package api

import (
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"regexp"

	"github.com/sipeed/picoclaw/pkg/config"
)

// registerConfigRoutes binds configuration management endpoints to the ServeMux.
func (h *Handler) registerConfigRoutes(mux *http.ServeMux) {
	mux.HandleFunc("GET /api/config", h.handleGetConfig)
	mux.HandleFunc("PUT /api/config", h.handleUpdateConfig)
	mux.HandleFunc("PATCH /api/config", h.handlePatchConfig)
}

// handleGetConfig returns the complete system configuration.
//
//	GET /api/config
func (h *Handler) handleGetConfig(w http.ResponseWriter, r *http.Request) {
	cfg, err := config.LoadConfig(h.configPath)
	if err != nil {
		http.Error(w, fmt.Sprintf("Failed to load config: %v", err), http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Type", "application/json")
	if err := json.NewEncoder(w).Encode(cfg); err != nil {
		http.Error(w, "Failed to encode response", http.StatusInternalServerError)
	}
}

// handleUpdateConfig updates the complete system configuration.
//
//	PUT /api/config
func (h *Handler) handleUpdateConfig(w http.ResponseWriter, r *http.Request) {
	body, err := io.ReadAll(io.LimitReader(r.Body, 1<<20))
	if err != nil {
		http.Error(w, "Failed to read request body", http.StatusBadRequest)
		return
	}
	defer r.Body.Close()

	var cfg config.Config
	if err := json.Unmarshal(body, &cfg); err != nil {
		http.Error(w, fmt.Sprintf("Invalid JSON: %v", err), http.StatusBadRequest)
		return
	}
	if execAllowRemoteOmitted(body) {
		cfg.Tools.Exec.AllowRemote = config.DefaultConfig().Tools.Exec.AllowRemote
	}

	if errs := validateConfig(&cfg); len(errs) > 0 {
		w.Header().Set("Content-Type", "application/json")
		w.WriteHeader(http.StatusBadRequest)
		json.NewEncoder(w).Encode(map[string]any{
			"status": "validation_error",
			"errors": errs,
		})
		return
	}

	if err := config.SaveConfig(h.configPath, &cfg); err != nil {
		http.Error(w, fmt.Sprintf("Failed to save config: %v", err), http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(map[string]string{"status": "ok"})
}

func execAllowRemoteOmitted(body []byte) bool {
	var raw struct {
		Tools *struct {
			Exec *struct {
				AllowRemote *bool `json:"allow_remote"`
			} `json:"exec"`
		} `json:"tools"`
	}
	if err := json.Unmarshal(body, &raw); err != nil {
		return false
	}
	return raw.Tools == nil || raw.Tools.Exec == nil || raw.Tools.Exec.AllowRemote == nil
}

// handlePatchConfig partially updates the system configuration using JSON Merge Patch (RFC 7396).
// Only the fields present in the request body will be updated; all other fields remain unchanged.
//
//	PATCH /api/config
func (h *Handler) handlePatchConfig(w http.ResponseWriter, r *http.Request) {
	patchBody, err := io.ReadAll(io.LimitReader(r.Body, 1<<20))
	if err != nil {
		http.Error(w, "Failed to read request body", http.StatusBadRequest)
		return
	}
	defer r.Body.Close()

	// Validate the patch is valid JSON
	var patch map[string]any
	if err = json.Unmarshal(patchBody, &patch); err != nil {
		http.Error(w, fmt.Sprintf("Invalid JSON: %v", err), http.StatusBadRequest)
		return
	}

	// Load existing config and marshal to a map for merging
	cfg, err := config.LoadConfig(h.configPath)
	if err != nil {
		http.Error(w, fmt.Sprintf("Failed to load config: %v", err), http.StatusInternalServerError)
		return
	}

	existing, err := json.Marshal(cfg)
	if err != nil {
		http.Error(w, "Failed to serialize current config", http.StatusInternalServerError)
		return
	}

	var base map[string]any
	if err = json.Unmarshal(existing, &base); err != nil {
		http.Error(w, "Failed to parse current config", http.StatusInternalServerError)
		return
	}

	// Recursively merge patch into base
	mergeMap(base, patch)

	// Convert merged map back to Config struct
	merged, err := json.Marshal(base)
	if err != nil {
		http.Error(w, "Failed to serialize merged config", http.StatusInternalServerError)
		return
	}

	var newCfg config.Config
	if err := json.Unmarshal(merged, &newCfg); err != nil {
		http.Error(w, fmt.Sprintf("Merged config is invalid: %v", err), http.StatusBadRequest)
		return
	}

	if errs := validateConfig(&newCfg); len(errs) > 0 {
		w.Header().Set("Content-Type", "application/json")
		w.WriteHeader(http.StatusBadRequest)
		json.NewEncoder(w).Encode(map[string]any{
			"status": "validation_error",
			"errors": errs,
		})
		return
	}

	if err := config.SaveConfig(h.configPath, &newCfg); err != nil {
		http.Error(w, fmt.Sprintf("Failed to save config: %v", err), http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(map[string]string{"status": "ok"})
}

// validateConfig checks the config for common errors before saving.
// Returns a list of human-readable error strings; empty means valid.
func validateConfig(cfg *config.Config) []string {
	var errs []string

	// Validate model_list entries
	if err := cfg.ValidateModelList(); err != nil {
		errs = append(errs, err.Error())
	}

	// Gateway port range
	if cfg.Gateway.Port != 0 && (cfg.Gateway.Port < 1 || cfg.Gateway.Port > 65535) {
		errs = append(errs, fmt.Sprintf("gateway.port %d is out of valid range (1-65535)", cfg.Gateway.Port))
	}

	// Pico channel: token required when enabled
	if cfg.Channels.Pico.Enabled && cfg.Channels.Pico.Token == "" {
		errs = append(errs, "channels.pico.token is required when pico channel is enabled")
	}

	// Telegram: token required when enabled
	if cfg.Channels.Telegram.Enabled && cfg.Channels.Telegram.Token == "" {
		errs = append(errs, "channels.telegram.token is required when telegram channel is enabled")
	}

	// Discord: token required when enabled
	if cfg.Channels.Discord.Enabled && cfg.Channels.Discord.Token == "" {
		errs = append(errs, "channels.discord.token is required when discord channel is enabled")
	}

	if cfg.Tools.Exec.Enabled {
		if cfg.Tools.Exec.EnableDenyPatterns {
			errs = append(
				errs,
				validateRegexPatterns("tools.exec.custom_deny_patterns", cfg.Tools.Exec.CustomDenyPatterns)...)
		}
		errs = append(
			errs,
			validateRegexPatterns("tools.exec.custom_allow_patterns", cfg.Tools.Exec.CustomAllowPatterns)...)
	}

	return errs
}

func validateRegexPatterns(field string, patterns []string) []string {
	var errs []string
	for index, pattern := range patterns {
		if _, err := regexp.Compile(pattern); err != nil {
			errs = append(errs, fmt.Sprintf("%s[%d] is not a valid regular expression: %v", field, index, err))
		}
	}
	return errs
}

// mergeMap recursively merges src into dst (JSON Merge Patch semantics).
// - If a key in src has a null value, it is deleted from dst.
// - If both dst and src have a nested object for the same key, merge recursively.
// - Otherwise the value from src overwrites dst.
func mergeMap(dst, src map[string]any) {
	for key, srcVal := range src {
		if srcVal == nil {
			delete(dst, key)
			continue
		}
		srcMap, srcIsMap := srcVal.(map[string]any)
		dstMap, dstIsMap := dst[key].(map[string]any)
		if srcIsMap && dstIsMap {
			mergeMap(dstMap, srcMap)
		} else {
			dst[key] = srcVal
		}
	}
}