//go:build ignore

package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"go/format"
	"log"
	"os"
	"path/filepath"
	"regexp"
	"slices"
	"strings"

	"github.com/microsoft/typescript-go/internal/repo"
)

var (
	libInputDir     = filepath.Join(repo.TypeScriptSubmodulePath(), "src", "lib")
	copyrightNotice = filepath.Join(repo.TypeScriptSubmodulePath(), "scripts", "CopyrightNotice.txt")
)

func main() {
	log.SetFlags(log.LstdFlags | log.Lshortfile)

	libs := readLibs()
	generateLibs(libs)
	generateLibList(libs)
	generateEmbedded(libs)
}

type lib struct {
	target  string   // target relative to libs dir
	sources []string // sources relative to src/lib dir
}

func generateLibs(libs []lib) {
	const outputDir = "libs"

	copyright := readCopyright()

	if err := os.RemoveAll(outputDir); err != nil {
		log.Fatalf("failed to remove libs directory: %v", err)
	}

	if err := os.MkdirAll(outputDir, 0o755); err != nil {
		log.Fatalf("failed to create libs directory: %v", err)
	}

	for _, lib := range libs {
		var output bytes.Buffer
		output.Write(copyright)

		for _, source := range lib.sources {
			sourcePath := filepath.Join(libInputDir, source)
			b, err := os.ReadFile(sourcePath)
			if err != nil {
				log.Fatalf("failed to read %s: %v", sourcePath, err)
			}

			output.WriteByte('\n')
			output.Write(removeCRLF(b))
		}

		outputPath := filepath.Join(outputDir, lib.target)
		if err := os.WriteFile(outputPath, output.Bytes(), 0o644); err != nil {
			log.Fatalf("failed to write %s: %v", outputPath, err)
		}
	}
}

func generateLibList(libs []lib) {
	var code bytes.Buffer
	code.WriteString("// Code generated by generate.go; DO NOT EDIT.\n\n")
	code.WriteString("package bundled\n\n")

	code.WriteString("// LibNames is the list of all bundled lib files, sorted by name.\n")
	code.WriteString("// For the list of libs sorted by load order, use [tsoptions.Libs].\n")
	code.WriteString("var LibNames = []string{\n")
	for _, lib := range libs {
		code.WriteString("\t\"" + lib.target + "\",\n")
	}
	code.WriteString("}\n")

	writeCode("libs_generated.go", code.Bytes())
}

func generateEmbedded(libs []lib) {
	libVarNames := make([]string, len(libs))
	for i, lib := range libs {
		libVarNames[i] = "libs_" + strings.ReplaceAll(lib.target, ".", "_")
	}

	var code bytes.Buffer
	code.WriteString("//go:build !noembed\n\n")
	code.WriteString("// Code generated by generate.go; DO NOT EDIT.\n\n")
	code.WriteString("package bundled\n\n")
	code.WriteString("import (\n")
	code.WriteString("\"io/fs\"\n\n")
	code.WriteString("_ \"embed\"\n")
	code.WriteString(")\n\n")

	code.WriteString("var (\n")
	for i, lib := range libs {
		varName := libVarNames[i]
		code.WriteString("//go:embed libs/" + lib.target + "\n")
		code.WriteString("" + varName + " string\n")
	}
	code.WriteString(")\n\n")

	code.WriteString("var embeddedContents = map[string]string{\n")
	for i, lib := range libs {
		varName := libVarNames[i]
		code.WriteString("\t\"libs/" + lib.target + "\": " + varName + ",\n")
	}
	code.WriteString("}\n\n")

	code.WriteString("var libsEntries = []fs.DirEntry{\n")
	for i, lib := range libs {
		varName := libVarNames[i]
		fmt.Fprintf(&code, "\t&fileInfo{name: %q, size: int64(len(%s))},\n", lib.target, varName)
	}
	code.WriteString("}\n")

	writeCode("embed_generated.go", code.Bytes())
}

var (
	// Match escaped characters, double-quoted strings, single-line comments, and multi-line comments.
	reJSONComments = regexp.MustCompile(`\\.|"(?:\\.|[^"])*"|//.*|/\*[\s\S]*?\*/`)
	// Match double-quoted strings (to skip) or trailing commas before ] or }.
	reTrailingComma = regexp.MustCompile(`"(?:\\.|[^"])*"|,\s*([}\]])`)
)

// stripJSONC replaces comments and trailing commas with spaces in JSONC content,
// producing valid JSON. The input slice is mutated in place.
func stripJSONC(b []byte) {
	for _, loc := range reJSONComments.FindAllIndex(b, -1) {
		if b[loc[0]] == '/' {
			for i := loc[0]; i < loc[1]; i++ {
				if b[i] != '\n' {
					b[i] = ' '
				}
			}
		}
	}
	for _, loc := range reTrailingComma.FindAllSubmatchIndex(b, -1) {
		// loc[2]:loc[3] is the capture group; -1 means this matched a string, not a comma.
		if loc[2] < 0 {
			continue
		}
		// Blank the comma (at loc[0]), keep whitespace and closing bracket.
		b[loc[0]] = ' '
	}
}

func readLibs() []lib {
	libsFile := filepath.Join(libInputDir, "libs.json")

	b, err := os.ReadFile(libsFile)
	if err != nil {
		log.Fatalf("failed to open libs.json: %v", err)
	}
	stripJSONC(b)

	var meta struct {
		Libs  []string          `json:"libs"`
		Paths map[string]string `json:"paths"`
	}

	if err := json.Unmarshal(b, &meta); err != nil {
		log.Fatalf("failed to parse libs.json: %v", err)
	}

	var libs []lib
	for _, libName := range meta.Libs {
		sources := []string{libName + ".d.ts"}
		var target string
		if path, ok := meta.Paths[libName]; ok {
			target = path
		} else {
			target = "lib." + libName + ".d.ts"
		}
		libs = append(libs, lib{target: target, sources: sources})
	}

	slices.SortFunc(libs, func(a lib, b lib) int {
		return strings.Compare(a.target, b.target)
	})

	return libs
}

func readCopyright() []byte {
	b, err := os.ReadFile(copyrightNotice)
	if err != nil {
		log.Fatalf("failed to read copyright notice: %v", err)
	}
	return removeCRLF(b)
}

func removeCRLF(b []byte) []byte {
	return bytes.ReplaceAll(b, []byte("\r\n"), []byte("\n"))
}

func writeCode(filename string, code []byte) {
	formatted, err := format.Source(code)
	if err != nil {
		log.Fatalf("failed to format source: %v", err)
	}

	if err := os.WriteFile(filename, formatted, 0o644); err != nil {
		log.Fatalf("failed to write %s: %v", filename, err)
	}
}