package main

import "core:fmt"
import "core:mem"
import vmem "core:mem/virtual"
import "core:net"
import "core:strings"
import "core:strconv"

// HTTP Method enumeration
HTTP_Method :: enum {
	GET,
	POST,
	PUT,
	DELETE,
	OPTIONS,
	HEAD,
	PATCH,
}

method_from_string :: proc(s: string) -> HTTP_Method {
	switch s {
	case "GET":     return .GET
	case "POST":    return .POST
	case "PUT":     return .PUT
	case "DELETE":  return .DELETE
	case "OPTIONS": return .OPTIONS
	case "HEAD":    return .HEAD
	case "PATCH":   return .PATCH
	}
	return .GET
}

// HTTP Status codes
HTTP_Status :: enum u16 {
	OK                    = 200,
	Created               = 201,
	No_Content            = 204,
	Bad_Request           = 400,
	Unauthorized          = 401,
	Forbidden             = 403,
	Not_Found             = 404,
	Method_Not_Allowed    = 405,
	Conflict              = 409,
	Payload_Too_Large     = 413,
	Internal_Server_Error = 500,
	Service_Unavailable   = 503,
}

// HTTP Header
HTTP_Header :: struct {
	name:  string,
	value: string,
}

// HTTP Request
HTTP_Request :: struct {
	method:  HTTP_Method,
	path:    string,
	headers: []HTTP_Header,
	body:    []byte,
}

// Get header value by name (case-insensitive)
request_get_header :: proc(req: ^HTTP_Request, name: string) -> Maybe(string) {
	for header in req.headers {
		if strings.equal_fold(header.name, name) {
			return header.value
		}
	}
	return nil
}

// HTTP Response
HTTP_Response :: struct {
	status:  HTTP_Status,
	headers: [dynamic]HTTP_Header,
	body:    [dynamic]byte,
}

response_init :: proc(allocator: mem.Allocator) -> HTTP_Response {
	return HTTP_Response{
		status  = .OK,
		headers = make([dynamic]HTTP_Header, allocator),
		body    = make([dynamic]byte, allocator),
	}
}

response_set_status :: proc(resp: ^HTTP_Response, status: HTTP_Status) {
	resp.status = status
}

response_add_header :: proc(resp: ^HTTP_Response, name: string, value: string) {
	append(&resp.headers, HTTP_Header{name = name, value = value})
}

response_set_body :: proc(resp: ^HTTP_Response, data: []byte) {
	clear(&resp.body)
	append(&resp.body, ..data)
}

// Request handler function type
// Takes context pointer, request, and request-scoped allocator
Request_Handler :: #type proc(ctx: rawptr, request: ^HTTP_Request, request_alloc: mem.Allocator) -> HTTP_Response

// Server configuration
Server_Config :: struct {
	max_body_size:              int,  // default 100MB
	max_headers:                int,  // default 100
	read_buffer_size:           int,  // default 8KB
	enable_keep_alive:          bool, // default true
	max_requests_per_connection: int, // default 1000
}

default_server_config :: proc() -> Server_Config {
	return Server_Config{
		max_body_size              = 100 * 1024 * 1024,
		max_headers                = 100,
		read_buffer_size           = 8 * 1024,
		enable_keep_alive          = true,
		max_requests_per_connection = 1000,
	}
}

// Server
Server :: struct {
	allocator:   mem.Allocator,
	endpoint:    net.Endpoint,
	handler:     Request_Handler,
	handler_ctx: rawptr,
	config:      Server_Config,
	running:     bool,
	socket:      Maybe(net.TCP_Socket),
}

server_init :: proc(
	allocator: mem.Allocator,
	host: string,
	port: int,
	handler: Request_Handler,
	handler_ctx: rawptr,
	config: Server_Config,
) -> (Server, bool) {
	endpoint, endpoint_ok := net.parse_endpoint(fmt.tprintf("%s:%d", host, port))
	if !endpoint_ok {
		return {}, false
	}

	return Server{
		allocator   = allocator,
		endpoint    = endpoint,
		handler     = handler,
		handler_ctx = handler_ctx,
		config      = config,
		running     = false,
		socket      = nil,
	}, true
}

server_start :: proc(server: ^Server) -> bool {
	// Create listening socket
	socket, socket_err := net.listen_tcp(server.endpoint)
	if socket_err != nil {
		fmt.eprintfln("Failed to create listening socket: %v", socket_err)
		return false
	}

	server.socket = socket
	server.running = true

	fmt.printfln("HTTP server listening on %v", server.endpoint)

	// Accept loop
	for server.running {
		conn, source, accept_err := net.accept_tcp(socket)
		if accept_err != nil {
			if server.running {
				fmt.eprintfln("Accept error: %v", accept_err)
			}
			continue
		}

		// Handle connection in separate goroutine would go here
		// For now, handle synchronously (should spawn thread)
		handle_connection(server, conn, source)
	}

	return true
}

server_stop :: proc(server: ^Server) {
	server.running = false
	if sock, ok := server.socket.?; ok {
		net.close(sock)
		server.socket = nil
	}
}

// Handle a single connection
handle_connection :: proc(server: ^Server, conn: net.TCP_Socket, source: net.Endpoint) {
	defer net.close(conn)

	request_count := 0
	for request_count < server.config.max_requests_per_connection {
		request_count += 1

		// Growing arena for this request
		arena: vmem.Arena
		arena_err := vmem.arena_init_growing(&arena)
		if arena_err != .None {
			break
		}
		defer vmem.arena_destroy(&arena)

		request_alloc := vmem.arena_allocator(&arena)

		// TODO: Double check if we want *all* downstream allocations to use the request arena?
		old := context.allocator
		context.allocator = request_alloc
		defer context.allocator = old

		request, parse_ok := parse_request(conn, request_alloc, server.config)
		if !parse_ok {
			break
		}

		response := server.handler(server.handler_ctx, &request, request_alloc)

		send_ok := send_response(conn, &response, request_alloc)
		if !send_ok {
			break
		}

		// Check keep-alive
		keep_alive := request_get_header(&request, "Connection")
		if ka, ok := keep_alive.?; ok {
			if !strings.equal_fold(ka, "keep-alive") {
				break
			}
		} else if !server.config.enable_keep_alive {
			break
		}

		// Arena is automatically freed here
	}
}

// Parse HTTP request
parse_request :: proc(
	conn: net.TCP_Socket,
	allocator: mem.Allocator,
	config: Server_Config,
) -> (HTTP_Request, bool) {
	// Read request line and headers
	buffer := make([]byte, config.read_buffer_size, allocator)

	bytes_read, read_err := net.recv_tcp(conn, buffer)
	if read_err != nil || bytes_read == 0 {
		return {}, false
	}

	request_data := buffer[:bytes_read]

	// Find end of headers (\r\n\r\n)
	header_end_idx := strings.index(string(request_data), "\r\n\r\n")
	if header_end_idx < 0 {
		return {}, false
	}

	header_section := string(request_data[:header_end_idx])
	body_start := header_end_idx + 4

	// Parse request line
	lines := strings.split_lines(header_section, allocator)
	if len(lines) == 0 {
		return {}, false
	}

	request_line := lines[0]
	parts := strings.split(request_line, " ", allocator)
	if len(parts) < 3 {
		return {}, false
	}

	method := method_from_string(parts[0])
	path := strings.clone(parts[1], allocator)

	// Parse headers
	headers := make([dynamic]HTTP_Header, allocator)
	for i := 1; i < len(lines); i += 1 {
		line := lines[i]
		if len(line) == 0 {
			continue
		}

		colon_idx := strings.index(line, ":")
		if colon_idx < 0 {
			continue
		}

		name := strings.trim_space(line[:colon_idx])
		value := strings.trim_space(line[colon_idx+1:])

		append(&headers, HTTP_Header{
			name  = strings.clone(name, allocator),
			value = strings.clone(value, allocator),
		})
	}

	// Read body if Content-Length present
	body: []byte

	content_length_header := request_get_header_from_slice(headers[:], "Content-Length")
	if cl, ok := content_length_header.?; ok {
		content_length := strconv.parse_int(cl) or_else 0

		if content_length > 0 && content_length <= config.max_body_size {
			// Check if we already have the body in buffer
			existing_body := request_data[body_start:]

			if len(existing_body) >= content_length {
				// Body already in buffer
				body = make([]byte, content_length, allocator)
				copy(body, existing_body[:content_length])
			} else {
				// Need to read more
				body = make([]byte, content_length, allocator)
				copy(body, existing_body)

				remaining := content_length - len(existing_body)
				body_written := len(existing_body)

				for remaining > 0 {
					chunk_size := min(remaining, config.read_buffer_size)
					chunk := make([]byte, chunk_size, allocator)

					n, err := net.recv_tcp(conn, chunk)
					if err != nil || n == 0 {
						return {}, false
					}

					copy(body[body_written:], chunk[:n])
					body_written += n
					remaining -= n
				}
			}
		}
	}

	return HTTP_Request{
		method  = method,
		path    = path,
		headers = headers[:],
		body    = body,
	}, true
}

// Helper to get header from slice
request_get_header_from_slice :: proc(headers: []HTTP_Header, name: string) -> Maybe(string) {
	for header in headers {
		if strings.equal_fold(header.name, name) {
			return header.value
		}
	}
	return nil
}

// Send HTTP response
send_response :: proc(conn: net.TCP_Socket, resp: ^HTTP_Response, allocator: mem.Allocator) -> bool {
	// Build response string
	builder := strings.builder_make(allocator)
	defer strings.builder_destroy(&builder)

	// Status line
	strings.write_string(&builder, "HTTP/1.1 ")
	strings.write_int(&builder, int(resp.status))
	strings.write_string(&builder, " ")
	strings.write_string(&builder, status_text(resp.status))
	strings.write_string(&builder, "\r\n")

	// Headers
	response_add_header(resp, "Content-Length", fmt.tprintf("%d", len(resp.body)))

	for header in resp.headers {
		strings.write_string(&builder, header.name)
		strings.write_string(&builder, ": ")
		strings.write_string(&builder, header.value)
		strings.write_string(&builder, "\r\n")
	}

	// End of headers
	strings.write_string(&builder, "\r\n")

	// Send headers
	header_bytes := transmute([]byte)strings.to_string(builder)
	_, send_err := net.send_tcp(conn, header_bytes)
	if send_err != nil {
		return false
	}

	// Send body
	if len(resp.body) > 0 {
		_, send_err = net.send_tcp(conn, resp.body[:])
		if send_err != nil {
			return false
		}
	}

	return true
}

// Get status text for status code
status_text :: proc(status: HTTP_Status) -> string {
	switch status {
	case .OK:                    return "OK"
	case .Created:               return "Created"
	case .No_Content:            return "No Content"
	case .Bad_Request:           return "Bad Request"
	case .Unauthorized:          return "Unauthorized"
	case .Forbidden:             return "Forbidden"
	case .Not_Found:             return "Not Found"
	case .Method_Not_Allowed:    return "Method Not Allowed"
	case .Conflict:              return "Conflict"
	case .Payload_Too_Large:     return "Payload Too Large"
	case .Internal_Server_Error: return "Internal Server Error"
	case .Service_Unavailable:   return "Service Unavailable"
	}
	return "Unknown"
}