// 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 modload

import (
	"cmd/go/internal/base"
	"cmd/go/internal/cfg"

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

var modFile *modfile.File

// A modFileIndex is an index of data corresponding to a modFile
// at a specific point in time.
type modFileIndex struct {
	data         []byte
	dataNeedsFix bool // true if fixVersion applied a change while parsing data
	module       module.Version
	goVersionV   string // GoVersion with "v" prefix
	require      map[module.Version]requireMeta
	replace      map[module.Version]module.Version
	exclude      map[module.Version]bool
}

// index is the index of the go.mod file as of when it was last read or written.
var index *modFileIndex

type requireMeta struct {
	indirect bool
}

// Allowed reports whether module m is allowed (not excluded) by the main module's go.mod.
func Allowed(m module.Version) bool {
	return index == nil || !index.exclude[m]
}

// Replacement returns the replacement for mod, if any, from go.mod.
// If there is no replacement for mod, Replacement returns
// a module.Version with Path == "".
func Replacement(mod module.Version) module.Version {
	if index != nil {
		if r, ok := index.replace[mod]; ok {
			return r
		}
		if r, ok := index.replace[module.Version{Path: mod.Path}]; ok {
			return r
		}
	}
	return module.Version{}
}

// indexModFile rebuilds the index of modFile.
// If modFile has been changed since it was first read,
// modFile.Cleanup must be called before indexModFile.
func indexModFile(data []byte, modFile *modfile.File, needsFix bool) *modFileIndex {
	i := new(modFileIndex)
	i.data = data
	i.dataNeedsFix = needsFix

	i.module = module.Version{}
	if modFile.Module != nil {
		i.module = modFile.Module.Mod
	}

	i.goVersionV = ""
	if modFile.Go != nil {
		// We're going to use the semver package to compare Go versions, so go ahead
		// and add the "v" prefix it expects once instead of every time.
		i.goVersionV = "v" + modFile.Go.Version
	}

	i.require = make(map[module.Version]requireMeta, len(modFile.Require))
	for _, r := range modFile.Require {
		i.require[r.Mod] = requireMeta{indirect: r.Indirect}
	}

	i.replace = make(map[module.Version]module.Version, len(modFile.Replace))
	for _, r := range modFile.Replace {
		if prev, dup := i.replace[r.Old]; dup && prev != r.New {
			base.Fatalf("go: conflicting replacements for %v:\n\t%v\n\t%v", r.Old, prev, r.New)
		}
		i.replace[r.Old] = r.New
	}

	i.exclude = make(map[module.Version]bool, len(modFile.Exclude))
	for _, x := range modFile.Exclude {
		i.exclude[x.Mod] = true
	}

	return i
}

// modFileIsDirty reports whether the go.mod file differs meaningfully
// from what was indexed.
// If modFile has been changed (even cosmetically) since it was first read,
// modFile.Cleanup must be called before modFileIsDirty.
func (i *modFileIndex) modFileIsDirty(modFile *modfile.File) bool {
	if i == nil {
		return modFile != nil
	}

	if i.dataNeedsFix {
		return true
	}

	if modFile.Module == nil {
		if i.module != (module.Version{}) {
			return true
		}
	} else if modFile.Module.Mod != i.module {
		return true
	}

	if modFile.Go == nil {
		if i.goVersionV != "" {
			return true
		}
	} else if "v"+modFile.Go.Version != i.goVersionV {
		if i.goVersionV == "" && cfg.BuildMod == "readonly" {
			// go.mod files did not always require a 'go' version, so do not error out
			// if one is missing — we may be inside an older module in the module
			// cache, and should bias toward providing useful behavior.
		} else {
			return true
		}
	}

	if len(modFile.Require) != len(i.require) ||
		len(modFile.Replace) != len(i.replace) ||
		len(modFile.Exclude) != len(i.exclude) {
		return true
	}

	for _, r := range modFile.Require {
		if meta, ok := i.require[r.Mod]; !ok {
			return true
		} else if r.Indirect != meta.indirect {
			if cfg.BuildMod == "readonly" {
				// The module's requirements are consistent; only the "// indirect"
				// comments that are wrong. But those are only guaranteed to be accurate
				// after a "go mod tidy" — it's a good idea to run those before
				// committing a change, but it's certainly not mandatory.
			} else {
				return true
			}
		}
	}

	for _, r := range modFile.Replace {
		if r.New != i.replace[r.Old] {
			return true
		}
	}

	for _, x := range modFile.Exclude {
		if !i.exclude[x.Mod] {
			return true
		}
	}

	return false
}