package kiosk

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

	"github.com/yuin/goldmark"
	gast "github.com/yuin/goldmark/ast"
	"github.com/yuin/goldmark/text"
)

// DeriveOptions changes the persisted name and description overrides. A
// nil field keeps the override already in plugin.yaml; a pointer to ""
// clears it; any other value sets it.
type DeriveOptions struct {
	Name        *string
	Description *string
}

// goMod is the part of `go mod edit -json` output Derive reads.
type goMod struct {
	Module struct {
		Path string
	}
	Require []goModRequire
}

type goModRequire struct {
	Path     string
	Version  string
	Indirect bool
}

// version returns the go.mod require version of path, or "".
func (m goMod) version(path string) (string, bool) {
	for _, r := range m.Require {
		if r.Path == path {
			return r.Version, true
		}
	}
	return "", false
}

var pseudoVersionRe = regexp.MustCompile(`^v\d+\.\d+\.\d+-(?:[0-9A-Za-z.-]+\.)?\d{14}-[0-9a-f]{12}$`)

// isPseudoVersion reports whether v is a Go pseudo-version.
func isPseudoVersion(v string) bool { return pseudoVersionRe.MatchString(v) }

// Derive builds the manifest of the plugin in dir from its sources: the
// module and the version minimums from the nearest go.mod, the ID and
// requirements from plugin.go, the name and description from README.md.
// Overrides come from an existing plugin.yaml in dir, changed by opts.
// No plugin code is compiled or run. The returned strings are warnings.
func Derive(ctx context.Context, dir string, opts DeriveOptions) (Manifest, []string, error) {
	abs, err := filepath.Abs(dir)
	if err != nil {
		return Manifest{}, nil, fmt.Errorf("kiosk: resolve %s: %w", dir, err)
	}
	if st, err := os.Stat(abs); err != nil || !st.IsDir() {
		return Manifest{}, nil, fmt.Errorf("kiosk: %s is not a plugin directory", dir)
	}
	root, err := moduleRoot(abs)
	if err != nil {
		return Manifest{}, nil, err
	}
	mod, err := readGoMod(ctx, root)
	if err != nil {
		return Manifest{}, nil, err
	}
	var warnings []string
	m := Manifest{Schema: SchemaVersion, Module: mod.Module.Path}
	m.Package, err = packagePath(mod.Module.Path, root, abs)
	if err != nil {
		return Manifest{}, nil, err
	}

	fw, ok := mod.version(FrameworkModule)
	switch {
	case !ok:
		return Manifest{}, nil, fmt.Errorf("kiosk: %s does not require %s; the framework require is the plugin's framework minimum", filepath.Join(root, "go.mod"), FrameworkModule)
	case fw == "v0.0.0":
		return Manifest{}, nil, fmt.Errorf("kiosk: %s requires %s v0.0.0, which is not a released version; require a framework tag", filepath.Join(root, "go.mod"), FrameworkModule)
	case isPseudoVersion(fw):
		warnings = append(warnings, fmt.Sprintf("framework minimum %s is a pseudo-version; require a framework tag before publishing", fw))
	}
	m.Framework = fw

	r := newResolver(ctx, abs)
	r.modLoaded, r.root, r.mod = true, root, mod
	ident, err := r.identity(abs)
	if err != nil {
		return Manifest{}, nil, err
	}
	m.ID = ident.ID
	reqs, w, err := r.minimums(ident.Requires)
	warnings = append(warnings, w...)
	if err != nil {
		return Manifest{}, warnings, err
	}
	m.Requires = reqs

	existing, err := readExisting(abs)
	if err != nil {
		return Manifest{}, nil, err
	}
	ov := Overrides{}
	if existing.Overrides != nil {
		ov = *existing.Overrides
	}
	if opts.Name != nil {
		ov.Name = strings.TrimSpace(*opts.Name)
	}
	if opts.Description != nil {
		ov.Description = strings.TrimSpace(*opts.Description)
	}
	if ov != (Overrides{}) {
		m.Overrides = &ov
	}

	h1, summary, err := readReadme(filepath.Join(abs, "README.md"))
	if err != nil {
		return Manifest{}, nil, err
	}
	m.Name = h1
	if ov.Name != "" {
		m.Name = ov.Name
	} else if h1 == m.ID {
		return Manifest{}, nil, fmt.Errorf("kiosk: README.md's H1 is the plugin ID %s, not a display name; pass --name=\"…\" (it is kept in %s)", m.ID, FileName)
	}
	m.Description = summary
	if ov.Description != "" {
		m.Description = ov.Description
	}
	if m.Description == "" {
		return Manifest{}, nil, fmt.Errorf("kiosk: README.md has no summary paragraph after its H1; add the one-sentence summary or pass --description=\"…\"")
	}
	return m, warnings, nil
}

// moduleRoot walks up from dir to the nearest directory with a go.mod.
func moduleRoot(dir string) (string, error) {
	for d := dir; ; {
		if st, err := os.Stat(filepath.Join(d, "go.mod")); err == nil && !st.IsDir() {
			return d, nil
		}
		parent := filepath.Dir(d)
		if parent == d {
			return "", fmt.Errorf("kiosk: no go.mod in %s or above", dir)
		}
		d = parent
	}
}

// packagePath is the import path of dir inside the module rooted at root.
func packagePath(modPath, root, dir string) (string, error) {
	rel, err := filepath.Rel(root, dir)
	if err != nil {
		return "", fmt.Errorf("kiosk: package path: %w", err)
	}
	if rel == "." {
		return modPath, nil
	}
	return modPath + "/" + filepath.ToSlash(rel), nil
}

// readGoMod runs `go mod edit -json` in root.
func readGoMod(ctx context.Context, root string) (goMod, error) {
	out, err := runGo(ctx, root, "mod", "edit", "-json")
	if err != nil {
		return goMod{}, err
	}
	var m goMod
	if err := json.Unmarshal(out, &m); err != nil {
		return goMod{}, fmt.Errorf("kiosk: read %s: %w", filepath.Join(root, "go.mod"), err)
	}
	if m.Module.Path == "" {
		return goMod{}, fmt.Errorf("kiosk: %s has no module path", filepath.Join(root, "go.mod"))
	}
	return m, nil
}

// runGo runs the go command in dir without a shell and returns stdout.
// Workspaces are off: a plugin manifest describes the module on its own.
func runGo(ctx context.Context, dir string, args ...string) ([]byte, error) {
	cmd := exec.CommandContext(ctx, "go", args...)
	cmd.Dir = dir
	env := os.Environ()
	filtered := make([]string, 0, len(env)+1)
	for _, e := range env {
		if !strings.HasPrefix(e, "GOWORK=") {
			filtered = append(filtered, e)
		}
	}
	cmd.Env = append(filtered, "GOWORK=off")
	var stderr bytes.Buffer
	cmd.Stderr = &stderr
	out, err := cmd.Output()
	if err != nil {
		return nil, fmt.Errorf("kiosk: go %s in %s: %w\n%s", strings.Join(args, " "), dir, err, bytes.TrimSpace(stderr.Bytes()))
	}
	return out, nil
}

// readExisting parses dir's plugin.yaml, or returns the zero manifest when
// there is none.
func readExisting(dir string) (Manifest, error) {
	raw, err := os.ReadFile(filepath.Join(dir, FileName))
	if errors.Is(err, os.ErrNotExist) {
		return Manifest{}, nil
	}
	if err != nil {
		return Manifest{}, fmt.Errorf("kiosk: read %s: %w", filepath.Join(dir, FileName), err)
	}
	m, err := Parse(raw)
	if err != nil {
		return Manifest{}, fmt.Errorf("%w\n(delete %s and rerun summer plugin:manifest; pass --name/--description again if it had overrides)", err, filepath.Join(dir, FileName))
	}
	return m, nil
}

// readReadme returns the plain text of the README's first H1 and of the
// first paragraph after it, whitespace collapsed.
func readReadme(path string) (name, summary string, err error) {
	src, err := os.ReadFile(path)
	if err != nil {
		return "", "", fmt.Errorf("kiosk: the plugin needs a README.md whose H1 is the plugin name: %w", err)
	}
	doc := goldmark.New().Parser().Parse(text.NewReader(src))
	var h1 gast.Node
	for n := doc.FirstChild(); n != nil; n = n.NextSibling() {
		if h, ok := n.(*gast.Heading); ok && h.Level == 1 {
			h1 = h
			break
		}
	}
	if h1 == nil {
		return "", "", fmt.Errorf("kiosk: %s has no H1; its first-level heading is the plugin name", path)
	}
	name = plainText(h1, src)
	if name == "" {
		return "", "", fmt.Errorf("kiosk: %s has an empty H1", path)
	}
	for n := h1.NextSibling(); n != nil; n = n.NextSibling() {
		if p, ok := n.(*gast.Paragraph); ok {
			summary = plainText(p, src)
			break
		}
		if _, ok := n.(*gast.Heading); ok {
			break
		}
	}
	return name, summary, nil
}

// plainText is the text content of n with whitespace collapsed: code
// spans and link texts keep their text, markup is dropped.
func plainText(n gast.Node, src []byte) string {
	var b strings.Builder
	_ = gast.Walk(n, func(c gast.Node, entering bool) (gast.WalkStatus, error) {
		if !entering {
			return gast.WalkContinue, nil
		}
		switch t := c.(type) {
		case *gast.Text:
			b.Write(t.Segment.Value(src))
			if t.SoftLineBreak() || t.HardLineBreak() {
				b.WriteByte(' ')
			}
		case *gast.String:
			b.Write(t.Value)
		case *gast.AutoLink:
			b.Write(t.Label(src))
			return gast.WalkSkipChildren, nil
		case *gast.RawHTML:
			return gast.WalkSkipChildren, nil
		}
		return gast.WalkContinue, nil
	})
	return strings.Join(strings.Fields(b.String()), " ")
}

// lastReturn is the single result of fn's last top-level return, or nil.
func lastReturn(fn *ast.FuncDecl) ast.Expr {
	var res ast.Expr
	for _, stmt := range fn.Body.List {
		if ret, ok := stmt.(*ast.ReturnStmt); ok && len(ret.Results) == 1 {
			res = ret.Results[0]
		}
	}
	return res
}