package sourcemaps

import (
	"container/list"
	"encoding/base64"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strconv"
	"strings"
	"sync"

	sm "github.com/go-sourcemap/sourcemap"
)

var frameRE = regexp.MustCompile(`(.*?)(https?://[^ )]+|[^ )]+):(\d+):(\d+)(\)?\s*)$`)

// defaultCacheBytes bounds the on-disk size of the maps kept parsed in memory.
// A parsed map costs several times its file size, so this is a heap budget of
// roughly 4-5x. Override with OTEL_SOURCEMAP_CACHE_MB.
const defaultCacheBytes = 64 << 20

// Resolver indexes uploaded maps by file name at startup and parses them lazily
// on first use, keeping the most recently used ones within a size budget. A
// release ships hundreds of chunks, so parsing them all up front does not fit
// in memory.
type Resolver struct {
	dir string

	mu         sync.Mutex
	index      map[string]string // key(release, source) -> file name
	cache      map[string]*list.Element
	lru        *list.List // front = most recently used; values are *cacheEntry
	cacheBytes int64
	maxBytes   int64
}

type cacheEntry struct {
	key      string
	consumer *sm.Consumer
	size     int64
}

func New(dir string) (*Resolver, error) {
	if dir == "" {
		dir = "./sourcemaps"
	}
	if err := os.MkdirAll(dir, 0750); err != nil {
		return nil, err
	}
	maxBytes := int64(defaultCacheBytes)
	if mb, err := strconv.Atoi(os.Getenv("OTEL_SOURCEMAP_CACHE_MB")); err == nil && mb > 0 {
		maxBytes = int64(mb) << 20
	}
	r := &Resolver{
		dir:      dir,
		index:    make(map[string]string),
		cache:    make(map[string]*list.Element),
		lru:      list.New(),
		maxBytes: maxBytes,
	}
	r.scan()
	return r, nil
}

// fileName encodes release and source reversibly so maps can be reloaded
// from disk after a restart.
func fileName(release, source string) string {
	enc := base64.RawURLEncoding
	return enc.EncodeToString([]byte(release)) + "." + enc.EncodeToString([]byte(normalize(source))) + ".map"
}

func parseFileName(name string) (release, source string, ok bool) {
	parts := strings.Split(strings.TrimSuffix(name, ".map"), ".")
	if len(parts) != 2 || !strings.HasSuffix(name, ".map") {
		return "", "", false
	}
	rel, err1 := base64.RawURLEncoding.DecodeString(parts[0])
	src, err2 := base64.RawURLEncoding.DecodeString(parts[1])
	if err1 != nil || err2 != nil {
		return "", "", false
	}
	return string(rel), string(src), true
}

// scan indexes previously uploaded maps by file name without reading them;
// legacy-named files are skipped.
func (r *Resolver) scan() {
	entries, err := os.ReadDir(r.dir)
	if err != nil {
		return
	}
	for _, e := range entries {
		release, source, ok := parseFileName(e.Name())
		if !ok || e.IsDir() {
			continue
		}
		r.index[key(release, source)] = e.Name()
	}
}

// get returns the parsed map for k, loading it from disk on a cache miss. It
// returns nil when no map is indexed or the file is unreadable.
func (r *Resolver) get(k string) *sm.Consumer {
	r.mu.Lock()
	defer r.mu.Unlock()
	if el, ok := r.cache[k]; ok {
		r.lru.MoveToFront(el)
		return el.Value.(*cacheEntry).consumer
	}
	name, ok := r.index[k]
	if !ok {
		return nil
	}
	b, err := os.ReadFile(filepath.Join(r.dir, name))
	if err != nil {
		return nil
	}
	_, source, _ := parseFileName(name)
	consumer, err := sm.Parse(source+".map", b)
	if err != nil {
		return nil
	}
	r.put(k, consumer, int64(len(b)))
	return consumer
}

// put caches a parsed map and evicts least recently used ones over budget,
// always keeping the newest entry. Callers hold r.mu.
func (r *Resolver) put(k string, consumer *sm.Consumer, size int64) {
	if el, ok := r.cache[k]; ok {
		r.cacheBytes -= el.Value.(*cacheEntry).size
		r.lru.Remove(el)
	}
	r.cache[k] = r.lru.PushFront(&cacheEntry{key: k, consumer: consumer, size: size})
	r.cacheBytes += size
	for r.cacheBytes > r.maxBytes && r.lru.Len() > 1 {
		last := r.lru.Back()
		e := last.Value.(*cacheEntry)
		r.lru.Remove(last)
		delete(r.cache, e.key)
		r.cacheBytes -= e.size
	}
}

// Entry describes one loaded source map.
type Entry struct {
	Release string `json:"release"`
	Source  string `json:"source"`
}

// List returns every loaded map, sorted by release then source.
func (r *Resolver) List() []Entry {
	r.mu.Lock()
	defer r.mu.Unlock()
	out := make([]Entry, 0, len(r.index))
	for k := range r.index {
		release, source, _ := strings.Cut(k, "\x00")
		out = append(out, Entry{Release: release, Source: source})
	}
	sort.Slice(out, func(i, j int) bool {
		if out[i].Release != out[j].Release {
			return out[i].Release < out[j].Release
		}
		return out[i].Source < out[j].Source
	})
	return out
}

func key(release, source string) string { return release + "\x00" + normalize(source) }

func normalize(source string) string {
	source = strings.Split(source, "?")[0]
	if i := strings.Index(source, "/assets/"); i >= 0 {
		return source[i:]
	}
	return strings.TrimPrefix(source, "./")
}

func (r *Resolver) Upload(release, source string, body io.Reader) error {
	if strings.TrimSpace(release) == "" || strings.TrimSpace(source) == "" {
		return fmt.Errorf("release and source are required")
	}
	b, err := io.ReadAll(io.LimitReader(body, 50<<20))
	if err != nil {
		return err
	}
	consumer, err := sm.Parse(source+".map", b)
	if err != nil {
		return fmt.Errorf("invalid source map: %w", err)
	}
	name := filepath.Join(r.dir, fileName(release, source))
	if err := os.WriteFile(name, b, 0600); err != nil {
		return err
	}
	k := key(release, source)
	r.mu.Lock()
	r.index[k] = fileName(release, source)
	r.put(k, consumer, int64(len(b)))
	r.mu.Unlock()
	return nil
}

func safe(s string) string {
	s = strings.ReplaceAll(s, "/", "_")
	s = strings.ReplaceAll(s, "\\", "_")
	return strings.Map(func(r rune) rune {
		if (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') || (r >= '0' && r <= '9') || strings.ContainsRune("._-", r) {
			return r
		}
		return '_'
	}, s)
}

func (r *Resolver) ResolveStack(release, stack string) string {
	if release == "" || stack == "" {
		return stack
	}
	lines := strings.Split(stack, "\n")
	for i, line := range lines {
		m := frameRE.FindStringSubmatch(line)
		if m == nil {
			continue
		}
		genLine, _ := strconv.Atoi(m[3])
		genCol, _ := strconv.Atoi(m[4])
		consumer := r.get(key(release, m[2]))
		if consumer == nil {
			continue
		}
		source, name, srcLine, srcCol, ok := consumer.Source(genLine, genCol)
		if !ok {
			continue
		}
		label := source
		if name != "" {
			label += " (" + name + ")"
		}
		lines[i] = fmt.Sprintf("%s%s:%d:%d%s  [mapped from %s:%d:%d]", m[1], label, srcLine, srcCol, m[5], m[2], genLine, genCol)
	}
	return strings.Join(lines, "\n")
}

// Frame is one parsed stack frame, with original-source details when a map
// for its file was uploaded. Status explains why a frame is or is not mapped:
// "mapped", "no-release", "no-map" (no map uploaded for this file/release) or
// "unmapped" (a map exists but has no mapping for this position).
type Frame struct {
	Raw      string `json:"raw"`
	Function string `json:"function,omitempty"`
	File     string `json:"file"`
	Line     int    `json:"line"`
	Column   int    `json:"column"`
	Status   string `json:"status"`

	Source     string   `json:"source,omitempty"`
	Name       string   `json:"name,omitempty"`
	SrcLine    int      `json:"srcLine,omitempty"`
	SrcColumn  int      `json:"srcColumn,omitempty"`
	Context    []string `json:"context,omitempty"`    // original source lines around SrcLine
	ContextTop int      `json:"contextTop,omitempty"` // 1-based line number of Context[0]
}

const frameContext = 6

// ResolveFrames parses every frame in the stack and maps it through the
// uploaded source maps, including surrounding original source when the map
// embeds sourcesContent.
func (r *Resolver) ResolveFrames(release, stack string) []Frame {
	var frames []Frame
	for _, line := range strings.Split(stack, "\n") {
		m := frameRE.FindStringSubmatch(line)
		if m == nil {
			continue
		}
		ln, _ := strconv.Atoi(m[3])
		col, _ := strconv.Atoi(m[4])
		fn := strings.TrimSpace(strings.TrimSuffix(strings.TrimPrefix(strings.TrimSpace(m[1]), "at "), "("))
		f := Frame{Raw: strings.TrimSpace(line), Function: fn, File: m[2], Line: ln, Column: col, Status: "mapped"}
		switch consumer := r.get(key(release, m[2])); {
		case release == "":
			f.Status = "no-release"
		case consumer == nil:
			f.Status = "no-map"
		default:
			source, name, sl, sc, ok := consumer.Source(ln, col)
			if !ok {
				f.Status = "unmapped"
				break
			}
			f.Source, f.Name, f.SrcLine, f.SrcColumn = source, name, sl, sc
			if content := consumer.SourceContent(source); content != "" {
				src := strings.Split(content, "\n")
				top := max(sl-frameContext, 1)
				bottom := min(sl+frameContext, len(src))
				if top <= bottom {
					f.Context, f.ContextTop = src[top-1:bottom], top
				}
			}
		}
		frames = append(frames, f)
	}
	return frames
}