// Copyright (c) 2026 Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
// SPDX-License-Identifier: BSD-3-Clause

package lsp

import (
	"bufio"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/url"
	"strconv"
	"strings"
	"sync"

	"sourcedock.dev/petrbalvin/gasm-sdk/lint"
	"sourcedock.dev/petrbalvin/gasm-sdk/token"
)

// Server is a GAsm language server bound to a byte stream.
type Server struct {
	in      *bufio.Reader
	out     io.Writer
	mu      sync.Mutex // guards writes to out
	docs    map[string]string
	ws      workspaceIndex // the on-disk workspace beyond the open documents
	version string         // reported in the initialize result ("" omits it)
}

// New returns a server reading from in and writing to out.
func New(in io.Reader, out io.Writer) *Server {
	return &Server{
		in:   bufio.NewReader(in),
		out:  out,
		docs: make(map[string]string),
	}
}

// SetVersion records the server version reported in the initialize result.
func (s *Server) SetVersion(v string) { s.version = v }

// Run serves requests until the input is exhausted or an exit is requested.
func (s *Server) Run() error {
	for {
		msg, err := s.read()
		if err == io.EOF {
			return nil
		}
		if errors.Is(err, errMalformed) {
			// The message was already answered with a -32700 response;
			// one malformed frame must not end the session.
			continue
		}
		if err != nil {
			return err
		}
		if exit := s.dispatch(msg); exit {
			return nil
		}
	}
}

// errMalformed marks a message that could not be framed or decoded.  The
// server answers it with a -32700 parse error before returning it, so the
// read loop continues instead of propagating a process exit.
var errMalformed = errors.New("malformed JSON-RPC message")

// read parses one Content-Length framed JSON-RPC message.  A Content-Length
// value that does not parse, or a body that is not valid JSON, is answered
// with a -32700 response against the null id (as the JSON-RPC specification
// requires when the request itself cannot be decoded) and reported as
// errMalformed; the header block is consumed first so the next frame is
// read from its true start.
func (s *Server) read() (*rpcMessage, error) {
	length := -1
	var headerErr string
	for {
		line, err := s.in.ReadString('\n')
		if err != nil {
			return nil, err
		}
		line = strings.TrimRight(line, "\r\n")
		if line == "" {
			break
		}
		if k, v, ok := strings.Cut(line, ":"); ok && strings.EqualFold(strings.TrimSpace(k), "Content-Length") {
			n, err := strconv.Atoi(strings.TrimSpace(v))
			if err != nil || n < 0 {
				headerErr = "invalid Content-Length header: " + strconv.Quote(strings.TrimSpace(v))
				continue
			}
			length = n
		}
	}
	if headerErr != "" {
		s.parseError(headerErr)
		return nil, errMalformed
	}
	if length < 0 {
		return nil, fmt.Errorf("missing Content-Length header")
	}
	body := make([]byte, length)
	if _, err := io.ReadFull(s.in, body); err != nil {
		return nil, err
	}
	var msg rpcMessage
	if err := json.Unmarshal(body, &msg); err != nil {
		s.parseError("invalid JSON body: " + err.Error())
		return nil, errMalformed
	}
	return &msg, nil
}

// send marshals and writes one framed message.
func (s *Server) send(msg *rpcMessage) error {
	msg.JSONRPC = "2.0"
	body, err := json.Marshal(msg)
	if err != nil {
		return err
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	if _, err := fmt.Fprintf(s.out, "Content-Length: %d\r\n\r\n", len(body)); err != nil {
		return err
	}
	_, err = s.out.Write(body)
	return err
}

func (s *Server) respond(id *json.RawMessage, result any) {
	// JSON-RPC 2.0 requires the result member to be present even when its
	// value is null (shutdown, a hover over nothing); a nil result is
	// marshalled as an explicit null rather than dropped by omitempty.
	// Notifications never take this path, so they grow no member.
	if result == nil {
		result = json.RawMessage("null")
	}
	_ = s.send(&rpcMessage{ID: id, Result: result})
}

func (s *Server) respondError(id *json.RawMessage, code int, msg string) {
	_ = s.send(&rpcMessage{ID: id, Error: &rpcError{Code: code, Message: msg}})
}

// parseError answers a -32700 parse error against the null id: when the
// request could not be decoded there is no id to echo back.
func (s *Server) parseError(msg string) {
	id := json.RawMessage("null")
	s.respondError(&id, errParse, msg)
}

func (s *Server) notify(method string, params any) {
	raw, _ := json.Marshal(params)
	_ = s.send(&rpcMessage{Method: method, Params: raw})
}

// dispatch routes one message.  It returns true when the server should stop.
// A panic in any handler is recovered and answered as an internal error:
// handlers parse live editor buffers, so malformed input must never take
// the whole server down.
func (s *Server) dispatch(msg *rpcMessage) (exit bool) {
	defer func() {
		if r := recover(); r != nil {
			if msg != nil && msg.ID != nil {
				s.respondError(msg.ID, errInternalError, fmt.Sprintf("internal error: %v", r))
			}
		}
	}()

	switch msg.Method {
	case "initialize":
		var ip initializeParams
		if len(msg.Params) > 0 {
			json.Unmarshal(msg.Params, &ip)
		}
		s.ws.roots = ip.roots()
		info := map[string]string{"name": "gasm"}
		if s.version != "" {
			info["version"] = s.version
		}
		s.respond(msg.ID, initializeResult{
			Capabilities: ServerCapabilities{
				TextDocumentSync:           1, // full sync
				CompletionProvider:         map[string]any{},
				HoverProvider:              true,
				DefinitionProvider:         true,
				ReferencesProvider:         true,
				RenameProvider:             true,
				DocumentSymbolProvider:     true,
				DocumentFormattingProvider: true,
				SemanticTokensProvider: map[string]any{
					"legend": SemanticTokensLegend{
						TokenTypes:     semanticTokenTypes,
						TokenModifiers: []string{},
					},
					"full": true,
				},
				InlayHintProvider:         true,
				DocumentHighlightProvider: true,
				CodeActionProvider:        true,
				SignatureHelpProvider:     map[string]any{"triggerCharacters": []string{"("}},
				WorkspaceSymbolProvider:   true,
				DiagnosticProvider:        map[string]any{"interFileDependencies": false, "workspaceDiagnostics": false},
				DocumentLinkProvider:      map[string]any{},
				FoldingRangeProvider:      true,
				Workspace:                 map[string]any{"didChangeWatchedFiles": map[string]any{}},
			},
			ServerInfo: info,
		})

	case "initialized", "textDocument/didSave":
		// Notifications with nothing to do.

	case "textDocument/didOpen":
		var p didOpenParams
		if json.Unmarshal(msg.Params, &p) == nil {
			s.docs[p.TextDocument.URI] = p.TextDocument.Text
			s.publish(p.TextDocument.URI)
		}

	case "textDocument/didChange":
		var p didChangeParams
		if json.Unmarshal(msg.Params, &p) == nil && len(p.ContentChanges) > 0 {
			// Full sync: the last change carries the whole document.
			text := p.ContentChanges[len(p.ContentChanges)-1].Text
			s.docs[p.TextDocument.URI] = text
			s.publish(p.TextDocument.URI)
		}

	case "textDocument/didClose":
		var p didCloseParams
		if json.Unmarshal(msg.Params, &p) == nil {
			delete(s.docs, p.TextDocument.URI)
			// Clear diagnostics for the closed document.
			s.notify("textDocument/publishDiagnostics", publishDiagnosticsParams{
				URI: p.TextDocument.URI, Diagnostics: []Diagnostic{},
			})
		}

	case "textDocument/completion":
		var p completionParams
		json.Unmarshal(msg.Params, &p)
		s.respond(msg.ID, s.completion(p))

	case "textDocument/hover":
		var p hoverParams
		json.Unmarshal(msg.Params, &p)
		s.respond(msg.ID, s.hover(p))

	case "textDocument/definition":
		var p definitionParams
		json.Unmarshal(msg.Params, &p)
		s.respond(msg.ID, s.definition(p))

	case "textDocument/documentSymbol":
		var p documentSymbolParams
		json.Unmarshal(msg.Params, &p)
		s.respond(msg.ID, s.documentSymbols(p))

	case "textDocument/references":
		var p referenceParams
		json.Unmarshal(msg.Params, &p)
		s.respond(msg.ID, s.references(p))

	case "textDocument/rename":
		var p renameParams
		json.Unmarshal(msg.Params, &p)
		s.respond(msg.ID, s.rename(p))

	case "textDocument/formatting":
		var p documentFormattingParams
		json.Unmarshal(msg.Params, &p)
		s.respond(msg.ID, s.documentFormatting(p))

	case "textDocument/inlayHint":
		var p inlayHintParams
		json.Unmarshal(msg.Params, &p)
		s.respond(msg.ID, s.inlayHints(p))

	case "textDocument/codeAction":
		var p codeActionParams
		json.Unmarshal(msg.Params, &p)
		s.respond(msg.ID, s.codeActions(p))

	case "textDocument/signatureHelp":
		var p signatureHelpParams
		json.Unmarshal(msg.Params, &p)
		s.respond(msg.ID, s.signatureHelp(p))

	case "textDocument/documentHighlight":
		var p documentHighlightParams
		json.Unmarshal(msg.Params, &p)
		s.respond(msg.ID, s.documentHighlights(p))

	case "textDocument/semanticTokens/full":
		var p semanticTokensParams
		json.Unmarshal(msg.Params, &p)
		s.respond(msg.ID, s.semanticTokens(p))

	case "textDocument/diagnostic":
		var p diagnosticParams
		json.Unmarshal(msg.Params, &p)
		s.respond(msg.ID, documentDiagnosticReport{Kind: "full", Items: s.diagnosticsFor(p.TextDocument.URI)})
	case "textDocument/documentLink":
		var p documentLinkParams
		json.Unmarshal(msg.Params, &p)
		s.respond(msg.ID, s.documentLinks(p.TextDocument.URI))
	case "textDocument/foldingRange":
		var p foldingRangeParams
		json.Unmarshal(msg.Params, &p)
		s.respond(msg.ID, s.foldingRanges(p.TextDocument.URI))
	case "workspace/symbol":
		var p workspaceSymbolParams
		json.Unmarshal(msg.Params, &p)
		s.respond(msg.ID, s.workspaceSymbols(p))

	case "workspace/didChangeWatchedFiles":
		var p didChangeWatchedFilesParams
		if json.Unmarshal(msg.Params, &p) == nil {
			for _, ch := range p.Changes {
				s.ws.watched(uriPath(ch.URI), ch.Type == fileDeleted)
			}
		}

	case "shutdown":
		s.respond(msg.ID, nil)

	case "exit":
		return true

	default:
		if msg.ID != nil {
			s.respondError(msg.ID, errMethodNotFound, "method not supported: "+msg.Method)
		}
	}
	return false
}

// publish parses and lints a document and pushes the diagnostics to the client.
func (s *Server) publish(uri string) {
	s.notify("textDocument/publishDiagnostics", publishDiagnosticsParams{URI: uri, Diagnostics: s.diagnosticsFor(uri)})
}

// toRange converts one-based line/column plus an optional end position into an
// LSP range (zero-based).
func toRange(line, col int, end token.Position) Range {
	start := Position{Line: line - 1, Character: col - 1}
	finish := start
	if end.IsValid() {
		finish = Position{Line: end.Line - 1, Character: end.Column - 1}
	} else {
		finish.Character = start.Character + 1
	}
	return Range{Start: start, End: finish}
}

func lintSeverity(s lint.Severity) int {
	switch s {
	case lint.Error:
		return sevError
	case lint.Warning:
		return sevWarning
	case lint.Information:
		return sevInformation
	default:
		return sevHint
	}
}

// uriPath strips a file:// scheme and percent-decodes the path component.
// LSP clients percent-encode URIs, so a raw slice would break every on-disk
// lookup for paths containing spaces or non-ASCII characters.
func uriPath(uri string) string {
	if rest, ok := strings.CutPrefix(uri, "file://"); ok {
		if decoded, err := url.PathUnescape(rest); err == nil {
			return decoded
		}
		return rest
	}
	return uri
}