package main

import (
	"encoding/json"
	"errors"
	"io"
	"net/http"
	"os"
	"slices"
	"strconv"
	"strings"
)

// A REST API (described by OpenAPI at /api/openapi.json) with the same
// features, tokens, scopes, limits and audit log as the MCP server: every
// operation runs one of the MCP tools (mcpTools), so the two cannot drift.
// The routes below say how a request becomes a tool's arguments.

type apiRoute struct {
	method, path, tool string
	summary            string
}

var apiRoutes = []apiRoute{
	{"GET", "/api/v1/status", "get_status", "State now: uplink, pings, system, whether settings are unapplied"},
	{"GET", "/api/v1/settings", "get_settings", "The saved settings and their ETag"},
	{"PATCH", "/api/v1/settings", "update_settings", "Edit the saved settings with a JSON merge patch (saved, not applied)"},
	{"GET", "/api/v1/settings/check", "check_settings", "Evaluate the saved settings without applying them"},
	{"GET", "/api/v1/changes", "get_pending_changes", "The difference between the confirmed and the saved settings"},
	{"DELETE", "/api/v1/changes", "discard_changes", "Throw the unapplied changes away"},
	{"GET", "/api/v1/interfaces", "list_interfaces", "Network cards and VLAN devices"},
	{"GET", "/api/v1/dhcp-leases", "list_dhcp_leases", "DHCP clients holding a lease"},
	{"GET", "/api/v1/update", "get_update_status", "The installed release and the last update run"},
	{"GET", "/api/v1/apply-log", "get_apply_log", "The log and result of the last apply"},
	{"GET", "/api/v1/logs", "get_logs", "Lines of the system journal"},
}

func toolNamed(name string) *mcpTool {
	for i := range mcpTools {
		if mcpTools[i].name == name {
			return &mcpTools[i]
		}
	}
	return nil
}

func apiError(w http.ResponseWriter, code int, msg string) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(code)
	_ = json.NewEncoder(w).Encode(map[string]string{"error": msg})
}

func (a *app) registerAPI(mux *http.ServeMux) {
	for _, rt := range apiRoutes {
		mux.HandleFunc(rt.method+" "+rt.path, a.apiHandler(rt))
	}
	mux.HandleFunc("GET /api/v1/options", a.apiOptions)
	mux.HandleFunc("GET /api/openapi.json", a.apiSpec)
}

func (a *app) apiHandler(rt apiRoute) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Cache-Control", "no-store")
		tok, ok := a.bearer(w, r)
		if !ok {
			return
		}
		tool := toolNamed(rt.tool)
		if !tok.allows(tool.scope) {
			apiError(w, http.StatusForbidden, "this token may not "+tool.scope+" (scope)")
			return
		}
		args, err := apiArgs(w, r, tool)
		if err != nil {
			apiError(w, http.StatusBadRequest, err.Error())
			return
		}
		res, err := a.runTool(tok, tool, args)
		if err != nil {
			var bad argError
			switch {
			case errors.Is(err, errStale):
				apiError(w, http.StatusConflict, err.Error())
			case errors.As(err, &bad) || tool.scope == scopeChange:
				apiError(w, http.StatusBadRequest, err.Error())
			default:
				apiError(w, http.StatusInternalServerError, err.Error())
			}
			return
		}
		if text, ok := res.(string); ok {
			w.Header().Set("Content-Type", "text/plain; charset=utf-8")
			_, _ = io.WriteString(w, text+"\n")
			return
		}
		if m, ok := res.(map[string]any); ok && rt.tool == "get_settings" {
			if e, ok := m["etag"].(string); ok {
				w.Header().Set("ETag", `"`+e+`"`)
			}
		}
		if m, ok := res.(map[string]any); ok && rt.tool == "update_settings" {
			if e, ok := m["etag"].(string); ok {
				w.Header().Set("ETag", `"`+e+`"`)
			}
		}
		w.Header().Set("Content-Type", "application/json")
		enc := json.NewEncoder(w)
		enc.SetIndent("", "  ")
		_ = enc.Encode(res)
	}
}

// apiArgs builds a tool's arguments from the request: the query for GET
// (typed by the tool's schema), If-Match and the body for the settings patch.
func apiArgs(w http.ResponseWriter, r *http.Request, tool *mcpTool) (json.RawMessage, error) {
	switch r.Method {
	case http.MethodPatch:
		body, err := io.ReadAll(http.MaxBytesReader(w, r.Body, 1<<20))
		if err != nil {
			return nil, errors.New("request too large")
		}
		var patch any
		if err := json.Unmarshal(body, &patch); err != nil {
			return nil, errors.New("the body must be a JSON merge patch")
		}
		etag := strings.Trim(strings.TrimPrefix(r.Header.Get("If-Match"), "W/"), `"`)
		if etag == "" {
			return nil, errors.New("send the settings' ETag in If-Match (GET /api/v1/settings)")
		}
		return json.Marshal(map[string]any{"etag": etag, "patch": patch})
	case http.MethodGet:
		props, _ := tool.schema["properties"].(map[string]any)
		args := map[string]any{}
		for name, p := range props {
			v := r.URL.Query().Get(name)
			if v == "" {
				continue
			}
			if typ, _ := p.(map[string]any)["type"].(string); typ == "integer" {
				n, err := strconv.Atoi(v)
				if err != nil {
					return nil, errors.New(name + " must be a whole number")
				}
				args[name] = n
			} else {
				args[name] = v
			}
		}
		return json.Marshal(args)
	}
	return nil, nil
}

func (a *app) apiOptions(w http.ResponseWriter, r *http.Request) {
	tok, ok := a.bearer(w, r)
	if !ok {
		return
	}
	_ = tok
	data, err := os.ReadFile(a.optionsFile)
	if a.optionsFile == "" || err != nil {
		apiError(w, http.StatusNotFound, "no option documentation on this router")
		return
	}
	w.Header().Set("Content-Type", "application/json")
	_, _ = w.Write(data)
}

// apiSpec serves the OpenAPI description. It describes the interface only (no
// router data), so it needs no token.
func (a *app) apiSpec(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	enc := json.NewEncoder(w)
	enc.SetIndent("", "  ")
	_ = enc.Encode(openAPISpec(a.sys.installedRelease().Version))
}

func openAPISpec(version string) map[string]any {
	errResp := func(d string) map[string]any {
		return map[string]any{"description": d, "content": map[string]any{"application/json": map[string]any{"schema": map[string]any{"$ref": "#/components/schemas/Error"}}}}
	}
	paths := map[string]any{}
	for _, rt := range apiRoutes {
		tool := toolNamed(rt.tool)
		op := map[string]any{
			"operationId": rt.tool,
			"summary":     rt.summary,
			"description": tool.description,
			"tags":        []string{tool.scope},
			"security":    []any{map[string]any{"bearer": []string{}}},
			"x-scope":     tool.scope,
			"responses": map[string]any{
				"200": map[string]any{"description": "The result of " + rt.tool, "content": map[string]any{
					"application/json": map[string]any{"schema": map[string]any{}},
					"text/plain":       map[string]any{"schema": map[string]any{"type": "string"}},
				}},
				"401": errResp("No or an unknown token."),
				"403": errResp("The token's scope does not allow this."),
			},
		}
		var params []any
		switch rt.method {
		case "GET":
			props, _ := tool.schema["properties"].(map[string]any)
			required, _ := tool.schema["required"].([]string)
			for name, p := range props {
				params = append(params, map[string]any{"name": name, "in": "query", "schema": p, "description": p.(map[string]any)["description"], "required": slices.Contains(required, name)})
			}
			if rt.tool == "get_logs" {
				op["responses"].(map[string]any)["400"] = errResp("An argument is not valid.")
			}
		case "PATCH":
			props := tool.schema["properties"].(map[string]any)
			params = append(params, map[string]any{"name": "If-Match", "in": "header", "required": true,
				"description": props["etag"].(map[string]any)["description"], "schema": map[string]any{"type": "string"}})
			op["requestBody"] = map[string]any{"required": true, "content": map[string]any{
				"application/merge-patch+json": map[string]any{"schema": props["patch"]},
				"application/json":             map[string]any{"schema": props["patch"]},
			}}
			op["responses"].(map[string]any)["400"] = errResp("The patch is refused (see the message).")
			op["responses"].(map[string]any)["409"] = errResp("The settings changed since the ETag was read.")
		}
		if params != nil {
			op["parameters"] = params
		}
		entry, _ := paths[rt.path].(map[string]any)
		if entry == nil {
			entry = map[string]any{}
			paths[rt.path] = entry
		}
		entry[strings.ToLower(rt.method)] = op
	}
	paths["/api/v1/options"] = map[string]any{"get": map[string]any{
		"operationId": "get_options", "summary": "Every router option: type, default, description", "tags": []string{scopeRead},
		"security":  []any{map[string]any{"bearer": []string{}}},
		"responses": map[string]any{"200": map[string]any{"description": "The options (JSON)", "content": map[string]any{"application/json": map[string]any{"schema": map[string]any{}}}}, "404": errResp("Not available.")},
	}}
	return map[string]any{
		"openapi": "3.1.0",
		"info": map[string]any{
			"title":   "nixos-router",
			"version": version,
			"description": "The router's management API, equal to its MCP server: read its state and logs, edit the saved settings. " +
				"Changes are saved, never applied: a person applies them in the web UI. Tokens are made on the API access page (scope read or change).",
		},
		"servers": []any{map[string]any{"url": "/"}},
		"paths":   paths,
		"components": map[string]any{
			"securitySchemes": map[string]any{"bearer": map[string]any{"type": "http", "scheme": "bearer", "description": "A token from the API access page (rtr_…)."}},
			"schemas":         map[string]any{"Error": map[string]any{"type": "object", "properties": map[string]any{"error": map[string]any{"type": "string"}}, "required": []string{"error"}}},
		},
	}
}