package build

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

// 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
	}
	if err := checkModelsLeaf(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
	applyGoWork(cmd, appDir)
	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/modules/backpack\"\n")
	b.WriteString("\t\"git.golem15.com/golem15/summercms/modules/bonfire\"\n")
	b.WriteString("\t\"git.golem15.com/golem15/summercms/modules/cabana\"\n")
	b.WriteString("\t\"git.golem15.com/golem15/summercms/modules/compass\"\n")
	b.WriteString("\t\"git.golem15.com/golem15/summercms/modules/lagoon\"\n")
	b.WriteString("\t\"git.golem15.com/golem15/summercms/modules/pact\"\n")
	b.WriteString("\t\"git.golem15.com/golem15/summercms/modules/party\"\n")
	b.WriteString("\t\"git.golem15.com/golem15/summercms/modules/surf\"\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("\tcommands := lagoon.RuntimeCommands(app, plugins)\n")
	b.WriteString("\tcommands = append(commands, surf.ServeCommand(app, plugins))\n")
	b.WriteString("\tcommands = append(commands, surf.RouteListCommand(app, plugins))\n")
	b.WriteString("\tcommands = append(commands, cabana.RuntimeCommands(app)...)\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, err := bonfire.NewRoot(%s, commands, out)\n", strconv.Quote(m.Binary))
	b.WriteString("\tif err != nil {\n")
	b.WriteString("\t\treturn err\n")
	b.WriteString("\t}\n")
	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
}