			results = append(results, NewResult(file, r.Syntax, reasonReplaceDuplicate))
		}

		uniqReplace[r.Old.Path+r.Old.Version] = struct{}{}
	}

	return results
}

func check(o Options, r *modfile.Replace) string {
	if isLocal(r) {
		if o.ReplaceAllowLocal {
			return ""
		}

		return fmt.Sprintf("%s: %s", reasonReplaceLocal, r.Old.Path)
	}

	for _, v := range o.ReplaceAllowList {
		if r.Old.Path == v {
			return ""
		}
	}

	return fmt.Sprintf("%s: %s", reasonReplace, r.Old.Path)
}

// Filesystem paths found in "replace" directives are represented by a path with an empty version.
// https://github.com/golang/mod/blob/bc388b264a244501debfb9caea700c6dcaff10e2/module/module.go#L122-L124
func isLocal(r *modfile.Replace) bool {
	return strings.TrimSpace(r.New.Version) == ""
}