// Package client is a small Go client for Jarl's REST API, used by the
// jarl CLI.
package client

import (
	"bytes"
	"context"
	"crypto/tls"
	"crypto/x509"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net"
	"net/http"
	"net/url"
	"os"
	"strings"
	"time"

	"jarl/internal/api"
	"jarl/internal/version"
)

// Client talks to a Jarl server.
type Client struct {
	BaseURL string
	Token   string
	HTTP    *http.Client
	// Changeset, if set, stages changes into this changeset instead of
	// applying them.
	Changeset int64
	DryRun    bool
	Force     bool
	// Preflight lets only requests through that can't change anything:
	// reads and dry runs. Running a command on several servers uses it to
	// check the command everywhere before running it anywhere.
	Preflight bool
	// Mutated records that a preflight run sent a (dry-run) change.
	Mutated bool
}

// ErrNoPreflight is returned in Preflight mode for a request that would
// change something and has no dry run.
var ErrNoPreflight = errors.New("this command can't be checked without running it, so it can't run on several servers at once; run it on one server at a time with --server NAME")

// Options configure New.
type Options struct {
	Server   string
	Token    string
	Insecure bool   // skip TLS certificate verification
	CACert   string // PEM file with an extra trusted CA
	Timeout  time.Duration
}

// New creates a client.
func New(o Options) (*Client, error) {
	if o.Server == "" {
		return nil, fmt.Errorf("no server configured: use --server, JARL_SERVER or 'jarl config set server https://...'")
	}
	tr := http.DefaultTransport.(*http.Transport).Clone()
	base := strings.TrimSuffix(o.Server, "/")
	if path, ok := SocketPath(o.Server); ok {
		// jarld's local unix socket: every request goes to the socket,
		// whatever the URL's host.
		tr.Proxy = nil
		tr.DialContext = func(ctx context.Context, _, _ string) (net.Conn, error) {
			return (&net.Dialer{}).DialContext(ctx, "unix", path)
		}
		base = "http://jarld"
	} else if u, err := url.Parse(o.Server); err != nil || (u.Scheme != "http" && u.Scheme != "https") || u.Host == "" {
		return nil, fmt.Errorf("invalid server URL %q (use e.g. https://dns.example.com:8053, or unix:///run/jarl/jarl.sock)", o.Server)
	}
	tc := &tls.Config{MinVersion: tls.VersionTLS12, InsecureSkipVerify: o.Insecure} //nolint:gosec // explicit user choice
	if o.CACert != "" {
		pem, err := os.ReadFile(o.CACert)
		if err != nil {
			return nil, err
		}
		pool, err := x509.SystemCertPool()
		if err != nil || pool == nil {
			pool = x509.NewCertPool()
		}
		if !pool.AppendCertsFromPEM(pem) {
			return nil, fmt.Errorf("no certificates in %s", o.CACert)
		}
		tc.RootCAs = pool
	}
	tr.TLSClientConfig = tc
	timeout := o.Timeout
	if timeout == 0 {
		timeout = 2 * time.Minute
	}
	return &Client{BaseURL: base, Token: o.Token, HTTP: &http.Client{Transport: tr, Timeout: timeout}}, nil
}

// SocketPath returns the path of a unix:// server URL
// ("unix:///run/jarl/jarl.sock").
func SocketPath(server string) (string, bool) {
	path, ok := strings.CutPrefix(server, "unix://")
	if !ok || !strings.HasPrefix(path, "/") {
		return "", false
	}
	return path, true
}

// Error is an API error.
type Error struct {
	Status int
	Info   api.ErrorInfo
}

func (e *Error) Error() string {
	if e.Info.Message != "" {
		return e.Info.Message
	}
	return fmt.Sprintf("HTTP %d", e.Status)
}

// Problem is a validation problem (a subset of the server's fields).
type Problem struct {
	Severity string `json:"severity"`
	Code     string `json:"code"`
	Message  string `json:"message"`
	Zone     string `json:"zone"`
	View     string `json:"view"`
}

// CheckMessage is a named-checkconf message.
type CheckMessage struct {
	Text   string `json:"text"`
	Error  bool   `json:"error"`
	Object string `json:"object"`
}

// Problems returns the validation problems attached to the error.
func (e *Error) Problems() []Problem {
	var ps []Problem
	if len(e.Info.Problems) > 0 {
		json.Unmarshal(e.Info.Problems, &ps)
	}
	return ps
}

// Check returns named-checkconf messages attached to the error.
func (e *Error) Check() []CheckMessage {
	var ms []CheckMessage
	if len(e.Info.Check) > 0 {
		json.Unmarshal(e.Info.Check, &ms)
	}
	return ms
}

// Do sends a request. body is marshaled as JSON; out (if not nil) receives
// the JSON response.
func (c *Client) Do(ctx context.Context, method, path string, query url.Values, body, out any) error {
	if c.Preflight && method != http.MethodGet && path != "/system/check" {
		if !isDryRun(query, body) {
			return ErrNoPreflight
		}
		c.Mutated = true
	}
	u := c.BaseURL + api.Prefix + path
	if len(query) > 0 {
		u += "?" + query.Encode()
	}
	var rd io.Reader
	if body != nil {
		b, err := json.Marshal(body)
		if err != nil {
			return err
		}
		rd = bytes.NewReader(b)
	}
	req, err := http.NewRequestWithContext(ctx, method, u, rd)
	if err != nil {
		return err
	}
	if body != nil {
		req.Header.Set("Content-Type", "application/json")
	}
	req.Header.Set("Accept", "application/json")
	req.Header.Set("User-Agent", "jarl-cli/"+version.Version)
	if c.Token != "" {
		req.Header.Set("Authorization", "Bearer "+c.Token)
	}
	resp, err := c.HTTP.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	data, err := io.ReadAll(resp.Body)
	if err != nil {
		return err
	}
	if resp.StatusCode >= 400 {
		var eb api.ErrorBody
		if json.Unmarshal(data, &eb) != nil || eb.Error.Message == "" {
			eb.Error.Message = fmt.Sprintf("HTTP %d: %s", resp.StatusCode, strings.TrimSpace(string(data)))
		}
		return &Error{Status: resp.StatusCode, Info: eb.Error}
	}
	if out == nil || len(data) == 0 {
		return nil
	}
	if s, ok := out.(*string); ok {
		*s = string(data)
		return nil
	}
	return json.Unmarshal(data, out)
}

// isDryRun reports whether a request asks for a dry run, in its query or
// its body.
func isDryRun(query url.Values, body any) bool {
	if query.Get("dry_run") == "1" {
		return true
	}
	switch b := body.(type) {
	case api.BatchRequest:
		return b.DryRun
	case *api.BatchRequest:
		return b != nil && b.DryRun
	case map[string]any:
		v, _ := b["dry_run"].(bool)
		return v
	case map[string]bool:
		return b["dry_run"]
	}
	return false
}

// Get is Do with GET.
func (c *Client) Get(ctx context.Context, path string, query url.Values, out any) error {
	return c.Do(ctx, http.MethodGet, path, query, nil, out)
}

// Mutate sends a configuration change, honoring Changeset, DryRun and
// Force.
func (c *Client) Mutate(ctx context.Context, method, path string, query url.Values, body any) (*api.MutationResponse, error) {
	q := url.Values{}
	for k, v := range query {
		q[k] = v
	}
	if c.Changeset > 0 {
		q.Set("changeset", fmt.Sprint(c.Changeset))
	}
	if c.DryRun {
		q.Set("dry_run", "1")
	}
	if c.Force {
		q.Set("force", "1")
	}
	var out api.MutationResponse
	err := c.Do(ctx, method, path, q, body, &out)
	return &out, err
}

// Result is the part of an engine result the CLI shows.
type Result struct {
	ChangesetID int64          `json:"changeset_id"`
	Applied     bool           `json:"applied"`
	Valid       bool           `json:"valid"`
	Problems    []Problem      `json:"problems"`
	Existing    []Problem      `json:"existing_problems"`
	Check       []CheckMessage `json:"check"`
	Diff        string         `json:"diff"`
	Files       []string       `json:"files_changed"`
	Serials     []struct {
		Zone string `json:"zone"`
		View string `json:"view"`
		Old  uint32 `json:"old"`
		New  uint32 `json:"new"`
	} `json:"serials"`
	Reloaded []string `json:"reloaded"`
	Warnings []string `json:"warnings"`
	Ops      []struct {
		Seq     int    `json:"seq"`
		Op      string `json:"op"`
		ID      int64  `json:"id"`
		Summary string `json:"summary"`
	} `json:"ops"`
	Error *struct {
		Code    string `json:"code"`
		Message string `json:"message"`
	} `json:"error"`
}

// ParseResult decodes the result embedded in a mutation response or error.
func ParseResult(raw json.RawMessage) *Result {
	if len(raw) == 0 {
		return nil
	}
	var r Result
	if json.Unmarshal(raw, &r) != nil {
		return nil
	}
	return &r
}