package build

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"go/format"
	"io"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
	"strings"
	"time"
	"unicode"

	"github.com/knadh/koanf/parsers/yaml"
)

const manifestName = "summer.yaml"

// Manifest is the ordered app plugin list used to generate imports.
type Manifest struct {
	Module  string
	Binary  string
	Plugins []Plugin
}

// Plugin is one compiled plugin module in manifest order.
type Plugin struct {
	ID     string
	Module string
}

// LoadManifest reads and validates summer.yaml at path.
func LoadManifest(path string) (Manifest, error) {
	raw, err := os.ReadFile(path)
	if err != nil {
		return Manifest{}, fmt.Errorf("build: read %s: %w", path, err)
	}
	tree, err := yaml.Parser().Unmarshal(raw)
	if err != nil {
		return Manifest{}, fmt.Errorf("build: parse %s: %w", path, err)
	}
	m := Manifest{
		Module: strings.TrimSpace(asString(tree["module"])),
		Binary: strings.TrimSpace(asString(tree["binary"])),
	}
	if err := validateModulePath(m.Module); err != nil {
		return Manifest{}, fmt.Errorf("build: module: %w", err)
	}
	if err := validateBinary(m.Binary); err != nil {
		return Manifest{}, fmt.Errorf("build: binary: %w", err)
	}

	seenID := make(map[string]struct{})
	seenMod := make(map[string]struct{})
	for i, item := range asSlice(tree["plugins"]) {
		entry := asMap(item)
		if entry == nil {
			return Manifest{}, fmt.Errorf("build: plugins[%d] must be a mapping with id and module", i)
		}
		p := Plugin{
			ID:     strings.TrimSpace(asString(entry["id"])),
			Module: strings.TrimSpace(asString(entry["module"])),
		}
		if p.ID == "" {
			return Manifest{}, fmt.Errorf("build: plugins[%d] is missing id", i)
		}
		if strings.ContainsAny(p.ID, " \t\r\n\"'`") {
			return Manifest{}, fmt.Errorf("build: plugins[%d] has invalid id %q", i, p.ID)
		}
		if _, dup := seenID[p.ID]; dup {
			return Manifest{}, fmt.Errorf("build: duplicate plugin id %q", p.ID)
		}
		if err := validateModulePath(p.Module); err != nil {
			return Manifest{}, fmt.Errorf("build: plugins[%d] module: %w", i, err)
		}
		if _, dup := seenMod[p.Module]; dup {
			return Manifest{}, fmt.Errorf("build: duplicate plugin module %q", p.Module)
		}
		seenID[p.ID] = struct{}{}
		seenMod[p.Module] = struct{}{}
		m.Plugins = append(m.Plugins, p)
	}
	return m, nil
}

// App generates app sources from summer.yaml and runs go build in appDir.
func App(ctx context.Context, appDir string, out io.Writer) error {
	if appDir == "" {
		return fmt.Errorf("build: app directory is empty")
	}
	if !filepath.IsAbs(appDir) {
		abs, err := filepath.Abs(appDir)
		if err != nil {
			return fmt.Errorf("build: resolve app directory: %w", err)
		}
		appDir = abs
	}
	if out == nil {
		out = os.Stdout
	}
	m, err := LoadManifest(filepath.Join(appDir, manifestName))
	if err != nil {
		return err
	}
	if err := generate(appDir, m); err != nil {
		return err
	}

	binRel := filepath.Join("bin", m.Binary)
	if err := os.MkdirAll(filepath.Join(appDir, "bin"), 0o755); err != nil {
		return fmt.Errorf("build: create bin dir: %w", err)
	}

	cmd := exec.CommandContext(ctx, "go", "build", "-o", binRel, ".")
	cmd.Dir = appDir
	cmd.Stdout = out
	cmd.Stderr = out
	start := time.Now()
	if err := cmd.Run(); err != nil {
		return fmt.Errorf("build: go build: %w", err)
	}
	fmt.Fprintf(out, "built %s in %s\n", m.Binary, time.Since(start).Round(time.Millisecond))
	return nil
}

func generate(appDir string, m Manifest) error {
	mainSrc, err := generateMain(m)
	if err != nil {
		return err
	}
	pluginsSrc, err := generatePluginsGen(m)
	if err != nil {
		return err
	}
	if err := writeIfChanged(filepath.Join(appDir, "main.go"), mainSrc); err != nil {
		return err
	}
	if err := writeIfChanged(filepath.Join(appDir, "plugins.gen.go"), pluginsSrc); err != nil {
		return err
	}
	return nil
}

func generateMain(m Manifest) ([]byte, error) {
	var b strings.Builder
	b.WriteString("// Code generated by summer build. DO NOT EDIT.\n\n")
	b.WriteString("package main\n\n")
	b.WriteString("import (\n")
	b.WriteString("\t\"fmt\"\n")
	b.WriteString("\t\"io\"\n")
	b.WriteString("\t\"os\"\n\n")
	b.WriteString("\t\"git.golem15.com/golem15/summercms/backpack\"\n")
	b.WriteString("\t\"git.golem15.com/golem15/summercms/bonfire\"\n")
	b.WriteString("\t\"git.golem15.com/golem15/summercms/compass\"\n")
	b.WriteString("\t\"git.golem15.com/golem15/summercms/pact\"\n")
	b.WriteString("\t\"git.golem15.com/golem15/summercms/party\"\n")
	b.WriteString(")\n\n")
	b.WriteString("func main() {\n")
	b.WriteString("\tif err := run(os.Args[1:], os.Stdout); err != nil {\n")
	b.WriteString("\t\tfmt.Fprintln(os.Stderr, err)\n")
	b.WriteString("\t\tos.Exit(1)\n")
	b.WriteString("\t}\n")
	b.WriteString("}\n\n")
	b.WriteString("func run(args []string, out io.Writer) error {\n")
	b.WriteString("\tcfg, err := compass.Load(\"config\")\n")
	b.WriteString("\tif err != nil {\n")
	b.WriteString("\t\treturn err\n")
	b.WriteString("\t}\n")
	b.WriteString("\tapp := backpack.New(cfg)\n")
	b.WriteString("\tplugins, err := party.Activate(app, PluginIDs)\n")
	b.WriteString("\tif err != nil {\n")
	b.WriteString("\t\treturn err\n")
	b.WriteString("\t}\n")
	b.WriteString("\tvar commands []bonfire.Command\n")
	b.WriteString("\tfor _, plugin := range plugins {\n")
	b.WriteString("\t\tif hasCommands, ok := plugin.(pact.HasCommands); ok {\n")
	b.WriteString("\t\t\tcommands = append(commands, hasCommands.Commands()...)\n")
	b.WriteString("\t\t}\n")
	b.WriteString("\t}\n")
	fmt.Fprintf(&b, "\troot := bonfire.NewRoot(%s, commands, out)\n", strconv.Quote(m.Binary))
	b.WriteString("\troot.SetArgs(args)\n")
	b.WriteString("\treturn root.Execute()\n")
	b.WriteString("}\n")
	return formatSource([]byte(b.String()))
}

func generatePluginsGen(m Manifest) ([]byte, error) {
	var b strings.Builder
	b.WriteString("// Code generated by summer build. DO NOT EDIT.\n\n")
	b.WriteString("package main\n\n")
	if len(m.Plugins) > 0 {
		b.WriteString("import (\n")
		for _, p := range m.Plugins {
			fmt.Fprintf(&b, "\t_ %s\n", strconv.Quote(p.Module))
		}
		b.WriteString(")\n\n")
	}
	b.WriteString("// PluginIDs is the ordered plugin list from summer.yaml.\n")
	b.WriteString("var PluginIDs = []string{\n")
	for _, p := range m.Plugins {
		fmt.Fprintf(&b, "\t%s,\n", strconv.Quote(p.ID))
	}
	b.WriteString("}\n")
	return formatSource([]byte(b.String()))
}

func formatSource(src []byte) ([]byte, error) {
	formatted, err := format.Source(src)
	if err != nil {
		return nil, fmt.Errorf("build: format generated go: %w", err)
	}
	return formatted, nil
}

func writeIfChanged(path string, content []byte) error {
	existing, err := os.ReadFile(path)
	if err == nil && bytes.Equal(existing, content) {
		return nil
	}
	if err != nil && !errors.Is(err, os.ErrNotExist) {
		return fmt.Errorf("build: read %s: %w", path, err)
	}
	if err := os.WriteFile(path, content, 0o644); err != nil {
		return fmt.Errorf("build: write %s: %w", path, err)
	}
	return nil
}

func validateBinary(name string) error {
	if name == "" {
		return fmt.Errorf("is empty")
	}
	if name != filepath.Base(name) || strings.ContainsRune(name, os.PathSeparator) {
		return fmt.Errorf("%q must be a bare file name", name)
	}
	if name == "." || name == ".." {
		return fmt.Errorf("%q is not a valid binary name", name)
	}
	for _, r := range name {
		if r > unicode.MaxASCII || !(unicode.IsLetter(r) || unicode.IsDigit(r) || r == '.' || r == '_' || r == '-') {
			return fmt.Errorf("%q contains invalid characters", name)
		}
	}
	return nil
}

func validateModulePath(path string) error {
	if path == "" {
		return fmt.Errorf("is empty")
	}
	if strings.HasPrefix(path, "-") {
		return fmt.Errorf("%q must not start with -", path)
	}
	if strings.ContainsAny(path, " \t\r\n\\\"'`$;&|*?<>()[]{}") {
		return fmt.Errorf("%q contains invalid characters", path)
	}
	if filepath.IsAbs(path) || strings.Contains(path, `\`) {
		return fmt.Errorf("%q is not a valid module path", path)
	}
	for _, seg := range strings.Split(path, "/") {
		if seg == "" || seg == "." || seg == ".." {
			return fmt.Errorf("%q has an invalid path segment", path)
		}
		if strings.Contains(seg, "@") {
			return fmt.Errorf("%q must not contain a version suffix", path)
		}
	}
	return nil
}

func asString(v any) string {
	s, _ := v.(string)
	return s
}

func asSlice(v any) []any {
	switch s := v.(type) {
	case []any:
		return s
	case nil:
		return nil
	default:
		return nil
	}
}

func asMap(v any) map[string]any {
	switch m := v.(type) {
	case map[string]any:
		return m
	case map[any]any:
		out := make(map[string]any, len(m))
		for k, val := range m {
			ks, ok := k.(string)
			if !ok {
				continue
			}
			out[ks] = val
		}
		return out
	default:
		return nil
	}
}