package build

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

	"git.golem15.com/golem15/summercms/modules/kiosk"
	"git.golem15.com/golem15/summercms/modules/party"
)

// buildMeta is the plugin metadata and framework version summer build
// bakes into plugins.gen.go.
type buildMeta struct {
	Plugins   []party.Info
	Framework string
}

// listedPackage is the part of `go list -json` output the metadata step
// reads for one plugin package.
type listedPackage struct {
	ImportPath string
	Dir        string
	Module     *listedPackageModule
	Error      *struct{ Err string }
}

type listedPackageModule struct {
	Path    string
	Version string
	Dir     string
	Main    bool
	Replace *struct {
		Path    string
		Version string
		Dir     string
	}
}

// listPackages runs `go list` for the plugin packages; tests replace it.
var listPackages = goListPackages

// goListPackages resolves import paths to directories and modules with one
// `go list -e -json` in appDir, honouring the app's go.work.
func goListPackages(ctx context.Context, appDir string, paths []string) ([]listedPackage, error) {
	args := append([]string{"list", "-e", "-json=ImportPath,Dir,Module,Error", "--"}, paths...)
	cmd := exec.CommandContext(ctx, "go", args...)
	cmd.Dir = appDir
	applyGoWork(cmd, appDir)
	var stderr bytes.Buffer
	cmd.Stderr = &stderr
	out, err := cmd.Output()
	if err != nil {
		return nil, fmt.Errorf("go list: %w: %s", err, bytes.TrimSpace(stderr.Bytes()))
	}
	var pkgs []listedPackage
	dec := json.NewDecoder(bytes.NewReader(out))
	for dec.More() {
		var p listedPackage
		if err := dec.Decode(&p); err != nil {
			return nil, fmt.Errorf("go list: %w", err)
		}
		pkgs = append(pkgs, p)
	}
	return pkgs, nil
}

// idOnlyMeta is the metadata of a build that knows nothing but the IDs.
func idOnlyMeta(m Manifest) buildMeta {
	infos := make([]party.Info, len(m.Plugins))
	for i, p := range m.Plugins {
		infos[i] = party.Info{ID: p.ID}
	}
	return buildMeta{Plugins: infos}
}

// resolveBuildMeta resolves the plugin metadata and the effective
// framework version. It never fails: what it cannot resolve stays empty
// and comes back as a warning, so metadata never breaks a build.
func resolveBuildMeta(ctx context.Context, appDir string, m Manifest) (buildMeta, []string) {
	infos, warnings := resolvePluginInfo(ctx, appDir, m)
	fw, err := EffectiveFramework(ctx, appDir)
	if err != nil {
		warnings = append(warnings, err.Error())
	}
	return buildMeta{Plugins: infos, Framework: fw}, warnings
}

// resolvePluginInfo returns one party.Info per summer.yaml plugin, in
// manifest order: module and package from go list, name and description
// from the plugin's plugin.yaml, and the version per D-07. No filesystem
// path is ever stored.
func resolvePluginInfo(ctx context.Context, appDir string, m Manifest) ([]party.Info, []string) {
	infos := idOnlyMeta(m).Plugins
	if len(m.Plugins) == 0 {
		return infos, nil
	}
	paths := make([]string, len(m.Plugins))
	for i, p := range m.Plugins {
		paths[i] = p.Module
	}
	pkgs, err := listPackages(ctx, appDir, paths)
	if err != nil {
		return infos, []string{fmt.Sprintf("plugin metadata: %v; PluginInfo carries plugin IDs only", err)}
	}
	byPath := make(map[string]listedPackage, len(pkgs))
	for _, p := range pkgs {
		byPath[p.ImportPath] = p
	}
	var warnings []string
	for i, p := range m.Plugins {
		pkg, ok := byPath[p.Module]
		if !ok || pkg.Dir == "" {
			reason := "package not found"
			if ok && pkg.Error != nil {
				reason = pkg.Error.Err
			}
			warnings = append(warnings, fmt.Sprintf("plugin metadata: %s: %s", p.ID, reason))
			continue
		}
		info := &infos[i]
		info.Package = pkg.ImportPath
		if pkg.Module != nil {
			info.Module = pkg.Module.Path
		}
		if w := readPluginYAML(pkg.Dir, info); w != "" {
			warnings = append(warnings, fmt.Sprintf("plugin metadata: %s: %s", p.ID, w))
		}
		pluginVersion(ctx, pkg, info)
	}
	return infos, warnings
}

// readPluginYAML copies name and description from dir/plugin.yaml into
// info. It returns a warning when the file exists but cannot be used.
func readPluginYAML(dir string, info *party.Info) string {
	raw, err := os.ReadFile(filepath.Join(dir, kiosk.FileName))
	if errors.Is(err, os.ErrNotExist) {
		return ""
	}
	if err != nil {
		return fmt.Sprintf("%s: %v; ignored", kiosk.FileName, err)
	}
	pm, err := kiosk.Parse(raw)
	if err != nil {
		return fmt.Sprintf("%s: %v; ignored", kiosk.FileName, err)
	}
	if pm.ID != info.ID {
		return fmt.Sprintf("%s describes %s, not %s; ignored", kiosk.FileName, pm.ID, info.ID)
	}
	info.Name, info.Description = pm.Name, pm.Description
	if info.Module == "" {
		info.Module = pm.Module
	}
	return ""
}

// pluginVersion sets info.Source and info.Version (D-07): the module
// version for a plugin from the module cache, git describe for a plugin
// directory that is its own repository, nothing for an in-app plugin.
func pluginVersion(ctx context.Context, pkg listedPackage, info *party.Info) {
	mod := pkg.Module
	switch {
	case mod == nil:
		info.Source = party.SourceLocal
	case mod.Replace != nil && mod.Replace.Version != "":
		info.Source, info.Version = party.SourceModule, mod.Replace.Version
	case !mod.Main && mod.Replace == nil:
		info.Source, info.Version = party.SourceModule, mod.Version
	default:
		root := mod.Dir
		if root == "" {
			root = pkg.Dir
		}
		if isOwnRepository(ctx, root) {
			info.Source = party.SourceSubmodule
			info.Version = gitDescribe(ctx, root)
		} else {
			info.Source = party.SourceLocal
		}
	}
}

// isOwnRepository reports whether dir is the top level of a git work tree
// (its own repository or a submodule), not a directory inside the app's.
func isOwnRepository(ctx context.Context, dir string) bool {
	out, err := gitOutput(ctx, dir, "rev-parse", "--show-toplevel")
	if err != nil {
		return false
	}
	return samePath(strings.TrimSpace(string(out)), dir)
}

// gitDescribe is `git describe --tags --match v[0-9]* --always` in dir,
// without --dirty: an uncommitted change in a plugin must not rewrite the
// app's tracked plugins.gen.go (research Pitfall 6).
func gitDescribe(ctx context.Context, dir string) string {
	out, err := gitOutput(ctx, dir, "describe", "--tags", "--match", "v[0-9]*", "--always")
	if err != nil {
		return ""
	}
	return strings.TrimSpace(string(out))
}

func gitOutput(ctx context.Context, dir string, args ...string) ([]byte, error) {
	cmd := exec.CommandContext(ctx, "git", append([]string{"-C", dir}, args...)...)
	var stderr bytes.Buffer
	cmd.Stderr = &stderr
	out, err := cmd.Output()
	if err != nil {
		msg := strings.TrimSpace(stderr.String())
		if msg == "" {
			msg = err.Error()
		}
		return nil, errors.New(msg)
	}
	return out, nil
}

func samePath(a, b string) bool {
	ra, err := filepath.EvalSymlinks(a)
	if err != nil {
		ra = a
	}
	rb, err := filepath.EvalSymlinks(b)
	if err != nil {
		rb = b
	}
	return filepath.Clean(ra) == filepath.Clean(rb)
}

// goModJSON is the part of `go mod edit -json` and `go work edit -json`
// output EffectiveFramework reads.
type goModJSON struct {
	Require []struct {
		Path    string
		Version string
	}
	Replace []struct {
		Old struct{ Path string }
		New struct{ Path, Version string }
	}
	Use []struct {
		DiskPath string
	}
}

func editJSON(ctx context.Context, dir string, args ...string) (goModJSON, error) {
	cmd := exec.CommandContext(ctx, "go", args...)
	cmd.Dir = dir
	var stderr bytes.Buffer
	cmd.Stderr = &stderr
	out, err := cmd.Output()
	if err != nil {
		return goModJSON{}, fmt.Errorf("go %s: %w: %s", strings.Join(args, " "), err, bytes.TrimSpace(stderr.Bytes()))
	}
	var j goModJSON
	if err := json.Unmarshal(out, &j); err != nil {
		return goModJSON{}, fmt.Errorf("go %s: %w", strings.Join(args, " "), err)
	}
	return j, nil
}

// EffectiveFramework returns the framework version an app in appDir builds
// against (research F3). When go.work or go.mod replaces the framework with
// a local directory, or go.work uses one, it is the newest tag reachable
// from that checkout (`git describe --tags --abbrev=0`); a replace with a
// module version gives that version; otherwise it is the go.mod require.
// When git fails it returns the require version together with a non-nil
// error the caller prints as a warning.
func EffectiveFramework(ctx context.Context, appDir string) (string, error) {
	gomod, err := editJSON(ctx, appDir, "mod", "edit", "-json", filepath.Join(appDir, "go.mod"))
	if err != nil {
		return "", fmt.Errorf("framework version: %w", err)
	}
	required := ""
	for _, r := range gomod.Require {
		if r.Path == frameworkModule {
			required = r.Version
		}
	}
	localDir, version := "", ""
	for _, r := range gomod.Replace {
		if r.Old.Path == frameworkModule {
			localDir, version = r.New.Path, r.New.Version
			if version == "" && !filepath.IsAbs(localDir) {
				localDir = filepath.Join(appDir, localDir)
			}
		}
	}
	if gw := findGoWork(appDir); gw != "" {
		work, err := editJSON(ctx, appDir, "work", "edit", "-json", gw)
		if err != nil {
			return required, fmt.Errorf("framework version: %w; using the go.mod require %s", err, required)
		}
		base := filepath.Dir(gw)
		for _, u := range work.Use {
			dir := u.DiskPath
			if !filepath.IsAbs(dir) {
				dir = filepath.Join(base, dir)
			}
			if mod, err := readModulePath(filepath.Join(dir, "go.mod")); err == nil && mod == frameworkModule {
				localDir, version = dir, ""
			}
		}
		for _, r := range work.Replace {
			if r.Old.Path == frameworkModule {
				localDir, version = r.New.Path, r.New.Version
				if version == "" && !filepath.IsAbs(localDir) {
					localDir = filepath.Join(base, localDir)
				}
			}
		}
	}
	switch {
	case version != "":
		return version, nil
	case localDir == "":
		return required, nil
	}
	out, err := gitOutput(ctx, localDir, "describe", "--tags", "--abbrev=0", "--match", "v[0-9]*")
	if err != nil {
		return required, fmt.Errorf("framework version: git describe in %s: %v; using the go.mod require %s", localDir, err, required)
	}
	return strings.TrimSpace(string(out)), nil
}