package spec

import (
	"context"
	"errors"
	"fmt"
	"math"
	"net/url"
	"sort"
	"strings"

	"github.com/getkin/kin-openapi/jsoninfo"
)

// Servers is specified by OpenAPI/Swagger standard version 3.
type Servers []*Server

// Validate returns an error if Servers does not comply with the OpenAPI spec.
func (servers Servers) Validate(ctx context.Context) error {
	for _, v := range servers {
		if err := v.Validate(ctx); err != nil {
			return err
		}
	}
	return nil
}

// BasePath returns the base path of the first server in the list, or /.
func (servers Servers) BasePath() (string, error) {
	for _, server := range servers {
		return server.BasePath()
	}
	return "/", nil
}

func (servers Servers) MatchURL(parsedURL *url.URL) (*Server, []string, string) {
	rawURL := parsedURL.String()
	if i := strings.IndexByte(rawURL, '?'); i >= 0 {
		rawURL = rawURL[:i]
	}
	for _, server := range servers {
		pathParams, remaining, ok := server.MatchRawURL(rawURL)
		if ok {
			return server, pathParams, remaining
		}
	}
	return nil, nil, ""
}

// Server is specified by OpenAPI/Swagger standard version 3.
// See https://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.0.3.md#serverObject
type Server struct {
	ExtensionProps `json:"-" yaml:"-"`

	URL         string                     `json:"url" yaml:"url"`
	Description string                     `json:"description,omitempty" yaml:"description,omitempty"`
	Variables   map[string]*ServerVariable `json:"variables,omitempty" yaml:"variables,omitempty"`
}

// BasePath returns the base path extracted from the default values of variables, if any.
// Assumes a valid struct (per Validate()).
func (server *Server) BasePath() (string, error) {
	if server == nil {
		return "/", nil
	}

	uri := server.URL
	for name, svar := range server.Variables {
		uri = strings.ReplaceAll(uri, "{"+name+"}", svar.Default)
	}

	u, err := url.ParseRequestURI(uri)
	if err != nil {
		return "", err
	}

	if bp := u.Path; bp != "" {
		return bp, nil
	}

	return "/", nil
}

// MarshalJSON returns the JSON encoding of Server.
func (server *Server) MarshalJSON() ([]byte, error) {
	return jsoninfo.MarshalStrictStruct(server)
}

// UnmarshalJSON sets Server to a copy of data.
func (server *Server) UnmarshalJSON(data []byte) error {
	return jsoninfo.UnmarshalStrictStruct(data, server)
}

func (server Server) ParameterNames() ([]string, error) {
	pattern := server.URL
	var params []string
	for len(pattern) > 0 {
		i := strings.IndexByte(pattern, '{')
		if i < 0 {
			break
		}
		pattern = pattern[i+1:]
		i = strings.IndexByte(pattern, '}')
		if i < 0 {
			return nil, errors.New("missing '}'")
		}
		params = append(params, strings.TrimSpace(pattern[:i]))
		pattern = pattern[i+1:]
	}
	return params, nil
}

func (server Server) MatchRawURL(input string) ([]string, string, bool) {
	pattern := server.URL
	var params []string
	for len(pattern) > 0 {
		c := pattern[0]
		if len(pattern) == 1 && c == '/' {
			break
		}
		if c == '{' {
			// Find end of pattern
			i := strings.IndexByte(pattern, '}')
			if i < 0 {
				return nil, "", false
			}
			pattern = pattern[i+1:]

			// Find next matching pattern character or next '/' whichever comes first
			np := -1
			if len(pattern) > 0 {
				np = strings.IndexByte(input, pattern[0])
			}
			ns := strings.IndexByte(input, '/')

			if np < 0 {
				i = ns
			} else if ns < 0 {
				i = np
			} else {
				i = int(math.Min(float64(np), float64(ns)))
			}
			if i < 0 {
				i = len(input)
			}
			params = append(params, input[:i])
			input = input[i:]
			continue
		}
		if len(input) == 0 || input[0] != c {
			return nil, "", false
		}
		pattern = pattern[1:]
		input = input[1:]
	}
	if input == "" {
		input = "/"
	}
	if input[0] != '/' {
		return nil, "", false
	}
	return params, input, true
}

// Validate returns an error if Server does not comply with the OpenAPI spec.
func (server *Server) Validate(ctx context.Context) (err error) {
	if server.URL == "" {
		return errors.New("value of url must be a non-empty string")
	}

	opening, closing := strings.Count(server.URL, "{"), strings.Count(server.URL, "}")
	if opening != closing {
		return errors.New("server URL has mismatched { and }")
	}

	if opening != len(server.Variables) {
		return errors.New("server has undeclared variables")
	}

	variables := make([]string, 0, len(server.Variables))
	for name := range server.Variables {
		variables = append(variables, name)
	}
	sort.Strings(variables)
	for _, name := range variables {
		v := server.Variables[name]
		if !strings.Contains(server.URL, "{"+name+"}") {
			return errors.New("server has undeclared variables")
		}
		if err = v.Validate(ctx); err != nil {
			return
		}
	}
	return
}

// ServerVariable is specified by OpenAPI/Swagger standard version 3.
// See https://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.0.3.md#server-variable-object
type ServerVariable struct {
	ExtensionProps `json:"-" yaml:"-"`

	Enum        []string `json:"enum,omitempty" yaml:"enum,omitempty"`
	Default     string   `json:"default,omitempty" yaml:"default,omitempty"`
	Description string   `json:"description,omitempty" yaml:"description,omitempty"`
}

// MarshalJSON returns the JSON encoding of ServerVariable.
func (serverVariable *ServerVariable) MarshalJSON() ([]byte, error) {
	return jsoninfo.MarshalStrictStruct(serverVariable)
}

// UnmarshalJSON sets ServerVariable to a copy of data.
func (serverVariable *ServerVariable) UnmarshalJSON(data []byte) error {
	return jsoninfo.UnmarshalStrictStruct(data, serverVariable)
}

// Validate returns an error if ServerVariable does not comply with the OpenAPI spec.
func (serverVariable *ServerVariable) Validate(ctx context.Context) error {
	if serverVariable.Default == "" {
		data, err := serverVariable.MarshalJSON()
		if err != nil {
			return err
		}
		return fmt.Errorf("field default is required in %s", data)
	}
	return nil
}
