// Copyright (c) 2026 Probo Inc <hello@probo.com>.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

package agent

import (
	"context"
	"fmt"
	"io"

	"go.gearno.de/kit/log"
	"go.probo.inc/probo/pkg/llm"
)

const (
	DefaultMaxTurns              = 10
	DefaultMaxEmptyOutputRetries = 2
)

type (
	Option func(*Agent)

	Agent struct {
		name                  string
		handoffDescription    string
		instructions          string
		instructionsFunc      func(ctx context.Context, a *Agent) string
		model                 string
		modelSettings         ModelSettings
		tools                 []Tool
		handoffs              []*Handoff
		mcpServers            []*MCPServer
		maxTurns              int
		maxEmptyOutputRetries int
		maxToolDepth          int
		client                *llm.Client
		logger                *log.Logger
		hooks                 []RunHooks
		agentHooks            AgentHooks
		inputGuardrails       []InputGuardrail
		outputGuardrails      []OutputGuardrail
		session               Session
		sessionID             string
		outputType            *OutputType
		toolUseBehavior       ToolUseBehavior
		resetToolChoice       bool
		responseFormat        *llm.ResponseFormat
		approval              *ApprovalConfig
	}
)

func New(name string, client *llm.Client, opts ...Option) *Agent {
	a := &Agent{
		name:                  name,
		client:                client,
		maxTurns:              DefaultMaxTurns,
		maxEmptyOutputRetries: DefaultMaxEmptyOutputRetries,
		maxToolDepth:          DefaultMaxToolDepth,
		toolUseBehavior:       RunLLMAgain(),
		resetToolChoice:       true,
		logger:                log.NewLogger(log.WithOutput(io.Discard)),
	}

	for _, opt := range opts {
		opt(a)
	}

	a.logger = a.logger.Named("agent").With(log.String("agent", name))

	return a
}

func (a *Agent) Name() string {
	return a.name
}

func (a *Agent) AsTool(name, description string) Tool {
	return newAgentTool(a, name, description)
}

func (a *Agent) HandoffDescription() string {
	return a.handoffDescription
}

// Clone creates a shallow copy of the agent with the given options applied.
func (a *Agent) Clone(opts ...Option) *Agent {
	cp := *a

	cp.tools = make([]Tool, len(a.tools))
	copy(cp.tools, a.tools)

	cp.handoffs = make([]*Handoff, len(a.handoffs))
	copy(cp.handoffs, a.handoffs)

	cp.mcpServers = make([]*MCPServer, len(a.mcpServers))
	copy(cp.mcpServers, a.mcpServers)

	cp.hooks = make([]RunHooks, len(a.hooks))
	copy(cp.hooks, a.hooks)

	cp.inputGuardrails = make([]InputGuardrail, len(a.inputGuardrails))
	copy(cp.inputGuardrails, a.inputGuardrails)

	cp.outputGuardrails = make([]OutputGuardrail, len(a.outputGuardrails))
	copy(cp.outputGuardrails, a.outputGuardrails)

	if a.approval != nil {
		newApproval := ApprovalConfig{
			ShouldApprove: a.approval.ShouldApprove,
		}
		if len(a.approval.ToolNames) > 0 {
			newApproval.ToolNames = make([]string, len(a.approval.ToolNames))
			copy(newApproval.ToolNames, a.approval.ToolNames)
			newApproval.toolNameSet = buildToolNameSet(newApproval.ToolNames)
		}

		cp.approval = &newApproval
	}

	for _, opt := range opts {
		opt(&cp)
	}

	return &cp
}

// clone creates a shallow copy suitable for overriding pointer fields
// (e.g. responseFormat) without affecting the original. Slice fields remain
// shared; use the exported Clone method when slice mutations are needed.
func (a *Agent) clone() *Agent {
	cp := *a
	return &cp
}

func WithInstructions(s string) Option {
	return func(a *Agent) {
		a.instructions = s
		a.instructionsFunc = nil
	}
}

func WithInstructionsFunc(fn func(ctx context.Context, a *Agent) string) Option {
	return func(a *Agent) {
		a.instructionsFunc = fn
		a.instructions = ""
	}
}

func WithHandoffDescription(desc string) Option {
	return func(a *Agent) {
		a.handoffDescription = desc
	}
}

func WithModel(m string) Option {
	return func(a *Agent) {
		a.model = m
	}
}

func WithModelSettings(s ModelSettings) Option {
	return func(a *Agent) {
		a.modelSettings = s
	}
}

func WithTools(tools ...Tool) Option {
	return func(a *Agent) {
		a.tools = append(a.tools, tools...)
	}
}

func WithHandoffs(agents ...*Agent) Option {
	return func(a *Agent) {
		for _, ag := range agents {
			if ag != nil {
				a.handoffs = append(a.handoffs, &Handoff{Agent: ag})
			}
		}
	}
}

func WithHandoffConfigs(handoffs ...*Handoff) Option {
	return func(a *Agent) {
		for _, h := range handoffs {
			if h != nil && h.Agent != nil {
				a.handoffs = append(a.handoffs, h)
			}
		}
	}
}

func WithMaxTurns(n int) Option {
	return func(a *Agent) {
		if n < 1 {
			n = 1
		}

		a.maxTurns = n
	}
}

// WithMaxEmptyOutputRetries bounds the number of times the core loop
// will re-ask the model to produce a structured output after it
// returned a thinking-only empty response on a synthesis turn.
func WithMaxEmptyOutputRetries(n int) Option {
	return func(a *Agent) {
		if n < 0 {
			n = 0
		}

		a.maxEmptyOutputRetries = n
	}
}

func WithMaxToolDepth(n int) Option {
	return func(a *Agent) {
		if n < 1 {
			n = 1
		}

		a.maxToolDepth = n
	}
}

func WithTemperature(t float64) Option {
	return func(a *Agent) {
		a.modelSettings.Temperature = &t
	}
}

func WithTopP(p float64) Option {
	return func(a *Agent) {
		a.modelSettings.TopP = &p
	}
}

func WithFrequencyPenalty(p float64) Option {
	return func(a *Agent) {
		a.modelSettings.FrequencyPenalty = &p
	}
}

func WithPresencePenalty(p float64) Option {
	return func(a *Agent) {
		a.modelSettings.PresencePenalty = &p
	}
}

func WithMaxTokens(n int) Option {
	return func(a *Agent) {
		a.modelSettings.MaxTokens = &n
	}
}

func WithToolChoice(tc llm.ToolChoice) Option {
	return func(a *Agent) {
		a.modelSettings.ToolChoice = &tc
	}
}

func WithParallelToolCalls(enabled bool) Option {
	return func(a *Agent) {
		a.modelSettings.ParallelToolCalls = &enabled
	}
}

func WithThinking(budgetTokens int) Option {
	return func(a *Agent) {
		a.modelSettings.Thinking = &llm.ThinkingConfig{
			Enabled:      true,
			BudgetTokens: budgetTokens,
		}
	}
}

func WithLogger(l *log.Logger) Option {
	return func(a *Agent) {
		a.logger = l
	}
}

func WithHooks(hooks ...RunHooks) Option {
	return func(a *Agent) {
		a.hooks = append(a.hooks, hooks...)
	}
}

func WithAgentHooks(hooks AgentHooks) Option {
	return func(a *Agent) {
		a.agentHooks = hooks
	}
}

func WithInputGuardrails(guards ...InputGuardrail) Option {
	return func(a *Agent) {
		a.inputGuardrails = append(a.inputGuardrails, guards...)
	}
}

func WithOutputGuardrails(guards ...OutputGuardrail) Option {
	return func(a *Agent) {
		a.outputGuardrails = append(a.outputGuardrails, guards...)
	}
}

func WithSession(s Session, sessionID string) Option {
	return func(a *Agent) {
		a.session = s
		a.sessionID = sessionID
	}
}

func WithOutputType(t *OutputType) Option {
	return func(a *Agent) {
		a.outputType = t
	}
}

func WithToolUseBehavior(b ToolUseBehavior) Option {
	return func(a *Agent) {
		a.toolUseBehavior = b
	}
}

func WithResetToolChoice(reset bool) Option {
	return func(a *Agent) {
		a.resetToolChoice = reset
	}
}

func WithMCPServers(servers ...*MCPServer) Option {
	return func(a *Agent) {
		for _, s := range servers {
			if s != nil {
				a.mcpServers = append(a.mcpServers, s)
			}
		}
	}
}

func WithApproval(config ApprovalConfig) Option {
	config.toolNameSet = buildToolNameSet(config.ToolNames)

	return func(a *Agent) {
		a.approval = &config
	}
}

func (a *Agent) resolveTools(ctx context.Context) ([]ToolDescriptor, map[string]ToolDescriptor, error) {
	var all []ToolDescriptor

	for _, t := range a.tools {
		all = append(all, t)
	}

	for _, h := range a.handoffs {
		all = append(all, h.tool())
	}

	for _, s := range a.mcpServers {
		mcpTools, err := s.Tools(ctx)
		if err != nil {
			return nil, nil, fmt.Errorf("cannot resolve MCP tools from %q: %w", s.name, err)
		}

		for _, t := range mcpTools {
			all = append(all, t)
		}
	}

	toolMap := make(map[string]ToolDescriptor, len(all))
	for _, t := range all {
		name := t.Name()
		if _, exists := toolMap[name]; exists {
			return nil, nil, fmt.Errorf("cannot resolve tools: duplicate tool name %q", name)
		}

		toolMap[name] = t
	}

	return all, toolMap, nil
}

func (a *Agent) buildSystemPrompt(ctx context.Context) string {
	instr := a.instructions
	if a.instructionsFunc != nil {
		instr = a.instructionsFunc(ctx, a)
	}

	data := systemPromptData{
		Instructions: instr,
	}

	for _, h := range a.handoffs {
		desc := h.toolDescription()
		if len([]rune(desc)) > 200 {
			desc = string([]rune(desc)[:200]) + "..."
		}

		data.Handoffs = append(
			data.Handoffs,
			systemPromptHandoff{
				Name:        h.Agent.name,
				Description: desc,
			},
		)
	}

	return buildSystemPrompt(data)
}