package governance

import (
	"fmt"
	"math/rand/v2"
	"strings"

	"github.com/google/cel-go/cel"
	"github.com/maximhq/bifrost/core/schemas"
	configstoreTables "github.com/maximhq/bifrost/framework/configstore/tables"
)

// DefaultRoutingChainMaxDepth is the default maximum depth for routing rule chain evaluation.
const DefaultRoutingChainMaxDepth = 10

// ScopeLevel represents a level in the scope precedence hierarchy
type ScopeLevel struct {
	ScopeName string // "virtual_key", "team", "customer", or "global"
	ScopeID   string // empty string for global scope
}

// RoutingDecision is the output of routing rule evaluation
// Represents which provider/model to route to and fallback chain
type RoutingDecision struct {
	Provider        string   // Primary provider (e.g., "openai", "azure")
	Model           string   // Model to use (or empty to use original)
	KeyID           string   // Optional: pin a specific API key by UUID ("" = no pin)
	Fallbacks       []string // Fallback chain: ["provider/model", ...]
	MatchedRuleID   string   // ID of the rule that matched
	MatchedRuleName string   // Name of the rule that matched
}

// RoutingContext holds all data needed for routing rule evaluation
// Reuses existing configstore table types for VirtualKey, Team, Customer
type RoutingContext struct {
	VirtualKey               *configstoreTables.TableVirtualKey // nil if no VK
	Provider                 schemas.ModelProvider              // Current provider
	Model                    string                             // Current model
	RequestType              string                             // Normalized request type (e.g., "chat_completion", "embedding") from HTTP context
	Fallbacks                []string                           // Fallback chain: ["provider/model", ...]
	Headers                  map[string]string                  // Request headers for dynamic routing
	QueryParams              map[string]string                  // Query parameters for dynamic routing
	BudgetAndRateLimitStatus *BudgetAndRateLimitStatus          // Budget and rate limit status by provider/model
}

type RoutingEngine struct {
	store         GovernanceStore
	logger        schemas.Logger
	chainMaxDepth *int // pointer to live config value; changes are reflected immediately
}

// NewRoutingEngine creates a new RoutingEngine
func NewRoutingEngine(store GovernanceStore, logger schemas.Logger, chainMaxDepth *int) (*RoutingEngine, error) {
	if store == nil {
		return nil, fmt.Errorf("store cannot be nil")
	}
	if logger == nil {
		return nil, fmt.Errorf("logger cannot be nil")
	}
	if chainMaxDepth == nil {
		return nil, fmt.Errorf("chainMaxDepth cannot be nil")
	}
	if *chainMaxDepth <= 0 {
		return nil, fmt.Errorf("chainMaxDepth must be greater than 0")
	}

	return &RoutingEngine{
		store:         store,
		logger:        logger,
		chainMaxDepth: chainMaxDepth,
	}, nil
}

// EvaluateRoutingRules evaluates routing rules for a given context and returns a routing decision.
// Implements scope precedence: VirtualKey > Team > Customer > Global (first-match-wins within each iteration).
// When a matched rule has chain_rule=true, the resolved provider/model is fed back into the evaluator
// and the full scope chain is re-evaluated with the updated context. This repeats until:
//  1. No rule matches the current context
//  2. A terminal rule matches (chain_rule=false, the default)
//  3. A cycle is detected (a provider/model state was already visited)
//  4. The chain exceeds the configured max depth (chainMaxDepth, default 10)
func (re *RoutingEngine) EvaluateRoutingRules(ctx *schemas.BifrostContext, routingCtx *RoutingContext) (*RoutingDecision, error) {
	if routingCtx == nil {
		return nil, fmt.Errorf("routing context cannot be nil")
	}

	re.logger.Debug("[RoutingEngine] Starting rule evaluation for provider=%s, model=%s", routingCtx.Provider, routingCtx.Model)

	// Mutable provider/model that advances through the chain; all other context fields are immutable.
	currentProvider := routingCtx.Provider
	currentModel := routingCtx.Model

	// Track visited provider/model states to detect cycles (e.g. A→B→A).
	visited := map[string]struct{}{
		fmt.Sprintf("%s|%s", currentProvider, currentModel): {},
	}

	var finalDecision *RoutingDecision

	for chainStep := 0; ; chainStep++ {
		// TERMINATION 4: Chain exceeded configured max depth.
		maxDepth := *re.chainMaxDepth
		if chainStep >= maxDepth {
			re.logger.Warn("[RoutingEngine] Routing rule chain exceeded max depth (%d), stopping", maxDepth)
			ctx.AppendRoutingEngineLog(schemas.RoutingEngineRoutingRule, fmt.Sprintf("Chain exceeded max depth (%d) at step %d, stopping. Final resolved: provider=%s, model=%s", maxDepth, chainStep, currentProvider, currentModel))
			break
		}

		if chainStep > 0 {
			ctx.AppendRoutingEngineLog(schemas.RoutingEngineRoutingRule, fmt.Sprintf("Chain step %d: re-evaluating with provider=%s, model=%s", chainStep, currentProvider, currentModel))
		}

		// Build CEL variables for the current chain step's provider/model.
		iterCtx := *routingCtx
		iterCtx.Provider = currentProvider
		iterCtx.Model = currentModel
		// Refresh budget/rate-limit status for the current provider/model so chained
		// rules that test budget_used, tokens_used, or request see fresh data.
		iterCtx.BudgetAndRateLimitStatus = re.store.GetBudgetAndRateLimitStatus(ctx, currentModel, currentProvider, routingCtx.VirtualKey, nil, nil, nil)

		variables, err := extractRoutingVariables(&iterCtx)
		if err != nil {
			re.logger.Error("[RoutingEngine] Failed to extract routing variables: %v", err)
			return nil, fmt.Errorf("failed to extract routing variables: %w", err)
		}

		scopeChain := buildScopeChain(routingCtx.VirtualKey)
		re.logger.Debug("[RoutingEngine] Scope chain (step=%d): %v", chainStep, scopeChainToStrings(scopeChain))
		if chainStep == 0 {
			ctx.AppendRoutingEngineLog(schemas.RoutingEngineRoutingRule, fmt.Sprintf("Scope chain: %v", scopeChainToStrings(scopeChain)))
		}

		var stepDecision *RoutingDecision
		var matchedRule *configstoreTables.TableRoutingRule
		var matchedTargetWeight float64

	outerLoop:
		for _, scope := range scopeChain {
			scopeID := scope.ScopeID

			rules := re.store.GetScopedRoutingRules(ctx, scope.ScopeName, scopeID)
			re.logger.Debug("[RoutingEngine] Evaluating scope=%s, scopeID=%s, ruleCount=%d", scope.ScopeName, scopeID, len(rules))

			if len(rules) == 0 {
				continue
			}

			ruleNames := make([]string, 0, len(rules))
			for _, r := range rules {
				ruleNames = append(ruleNames, r.Name)
			}
			ctx.AppendRoutingEngineLog(schemas.RoutingEngineRoutingRule, fmt.Sprintf("Evaluating scope %s: %d rules [%s]", scope.ScopeName, len(rules), strings.Join(ruleNames, ", ")))

			for _, rule := range rules {
				re.logger.Debug("[RoutingEngine] Evaluating rule: name=%s, expression=%s", rule.Name, rule.CelExpression)

				program, err := re.store.GetRoutingProgram(ctx, rule)
				if err != nil {
					re.logger.Warn("[RoutingEngine] Failed to compile rule %s: %v", rule.Name, err)
					ctx.AppendRoutingEngineLog(schemas.RoutingEngineRoutingRule, fmt.Sprintf("Rule '%s' skipped: compile error: %v", rule.Name, err))
					continue
				}

				matched, err := evaluateCELExpression(program, variables)
				if err != nil {
					re.logger.Warn("[RoutingEngine] Failed to evaluate rule %s: %v", rule.Name, err)
					ctx.AppendRoutingEngineLog(schemas.RoutingEngineRoutingRule, fmt.Sprintf("Rule '%s' skipped: eval error: %v", rule.Name, err))
					continue
				}

				re.logger.Debug("[RoutingEngine] Rule %s evaluation result: matched=%v", rule.Name, matched)

				if !matched {
					ctx.AppendRoutingEngineLog(schemas.RoutingEngineRoutingRule, fmt.Sprintf("Rule '%s' [%s] → no match", rule.Name, rule.CelExpression))
					continue
				}

				target, ok := selectWeightedTarget(rule.Targets)
				if !ok {
					re.logger.Debug("[RoutingEngine] Rule %s matched but has no valid targets (empty list or all-negative weights), skipping — note: all-zero weights use uniform selection and would not reach here", rule.Name)
					ctx.AppendRoutingEngineLog(schemas.RoutingEngineRoutingRule, fmt.Sprintf("Rule '%s' [%s] → matched but no valid targets (empty or all-negative weights), skipping", rule.Name, rule.CelExpression))
					continue
				}

				provider := string(currentProvider)
				if target.Provider != nil && *target.Provider != "" {
					provider = *target.Provider
				}

				model := currentModel
				if target.Model != nil && *target.Model != "" {
					model = *target.Model
				}

				keyID := ""
				if target.KeyID != nil {
					keyID = *target.KeyID
				}

				stepDecision = &RoutingDecision{
					Provider:        provider,
					Model:           model,
					KeyID:           keyID,
					Fallbacks:       rule.ParsedFallbacks,
					MatchedRuleID:   rule.ID,
					MatchedRuleName: rule.Name,
				}
				matchedRule = rule
				matchedTargetWeight = target.Weight
				break outerLoop
			}
		}

		// TERMINATION 1: No rule matched this iteration.
		if stepDecision == nil {
			break
		}

		// Accumulate: last match wins for all fields.
		finalDecision = stepDecision
		ctx.SetValue(schemas.BifrostContextKeyGovernanceRoutingRuleID, stepDecision.MatchedRuleID)
		ctx.SetValue(schemas.BifrostContextKeyGovernanceRoutingRuleName, stepDecision.MatchedRuleName)

		chainSuffix := ""
		if matchedRule.ChainRule {
			chainSuffix = " [chain_rule=true, continuing]"
		}
		re.logger.Debug("[RoutingEngine] Rule matched! Selected target (weight=%.2f): provider=%s, model=%s, fallbacks=%v%s", matchedTargetWeight, stepDecision.Provider, stepDecision.Model, stepDecision.Fallbacks, chainSuffix)
		ctx.AppendRoutingEngineLog(schemas.RoutingEngineRoutingRule, fmt.Sprintf("Rule '%s' [%s] → matched, selected target (weight=%.2f): provider=%s, model=%s, fallbacks=%v%s", matchedRule.Name, matchedRule.CelExpression, matchedTargetWeight, stepDecision.Provider, stepDecision.Model, stepDecision.Fallbacks, chainSuffix))

		// TERMINATION 2: Rule is terminal (chain_rule=false, the default).
		if !matchedRule.ChainRule {
			break
		}

		// TERMINATION 3: Cycle detection — if the next state was already visited, continuing would loop forever.
		nextState := fmt.Sprintf("%s|%s", stepDecision.Provider, stepDecision.Model)
		if _, seen := visited[nextState]; seen {
			re.logger.Debug("[RoutingEngine] Chain cycle detected at step=%d (state=%s already visited), stopping", chainStep, nextState)
			ctx.AppendRoutingEngineLog(schemas.RoutingEngineRoutingRule, fmt.Sprintf("Chain cycle detected at step %d (provider=%s, model=%s already visited), stopping. Final resolved: provider=%s, model=%s", chainStep, stepDecision.Provider, stepDecision.Model, stepDecision.Provider, stepDecision.Model))
			break
		}
		visited[nextState] = struct{}{}

		// Advance context for next chain iteration.
		currentProvider = schemas.ModelProvider(stepDecision.Provider)
		currentModel = stepDecision.Model
	}

	if finalDecision == nil {
		re.logger.Debug("[RoutingEngine] No routing rule matched, using default routing")
	}
	return finalDecision, nil
}

// selectWeightedTarget picks one target from the slice using weighted random selection.
// Each target's Weight contributes proportionally to its probability of being chosen.
// Weights do not need to be normalised to 100; the function normalises internally.
// Returns ok=false only when len(targets)==0 or all targets have negative weights (filtered out).
// When all valid targets have weight==0 the function falls back to uniform random selection
// and still returns ok=true, so zero-weight targets are valid and handled.
func selectWeightedTarget(targets []configstoreTables.TableRoutingTarget) (configstoreTables.TableRoutingTarget, bool) {
	if len(targets) == 0 {
		return configstoreTables.TableRoutingTarget{}, false
	}

	// Filter out negative weights as a precaution against malformed DB data.
	// Negative weights are blocked at write time by validateRoutingTargets, but
	// we guard here defensively so a bad row cannot corrupt the cumulative range.
	valid := make([]configstoreTables.TableRoutingTarget, 0, len(targets))
	for _, t := range targets {
		if t.Weight >= 0 {
			valid = append(valid, t)
		}
	}
	if len(valid) == 0 {
		return configstoreTables.TableRoutingTarget{}, false
	}

	total := 0.0
	for _, t := range valid {
		total += t.Weight
	}

	// All weights are 0 — select uniformly at random among valid targets.
	if total == 0 {
		return valid[rand.IntN(len(valid))], true
	}

	if len(valid) == 1 {
		return valid[0], true
	}

	r := rand.Float64() * total
	cumulative := 0.0
	for _, t := range valid {
		cumulative += t.Weight
		if r < cumulative {
			return t, true
		}
	}
	return valid[len(valid)-1], true
}

// buildScopeChain builds the scope evaluation chain based on organizational hierarchy
// Returns scope levels in precedence order (highest to lowest)
// VirtualKey > Team > Customer > Global
func buildScopeChain(virtualKey *configstoreTables.TableVirtualKey) []ScopeLevel {
	var chain []ScopeLevel

	// VirtualKey level (highest precedence)
	if virtualKey != nil {
		chain = append(chain, ScopeLevel{
			ScopeName: "virtual_key",
			ScopeID:   virtualKey.ID,
		})

		// Team level
		if virtualKey.Team != nil {
			chain = append(chain, ScopeLevel{
				ScopeName: "team",
				ScopeID:   virtualKey.Team.ID,
			})

			// Customer level (from Team)
			if virtualKey.Team.Customer != nil {
				chain = append(chain, ScopeLevel{
					ScopeName: "customer",
					ScopeID:   virtualKey.Team.Customer.ID,
				})
			}
		} else if virtualKey.Customer != nil {
			// Customer level (VK attached directly to customer, no Team)
			chain = append(chain, ScopeLevel{
				ScopeName: "customer",
				ScopeID:   virtualKey.Customer.ID,
			})
		}
	}

	// Global level (lowest precedence)
	chain = append(chain, ScopeLevel{
		ScopeName: "global",
		ScopeID:   "",
	})

	return chain
}

// evaluateCELExpression evaluates a compiled CEL program with given variables
func evaluateCELExpression(program cel.Program, variables map[string]interface{}) (bool, error) {
	if program == nil {
		return false, fmt.Errorf("CEL program is nil")
	}

	// Evaluate the program
	out, _, err := program.Eval(variables)
	if err != nil {
		// Gracefully handle "no such key" errors - when a header/param is missing, treat as non-match
		if strings.Contains(err.Error(), "no such key") {
			return false, nil
		}
		return false, fmt.Errorf("CEL evaluation error: %w", err)
	}

	// Convert result to boolean
	matched, ok := out.Value().(bool)
	if !ok {
		return false, fmt.Errorf("CEL expression did not return boolean, got: %T", out.Value())
	}

	return matched, nil
}

// extractRoutingVariables builds a map of CEL variables from routing context
// This map is used to evaluate CEL expressions in routing rules
func extractRoutingVariables(ctx *RoutingContext) (map[string]interface{}, error) {
	if ctx == nil {
		return nil, fmt.Errorf("routing context cannot be nil")
	}

	variables := make(map[string]interface{})

	// Basic request context
	variables["model"] = ctx.Model
	variables["provider"] = string(ctx.Provider)
	variables["request_type"] = ctx.RequestType // Normalized request type (e.g., "chat_completion", "embedding")

	// Headers and params - normalize headers to lowercase keys for case-insensitive CEL matching
	// This allows CEL expressions like headers["content-type"] to work regardless of how the header was sent
	normalizedHeaders := make(map[string]string)
	if ctx.Headers != nil {
		for k, v := range ctx.Headers {
			// Store with lowercase key for case-insensitive matching in CEL
			normalizedHeaders[strings.ToLower(k)] = v
		}
	}
	variables["headers"] = normalizedHeaders

	// Normalize query params to lowercase keys for case-insensitive CEL matching
	normalizedParams := make(map[string]string)
	if ctx.QueryParams != nil {
		for k, v := range ctx.QueryParams {
			normalizedParams[strings.ToLower(k)] = v
		}
	}
	variables["params"] = normalizedParams

	// Extract VirtualKey context if available
	if ctx.VirtualKey != nil {
		variables["virtual_key_id"] = ctx.VirtualKey.ID
		variables["virtual_key_name"] = ctx.VirtualKey.Name
	} else {
		variables["virtual_key_id"] = ""
		variables["virtual_key_name"] = ""
	}

	// Extract Team context if available (from VirtualKey)
	if ctx.VirtualKey != nil && ctx.VirtualKey.Team != nil {
		variables["team_id"] = ctx.VirtualKey.Team.ID
		variables["team_name"] = ctx.VirtualKey.Team.Name
	} else {
		variables["team_id"] = ""
		variables["team_name"] = ""
	}

	// Extract Customer context if available (from Team or directly from VirtualKey)
	if ctx.VirtualKey != nil {
		if ctx.VirtualKey.Team != nil && ctx.VirtualKey.Team.Customer != nil {
			variables["customer_id"] = ctx.VirtualKey.Team.Customer.ID
			variables["customer_name"] = ctx.VirtualKey.Team.Customer.Name
		} else if ctx.VirtualKey.Customer != nil {
			variables["customer_id"] = ctx.VirtualKey.Customer.ID
			variables["customer_name"] = ctx.VirtualKey.Customer.Name
		} else {
			variables["customer_id"] = ""
			variables["customer_name"] = ""
		}
	} else {
		variables["customer_id"] = ""
		variables["customer_name"] = ""
	}

	// Populate budget and rate limit variables for current provider/model combination
	if ctx.BudgetAndRateLimitStatus != nil {
		variables["budget_used"] = ctx.BudgetAndRateLimitStatus.BudgetPercentUsed
		variables["tokens_used"] = ctx.BudgetAndRateLimitStatus.RateLimitTokenPercentUsed
		variables["request"] = ctx.BudgetAndRateLimitStatus.RateLimitRequestPercentUsed
	} else {
		// No budget/rate limit configured, provide 0 values
		variables["budget_used"] = 0.0
		variables["tokens_used"] = 0.0
		variables["request"] = 0.0
	}

	return variables, nil
}

// scopeChainToStrings converts a scope chain to a string representation for logging
func scopeChainToStrings(chain []ScopeLevel) []string {
	scopes := make([]string, 0, len(chain))
	for _, scope := range chain {
		if scope.ScopeID == "" {
			scopes = append(scopes, scope.ScopeName)
		} else {
			scopes = append(scopes, fmt.Sprintf("%s(%s)", scope.ScopeName, scope.ScopeID))
		}
	}
	return scopes
}

// createCELEnvironment creates a new CEL environment for routing rules
func createCELEnvironment() (*cel.Env, error) {
	return cel.NewEnv(
		// Basic request context
		cel.Variable("model", cel.StringType),
		cel.Variable("provider", cel.StringType),
		cel.Variable("request_type", cel.StringType), // Normalized request type (e.g., "chat_completion", "embedding", "text_completion")

		// Headers and params (dynamic from request)
		cel.Variable("headers", cel.MapType(cel.StringType, cel.StringType)),
		cel.Variable("params", cel.MapType(cel.StringType, cel.StringType)),

		// VirtualKey/Team/Customer context
		cel.Variable("virtual_key_id", cel.StringType),
		cel.Variable("virtual_key_name", cel.StringType),
		cel.Variable("team_id", cel.StringType),
		cel.Variable("team_name", cel.StringType),
		cel.Variable("customer_id", cel.StringType),
		cel.Variable("customer_name", cel.StringType),

		// Rate limit & budget status (real-time capacity metrics as percentages)
		cel.Variable("tokens_used", cel.DoubleType),
		cel.Variable("request", cel.DoubleType),
		cel.Variable("budget_used", cel.DoubleType),
	)
}