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

package lsp

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

	"sourcedock.dev/petrbalvin/gasm-devkit/arch"
	"sourcedock.dev/petrbalvin/gasm-devkit/lint"
	"sourcedock.dev/petrbalvin/gasm-devkit/parser"
	"sourcedock.dev/petrbalvin/gasm-devkit/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
}

// 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),
	}
}

// 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 err != nil {
			return err
		}
		if exit := s.dispatch(msg); exit {
			return nil
		}
	}
}

// read parses one Content-Length framed JSON-RPC message.
func (s *Server) read() (*rpcMessage, error) {
	length := -1
	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") {
			length, _ = strconv.Atoi(strings.TrimSpace(v))
		}
	}
	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 {
		return nil, err
	}
	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) {
	_ = 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}})
}

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.
func (s *Server) dispatch(msg *rpcMessage) (exit bool) {
	switch msg.Method {
	case "initialize":
		s.respond(msg.ID, initializeResult{
			Capabilities: ServerCapabilities{
				TextDocumentSync:       1, // full sync
				CompletionProvider:     map[string]any{},
				HoverProvider:          true,
				DocumentSymbolProvider: true,
				SemanticTokensProvider: map[string]any{
					"legend": SemanticTokensLegend{
						TokenTypes:     semanticTokenTypes,
						TokenModifiers: []string{},
					},
					"full": true,
				},
			},
			ServerInfo: map[string]string{"name": "gasm", "version": "0.1.0"},
		})

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

	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) {
	text := s.docs[uri]
	f, _ := parser.Parse(uri, text)
	cfg := lint.Config{Arch: arch.FromFilename(uriPath(uri))}
	diags := lint.File(f, cfg)

	out := make([]Diagnostic, 0, len(diags))
	for _, d := range diags {
		out = append(out, Diagnostic{
			Range:    toRange(d.Pos.Line, d.Pos.Column, d.End),
			Severity: lintSeverity(d.Severity),
			Code:     d.Code,
			Source:   "gasm",
			Message:  d.Message,
		})
	}
	s.notify("textDocument/publishDiagnostics", publishDiagnosticsParams{URI: uri, Diagnostics: out})
}

// 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 returns the path component.
func uriPath(uri string) string {
	if rest, ok := strings.CutPrefix(uri, "file://"); ok {
		return rest
	}
	return uri
}